Hunting for the perfect phase change material (PCM) for the built environment

Almost 50% of the UK total carbon emissions come from the built environment, much of which is an outcome of heating and cooling of low energy-efficient buildings. The climate change trends predict an increase in temperatures within the UK, which in due course will lead to a rise in energy consumption to maintain indoor thermal comfort. Phase change materials, also known as (PCMs) are substances that store and release high thermal energy during phase transition. When incorporated into the built environment, PCMs offer tremendous promise as they can reduce carbon emissions and energy bills, along with improve thermal comfort for occupants of buildings. The purpose of this PhD project is to find or develop cost-effective and sustainable PCM as a potential solution to the impact of climate change on the built environment. As preliminary phase of this PhD, a literature review will be conducted on existing PCM for the built environment and their limitations. This will lead to proposing possible solutions of which some of them are the ones that this PhD is planning to address. In the past, most research related to the use of PCMs in the built environment has been done for solid-liquid PCMs. Therefore, in this research project both solid-liquid and solid-solid PCMs will be studied with emphasis on solid-solid PCMs.
Potential PCMs such as calcium chloride hexahydrate, sodium sulphate decahydrate, polyethylene glycol (PEG), PureTemp 24X, X25, X30, X40, X55 and X70 will undergo several investigation stages. The first stage is the screening stage, where some of the key properties such as: latent heat energy, melting/transition point, thermal conductivity, costs, and safety of the PCM will be studied. The safety of novel PCMs can be quantified by measuring their effect on living organisms such as bacteria and algae, however, for known PCMs reliable literature sources will be used to determine their safety.
In the second stage, any PCMs found to have the appropriate phase change temperature (Approx. 18 - 30 C), high latent heat energy, high melting point, high thermal conductivity, low environmental & health risks, and are widely available; would be incorporated into different building materials (e.g., concrete, bricks, plaster, and gypsum boards) and their composites will undergo tests like durability tests, thermal cycling, DSC, TGA, and SEM.
In the final stage, other studies such as Life Cycle Analysis and energy-saving performance will be conducted on the PCM composites.
For PCMs that have a higher phase transition temperature than the desired range (18 - 30 C), their physicochemical properties will be modified. In chemistry modifying the physicochemical properties of a material is called Tuning. There are many ways of tuning the properties of a material, however, the most common method is the introduction of foreign substances (impurities or additives) to the pure material. It is important to note that any potential additives used; must have the ability to interact with the PCMs at a molecular level. Therefore, additives must either have a common functional group (In the case of organic PCMs) or a common cation or anion (In the case of inorganic PCMs). This will ensure that the additive will disturb the intermolecular interaction between the PCM's molecules and ultimately alter its phase change temperature.
Another aspect this PhD project will cover is creating a database that includes all the potential PCMs which could be incorporated into the built environment with emphasis on biobased PCMs.