AA E+E ENVIRONMENTAL & ENERGY STUDIES PROGRAMME ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE GRADUATE SCHOOL MSc SUSTAINABLE ENVIRONMENTAL DESIGN DISSERTATION PROJECT 2009-10
TRANSFORMATIONS AT THE STREET LEVEL OF ATHENS Focusing on pedestrian roads
Abstract In the urban fabric of Athens, and more specifically at its centre, the high density and the geometry of the buildings can be the main reason for the diurnal temperature deviations that can be observed. The high global incident radiation as well as the storage capacity of the surrounding materials in a street and its surroundings, such as concrete, brick, concrete tiles and asphalt, converts the built environment to a radiator which releases its heat at night. Additionally, anthropogenic heat due to the intense use of private means of transportation as well as due to the use of mechanical cooling systems during summer, may exacerbate the problem. Moreover, the lack of vegetation and hence the lack of shading and evaporation usually leads to creation of unpleasant areas, especially for the inhabitants at the centre. Regarding the potential of occupying the outdoor spaces in such a climate, which could be more than half of the year, there might be a possibility of transforming low traffic streets into pedestrian zones, providing in this way a more comfortable and friendly environment.
E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ANNA-MELPOMENI DANOU ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE
Authorship Declaration Form AA E+E MSc & MArch SUSTAINABLE ENVIRONMENTAL DESIGN 2009-10 DISSERTATION PROJECT SUBMISSION TITLE: TRANSFORMATIONS AT THE STREET LEVEL OF ATHENS NUMBER OF WORDS: STUDENT NAME: ANNA-MELPOMENI DANOU
DECLARATION: “I certify that the contents of this document are entirely my own work and that any quotation or paraphrase from the published or unpublished work of others is duly acknowledged.” Signature:
Anna-Melpomeni Danou Date: 2010-09-17, London PROGRAMME: MSc / MArch SUSTAINABLE ENVIRONMENTAL DESIGN 2009-10
E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ANNA-MELPOMENI DANOU ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE
Table of Contents 1. Introduction ..........................................................................................................................................................11 1.1 The lack and the need of outdoor public spaces in Athens 1.2 The governmental strategies 1.3 The case of the pedestrian roads - types and activities (‘open street’ and canyons) 1.4. Methodology 2. Theoretical Background .....................................................................................................................................15 2.1. Outdoor comfort 2.1.1. Outdoor comfort - a general overview 2.1.2. Pedestrian comfort - Thermal Physiological Balance 2.1.3. Outdoor comfort - Psychological adaptation 2.1.4. Thermal Comfort Assessment 2.2. Urban spaces and diversity - Mapping environmental performance of open urban spaces 2.3. The street typology 2.3.1. Street geometry and solar access 2.3.2. Street Canyon geometry and impact on pedestrians’ comfort 2.3.3. Impact of vegetation 2.3.4. Street Canyon and air flow 2.4. Conclusions of theoretical backround 3. Context & Precedents .........................................................................................................................................35 3.1. Climatic context - Urban mesoclimate 3.2. Bioclimatic evaluation 3.3 Precedents 3.4. Conclusion of climatic context and precedents 4. Fieldwork .............................................................................................................................................................47 4.1. Introduction 4.2. Occupancy of Pedestrian roads (walkers) 4.3. Impact of geometry on microclimate 4.4. Occupancy of Pedestrian roads (occupants at rest) 4.5. Comparison of the urban with the suburban context - the effect of the vegetation 4.6. Fieldwork conclusions 5. Analytic work .......................................................................................................................................................63 5.1. Solar radiation studies 5.1.1. Solar radiation distribution on facets of symmetrical canyons 5.1.2. Effect of vegetation on canyons’ facets 5.1.3. Solar radiation impinging on pedestrian 5.1.4 Conclusions of solar analysis 5.2 ENVI-met case studies 5.2.1 Impact of building geometry 5.2.2. Impact of vegetation 5.2.3 The cases of the ‘open’ street and shallow street 6. Future research and applicability ......................................................................................................................88 6.1. Macroscale-urban ventilation 6.2. Mesoscale-street design 6.3 Microscale-urban furniture design 7. Conclusions .........................................................................................................................................................91 8.References ............................................................................................................................................................93 9. Appendices ..........................................................................................................................................................95 9.1 Climatic context 9.2 Limitation using Envi-met v.4.0 9.3 Air temperature and geometry (first group of simulations) 9.4 Air temperature and impact of vegetation (second group of simulations) 9.5 Air temperature in the case of ‘open’ street and shallow street (third group of simulations) 9.6 Wind in the case of the ‘open’ street and shallow street 9.7 Specific humidity (q) 9.8 Solar exposure of a plane 1m above ground
E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ANNA-MELPOMENI DANOU ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE
Aknowledgments I, Anna Melpomeni Danou, would like to thank the members of the Environment and Energy Studies Programme staff, and especially Dr. Simos Yannas for his invaluable guidance and his patience throughout the development of this dissertation and the course overall. For the weather data during the fieldwork period thanks are owed to Dr. Harry Kambezidis at the National Observatory in Athens and Maria Karalia at the National Meteorological Station in Elliniko district. I would like specially to thank Nikos Belavilas, associate professor at the National Technical University of Athens, who kindly provided me with the GIS map of Athens, numerical data of the introduction, the ifrared camera Flir i40, as well as for his precious advice during the fieldwork period. Valuable was the suggestion of Dr. Marialena Nikolopoulou reagarding literature on hot-dry dry climate similar to mediterranean climate. Special thanks are owed to Dr. Eleftheria Alexandri, who kindly provided me with her PhD thesis that was conducted at Cardiff University, Welsh School of Architecture entitled “Investigations into Mitigating the Heat Island Effect through Green Roofs and Green Walls”. I also have to thank Dimitris Diamantopoulos, architect engineer, who spent his valuable time during the interview with regards to the reformation of to traffic streets into the “Athenian Walk”. In the analytic part, regarding the numerical simulations with ENVImet v. 4 special thanks are owed to the author of the software Dr. Michael Bruce who kindly answered directly all of my questions. as well as to Konstantina Saranti, graduate student of the E+E environment and enery studies programme (MArch 2010), not only for her really helpful advice on simulating with ENVImet v. 4, but also for all her COMFORT-ing answers and for providing me with the Arens et al. research papers (1981). Useful was also Christina’s Doumpioti help, current studio master tutor in Emergent Technologies and Design Programme of the AA, who helped me with the Rhinoceros 4.0 shoftware and the bench in chapter. I have to thank also my sister Dr. Aliki Danou for the proof reading and english correction. The fieldwork part could not be completed without my father’s help, Andeas Danos, architect engineer, who was continuously taking photos in the centre of Athens over more than four months. Finally, I acknowledge the Onasseio Foundation for the generous offer of a scholarship to undertake the MSc in Sustainable and Environmental Design at the Architectural Association School of Architecture.
1. Introduction In a city like Athens, during summer, significant variations in air and surface temperatures can be observed, comparing an urban and a suburban context. This phenomenon is well known as “heat island effect” or “reverse oasis” (Gartland, 2008). Higher temperatures and increased air pollution are serious causes that affect humans’ mortality (Gartland, 2008). Givoni (1998) also mentions that in the case of Athens, occasions of cardiovascular problems were observed mostly in the elderly people due to high temperatures and increased air pollution. What is the role of a dense area on making this problem even greater? What are the solutions, on mitigating the heat island effect, considering the existing condition? 1.1 The lack and the need of outdoor public spaces in Athens After an extensive research that was conducted by the Urban Environment Laboratory in the National Technical University of Athens [N.T.U.A.], with regards to the proportion of the outdoor spaces and the city inhabitants, the conclusion of the problematic condition of the insufficient outdoor spaces for the actual population was subsequent. More specifically, the existing open spaces are 3.84m2/inhabitant. From these spaces 1/5 – 1/3 are even spaces which comprise buildings with low building coefficient, or paved open spaces with hard materials such as concrete tiles, lightweight concrete, etc. Thus, the actual green space becomes 2.5m2/ inhabitant, value that hasn’t changed since 1985. Just for the record the international standards require 8-12m2/inhabitant (Organisation of Planning and Environmental Protection of Athens, 2004). Nevertheless, there is a great potential of increasing the outdoor and/or green spaces by redesigning the areas which comprise the ex-Olympic Games premises. In the above values a 1.23m2/inhabitant could be added. Additionally to this, different kind of solutions may mitigate even more the problem: a. an increment of the number of the pocket size parks and the re-use of the inward-looking courtyards (‘akalyptos”\’) of the multi-storey buildings (‘polykatoikia’), b. the re-use of the roof tops and c. the increment of the number of the pedestrian roads, by impoverishing at the same time the use of the private means of transportation. All the above solutions can conclude to a better distribution of the green, mitigating this way the intensity of the heat island effect in the centre of the city.
Fig. 1.01 Increment of population in Athens from 1853-2008 source: after wikipedia-http://el.wikipedia.org/
It has always been a need of every inhabitant in a city to socialise with the others. Outdoor spaces have played a significant role on accomplishing the above mentioned goal. The exchange of concerns, doubts, worries, thoughts but also joyful and relaxed moments is essential for the healthy social life of the occupants. From the environmental point of view, exploring the limits of how to maximise the comfortable hours that someone might spend outdoors is the basic idea of this dissertation.
1.2 The governmental strategies (http://www.minenv.gr/3/31/313/31303/e3130304.html) A governmental organisation, Organisation of Planning and Environmental Protection of Athens, has been created under the auspices of the pilot programme “Athens-Attica 2014” governed by the newly established Ministry for the Environment and Climate Change. It is the body, which is delegated the overall administrative management of physical planning, urban planning and environmental matters of Athens and its wider area. One of the priorities of the programme is to improve the quality of the public spaces - the “backbone” of the programme. For the completion of a pedestrian network (4km in total) which connects the archaeological monuments of Athens, future pedestrianisations of certain roads are planned: Vassilissis Olgas street and Panepistimiou avenue. The latter is currently one of the main avenues of the city! The scale of the above mentioned transformation will be extended up to a whole district full of restaurants and cafes, named “Psiri”.
Fig. 1.03 Panepistimiou av. 29/07/10 @ 18:50 source: author
Fig. 1.02 The pedestrianisation of two wide streets - A. Vassilissis Olgas, B. Panepistimiou av. source: author
Fig. 1.04 Vassilissis Olgas 29/07/10 @ 18:40 source: author
Just for the record the programme also comprises transformations of squares, like the Theatre Square and the creation of green roofs, wherever this is necessary and possible, according to the performance of the buildings. Nothing though has been mentioned so far for the pocket size parks as well as for the inward-looking courtyards of the multi-storey buildings. The problem with the latter open spaces can be attributed to the inconvenient conditions of the multiple owners of the flats, where a united solutions, regarding its use and maintenance, is often very hard to achieve. Furthermore, characteristically is the governmental unconcern for the potential pocket size parks. There are not a few cases where the inhabitants had taken their own initiative either to create a new park (Zoodohou pigis & Navarinou), or to prevent destroying one (Kyprou & Patision).
1.3 The case of the pedestrian roads - types and activities (‘open street’ and canyons) The focus of this dissertation is on the pedestrian roads, as many times the absence of squares and/or parks is substituted by the streets. The streets is the place where someone will meet with his neighbours or his friends, will stroll observing the antiquities mostly exposed to the direct solar radiation. Some other times, he will stroll looking for something to buy or unfortunately he will struggle to avoid the parked motor bikes. In many cases the walker does not have a choice as to whether to walk in the shade or sun. The pedestrian roads can be divided into the following typologies with regards to the use: 1. Pedestrian road as a stop 2. Pedestrian road as a connector of the archaeologic monuments 3. Pedestrian road as a connector of trade 4. Pedestrian road as a pathway and way to enter the buildings 5. Pedestrian road as a parking area
Fig. 1.05 Types of pedestrian roads in Athens source: author
5 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
1.4. Methodology The potential of increasing the outdoor urban space by converting part of the existing street network of Athens into pedestrian zones, can promote the quality of the outdoor life in the dense urban environment. This, together with the climatic conditions of a mid-latitude city, may lead to the hypothesis that people might spend more time outdoors during summer if certain environmental conditions are accomplished. Hence the time spend indoors will be proportionally decreased and hopefully the vicious cycle of heating up the outdoor environment with the intense use of mechanical cooling systems such as air conditioning may stop. In an outdoor urban environment, several factors such as the urban layout, orientation, urban materiality, green distribution and anthropogenic heat release, may affect significantly the environmental parameters and hence pedestrians’ thermal comfort. Focusing on pedestrian road typology, the canyons and the ‘open’ streets in Athens were found to be equally important for further investigation. Factors such as geometry, orientation, the level of green distribution with regards to solar radiation and wind distribution within the urban fabric are primal. How might all these may contribute to outdoor thermal comfort? These are issues discussed in the first part of the dissertation. The second part presents the climatic context of Athens and the potential passive design strategies for summer. Informative case studies in cities with similar climatic conditions overlap the bioclimatic evaluation, confirming the potential for the summer comfort band to expand due to clothing and metabolic power alternation, shading, air movement and evaporative cooling. In the fieldwork part, the geometry of ‘open’ street was further investigated with regards to solar radiation and wind circulation, as little information was found following literature review. To examine the impact of vegetation on the pedestrian, an dense urban area was compared to a vegetated suburban area. Occupancy in pedestrian streets was divided into to groups (seated and wakers) by keeping the factor of metabolic power constant, so occupants’ responses could be compared. The issue of direct evaporative cooling regarding occupants’ satisfaction was also analysed at this part. In the analytic part, in order to define thresholds with regards to solar radiation intensity and duration, a detailed solar radiation analysis on street facets and on pedestrians, regarding the diurnal variations, was carried out. The second part of the analytic work comprises microclimatic simulations for canyons with and without trees. In addition, the investigation of the potential increment of urban ventilation and hence air flow within canyons with compact buildings at both side and buildings with two types of galleries was also part of the analytic work. The final part consists of a case of an ‘open’ street and the mapping of the environmental performance of four different spots within the street. The final part presents a future research methodology and the applicablitity of certain solutions not only with regards to pedestrian comfort but also with the heating and cooling demands of the built environment.
2. Theoretical Background 2.1. Outdoor comfort 2.1.1. Outdoor comfort - a general overview “The duration and intensity of use of outdoor spaces is closely linked to how comfortable they are” (Yannas, Designing for Summer Comfort, Ed. 2000) Outdoor thermal comfort is an indicator presenting the correlation between environmental parameters and thermal comfort sensation. Researchers comment on and furthermore explain the outcomes that were based on fieldwork undertaken in-situ (Fig. 2.01, Nikolopoulou et al. 1998 and 2001) on an outdoor space, or by simulating a model of human thermoregulatory system (Fig. 2.02, in Negev, Pearlmutter et al. 2003). To evaluate thermal comfort, environmental parameters, such as air and surface temperature, wind speed, and humidity have to be recorded. Subjective human behaviour and interviewees’ responses cannot be neglected. Nikolopoulou and Steemers (2000) suggest that there must be a in differentiation defining thermal comfort between routes and resting spaces. In routes, people lack the ability of choosing where to stay, whereas in resting spaces they are more flexible. Nevertheless, a discomfort of pedestrians won’t cause them a serious distress as the time of exposure in the case of streets is short. A question which arises from this suggestion is whether it is possible to evaluate interviewees’ actual thermal sensation in streets or not. What if the street is not only a path, but also a meetingresting point? To understand what thermal sensation is and what adaptations people may make in each environment it is necessary to study the impact of the physical, physiological and psychological adaptation. A thorough investigation of humans’ behaviour in resting spaces in Cambridge (Nikolopoulou and Steemers, 2000) has shown that physical and psychological adaptation are complementary and this duality can increase the use of outdoor spaces, strengthening social interaction. The previous analysis focuses on the thermal comfort sensation. The impact of the environmental parameters on occupants’ thermal comfort is a starting point. The potential of controlling heat gains in outdoor spaces may be the solution in increasing the comfort boundaries. Yannas (2000) suggests that wide streets, if protected from solar radiation, can become efficient in terms of thermal comfort during summer. On the contrary, during summer, narrow streets are exposed to solar radiation as much as wider streets but lack the potential of sufficient ventilation, as less air movement is recored.
Fig. 2.01 Network demonstrating inter-relationships between the different parameters of psychological adaptation source: Nikolopoulou and Steemers, 2000
Fig. 2.02 Schematic model of energy exchange between cylindrical body and surrounding canyon source: Pearlmutter et al., 2003
2.1.2. Pedestrian comfort - Thermal Physiological Balance Pedestrian comfort is highly related to the heat exchange of humans and their surrounding environment (Yannas 2000; Ramos and Steemers 2003; Alucci and Monteiro 2004). Humansâ€™ thermal balance can be defined by the following equation: S=M+Q+C+K+E+Res [W/m2] (1) where: S: heat storage in the body [W/m2] M: metabolic power [W/m2] Q: heat exchange on skin by radiation [W/m2] C: heat exchange on skin by convection [W/m2] K: heat exchange on skin by conduction [W/m2] E: heat loss by evaporation at skin surface [W/m2] Res: respiration heat loss [W/m2] The heat exchange on skin by radiation is affected by the shortwave radiation: direct (HD), diffuse (Hd), reflected (Hr) as well as by the longwave radiation (L) which is emitted from the ground floor and walls which surround the human body (see Fig.2.03). Q=L+R [W/m2] (2) R=HD+Hd+Hr [W/m2] (3) L=Lfloor+Lwalls [W/m2] (4)
Fig. 2.03 Thermal-Physiological Balance source: after Yannas, 2000; Ramos and Steemers, 2003; Alucci and Monteiro, 2004
Physical adapatation Normally, a human being may control his thermal sensation, by making personal changes. By altering his/her clothing level, place and position, or metabolic power, the comfort band can be extended. This is well known as the reactive adaptation. The interactive adaptation, on the other hand, has to do more with the changes that an occupant makes to the environment. These can be indoors or outdoors, modifications such as opening a window, controlling a thermostat, opening or closing a parasol, awnings, can extend the time humans spend in a place. How often, though, do people have the ability to control devices in an outdoor space? Research has proved that people are more amenable to staying longer in an outdoor space if their control is substantial. 16
A way to affect human comfort at the pedestrian level is to control the shortwave and longwave radiation which according to Yannas (2000) have a total contribution on heat gains upto 69% with 55% attributed to shortwave radiation. In comparison, the heat gains through the convection with the air, has only a contribution of 7% on humans’ gain (see Table 2-1). Thus, the implication of the solar radiation for pedestrian’s comfort is apparent. Table 2-1. Control on heat gains source: Yannas, 2000
2.1.3. Outdoor comfort - Psychological adaptation It has already been mentioned that outdoor comfort from the objective point of view is related to the psychological adaptation of the occupants. A recent study (Nikolopoulou and Steemers, 2000) revealed the implication of the psychological parameters that affect occupants’ sensation in outdoor spaces (Fig. 2.04). More specifically, the authors concluded that although an agreement of the predicted percentage dissatisfaction [PPD] with the actual percentage dissatisfaction [APD] occurs when investigating indoor spaces, a discrepancy in outdoor spaces was recorded due to the impact of the psychological parameters (see Fig. 2.05). In the case of the pedestrian roads, a possible confounding factor when surveys occur, may be the variation on the past time of exposure of the walkers in certain weather conditions. For instance, in the case of a pedestrian who reaches a specific point after being exposed to direct solar radiation for 30 minutes versus another one who is walking for the same time but is partly in the shade, their previous short-term experience may affect their answers. Thus, the investigation of walkers’ thermal sensation may present multiple difficulties. Efficient solutions, for both physiological and psychological adaptation, were found to be occupants’ freedom of choice, as well as the movable structures, the transitional spaces and elements that may change during the day according to the sun’s position.
