Net-Zero Energy in New Hampshire: Page 2 of 3

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Lubberland’s Edge sits above a marshy estuary, a sanctuary for wildlife. With its many windows, the home is designed to maximize appreciation of flora and fauna, and provide a cozy, energy-efficient nest for its inhabitants.
The west side of the home sports the main entry and a screened porch, both amply shaded from the hot summer-afternoon sun.
Large, triple-pane, low-e windows maximize efficiency, solar gain, and the expansive views. A concrete slab floor provides thermal mass for storing passive solar gain.
The main living area is angled slightly southeast from the main structure. Excess solar gain is controlled seasonally by large eaves.
The open, modern living space defies the farmhouse-style exterior. The well-insulated, passive solar home rarely requires supplemental heat from the wood heater.
The large east windows gain morning light for quick warm-ups on winter days, while the west side is shaded, and protected from afternoon overheating.
The kitchen takes advantage of energy-efficient technologies, including an induction cooktop. The range hood is ducted through the HRV.
Second-story clerestory windows keep the landing well-illuminated, naturally.
Water-efficient fixtures in the bathroom also provide some energy savings.
Twelve-inch-thick, double-stud walls were filled with cellulose for an insulation value of R-45. Ceilings are insulated to R-70; the floor is insulated to R-26.
The Whirlpool Hybrid Care dryer, which has a heat pump, doesn’t require an external vent.
The Zehnder ventilation system, from left to right: ComfoFond L Eco 550 ground-loop-based preheater; ComfoAir 550 energy recovery ventilation unit; and ComfoCool 550 cooling unit.
The PV modules and DC optimizers during installation.
The 7.6 kW SolarEdge StorEdge inverter.
System Costs Installed Cost: $16,822 Less Incentives, Rebates, Tax Credits: $3,750 state rebate and $5,046 for the 30% federal tax incentive Net installed cost: $8,026
As of mid-November 2016, the system had produced almost 14.5 MWh.

Almost Airtight

Most homes have air infiltration from numerous gaps and cracks. Although these can provide ventilation, they are also paths for conditioned air to exit and moisture and unconditioned air to enter. They can also cause winter comfort issues, when drafts can chill the occupants and create uneven temperatures throughout the home.

“Who wants anything that leaks?” says Matt Silva, general manager for Futuro Construction. “A tight home is a comfortable home because you don’t have the drafts.”

Lubberland’s Edge was tightly constructed for comfort, energy efficiency, and quietness. This was achieved by an air barrier with taped seams, and sealing other gaps or penetrations. European Internorm-brand doors and its Home Pure KF 500 line of triple-pane windows help seal the house when closed. West- and east-facing windows (with U-factors as low as 0.107) provide daylighting, views, and some solar gain, without creating drafts and comfort issues. The HT 400 doors have U-factors as low as 0.13.

To meet the Passive House standard (see sidebar), the house must pass a blower-door test of 0.6 air exchanges per hour (ACH) at 50 Pascals negative pressure. This test uses a calibrated fan, a manometer to measure pressure, and a fan temporarily sealed into an opening of the home. Lubberland’s Edge was tested twice—when only the outer dwelling shell had been finished—and both readings were less than 0.6 ACH. By contrast, the 2012 International Energy Conservation Code requires a maximum score of 3 ACH.

Advanced Performance

Norbert and Robin wanted a home that was comfortable throughout the four distinct New England seasons. The design and tight construction significantly reduce the dwelling’s heating and cooling load but that also requires mechanical ventilation to exhaust stale air and excess moisture while supplying fresh air. Owing to its tight construction, exhaust fans were not an option. Such ventilation systems rely on gaps and cracks in the home envelope to supply the required makeup air for proper operation. Exhaust fans also vent conditioned air out of the home, without capturing energy, and require additional penetrations in the home envelope.

Lubberland’s Edge features four high-efficiency systems for heating, cooling, and ventilating the home. Norbert, who works for heating and ventilation equipment manufacturer Zehnder America, designed the ventilation systems for the home, and Kaplan Thompson Architects designed the heating and cooling systems.

The Zehnder ComfoFond-L eco geothermal heating and cooling system uses near-constant ground temperatures to temper the air coming into the dwelling. The unit preheats the incoming air in the winter and precools and removes some moisture from the intake air in the summer before entering the energy recovery ventilator (ERV). A 150-foot-deep well was dug for the geothermal ground loop and the unit consumes between 5 and 70 watts.

The Zehnder ComfoAir 550 ERV continuously supplies fresh, filtered air while exhausting an equal amount of stale air from the kitchen and bathrooms, removing excess moisture, odors, and cooking fumes. It supplies fresh air to the bedrooms and living spaces after the air has been tempered by the ComfoFond-L eco. In the colder months, heat from the exhaust air is transferred to the intake air by the ERV’s heat exchanger, saving energy. In the summer months, the ERV precools the intake air.

When summer temperatures spike, a control turns on the Zehnder ComfoCool, a heat-pump cooling system that consumes between 700 and 850 watts. Supplemental winter heat comes from a Zehnder towel warmer radiator in each of the two bathrooms and a wood heater in the living room. Norbert and Robin use the wood heater primarily for ambiance.

Lubberland’s Edge has an induction range, LED lights, and a Whirlpool Hybrid Care dryer with heat-pump technology. It is ventless, which eliminates a penetration in the envelope, and the dryer is more energy-efficient than a conventional dryer.

“I was a bit hesitant about the ventless dryer, but am pleased to say that it works great!” says Robin. There’s an ERV vent in the washer and dryer closet to avoid excessive moisture from the dryer. The drying time is similar to the drying time from the vented dryer in their previous home.

Comments (2)

Christopher Yaun's picture

Excellant choice. Heather and I live in a similar house in Portsmouth finished in 2008. We use less than 1/5th the energy of an Energy star home. The passive house is extra comfortable. There are no drafts. Because walls are super insulated they do not suck heat from your body. Because dry outside air is not drafting through the house it is easy to keep the humidity higher. That combination of higher humidity and no draft means we are comfortable at lower air temps. The passive house is an excellant solution.

solarKings's picture

Very nice article, but for the 25YR solar PV system, I would have gone with a decentralized power topology which offers complete reliability and true fault-tolerance using Enphase microinverter technology. Centralized solar solutions, even with power optimizers, still contain a single point-of-failure which can disable the entire solar PV solution for an unknown period of time. Not optimal.

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