Phase Change Materials in the Building Industry by Henk de Haan

Phase Change Materials in the building industry Henk de Haan Smart & Bioclimatic Design, semester 1, 2011-2012

Contents Introduction Latent heat storage Critical material properties Types of PCM material Containment and integration PCM application in the building industry Commercial PCM products Buildings using PCM materials Is there a future for PCM? Conclusion Integration in a design References Smart & Bioclimatic Design, semester 1, 2011-‐2012 Phase Change Materials in the building industry Henk de Haan (1352555) Hand-‐in date: 4 November 2011

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Front image: Alterswohnungen, Domat/Ems, Switserland (2004) by Schwarz Architekten (www.schwarz.ch) and graph of a test result comparing a reference wall with a PCM wall (Schossig et al., 2005)

Introduction We live in a world in which the climate is changing, natural sources are depleting, and fossil fuels are running out. For a large part these problems seem only to be solvable by decisive political action and on world scale. But on smaller scales it has led people to consider the issue sustainability in their own lives and environments too. This could also be said of the field of architecture, in which ‘sustainable design’ has become more and more of an issue over the last few decades. This has been mainly driven by the wish to reduce energy costs and the unnecessary use of material (Dobbelsteen, 2011). ‘Smart and Bioclimatic Design’ could be seen as a strategy to tackle these problems, and lead to a more sustainable built environment – an environment with more ‘Bærkraft’, to use the original Norwegian word: ‘an environment which has the strength to carry itself’ (Lassen, 2011). Smart and Bioclimatic Design is defined by van der Ham (2011) as a ‘design approach that deploys local characteristics intelligently into the sustainable design of buildings and urban areas’. In this essay I will focus on the application of ‘phase changing materials’ (PCMs) in buildings as a smart and bioclimatic design strategy. This category of materials is applied in buildings to absorb excess heat and cold and so reduce heating and cooling peak loads, and at the same time increase thermal comfort. In the first section of this article I will explain the main working principles of PCMs, their critical material properties, and the various ways in which they can be integrated into buildings. Then I will discuss the application of PCMs in the building industry, beginning with a historical overview, and then moving on to current developments, commercial PCM products on the market, and some examples of buildings in which PCM materials have been applied. Based on this I will discuss which types of application are more or less successful an why, and finally come up with some design proposals for the integration of PCMs in a design of my own. Latent heat storage Apart from the problem of sustainable energy production, the storage of energy is also an issue. If heat and cold could be stored better in buildings, peak loads would be lowered, lowering the demand for Figure 1 -‐ Equivalent heat storage, the amount of energy (Kundhair et al., 2004). PCMs have the ability to concrete needed versus the amount of PCM (of an store a large amount of energy per unit, which makes unspecified type) (Bouwman, I. M., 2008) them an interesting option for use in the building industry, see Figure 1 for a comparison of the heat storage of a PCM versus the heat storage of concrete, a material often acclaimed for its ‘thermal mass’ (although this picture is not from a scientific source, it gives an indication of how they compare). Phase change materials able to store such a large amount of thermal energy because they make use of latent heat storage. Energy storage can be done in various ways: mechanically, electrically or thermally. Within thermal energy storage there are two forms: latent and sensible heat storage (see Figure 2). Sensible Figure 2 -‐ Types of heat storage (Buddhi et al., 2007) heat storage materials store heat by raising their temperature (Sharma et al., 2009). A clear example of sensible heat storage is the metal skin of a car that heats up in the sun. But also a thick concrete wall stores heat by raising its temperature, though this will be less noticeable due to the high thermal mass of

