.

Fig. 7: Modern architecture is increasingly characterised by lighter constructions and energy-optimised planning, without compromising on comfort. PCMs integrated into building materials – e.g. in the form of plasterboards – deliver a pleasant indoor atmosphere by balancing temperatures.
© BASF

Fig. 11: Measurements from two test rooms with 15-mm PCM gypsum plaster on all opaque interior surfaces apart from the floor. Under ideal conditions, a temperature reduction of around 3.5 K can be achieved using a PCM.
© Fraunhofer ISE

Fig. 12: PCM plasterboard from Knauf.
© ZAE Bayern

Fig. 13: Interior gypsum plaster with PCM.
© Maxit Deutschland

Fig. 14: PCM board from DuPont Energain.
© ZAE Bayern

Fig. 15: PCM cooling ceiling
© Dörken

Fig. 15b: PCM sun protection
© ZAE Bayern

Fig. 15c: GLASSXcrystal facade building element.
© GLASSX
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Building materials and indoor environment

The heat capacity of lightweight-construction buildings can be significantly increased by including latent heat storage materials in the surfaces of the building fabric. The effect is improved “passive” building cooling and indoor temperature regulation, thus resulting in energy savings and increased comfort. Building materials with PCMs for passive building cooling are already commercially available.

It is often pleasantly cool in the summer in buildings with exposed solid concrete walls or masonry. This cooling effect is made possible by the high heat capacity of the building fabric itself. Solid, exposed building components function as heat buffers – they can absorb heat during the day and then release it again at night. In contrast, the room temperature quickly rises in buildings with low heat capacities, such as lightweight constructions with components made of wood or plasterboard.

Protection against heat and cold in buildings is generally the result of a combination of heat storage in the building mass and appropriate insulation measures. Heat is absorbed and released by the building mass without special technical equipment being necessary, hence the term “passive temperature stabilisation”. Because of their high storage capacity in a narrow temperature range, PCMs are ideally suited for improving the ability of various materials to provide passive temperature stabilisation. This effect has been finding commercial use in building services technology for a number of years now.

The work of the research projects “Innovative PCM technology” and “Micro-encapsulated latent heat storage devices” has provided the foundation for many of the developments and products that will be described here. The research work on the applications of PCM technology have now been bundled as part of the German Federal Ministry of Economics and Technology’s EnOB research initiative. Three methods of integrating PCMs into buildings have been investigated: integration into the exterior plasterwork, into the masonry, and into interior plasterwork. For each of these three cases, the melting temperatures were varied in simulation studies as a function of the specific application and the amounts used.

The issues of energy savings, increased comfort and, in the case of exterior applications, component protection were all evaluated. Because of the significantly lower heat flows and the direct influence of surface temperatures on users’ perceived comfort, the use of PCMs is the most promising in interior applications. When PCMs are used in our climate zone, the savings in heating energy have been too small so far in standard residential and office buildings. On the other hand, the use of PCMs in building materials significantly increases user comfort in buildings in the summer. If appropriate measures are taken during building planning, itmay even not be necessary to employ any other cooling measures.

The use of PCMs in lightweight constructions has great potential, particularly in office buildings because of their strongly fluctuating load profiles between day and night. The melting point should be chosen such that temperatures above 26 °C arise only for very limited periods and temperatures above 28 °C are fully avoided if possible. This means that the majority of melting heat should be absorbed under 25 °C. Night-time unloading of the storage device is essential in order for the system to work properly and should be provided for by suitable measures. The loads occurring should generally be in reasonable proportion to the storage capacity of the system. It should be ensured that sufficient PCM surfaces are provided and that these are not blocked. These materials will only be a replacement for a sunscreen system if there is no or very little irradiation.

