8.3 Applications of phase change materials for sustainable energy  (Page 3/26)

Applications of pcms

The three applications of PCMs listed below (solar energy, buildings, and vehicles) are only a small portion of the many areas where they can be used (catering, telecom shelters, electronics, etc.). The applications of PCMs in these areas have been widely studied in order to minimize the greenhouse effect and to minimize the need for foreign gasoline which costs U.S. economy millions of dollars every year.

Increasing concerns of the impact of fossil fuels on the environment and their increasing cost has led to studies on thermal energy storage for the space heating and cooling of buildings. Extreme cold or warm weather increases the demand on heating or cooling. If the thermal energy of heat or coolness is stored and then provided during the day or night, part of the peak loads can be shifted to off-peak hours. Therefore, an effective energy management and economic benefit can be achieved.

Solar energy is recognized as one of the most promising alternative energy resource options. However, it is intermittent by nature: there is no sun at night. The reliability of solar energy can be increased by storing it when in excess of the load and using the stored energy whenever needed.

The minimization of heat loss or gain through walls, ceilings, and floors has been studied for a long time and PCM applications have been considered for more than 30 years to minimize these losses/gains, and thus reduce the cost of electricity or natural gas use in buildings. Studies on viability of PCMs in vehicle applications are also growing widely. Denaturation of food during transport brings a major problem which is being partially solved by refrigerated trucks. However, this causes not only more expensive foods, but also irreversible environmental effects on living organisms.

Solar energy applications

Solar thermal energy is a technology for harnessing solar energy for thermal energy. The solar energy is absorbed by the earth and is dissipated throughout the ground at different rates that is dependent on the compositions of the ground and amount of water. Ground temperature is stable and solar energy can be transferred between the ground and space heating/cooling places. Water heaters that use solar energy play an important role for this purpose and they started to become popular in the late 1960s (Figure Solar Heater ). In order to utilize the energy from the sun at all times, this precious energy should be stored and used when needed. Passive systems using PCMs have been good candidates for thermal energy storage and have been applied since 1980s. At first, the water heaters were supported by filling the bottom of the heaters with PCMs, which was a first step in storing energy in heating systems. However, the quantity of the available energy in the storage system was limited by low thermal conductivity of the PCM. Improvements on thermal storage systems and developments in the incorporation of PCMs that utilize the solar energy have been extensively studied since then.