Literature Review: Phase Change Materials

A key area of significance to incorporate into our façade  was phase change materials. Phase change materials readily and predictably change their phase with a certain input of energy and store this energy to be released at a later point.  Being able to forecast these changes makes them very useful for designers.

Many new built lightweight structures lack thermal mass meaning that these buildings have a tendancy to overheat in Summer, but are difficult to heat in Winter.  Heating and cooling systems are often incorporated into the building to compensate for this but it is possible to duplicate the effect of thermal mass using phase change materials.  Past studies have shown that some pcm’s are capable of storing 5-14 times more thermal energy per unit volume than conventional thermal storage materials.  This means pcm’s are useful tools to help regulate temperature as can be shown in the figure on the right.
Comparison of temperature variations inside a room with and withour phase change materials installed
http://www.micronal.de/
Graph showing how temperature varies with thermal energy. Graph highlights the sensible and latent components of the thermal energy.http://www.duran-heat.com/


But how exactly do PCMs work?  If you imagine an ice cube floating in a glass of water,  the ice will absorb heat from the water without increasing its temoerature.  As the ice cube absorbs this heat, it melts changing state from a solid to a liquid cooling the drink at the same time.  This stored heat being released from within the ice cube is known as the latent heat and is key to the operation of phase change materials.

The latent heat component of phase change materials means that they will absorb and store excess heat over a certain temperature and then release this heat back into the room at a later stage when the room temperature drops below a certain temperature. This means they are capable of reducing both heating and cooling demands. Phase change materials in buildings currently have a range of flexible applications and there are many companies already manufacturing pcm products in the form of plaster (Gypsum boards, cement), ceiling tiles, PURcoating etc. They come in three different categories organic, inorganic and eutectics though the foremost is the most commonly used in buildings.  
Picture shows how phase change materials absorb heat above a certain temperature and release the heat when it drops below a certain temperature
http://phasechange.com.au/
Phase change materials can have many advantages including reduced heating loads, reduced energy costs and enhanced occupant comfort though they may significantly  increase capital costs of the façade  and so careful analysis of energy saving must be carried out in order to prove that an investment in such materials would be economically viable.