Fig. 2.04 Physiological and Psychological adaptation source: after Nikolopoulou and Steemers, 2000
Fig. 2.05 Discrepancy of dissatisfaction source: Nikolopoulou and Steemers, 2000
2.1.4. Thermal Comfort Assessment Many studies have been conducted with regards to the indoor thermal comfort, in climate chambers or free running buildings (Nicol, F. and L. Pagliano, 2007). Recently, there has been an increase in the interest in the behaviour of occupants outdoors (Nikolopoulou, 2000; Corbella et al., 2001; Givoni et al. 2003; Ramos and Steemers, 2003; Alucci and Monteiro 2004; Matzarakis, 2007; Lin et al., 2010). Comparing the comfort simulation of an indoor space, with that of an outdoor space the parameters that may affect the predicted percentage dissatisfied occupants [PPD] are multiple. For instance, in a location with hot dry summers, solar radiation is one of the most important factors that a researcher must take into consideration. On the contrary, this factor does not make any difference in an indoor space. Additionally to this, the unpredictable air movement moulds a rather complicated environment. The unpredictability of occupants’ activities and clothing insulation make any prediction even more difficult. There is no consensual comfort index for outdoor spaces, as there is for indoor spaces, where physical parameters are controlled. This is the reason why researchers are focusing mostly on fieldwork experiments (Corbella et al., 2001; Givoni et al. 2003, Nikolopoulou, 2004). In this dissertation though, all comfort theoretical calculations were done by using the Berkley, CA simulation tool which was created for the American Society of Heating, Refrigeration, and Air-Conditioning Engineers [ASHRAE] (Fig. 2.06). The results are more reliable in predicting thermal sensation of a group of people in sedentary activity, wearing light clothing in leeward condition. This can be explained as it is based on Fanger’s (1970) equation (5), which was calculated from field experiments indoors. It gives a gradient result of dissatisfied people not only with regards to the four environmental parameters (air temperature, mean radiant temperature, relative humidity, air speed), the metabolic rate and the clothing level, but also with regards to the time of exposure in a certain condition. However, it does not include the heat storage of the human body, factor that may affect significant one being outdoors. An additional problem is that this software does not take into account air temperatures and mean radiant temperatures above 35oC. This is a particular issue for tropical climates or just climates with hot summers. Mean radiant temperature [mrT] The mean radiant temperature [mrT] is a crucial factor in extending the assessment of human comfort from indoors to outdoors (Toudert and Mayer, 2005). It is “the uniform surface temperature of an imaginary enclosure in which an occupant would exchange the same amount of radiant heat as in the actual non-uniform space” (ASHRAE 55-92).The mrT is a factor which sums up the shortwave radiation and longwave radiation as well as the direct solar radiation impinging normal on a surface (see also equation 6). Thus, in open urban environments where the sky view factor is high (e.g. SVF=0.95) the solar radiation reaching the street level can be close even to the solar radiation of an unobstructed surface. Consequently, in this case the mrT will be proportionally high. In the case of the streets now, this can be interpreted as a significant factor for the very shallow streets, or for the streets that are asymmetrical and/or unobstructed from one or both sides. There are several ways to calculate the mrT. For leeward conditions, when the mean radiant temperature is equal to the global temperature [GT] a practical way to measure it in field experiments, is to measure the GT with a black globe thermometer, which responds to radiant inputs as well as to air temperature. Szokolay (2008) suggests a 150-mm diameter copper ball, (recently) painted matt black, with a thermometer at its centre. Ping pong balls were found to have the same effect on measuring the GT. In ‘Rediscovering the Urban Realm and Open Spaces’ (RUROS, 2004) the authors introduced a simplified graphic way based on computer simulations, for evaluating mrT in street configurations. They created several maps to assess the mrT with regards to three different climatic zones (Latitudes: 55o, 45o, 37o) and two different groups of materials: cool materials and daily warm materials, for low wind speed urban contexts (Fig. 2.07). In order for this research to have an applicability in all climatic zones it has to be broadened to all latitudes, especially the ones close to the equator (e.g. 20o). An alternative way to estimate the mrT based on computer simulations is Envi-met v.4.0 created by Michael Bruse and team. The software has an output selection for mrT maps as cut planes, in all axes. The software covers a wide range of latitudes. 18
Fig. 2.06 Berkley CA tool Predicted Mean Vote [PMV] and Percentage Predicted Dissatisfaction [PPD] source: author
(5) f(M, Icl, v, tr, ta, Pw) = 0 where M: metabolic rate, met Icl: cloth index, clo v: air velocity, m/s tr: mean radiant temperature, oC ta: ambient air temperature, oC Pw: vapour pressure of water in ambient air, Pa source: http://personal.cityu.edu.hk/~bsapplec/newpage315.htm
where: Ei: longwave radiation component Di: diffuse and diffusely reflected short-wave radiation component Fi: angle-weighting factor I: direct solar radiation impinging normal to the surface fp: surface projection factor αk: absorption coefficient (approx. 0.7) εp: emissivity of the human body (approx. 0.97) σ: Stefan-Boltzamann constant (5.67x10-8 W/m2K4) source: Toudert, 2006
Note Simplified method to evaluate mrT: 1.define the latitude of the location 2.verify the orientation of the urban space and the sections in terms of H/W ratio 3. define the period of day 4. read in the appropriate graph the approximate mrT value. source: RUROS project 2004
Fig. 2.07 Maps to assess the mrT with the simplified method Left - EW streets at noon Right - NS streets at noon source: RUROS project 2004
2.2. Urban spaces and diversity - Mapping environmental performance of open urban spaces Arens and Bosselmann (1989) created a method by using a comfort-prediction program. By plotting the outdoor temperature, humidity, wind direction, wind velocity and rain for each hour, they managed to predict the impact of the environmental parameters on humans’ comfort, for a full year. In Fig. 2.08, a case study in Boedekker park, San Francisco, CA, during spring conditions, has been plotted for the existing conditions and mitigated development. They used a modified version of a mathematical model of the human thermoregulatory system developed by Pharo Gagge at the J. B. Pierce Foundation Laboratory. The model is sensitive to variations in activity (metabolic rate) and clothing, and in ambient temperature, radiation, relative air velocity and humidity. In more recent studies (Ruros project 2004; Steemers, 2004), researchers suggest mapping the key parameters such as, sky view factor, sunlight and wind and temperature in order to present the spatial diversity, through different times of a day, in an open space. More specifically, in All Saint’s Garden, in the city of Cambridge, they overlapped the thermal, spatial, solar and wind conditions to present the preferred areas within the selected site based upon their potential for view of the sky and sunny and still conditions, sunny and windy, and shady and still, as well as shady and windy (Fig. 2.09). In both studies the researchers manage to overlay the environmental conditions with regards to the preferred areas. In the case of the streets, usually, the sky view factor is on average the same at most points along the street. Thus, the predominant factors which may affect occupants’ perception is the solar and wind conditions.
Fig. 2.08 The spring condition in Boedekker park, San Francisco, CA source: Arens and Bosselman, 1989
Fig. 2.09 Open space diversity Profile. Image on the left shows the resultant overlay between threshold maps of sky view factor, solar shadowing and wind shadowing. Graph shows the distribution of various environmental combinations present at the site source: after RUROS project 2004
2.3. The street typology 2.3.1. Street geometry and solar access Many studies have been conducted with regards to the ‘street canyon’ geometry and solar access (Oke, 1988, Arnfield 1990). The ‘street canyon’ or ‘urban canyon’ “is the artefact of an urban environment similar to a natural canyon. It is manifested by streets cutting through dense blocks of structures, especially skyscrapers, which causes a canyon effect” (http://en.wikipedia.org/wiki/Street_canyon) Oke (1988) presented a dilemma in designing four goals: a. maximize shelter, b. maximaze solar access. The two pairs, a with b and c question of which scenario the urban planners around 40o, arises.
buildings, especially in mid-latitude cities, according to dispersion, c. maximize urban warmth, d. maximize with d, require opposite structures. Consequently, the and designers should follow for a city with a latitude of
The focus of this chapter is the manipulation of solar access. During the winter period, the need for solar radiation, indoors and outdoors, is obvious. On the contrary, the issue of solar control during the summer period, in a city of around 40oN, is crucial. Although the two periods (winter-summer) require different designs, researchers (Oke, 1988, Arnfield 1990) concluded with a variety of guidelines, according to the street canyon proportions and different latitudes. In the case of Athens (37.58oN), an E-W oriented canyon with H/W of 0.7 is a benchmark for accession of adequate direct-beam and diffuse solar radiation in the winter solstice (Fig.2.10). Using this benchmark ratio, how does the direct and secondarily the diffuse solar radiation affect pedestrians’ thermal comfort during the summer? Is shading needed and, if so,where? If yes, which is the most efficient way?
Fig. 2.10 The area of an equator-facing wall in an E-W oriented street canyon that potentially receives direct-beam solar radiation at noon in the winter solstice as a function of latitude and H/W. The lit area is expressed as a percentage fraction of the total wall area source: after Oke, 1988
Arnfield (1990) extended Oke’s research by defining benchmarks for the street design in different latitudes, according to the irradiance on floor, walls and on a model pedestrian, for winter, summer and annually, on N-S and E-W oriented streets. He also calculated the mean irradiance on N-S and E-W oriented streets (Grid). He concluded that in a mid-latitude city (35o - 55o) in June the floors are more irradiated than the walls, especially for the E-W oriented streets. Looking at the N-S oriented streets this is more decisive in a canyon with a H/W ratio of 2 or shallower. The floor irradiance is affected more from the canyon proportion, whereas the irradiance in the vertical facets is affected more by the orientation (i.e. low altitude angles early morning and late afternoon) The numerical studies conducted by Arnfield, present the magnitude of irradiance in a canyon according to different orientations and height to width ratios (see Fig. 2.11). The question is whether there are irradiance deviations within a canyon of various H/W ratios and different orientations. In other words, does a pedestrian have the possibility to choose where to walk, stand or sit, within the canyon?
Floor irradiance [W/m2] ted
Wall irradiance [W/m2]
1 2 3 4 H/W
Fig. 2.11 Canyon floor and wall irradiance in June source: Arnfield, 1990
Although researchers worked extensively with the geometry of mostly symmetrical canyons, little attention has been paid to the asymmetrical ones and/or open canyons. By ‘open’ canyons, if we choose to call them this, we mean the streets which are unobstructed from building shading from one and/ or both sides (Fig.2.12). This typology is not often seen in a dense urban area, although it cannot be overlooked. Frequently, tree rows exist on one side or both sides. Open streets can be paralleled with the very shallow urban canyons, as in both cases there is high level of insolation impinging on the ground. Most of the researchers examined the impact of geometry on the reduction of radiation at pedestrian level, either by defining the levels of radiation (global, direct, diffuse, reflected), or by estimating the physiological equivalent temperature [PET]. This is a comfort index which is based on human energy balance and takes into account the thermo-regulatory capacity of a human body. PET includes air temperature, mean radiant temperature, relative humidity, wind speed, human clothing and activity (Lin et al., 2010). Air temperature itself was found to give insufficient information regarding pedestrian comfort, although it is the first indicator that researchers may look regarding the cooling loads in building. In a case study in a hot dry climate, Johansson et al. (2001) compared two symmetrical canyons; a very narrow one (SVF=0.05) and a typical one (SVF=0.64). When assessing outdoor thermal comfort they assumed the mean radiant temperature equaling the air temperature. They concluded that the case of the narrow streets, as the radiation is insignificant, the error would be minimal. On the other hand, in the shallow one the error could not be ignored.
Fig. 2.12 An ‘open’ street surrounded with trees. A future pedestrian road source: www.bing.com/maps/
Air temperature Toudert and Mayer (2006) studied various geometrical configurations in Ghardaia of Algeria (32.40oN, 3.80oE). They concluded that the air temperature appears to be more sensitive to aspect ratio than to the orientation. The E-W streets are slightly warmer than the N-S streets, particularly as the aspect ratio increases. This is due to longer exposure to solar radiation in E-W streets. On average, the E-W street canyon with H/W=0.5 is the warmest whereas the N-S street with H/W=4 is the coolest (see Fig. 2.13). A maximum difference of about 3K between the widest and the deepest profiles was found at around 15:00 LST for both orientations.
Fig. 2.13 Diurnal variation of the simulated air temperature Ta at 1.2m above the ground in the middle of the street canyons of an aspect ratio of H/W=0.5, 1, 2 and 4,oriented E-W and N-S, for a subtropical location on a typical summer day source: after Toudert and Mayer, 2006
Fig. 2.14 Model tested in a hot-arid climate, Neveg (southern Israel) source: after Pearlmutter, 1998
Pearlmutter (1998) proved that in an E-W oriented symmetrical canyon (Fig 2.14), the air temperature at head height during the afternoon was warmer by up to 3K, as compared to the air temperature above the roofs. This was explained by the fact that the canyon acted as a “pocket” trapping the air, whereas above the roofs the ventilation was sufficient to cool down the ambient air through the convection process. On the contrary, surface temperatures of canyon’s facets were around 10K less as compared to the roof surface temperature. In a more recent study, Johansson et al (2001; 2006) investigated a very deep canyon in Morocco (33O58’N, hot dry climate). They compared a deep canyon (H/W=9.7, SVF=0.05) in the traditional part of the city with a shallower canyon in the modern part of the city (H/W=0.6, SVF=0.64). During the summer period, the average difference in maximum daytime air temperature was 6K. During the period of the fifteen hottest days this difference came up to 10K (Fig.2.15).
Fig. 2.15 Average air temperature for the summer period (left) and for the 15 hottest days (right) in the deep and shallow canyons and rural station source: after Johansson, 2006 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Solar radiation fluxes Toudert and Mayer (2006) also concluded that the direct solar radiation decreases as the aspect ratio increases. On the contrary, the diffusely reflected radiation rises with the increase of the aspect ratio. Nevertheless, this did not exceed 250W/m2, in all examined cases in Ghardaia of Algeria (32.40oN, 3.80oE). The diffusely reflected component increases as walls become higher (see Fig. 2.16). For an E-W oriented street, a H/W=2 was considered as the threshold with respects to solar access. This happens because global radiation received varies only minimally for aspect ratios of 2 or less. N-S streets are less irradiated for a longer period as compared with E-W. In this case, the building obstruction on street level is much more significant (Fig. 2.17).
Fig. 2.16 Radiation distribution within various canyons in Athens Left: shortwave reflected component with a 0.2 albedo for walls and floor -Right: different altitude angles on an equator faĂ§ade at noon source: author
Fig. 2.17 Shadow range during the hours of 9:00-16:00 on 21st June for an E-W (left) and N-S (right) oriented streets in Athens with an aspect ratio H/W=2 source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Pearmutter (1998) came up with a remarkable conclusion. During most summer daytime hours, a pedestrian in the unitary canyon absorbs less thermal energy from the environment than a person above the roof level. Thus, although the air temperature may be elevated within the canyon and the wind obstructed, the significantly lower magnitude of solar radiation absorbed by a pedestrian (direct and diffuse) compensates for the reduction of heat loss through the convection process. Hence, as solar radiation is highly correlated to mean radiant temperature, the latter becomes a very important factor in a pedestrianâ€™s heat exchange with his/her ambient environment. Nevertheless, while investigating an outdoor environment, it is very important to find initially a balance between all the physical parameters. Thus, as leeward conditions are the most predominant in the centre of a city (dense urban environment), what can firstly be investigated are various geometrical configurations with regards to wind penetration at low level (up to 3m), within a canyon.
2.3.2. Street Canyon geometry and impact on pedestrians’ comfort Both Oke (1988) and Arnfield (1990) investigated thoroughly the issue of the canyon’s geometry and its impact on the solar access to the canyon’s facets, throughout the year. Arnfield introduced the topic of canyons’ geometry and the effect on a pedestrian. Oke also mentioned that there is insufficient information regarding canyon climate and comfort. Comfort for whom? For the occupants of the buildings, the pedestrians, or both? More specifically, Arnfield (1990) defined benchmarks for a pedestrian in canyons of various aspect ratios in latitudes between 0o-70o for two orientations (N-S, E-W) and calculated their average (GRID). From Fig. 2.18 what can be observed is that for a latitude of around 40o, comparing a canyon with H/W=0.5 to one with H/W=4, there is a difference of around max. 25W/m2. Generally, there is a very small dependance on irrandiance and latitude for all aspect ratios. Additionally, as it was expected, the irradiance decreases as the aspect ratio increases. Nevertheless, all the above points are general conclusions and and do not provide any information on the diurnal deviation of incident solar radiation on pedestrians. Thus, it can be concluded there were two points that were overlooked in this study. First of all, it did not show the hourly values of irradiance for a winter and summer day. Consequently, there are no irradiance data to evaluate with regards to the time of exposure of a pedestrian. The pedestrian model was at 97% vertical surfaces and 3% horizontal. The second point is the lack of information with regards to irradiance on different parts of a body, for instant head and the rest of the body.
