On the precise and estimated calculation of the main thermal time constant of dwellings

An approximation calculation of the main thermal time constant has been used by researchers and engineers to gain a general understanding of how a building might respond to external dynamic solicitations. Those approximations assume generally that the building can be modeled by a simplified representation of thermal resistances and capacities. However, caution is necessary when using this approximation, as it may underestimate the thermal time constant value. In our study, the main thermal time constant is accurately calculated using modal analysis as both the physical representation and the solution method, while considering a large number of dwellings (246 377) under different ventilation rates (0, 0.5 and 5 volumes per hour). Then, clusters of dwelling with similar properties are identified. Finally, an estimated main thermal time constant is calculated for some clusters and compared to the precise one. The comparison shows that the error in time constant varies from cluster to cluster, and indoor temperature calculated with the estimated time constant may lead to overestimation in terms of overheating indicators and monthly cooling needs.