Natural convection from heated room surfaces

Current convective heat transfer coefficients (CHTCʹs) for internal room surfaces have, in most cases, been based upon data for small, free-edge heated plates. An extensive survey of CHTC data has shown that a very wide variation exists in CHTC values for vertical and horizontal surfaces. For example, a CHTC value in the range 1–6 W m−2 K−1 has been obtained for walls. Both building thermal and CFD models require accurate CHTCʹs for calculations of the thermal conditions and the air movement in a room. However, most such models use convective coefficients obtained for free-edge heated plates. This paper presents convective heat transfer coefficients for the heated surfaces of an environmental chamber and a small box measured under controlled conditions. Using uniformally heated plates attached to an internal surface of the chamber or the box and by accurately measuring the surface and air temperatures, the CHTCʹs were deduced after allowing for conduction and radiation losses from the plates. Data is presented for a heated wall, a floor and a ceiling for natural convection.