From an operating energy perspective, the thermal inertia of heavy materials is well known, both in warm and cold climates. The figure below shows the comparative thermal inertia of various building materials.
The heat capacity of concrete is about 2,400 KJ/m3/0K. With an average concrete volume of 30 m3 for an apartment, energy in the order of 70 MJ will be stored in the concrete frame for each degree the temperature is raised or lowered. This energy can be released to contribute to heating or cooling the space when the temperature changes. To get an idea about how much energy this is, it can be compared to the total energy consumption required to heat an apartment in a modern building: on an annual basis, this is a maximum of 150 kW/m2 (45 GJ for an apartment of 80 m2). The daily energy consumption in the cold season is less than 250 MJ.
Several systems have been developed to use thermal mass in precast structures, see below. Air is circulated in the voids of hollow core floor and roof slabs. This system reduces the size of the required mechanical system and creates energy savings both for heating in the winter as well as cooling in the summer. For heating, energy savings in the order of 35% can be achieved with this system. A reduction in cooling power consumption can be about 40%.
The underside of concrete floor and roof slabs should be exposed to get the full benefits of thermal mass. Doing away with a suspended ceiling can reduce the overall building height and can result in 5% to 7% savings in construction costs. Using the thermal mass of concrete is extremely important from an environmental point of view as it provides a long-term economic gain for a building owner through reduced life cycle costs.
The mass of concrete can provide excellent acoustic insulating properties for air-borne sound. This makes concrete ideal for external walls in buildings facing roads with heavy traffic and as insulation between different areas in a building. Precast concrete panels are often used as noise barriers beside roads and railroads.
For more information on TermoBuild Technology see the AIA/CSI Presentation
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