concrete. Properties that determine how much energy is stored are the specific heat of the material, its mass, and the temperature change of the surroundings (Pasupathy et al., 2008). In contrast, latent heat storage takes place without significantly raising the temperature of the storage material. It ‘is based on the heat absorption or release when a storage material undergoes a phase change from solid to liquid or liquid to gas or vice versa’ (Pasupathy et al., 2008). In this form of heat storage the heat is stored and released by the chemical bonds of the material (Buddhi et al., 2007). Phase change materials are materials can store heat both sensibly (when they are in gas / liquid / solid state) and latently (when they go through a phase change from one of these ‘stable’ states to another), see Figure 3. This means that if such a material with a suitable melting / solidifying temperature is applied in a façade element, it can absorb solar heat without warming up the room behind. PCMs can be seen as ‘artificial thermal mass’ (Fraser, 2009) because they can reach the same heat capacity and heat buffering effect as for instance a thick concrete wall, but with a much thinner layer of material. Commercial PCM producers make various claims about their PCM products, for instance that a 15 mm layer of gypsum board containing PCM is equivalent to a 140 mm concrete wall (BASF, 2008), or the example from Bouwman (Figure 1). These claims can not be substantiated scientifically, but it is clear Figure 3 -‐ Sensible vs Latent heat storage, the phase that PCM stores much more heat per unit volume than change temperature (melting p oint) of this p articular PCM is 26 degrees (Isa et al., 2010). sensible heat storing materials. Critical material properties A list of critical properties for PCM materials is given by Buddhi et al (2007). It includes thermophysical, kinetic and chemical properties, but also cost and availability of the material are important. The parameters for the amount of energy storage are the thermal capacity of the material and its latent heat of phase change (Lassen, 2011). One of the most important material properties to take in account is the melting temperature. Various researchers have concluded that this should be 1 to 3 degrees above the desired room temperature to be effective for cooling, and 1 to 3 degrees under the desired room temperature if the goal is to use PCM for heating (for instance: Peippo et al., 1991). See Figure 4 for a complete list of important material properties.

Figure 4 -‐ Critical PCM Properties (Buddhi et al., 2007).

Types of PCM material There are various categories of materials that can be used as PCM. Sharma et al. (2009) uses a classification in three categories: organic, inorganic and eutectic PCM, each with their own material properties, which make them more or less applicable in the building industry. Within the inorganic category there are salt hydrates and metallics. Salt hydrates were the first category of materials to be used as PCM, mainly because of their low cost and because they are not flammable, which is a problem with some organic PCM Figure 5 -‐ Classification of PCM Materials (Sharma et al., 2009) types (Pasupathy et al., 2008). Other positive properties of inorganic PCM materials are their high latent heat per unit, their comparatively low volume change between phases and their relatively high thermal conductivity (Buddhi et al., 2007 and Sharma et al., 2009). Salt hydrates do have some important disadvantages, the most important being ‘supercooling’ and ‘phase segregation’ – without going in to all the chemical details, this means the material will only work for a limited amount of phase changes, gradually losing its heat storage capacity. This has led to the name ‘limited utility PCM’ for this group of materials (Pasupathy et al., 2008). The focus has now moved more towards organic PCM materials, the main categories of which are parrafins and fatty acids. The application of this group of materials was not seriously tried at first because their flammability risk was considered to be too high to use them in building components. Although this problem could be overcome, they also have a lower heat capacity than salt hydrates and are more expensive (Kundhair et al., 2004). But, ‘it has now been realized that some of these materials have strong advantages, such as physical and chemical stability, good thermal behavior, and adjustable transition zone’ (Kundhair et al., 2004). Last, there are eutectic PCM materials. These are composites of various materials; they are produced aiming to improve the quality of individual products – mainly the reduction of flammability and the adjustment of the melting temperature (Zhang et al., 2007). This is especially important when PCMs are integrated in buildings. Containment and integration When you have found a PCM material with the right melting point and good further properties, how can it be integrated in a building? There are systems in which PCM stores heat from man-‐made hot/cold sources (Pasupathy et al., 2008), but in this essay I will focus on direct application, where PCM is integrated in a building component (roof, wall or floor), and stores or releases its heat under direct influence of the climatic conditions (sun, Figure 6 -‐ Typology of PCM integration and effects (Zang et al., 2007)

