Comparative study of dynamic thermal performance of photovoltaic double skin façades influenced by glass transmittance and natural ventilation

Abstract

As a promising facade technology for building energy efficiency, the overall performance of double skin façade integrated with semi-transparent photovoltaic glass (STPV-DSF) was affected by multiple factors. The combined effects of two important factors, namely glass transmittance (τ) and natural ventilation, on the dynamic thermophysical behaviors of STPV-DSF were investigated in detail. Three parallel DSF cells, including two STPV-DSFs (τ = 20% and τ = 40%) and one clear glass DSF, combined with three ventilation modes (i.e. non-ventilation, external circulation and noontime external-internal circulation) were adopted for in-situ experiments on a test rig in both summer and winter. Results showed that both factors would affect the solar heat transmission through DSFs and the influence of natural ventilation was not as significant as that of glass transmittance in summer daytime. The influence of natural ventilation on thermal transmittance became more significant during nighttime, causing lower U-values. The lowest SHGC was achieved by τ = 20% STPV-DSF under external circulation in summer of merely 0.053 and the highest was for the clear glass DSF with non-ventilation in winter of 0.534. By employing the external-internal circulation only around noontime in winter, fresh air was preheated through the cavity to a temperature of 22–27 °C, which can be introduced indoors without increasing the heating load. Impact of lowered operation temperature of CdTe PV modules by natural ventilation on the improvement of power output efficiency was found insignificant. The energy efficiency potential of STPV-DSF may be weakened with the decrease of glass transmittance regarding the accentuated imbalance of the reduced cooling load and the increased heating load between the two seasons compared with that of the clear glass DSF.