Overheating assessment in Passivhaus dwellings: the influence of prediction tools

Abstract

Thermal comfort during the summer in the Passivhaus concept relies mainly on natural ventilation to provide indoor cooling. Do airflow modeling tools accurately predict overheating in summer and for anticipated warmer climates? What effect do simplifications of airflow modeling techniques have on the overheating assessment of Passivhaus dwellings? Measured data and a calibrated thermal model are employed in the present study to address this question. The calibrated model is then used to create a standalone building energy model (BEM), a BEM coupled with an airflow network model (AFN), and a BEM coupled with an AFN supported by the wind pressure coefficients obtained from computational fluid dynamics (CFD) simulation. The outcome of each modeling approach was then compared against each other within three different European climates. Results showed that the overheating frequency prediction found with the default design infiltration and natural ventilation inputs commonly used in the literature agreed fairly with those obtained from the AFN + CFD in temperate or colder climates (< 2% difference), but were significantly underestimating overheating in Passivhaus buildings located at warmer climates (9.4% difference). For Passivhaus dwellings in warmer climates, the airflow modeling approach is unlikely to provide for an accurate estimation of the overheating incidence.