Fig. 2.18 Irradiance on pedestrians [W/m2], where x axis is the latitude and y axis is the irradiance source: Arnfield, 1990 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
2.3.3. Impact of vegetation Many researchers (Dimouli and Nikolopoulou, 2000; Papadakis et al., 2001; Shashua-Bar and Hoffman, 2003; Alexandri, 2005; Ali-Toudert and Mayer, 2007) have been recently worked on the issue of the impact of vegetation on the microclimate. There is a general agreement that vegetation reduces air temperature by direct shading of urban facets and moderates solar heat gains through evaportranspiration of the plants (conversion of incident solar radiation to latent heat). Additionally, vegetation impoves remarkably the air quality by trapping Greenhouse gases (CO2, CH4) and aerosols. Air temperature As streets cover more than a quarter of the urban area, they play a signigficant role in the local microclimate. Shashua-Bar and Hoffman (2003) studied the impact of vegetation in a minor scale, in streets. They point out, after Oke’s article “The Micrometeorology of the Urban Forest” , that trees receive, apart from the direct solar radiation, large amounts of reflected shortwave energy from the irradiated walls and floor of the streets. Additionally, Oke mentions that a tree may also receive boosted inputs of longwave energy from the built environment (through evaportranspiration). Furthermore, Shashua-Bar and Hoffman clearly stated that heat losses dissipate from trees in two ways: the latent one (evaportranspiration) and the sensible one (convection). The two components depend on the water balance and wind condition around the tree. When the climate is hot-dry, the leaf temperature is about the same as the air temperature above the tree canopy, whereas it is warmer as compared to the air temperature below it (Table 2-2). Thus, the authors concluded that the exchange is predominantly downwards. This can be beneficial mostly for the pedestrians. Table 2-2. Air and leaf temperature in Hayeled [oC] source: after Shashua-Bar and Hoffman (2003)
Wind speed Little attention has been paid to the critical point of the presence of trees in a compact urban area with regards to pedestrians’ comfort. Trees may affect wind penetration in the urban fabric, especially at street level, considering that they function as windbreaks. This might be beneficial during winter time, but on the contrary during the hottest period, it may affect pedestrian’s thermal comfort significantly. Thus, a comparative study of examining the convection rate in certain wind speeds, when streets are unplanted, to the obstruction of solar radiation on facets, when streets are planted with trees, is necessary. Wall temperatures Field experiments by Papadakis et al. (2001) on a SE façade at the Agricultural University of Athens aimed to prove the effect of solar control of buildings by shading with deciduous trees. Wall temperatures, ambient air temperature and wind speeds were the primary physical parameters referred to in this study. They compared a shaded to an unshaded part of the same façade. A decrease of around 500W/m2 was observed at the shaded part of the wall. This reduction with the evaporative effect of trees contributed to cooling the ambient air up to 3K. During the daytime the air temperature in the shaded area was lower than the corresponding one in the unshaded area. This was explained, not only by the lower values of incoming solar radiation, but also because air temperature was higher than the wall temperature in the shaded area (see Fig. 2.19). Thus, the cooling effect of the ambient air through convection took place. On the contrary, in the irradiated area the opposite effect occured. Wall temperature was higher than the ambient air temperature. During night time, both air temperature and walls’ temperature in two areas came close together. In the case of the shaded area, walls were slightly warmer (up to 1K). This can be explained by the low average wind speed values observed on the shaded part (0.2m/s), whereas a 0.6m/s was observed on the irradiated area. 26
Fig. 2.19 (a) Solar radiation in the shaded area (thin line) and unshaded area (thick line) (b) Net radiation in the shaded area (thin line) and unshaded area (thick line) (c) Wall temperatures in the shaded area (thin line) and unshaded area (thick line) (d) Air temperature in the shaded area (thin line) and unshaded area (thick line) note: with red average temperatures for unshaded area, with blue average temperatures for shaded area source: after Papadakis et al., 2001
Despite the overall advantages of deciduous trees, even these may contribute negatively on heat storage in exterior walls, as their logs and branches block part of the welcome solar radiation during winter. This might be the reason why other researchers focused on the effect of ‘vegetated walls’. A vegetated wall or green façade describes “the cases where vegetation is applied to the vertical elements of a building” (Alexandri, 2005). The planting medium is usually not adjacent to the building element, but on another surface, either on the ground or on container (see also Fig. 2.20). Alexandri also stated in her PhD thesis entitled “Investigations into Mitigating the Heat Island Effect through Green Roofs and Green Walls”, that green walls can be beneficial for both the construction itself and the thermal conditions of both the interior and the exterior of the building. The author managed to establish a two-dimensional model to express the effect of vegetation on the built environment at the microscale. She further tested it with canyons of various aspect ratios in different climates (e.g. Mediterranean Climate, Steppe Climate, Savana Climate, Humid Subtropical Climate, Temperate Climate, Desert or Arid Climate).
Fig. 2.20 Hydroponics - a new trend with regards to vegetated walls “a method of growing plants using mineral nutrient solutions, without soil” source: http://news.architecture.sk/2010/03/iam-lost-in-paris-rsien.php E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
According to Alexandri (2005) vegetated south facing walls in Athens (mediterranean climate), recorded a significant alteration on surface temperature (maximum decrease of 16.2K and mean daytime decrease of 12.3K) especially at the upper floors of a shallow canyon (H5W10). She also added that vegetated walls contribute to lowering the temperature of asphalt surfaces (maximum decrease 1.5K), whereas the average air temperature reduction is even lower (0.8K, see also Table 2-3). This alteration can be attributed to the decrement of reflected short-wave radiation from walls. Nevertheless, the above mentioned intervention, is possibly more significant in minimising the cooling loads of the built environment and mitigating the heat island effect, rather than affecting pedestriansâ€™ thermal comfort directly. At two points 1m above ground (a, d, see Fig. 2.21) close to the walls of the canyon the air temperature decrease ranges from 1.2K - 3.1K. In a rather shallow canyon though, based on previous theoretical analysis, the magnitude of direct solar radiation is relatively high. The assumption that tree shading, will be more effective in this case, can be made. Table 2-3 Comparison of temperature decreases [oC] inside the canyon (top) and of the canyon walls (bottom) for green-roofs, green-walls and green-all, for H5W10, E-W orientation, wind flow perpendicular to the canyon, Athens source: Alexandri, 2005
Comfort Assessments Ali-Toudert and Mayer (2005; 2007) did several studies regarding the street canyon geometry and comparison of urban streets with and without trees. In particular, they examined different geometrical characteristics, various height to width ratios, asymmetrical canyons, canyons with galleries and overhangs. They also investigated all these geometrical configurations with regards to the impact of the trees. A basic experiment of a canyon with H/W=2, with and without trees, was conducted, by using the numerical modelling software of microclimatic conditions [Envi-met 3.0]. The street was E-W oriented (worst case scenario). They concluded that the largest differences in the reduction of direct solar irradiance occured between 9:00-10:00 and 16:00-17:00 (see Fig. 2.22), 850W/m2. This can be translated into a decrease of 22K of the physiologically equivalent temperature [PET](see also Table 2-4), directly under the crowns, not only because of less direct solar radiation, but also because there was a reduction of the upward (from street surface) long-wave irradiance.
Fig. 2.21 Geometry and grid of the wake interference flow canyon (H5W10) for the “greenwalls” case [gr-w] source: Alexandri, 2005
Fig. 2.22 (a) Differences in long-wave radiation (ΔL-upwards) emitted by the ground surfaces between street with a row of trees against a street without trees (b) and (c) PET distribution across urban canyons oriented E-W with H/W=2 with and without a row of trees source: after Toudert and Mayer, 2007 Table 2-4 Ranges of the physiological equivalent temperature [PET] for different grades of thermal perception by human beings and physiological stress on human beings; metabolic power: 80W; clothing insulation: 0.9 clo source: Mantzarakis, 2007
Note PET range may be significanlty different for different climatic zones as occupants adapt to certain climatic conditions after a continuant exposure to them.
2.3.4. Street Canyon and air flow Wind and geometry Researchers have found a strong correlation between air flow and proportions of a canyon. Oke (1988) defined three different types of air flow within a canyon, when wind is perpendicular to the street: isolated roughness, wake interference and skimming flow (Fig. 2.23). The different types of flow are highly related to the geometrical characteristics of a canyon (i.e. building’s height H, length L and width W, see also Fig. 2.24). Wind in a field experiment Santamouris et al. (1999) conducted a field experiment in a deep pedestrian road in Athens (H/W=2.5), Valaoritou street, oriented NW-SE 30o from S-N. They dealt with the air temperature and surface temperature distribution along the canyon’s facets (street and walls) as well as with the wind distribution. Focusing on the wind distribution, they concluded that when the wind is perpedicular to the street axis, the air flow inside the canyon is mainly characterised by either a circulatory vortex or a double votex. A strong relation was found between the velocity inside the canyon and the velocity above the roof tops when the wind flow was parallel to the street axis. They also observed an ‘end’ effect on the air flow inside the canyon. More specifically, when the wind speed was perpedicular to the street axis the majority of the wind measurements were recorded in a range of 0-0.6m/s with a downward direction (see also Fig. 2.25 and 2.26), when the 93% of the wind flow out of the canyon was lower than 5m/s with a predominant direction of SE-NW. When air flow parallel to street axis was examined, similar recordings of wind speeds were measured. A strong correlation was found between the ambient wind speed parallel to the street axis [Vx] and the along wind speeds inside the canyon [u]. The greater the Vx the greater the wind speeds within the canyon.Nevertheless, they couldn’t corroborate Nakamura and Oke (1989) linear correlation u= pVx, as this equation is related to wind speeds of up to 5m/s and the majority measured wind speeds measured in Valaoritou (95%) were lower than 4m/s. The vertical component of the air in the canyon [w] is directly related to the along wind speeds [u]. According to Arnfield and Mills (1994) when there are no along winds in the canyon, the mean vertical canyon velocity is close to zero. On the contrary, Santamouris et al. measured an important downward air movement close to the walls, which was attributed to the length of the street (150m). For air flow in an angle to the street axis, limited field measurements were taken and the research was mainly based on wind tunnel and numerical calculations. The highest median quartile (0.33-0.6m/s) was recorded when the wind speed out of the canyon ranged between 4-5m/s. Wind and comfort Researchers (Penwarden, 1973; Arens;1981) have found a correlation between the beneficial air movement and thermal sensation. Characteristically, on Penwarden’s charts (Fig. 2.27) regarding the comfort condition for strolling in entirely sunny (direct solar radiation) and shady conditions (diffuse solar radiation), what can be extracted is that the effect of an increased wind speed on air temperature is greater at low speeds (3.5m/s and 2.5m/s, respectively). Arens found a benchmark of 4m/s, when turbulence effect is negligible. The greater the turbulence effect, the lower the acceptable wind speeds. He also mentioned that wind speeds below 0.26m/s have practically the same thermal effect as being in a still condition, whereas the upper limit of acceptable wind speeds outdoors can reach the 6m/s. Penwarden (1973), on the other hand, created a table (Table 2-5), regarding the wind speeds and their effects in the occuppants in indoor and outdoor conditions. At wind speeds of up to 5.5m/s only people’shair will be disturbed and the clothes will flap. He gives though an extened range up to 7.9m/s where an occupant outdoors would rather feel uncomfortable as dry soil will start to blow in the air. To conclude, there is an agreement between both researches, that an upper limit of 6m/s, is beneficial for occupant’s thermal sensation in an outdoor space. This value can be considered as a benchmark. 30
Fig. 2.23 The flow regime associated with air flow over building arrays of increasing H/W ratio a. 0.005<H/W<0.4, b.0.4<H/W<0.7, c. 0.7<H/W source: Oke, 1988
Fig. 2.24 Threshold lines dividing flow into three regimes as functions of the building (L/H) and canyon (H/W) geometries source: Oke, 1988
Fig. 2.25 Wind above the canyon - Divided in three components source: author
Fig. 2.26 Perpendicular flow - Along canyon, u, against vertical wind speed, w source: after Santamouris et al, 1999 Table 2-5 Wind speeds and their effect on human body source: Penwarden, 1973
Fig. 2.27 Wind speeds and their effect on human body source: after Penwarden, 1973 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Wind and pollution Wind is not only necessary for the improvement of pedestriansâ€™ comfort. It helps also in cooling down the highly irradiated (during summer) buildings and in pollution dissipation. In this dissertation,these two topics will not be disscused at all, although they are equally important. As a conclusion, it is worth noting the reduction of the wind speeds within a deep canyon (H/W=2.5), in the field experiment of Santamouris et al., regardless of the wind direction. The study though does not include various profiles of canyons. What would happen in a shallower canyon (i.e. isolated roughness flow, wake interference flow)? How wind speeds are affected by the tree canopy in an open street? How galleries at street level may amend urban ventilation?
2.4. Conclusions of theoretical backround When dealing with thermal comfort in pedestrian streets, the following issues have to be considered: ---It was found that occupants outdoors may control their thermal sensation primarily when reactive (clothing, position) and/or interactive adaptative (parasols, awnings) opportunities take place. Solar wind conditions are basic factors that affect outdoor comfort. There is a need to map the environmental conditions with regards to the actual dissatisfied occupants. ---When assessing outdoor thermal comfort mean radiant temperature is a predominant factor that has to be plotted. This might be even more significant in streets which are highly exposed to solar radiation. Shallow canyons are affected more by direct solar radiation, whereas in deep canyons also the factor of the diffuse and diffusely reflected component, and hence the albedos of the walls, cannot be neglected. ---There might be a difficulty in assessing pedestrian comfort with regards to walking activity due to past time of exposure of the walkers in certain weather conditions. ---There is no consensual comfort index for outdoor spaces. The Berkley, CA simulation tool does not include the heat storage of the human body, as solar radiation is negligible indoors. Thus, any results might deviate from the reality. This is probably the reason why researchers focus mostly on fieldwork experiments. ---An important question that arose was whether there are there any irradiance deviations within a canyon of various aspect ratios and orientations or not. In other words, whether a pedestrian has the possibility to choose where to walk, stand or sit, within the canyon. ---A solar analysis of various aspect ratios and orientations with and without tree shading (horizontal shading may reduce irradiance of floors) is needed to assess the diurnal reduction of incident (direct and diffuse) solar radiation, during the summer period. In addition, the diurnal irradiance on pedestrians with regards to time of exposure is also an important factor that has to be investigated. ---To examine the potential of increase of air movement at pedestrian level, an investigation of air flow in various geometrical configurations is required.
Table. 3-1 Climatic data of Athens source: Meteonorm v.6.1
Fig. 3.01 Map of Greece - Position of Athens
3. Context & Precedents 3.1. Climatic context - Urban mesoclimate Athens is located in the centre of Greece (37°.58’ N, 23°, 43’ E, Fig. 3.01) and is the capital of the country. The climate of Athens is a warm Mediterranean climate, with seasonal variations, mild-humid winters and warm-dry summers. The Athenian climate has spatial variations (Evagelinos et al. 2003) as each area’s mesoclimate is affected by predominant elements. There are three mesoclimate types according to Evagelinos et al. (2003): a. the coastal mesoclimate affected by the sea, b. the mesoclimate of mountains, affected by large mountainous volumes and c. the urban mesoclimate affected by the intense urbanisation. The mean monthly temperatures range from 9.5oC in January, which is the coldest month of the year, to 28.4oC in July, with a potential of reaching maximum temperatures up to 38.2oC (Table 3-1). In the late spring months and early autumn months, mean monthly temperatures range from 20.6oC in May to 19.1oC in October. Additionally, the yearly average frequency of sky types is 68% sunny sky, 21% intermediate and 11% cloudy, an evidence of the significant presence of sun throughout the year (Fig. 3.02).
Fig. 3.02 Frieqeuncy of sky types source: www.satel-light.com
Thus, the effect of incident radiation on the perception of a pedestrian’s comfort, during summer (91% avarege sunny sky) is crucial. It is welcome during the colder months, from November until April, due to its contribution to heat gains, but unpleasant during the warmer months from May until September. NNE winds are prevail all year, however, the prevailing wind in summer months has a more north orientation with prevail 3.6 m/sec while north and north-east winds are mostly observed in winter months with speed of 3.2 m/s. Hence, the cooling effect should be promoted during summer months, with the additional provision of shade that could increase the comfort band. Relative humidity in winter reaches a monthly average in December of 71%, while in July and August it decreases, reaching the average monthly minimum levels of 43-44%. Although the average may be around 44%, the afternoon relative humidity can be as low as 35%. The problem of low humidity level, especially in the afternoon during summer months, could be solved by increasing vegetation as well as with other applications of evaporative cooling methods. (see also Appendix 9.1)
Solar radiation During summer months in Athens (June-August) between 12:00-14:00, the global horizontal radiation varies from 724W/m2-802W/m2. In June, during peak hours, direct horizontal radiation is around 100W/ m2 less than in July and August. On the contrary, diffuse horizontal radiation is slightly higher. July and August average daily values are rather similar, although in July the global and direct horizontal radiations throughout all daytime hours is higher (Fig. 3.03). This is more obvious in figure 3.04 from the average values of the daytime period for each month. After Velazquez et al. (1991), it can be concluded that the level of global radiation in Athens is close to the one in Seville (June: 840W/m2, July: 863W/m2, August: 827W/m2). The two climates are very similar during the hottest period as same values were recorded for the relative humidity at the hour with the peak temperature (RH=35%). During winter, Arens (1981) proved the importance of solar radiation for a person being outdoors, regarding the breadth of his comfort band. He designed a graph for solar altitude of 45o (average value for the U.S.), where a total (direct and diffuse) solar radiation of 70W/m2 contributes to an acceptable Ta of 19oC as well as a solar radiation of 490W/m2 contributing to an also acceptable Ta of 6oC!
