Characteristic parameters of a hypocaust construction

Hypocaust, an ancient Roman concept for keeping the inside of buildings warm, has been explained with a survey of a few modern buildings based on these concepts and using solar heat employing a number of design variations. Results expressed in terms of energy requirements per m2 of floor area per degree day comes out to be minimum (15.4 kJ m−2 per DD per annum) for a solar chimney and maximum for solar air collectors (128.4 kJ m−2 per DD per annum). The basic parameters that determine the performance of a hypocaust construction are size of the cavity determining the heat transfer between the flowing fluid and the building component and the storage capacity of the hypocaust element. The optimum width of the cavity comes out to be between 50 mm and 100 mm. Heat storage capacity of the building element used as hypocaust corresponds to 0.125°K temperature rise per hour in relation to the building heat load.