PCM in the home: latent heat storage explained
A phase change material, or PCM, stores heat by melting and releases it by freezing at a set temperature. In a home it can soften temperature swings and store solar heat in a smaller volume than water or masonry, but it is still a specialist product with real trade-offs in cost, durability and evidence.
How does a phase change material store heat?
Most heat storage works by changing temperature, called sensible heat. A PCM adds latent heat, the energy absorbed when a substance changes from solid to liquid at a nearly constant temperature. While the material melts, it takes in a large amount of heat without getting any warmer. When it freezes, it gives that heat back at about the same temperature.
Ice is the familiar case. Melting a kilogram of ice absorbs far more energy than warming a kilogram of water by a few degrees. Building PCMs use other substances with melting points chosen near room temperature, such as paraffin-type waxes or salt hydrates. Their latent heat is often in the region of 150 to 250 kilojoules per kilogram, but values depend on the product, so check the data sheet.
Where are PCMs used in homes?
The common applications are modest.
- Wallboard and ceiling panels. Capsules of PCM in the board absorb heat when the room warms and release it when it cools, flattening daytime peaks.
- Heat storage tanks. Containers of PCM inside a tank or buffer let it hold more heat in less space than water alone. Standard water tanks are covered in thermal storage tanks for water.
- Floor and solar air systems. Some solar air heating and sunspace designs use PCM to store daytime heat for the evening, related to the ideas in solar air heating.
- Do-it-yourself setups. Hobbyists have tried waxes and salts in tanks, with mixed results and fire or leakage risks to consider.
How does it compare with ordinary thermal mass?
Concrete, brick and water store heat as their temperature changes, and in a passive solar house this effect is useful. A PCM concentrates the storage at one temperature, so a thin layer can do the job of a much thicker slab. That helps in light-framed houses, which have little mass. Our guide to thermal mass in homes explains the sensible-heat approach, and passive solar design shows where mass belongs.
The catch is the melting point. A PCM only works if the room or tank temperature actually passes through its melting point, daily. If the material melts at 23 degrees C and the room never gets that warm, or never cools below it, the PCM does nothing. Matching the product to the use is the main design task.
What are the drawbacks and unknowns?
Cost per square metre is higher than ordinary drywall, and the benefit in a well-insulated, airtight house with decent glazing may be small, because those measures already limit temperature swings. Fire performance, leakage over many freeze and thaw cycles, and long-term stability vary between products. Any building product should carry the certifications your local code requires, so ask the supplier and your building inspector.
Evidence from Canadian homes is limited and most claims come from laboratory or European tests. Treat strong savings promises with care and ask for monitored results in a similar climate. Insulation, air sealing and windows normally give more for the money, as ranked in insulation upgrade priorities.
Did Drake Landing use phase change materials?
No. Drake Landing Solar Community in Okotoks, Alberta, stored heat in water tanks and in the ground. A field of 144 boreholes held summer solar heat for winter, described in borehole storage, and the same ground-store approach is explained in seasonal thermal energy storage. PCMs suit short cycles of hours to days, not months, so they solve a different problem from seasonal storage. For other options see energy storage types for homes.
Quick answers
What is a phase change material?
It is a substance that absorbs or releases large amounts of heat as it melts or freezes at a nearly constant temperature, such as wax or a salt hydrate chosen to melt near room temperature.
Are PCM wallboards worth it in Canada?
It depends on the house. In a lightweight house with large sunny windows they can reduce overheating, but in a well-insulated, airtight home the gain may be small compared with other upgrades.
Can phase change materials store heat for winter?
Not at residential scale. They suit daily cycles. Seasonal storage needs very large volumes, such as ground storage.
Is PCM safe in a home?
Products differ. Check fire ratings, leakage behaviour and code approvals with the supplier and local building authority before installing.