Experimental and numerical study of unsteady non-periodic wall heat transfer under step,ramp and cosine temperature perturbations

An experimental and numerical study of the transient non-periodic wall heat transfer problem is presented. A computer-controlled indoor/outdoor environment simulation system produces any desired variation of the air temperature, thus allowing measurement of the dynamic thermal behaviour of any test wall under the desired boundary conditions. Measurements of the temperature field within the wall, of the heat flow and of the convection coefficients at the wall surfaces are performed during step, ramp and cosine perturbations of the outdoor air temperature. The measurements are in very good agreement with the numerical predictions obtained by a developed finite difference solution procedure. The results showed that in building heat transfer applications, for example in air conditioning, the usual assumption of periodic outdoor conditions may lead to considerable errors in case of a significant temporary deviation of the temperature from periodicity.