Net ZEB Case Studies - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 366

distribution loads were assumed to be seasonally invariant. The total
internal gains were distributed into an hourly schedule based on results
from Armstrong et al. (2009). The occupant schedule assumed that three
adults occupied the space according to a typical working family. The
infiltration rate was input based on that measured for the house using a
blower door test. The infiltration rate at 50 Pa was measured to be 0.85
ACH, which is approximately equivalent to 0.043 ACH under typical
conditions with a pressure difference of 4 Pa. This was assigned at a fixed
rateandevenlydistributedtoallzones.Similarly,the0.3ACHofventilation
wasreducedtoaneffectiveventilation rateof0.12ACHbecauseoftheHRV,
which is approximately 60% effective. The HRV system was not explicitly
modeled.
7.2.4.4 Renewable Energy Systems
In adherence with the rest of the model's level of detail, the BIPV was
modeled as being thermally coupled to the roof. The 21 UniSolar PVL-136
amorphous silicon modules were modeled using EnergyPlus' one-diode
model (DOE, 2013). The simple inverter model was used with an assumed
operating efficiency of 92%.
Since EnergyPlus does not have a readily available air-based BIPV/T model,
a custom model was created in MATLAB. The limitation to this approach
is that the model is decoupled from the main EnergyPlus model (i.e., there
is not two-way communication between the models during simulation).
However,thisapproachcanbeusedtoassessthethermalenergyavailability
relative to household thermal energy demand, in an effort to approximate
its value.
7.2.4.5 Simulation Results
Figure 7.18 shows the measured and simulated heat pump energy
consumption. Monthly heating and cooling energy were converted to
electricity consumption using a COP of 3.7 (as measured to be the annual
average for ÉcoTerra's heat pump). The annual modeled electrical energy
consumption is 2519 kWh versus the 2524 kWh that was measured for the
same period. The results indicate that the thermal model is an accurate
representation of real performance and suitable for assessing the building
upgrades that are described in the sections that follow.