Empirical Relationship Describing Total Convective and Radiative Heat Loss in Buildings

Abstract

On the basis of theoretical considerations of convective-radiative heat transfer, a relationship was developed enabling the total convective and radiative heat flux QC+R emitted from any object at tw and its surroundings at t∞ to be calculated from known values of the surface temperature of such an object, i.e., the known temperature difference Δt=tw -t∞ and average air temperature Tav. This relationship is applied to thermal imaging cameras with the aim of developing appropriate software to enhance their measurement capabilities. They can then be used not only for monitoring and measuring temperature, local overheating, heat losses through insulation materials, thermal bridges, constructional defects, moisture, etc., but also for measuring the heat losses from any object, such walls and buildings. This empirical relationship includes constants relating to the object itself, such as its characteristic dimension l, surface area A, emissivity ε and temperature parameters, which depend on tw, t∞, Δt and Tav and on the physical properties of air. Experimental validation of the proposed relationship, performed for two values of the surface emissivity ε, showing the discrepancies ΔQC+R=1.75% (for ε=0.884) and 4.85% (for ε=0.932), has confirmed its correctness and its practicability.