Thermal mass in the context of homes refers to the use of materials that can absorb, store, and later release significant amounts of heat. Examples of high thermal mass materials are concrete, bricks, tiles, and stone. These materials can take a longer time to heat up. However, once heated, they also take a long time to cool down, slowly releasing the stored heat over time. Thermal mass and insulation are intrinsically linked as insulation materials contribute to a higher thermal mass.
Thermal mass in the home
In a home, thermal mass can be incorporated in many ways:
- Wall and Flooring Materials: Walls and floors made from concrete or brick have a high thermal mass. They can absorb heat from sunlight during the day or from internal heating systems, then release this heat as the building cools down, helping to maintain a stable indoor temperature.
- Water Tanks: Water has a high thermal mass and can also be used effectively. A large water tank inside a living space can act as a thermal store, absorbing excess heat during the day and releasing it at night.
- Phase Change Materials (PCMs): PCMs are substances that absorb and release thermal energy during the process of melting and freezing. They can be encapsulated in wall panels or other building components to store heat and help regulate indoor temperatures.
Role in passive solar design
In passive solar design, thermal mass plays an important role in managing heat gain and loss, thereby promoting energy efficiency and comfort within a building. Passive solar design takes advantage of the sun’s energy to heat and light homes and other buildings without the need for mechanical systems or active controls. The main elements of passive solar design are solar orientation, glazing, insulation, ventilation, and thermal mass.
The thermal mass absorbs heat from the sun during the day, reducing temperature increases within the building. As temperatures drop at night, the thermal mass slowly releases the stored heat, keeping the interior of the building warm. By absorbing heat during the day and releasing it at night, thermal mass helps to even out daily temperature swings. This can make the interior of the building more comfortable and reduce the need for mechanical heating or cooling. In some advanced passive solar designs, thermal mass can even be used for interseasonal heat storage. Heat captured in the summer is stored in a large mass and then slowly released during the colder winter months.
Forms of thermal masses in passive solar design
- Sunlit Floors and Walls: Sunlit floors and walls made from materials with high thermal mass can absorb heat during the day and release it at night. These might be concrete or tile floors or walls constructed from brick or stone.
- Thermal Storage Walls: Also known as Trombe walls, these are thick, dark-coloured walls placed behind glass. They absorb heat during the day and release it into the building at night.
- Earth-Sheltered Design: In earth-sheltered homes, the earth itself acts as a thermal mass, absorbing heat from the house during the summer to keep it cool, and releasing heat back to the house during the winter to keep it warm.
- Water Walls or Tanks: Water has high thermal mass, and large containers of water absorb and store solar heat.
Effectiveness
- Climate: In climates with a large difference between day and night temperatures, thermal mass can be very effective. During the day, the thermal mass absorbs heat, keeping the house cooler. At night, as temperatures drop, the thermal mass releases this heat, helping to keep the house warm. However, in hot and humid climates, or climates with little daily temperature variation, thermal mass may be less beneficial.
- Insulation: Insulation is key to preventing heat from escaping too quickly. Thermal mass needs to work in conjunction with good insulation for maximum effect.
- Placement: For the most effective use of thermal mass, high-mass materials should be located where they can absorb sunlight during the day or where they can absorb heat from the occupants or appliances.
- Colour: Darker surfaces absorb more heat than lighter ones. Therefore, darker materials will generally have a higher effective thermal mass than lighter materials.
Finally, it’s important to note that while thermal mass can help reduce the need for artificial heating and cooling, it doesn’t replace the need for it entirely. Depending on the local climate, supplemental heating or cooling systems may still be necessary. But used effectively, thermal mass can significantly improve a home’s energy efficiency, reducing both costs and environmental impact.
Thermal mass and insulation
Insulation and thermal mass work together in a building to control heat gain and loss, contributing to the overall energy efficiency and comfort of the home. Here’s how:
Insulation is a material that slows down the transfer of heat. It acts like a barrier, keeping heat inside the home in the winter and reducing the amount of heat that enters in the summer. Good insulation reduces the amount of energy needed to heat or cool the home, which can significantly lower energy bills.
Thermal mass, on the other hand, absorbs and stores heat energy and then slowly releases it over time. During the day, high thermal mass materials absorb heat, keeping the interior of the home cooler. At night, these materials slowly release the absorbed heat, warming the home.
Used together, insulation and thermal mass can greatly enhance a home’s energy efficiency:
- Reduced Heat Transfer: The insulation reduces the amount of heat that enters or leaves the home, which can keep the interior temperature more stable. The thermal mass absorbs and then slowly releases heat, smoothing out temperature fluctuations during the day.
- Enhanced Performance of Thermal Mass: Without insulation, the heat stored in the thermal mass could quickly be lost to the outside in the winter or overheat the house in summer. Good insulation ensures that the heat absorbed by the thermal mass is retained within the home and released slowly over time, reducing the need for mechanical heating or cooling.
- Regulated Indoor Temperatures: Together, insulation and thermal mass can help to regulate indoor temperatures, providing a more comfortable living environment. During the day, the thermal mass absorbs heat, preventing the home from overheating. At night, the thermal mass releases heat, helping to keep the home warm. The insulation reduces heat transfer with the outside, keeping the home warmer in the winter and cooler in the summer.
In summary, while thermal mass absorbs, stores, and slowly releases heat, insulation helps slow the rate at which that heat is transferred to or from the environment. For maximum energy efficiency and comfort, a home should be designed with both insulation and appropriate use of thermal mass.
