The Comfort of a Heat Recovery Ventilation (HRV) System in Cold Maine
“Where are the driveways?” asks one guest visiting Belfast Cohousing & Ecovillage (BCE). “How strange, these houses don’t have any driveways!” Even the layout of the homes demonstrates that this is not a typical subdivision. But that’s just the beginning.
My family recently purchased a high-performance house in BCE, a multigenerational community with 36 homes. Despite the cold winters here in Midcoast Maine, we have no furnace and no radiators. Our house is heated primarily from solar gains, its occupants, appliances, and modest use of baseboard electric heaters.
“My feet, hands, and nose get cold really easily,” explains Penny West, a BCE member. “This house is so lovely because there are no drafts. I used to freeze while doing computer work in my last place. I bought boots, wore my hat, but here it is lovely.”
During our cold winters, BCE residents often comment on how comfortable the homes are. Even during windy subzero nights, there are no drafts when we are sitting in front of the triple-pane windows and doors. With highly insulated walls, ceilings, and foundations, all of the rooms are naturally the same temperature, and there are no cold rooms in the houses. Generous amounts of sunlight make supplemental light unnecessary until evening.
Despite their airtight construction, the homes have a constant stream of fresh air entering the bedrooms as the stale air is removed from the kitchens and bathrooms with a Zehnder heat recovery ventilation (HRV) system. This allows very high air quality in the winter, without the need to open any windows.
Our Zehnder HRV system is up to 90 percent efficient at capturing the heat from the exhaust air before it exits the home. Through the heat exchanger, incoming outside air is filtered and enters inside the building close to room temperature before being dispersed, unlike in typical construction, where incoming air is the same as the outside temperature. Because we don’t have an exhaust fan in the bathroom or a vented hood in the kitchen, we can boost the HRV system by a switch in the bathroom or kitchen to remove condensation, smoke, and fumes. Exhaust fans, in contrast, are not energy efficient and encourage drafts by venting warm air out of the home without capturing the heat and bring unheated outside air into the home.
“I think the HRV is what revolutionized these houses,” says Brian Hughes, a carpenter for GO Logic and a BCE member. “People have been building super tight insulated houses since the 50s. The problem was that the air quality wasn’t good and people didn’t try having a super tight building again until they realized that with the heat exchanger, you can use a tiny bit of electricity and have really high air quality.”
The homes are so energy efficient that a 4-kilowatt solar system can provide enough electricity annually to completely power our two-bedroom home with four occupants. All of our neighbors with solar systems have near net-zero homes; thus their solar panels produce all or a vast majority of their home electricity. The homes without solar systems still have modest electric bills, despite having electric heat, and this winter the homes used almost no supplemental heat until December, despite a frigid fall.
The secrets of a high-performance house in the Northeast include unobstructed solar exposure, triple-pane windows and doors, lots of large windows on the south side of the home, airtight construction, and generous amounts of insulation. The additional insulation and high-quality windows add thousands to the construction costs, while the electric heaters and HRV system combined cost less than a standard HVAC system in typical new construction.
A five-day power outage from an ice storm last December gave BCE’s houses the opportunity to perform. The outside temperatures were below freezing throughout the outage, with temperatures dipping below 0 degrees Fahrenheit. While neighboring houses (with typical construction) were approaching freezing temperatures indoors after just 24 hours without power, the BCE homes cooled by only 2 degrees daily. It was sunny only on the coldest day of the outage, and our house warmed up by 9 degrees throughout that day.
Certainly, a lack of driveways is just one of the things that set our new high-performance house apart from other homes. The very cold and long winter gave us an opportunity to see how our house performed. We sat and watched many snowstorms while feeling cozy and warm inside. Now we are excited about gardening and preparing for spring.
Sarah Lozanova is a regular contributor to environmental and energy publications and websites including Mother Earth Living, Mothering, Energy International Quarterly, ThinkGreen.com, Triple Pundit, CleanTechnica, Green Business Quarterly, Natural Home, GreenBiz, Renewable Energy World, Windpower Engineering, and Solar Today. She currently lives with her family in the Belfast Cohousing & Ecovillage