Net ZEB Case Studies - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 348

two-thirds of the windows are operable and casement type, which facilitates
natural ventilation during the summer. The windows are not automatically
controlled; thus, the occupants are relied upon to open the windows as
needed in an attempt to improve comfort and reduce mechanical cooling
needs.
Shortly after construction, a blower door test was performed. The test
revealed an infiltration rate of 0.85 air changes per hour (ach) at 50 Pa
differential pressure. The design goal was originally 0.5 ACH; nonetheless,
the measured rate is considered very airtight.
To supplement passive solar gains, ÉcoTerra has a 55 m 2
building-integrated photovoltaic/thermal (BIPV/T) collector on the upper
part of the roof. The BIPV/T collector is a hybrid in that it converts incident
solar energy into both electrical and thermal energy. The outer layer of the
roof consists of 21-136 W amorphous silicon photovoltaic modules with an
areaof2.1m 2 eachandanominalefficiencyof6.3%.ThetotalPVarraypeak
capacity is 2.8 kW (direct current). These modules extend from the soffit
to the peak of the roof. This has the dual benefit of superior architectural
integration and that the upper end of the modules is protected by the roof
cap. The modules are epoxied onto the underlying black-colored steel roof.
There is a 4 cm thick air channel under the steel deck of the roof, as shown
in Figure 7.5 , that is used to heat air as it travels from the inlet of the roof
(at the soffit) to the outlet (at the peak). The underside of the channel is
composed of plywood sheathing and approximately 2.5 cm of spray foam
insulation behind it. Once the air has reached the peak, it is sucked by a
fan through round ducts that are evenly spaced across the roof, as shown
in Figure 7.6 . The variable speed fan sucks air from the roof at a nominal
rate of about 200 l/s (and consumes about 400 W of power at this rate).
The airflow rate was designed to be approximately double this; however,
complex ducting significantly increased pressure drops between the roof
andthesitesofthermalenergyuse.Insunnyconditions,theairtemperature
can increase by up to 40 °C from inlet to outlet of the collector.