Page 46 - Zero Net Energy Case Study Homes-Volume 2

CASE STUDY NO. 7
PERLITA PASSIVE HOUSE
(Above) Blower Door and pressure gauge as used in the Blower Door test. (Photos courtesy of Xavier Gaucher)
Building Envelope — Airtightness
Like all ZNE houses, design detailing and attentive construction supervision are required to pro- duce the energy efficiency that airtightness provides. (Refer to the Sidebar - Airtightness discus- sion in Case Study No. 6 that appears in this Volume 2.)
Passive House standards are particularly rigorous in this regard, requiring a Blower Door test that yields a maximum air leakage rate of 0.6 air changes per hour at 50 pascals of pressure, or 0.6 ACH50. In recognition of the differences that may occur with a renovation of an existing house, the Passive House standard for renovation is set at 1.0 ACH50.
The Perlita Passive House employed a special airtightness membrane product that is intended to seal the construction in a less labor intensive manner than tapes, gaskets and specialized caulking. A special construction drawing was used to guide the subcontractor on the installation of the air-tightness membrane product for the various conditions that would be encountered dur- ing construction. The net result was that the house achieved the standard of 1.0 ACH50 with the Blower Door test.
Heating, Ventilating and Cooling Systems; Domestic Hot Water
Because of the airtight construction, the house needs to be equipped with a system that provides quantifiable fresh air distribution with minimum power. In a highly energy-efficient house such as a Passive House, that usually means specifying a Heat Recovery Ventilator (HRV) with its built-in heat exchanger and simple ducting system for moving the fresh air to and from individual spaces. The air inside the house is heated or cooled as needed using a simple system like a mini-split heat pump, keeping the fresh air ventilation separate from the conditioned air supply.
The owners chose instead to use a combined system—a standard air-handling unit (AHU) with a 1.0 ton heat pump and a constant low-volume flow of fresh air. Since the cooling loads are significantly higher at this site’s inland location than for the coastal location of Case Study No. 6, this choice was more cost-effective in terms of equipment and ductwork and eliminated the need for two supply vents in each room. The disadvantage was energy efficiency since there is no heat exchanger as in the HRV. The good air-filtration, also a feature of an HRV, proved to be particularly noticeable during a recent wildfire event.
As in the previous ZNE case study home, the kitchen exhaust fan is a recirculating unit to avoid an additional penetration of the building envelope.
The heat pump water heater is located in the small, unconditioned basement space. (The own- ers refer to the basement as their wine cellar since the heat pump water heater cools the air in the room while it is making hot water.)
Lighting and Plug Loads
Lighting, plug loads and domestic hot water constitute roughly 75% of the energy use because of the high energy efficiency of the building envelope and the heating and cooling equipment. All lighting is done with high-efficiency LED sources and all appliances are high efficiency Energy Star®.
Since the house is designed to be all-electric, the cooking is done by induction cooktop and electric oven. The clothes dryer is a condensation dryer, which requires no vent to the exterior, thereby avoiding potential air leakage via another wall penetration.
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Zero Net Energy Case Study Homes: Volume 2