8.3 Applications of phase change materials for sustainable energy  (Page 5/26)

Building applications

PCMs can be used for temperature regulation, heat or cold storage with high storage density, and thermal comfort in buildings that require a narrow range of temperature (Figure Typical Application of PCM in Buildings ). Therefore, if the solar energy is stored effectively, it can be utilized for night cold. The use of PCMs brings an opportunity to meet the demand for heating. It helps to store the energy which is available during daytime and to keep the temperature of the building in the comfort level.

Energy storage in the walls or other components of the building may be enhanced by encapsulating PCM within the surfaces of the building. The latent heat capacity of the PCM is used to capture solar energy or man-made heat or cold directly and decrease the temperature swings in the building. It also maintains the temperature closer to the desired temperature throughout the day. Researchers have proposed macro or micro level encapsulated PCM in concrete, gypsum wallboard, ceiling and floor in order to achieve a reasonably constant temperature range.

Today, it is possible to improve the thermal comfort and reduce the energy consumption of buildings without substantial increase in the weight of the construction materials by the application of micro and macro encapsulated PCM. The maximum and minimum peak temperatures can be reduced by the use of small quantities of PCM, either mixed with the construction material or attached as a thin layer to the walls and roofs of a building. In addition, the energy consumption can also be reduced by absorbing part of the incident solar energy and delaying/reducing the external heat load.

The absorption of heat gains and the release of heat at night by a paraffin wax-based PCMs encapsulated within a co-polymer and sandwiched between two metal sheets (PCM board) have been used in some building materials. The PCM boards on a wall reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than the other walls during the heat releasing process. The heat flux density of a PCM wall in the melting zone is almost twice as large as that of an ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy.

Unlike structural insulated panels, which exhibit fairly uniform thermal characteristics, a PCM’s attributes vary depending upon environmental factors. The structural insulated panel works at all times, resisting thermal flow from hot temperatures to colder temperatures. The thermal flux is directly proportional to the temperature difference across the structural insulated panel insulation. The usefulness of PCM is seen when the in-wall temperatures are such that it causes the PCM to change state. It can be inferred that the greater the temperature difference between day and night, the better the PCM works to reduce heat flux. The use of a phase change material structural insulated panel wall would be excellent for geographic areas where there is typically a large temperature swing, warm during the day and cool at night.