ambient temperature). A basic overview of possible applications of PCM in building components is given in Figure 6 by Zang et al. (2007). There are three basic strategies for the containment of PCM is these building components: direct integration, immersion and encapsulation (Zhang et al., 2007). The most simple and economical method is direct integration in which the PCM is mixed in with the building material – mostly gypsum or concrete (Kundhair et al., 2004 and Zhang et al., 2007). Immersion means that a porous material is bathed in fluid PCM, which it absorbs due to capillary action. The advantage of this method is that it allows ordinary building materials to be changed into PCM containers whenever necessary. Building materials used for this are concrete blocks, gypsum board and bricks (Zhang et al., 2007). These methods do have some problems: some PCMs can damage the constructive materials, or can start leaking out in the long run. Another problem is that the heat transfer of the PCM decreases in the long run. These problems have led to the development of encapsulation methods: micro and macro encapsulation (Pasupathy et al., 2008). Macro encapsulation involves ‘some form of package such as tubes, pouches, spheres, panels or other receptacle. These containers can serve directly as heat exchangers or they can be incorporated in building products’ (Pasupathy et al., 2008, p. 1156). A problem with this method is phase separation; the PCM tends to solidify around the edges, decreasing its thermal conductivity over time (Pasupathy et al., 2008). Another difficult point is that the macro-‐capsules have to be protected against damage when the building is in use (for instance against drilling in walls) (Schossig et al., 2005). This problem is avoided by using micro encapsulation, ‘whereby small, spherical or rod-‐shaped particles are enclosed in a thin and high molecular weight polymeric film’ (Pasupathy et al., 2008, p. 1156). Here the volumes are so small that this problem does not occur (Kundhair et al., 2004). Most ‘micro-‐ encapsulated PCMs can undergo more than 10,000 phase transition cycles that make the product life span last for more than 30 years’ (Isa et al., 2010). Micro-‐ Figure 7 -‐ Microscopic p icture of micro-‐encapsulated encapsulation is effective in PCM working terms, PCM showing that it still retains its shape after 1000 phase change cycles (Kundhair et al., 2004) avoiding the problems with methods of incorporating

Figure 8 -‐ Schematic view of a lightweight wall with micro-‐ encapsulated PCM plasterboard (Schossig et al, 2005)

that other methods have, a drawback could be that it affects the constructive strength of the material it is incorporated in (Kundhair et al., 2004). Another drawback, according to some researchers, is the higher cost of micro-‐encapsulated PCM materials (Zalba et al., 2003). On the other hand, other researchers say ‘these micro-‐capsules can be incorporated simply and economically into construction materials (Pasupathy et al., 2008, quoted in Fraser, 2009). A last questionable property of micro-‐encapsulated PCM is if it is Cradle-‐to-‐Crade or even recycleable at the end of it’s life time (Lassen, 2011). I did not find any useable information about this.

PCM application in the building industry Now that the basic working principle of PCM, the various types, and manners of integrating them into building components have been explained, I will focus on some commercially available PCMs, and on some buildings in which these products have been applied. The first documented attempt to use PCM in a building was a house by the Hungarian-‐American scientist and inventor Maria Telkes, built in 1948 in Dover (USA). ‘…Solar energy was accumulated using 18 solar collectors made of thin gauge galvanised absorber plates, black painted and covered by double 1.2 x 3.0m glazing panels. The heat generated from these panels was passed through a duct via a fan to three heat storage bins situated on either side of the rooms. The heat storage bins contained five gallon drums filled with sodium sulphate decahydrate (Glauber’s salt). With a total of 21 tons of this PCM, the system had the potential heat storage capacity of 11 GJ, sufficient to store energy equal to 12 days of heating load, when used between the room temperature and 32°C temperature (melting point). […]The system operated successfully for 2 years, providing a comfortable temperature of 21°C with no secondary back-‐up heating system required. However, the experiment ended in failure due to the decomposition of the salt’ (Kenisarin et al., 2007, p. 1949). In Zang’s scheme (Figure 6) this would be an example of the left-‐ middle option. Apart from this house and some other one-‐off experiments, interest in PCM (and latent heat storage in general) only really returned after the 1970s oil crisis. Some research was then done on the use of PCM in Trombe walls (referred to by Buddhi et al., 2007). Since then a lot of research has been done on different PCM materials, encapsulations, and their performance, but there has still not really been a take-‐ off point as there has been with for instance the integration of sun panels on buildings. PCM is still not a very conventional technology. Probably the most extensive research on the effect of PCM in a building component was done by Schossig et al. (2005), who did simulations and experiments in full-‐scale rooms for about five years at the German Fraunhofer institute. This research used Micro-‐encapsulated PCM integrated in interior wall panels. With a melting temperature range between 24°C and 27°C, they found the temperature hardly exceeded 26°C, decreasing the need for mechanical cooling devices and increasing thermal comfort. During the night the temperatures stayed higher in the test room, as the PCM slowly releases its heat again (Schossig et al., 2005). To function properly two things are important: first, that ‘PCM areas are dimensioned according to the expected loads and existing shading devices’ and secondly ‘…to ensure that the stored heat can be discharged during the night with adequate ventilation’ (Schossig et al., 2005, Figure 2 -‐ Test result comparing a reference wall with a wall with p.305). micro-‐encapsulated PCM with a melting point between 24 and 26 degrees (Schossig et al, 2005) Commercial PCM products Zalba et al. (2003) gives a list of 45 commercially available PCMs, but only a few of them have a melting point around room temperature, making them apt for use in the building industry. The listed materials do not seem to be available in building products. During the last decade some PCM products specifically for the building industry have come on the market, which could make the application of PCM more obvious for architects and clients. The companies BASF and Dupont are the main producers.

