5. Summary
In this study we assess the effects of retrofitting an office building
in Yuma, AZ with a building integrated photovoltaic (BIPV) roof
system. The BIPV system consists of thin film PV that is laminated
to a white membrane, which in turn lies above a 3.8 cm layer of
insulation. The PV covered 36% of the white membrane surface.
The solar absorptance of the roof decreased to 0.38 from 0.75 after
installation of the BIPV system, lowering daily mean roof surface
temperatures by about 5 ◦C. Roof underside and attic temperature
decreases were smaller in magnitude than roof top surface
temperature reductions. Indoor air temperatures remained nearly
constant throughout the measurement period, though some fluctuations
occurred; these fluctuations were likely due to the inability
of the HVAC system to meet cooling load. Summertime heat flux
through the roof deck significantly decreased after installation of
the BIPV system, primarily a consequence of the insulation in the
BIPV system; the lower solar absorptance of the BIPV roof deck also
contributed. Summertime heat flux from the attic into the indoor
conditioned space was minimally affected by the presence of the
BIPV system, suggesting that the BIPV did not appreciably reduce
HVAC energy consumption. (Reductions in roof underside temperature
may have lowering ceiling heat flux by decreasing radiative
heat flux from the bottom of the roof to the floor of the attic. However,
this effect was not quantified.)
We were unable to accurately quantify the effect of the BIPV
system on HVAC energy consumption due to repairs that were
done on the HVAC system about three weeks after installation
of the PV. These repairs altered HVAC energy consumption and
thus confounded the pre- and post-retrofit comparison. However,