Fig. 3.03 Diurnal global, diffuse and direct horizontal radiation for summer months: a. June, b. July, c, August source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 3.05 Expansion of winter comfort band with the contribution of solar radiation source: after Arens, 1981
Fig. 3.04 Average global, diffuse and direct horizontal radiation for summer months source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Solar radiation on occupant outdoors The contribution of incident radiation to heat gains of a pedestrian occupying a space unobstructed from incident solar radiation can also be related to the clothing absorbance of the occupant. This would be welcome during the colder months, from November until April, due to its contribution to heat gains, though unpleasant during the warmer months from May until September. For instance, on a typical summer day, at 12:00 pm, the impact of incident solar radiation falling on an occupant with clothing absorbance of 0.6 can cause a 9K increment on operative temperature. Some researchers (Arens, 1981; Alucci and Monteiro, 2004) have indicated the effect of directional radiation on comfort. Hypothetically, a human inside of a sphere will record a difference in radiant temperature between the two hemispheres. During summer, when the altitude angle is characteristically large in such climate, the upper hemisphere will receive more radiation. If the difference, in the radiant temperature of two sides of a plane at the center of the sphere exceeds 20K a great discomfort may occur. Hence, in the case of the streets, more careful attention is needed when dealing with the protection of the upper part of the humanâ€™s body (e.g. head) rather than with the lower part of the body, which is mainly subject to diffuse and diffusely reflected shortwave radiation component and/or longwave radiation. Concequently, it can be concluded that it is better to shade a pedestrian above his head, instead of just reducing the albedos and the thermal capacity of the surrounding facets. It is well known though that the thermal properties of urban materials may reduce the heat island intensity in the centre of the city significantly and furthermore this kind of intervention may diminish the cooling load of thebuildings significantly. This issue though, will not be discussed in this dissertation.
Fig. 3.06 Increment of operative and mean radiant temperature for various clothing apsorbtances source: CIBSE Guide A p. 1-15
Fig. 3.07 A hypothetical black human body related to two hemispheres The contribution of incident solar radiation in comparison with the reflected component and longwave radiation source: authour
Wind and occupant The issue of turbulence intensity and acceptable wind speeds has been thoroughly investigated for indoor environments. What can be seen from Fig. 3.08 is the effect of turbulance intensity, at wind speeds of up to 0.5m/s, at various air temperatures, on percentage of dissatisfied occupants. Many researchers (Penwarden, 1973; Arens;1981) have been identified benchmarks for acceptable wind speeds in an outdoor environment. Wind speeds of up to 6m/s are acceptable outdoors (Fig. 3.09), whereas up to 4m/s the impact on comfort is more significant, when turbulence is negligible. At speeds above this, the wind shows a smaller rate of impact in comfort (see also chapter 2.3.4. Street Canyon and air flow). In an urban environment the wind is usually forceless, at the street level, due to high obstruction of the buildings. Although at 10m above ground wind speeds of around 3m/s can be recorded (see also Fig.3.10). The ultimate aim is to provide the potential of wind reaching the pedestrian level. The contribution of wind to comfort is first of all due to direct heat losses through convection, when air attaches to humansâ€™ skin. However, it may also help to cool down the air temperature when air reaches a body of water (indirect evaporative cooling, Fig.3.11). Givoni (1998) suggests that the water body should be
6.00m/s 2.00m/s 1.00m/s 0.26m/s shading line
Fig. 3.08 Effect of turbulence intensity with regards to air speed and air temperature tested in a climate chamber source: CIBSE guide A, 2006
Fig. 3.09 Expansion of summer comfort band with the contribution of air movement source: after Arens, 1981
Fig. 3.10 Wind speed in Athens measured at 10m above ground for the period 01/07/2010-12/07/2010 source: after National Observatory of Athens
Fig. 3.11 Graphic representation of indirect evaporative cooling outdoors source: author
3.2. Bioclimatic evaluation In order to examine the Athenian climate and the potential of passive control strategies applied outdoors, a bioclimatic evaluation was necessary. Occupancy in pedestrian streets is mainly characterised by the sedentary (1Met), standing (1.2Met) or walking activities (2Met for walking speed 0.9m/s). Szokolay (2004/2008) thoroughly presents the passive control strategies which initially refer to indoor spaces. Thus, when plotting the psychrometric chart, the clothing insulation for the winter period is selected to be 1.0 Clo and for summer 0.5 Clo, correlated to the most frequent activity, taking place indoors (sedentary 1Met). Often in indoor spaces, such as offices, there is a dress code which occupants must follow and hence the reactive adaptative opportunity, by altering clothing insulation, is reduced. Additionally, the possibility to operate a mechanical heating or cooling system often decreases this adaptive opportunity. People may not think first to put on a jumper but rather to switch on the heating system. However, in an outdoor place, occupants are more tolerant to certain physical paremeters as they alter their clothing insulation just by instict (reactive adaptive opportunity). To examine the potential of reactive adaptation by alteration of clothing insulation and metabolic power, two psychrometric charts were plotted (Fig. 3.13a and 3.13b). To observe the diurnal variations of the Athenian climate, 12 lines (one for each month) were produced against Fanger’s (1970/1982) PMV model for 90% of acceptability using thought Auliciems equation to calculate neutral temperature. Fanger (1970) noted that “man’s thermoregulatory system is quite effective and will therefore create heat balance within wide limits of the environmental variables, even if comfort does not exist” (p.21). Nevertheless, the experiments that he conducted were in a climate chamber with young people (students in university) in standard activity and clothing insulation. This may be the reason why Fanger concluded that neutral temperature of a large group (for example 90%) is not dependent on age, gender, menstrual cycle, race, obesity, time of a day or physiological acclimatisation. Auliciems (1981), on the other hand, based his equation on a psycho-psysiological model (Fig. 3.12). Various parameters which are important, for someone being outdoors, have been taken into consideration. As can be seen from Fig. 3.13a clothing alteration from 0.5Clo to 0.3Clo has a very small effect on thermal comfort especially in the afternoon hours of the two summer months (July and August). On the contrary, it is a very effective way of adaptation during the mid-seasons. The coldest months (OctoberApril), when solar radiation is very welcome outdoors, as explained in the previous chapter, are out of the comfort band. Moreover, when an increase of metabolic power occurs a discomfort may occur not only throughout the whole day in July and August but also in the afternoon hours of June and September (Fig. 3.13b). An efficient solution seems to be the increment of air movement for both sedentary and walking activities (Fig. 3.13c and 3.13d). Low wind speeds (0.5m/s) are beneficial for a seated person. They are sufficient to bring an occupant outdoors in comfort. Regarding someone who walks, wind speeds of up to 5m/s in the afternoon hours are effective.
Fig. 3.12 The psycho-psysiological model of thermal perception by Auliciems, 1981 source: Szokolay, 2008 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Fig. 3.13a Psychrometric chart - Clothing alteration (winter 1.0-1.6Clo, summer 0.3-0.5 Clo) source: after Fanger, 1970; Auliciems, 1981; Szokolay, 2008
Fig. 3.13b Psychrometric chart - Metabolic power alteration for 2Met (winter 1.0Clo, summer 0.5Clo) source: after Fanger, 1970; Auliciems, 1981; Szokolay, 2008
Fig. 3.13c Psychrometric chart - Air movement (1 Met) source: after Fanger, 1970; Arens, 1981; Auliciems, 1981; Szokolay, 2008
Fig. 3.13d Psychrometric chart - Air movement (2 Met) source: after Fanger, 1970; Arens, 1981; Auliciems, 1981; Szokolay, 2008 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Fig. 3.13e Psychrometric chart - direct and indirect evaporative cooling source: after Fanger 1970; Auliciems, 1981; Szokolay, 2008
In the case where wind is negligible, the passive strategy of mostly indirect evaporative cooling is also effective (Fig. 3.13e). A seated occupant will be more comfortable during the afternoon hours of July and August when a water pond lie close to him. Hence, case studies conducted in similar climates (hot-dry summers) could provide valuable information regarding shading, evaporation and air movement. This may be the initial key to the evolution of these passive stategies and may lead to prototype solutions which can be modify the existing urban fabric or may intervene in a smaller scale.
Fig. 3.14 Diagram for effective passive control in a hot dry climate Right: red are the affected physical parameters of each element: geometry, vegetation, water source: author
3.3. Precedents The ‘Avenue of Europe’ towards the ‘Bioclimatic Rotunda’ The ‘Avenue of Europe’ (Fig. 3.15 and 3.16) was the feature of the EXPO 1992 in Seville. As described in the previous chapter, Seville’s climate has similar characteristics to that of Athens with regards to the summer period (hot dry summers). However, larger diurnal air temperature variations can occur in Seville (see also Fig. 3.19). Thus, the example of the shaded ‘Avenue of Europe’ with the installation of the evaporative cooling tower has been studied extensively, in order to idendify its overall performance in an outdoor environment. Three were the basic elements which composed the space: The ‘garden’, the ‘towers’ and the ‘covering’. The garden (300mx40m) consisted of four plazas or islands. These were reinforced concrete elements, placed 30cm above the water level. At the perimetre of the garden, there were 12 gates which were landmarked by the Passive Downdraught Evaporative Cooling (PDEC) towers and provided extra ‘direct’ evaporation. The covering was a plastic material which shaded the space. In detail, the covering ensured by shading appropriate surface temperatures. However, Alvarez et al.(1991) noted that shading was not enough as the amount of solar radiation obstructed was insufficient and therefore did not permit the occupants to feel comfortable. Thus, evaporative cooling, not only indirect (water ponds) but also direct (towers), was installed. Additionally, the ponds did not only contribute positively with regards to the cooling of ambient air, but also affected the overall mean radiant temperature as direct, diffuse, diffusely reflected and long-wave radiant exchange was controlled. A critical point about this issue was the total surface area of the ponds and hence the average surface temperature of the whole area. The PDECs augmented significantly the amount of water in the air, raising the level of relative humidity.
Fig. 3.15 The Avenue of Europe - Axonometric view source: Proc. Plea conference Seville, Spain, 1991
Fig. 3.17 The bioclimatic Rotunda source: Proc. Plea conference Seville, Spain, 1991
Fig. 3.16 The Avenue of Europe source: Proc. Plea conference Seville, Spain, 1991
Fig. 3.18 Diurnal patterns of the bioclimatic Rotunda (exit of tower) and the building’s indoor air temperatures, measured during two days DBT=dry bulb temperature, WBT=wet bulb temperature, Texit =temperature at exit of tower, Tin=temperature indoors source: Givoni, 1998
g line shadin
Fig. 3.19 Phychrometric chart for Seville’s climate (summer)- Air movement and evaporative cooling source: after Fanger 1970; Arens, 1981; Auliciems, 1981; Szokolay, 2008
The Bioclimatic Rotunda (Fig. 3.17) was another pavillion in EXPO 1992. It was a system originally developed by Givoni (1998). This prototype can also be applied to a building. Fine drops of water are sprayed vertically downwards from the top of an open shaft. The water is collected in a small pond at the bottom of the shaft and it is pumped to the top of the tower. The evaporation from the drops cools the water and the air of the shaft. The air temperature can come close to the Wet Bulb Temperature (WBT). Just for the record the maximum ΔΤa that was recorded, during two days of measurements, was 17K! (see Fig. 3.18). This system is mainly characterised by its direct evaporation of the air that is trapped at the top of the tower with a wind catcher and by the peripheral pipe installation with micronizers. The psychrometric chart in figure 3.19 presents the diurnal temperature variations for the summer months in Seville (June-September). As it can be seen from the chart, half of a typical summer day is out of comfort. In the location where the ‘Avenue of Europe’ and the ‘Bioclimatic Rotunda’ were installed, building shade was missing but the wind was unobstructed. Both pavillions provided the occupants with shade and in the case of the ‘Avenue’ wind flow for indirect evaporation was the goal. Indirect evaporative cooling (water ponds in the ‘Avenue’) can expand comfort band for augmented Ta at the same level of relative humidity. In addition, direct evaporative cooling is beneficial for the afternoons of all summer months. However, what was missing from these installations was an occupant survey with regards to their thermal sensation and satisfaction. A question that needs to be answered, from occupants’ perspective, is which of the two ways of evaporation is more pleasant.
An intervention in a street in Thessaloniki (40°38’N), Northern Greece The redevelopment of a busy street (Karaoli & Dimitriou, E-W with a 20o angle) to a vegetated and shaded pedestrian way was part the EU RUROS programme (Fig. 3.20). This precedent was selected to be examined, first of all because Thessaloniki presents climatic similarities with Athens. Secondly, the researchers (RUROS, 2004; Chatzidimitiou, Chrissomalidou and Yannas, 2005) dealt with inteventions regarding shading, vegetation, water ponds and their impact on microclimate - issues that are of interest in this dissertation. The case of Karaoli & Dimitriou was a comparative study of monitoring a busy traffic street and simulations as it would be as a pedestrian road. The spatial characteristics of the streets (H/W=0.43 and and L/ W=61.67) define a shallow and lengthy street. Limitations, such as keeping an asphalt route for the supply of the shops, impeded the design proposal. A comparison of partial (shading cover above central axis of street) and full (overhang in entire open space) shading was conducted. When partially shaded the street, a negligible decrease in air temperature (0.2K) was recorded in the simulation. On the contrary, in the case of full shade the air temperature slightly increased. This was attributed to the fact that the overhang was opaque and the air flow was blocked. Using the above shading methods, surface temperatures on the ground were reduced. In the case of partial shade, this was more effective when a central point was shaded from noon (reduction of 12.9K compared to no shading). Additionally, full shade impeded solar radiation at all points and a 11.2K reduction was recorded for all simulated spots. Authors refer to monitoring of tree shade. Tree shade is responsible for a reduction of air temperature of around 2.8K, as compared with the surrounding. 80% of this reduction was attributed directly to shading and consequently the other 20% to evapotranspiration. This can also be confirmed from the authors’ simulation of the two ways of shading (overhang vs trees, see also Fig. 3.21). Lower surface and radiant temperatures were noted in spots under shade. However, vegetation caused lower air, surface and radiant temperatures due to the overall increase of latent heat flux by evapotranspiration. Regarding the water ponds in comparison to wet soil, the authors concluded that wet soil is more effective in decreasing air temperature, whereas the high thermal mass and low reflectivity of water seems to have a higher effect on reducing surface and radiant temperatures. Additionally, authors found that water has an effect on reducing temperatures (surface and radiant) in the air layer just the above the water surface. This was confirmed when a case of water bodies in both sides of the street, were compared with a case of water bodies just on north side. However, there were no data regarding the speed and direction of the wind reaching the water body. Is there any correlation between wind speed and how far a water pond can affect its ambient air? If so, which are the thresholds of distance with regards to wind speed?
Fig. 3.20 Plan of Karaoli & Dimitriou streeta. at the original conditions, b. with the proposed interventions source: Chatzidimitriou, Chrissomallidou and Yannas, 2005
Fig. 3.21 Plan of Karaoli & Dimitriou streeta. at the original conditions, b. with the proposed interventions source: after Chatzidimitriou, Chrissomallidou and Yannas, 2005
3.4. Conclusion of climatic context and precedents ---A basic goal when dealing with hot-dry summers, as the psychrometric analysis showed, is to provide the potential of wind to reach the pedestrian level, as well as to provide evaporation. ---Case studies conducted in similar climates (hot-dry summers) provided valuable information regarding shading, evaporation and air movement. Shading (urban geometry and trees) is the initial strategy to cool down the outdoor environment (reduced mrT). Long diurnal deviations give a sign that evaporation (trees, water bodies, micronizers) is another passive strategy. ---A crucial point in reducing mrT is the surface area of shaded spots and shaded water ponds. ---A survey of thermal sensation and satisfaction of occupants with regards to direct and indirect evaporative cooling is required. Which of the two methods is more pleasant from the occupantsâ€™ point of view? ---How does wind speed and direction affect indirect evaporation? Is there any correlation between wind speed and how far a water pond can affect its ambient air? If so, what are the thresholds of distance with regards to wind speed?
4. Fieldwork 4.1. Introduction Very little information exists, regarding the exposed and highly irradiated pedestrian roads (shallow canyons and/or open streets). Even less studies have been conducted focusing on pedestrian behaviour (specially walker occupant). The place of interest for the on site observations is located in a part of the pedestrian network, named ‘Megalos Peripatos, Long Walk’, which connects the archaeologic monuments of Athens (see also Fig. 4.03). Such monuments are the Parthenon, Arhea Agora, Irodion theatre, Andrianou Gate etc. This part, named ‘Athinaikos peripatos, Athenian walk’, comprises two streets, Dionyssiou Areopagitou and Apostolou Pavlou (Fig. 4.03), one being the extension of the other. The fieldwork started on the 2nd of July 2010. On the 2nd and the 3rd of July, by just observing the movement of the pedestrians as well as recording the most occupied and empty spots, the most interesting places for detailed research were defined. A significant factor that affected the final selection was the locations that people preferred to or not to stop at with regards to the physical parameters (Ta, surface temperatures, RH, wind). At this stage, the hypothesis that the number of pedestrians and seated people would be reduced during the harsh hours of a typical summer day was confirmed (Fig. 4.01 and 4.02).