Figure 8 -‐ Schematic view of the working Glass X Chrystal (www.glassx.ch)

BASF produces ‘Micronal’ since 2004, a product of micro-‐encapsulated PCM gypsum, and ‘Maxit Clima’ since 2005, a form of micro-‐encapsulated PCM gypsum which can be applied wet. These products were developed together with Fraunhofer institute. Dupont produces ‘Energain’ since 2006, a form of aluminum-‐ laminated panels with PCM. These products all make use of micro-‐encapsulated paraffin (Fraser, 2009). A product by Dörken using macro-‐encapsulated salt hydrates is also available, called ‘Delta-‐Cool 24’, this is mainly intended for lowered ceilings (Fraser, 2009). Another interesting group of products made by the Swiss company is Glass X, they incorporate salt hydrates in capsules between glass, making it one of the only visible applications of PCM in building products that I could find (www.glassx.ch).

Buildings using PCM materials In the following section I will give some examples of buildings that make use of PCM materials for passive heating and/or cooling. Badenova building, Offenburg, Germany (2003) This building was designed by Lehmann architects in collaboration with solar energy experts Stahl+Weiss. It makes use of various solar energy technologies. No hard data about the energy use of the building are available, but according to the architect the buildings running costs are significantly lower compared to an air-‐conditioned building (www.lehmann-‐ architekten.de). The PCM used in the building is BASF’s Micronal, invisibly used as interior partition Figure 3 (source: www.lehmann-‐architekten.de)

walls. This could be seen as a test-‐case for Micronal, as this product apparently was only on the market in 2004 (Fraser, 2009).

Figure 4 (source: www.publicdomainarchitecten.nl, photo by Ossip van Duivenbode)

Floating Pavillion, Rotterdam (2010) Designed by Deltasync and Public Domain Architects, this is an ‘almost autarkic’ building, which makes use of a whole scala of sustainable technologies (www.publicdomainarchitecten.nl). Again, PCM is not one of the spectacular elements in the design, it is only used in the ceiling of the auditorium, to take up excess heat when it is full of people (www.deltasync.nl). The PCM is probably incorporated in gypsum board.

Figure 6 -‐ 3-‐Liter-‐Haus after renovation (Greifenhagen, 2003)

Figure 5 -‐ Application of Maxit Clima at the 3-‐Liter-‐Haus (Greifenhagen, 2003)

