Computational fluid dynamic modelling of thermal periodic stabilized regime in passive buildings

The influence of the architectural envelope on indoor microclimate conditions has been widely studied in recent years because of the optimization of passive strategies and thermal performances of buildings. In this study a transient periodic temperature has been imposed on a side wall of an enclosure: the variation of the temperature in all the points of the body follows the same periodic law of the imposed thermal forcing after a certain time. This condition is called periodic stabilized regime. This phenomenon happens especially during the summer season when the daily temperature has very different values between day and night. Despite that, nowadays building microclimatic conditions are analyzed imposing a fixed temperature on the indoor environment. There are not analytical and numerical solutions describing the case of a temperature free to evolve under an outdoor thermal forcing. This situation finds a practical example in passive buildings where there are no HVAC systems or equipment. Periodic stabilized regime has been analyzed imposing different material properties on the solid body of the enclosure. Conductive and convective phenomena have been numerically investigated through Computational Fluid Dynamics (CFD) and analytically validated using a function that reproduces the daily variation of the outdoor temperature. The aim of this paper is to supply the basis to build a predictive tool able to simulate the indoor thermal profile of an environment subjected to outdoor thermal conditions also in the case where the indoor temperature is free to evolve.