Reducing cooling loads with under roof air cavities.

In the present paper a model for steady-state thermal analysis of ventilated and unventilated light rook is proposed. The aim of the work is tostudy the influence of thermo-physical and geometric parameters of the roof and boundary conditions (solar radiation) on the entering heat flowand the temperature distribution within the roof structure. Knowledge of this relationship, in fact, is important to optimise the roof "thermal"design in order to reach acceptable indoor conditions with low energy costs.In the first part of the paper a calculation procedure for the forecast of internal temperatures and induced air flow rates is presented The modelcan be used to analyse both closed and ventilated air cavities for different boundary conditions. From the mathematical point of view it iscomposed by a system of non-linear equation solved numerically.The model output are: air temperature distributions, surface temperatures, heat fluxes and air flow rates (in the case of ventilated cavities).The second part of the paper deals with the development of two simplified models, directly providing the entering heat flows. A nondimensionalanalysis based on the II-theorem provided the structure of the monomial expression, and the free parameters were determinedthrough a parametric analysis performed by the complete model described in the first part.The resulting model predicts the performance of light roofs with good accuracy.