Net ZEB Case Studies - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 369

the EnergyPlus model took about five days, which is an order of magnitude
longer than for the HOT2000 model.
Major savings that can be achieved through changing the controls of the
house were explored first. The “equipment” category of energy use is mainly
comprised of the distribution fan built into the heat pump. The fan is
currently operated at a constant rate, even when fresh air and conditioning
requirements are met. Simulations were run to determine the potential
benefit from reducing the fan (when heating and cooling are unneeded)
to only operate when the mean air temperature difference between zones
exceeds 2 °C. The simulation indicates that the fan can be set to low speed
for 8% of the year, yielding fan energy savings of about 130 kWh. Additional
savings (460 kWh/yr) can be achieved by removing the air cleaner, which
can be considered redundant to the air filter in the heat recovery ventilator
(HRV), and unnecessary in the rural setting.
In order to assess the best opportunities for improvement to the envelope,
the sources of heat loss were predicted for the house during the heating
season ( Figure 7.19 ). While the window losses account for 21% of total
losses, the net energy balance for the windows including solar gains is
positive - by about 1000 kWh. Since the house is relatively airtight, there
is little benefit to further sealing the envelope. Similarly, the ventilation
rate cannot be lowered and the house is already equipped with an HRV.
A modest reduction in the effective ventilation rate would be possible with
an HRV of a higher effectiveness (e.g., 80%). However, upgrades to the
envelope represents the main practical potential to reduce total heat loss.