14) Energy Recovery or just Heat Recovery? ERV vs. HRV
A ventilation system is a must-have when building a passive house. Described as the 'lungs' of your house, it brings in air and oxygen to keep your home healthy.
Airtightness is critical to an energy-efficient house. It's all about how much air is heated, and how much flows out through the cracks, the window seals, the doors, wherever:
In thinking about it, you can see that there has been a constant evolution to increased airtightness in home building, and I would guess it's directly proportional to the cost of energy. When heat was cheap, who cared how much escaped? Houses built 200 years ago weren't worried about drafts, few had any insulation other than corncobs. Cold out? Just throw an extra log on the hearth. In early America there was more wood than you knew what to do with. It was cheap, maybe cheaper than dirt. If you've ever lived in a drafty house and had to pay for fossil fuel, you've probably taped the windows, or put felt on the door seals. Passive houses don't have that problem. They're so airtight that what you have to worry about is the healthiness of the non-flowing trapped air. So the problem is: how do you bring fresh air into a house, without losing the hard-earned heat in the air you send outside?
The answer is a heat exchanger that captures the heat in
the outgoing air and warms the incoming air. Specifically an HRV: Heat Recovery Ventilation via a Heat Recovery Ventilator. These exchangers actually recover 85% of the heat expelled to the outside of the house.
For our South Woodstock situation, we're actually opting for the higher level heat exchanger which is designated as the ERV, or Energy Recovery Ventilator. Preferred for homes in the north country, in addition to heat, they moderate humidity, which is important in cold climate homes. Have you ever heard about people who put steam kettles on their woodstoves? The reason is that humid wet air holds heat better than dry air. Our ancestors knew that to live comfortably in cold places, you needed to have moisture in the air. Same with a passive house. And that's where an ERV comes in. Here's a link to the difference between HRV and ERV.
Humidity is an important, yet relatively unrecognized aspect of human comfort. While we all know that the sopping wet humid Florida summers are miserable, there's another end of the spectrum: you can be too dry. Besides increasing your heating bills, low humidity is a health risk.
After looking at all the options, we aim to put in a Zehnder ERV system.
