placed batts had large air gaps. The duct work, which was on the
floor of the attic above the ceiling insulation, was also found to have
large areas of missing or deteriorated insulation and at least one visibly
leaky connection (see electronic supplementary material Fig.
A1).
Two constant air volume (CAV) air handling unit (AHU) systems
serve the building, one for the south half of the building (AHU1)
and another for the north (AHU2) (see electronic supplementary
material Fig. A2). The cooling equipment that serves these systems
is about ten years old and consists of direct expansion (DX) evaporator
coils with individual water-cooled compressors. They share
an indoor water-spray evaporative condenser that draws air from
outdoors and discharges wet air to outdoors (Table 1). Each compressor
has a rated cooling capacity of 8.8 tons (30 kW). The AHUs
do not have economizers and share a common open air inlet on
the top of the roof; dampers are manually operated. Building heat
is provided by a boiler that supplies hot water to the AHU heating
coils.
2.2. Description of building integrated photovoltaic (BIPV) system
In June 2009 the roof of Building 228 was retrofitted with a BIPV
system made by Solar Integrated (now owned by Uni-solar; Auburn
Hills, MI). The BIPV system was installed above the original roof
7–13 June 2009. The PV modules were connected to the grid on 11
August 2009.
The BIPV system (Fig. 1) has a bottom layer of rigid thermal insulation
(3.8 cm expanded polystyrene), which also includes channels
for the PV’s electrical conduit. Above the insulation there is a
6.35 mm roof board made from a gypsum core sandwiched between
two fiberglass mats; the roof board adds rigidity, puncture resistance,
and fire protection. The top layer of the BIPV system contains
a 60 mil (1.5 mm) thick white single-ply PVC roofing membrane
(model S327) made by Sika Sarnafil. The nominal initial and 3-
year aged solar reflectances of the white membrane, as reported
by the Cool Roof Rating Council’s Rated Products Directory, are 0.83
and 0.63, respectively [21]. Thin film amorphous silicon triple junction
PV cells are factory laminated to the single-ply membrane. The
nominal panel-level efficiency of the PV is 0.068. Including losses
from the other components of the PV system (e.g., wiring, inverter)
the estimated nominal PV system efficiency is about 0.05 [22]. The
single-ply membrane covers the entire roof but the photovoltaic
cells can be laminated anywhere on the white membrane.
Fig. 2 shows the areas of the roof that bear laminated photovoltaic
cells. The system as installed contained 309 m2 of PV and
552 m2 of exposed white membrane (Table 1). Immediately following
the installation of the BIPV the solar reflectances of the white