E N E R G Y A U D I T .
E N E R G Y A U D I T C O N T E N T S . Space Heating Scatterplots
Heat Distribution And Using The Data Logger.
Heating Systems And Tariff.
Energy Use Compared To Degree Days.
The NPI Calculation.
Using The Bedzed Benchmark.
Energy Audit Methodology Breakdown.
S p a c e H e a t i n g S c a t t e r p l o t . The scatter plots below correlate the Heating Degree Days data against the Heating Load (kWh) and drawing a resultant mean trend line through the point plotted. The further that the individual points are from the line of best fit, the less the heating system in questions’ responsiveness to changes in External temperature. Flat 29 had the best correlation out of all the flats assessed. This may be resultant from the increased thermal mass caused by additional insulation on the exposed wall and the cork flooring allowing the building fabric to store heat for longer than other flats would.
C o n t r o l C h a r t . The control chart is used to see how the actual energy consumption of heating compares to the performance drawn in the previous baseline. It must be noted that negative readings infer energy efficient behaviour and consequential savings. Flats 29 and 38 particularly show this positive behaviour.
C U S U M C h a r t . Through the cumulative sum of the difference (CUSUM) Chart we can see evidence of the energy efficiency of a building. Here the graph shows the patterns in monthly data over the course of a year. An upward incline on the CUSUM chart indicates that energy consumption, at that time, is increasing. Savings are indicated by a decrease / a downwards slope in the line. CUSUM are helpful as they represent the overall trends occurring in energy consumption and savings (here, in regards to heating). This is particularly useful to notice fluctuations of energy consumption. It is beneficial in this instance, as it allows the author to alert the occupants to act upon excessive energy consumption.
Using Flat 38 as an example, we can see increasing energy consumption between the months of September and January. There is then a decrease in consumption after this point as the summer months approach and the need for space heating becomes considerably less. This is a normal distribution as heating needs decrease as it gets closer to summer.
E n e r g y U s e C o m p a r e d T o D e g r e e D a y s . These graphs are used for comparing the actual space heating energy consumption to the heating degree days (specific to the locality). The red constant, dotted line shows the base load of the building. This is a kWh figure is equal to the lowest monthly energy consumption of the year in question. This graph is utilised by recording the points at which the degree day line exceeds the value / bar height of the energy consumption. This means that the building is likely to overheat. In contrast however, if the degree day line is below the energy consumption figure, the flat is in need of additional heating. So overall we can tell if a system has an efficient heating system as the more efficient it is, the closer the two sets of plotted data (energy consumption / degree days) correlate.
T h e N P I C a l c u l a t I o n . The NPI is used as a ‘yardstick’ to state annual energy consumption (kWh/m2/year) of a building. It allows for patterns in occupancy, weather and exposure of the building. Highest Annual Energy Use: Flat 38. Lowest Annual Energy Use: Flat 10 This unit (Flat 10) does not use the under‐floor heating and uses an electric heater. Internal temperature readings also confirmed that Flat 10 maintains a lower temperature band than the other flats there requires less energy to heat the flat to optimum temperature
Actual Energy Use Weather Correction Exposure Correction Occupancy Correction
Building Annual Energy Use (kWh/m2/year) Flat 10 Flat 29 Electric Electric 2780 7905
Corrected Energy Use NPI kWh/m2/year
U s i n g t h e B e d z e d B e n c h m a r k . Bedzed stated that they consumed 34.4kWh/m2/year in 2007. When comparing Bedzed to Thackley End, it was noted that Thackley Ends lowest case study flat energy consumption doubles that of Bedzed’s. A result of considerable cause for heat losses: limited building fabric insulation, single glazing and cold bridging via means of the window, it’s frame, and the continuing, thermally unabridged concrete slabs and block work. There is definitely ample opportunity to improve Thackley End‘s energy efficiency.
S a n k e y D i a g r a m s . The Sankey diagrams, as shown below, show how annual energy consumption is distributed between base loading and heating load. The lowest energy consumption months was taken as the base load (as shown in energy use compared to degree days graphs). The Sankey diagram shows Flat 38 to have a very high base load and low heating load. It is presumed hat this is an anomaly caused by the resident changing their fuel bills from 3 to 6 months. Therefore, when the bill figure was divided by 6( to get a monthly figure for CUSUM / Control charts) the same energy consumption figure was given for each month. Therefore odd findings ensued, most notably with the base load being greater than the heating load (under normal circumstance this ratio should be the other way round).
