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Net Zero House

Testing for Energy Leaks

Net Zero House

Testing for Energy Leaks

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    Pre-drywall blower-door testing done in conjunction with an infrared camera helped to locate air leaks.

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    Scanning for thermal leaks with the infrared camera

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    The tightly insulated interior

I worked with the plan, elevations, and wall sections simultaneously, while Andy used Energy 10 software (sbicouncil.org) and his own spreadsheets to model energy use. One of the most difficult challenges was deciding which views to take advantage of without exceeding the square-foot percentage of glazing dictated by the energy-efficient design. For example, I would ordinarily have eliminated most of the north-facing windows, but the view up the valley to the north was not to be ignored. So we ended up greatly reducing the number of east- and west-facing windows and adding others on the north elevation — in the master bedroom and above the kitchen counter. While we do pay a small energy penalty in the winter, the views and natural light we receive more than make up for it.   

We chose fiberglass-frame triple-glazed windows from Thermotech, with U-values of .17 (R5.8) for the operable casements and awnings and .15 (R6.7) for the fixed units. South-facing glass would have a .61 SHGC (solar heat gain coefficient) and the rest of the windows .37 SHGC. In shopping for highly efficient custom windows, we found Thermotech’s pricing competitive, and that influenced our decision. However, since the windows were installed and we’ve been living in the house, we’ve experienced some problems with the windows and found the customer support poor, so I wouldn’t recommend the product.

We used advanced framing techniques to the greatest extent possible, with studs on 2-foot centers and the entire building designed in 2-foot modules for ease of construction. We took advantage of solar heat gain by including a 4-inch-thick radiant slab in the first-floor living area, and 5„8-inch skim-coat-plastered drywall throughout the house.

Plug and appliance loads. We specified fluorescent lights and the most efficient conventional appliances we could find. We also chose the highest-efficiency HRV available in our market at the time.

Hot-water savings. Besides conserving hot water, using low-flow shower heads also cuts down on pumping energy (as do low-flow toilets). For further savings, we also included a gravity film heat exchanger, or GFX (WaterFilm Energy, gfxtechnology.com) — a simple copper coil that wraps the drainpipe coming from the showers. The GFX reclaims heat from shower water that would otherwise be lost down the drain, using it to preheat incoming cold water to the domestic hot-water tank. DOE studies have shown up to 30 percent savings in water-heating energy with these devices. (In our case, because we monitor how much hot water we use and the electricity used to heat it, Andy was able to determine that we’re also saving 30 percent.)