Fig. 4.01 Apostolou Pavlou - 09/07/2010 @14:00 source: author
Fig. 4.02 Apostolou Pavlou - 07/07/2010 @19:15 source: author
Fig. 4.03 Red line, the Long Walk (‘Megalos Peripatos’) which connects the archaelogical monuments - Total length 4km -Dotted line, the uncompleted part of the network Black rectangles, the Athenian Walk (‘Athinaikos peripatos’)-black circle, the National Observatory of Athens where weather data were collected for the fieldwork period source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Thus, the question that emerged was whether it is possible to increase the number of pedestrians, as well as the number of seated people in cafeterias, restaurants, etc, during the harsh hours of summer daytime (10:00-18:00) and how. It is important to mention that between 10:00-18:00 most local people work during weekdays. Hence, the increase refers to the weekend days and mostly to tourists during the weekdays. As the place of interest is directly related to the use by tourists, initially the occupants were divided into two categories: the tourists and the locals. It is well known that occupantsâ€™ comfort band in outdoor spaces can be easily expanded as they can choose where to stay or stand. This being an important factor which affects the time spent outdoors, it is worth mentioning that a lack of choice for the pedestrian tourists of where to stand, sit or even walk, was noted during this fieldwork. During the fieldwork, it was observed that groups of over 30 people were in an inconvenient condition as there was only one resting spot that they could all fit in (see Fig. 4.04 and 4.06). Fig. 5.04 shows a sprawling of a group of tourists who wear hats in the sunny part of the road whilst the rest of the group remains in the shade. Furthermore, another observation that is related to the visitors of the Parthenon is that the most efficient and/or with direct results adaptive opportunity was the consumption of water and fizzy drinks rather than just moving into the shade. Considering the time of exposure in the direct sun, which in this case is more than 30 minutes, the question that arises is whether intermediate shaded stops would have mitigated the overheating problem.
Fig. 4.04 The small olive grove - 09/07/10 @ 11:30 SPOT 1 source: author
Fig. 4.05 Middle of Dionisiou Areopagitou - 06/07/10 @ 12:30 source: author
Fig. 4.06 With orange - place of fieldwork - 1. small olive grove source: author
4.2. Occupancy of Pedestrian roads (walkers) The occupants of the pedestrian roads could also be divided into two other categories: the walkers (2 Met for a walking speed of 0.9 m/s) and the seated people (1 Met). In order to observe the walkers, the route from spot 1 to 5 (Fig. 4.06) was divided into 4 parts. The period of the most harsh hours (12:00-15:00) was chosen as this was thought to be the most interesting with regards to the occupantsâ€™ behaviour. Sporadic measurements were taken from one point to the next, to relate the frequency of the occupancy with the environmental parameters. The route started from the small olive grove and ended in the cafe area in Apostolou Pavlou. The instruments used in this experiment were: one Testo 410-2 (3in1) which records the air temperature, the relative humidity and the wind speed, one Testo 810 (laser surface temperature meter), one Testo 540 (illuminance meter) and an ifrared camera Flir i40 to record thermal images (Fig. 4.07 and 4.08). On the 9th of July 2010, and when the spot measurments were taken, the sky was clear with some sporadic clouds. The first spot (1), shown in figure 4.09, was voted by the seated people as pleasant. The air temperature at 13:45 was 30.4oC, whereas the surface temperature of the cube rocks (in the shade) was 33.7oC. The notes were taken just for one bench at which, in a period of 15min, 18 people had a short stop, while 150 where standing and walking nearby this bench. The interesting observation at this point was that for a period of 20 minutes that was cloudy no one chose this bench to rest after the descent from the Acropolis, where the majority of the walkers prefered at that time a bottle of water. The thermal images present the temperature deviation of the air which surrounds a humanâ€™s body and the hard materials of the pavement and the bench. In figure 4.10 a seated woman releases more heat to the outdoor environment than the marble bench and the cube rock, while in figure 4.11 people who are approaching the bench-spot, are receiving the heat released and reflected from the cube rock pavement.
Fig. 4.07 From left to right: 3in1, laser surface temperature meter and illuminance meter source: author
Ta = 30.4 oC
Fig. 4.08 Infrared camera source: author
Fig. 4.09 Sitting Bench that was observed in detail source: author
Fig. 4.10 IR - woman seated in the road side of the olive grove source: author
Fig. 4.11 IR - woman seated in the road side of the olive grove source: author
Fig. 4.12 Cafe area in Apostolou Pavlou- 09/07/10 @ 15:00 source: author
stop with cold/hot drinks
place of interest
Ta = 32.4 oC Fig. 4.13 Small pinewood - 05/07/10 @ 17:30 source: author
Ta = 34.9 oC
2 Fig. 4.14 Unobstructed walkway with short olive trees (3m) 09/07/10 @ 14:00 source: author
The second spot (2) was voted by the walkers as unpleasant. More characteristically, a 40 year old woman and her two children aged 5-8 years were walking in the sun for more than 10 minutes and they complained that this spot was very hot: “it would be better if there was a vegetated gallery”, mentioned the lady. A second group of young boys, who were walking for 10 minutes, proposed taller trees instead of the short olive trees. They also mentioned that it would be difficult to build a pergola at this spot. At 13:50 the air temperature was 34.9oC, whereas the surface temperature of the cube rocks (exposed to direct solar radiation) was 50.0oC. This point is exposed to the sun during the whole day. The east part of Apostolou Pavlou at this point has a marvelous view of the antiquities. The density of the olive trees (every 20-25m) as well as their height (3m) are factors which allow the incident solar radiation to heat up the hard materials. The initial proposal of the architect, Dimitris Diamantopoulos, at this point, was the creation of a small platform that would be in direct contact with the antiquities. After a short interview with the architect, two points were clarified. The first point was the choice of the olive trees. His answer was that they couldn’t plant, for example, sycamore trees as the infrastracture network of the street whould be affected or even damaged by the roots of the trees. The second point was related to the nature of the finishing materials in an unobstructed landscape. Soft materials, such as grass, couldn’t be installed at this spot because of technical restrictions. The Athenian walk was designed with the prevision of the creation of a tram network. Thus, a 6m wide path made of hard materials was a requirment, maintaining the same underground supply network which can support a tram network in the future. The third spot (3) was voted by the walkers as pleasant, after a 15 minute stay, with regards to the environmental parameters (Ta=32.4oC, RH=29.4%, wind speed=0.7m/s-1.2m/s). Nevertheless, after a week of observationthis place was always unoccupied! There are two possible reasons why this spot was always found to be abandoned. First of all, it can be seen from figure 4.15 that there is a lack of urban furniture, i.e. benches. Secondly, the foliage of the pine trees creates an enclosed space by reducing wind speeds. In an unobstructed point, 10m above ground, the wind speed at that time was 4.2m/s (National Observatory of Athens). The issue of security in such place might be more significant during the nighttime. The question that arises at this point is if the environmental parameters (air temperature and surface temperature, relative humidity, wind speed) are enough to justify whether an outdoor space is pleasant or not.
Fig. 4.16 Concrete bench at spot 2 09/07/10 @ 13:50 source: author
Fig. 4.15 Apostolou Pavlou-third spot: lack of benches 05/07/10 @ 17:30 source: author
Fig. 4.17 The third spot in Apostolou Pavlou- 09/07/10 @ 15:00 source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
The fourth spot (4) was voted by the seated people, customers of the cafes, as pleasant. It is analysed in detail in chapter 4.4. This spot was selected to be examined for two different reasons: a. unobstruction in comparison to a narrow canyon (Pittaki, spot 6, see also Fig.4.19-21) and b. sun exposure in comparison to the cafeterias in Iraklidon (spot 5), where there are man-made awnings and micronizers, which create a cool spot throughout the day. The wider part of the pedestian road comprises the outdoor part of the cafeterias. Thus, this spot is full of pedestrians as well as seated people, especially after 19:00. Even during the weekend period the activityis more intense during the afernoon and night time hours. Figure 4.22 is a summary bar chart of all four spots with regards to the percentage of dissatisfied occupants. Measuring the mean radiant temperature on site is a rather complex issue. Thus, a first experiment, assuming that mrT equals Ta, was conducted to compare the actual responses with the theoretical results that the Berkley, CA simulation tool gives. It is well known that mrT affects humansâ€™ comfort significantly. It was found that the actual results showed similarities with the theoretical results. It is worth noting that the sample of the occupants was very small, therefore this is only a general trend. Despite this, it is worth pointing out the high level of dissatisfaction observed and predicted on spot 2, where there was no solar protection.
Fig. 4.18 Key section of Apostolou Pavlou (SVF=0.95) source: author
Fig. 4.20 West facades of the buildings in Apostolou PavlouGround floor: cafes-Upper floors: cafes and dwellings. White parasols were closed at that moment 04/07/10 @ 20:30 source: author
Fig. 4.19 Key section of Pittaki (SVF=0.25) source: author
Fig. 4.22 Summary bar chart for all four spots Note that mrT was assumed to be equal to air temperature source: author
Fig. 4.21 Key for all the points of interest source: author
4.3. Impact of geometry on microclimate Apostolou Pavlou street: SVF=0.95. Pittaki street : SVF=0.25 The main reason that the above two pedestrian streets (19o from the N-S), in the centre of Athens, were chosen to be studied, was in order to compare an ‘open’ street with a deep canyon. The question that this study sought to address was “What is the impact of street geometry on the local microclimate?”. Additionally, the distance between them had to be minimal, in this case 500m (same mesoclimate: urban). In the case of Apostolou Pavlou, the buildings are located on the west side of the road. The majority of the buildings are retrofitted neoclassic buildings with an average height of 10m. The construction is conventional heavyweight, plastered double brick with insulated cavity. At the point where the permanent spot measurements were taken, the width of the road is around 60m. In the case of Pittaki, 15m high buildings are on both sides of the street. The ground level of this street is mainly used for trade (second hand shops). The buildings are from the ‘60s made of brick masonry. At the point where the permanent spot measurements were taken, the width of the road is 4.75m.
Fig. 4.23 View from west part for Apostolou Pavlou (SVF=0.95) during daytime source: author
Fig. 4.24 View from the west on Pittaki (SVF=0.25) source: author
9.soil with a bit of gravel 8.soil with gravel 7.grass 6.light grey cube rocks 5.soil 4.dark grey cube rocks 3.grass 2.dark grey cube 1.light grey marble tiles
Fig. 4.25 Apostolou Pavlou (SVF=0.95), in detail the materiality on ground - with red dashed line the axis of the permanent spot measurements source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
The spot measurements were taken on the 4th of July 2010, from 6:00 to 22:00, every two hours. The peak of the air temperature was 34.2oC at 14:00 (National Observatory of Athens). From figures 4.25c and 4.25d it can be observed that both the air temperature and the surface temperature on the ground floor (both streets had dark coloured cube rocks) were higher in Apostolou Pavlou during the whole day. The ΔΤa shows a peak at 14:00, of 5.71K where the air temperature was recorded at its peak. During the nighttime, the air temperature at the narrowest canyon was expected to be higher than the one in the open pedestrian road. Nevertheless, the outcome was the opposite. Pittaki (SVF=0.25), was slightly cooler than Apostolou Pavlou (SVF=0.95) both at 6:00 and at 22:00, ΔΤa=1K. Figure 4.25d presents the surface temperature at the centre of the ground floor of the streets. The largest ΔΤs can be observed at 16:00: 21K! Looking at the west walls (east facing), figure 5.25e, the largest ΔΤs is noted at 10:00 (5.3K), as expected. At 6:00 the surface temperature of the wall was 1.6K higher in the case of the narrowest canyon. To conclude, it is worth mentioning that, although the narrowest canyon was generally throughout the whole day and night cooler, the cooling rate was lower than in the more shallow canyon (more obvious between 14:00 and 16:00). This can be attributed to obstruction of air movement due to compactness. Additionally, the observation of the higher surface temperature of the west wall in Pittaki at 6:00 can signify a slower cooling rate of the walls compared to the floor. a
Fig. 4.26 Comparison of two streets: a. Ap. Paulou street, b. Pittaki street, c. Comparison of air temperatures at the centre of the streets, d. Comparison of surface temperature on the ground floor (centre), e. Comparison of surface temperature on the west walls source: author
Fig. 4.27 Fish eye images have been taken with an analogic camera a-c Pittaki street, d. Iraklidon street (spot 5), e. Ap. Pavlou (spot 4) street at the centre, f. Ap Paulou close to the east-facing wall model of camera: fisheye 2 Lomography source: author
Fig. 4.28 Calculation of sky view factor: a-c Pittaki street, d. Iraklidon street (spot 5), e. Ap. Pavlou (spot 4) street at the centre, f. Ap Paulou close to the east-facing wall source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Fig. 4.29 Perspective views: a-c Pittaki street, d. Iraklidon street (spot 5), e. Ap. Pavlou (spot 4) street at the centre, f. Ap Paulou close to the east-facing wall source: author
4.4. Occupancy of Pedestrian roads (occupants at rest) After a first observation at the cafeterias in Apostolou Pavlou (spot 4) and Iraklidon (spot 5) the extensive use of parasols and awnings was recorded. Additionally to this, another important factor for investigation was the equally extensive use of the evaporative cooling systems in spot 5. Both systems work with micronizers. In one case they are attached to a fan (see Fig. 4.30a and 4.30b) and in the other one they are fixed to a plastic pipe (φ=15mm, see Fig. 4.31a and 4.31b). In the case of the fans, an increase in the air movement, as well as the distribution of the water droplets in different directions lead to a well-cooled environment. In the case of the pipe most of the dew drops are lost in the sunlit pavement, due to the spraying direction. Nevertheless, both ways can be considered as ‘direct evaporating cooling methods’ as the “latent heat of evaporation is taken from the air, so it is cooled, but the humidity of the supply air is increased” (Szokolay, 2008,p.63) . On the 8th of July 2010, an occupant survey was conducted between 13:10-15:15. The weather that day was relatively temperate and mostly uniformly cloudy (Fig. 4.32), but from 13:00-15:30 the sky was clear. The seated occupants at the two spots (4 and 5, see also Fig. 4.33) were questionned with regards to the impact of the environmental parameters on their thermal sensation and satisfaction. The scale regarding their thermal sensation ranged from -2 (very cold) to +2 (very hot) and no one complained about the extremes. a
Fig. 4.30 The micronizers installed in fans: a switched off, b. in operation source: author
Fig. 4.31 The micronizers installed in a row: a switched off, b. in operation source: author
Fig. 4.32 Cloudy moment in spot 2, few minutes before the interviews were taken source: author
Fig. 4.33 Occupancy in spot 5 under the micronizers in a row - 04/07/10 @ 18:30 source: author
Fig. 4.34 Cafe A in Iraklidon 08/07/10 @ 12:00 source: author
Fig. 4.35 Cafe B in Iraklidon 04/07/10 @ 12:00 source: author
Fig. 4.36 Cafe C in Apostolou Pavlou 04/07/10 @ 14:40 source: author
The survey was conducted in three cafeterias (see Fig. 4.34-4.36). In the first cafeteria [A] the awnings were opened. The air temperature was 31.7oC, whereas the surface temperature of the ground floor (stone tiles) was 26.5oC and the relative humidity 36.8%. At the moment when the spot measurements were taken, the sky was clear and, under a dark-coloured awning (Fig. 4.34 on the right), the illuminance level at a height of 1m was 655 lux (86570 lux unobstructed). At this point it is worth mentioning that there is a significant impact on the reduction of direct and diffuse solar radiation not only by the awnings but also by the trees above them. The spot was always leeward (wind<0.5m/s) although the fans were in operation. The spot was voted as comfortable (77%). One of the interviewees, when asked about his thermal sensation, complained that at his body was feeling slightly too warm but his feet were cold! This was assumed to be an example of asymmetrical thermal discomfort due to a cold floor and lower body resistance as the occupant was wearing open shoes (see Fig. 4.37). In this cafe, the micronizers installed in the fans were switched off during the interviews. When people were asked if they had experienced the system in operation and if it was annoying, 100% answered that they did find it annoying, especially when the air movement was insufficient. In the second cafeteria [B] black parasols were installed (Fig. 4.35 and 4.38). The air temperature was 31.4oC whereas the surface temperature of the ground (concrete tiles) was 30.7oC and the relative humidity 37.7%. The illuminance level was 3156 lux under the black parasols. The wind speed fluctuated from 0.4m/s-1.5m/s. At this cafeteria, 59% (i.e. the majority) of all the interviewees were sitting while only 10% voted that the place was uncomfortable. When people where asked if the micronizers (Fig. 4.38) were annoying, 89% answered that they were pleasant, 5% answered that they were annoying, another 5% that they didnâ€™t affect the ambient environment significantly, while 26% stated that they found it annoying when the water reached their skin. In the third cafeteria [C] in Apostolou Pavlou, only 12% (i.e. the minority) were sitting at this place at 15:00, as this was practically unoccupied (Fig. 4.36 and 4.39)! When occupants were questioned regarding why the have chosen that spot instead of cafeterias A and B, they complained about the enclosed feeling the other cafeterias are creating, but even more about the noise pollution (volume and type of music). During the interviews, the white parasols were opened. The air temperature was 31oC, whereas the surface temperature of the ground (soil) was 24.9oC and the relative humidity 34.1%. The illuminance level was 11370 lux under the parasols. It was a leeward moment, when the occupants were questionned. All of them said that it was a pleasant spot, although they were feeling warm and would have preferred less sun. Micronizers didnâ€™t exist at this spot.
Fig. 4.37 Cafe A in Iraklidon 08/07/10 @ 13:15 source: author
Fig. 4.38 Cafe B in Iraklidon 08/07/10 @ 14:00 source: author
Fig. 4.39 Cafe C in Ap. Pavlou 08/07/10 @ 15:45 source: author
dense shade no wind no sky view no evaporation
dense shade wind sky view evaporation
light shade no wind no sky view no evaporation
Fig. 4.40 The wide part with the cafeterias in Apostolou Pavlou 17/07/10 @ 13:10 - the parasols are opened source: author
Figure 4.40 is a summary bar chart of the three cafeterias with regards to the percentage of dissatisfied occupants. In this case, the actual responses were very different from the predicted ones. Thus, a second experiment, assuming that mrT is close to the surface temperature of the ground, was conducted. In the case of the first cafeteria, the results are similar to the actual responses. This can be explained by the fact that solar radiation (direct, diffuse, reflected and longwave) is not significant at this spot. On the contrary, in the second cafeteria the discrepancy is still large (19%). This can only be explained by the impact of evaporative cooling in the overall thermal perception of the occupant. The direct solar radiation was negligible as the tables were under shade and facing north. In the third cafeteria (Fig. 4.41 and 4.42), the results had a downward trend. This was thought to be a significant error. The ground was covered with soil (Ts=24.9oC). The reality though (absence of occupancy and complaints), indicates that solar radiation is much more significant than the materiality of the ground. The tables are exposed on all sides to direct and diffuse radiation. However one limitation of this experiment was that the psychological parameters were not taken into account.
