Evaluation of hypocaust heating of buildings

Hilly areas usually need heating for comfort inside the building. Passive techniques such as direct gain, Trombe wall and the solarium can be incorporated for space heating. These techniques have already been studied in detail and are well understood. One of the principles to effectively provide space heating either by using solar air heaters or any waste hot exhaust gases is the hypocaust which has been explained and studied in detail in this paper. The building blocks which can be used for such construction, and are available in India, have been identified and their thermophysical properties measured. Using a lumped model technique, a mathematical analysis with a computer program has been developed to assess the performance of a building with a hypocaust. Numerical calculations have been performed for a hospital with a hypocaust to assess the effect, namely, under what conditions the building can achieve a comfortable temperature. It is seen that it is necessary for the building U-value to be reduced to 0.44 W/m² K for a hypocaust to insulate the building effectively. Exhaust gases from a 40 kW diesel generator set which may operate for eight hours at a flow rate of 0.0708 m³/s is able to give comfortable temperatures within the building. If a solar air heater is used, an area of 70 m² is required (mass flow rate 0.182 m³/s) to maintain comfortable temperatures (17–21°C) for a building of 200 m² floor area.