The basis for a room global temperature

Abstract

The design of heating and cooling appliances in buildings in routine cases normally proceeds on the assumption of a room index temperature which combines the separate effects of air temperature and of the longwave radiant field m the enclosure. It is pointed out that the basis for the index in current use in the U.K. and elsewhere is flawed, and this article is concerned with the logic of setting up a valid in ex temperature in its place. The argument depends first on reducing the surface-to-surface radiant exchange between enclosure surfaces to an approximately equivalent surface-to-star point exchange, using a least-squares fit. The fit proves to be quite good. It is next established that to a limited extent the star point temperature - a fictitious construct - will do duty for the space-averaged observable radiant temperature in the room. Thirdly, since the index temperature is taken to drive the radiant and convective heat flows from the room as a whole to one of its bounding surfaces, the question is discussed as to how reliably these physically dissimilar mechanisms can be formally merged in this way. Finally, simple expressions are given for enclosure heat needs in relation to comfort temperature and similar quantities. The arguments present some innovative features in building heat transfer.