We recently completed our net-zero farmhouse project. The house has a contemporary design and feel, but the exterior pays tribute to the classic farmhouse designs found throughout the Shenandoah Valley.

Some highlights of the project:

- 0.46 ACH50 final blower door test
- Exterior mineral wool insulation (Roxul Rockboard 80)
- Fiber cement siding (HardiePlank) and double-locked standing seam roof
- 5.6 kW PV system, with islandable capability
- Hearthstone Craftsbury woodstove with outside air intake
- Fujitsu slim duct high efficiency heat pumps
- Renewaire EV90P Energy Recovery Ventilator

This project combined energy efficiency with resilient design. Genesis Home and Energy installed an islandable PV system (discussed in a previous blog). Key electrical circuits will be maintained during a power outage: lighting, wall outlets, well pump, refrigerator and freezer, microwave, etc.

Although we were somewhat hesitant to install a woodstove in a tight house, the client wanted the ability to heat with locally harvested wood (ambiance, resiliency, radiant heat for comfort). No woodstove is airtight, so there were some risks:

- Backdrafting
- Depressurization of the house
- Lower indoor air quality

We mitigated these risks by making the house all-electric, and eliminating exhaust appliances. The range hood is recirculating. The dryer is a condensing, ventless model. We were also careful about specifying a woodstove with an outside air kit--and positioning the inlet and chimney to provide excellent draft.

John Semmelhack of Think Little fame completed several tests to determine if the woodstove would negatively affect the house. He found that the woodstove had a negligible effect on the house pressure (within the noise of precision). This measurement held when the woodstove was cold AND when it was operating.  He determined that the stove pulled between 10 - 15 CFM (cubic feet / minute) when operating. With the outside air intake the majority of that air is supplied from the exterior.

This simplified Sketchup drawing shows the conceptual view of our latest project, a net zero farmhouse. Genesis Home + Energy will design and install a 6kW photovoltaic system to service the house.

A Resilient House

Promethean Homes is proud to announce that we recently started construction of our first zero energy house. Like all of our projects we will build this one in a cost-conscious and energy-efficient manner.  However, this house will feature two additional systems designed for resiliency: an islandable PV array and a small wood burning stove.

Islandable PV System

So, let's ignore the question that's nagging you right now (is islandable even a word?) and move onto describing an islandable PV system.

Simply stated, an islandable PV system provides the benefits of a grid-tied system AND an off-grid system. During normal operation the PV system will sync with the electrical grid to provide electricity to the house.

When the grid is operational the PV system will feed electricity to the house AND to the electrical grid. When it produces more electricity than is consumed by the household that electricity will be fed back into the grid (to be used by neighboring houses and businesses). When it produces less electricity than is consumed by the household that deficit will be supplied from the grid.

But what happens when the grid goes down? In a standard grid-tied PV array the system disconnects from the grid and shuts down. This is a safety feature that prevents electricity from backfeeding the grid (which could potentially injure those people working to repair service lines or components).

An islandable PV system works in conjuction with a battery bank to supply power to the house while the grid is down. Key circuits will remain active:

• Well Pump
• Refrigerators and Freezers
• Lighting Circuits
• Dedicated Outlets

It works much like a whole-house generator. The controls disconnect from the grid, but then restart to supply power to just the house. Unlike a whole-house generator this system will produce power with ZERO noise.

Woodstove

Although the house will be equipped with two Fujitsu slim duct heat pumps, it will also feature a small cast-iron woodstove. The owner will be able to heat the house during a power outage---using a locally sourced biofuel.

This woodstove will be connected to a dedicated outdoor air supply. This will prevent the woodstove from depressurizing the house; it will also ensure that the appliance does not backdraft.

In addition to the resilience provided by this woodstove, let's not forget comfort and ambiance. The high-temperature radiant heat from a woodstove is nearly impossible to match.