Heat Transfer via Unconditioned Spaces: The Influence of the Adjustment Factor Evaluation Method

The aim of the paper is to determine the influence of the evaluation method of the heat transfer via unconditioned spaces in building energy need calculation procedure, taking into account the dispositions of the UNI/TS 11300-1 standard. Two different calculation methods for the adjustment factor btr,U are compared with reference to a case study of a '70 years condominium building: the simplified method, based on the tabulated values, available only for existing buildings, and the detailed one, based on the analytical calculation of the heat transfer coefficient Hue between unconditioned spaces and external environment, available for both new and existing buildings. In the latter case, the influence of thermal bridges between unconditioned rooms (cellars, attics, stairwells) and the outside and the ground is also considered. Results are discussed in terms of both btr,U factor and temperature Tu of the unconditioned spaces. The energy need of single apartments has also been calculated in order to evaluate the influence of the calculation procedure on heating millesimal table of the condominium. Results of simulations reveal significant differences on single units energy needs between the detailed and simplified method; the contribution of thermal bridges in Hue coefficient calculation is negligible.