3 Liter-‐Haus, Ludwigshafen, Germany (2001) This project involved the renovation of a neighbourhood of apartment blocks built in 1951, aiming to bring the energy consumption down from 25 to 3 liters per m2, and reduce heating energy consumption and CO2 emissions by 80% (Greifenhagen, 2003). To reach these goals again a combination of technologies was used. Also it forms the earliest example I could find where Maxit Clima – wet applied PCM gypsum – is used. This project and other examples show the use of PCM in renovation projects: adding a great amount of thermal buffering capacity, without adding a thick layer of material. This project uses the PCM as ‘air-‐conditioning in the wall’, to ensure ‘that the indoor climate is always comfortable and pleasant’ (Greifenhagen, 2003). Alterswohnungen, Domat/Ems, Switserland (2004) Glass X seems to be one of the few to specialize in the visible application of PCM materials. The company was founded and is owned by architect Dietrich Schwarz, forming a rare example of a combined technology development + architectural design work in the world of PCM (www.glassx.ch). Most projects use Glass X in combination with normal glazing, creating varied facades with transparent and translucent PCM parts, vaguely reminding one of Figure 7 -‐ Project by Schwarz Architekten (in Domat/Ems, traditional Japanese architecture. The ‘green’ Switserland, 2004) using a combination of Glass X and technology is used as part of the architectural normal glass in this facade (source: www.glassx.ch)

expression instead of as a technological add-‐on. As a rule of thumb – based on the reference projects on the Glass X website – you could say the proportions of glass vs. PCM should be about 50%-‐50% (www.glassx.ch).

Is there a future for PCM? The technology is available, the early problems have been solved, there are products on the market… so why are PCM materials still not widely used in the building industry? Although there has been a lot of research in PCM materials and their behavior, this seems to be done mostly from a purely technical point of view, without much connection to the architectural profession. Looking at a promotional picture from a Delta-‐Cool 24 brochure (Figure 14) you can ask yourself: is this still smart and bioclimatic design? Is it even design, or is it just as much an add-‐on solution as a mechanical cooling unit?

Figure 8 -‐ Image from Delta-‐Cool 24 brochure (Delta-‐ Cool, 2008)

Figure 95 (source: Bouwman, I. M., 2008)

If PCM really is just an add-‐on solution, it is in no way ‘deploying local characteristics intelligently’, the key point of smart and bioclimatic design (van der Ham, 2011). Hartland (2010) concludes that PCM is not spreading widely in the building industry for a few reasons: first, due to a lack of information about the actual energy savings and the pay back time in actual buildings (not experimental settings). The difficulty to find accurate information is mentioned in many researches (for instance Zalba et al., 2003). Secondly, many PCM products look exactly the same as their non-‐ PCM equivalent but cost much more – PCM gypsum board for example – or are applied out of site like the Delta-‐Cool product (Figure 14). According to Hartland architects and clients are willing to pay more for sustainable building technology, but ‘they expect visual gratification, or ‘added value’ for their effort’ (Máté, 2009, refered to in Hartland, 2010, p.27). This is not the case with many PCM products, Glass X and Dietrich Schwarz form an exception. I think this type of architect can set the future for the application of PCMs, using them more visually. As energy prices rise, and the price of PCM goes down (Bouwman, I. M., 2008), it may also become more and more of an option for the retrofitting of houses and offices, to lower their energy consumption and improve thermal comfort.

Conclusion PCMs are materials with a high heat storage capacity, especially during phase transitions,

when they store heat latently. There are various types and manners of incorporating PCMs that could be applied in buildings. The two most used material categories are salt hydrates and parrafins, of which parrafins are generally considered to last longer. Micro-‐encapsulation appears to be the best way of incorporating PCM, it avoids many of the drawbacks of other methods, but there are also products on the market which use different techniques. Although there are various PCM materials produced commercially for the building industry, only a relatively short list of buildings can be found in which PCM was actually applied, even though technical drawbacks from the past seem to have been solved. Reasons for this could be a lack of information on actual performance, the high start costs, and the invisibility of many PCM appliances. For the future the most promising uses for PCM, in my opinion, are in retrofitting projects and in visual application in façade panels. At the moment PCM is probably to expensive for retrofitting normal housing and offices, but this could change in the near future. A great advantage is its low mass and volume, and its good effect on the interior thermal comfort. PCM could now already be used in monumental buildings where the high costs can be accepted because the building is valued enough, and it would destroy the character of the building if it is thickly insulated. The Zonnestraal Sanatorium in Hilversum could be an example of such a building. In my opinion visual application of PCM like done by Schwarz / Glass X is the only way in which it can be used in a truly ‘smart and bioclimatic’ way for new

buildings, taking into account orientation and solar gain from the beginning, not just using the PCM as an add-‐on technology. Integration in a design Based on these conclusions I will now propose some ways in which PCM materials could be integrated in one of my previous design projects*. The assignment for this project was the reuse and extension of a row of prefabricated concrete industrial barracks in the Binckhorst area of The Hague. The new function for the complex was to be a commercial exposition center plus extra functions (restaurant, hotel rooms, office space and meeting rooms).

