Assessing noise and overheating in dwellings: aligning acoustic and thermal models for partially open windows

Abstract

A Building Regulation to limit overheating in dwellings came into force in England in June 2022. This requires that the provisions to mitigate overheating are usable by the occupants. The internal noise limits while using opening windows for ventilative cooling at night are 40 dBA Lnight and 55 dB LAMAX (10 th highest). A clarification to the guidance indicates that windows may be modelled as partially open; this enables justification of reliance on natural ventilation at night in noisier locations than if windows must be modelled as fully open. A simple acoustic model for a partially open window is examined for its accuracy. The thermal model relies on the CIBSE TM59 method, with the adaptive thermal comfort model when using opening windows. However, the ventilation performance of window openings is described in the thermal model with an "Equivalent area" (EA), and typically modellers assume an ideal aperture. Achieving a consistent understanding of the respective performance for a partially open window between the acoustic and thermal models is not simple. The basis of the models for the acoustic and ventilation performance of a partially open window are discussed. A description for a new characteristic, the "acoustic open area", is proposed.