M Ciampi

On the optimization of building envelope thermal performance

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 ω, the optimal structure of the building envelope is determined by the value of the dimensionless parameter σ = ωrc only, where rc is the wall thermal time constant. For σ < 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 three-layered wall); for σ > 18 symmetrical walls are still preferable, but with a number of layers increasing with σ (walls with more than three layers); for σ → ∞ 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 σ.

Cooling of buildings: energy efficiency improvement through ventilated structures

Abstract Some peculiar cases of ventilated facades, also occurring in conservative recovery interventions of the existing building heritage, are examined. For this purpose the influence of the variation of some environmental and geometrical factors on the energy performance of ventilated facades is investigated. Finally, the advantage of using solar chimneys to enhance air movement in naturally- ventilated buildings is examined. 1 Introduction In the last few years the passive solar systems for the cooling of buildings have been made the subject of numerous studies, both theoretical and experimental [l-51, owing to the remarkable reduction in undesirable summer overheating due to direct solar radiation achievable by using these systems. Among the particularly interesting passive solar systems are ventilated walls (VW), solar chimneys (SC) and roof solar collectors (RSC). Generally, the VW (facades VF and roofs VR), in which the air inlet is from the outdoor environment, are used for heat removal from the building [6-131; the SC and the RSC, in which air inlet occurs from the indoor room, are used to induce a natural ventilation to improve indoor air conditions making them more comfortable for the building occupants [2,3]. Because of the continuous rise in energy consumption in summertime due to the ever-growing demand for air-conditioning plants and split systems (in Italy the power required in the summer peak was equal to that required in the winter peak in 2001), the European Directive on the energy efficiency in buildings [l41 suggests carrying out priority strategies to further increase the thermal efficiency