Investigation on the energy performance of a novel BIPV system integrated with vacuum glazing

The development of vacuum glazed windows in recent decades provides a foreseeable energy saving potential in the design of ideal energy-efficient buildings. Based on the same concept of Dewar flask, the vacuum glazing consisted of two glass sheets and an evacuated layer which is merely 0.1mm wide, can achieve the U-value of 0.86W/m2K as reported. Currently, this advanced glazing technology is mainly applied to cold region due to the excellent thermal insulation performance of vacuum glazing. Not like the cold region where the temperature difference between indoor and outdoor is quite large, in the subtropical zone like Hong Kong, solar heat gain is the major part of total heat transfer through the glazing area, especially for those buildings with a large area of curtain wall. Building integrated photovoltaic (BIPV) is expected as an innovative idea of the building curtain wall design. Semi-transparent photovoltaic windows can convert solar energy into electricity as well. However, part of heat gain will be transferred into indoor environment which becomes additional cooling load. The proposed vacuum photovoltaic insulated glass unit (VPV IGU) in this paper combines vacuum glazing and solar photovoltaic technologies, which can utilize solar energy and reduce cooling loading of buildings at the same time. A detailed simulation study has been conducted by EnergyPlus and Berkeley Lab WINDOW. The simulation work has indicated that the cooling load can be reduced by 12.5% if the VPV IGU is used compared with common glazing products while power generation is not compromised compared with normal BIPV systems. The additional PV modules mounted on the building façade can enhance the electricity production to the optimum level.