Phase change materials (PCMs) store and release thermal energy while changing phase, usually between solid and liquid. In a building, a correctly selected PCM can absorb heat as temperature rises and release it as temperature falls. The melting range must match the operating temperature; a PCM that does not cycle under actual conditions provides little useful latent storage.
Sensible heat and latent heat
Sensible storage changes the material temperature. Latent storage uses the heat absorbed or released during a phase change. A simplified estimate for latent storage is:
Q = mL
where Q is stored heat, m is the mass of PCM, and L is latent heat per unit mass. If 100 kg of a PCM has a usable latent heat of 150 kJ/kg, the ideal latent storage is 15,000 kJ, or 15 MJ. Real building performance is lower or delayed by incomplete phase change, heat-transfer resistance, cycling range, and losses.
Where PCMs can be used in construction
| Location or method | How it works | Main concern |
|---|---|---|
| Wallboard, ceiling panel, or floor element | Adds thermal storage near the conditioned space. | Fire classification, leakage, location, and heat transfer. |
| Microencapsulated PCM in mortar or concrete | Small capsules are dispersed in the mixture. | Capsule damage, strength, shrinkage, workability, and cost. |
| PCM-impregnated porous aggregate | PCM is retained in pores or a sealed carrier. | Leakage, compatibility, and retained mechanical properties. |
| Macroencapsulated panel or tube | A larger sealed container is placed within the assembly. | Local expansion, container durability, maintenance, and fire behavior. |
Organic, inorganic, and eutectic PCMs
Organic PCMs include paraffins and fatty acids. They can offer stable cycling and low corrosivity, but flammability and low thermal conductivity may govern product selection. Inorganic PCMs include salt hydrates and some metallic systems. Salt hydrates can have high storage density, but phase separation, supercooling, corrosion, and water loss require control. Eutectic mixtures are selected to obtain a particular transition range. Product-level evidence matters more than the family name alone.
Selection checklist
- Melting and freezing range under the actual indoor or envelope temperature cycle.
- Usable latent heat, thermal conductivity, and charge/discharge rate.
- Cycling stability, phase separation, supercooling, volume change, and leakage.
- Compatibility with cementitious materials, metals, membranes, sealants, and finishes.
- Fire, smoke, toxicity, handling, and product-classification requirements.
- Effect on concrete strength, stiffness, shrinkage, moisture behavior, and durability.
- Installation, replacement, quality control, cost, and end-of-life plan.
PCMs in concrete
Direct addition of an unprotected liquid can interfere with hydration or leak from the hardened material. Encapsulation or a compatible carrier is normally used. Published improvements in temperature control cannot be transferred directly between products, dosages, specimen sizes, and climates. Trial mixtures should measure both thermal behavior and the concrete properties required by the project.
Limitations of energy-saving claims
A PCM does not automatically reduce annual energy use. Results depend on climate, orientation, insulation, ventilation, HVAC controls, internal gains, PCM amount, transition temperature, and whether the material fully resets between cycles. Whole-building simulation and monitored trials are more useful than a universal percentage.