Figure 10 -‐ Section over the (new) main hall with a north facing shed roof. To the left the old barracks with exposition space, to the right the new block with other functions (own drawing).

There are two quite obvious parts of the building where PCM products could be used. Firstly for retrofitting the existing barracks to improve their insulation and thermal comfort, without changing the structure too much. Here the use of PCM gypsum board or a comparable product would make sense. Secondly there are two part of the building with a lot of glass: the walkway and the shed roofed hall. Here you could think of Figure 11 -‐ Axonometric view of the building: left/top the old part, cut by a new connecting walk-‐way in one direction and the new shed roof hall in the other direction, to the right/front the new b lock with extra functions (own d rawing).

Figure 12 -‐ Sketch of the walk way with the facade half translucent glass X / half normal glass (own drawing)

the visible application of PCM, replacing some of the window area with translucent PCM materials as Glass X. In the analysis of the existing buildings we found out the prefab façade paneling and the prefab concrete truss structure supporting the roof where the most characteristic parts which should be preserved. Keeping the existing façade panels and spraying a form of wet applied PCM gypsum against the brick inner leaf of the structure would improve the insulation value of the façade. This brick was already painted white or plastered originally. The current roof can be replaced by a lightweight PCM gypsum layer on the inside, protected by a wood structure for strength and a waterproof layer on the outside.

The walkway which cuts through the original structure was seen as a big steel hollow truss section, supported by lift shafts and cladded with glass on the sides where it sticks out above the pitched roofs of the barracks (which is about half of the time). These glass surfaces are both in the northwestern and southeastern direction. Half of the glass could be replaced by a translucent PCM product like Glass X, using the truss diagonals as border between PCM areas and glass areas. Like this the open atmosphere of the walk way stays intact, but there is 50% less solar gain, and heat that does enter the space can be absorbed (see Figure 16). For the shed roof area a same principle could be used. The shed roof itself faces southeast with its closed part, which contains

Figure 13 -‐ Schematic set up of the shed sun panels. The inclination of the roof is based on the best angle roof part of the b uilding: the last 'layer' with lamellas could be left out if part of for these sun panels. This means the open parts of the roof face the glass is replaced by a translucent PCM northwest and are hardly exposed to solar gains. For the façade it facade (own d rawing).

is a different story, it faces southwest for a large part, and is fully glazed. In my original design I solved this potential problem by adding metal lamellas in front of the glass, blocking the direct sun but still allowing views out (see Figure 17). Reconsidering this with the knowledge of PCM materials you could choose to replace the lamellas by making parts of the façade translucent / PCM. An advantage of this is that you use one construction layer less, saving material. *At the moment I am not doing a design project, so I have taken another look at an old project for this assignment.

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Sharma, A.; Tyagi, V. V.; Chen, C. R.; Buddhi, D.; Review on thermal energy storage with phase change materials and applications, in: Renewable and Sustainable Energy Reviews, Vol. 13, 2009 (318-‐345) Zalba, B.; Marin, J. M.; Cabeza, L. F.; Mehling, H.; Review on thermal energy storage with phase change materials, heat transfer analysis and applications, in: Applied Thermal Engineering, Vol. 23, 2003 (251-‐ 283) Zhang, Y.; Zhou, G.; Kunping, L.; Qunli, Z.; Hongfa, D.; Application of latent heat thermal energy storage in buildings: State-‐of-‐the-‐art and outlook, in: Building and Environment, Vol. 42, 2007 (2197–2209) Websites

www.deltasync.nl www.glassx.ch www.lehmann-‐architecten.de www.publicdomainarchitecten.nl www.schwarz.ch