The importance of balanced ventilation
By Kurt Johnson
WE KNOW THERE are things in our homes that can make us sick. According to the EPA, our #1 environmental threat is indoor air pollution. And the World Health Organization (WHO) and the National Cancer Institute, have reported that 80% of our cancers are caused environmentally. Considering that the average American spends 90% of their time indoors today, flushing our stale indoor air with fresh air becomes even more important.
There are two strategies for addressing indoor air pollution. The first is to avoid bringing pollutants into our homes in the first place. This may seem simple, but the reality is otherwise. People themselves are a pollutant, and our daily activities generate pollution. Many common household products can also be a pollution source, including building materials and finishings, furniture, and cleaning products.
The second way that we can address indoor air pollution is to give the pollutants that do get into our homes a way to get out.
The minimum ventilation standard most often applied in Maine (the ASHRAE 62.2 standard for acceptable indoor air quality) recommends ventilating the home enough to exhaust all of the stale air and replace it with fresh air once every three hours. Traditional building approaches relied on leaky houses and exhaust fans to achieve ventilation. However, there are several challenges with this approach, particularly as our homes get tighter and more efficient.
First, natural leakage is unreliable. Sometimes the natural forces move enough air in and out of a home and sometimes they don’t. Wind and temperature are the driving force and both of these are changing on a daily, if not hourly, basis. The second is unpredictable distribution throughout the home. Unless the leaks are uniform throughout the home, some rooms get air exchange and some don’t. The same goes for running exhaust fans. You may get a reliable movement of air volume by running a fan, but the distribution throughout the house is inconsistent.
In addition, neither of these methods, relying on natural air leaks or running most exhaust fans, is energy efficient. Heat is lost in the air leaving the home, and the incoming fresh air needs to be heated up to house temperature. Most of us agree that it’s smart to build tighter and more energy efficient homes. So how do we build tight and ventilate right?
Balanced ventilation with heat recovery systems (also called HRVs and ERVs) bring fresh air into our homes, while capturing and using the heat from the expelled air to warm the incoming fresh air. They do this by running the two air streams through a heat exchanger core, and transferring the heat energy of the outgoing air to the inbound air. In the process, the fresh air gets pre-warmed, reducing wasted energy. But more importantly, these systems control the distribution of fresh air throughout the house, more effectively reducing indoor air pollution.
As we move forward with our responsible and sustainable building practices, it is important to include balanced approaches to ventilation.
Kurt Johnson, Immediate Past President, Maine Indoor Air Quality Council. The Maine Indoor Air Quality Council is a nonprofit organization dedicated to the creation of healthy, environmentally sustainable indoor environments.
This article is reprinted from the spring 2016 issue of Green & Healthy Maine Homes. Subscribe today!