Building materials with PCMs

As part of development work at the Fraunhofer ISE, various PCM building materials have been developed in cooperation with industrial partners and then monitored in test rooms under real external conditions. Figure 11 shows the potential of a PCM building material for achieving temperature reductions in buildings under ideal conditions. Used here was PCM gypsum plaster that was applied with a coating thickness of 15 mm to walls and ceilings. On day 1 (ideal case), the PCM storage was only slightly overloaded, and a temperature difference of up to 3.5 K was measured between the reference room and the PCM room. The subsequent days show that other heat protection measures – such as shading or the optimisation of indoor loads – should generally be implemented before PCM building materials are used. In addition, mechanical ventilation to regenerate the heat storage facility is essential, particularly on warm nights. If the PCM cannot release its heat, overheating may result the following day. Some products for passive building cooling are already available on the market and will be briefly introduced here.
The products are classified here depending on whether they use micro-encapsulated or macro-encapsulated PCMs:

  • Plasterboard: Knauf PCM Smartboard

PCM plasterboard available for drywall construction applications with around 30% mass fraction of PCM with a layer thickness of 15 mm.
Available melting range: 23 °C and 26 °C;
latent heat capacity around 90 Wh/m²;
manufacture and distribution: Knauf Gips KG.

  • Gypsum plaster: Maxit

Gypsum machine-applied plaster with around 20% mass fraction of PCM for a layer thickness of up to 15 mm. In addition, the plaster can also be activated using watercarrying systems. Available melting range: 21 °C, 23 °C and 26 °C; latent storage capacity around 70 Wh/m²; manufacture and distribution: Maxit Deutschland GmbH.

In contrast to the building materials described so far where micro-encapsulated PCMs are integrated as additives, DuPont has developed a board where paraffin is integrated into a plastic matrix.

  • Integrated storage container:

DuPont Energain® has a thickness of 5 mm and a weight of around 4.5 kg/m². Around 60% of its mass is paraffin, which has a melting range of 18 °C to 22 °C. These boards were tested in two identical rooms in a building at the University of Lyon, where one room was equipped with PCM boards and one was not.

Building integration

The building materials described so far mostly use microencapsulated PCMs as additives. It is thus possible to integrate these building materials into buildings in almost unlimited amounts and forms. Handling is no different than for conventional building materials. The approaches identified for the inclusion of PCMs have only been fully developed for paraffins and fatty acids. In contrast with building materials, PCM components can be fully prefabricated, meaning that no processing is necessary during installation. It is thus possible to use macro-encapsulated PCMs, such as salt hydrates, in the manufacture of these components.

Figure 15 shows examples of applications of PCM components: The first example is the integration of a PCM into a ceiling, where the PCM servesmainly to cool the room. Dörken employs encapsulated salt hydrates here. If the air temperature in the room rises, the warm air rises, melts the PCM and is thus cooled again. Maximum cooling rates of 40 W/m² to 45 W/m² can be achieved here. However, active ventilation is recommended to remove heat at night. The power required for fans should be taken into account in the energy balance.

Another attractive method of integrating PCMs into building components is the PCM composite sunscreen system. Just such a system has been developed by Warema in cooperation with ZAE Bayern as part of a project supported by the German Federal Ministry of Economics and Technology. Internally fitted sun protection is generally intended to reduce the amount of sunlight, but the sun protection equipment is actually heated up in the process and then releases its heat into the room. The integration of a PCM into the sun protection leads to reduced or delayed heating of the room. Investigations carried out on laboratory samples have shown that the maximum temperature of the sun protection fittings is delayed by 3 hours and the room stays 2 °C cooler. The radiation asymmetry can be reduced by 6 °C. As with all other applications, however, heat removal by means of night ventilation is necessary. This approach is currently being investigated in real installations as part of the “PCM demo” project.

The transparent facade building element by GLASSX is a passive system that is mainly used for heating, but can also be used for cooling a room. It consists of a number of layers: A PCM layer on the side facing into the room stores the heat of the incoming solar radiation. Multiple glazing on the facade prevents heat losses and prismatic glass that is fitted in the gaps allows the incoming sunlight to pass through only if it is at a shallow irradiation angle (i.e. in winter), thus protecting the interior from overheating in summer. Ceramic screen printing on the interior side gives architects freedom of design as regards colour selection. The system has been installed in around a dozen buildings in Switzerland so far. The cover picture on this Info brochure shows the use of PCM heat storage in the facade of a nursing home.

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