A Phase Change Material (PCM) is a substance with a high heat of fusion which, melting and solidifying at certain temperatures, is capable of storing or releasing large amounts of energy.
How PCMs Work
The only phase change used for PCMs is the solid-liquid change. Liquid-gas PCMs are not practical for use as thermal storage due to the large volumes or high pressures required to store the materials when in their gas phase. Liquid-gas PCMs do have a higher heat of transformation than solid-liquid PCMs.
Initially, the solid-liquid PCMs perform like conventional storage materials; their temperature rises as they absorb heat. Unlike conventional storage materials, however, when PCMs reach the temperature at which they change phase (their melting point) they absorb large amounts of heat without a significant rise in temperature.
When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat. Within the human comfort range of 20° C (68° F) to 30°C (86° F), some PCMs are very effective. They store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry, or rock.
Phase change materials are used in freezers packs, protective clothing and hard hats designed to keep people cool in hot environments. One of the most important recent breakthroughs with PCMs is in the building industry. BASF have developed a number of energy saving products. Through a physical trick, building materials can now store extra latent heat. For example, a revolutionary new wall plaster, incorporating one third phase changing material, has the same heat storage capacity as a 23 cm thick brick wall in the critical temperature range for living comfort of 22 to 26 °C. Additionally, phase changing materials can be integrated into both solid and liquid materials.
Concrete is used extensively for residential and commercial construction in many places in the world. The large thermal mass of the concrete can often be an advantage, as concrete stores energy as heat during the day and releases it during the night, which reduces the need for additional cooling or heating. In hot climates, the concrete heat bank and release of heat may not be wanted. BASF’s Micronal® PCM phase change materials used in the plaster sheeting described above, have been incorporated into aerated cement blocks for the first time. This substantially increases the heat storage capacity of its blocks, and means significant savings in the heating and cooling of buildings.