Fig. 4.41 The wide part with the cafeterias in Apostolou Pavlou 17/07/10 @ 13:10 the parasols opened source: author
Fig. 4.42 The wide part with the cafeterias in Apostolou Pavlou 17/07/10 @ 20:10 - the parasols in the row of the tables close to the road are closed, except from the corner one source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
4.5. Comparison of the urban with the suburban context - the effect of the vegetation To record the effect of tree shading on reducing ambient air temperature, two data loggers (measuring air temperature) were placed for a week (03/07/2010-10/07/2010) in two different contexts in the city of Athens. One was on the balcony (SW-facing) of the 4th floor of a multi-storey building in the city centre. The other one was attached to a ‘daphne laureola’ (N-facing) which was mostly under the shade of pine trees in a suburban area. The two areas are very different, with regards to the spatial characteristics. In the urban area, the predominant height of the buildings is around 15-18m (5-6 storeys) and they are characterised by the ‘courtyard’ typology. Additionally, the width of the streets is around 7m (H/W=2). On the contrary, in the suburban area, there are detached houses of one to two storeys, with a 30m distance between them (H/W=0.2). The graph showed a similar trend during the daytime hours. On the contrary, a discrepancy of around 3.3K was recorded during the night time on most days. It was only when the air temperature during the day did not exeed 30oC, that similar recordings occured during the night. However, although the air temperature was similar during the day, the occupants in the suburban area had a feeling of coolness, whilst the ones in the urban did not. This can be explained by three different reasons. One factor that was not taken in consideration was the mrT. Additionally, air movement in the suburban case would have been notable, but was not recorded. The last factor that could not be calculated was the evaportranspiration rate of the trees. The increase of temperature in both cases due to traffic was thought to be inconsequential in both cases. In the urban spot the front street of the building is Iraklidon street (pedestrian), while in the suburban spot, the traffic is negligible (1 car every 1.5 hour).
Tadmean 28.0 27.3 3.3K
Fig. 4.43 Air temperature in the urban (red) and suburban (blue) area source: author
south-west facing balcony
Fig. 4.44 Iraklidon street - Urban context source: www.bing.com/maps/ position of data-logger facing noth side
Fig. 4.45 Detached house - Suburban context source: author
4.6. Fieldwork conclusions ---For a comfortable outdoor environment environmental parameters (air temperature and surface temperature, relative humidity, wind speed) are the primary issues to be examined. As the fieldwork revealed the environmental parameters are not enough to justify whether a space is pleasant or not. They might be enough to assess thermal comfort/discomfort, but issues such as visual and acoustic comfort are equally important. In addition, the lack of urban furniture in an outdoor space often creates an abandoned space even if it accomplishes a thermally pleasant environment. ---The ‘open’ street not only in spot 2 but also where it was shaded with white parasols found to be unpleasant due to high level of exposure to direct solar radiation. Parasols although block the direct solar radiation from top, the sides remain unprotected and thus when sun has a low altitude angle, these are not very efficient. In addition, they impede the air movement as lower wind speeds were recorded in comparison with unobstructed wind at 10m. ---Direct evaporation seems to be pleasant when air movement is sufficient. On the other hand, water in contact with body skin revealed to be unpleasant. Further investigation though in this topic is required with a wider band of occupants’ responses. Consequently, debatable is the use of micronizers in dense urban configurations when wind is obstructed. ---Vegetation does not affect significantly the air temperature in daytime hours, but contributes on shading the landscape and increase the evaporation. During the nighttime, higher values of air temperature in urban area reveal the occurrence of a ‘heat island’ mainly due to heat storage of facets as anthropogenic heat release was thought to be negligible. Obstructed air movement makes this phenomenon even greater.
pine trees daphne laureola
Fig. 4.46 Key for suburban context source: Danos, 1991 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
6m 6m 6m
Fig. 5.01 Canyon models Top-insolation Bottom-absorbed solar radiation. source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1 Table 5-1. Albedos of walls,floor and trees source: after Dimouli and Nikolopoulou, 2000; Santamouris ed., 2001
5. Analytic work 5.1. Solar radiation studies The focus of the dissertation is how architects and urban designers may create an urban environment that will be more comfotable for one being outdoors. Thus, a more systematic research on the issue of pedestrians’ comfort, with regards to solar exposure, is required. 5.1.1. Solar radiation distribution on facets of symmetrical canyons Initially a study regarding the incident (direct and diffuse) solar radiation impeding on symmetrical canyons’ facets was conducted. Based on literature (Dimouli and Nikolopoulou, 2000; Santamouris ed., 2001), an albedo of 0.5 for a light-coloured brick wall was selected, 0.35 for the street facet representing a coverage with concrete tiles and 0.30 for deciduous trees in a hot dry climate (see Table 5-1). In the first experiment there were no trees. Looking at the incident solar radiation on the canyon’s facets (Fig. 5.02), the average daily solar radiation for July on vertical surfaces was calculated for the whole façades of the canyons.
Comparing the horizontal facet with the vertical one, it is obvious that the floor is receiving double the radiation impinging on vertical facets (high altitude angle during summer period, see also Fig. 5.03). For example, at 14:00, in a N-S canyon with HW=0.5, the floor is receiving 600 W/m2, whereas 300 W/m2 is reaching the walls. Generally, the floors at N-S canyons show a peak of insolation at 14:00 for all ratios, whilst the duration with regards to the intensity is more substantial on the E-W canyons (7 hours). On the other hand, the walls receive more radiation in a canyon with N-S orientation compared with an E-W oriented canyon (during early morning (9:00-12:00) and late afternoon (16:00-18:00)). In a E-W oriented canyon, the walls are more irradiated from 11:00 to 16:00. This difference can be explained by the solar position in each case (altitude and azimuth angles of the sun). 7h
Fig. 5.02 Insolation on facets of various canyons without trees source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.03 Correlation of strength of radiation impinging on an horizontal and vertical planeThe higher the ao the stroger the insolation on the floor and vice-versa source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
In conclusion, during the summer period at this latitude (37.58oN), special attention is needed on shading the floors of E-W oriented canyons. However, in a N-S canyon the walls require shading depending on the aspect ratio of the street. First of all, a combined solution of shading together with the installation of materials with low albedo and thermal storage capacity is needed in order to mitigate the overheating problem during summer as well as the overall heat island intensity. Looking at the absorbed solar radiation on wall facets (Fig. 5.04), what was important to examine was the magnitude of the radiation that will be converted into long-wave radiation and will affect pedestriansâ€™ comfort. Thus the walls, which were selected to be examined in the second case, were those of the ground floors (Fig. 5.05). A similar trend in the insolation on both floors and walls was observed when absorbed solar radiation was calculated. This was expected, of course, as the latter is proportional to the insolation, as a fraction of the albedos of the surfaces. Ground floor walls in a canyon with H/W=4 do not require any protection (mean absorbed solar radiation 30W/m2 for both orientations N-S, E-W). This magnidude can be justified just by the diffuse radiation as compared with an unobstructed north facing faĂ§ade with a similar average absorbed radiation of around 50W/m2 (Fig. 5.06).
GROUND FLOOR WALLS
It is worth mentioning, that in deep canyons, such as H/W=4, an intervention of a row of trees may not only make any difference regarding the obstruction of solar radiation but may cause significant reduction of illuminance level at the lower floors. Additionally, as the release of hot air is impeded in dense environments, placing trees may make it even harder (according to the density of the crown layer canopy). A limitation of this dissertation is that it does not cover the daylighting of indoor spaces nor the visual comfort of outdoor spaces. Nevertheless, these issues are equally important.
Fig. 5.04 Solar radiation absorbed on facets of various canyons source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.05 Selected facets for absorbed radiation in various canyons (from left to right: 0.5, 1, 2, 3,4) source: author
Fig. 5.06 Solar radiation absorbed on vertical surfaces at different orientations and at a horizontal plane source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
5.1.2. Effect of vegetation on canyons’ facets The building geometry showed to have a significant impact on the incident solar radiation reaching the lower level of a canyon. Shading can contribute to reducing the impiging solar radiation and therefore to reducing first of all surfaces’ temperature and consequently air ambient temperature. According to Alexandri (2005) on vegetated south facing walls in Athens a significant alteration of surface temperature was recorded, compared to walls without vegetation, especially at the upper floors of a shallow canyon (H5W10). However, the reduction of surface temperature of the floors is very small and hence air temperature is even less affected. Nevertheless, the above mentioned intervention, may be significant on minimising the cooling loads of the built environment and mitigating the heat island effect, though this is not significant for pedestrians’. Thus, a study with deciduous trees along the streets, to record the decrease of solar radiation impiging on facets as well as that of absorbed solar radiation, was conducted.
Fig. 5.07 Canyon model regarding the absorbed solar radiation in canyons with trees source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
The expected outcome from the study with the trees was a significant reduction of the insolation, primarily at the floor and secondarily on walls (height of trees 10m, crown layer 6mx4m). Regarding the walls, the reduction was more obvious in the shallower canyons for both orientations (N-S, E-W). In the E-W oriented canyons with H/W=0.5 and 1, at 14:00, a reduction of 113.25W/m2 and 105.93 W/m2 respectively, was recorded. On the contrary, in the deeper canyons (H/W=2, 3, 4) didn’t show any remarkable lowering of wall insolation (35.93 W/m2, 25.15 W/m2, 16.79 W/m2, respectively). In the N-S oriented canyons a similar trend with the E-W canyons was observed. Canyons with H/W=0.5 and 1 showed similar values with a very deep canyon (H/W=4). Of note, at 10:00, at H/W=0.5 and 1 a reduction of 174.21 W/m2 and 149.62 W/m2, respectively, was recorded. On the other hand, deep canyons showed a reduction lower than 30 W/m2. Same trends were observed for the evening peak of the north-south streets. As a conclusion, regarding walls’ irradiance reduction in both orientations, during the peak hours, canyons with H/W=0.5 and 1 proved to be more influenced (Fig. 5.09). The above mentioned trend on decrease of insolation can be explained by the fact that the trees overshadow the walls of the ground floor and first floor level (see also Fig. 5.08). Thus, the higher the buildings the lesser the average reduction of walls’ incident solar radiation. The previous study showed that the floors in E-W oriented streets need special protection. Therefore, trees were expected to obstruct incident solar radiation impinging on street level. Looking at the shallow canyons (H/W=0.5, 1) the reduction was not only quantitative, but also temporal (i.e. duration). Generally, the shallower the canyon, the greater the reduction of insolation, with a geometric progression. More specifically, at 14:00, in E-W oriented canyons with H/W=1, a reduction of almost 300W/m2 was observed, whereas in a H/W=3 the respective value was 100W/m2. In addition, the duration was reduced substantially from 7 hours to 3 hours for all aspect ratios. Figure 5.10 shows a threshold (H/W=2) for both orientations of wall irradiance comparing the base case with the intervention of trees. In N-S oriented streets, the floor irradiance may not change significantly with regards to the duration but can change considerably in terms of the intensity. Generally, floor irradiance at the peak hour, was diminished to 1/3 of the base case in N-S streets with trees. On the other hand, in E-W streets at the peak hour the impact of tree shading diminishes as H/W increases (Fig. 5.11).
Fig. 5.08 Shadow range during the hours of 9:00-16:00 on 4th July for N-S (top) and E-W (bottom) oriented streets with an aspect ratio H/W=4 Right- detail of street overshadowing without and with trees in an E-W oriented street with an aspect ratio H/W=1 source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.09 Insolation on facets of various canyons with trees source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.10 Trend of walls’ insolation at 14:00 in July for the E-W oriented canyons and at 10:00 in July for the N-S, with and without trees source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.11 Trend of floor’s insolation at 14:00 in July, for various canyons, N-S and E-W oriented, with and without trees source: Autodesk Ecotect Analysis 2010 with weather data E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
It is well known that the magnitude of sensible heat that a pedestrian receives, whenhe is in a canyon, it is due to long-wave radiation, which is released from the buildingsâ€™ walls and ground. This phenomenon is more intense when the air temperature is significantly lower in comparison with surface temperature of the facets (night-time). Thus, it is important to see the impact of tree shading in a canyon on the absorbed solar radiation on facets. Generally, as it was expected, the floor is more affected than the walls (Fig. 5.12-5.14). This is more obvious in the deep canyons. Practically, there is no significant reduction of absorption on walls for a canyon with H/W>2. This becomes particularly obvious when a canyon is N-S oriented. In an E-W canyon the trend after the intervention follows that of the base case with a small deviation as the canyons become shallower. On the other hand, the effect on floors is remarkable for all orientations. The absorbed solar radiation on ground in an E-W oriented canyon show a similar trend with the walls.
FLOORS GROUND FLOOR WALLS
Fig. 5.12 Solar radiation absorbed on facets of various canyons with trees source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.13 Trend of walls’ absorbed solar radiation at 14:00 in July for the E-W oriented canyons and at 10:00 in July for the N-S, with and without trees source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.14 Trend of floor’s absorbed solar radiation at 14:00 in July, for various canyons, N-S and E-W orentated, with and without trees source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
5.1.3. Solar radiation impinging on pedestrian Arnfield (1990) provided some benchmarks for the mean irradiance on a pedestrian in December, June and annually, for various orientations (see chapters 2.3.1 and 2.3.2). Hence, a more detailed research, to establish the diurnal variations of the incident solar radiation on a pedestrian, had to be conducted. The choice of July can be justified by the fact that, in Athens, during this month the global irradiace impinging on an horizontal plane, is at its peak (worst case scenario). Generally in all orientations, a pedestrian in a symmetrical canyon with H/W=1 or less is exposed for a large period (more than 4 hours) to radiation of 150W/m2. On E-W oriented canyon this period is more than double (10hours, see also Fig. 5.17 and Table 5-2). The simulations were conducted in two groups. Initially, the exposure of a pedestrian’s body and head (from now on just ‘body’) was calculated and, secondly, the exposure of an octagon assumed to be just the head. Comparing the exposure of a pedestrian body with a pedestrian’s head, what can be extracted is the special care the head requires, in all orientations. This, of course can be explained, by the fact that a pedestrian’s head is an horizontal plane whereas the body is in a vertical place. The body can be compared to the walls of a canyon, which as explained in previous chapters, are less irradiated compared with the floor. However, the strong direct solar radiation on the head may cause large temperature deviations with regards to the rest of the body. According to Arens et al. (1981), if the temperature difference is larger than 20K, this may cause a significant discomfort. A risk of hyperthermia may occur depending on time of exposure of a human, lack of protection (e.g. hat) and age. The elderly and the very young have a deficient or underdeveloped heat regulation mechanism and are therefore always at greater risk of suffering from sunstroke, even without doing any intense physical activity. 4h
Fig. 5.15 Irradiance on pedestrian source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.16 Left -the position of the pedestrian in the canyon - with white colour at the center of the street, Right - the pedestian model in plan source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Table 5-2. Increment of operative temperature for selected radiations and clothing absorptances source: author
Fig. 5.17 Increment of operative and mean radiant temperature for various clothing absorptances source: CIBSE guide A
NOTE Operative temperature “This index was produced by Winslow, Herrington & Gagge, as a result of work similar to Bedford’s. It is defined as the temperature of a uniform, isothermal “black” enclosure in which man would exchange heat by radiation and convection at the same rate as in the given non-uniform environment; or as the average of MRT and DBT weighted by their respective transfer coefficients.” “This index integrates the effect of air temperature and radiation, but ignores humidity and air movement.” source: Auliciems A. and S-V Szokolay, 1997
Fig. 5.18 Irradiance on pedestrian’s head source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.19 Selected surface representing pedestrian’s head source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
Fig. 5.20 Insolation analysis for summer period in Athens- Average daily values of sunlight hours in a plane at 1m above ground floor level Constant height H=12m source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1
An insolation analysis, of various streets, for the summer period was conducted using the Autodesk Ecotect Analysis 2010 simulating software. The width of streets varied from 6m-24m and the height was constant at 12m. These proportions were chosen for investigation to determine whether there are spatial differences of sunlit and shaded spots within the canyon itself. As expected, the E-W canyons were confirned to receive more radiation than in the other orientations. In the case of a street with H/W=0.5, the north side (22m wide) of the street receives somewhat less than double incident solar radiation compared to the south side. When the width of the street decreases (H/ W=1) the proportion of sunlit area to shaded area decreases (8.5m for 10 hours unshaded versus 3.5m for 5.5 hours unshaded). This is even more obvious on a street with H/W=2. In a deep canyon only the edges presented slightly higher exposure. In the case of the NW-SE and NE-SW grid the most sunlit areas are the intersections of the streets as well as the edges, therefore, these areas need particular attention. 5.1.4 Conclusions of solar analysis --- During the summer period at such a latitude (37.58oN), special attention is needed on shading the floors of E-W oriented canyons as well as the walls in an N-S oriented one. --- Additionally, as the hot air release is impeded in dense environments, placing trees may make it even harder (depending on the density of the crown layer canopy). A limitation of this dissertation is that it does not cover the daylighting of indoor spaces nor the visual comfort of outdoor spaces, issues which are equally important. --- A threshold of a street with H/W=2 was confirmed for both orientations regarding wallsâ€™ irradiance comparing the base case with the intervention of trees. In N-S oriented streets, the floor irradiance may not change significantly with regards to the duration but can change considerably in terms of the intensity. Generally, floor irradiance at the peak hour, was diminished to 1/3 of the base case in N-S streets with trees. On the other hand, in E-W streets at the peak hour the impact of tree shading diminishes as H/W increases. --- In deep canyons it is important to find the right balance between reducing the solar radiation (i.e. reducing mrT) and reducing daylight level of indoor spaces, in particular at lower levels. Another important factor in deep canyons, which was not unfortunately studied in this dissertation, is the choice of materials according to their albedos, as the diffuse and diffusely reflected short-wave radiation component is high (and therefore higher chance of visual discomfort).
