Air-based, open loop Building Integrated Photovoltaic/Thermal (BIPV/T) systems have proven to be an efficient means for generating renewable energy. They produce electrical energy, converting part of the incident solar radiation, and recover part of that radiation that turns to heat, while acting as the outer shell of the building. However, for the typical BIPV/T design with air entering at the bottom of the installation, flowing within a continuous air channel and exiting at the outlet of the system high PV temperatures may still occur. This is due to the fact that as air moves inside the air channel it accumulates heat and the heat exchange efficiency between the PV panels and the flowing air drops along the flow path of the air channel. In large building integrated PV installations, high PV temperatures may lead to quicker PV panel degradation, as well as lower electrical efficiency.
A multiple-inlet BIPV/T system aims to increased heat extraction from the PV panels, with the introduction of several intakes of fresh air along the height of the installation. This may lead to lower and more uniform PV temperatures, enhanced PV panel durability and higher electrical and thermal performance.
This study presents the development of a methodology for the modelling and design of multiple-inlet systems, as well as a numerical study of such a system. The modelling component consists of two aspects, namely, the fluid mechanics and the energy balance of the system. A flow model was developed, based on flow networking techniques, in order to assess the inlet flow distributions. The flow model incorporates wind effects in the form of exterior pressures, acquired through wind tunnel testing. The inlet flow distributions were used in a modified energy balance model that accounts for the flow conditions of the inlets and the air channels of the system. This was an improvement on the assumption of uniform flow from all the openings of the system, which has been common in the limited number of studies of multiple-inlet systems so far.
The developed models were applied for the numerical investigation of variations of multiple-inlet BIPV/T systems for a potential retrofit project on an office building in Montreal. The investigation was carried out assuming summer and winter conditions, as well as several cases of wind direction and velocity. A multiple-inlet system with optimized geometric features of the inlets was found have up to 1% higher electrical efficiency and 14% to 25% higher thermal efficiency than that of a single-inlet system, also resulting in lower and more uniform PV operating temperatures. The latter can be a crucial factor for the durability of large building integrated PV installations.