H e a t D i s t r i b u t i o n . L o g g e r D a t a . In these diagrams we can see the heat distribution within the flat types. The key relates to the temperatures measured by the loggers (ranges from minimum to maximum recorded). Temperatures were recorded between 12 noon to 2 pm in the day. Evidence of heat loss through the exposed walls was recorded from temperature being of a lower recording when close to said exposed wall. Although with double / triple glazed units in their flats, Flats 29 and 10 still proceeded to lose heat through the exposed walls. During the analysis period the loggers also recorded some extremely high temperatures in the flats, and as high as 250C in some. Due to high levels of glazing, extreme peaks in temperature can be recorded in the day as a result of solar irradiance. This glazing can also cause heat loss issues in winter months.
H e a t i n g S y s t e m s A n d T a r i f f . Thackley End flats were built with underfloor electric heating, however few of these systems sill work. So, some occupants have installed storage heating and electric heaters to cater for their thermal needs. Predominantly residents use the Economy 7 tariff which is utilised by, and preferable to, night storage heaters. This is because it’s tariff is structured and priced differently in regards to time of day. Electricity costs are significantly reduced in the evenings and so, to reduce energy costs, storage heaters are used to retain energy for heating the flat at a useful time in the day / evening. The thermostats in some of the flats, in particular flat 38, showed that the residents had little control over switching the heating on and off. As noted in the late Occupant Survey, the occupant at Flat 38 mentioned this. When the Economy 7 is working, they have no control over the heating level, using the thermostat. Also, having the under‐floor heating turned off in the day, can result to uncomfortably cool temperatures in the early evenings before the heating turns on. Therefore it seems it may be beneficial to change occupants onto a green energy tariff as this may lead to occupants being able to control their heating at all periods. In the images on this place we see how radiator systems and under‐floor systems distribute heat differently. Radiator systems (pictured in the plans to the right) create pools of thermal irradiance around the radiator source. This gradually heats the air n the space. There is a lot of localized temperature difference in the room, and thermal delight can be very different dependant on your positioning. Under‐floor heating systems (pictured below) heat the space from floor level upward, radiating through the air and heating the space evenly. By putting a gentle heat sources also at the point where we physically connect with the room (our feet) the perceived comfort becomes much greater. Under‐floor systems seek to store heat also in the building fabric, to slowly radiate heat throughout the day. Radiator systems however, do this but to a much lesser degre e of succe ss.
A p p l i a n c e s L a y o u t . These diagrams show the locations and appliance types in the case study flats analysed. Flats with a large number of appliances and electrical goods will have a resultant high plug load / energy demand. This equipment also transpires heat throughout it’s use, which can further increase internal temperatures. This can be undesirable to the flats due to their relatively small size and current problematic solar gain. Flat 10 (pictured left) had the highest recorded plug load of the Thackley End case study flats.
This graph shows the appliance loads for the individual flat Flat 10 has the highest appliance energy use whilst Flat 40 least.
R e c o m m e n d a t i o n s . No Cost Measures. Changing the electrical suppliers to an energy efficient company. Examples of these are Ecotricity and Green Electricity UK. However research must be carried out when changing electricity companies, due to some companies charging more for using Economy 7 tariff during peak times than for standard tariffs.
Low Cost Measures. Fix the system of thermostatic controls to allow better localised control of the heating for occupants with under‐floor heating. As well as being a practical solution this improves the wellbeing of the occupant.
Medium Cost Measures. Upon exhaustion of current appliances, replacements should be A – if possible A+ rated for energy efficiency. These will save on energy consumption and resultant costs. Replace existing stock of single glazed / steel framed windows to double glazing to reduce excessive heat losses.
Published on Apr 12, 2009
P30405 Post Occupancy Evaluation. Sustainable / Building Energy Audit. Thackley End, Oxford. Student: Andrea Luise Schrader. Tutor: Dr Raja...