Using TRNSYS the PVT system was modelled with a flow rate of 300 kg/hr (0.083 kg/s), equivalent to one building air change per hour, and with zero air flow, as would be the situation for a non-ventilated building integrated PV system. The results showed a difference of at most 1.3% between the PV efficiency operated under these two conditions, however, over the course of the year this small difference in PV efficiency results in quite a substantial increase in electrical output for the ventilated PVT system. This value was calculated to be 135 kWh/annum, assuming a PV cell packing factor of 0.85 and a value of 0.92 for transmission through the glass cover.