Phase change materials and chemical reactions

Sensible heat energy storage has the advantage of being relatively cheap but the energy density is low and there is a gliding discharging temperature. To overcome those disadvantages phase change materials (PCM's) could be used for thermal energy storage. The change of phase could be a melting or a vaporisation process. Melting processes have energy densities in the order of 100 kWh/m3 compared to 25 kWh/m3 for sensible heat storage.

Vaporisation processes are combined with a sorption process. This means that a heat pumping effect is included in the process. Energy has to be withdrawn at a low temperature when charging and be delivered at a high temperature when discharging the storage. Energy densities in the order of 300 kWh/m3 could be achieved.

Phase change materials could be included in e.g. building materials and thus contribute to lower energy consumption and power demand by storing solar energy during daytime and the cold during night-time.

The PCM could also be included in containers of different shape. One common container is the plastic nodule (STL) that is put into a tank where the heat transfer fluid (usually water) melts or solidifies the PCM. Several different PCMs with melting points ranging from - 21 oC up to 120 oC are commercially available

Phase change materials and chemical reactions are also utilised for heating and cooling purposes in small applications like pizza-warmers (wax), heating of consumables like saké, (CaO +H2O=Ca(OH)2), and hand-warmers (sodiumacetate trihydrate).