On the non-periodic unsteady heat transfer through walls
(EN)
Antonopoulos, KA
(EN)
Democritou, F
(EN)
Existing calculation methods of the transient heat flow through walls for air-conditioning applications, assume periodic outdoor conditions. Therefore, the effect of a temporary temperature rise on the indoor heat flow is usually neglected. In the present work an attempt is being made to model the related non-periodic transient problem. The method of approach is based on a finite-difference solution of the transient heat conduction equation within the wall. Outdoor air temperature deviation parameters are introduced, which characterize any temporary deviation of the outdoor air-temperature from periodicity. Indoor heat flow deviation characteristics are defined, which describe the deviation of the indoor heat flow from periodicity, provoked by the corresponding outdoor air temperature deviation. A parametric study is conducted, where the effects of the temperature deviation parameters on the indoor heat flow deviation characteristics are examined. It has been found that (a) the maximum heat flow deviation varies linearly with the mean temperature difference, (b) the restoration ratio is practically independent of the temperature amplitude difference, and (c) an increase in the wall thermal diffusivity results in a decrease of the maximum heat flow deviation. The practical importance of the present analysis is that it helps towards the estimation of peak loads under non-periodic outdoor conditions.
(EN)