5.2 ENVI-met case studies The following simulations were carried out, by using version 4.0 of ENVI-met numerical software, to assess the variations in air temperature, mean radiant temperature, wind speed and air flow in general for various cases. All simulations were calibrated for Athens (37.58oN, 23.43oE), for a typical summer day in July which coincided with the fieldwork month. The intention of the simulations was to examine the impact of building geometry on air temperature, mean radiant temperature and air flow at pedestrian level. Additionally, a second group was carried out to investigate the impact of vegetation again on pedestrian comfort. The last group of simulation is focused on the cases when a pedestrian is rather exposed to high levels of direct shortwave radiation within a shallow and/or â€˜openâ€™ street. The new 3D format of version 4.0 provides the users with the opportunity to create more detailed and realistic simulations of the urban microclimatic schemes. There are still though some unsolved problems and limitations analysed in Appendix 9.2. 5.2.1 Impact of building geometry A first group of simulations was carried out to assess the Ta, mrT and wind distribution in a street with constant width and various heights for two different orientations (N-S, E-W, see also Table 5-3 and Fig. 5.xx). The wind at 10m height was always constant from the prevailing direction for summer months (north). Air temperature Building geometry seems not to affect significantly the air temperature at a central spot within the canyon.The air temperature was plotted to investigate the convection rate for different geometrical configurations with various wind speeds at 10m height. In all cases, a very small diurnal deviation occured, with maximum Ta difference 2.78K at 15:00 (N-S streets, wind 6m/s) and 2.35K at 17:00 (E-W streets, wind 6m/s, see also Fig. 5.22d and 5.24d). Two significant factors proved to affect air temperature through the convection process: firstly, the large irradiated facets and, secondly, the increment of wind speed at 10m height and hence at pedestrian level due air movement. This will be explained in detail in the next chapter.
Table 5-3. Specification for the first group of simulations with Envi-met v.4.0 source: author
Fig. 5.21 Top: resolution of models x,y,z [m] (1,1,3) Bottom: dimensions of the model x,y,z (50,50,20) source: author
Fig. 5.23 Comparison of mrT (top) and direct shortwave radiation (bottom) at 16:00 [N-S, H/W=3] source: author c d
Fig. 5.22 a-c diurnal variations of Ta and mrT in N-S oriented canyons with various aspect ratios, d. Ta in detail when wind=6m/s source: author
40m wind 40m
Fig. 5.25 Comparison of mrT (top) and direct shortwave radiation (bottom) at 16:00 [E-W, H/W=3] source: author c d
Fig. 5.24 a-c diurnal variations of Ta and mrT in E-W oriented canyons with various aspect ratios, d. Ta in detail when wind=6m/s source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Mean radiant temperature
Generally building geometry proved to have a strong correlation with the mean radiant temperature. In N-S oriented canyons when aspect ratio increases (i.e. deep canyons) the mrT decreases from the duration point of view. On the other hand, in E-W oriented canyons a small decrease occurs when a canyon with H/W=0.5 was compared to H/W=1, whereas the orientation seems to not be an important factor for deep canyons (H/W=3). Similar trends in incident solar radiation (direct and difuse) were recorded in solar analysis, in the previous chapter. Hence a comparison of mrT and direct shortwave radiation was conducted to prove their relation. For both orientations mrT showed a high correlation with the direct shortwave radiation (see also fig. 5.23 and 5.25). Similar trends of mrT were recorded for all wind speeds. Thus, there is no direct influence of wind speed on mrT, which can also be proved by equation 7. Humidity Specific humidity [q] is not influenced by building geometry: (see also Appendix 9.2) (8)
where: e: vapour pressure p: pressure source:http://amsglossary.allenpress.com/glossary/ search?id=specific-humidity1
It was found that wind speed at 10m height has a strong impact on the wind at the street level (0.90m) for the cases of the perpendicular and the along the street wind. In figure 5.26 the polynomial correlation between the two levels (10m versus 0.90m) was demonstrated. In detail, when wind is perpendicular to street the aspect ratio plays a significant role. For deep canyons (H/W=3, skimming flow) the wind speed at street level increases characteristically with the increment of wind at 10m due to upward air movement coming from the short sides of the building (see Fig.5.27 and 5.29). The increased wind speeds near multi-storey buildings can also be confirmed by the unfortunate incidents of two deaths attributed to high wind speeds close to tall building (Penwarden, 1973). On the other hand, a canyon with H/W=1 (skimming flow) seems not to amplify the wind penetration at street level. In the case of a shallow canyon (H/W=0.5, wake interference flow), slightly higher speeds were recorded in a comparison with a unitary canyon (Fig.5.28). This was attributed to a downward air movement in the shallowest canyon.
Fig. 5.26 Wind speeds at street level, Top: wind perpendicular to street, Bottom: wind along the street source: author
However, when wind, at 10m height, is parallel to the street the greater the speeds at 10m, the greater the wind at street level (see also fig. 5.28). The higher the aspect ratio the greater the wind speed. A future research on the channelling effect might be conducted in locations where average wind speed is high (>6m/s) and the prevailing wind is along the canyons. In future research a detailed comparison of various L/H, by keeping constant the height of the building, can be explored.
Fig. 5.27 Wind speeds at street level (0.90m), Left column: H/W=0.5, Right column: H/W=3.0 (wind perpendicular) source: author
Fig. 5.28 Air movement in a canyon with H/W=0.5 and 6m/s (at 10m) perpendicular to street: arrows show the direction of wind and potential air temperature source: author
Fig. 5.29 Air movement in a canyon with H/W=3.0 and 6m/s (at 10m) perpendicular to street: arrows show the direction of wind and potential air temperature source: author
wind speed at10m 3m/s
with gallery 1
with gallery 2
Fig. 5.30 Wind flow at pedestrian level for various geometrical configurations source: author
Increment of wind flow with galleries In the previous chapter, the greater exposure of E-W oriented streets to direct shortwave radiation, was explained. This fact together with the north wind (perpendicular) was assumed to be the worst case conditions for a pedestrian within the canyon. Thus, a more detailed study for this orientation, with regards to the wind speeds reaching a pedestrian, was conducted. In detail, a comparison of two different galleries (see fig. 5.30 and 5.31), by keeping constant the wind at 10m (3m/s) for various aspect ratios (H/W=0.5, 1.0, 3.0), was demonstrated. A base case of building with no galleries showed high speeds at the outward corners of the north building, especially in deep canyons (max 4.35m/s, see also Fig. 5.30 top). In the case of gallery 1 (h=3m) when dealing with a deep canyon (H/W=3) similar values with the corners where recorded within the north gallery (Fig. 5.30 middle). In the case of gallery 2, the intensity of wind speed at the exit of the north gallery was reduced. In the south gallery, in both case studies, wind speeds of around 1.70m/s were recorded. Comparing the two types of galleries with the base case (no galleries, wind at centre, 0.45m/s), wind speeds were higher just at the centre of the deep canyon (2.8m/s). It can be assumed that, as at the exits of the south galleries the wind was 1/3 of that compared to the entrance of the north one, that there might not be a consecutive wind channelling effect in multiple galleries with a centre axis at the same y point (i.e. in a row). This is an issue thought that should be investigated in future experiment. In the shallow canyon, the intensity of higher wind speeds with regards to the distance from the galleries is more obvious given an even distribution of air movement due to the fact that buildings practically have a void at that point (see also Fig. 5.30 left column). A further issue that could be examined is the impact of voids not only on the increment of wind speed and consequently on effect of pedestrianâ€™s comfort, but also on convection rate of all levels of urban blocks. This might be a mitigating solution on decreasing the wall temperatures of building faĂ§ades and hence the cooling demand of indoor spaces.
Fig. 5.31 Wind speeds at street level (0.90m), Left column: H/W=3.0 with gallery 1, Right column: H/W=3.0 with gallery 2 source: author
5.2.2. Impact of vegetation Does vegetation contibute to lowering air temperature and mean radiant temperature and if so, how? How does the evapotranspiration rate affect humidity levels? This group of numerical studies was carried out for the worse case scenario, E-W oriented streets with wind (3m/s) perpendicular to the street axis. To define the distance up to which trees affect the ambient air, various widths (24m, 12m, 3m) and a constant height of 12m were selected. The rest of the specifications were kept as in the first group of simulations (see Table 5-3). The selected species was a small black locust (h=12m, w=6m, Fig. 5.xx), that grows in the mediterranean region. The absolute Leaf Area Density [LAD] ranges from 0.03m2/m3 to 0.30m2/m3 (Fig.5.33). This species can be characterised by the creation of light dense shadowing but on the other hand permits the air to permeate.
Fig. 5.32 View of black locust source: http://www.pbase.com/hjsteed/ image/35155072
Fig. 5.33 Absolute LAD for black locust source: author a
12m 6m 24m 6m
Fig. 5.34 Streets with H/W=0.5,1,3 and lack of vegetation: a. north spot within the street, b. south spot within the street source: author
Air temperature In the previous group of simulations it was found that air temperature is only slightly affected by the building geometry. In the case of vegetation similar results, to building geometry, were found. Two spots were selected to be investigated in detail, one on the north and the other one on the south side at the centre of the street. The maximum air temperature difference was recorded for a canyon with H/W=0.5 at 14:00 (1.15K). Mean radiant temperature Tree shade seems to affect significantly the mrT in all cases. At streets with no vegetation, the north spot at all aspect ratios showed a sensitivity to high levels of irradiance (60oC<mrT<80oC) during most of the daytime hours (9:00-17:00) in comparison with the south spot (mrT: 65oC-77oC and 70-75oC for 8:00am and 17:00 pm, respectively). On the other hand, when streets were shaded mrT did not exceed 47.5oC at either spot. Slightly higher values were recorded in the deepest canyon (H/W=3) as compared with the others. This can be attributed to the irradiated walls (storage capacity and albedo) and the higher diffuse and diffusely reflected short-wave radiation component in compact geometries. This was also proved by Toudert and Mayer (2006) (see also 2.3.1. Street geometry and solar access).
12m 6m 24m 6m
Fig. 5.35 Streets with H/W=0.5,1,3 with two rows (on both sides) of black locust trees (deciduous): a. north spot within the street, b. south spot within the street source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
Wind speed Comparing the example of a shallow canyon (H/W=0.5) with a deep one (H/W=3.0), vegetation in the latter case seems to impede wind penetration. This explains the higher air temperatures recorded in the deep canyon together with the lower values of wind speeds within it (Fig. 5.36). Thus, a comparative study of building geometry and trees with different LAD (leaf area density) versus wind velocities might be a future issue to be investigated. Humidity Specific humidity [q], as already mentioned, is not affected by building geometry (qmax=9.17g/kg at 16:00 for H/W=1). However, vegetation proved to have an impact on q. Higher values of q were recorded at the east side of all examined streets. This seems to happen due to the wind direction (Fig. 5.37). In a unitary canyon the impact of vegetation reaches up to points at the central axis of the canyon, whereas in the case of a shallow canyon the influence of vegetation seems to be lost after 6m, leaving the centre of the street drier. Similar q differences were recorded for a spot close to the trees and an unobstructed spot, for streets with H/W=1 and 3 (0.67g/kg and 0.62g/kg respectively). On the other hand, in a shallow street that deviation was 0.33g/kg. It is worth mentioning that all examined values were for 16:00. In conclusion, it seems that shallow canyons also need vegetation at the centre if the same levels of q required in all spots in a short section of the street.
Fig. 5.36 Wind distribution at 0.90m. Wind arrows are coloured with the potential air temperature (16:00pm): Left-H/W=0.5, Right-H/W=3.0 source: author
H/W=0.5 with twohumidity rows of trees 8.73-9.06g/kg Fig. 5.37 Specific at 0.90m for H/W=0.5 (left) and H/W=1.0 (right) - theH/W=1.0 higher level specific on the east side is attributed to the air withoftwo rows humidity of trees: 9.19-9.86g/kg movementH/W=3.0 with two rows of trees: 9.20-9.89g/kg source: author
Fig. 5.38 Key for 3rd group of numerical studies, from left to right: north, south, east, west At the centre a water body of 100m2 surface area source: author
5.2.3 The cases of the ‘open’ street and shallow street An E-W shallow and/or ‘open’ street (0.52<SVF<1) was selected to be investigated with regards to the various environmental conditions in four spots (N,S,E,W, see also Fig. 5.38). Specifically, the installation of a water body (10mx10m) was examined to define the limits of the effect of water in cooling down the air temperature through indirect evaporative cooling. The specifications of simulating 8 different case studies (see Fig. 5.40) were kept constant, as in the shallow canyon of the previous group of numerical studies. The design of galleries (cases 7 and 8) was carried out just to observe if there is any increment on wind speed by keeping all other spefications constant as in case 6. Air temperature In previous group of simulations, it was found that air temperature was only slightly is affected by the building geometry. However, it was only when an ‘open’ street (see Fig. 5.39, base case up to case 4, see also Appendix 9.5) was compared to a shallow canyon (case 4) that air temperature showed a decrease of on average around 3.15K in all four spots. When the water body was shaded around its perimetry with two also two rows of black locust trees on both sides (case 3),the maximum difference in Ta was recorded at the south (1.16K). This may be attributed to the direct shading of the water body and hence to the impact on mrT, but also to the indirect evaporative cooling. Shading of all spots with buildings and two rows of trees (case 4 and 5) presented a limited effect on air temperature (-0.21K) and that was only between 14:00-15:00, while when grass was installed instead of soil on the ground (case 5 and 6), there was only a negligible effect on air temperature.
Fig. 5.39 Streets with H/W=0.5,1,3 with two rows (on both sides) of black locust trees (deciduous): a. north spot within the street, b. south spot within the street source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
case 7: as case 6
case 8: as case 6
Fig. 5.40 The third group of numerical studes (base case: top left, case 8: bottom right source: author
Fig. 5.41 Mean radiant temperature for all four spots from base case to case 6 source: author
Mean radiant temperature A characteristic decrease on mrT occurred, in all cases due to shade, when the perimetrical row of trees around the water body was installed (case 2, see also Fig.5.41). Examining the north spot, a significant decrease occurred at 7:00 and 18:00 when the two rows of trees were installed (case 3). This happened as the south row blocks the direct shortwave radiation. At the south spot, similar levels of mrT reduction, as in north spot, were recorded from case 1 to case 2. However, at this spot, in case 4 mrT presented a noticeable increment (peak of around 15K) as compared with cases 2 and 3. It seems that the south facing wall (albedo 0.2) increased the diffuse and diffusely reflected short-wave radiation component towards the north spot. The mrT in case 3 showed a nadir, demonstrating the impact of direct solar radiation overall. At the west and east spots similar trends, were recorded, though in reverse.Obviously, in all cases the west spot is exposed to direct solar radiation during the afternoon hours, with a higher intensity from 15:00 to 17:00. On the other hand, on the east side this intensity was observed from 8:00 to 11:00. That time was when mrT in cases 4-6 exceeded the levels even of an unobstructed area. This was due to the absence of the diffuse and diffusely reflected short-wave radiation component in the â€˜openâ€™ street. It is well known that a variety of different environmental conditions may increase the tolerance of a human being outdoors. For example, circular movement around the water body throughout the day may increase the hours spent outdoors. Promoting this kind of circulation might be an effective solution. Wind speed Wind speed and direction from case 6 to cases 7 and 8 (Fig.5.42) showed similar trends with the deep canyon (H/W=3, Fig.5.31) in the first group of numerical studies. Hence, it seems that the building height above galleries is the factor reinforcing a channelling effect, within the gallery. The selected tree (0.03m2/ m3< LAD<0.30m2m3) allows the air to penetrate, as from case 4 to 5 wind speeds were recorded only slightly weakened (-0.13m/s maximum absolute decrease). If the contribution on reduction of mrT and amount of wind obstruction, it can be said overall trees have a beneficial effect. Humidity Specific humidity [q] is not affected by the water body (9.23g/Kg in base case and case 1). However, trees seem to contribute to the level of q when a canyon with H/W=0.5 with no trees was compared to cases 4 and 5 - the results (maximum values) were 8.87g/kg, 9.01g/kg and 9.21g/kg respectively.
Fig. 5.42 Wind speeds at street level (0.90m), Left: case 7, Right: case 8 for wind 3m/s at 10m source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
6. Future research and applicability 6.1. Macroscale-urban ventilation The urban density in the centre of Athens may generate a lack of urban ventilation. Recent precedents in cities with similar climatic condition, like Madrid, presented a trend of exploring the potential on designing urban courtyard blocks. The basic characteristic is the perforation of the block. Figure 6.01 shows an example of an apartment building in Carabanchel, Madrid, by Amann, Canovas, Maruri. In case of perforated blocks (Fig. 6.02), a comparative study of envelope exposure during the winter season to a sufficient level of ventilation (pollution dissipation all year around, cooling through convection during summer) not only at pedestrian level, but also at all upper floors, is required. Regarding the applicability of perforation in existing condition a solution might be initially that some shops (frequently unoccupied or abandoned) in the ground floor could be converted into galleries. By this way not only the ventilation rate will increase but also the inward-looking courtyards (‘akalyptos’), currently not being used, will be reconnected with the street and hopefully will be used again by the occupants of the buildings. 6.2. Mesoscale-street design It was found that in an E-W oriented ‘open street’, after shading with trees, the mrT in all examined spots presented a remarkable reduction. In the case of a wide street (W=24m), a need of shading the centre proved to be beneficial. Building in both side of the street increased the diffuse and diffusely reflected short-wave radiation component, even when albedo of walls was 0.2. The extention of the pedestrian network which connects the archaeologic monuments comprises an ‘open street’ with existing vegetation at both sides (see Fig. 6.05-6.07). This NE-SW oriented (with a deviation from E-W, 27o) will be converted into a pedestrian sreet in the recent future. Thus, there is a need of extending the analytic work (third group of simulations) for other orientations. NE-SW and NWSE streets proved from solar analysis to be less irradiated during a summer period. A selection of spots within the street (as it is a wide street, W=20m) for further investigation of their microclimatic condition, is required.
