Calculation of convective heat transfer coefficients of room surfaces for natural convection

Convective heat transfer from internal room surfaces has major effect on the thermal comfort, air movement and heating and cooling loads for the room. Recent studies have shown that the values of convective heat transfer coefficient used in building thermal models greatly influence the prediction of the thermal environment and energy consumption in buildings. In computational fluid dynamics (CFD) codes for room air movement prediction, accurate boundary conditions are also necessary for a reliable prediction of the air flow. However, most CFD codes use ‘wall functions’ derived from data relating to the flow in pipes and flat plates which may not be applicable to room surfaces. This paper presents results for natural convection heat transfer coefficients of a heated wall, a heated floor and a heated ceiling which have been calculated using CFD. Two turbulence models have been used to calculate these coefficients: a standard k — var epsilon model using ‘wall functions’ and a low Reynolds number k — var epsilon model. The computed results are compared with data obtained from two test chambers.