How a Zehnder HRV Helped This Amherst, Massachusetts Home Meet the Passive House Standard

An assistant physics professor in Amherst, Massachusetts, Alexi Arango, decided to apply his love of physics to his home and create a home that followed the Passive house standards, or PassivHaus, as it is known outside of the U.S. He had been interested in a house in Maine that was so efficient it did not require a furnace to heat it. Arango purchased an HRV from Zehnder America to help bring fresh air into the “Potwine Passive House” without losing heat or wasting energy.

Installing Special Windows in Special Places

The first step to making the home energy efficient was to figure out which way was “solar south.” South facing windows help to expose the home to sunlight evenly in the mornings and afternoons, capitalizing on the solar heat and light and reducing energy needs. The windows that are used also have bearing on heating, like windows with a high U factor energy rating will allow air leakage, letting heat out and cold air in during the winter. The windows that were installed in the home are triple-paned and have three layers of rubber seals to ensure air tightness and optimize HRV function.

Sealing the Building

In order to maximize comfort, energy efficiency, and HRV function, it is imperative that a home has a tight building seal. A tight building seal is also a critical element of the Passive House concept, so this was an important factor for Arango and the builders. A blower door test was done in one of the final phases of construction to check the air seal and to detect air leaks around the home, which were promptly sealed. After the number of air changes per hour was measured and found to be optimal, blown-in fiberglass insulation was installed to help the home further retain heat.

Installing a Zehnder ComfoAir 200 HRV

The Zehnder ComfoAir 200 was installed in the attic of the home and the flexible ducts from the HRV were routed to each bedroom. Carbon dioxide often builds up in bedrooms more than other areas in a home because the bedrooms are typically small areas in which people sleep and breathe with a door closed for roughly one-third of a day. Fresh air that flows into the bedrooms filters into the rest of the home, allowing the air to be fully cycled about eight times per day. The exhaust vents were placed in the bathrooms and kitchen.

HRV function

An HRV, or heat recovery ventilator, work to keep a home warm in the winter by taking cold, fresh air from outside and passing it through tiny “pores.” Each pore is surrounded by pores through which warm, stale air from the inside of the home is flowing in the other direction. Up to 95 percent of the heat energy passes from the warm air to the cold air through the pores, effectively retaining the heat in the home while cycling stale air out and fresh air in. This helps a home to meet low energy demand standards while also meeting the desired air change (ach) standards.

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