Innovative system components to maximize energy performance
Concrete is known for its high compressive strength, which is why it has been used successfully for decades. This material also has other positive properties, such as good thermal conductivity (2.1 W/m × K) and heat storage capacity (880 J/kg × K), which should be utilized in existing structural components. In the future, concrete components will be available to collect and store renewable energy. This valuable combination of absorbing and storing energy at the same time is proving to be a breakthrough in the current renewable energy supply of buildings. The idea is to be able to access the stored thermal energy when the sun is not shining and the wind is not blowing (“dark doldrums”). Concrete is considered to be the perfect heat storage material.
The above properties of concrete can be clearly illustrated by measurements taken on a concrete roof (Fig. 1). Behind a glass pane, the radiation generates a temperature that is significantly higher than that of the outside air. The concrete surface absorbs the warm air and heats up with a time lag. The temperature penetrates the concrete cross-section and heats the concrete mass with a certain delay. When the surface temperature begins to decrease, the core of the cross-section has reached its maximum temperature. When the outside air temperature drops in the evening and at night (≤ 5°C), energy can still be extracted from the concrete mass (≥ 20°C). A constant supply to the building is ensured even in the evening hours. The concrete slab acts as an absorber for renewable energy while ensuring heat storage at the same time.
Concrete walls work in a similar way and show an even higher performance in some instances. In spring and fall, the wall opposite the roof surface provides higher outputs. The low sun at this time of year results in higher temperatures on the wall.
A similar behavior can be found in foundation slabs that function as absorbers and ensure heat storage. Such components extract thermal energy evenly from the ground and store it.
