On the optimization of building envelope thermal performance. Multi-layered walls design to minimize heating and cooling plant intervention in the case of time varying external temperature fields

The optimal sequence of resistive and capacitive layers within building envelope is determined in order to minimize the air-conditioning plant intervention to keep the indoor air temperature constant against sinusoidal and impulsive external temperature variations. In the case of sinusoidal variations with angular frequency w, the optimal structure of the building envelope is determined by the value of the dimensionless parameter s=wrc only, where rc is the wall thermal time constant. For s<18 the interventions of the air conditioning plant are minimized if the whole heat capacity is lumped between two plane slabs with the same value of the thermal resistance (symmetrical threelayered wall); for s>18 symmetrical walls are still preferable, but with a number of layers increasing with s (walls with more than three layen); for s–>oo the optimal structure is the one of a homogeneous wall. In the case of impulsive stresses, the wall which facilitates the plant intervention, is a symmetrical three-layered one, as the previous case for low values of s.