Fig. 6.01 Apartment building in Carabanchel, Madrid source: author
Fig. 6.02 Level of perforation - examined in a comparative study source: author
Fig. 6.03 Ventilation in Urban scale - The channelling effect stops at the first gallery source: author
Fig. 6.04 View of ‘open’ street surrounded with trees. A future pedestrian road source: author
Fig. 6.05 View of ‘open’ street surrounded with trees. A future pedestrian road source: author
Fig. 6.06 An ‘open’ street surrounded with trees. A future pedestrian road source: www.bing.com/maps/
Fig. 6.07 View of ‘open’ street surrounded with trees. A future pedestrian road source: author
6.3 Microscale-urban furniture design There is a general agreement that the possibility of altering positions in an urban environment may increase significantly the time that someone spends outdoors (reactive adaptation). Additionally, the lack of urban furniture may create unpleasant environments, even when there are thermally comfortable. This was proved from fieldwork measurements and predicting ones by using Berkley, CA simulation tool. Interesting would be a future investigation of occupantsâ€™ behaviour in a small park, square, street, etc, where light, in terms of weight, benches are located. Hence, appropriate materials to mould it could be pumice stone mixed with a mounting mortar of clay or concreate. The proposed bench can also be examined as a small tank containing shaded water. It is well known though that only large surfaces of water bodies may affect pedestrianâ€™s comfort by reducing the mrT and by the indirect evaporative cooling. This factor together with the fact that the bench might conclude to be dirty indicate that is debatable issue.
Fig. 6.08 The proposed bench - with dotted blue line the level of water source: author
Fig. 6.08 The proposed bench, which two adults may move around shaded and unshaded spots source: author
7. Conclusions The main issue which has been discussed in this project is pedestrians’ thermal comfort in an urban context, during the summer period. Multiple other issues intersected with this topic through the investigation. The reduction of cooling loads indoors was not examined, although it is an equally important issue. During the hottest period, shading the urban facets was shown to contribute on the increment of pedestrians’ comfort and on mitigating heat island intensity. Urban ventilation through more perforated buildings, not only at the pedestrian level, seems to be a solution on promoting heat dissipation and anthropogenic heat release. A chain that connects interventions in three scales: urban design, street design and object design may increase the time that people will spend outdoors. A reconnection of the inward-looking courtyards with the streets, through galleries, will promote urban ventilation and will increase the available open spaces. A network of pedestrian zones with a variety of spaces, regarding the physical parameters, can expand the adaptive opportunities outdoors. Pedestrian streets, either shallow canyons or ‘open’ streets, need a careful design as they are practically totally exposed to strong solar radiation regardless of their orientation. This was proved by the fieldwork and analytic work. During summer, in shallow streets, buildings were confirmed to have a small impact on shading the ground. At the same time, the walls of the buildings affect negatively the mean radiant temperature as the diffuse and diffusely reflected component is increased. Tree shading seems to be a sufficient solution for shading and increasing the humidity level through evaportranspiration. On the contrary, when dealing with deep canyons the issue of the materiality, especially at top floors and on ground may decrease the radiation reaching the pedestrian level significantly. Direct evaporating cooling seems to be an efficient strategy during summer, especially in the afternoon hours. Occupants’ responses revealed a debatable issue of direct evaporation with regards to air movement. Unfortunately, indirect evaporative cooling in comparison with various wind speeds could not be examined due to simulating problems (see Appendix 9.2). Nevertheless, an observation of the occupants’ behaviour in an open space may be more important. The results may contribute positively to defining more accurate theoretical models that predict comfort outdoors. Pedestrians’ thermal sensation in walking activity proved by the fieldwork to be a rather complicated issue to be examined due the variations on the past time of exposure of the walkers in certain weather conditions. A limitation of this project is that it focuses only on the summer period and only on outdoor comfort. The dilemma, of how to design or intervene when dealing with mid-latitude cities, remains. There are missing comparative studies, such as daylighting analysis of indoor spaces and insolation plotting in the winter period, when streets are planted with trees. In addition, perforation increases envelope exposure which in winter can be considered as a problematic issue regarding the heat losses of the built environment.
8.References books-papers -Alexandri, E. (2005). Investigations into Mitigating the Heat Island Effect through Green Roofs and Green Walls. PhD thesis, Cardiff University Welsh School of Architecture -Arens et al. (1981). A new bioclimatic chart for environmental design. -Arens, E. and P. Bosselmannt (1989). Wind, Sun and Temperature-Predicting the Thermal Comfort of People in Outdoor Spaces. Building and Environment. Vol. 24. Pergamon. pp. 315-320, 1989. -Arnfield, A-J (1990). Street design and urban canyon solar access. Energy and Building. Vol. 14. pp117-131 -CIBSE (2006). Environmental Design. Guide A, 7th Edition. Chartered Institution of Building Services Engineers, London -Fanger, P. O. (1970). Thermal Comfort. Copenhagen: Danish Technical Press. -Gartland, L. (2008). Heat Islands: understanding and mitigating heat in urban areas. Earthscan. London -Givoni, B. (1998). Climate Considerations in Building and Urban Design. Wiley. New York -Givoni, B. (1994). Passive and Low Energy Cooling of Buildings. Van Nostrand Reinhold -Givoni, B. et al. (2003). Outdoor comfort research issues. Energy and Buildings. Vol. 35. Elsevier. pp77-86 -Gartland, L. (2008). Heat Islands: understanding and mitigating heat in urban areas.Earthscan. London -Johansson, E. (2006). Influence of urban geometry on outdoor thermal comfort in a hot dry climate: a case study in Fez, Morocco. Building and Environment. Vol.41. Elsevier. pp1326-1338 -Lin, T-P et al. (2010). Shading effect on long-term outdoor thermal comfort. Building and Environment. Vol.45. Elsevier. pp213221 -Mantzarakis, A. (2010). Climate, thermal comfort and tourism. -Nikolopoulou, M. (Ed. 2004). Designing open spaces in the urban environment: a bioclimatic approach, RUROS project. C.R.E.S. -Oke, T-R (1988). Street design and urban canopy layer climate. Energy and Building.Vol.11.pp 103-113 -Papadakis et al. (2001). An experiment investigation of the effect of shading with plants for solar control of buildings. Energy and Buildings. Vol.33.Elsevier. pp 831-836 -Santamouris, M. (1999). Thermal and air flow characteristics in a deep pedestrian canyon under hot weather conditions. Atmospheric Environment. Vol. 33. Pergamon. pp4503-4521 -Santamouris, M. (Ed. 2000). Energy and Climate in the Urban Environment. James & James (Science) Publishers Ltd.London. -Shashua-Bar L. and M.E.Hoffman. Geometry and orientation aspects in passive cooling of canyon streets with trees. Energy and Buildings. Vol.35. Elsevier. pp61-68 -Steemers K. and M-A. Steane (Eds 2004). Environmental Diversity in Architecture. Spon Press. London -Szokolay, S. (2004, 2008). Introduction to Architectural Science. The basis of sustainable design. Architectural Press. Oxford -Taylor B. (2008). The first line of defence: Passive design at an urban scale. Proc. Air conditioning and the low carbon cooling challenge, U.K. -Toudert F. and H. Mayer (2006). Effect of asymmetry, galleries, overhanging faรงades and vegetation on thermal comfort in urban street canyons. Solar energy. Vol.81.Elsevier. pp 742-754 -Toudert F. and H. Mayer (2006).Numerical study on the effect of aspect ratio and orientation of an urban street canyon on outdoor thermal comfort in hot dry climate. Building and Environment. Vol.41. Elsevier. pp94-108 -Yannas, S. (2002) Urban Climatology and Design. AA Graduate School E+E Programme, London -Yannas, S. (Ed. 2000). Designing for Summer Comfort. EC Altener Programme. Environment&Energy Studies Programme, AA Graduate School, London.
papers from plea conference -Alvarez, S. et al. (1991). The Avenue of Europe at EXPO ‘92: application of cool towers. Proc PLEA 1991, Sevilla-Spain. pp195-201 -Alvarez, S. et al. (1991). Full Scale experiments in EXPO ‘92-The Bioclimatic Rotunda. Proc PLEA 1991, Sevilla-Spain. pp209-217 -Alucci, M-P and L-M Monteiro (2004). Climate and thermal stress in outdoor spaces. Proc. PLEA 2004, Eindhoven-Netherlands -Baker N. (2000). We are all outdoor animals. Proc. PLEA 2000, Cambridge-UK. pp 553-555 -Bougiatioti F. and A. Oikonomou (2003). Thermal behaviour of materials used in the skin of the city in Greece. Proc. PLEA 2003, Santiago-Chile -Corbella, O. et al. (2001). Outdoor spaces and urban design case studies of two plazas in Rio de Janeiro. Proc. PLEA 2001, Florianopolis-Brazil, pp 665-671 -Dimouli A. and M. Nikolopoulou (2000). Vegetation in the urban environment: microclimatic analysis and benefits. PLEA 2000, Cambridge. pp 489-494 -Chatzidimitriou et al. (2005). Modifications of an urban street in northern Greece. Proc. PLEA. Beirut-Lebanon. pp689-694 -Evagelinos, E. et al (2003). Moving the Air Inside the Urban Fabric- A Proposal for the city of Athens. Proc. PLEA 2003. Volume 1. pp 617-622 -Nikolopoulou M. and K. Steemers (2000). Thermal comfort and psychological adaptation as a guide for designing urban spaces. Proc. PLEA 2000, Cambridge-UK. pp 565-570 -Pearlmutter, D. (1998). Street canyon geometry and microclimate: designing for urban comfort under arid conditions. Proc. PLEA 1998, Lisbon-Portugal. pp 163-166 -Pearlmutter, D. et al (2003). Analyzing the Microclimatic Influence of the Urban Canyon Geometry with an Open-air Scale Model. Plea Conference 2003. Volume 1. pp 617-622 -Ramos M-C and K. Steemers (2003). Comfort in urban spaces: The roles of physiological and psychological parameters. Proc. Plea 2003, Santiago-Chile -Toudert, F. and R. Bensalem (2001). A methodology for a climatic urban design. Proc. PLEA 2001, Florianopolis-Brazil, pp 469-473 -Velazquez, R. et al (1991). General aspects of the work on climatic control of outdoor spaces at EXPO ‘92. Proc PLEA 1991, Sevilla-Spain. pp171-177 -Yannas, S. (1998). Living with the city. Proc PLEA 1998, Lisbon-Portugal. pp 41-48 -Yannas, S. with O.D. Corbella and V.N. Corner (2001). Outdoor Spaces and Urban Design: case studies of two plazas in Rio de Janeiro. Proc. PLEA 2001, Florianopolis web sources http://www.minenv.gr/3/31/313/31303/e3130304.html (accessed 23-07-2010) http://en.wikipedia.org/wiki/Street_canyon (accessed 03-08-2010 http://www.enet.gr/?i=news.el.article&id=94116 (accessed 17-04-2010) http://www.enosipezon.gr/ (accessed 14-04-2010) http://www.satel-light.com/pub/Danou04142010190627/soutdoor.htm (accessed 14-04-2010) http://www.maps.google.co.uk/ http://www.bing.com/maps/ http://www.envi-met.com/ tools -Adobe Photoshop CS3 (graphic design tool) -Adobe InDesign CS3 (graphic design tool) -Autodesk Autocad 2006 (2D-3D drawings) -Autodesk 3D studio Max 9 32bit (3D drawings-Rendering) -METEONORM (v6. 1 2008). Meteotest. Global Meteorological Database for Solar Energy and Applied Climatology that can generate monthly and hourly weather data for any location. -WEATHER TOOL (2006). Useful graphical representations of hourly weather Data imported from Meteonorm -Autodesk Ecotect Analysis 2010 -EDSL TAS Building Simulator 9.1.3 -COMFORT (Environmental Analytics, Univ, Berkeley 2000) -ENVImet v.4.0 (microclimatic simulating software)
9. Appendices 9.1 Climatic context It is important to mention, that on Table 3-1 all the data were plotted for the latest period (1996-2005 for temperatures, 1981-2000 for radiation) by exporting them with the ‘METEO’ method. On the contrary, all the hourly values, on *.dat and *.epw files, were plotted using the ‘USER DEFINED’ and ‘ENERGY PLUS’ methods, respectively. In these cases, Meteonorm v.6.1 weather software cannot give results for the latest period. Thus, all the analytic work is restricted on the old period (1961-1990 for temperatures, 1981-1990 9.2 Limitation using Envi-met v.4.0 Panic Atm file In many cases when running Envi-met v.4.0 a termination of the calculating process may occur. Sometimes it happends in the beginning of simulation (first hour of simulation) and some others at the end (last hour of simulation). This is when the variables of temperature, humidity or CO2 are unstable during the simulation. Few cases that this may happen are when: 1. Wind speed at 10m was null. It was assumed that air temperature was unstable. 2. A complex geometry of single walls, in intersection, was designed. It was assumed that the software could not calculate the points were single walls were intersected. This still has to be confirmed by removing either the overhangs or the vertical fins and run again the simulation. 3. In cases 4-8 (when buildings installed in both sides of a street with width 24m) in the third group of simulations and in case 8 with wind speed at 10m equals 6m/s. The latter simulation unfortunately did not any results. Thus, a correlation of wind speed and indirect evaporative cooling could not be examined.
Fig. 9.01 Left-The case with the intersected single walls, Right-Sample from cases 4-8 source: author
Wind at 10m It is a limitation of the software that realistic scenarios regarding wind circulation cannot be tested. Wind is normally unpredictable as it may come from different directions and with various speeds during a day. In the software though wind at 10m is always stable (speed and direction) thoughout the day. That was the reason that a diurnal conditions was not plotted in the analysis of the microclimatic condition in various cases. Air temperature Researchers (Emmanuel, 2007; Jain, 2009) mention an underestimation of predicted diurnal range of air temperature. Thus, it is not only that there is no consensual comfort index for outdoor spaces but also the deviation of predicted values using numerical shoftwares, which may be by far unrealistic as these are compared with field experiments. Vegetation There is a lack of a variety in species of trees that can be found in all climatic zones. For the mediterranean territory species like pine trees, olive trees, fruit-bearing trees are very common. Planter software may give you the opportunity to create a new tree, but it is quite complicated and there is insufficient information regarding the input parameters such as leaf area density (LAD), CO2 fixation, root depth and albedo. E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
PET Model and PMV Model The are some incomplete features of ENVImet v.4 that hopefully will be solved in future and will be ready for use. Two of these are the two different ways on predicting thermal comfort conditions in outdoor environment: PET index, in ENVImet v.4, includes air temperature, mean radiant temperature, specific humidity (q), wind speed, human clothing, activity, age, weight, height and sex. This was why specific humidity was chosen to be recorded, in analytic work, instead of relative humidity. The latter did not show any significant change and also thought to be inaccurate as during an afternoon hour (16:00) relative humidity, in a street with no trees, was relatively high (RH=47.70%). The PMV Model (Predicted Mean Vote Model) that is being used in ENVImet v.4 is based on Fangers (1972) model, it relates the energy balance of the human body to the personal feeling of persons exposed to the corresponding climates.In ENVImet v.4, it has been adapted for outdoor climate by Jendritzky (1993). Jendritzky mentions on one of his paper (2010): “The meteorological input variables include air temperature Ta, water vapour pressure e, wind velocity v and mean radiant temperature Tmrt including short and long-wave radiation fluxes, in addition to metabolic rate and clothing insulation. In equation 10 the appropriate meteorological variables are attached to the relevant energy fluxes in W/m2. The physiological (internal) variables, such as the temperature of the core or the skin, the sweat rate, and the skin wetness, which all interact with the environmental heat conditions, are not mentioned here”. It is a big step that parameters such as heat storage of body but aslo heat exchanges around human’s body are taken into consideration (red rectangulars). These parameters may affect remarkably human’s perception.
(10) M W S
metabolic rate (activity) mechanical power storage (change in heat content of the body)
Peripheral (skin) heat exchanges QH turbulent flux of sensible heat Q* radiation budget QL turbulent flux of latent heat (diffusion of water vapour) QSW turbulent flux of latent heat (sweat evaporation) Respiratory heat exchanges QRe respiratory heat flux (sensible and latent) Thermal environmental parameters Ta air temperature Tmrt mean radiant temperature v wind velocity relative to the body e water vapour pressure source: Jendritzky and Tinz, 2009 http://www.globalhealthaction.net/index.php/gha/article/viewArticle/2005/2528#CIT0001 accessed 08-09-2010
9.3 Air temperature and geometry (first group of simulations)
Fig. 9.02 Air temperature in various canyons when wind at 10m was 0.5m/s and 3m/s source: author
9.4 Air temperature and impact of vegetation (second group of simulations)
Fig. 9.03 Air temperature in various canyons with trees and without trees source: author E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
9.5 Air temperature in the case of ‘open’ street and shallow street (third group of simulations)
Fig. 9.04 Air temperature in four spot for cases 1-6 (from top to bottom: North, East, West) source: author
9.6 Wind in the case of the ‘open’ street and shallow street
Fig. 9.05 Wind speed distribution in a shallow canyon with H/W=0.5 (case 6) source: author
9.7 Specific humidity (q)
H/W=0.5 with no trees: 8.87g/kg
H/W=1.0 with no trees: 9.17g/kg
H/W=3.0 with no trees: 9.20g/kg
H/W=3.0 with two rows of trees: 9.20-9.89g/kg
H/W=0.5 with perimetrical of water body and two rows of trees in both sides of street: 9.21g/kg
H/W=0.5 with trees perimetrical of water body: 9.01g/kg
Fig. 9.06 Specific humidity levels in various canyons source: author
9.8 Solar exposure of a plane 1m above ground
Fig. 9.07 Insolation analysis for summer period in Athens- Average daily values of sunlight hours in a plane at 1m above ground floor level Constant width W=6m source: Autodesk Ecotect Analysis 2010 with weather data imported from Meteonorm 6.1 E+E ENVIRONMENT AND ENERGY STUDIES PROGRAMME_MSc SUSTAINABLE ENVIRONMENTAL DESIGN_ DISSERTATION PROJECT 2010 ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE ANNA-MELPOMENI DANOU
In the urban fabric of Athens, and more specifically at its centre, the high density and the geometry of the buildings can be the main reaso...