Growing up, I would sleep with the window open well into the late fall, when overnight temperatures would finally lower the room temperature so far it was hard to get out of bed in the morning. I didn’t realize it at the time, but the open window improved my sleep and comfort by improving the indoor air quality in my room. However, the loss of thermal comfort and waste of heating energy was far from ideal. Today, we can install a heat recovery ventilator (HRV) or an energy recovery ventilator (ERV) and get the best of both worlds.
Many building science sources are now recommending balanced ventilation, and building codes are slowly moving to encourage or even require HRV’s or ERV’s. Technical descriptions of these systems are readily available on the internet, but fewer sources really delve into the complete scope of the benefits they deliver. These systems are often framed as an energy saving appliance, but in truth they are an indoor air quality device, while delivering some energy saving benefits on the side.
The basic purpose of residential ventilation systems is to remove polluted air from the occupied space. There are many sources of pollution in a home, starting with its occupants. Mammals breathe in oxygen and exhale carbon dioxide. If that carbon dioxide is allowed to build up, it has negative effects on alertness and cognition, the feeling that is often described as “stuffy.” There is also some evidence to show that it can allow airborne pathogens to spread more easily. Showers, clothes dryers, and wet pets are among the sources of water vapor and humidity in homes. Left unchecked, this moisture can lead to mold and rot. Cooking in the home, especially with gas fired appliances, introduces a range of post-combustion pollutants to the air. Many items found in the average home give off various pollutants, including VOCs and solvents. Finally, homes in some areas are prone to absorbing significant amounts of radon from the ground beneath our feet. The good news is that all these effects can be mitigated by circulating fresh outdoor air through the home.
Most of us are very familiar with simple exhaust fans in bathrooms and range hoods in kitchens, which have been standard in residential construction for decades. These fans are located near indoor sources of pollution in an effort to remove the polluted air at the source. However, when we remove air from the home without intentionally replacing it, the home becomes depressurized, which encourages outdoor air to leak into the home through gaps in the siding, around doors and windows, down chimneys, and through any other path it can enter the home.
Bringing fresh air into the home this way has some negative effects. That air is unconditioned, so it can make the indoor temperature and humidity change. This is the phenomenon that we often think of as a drafty home. That air also often picks up pollutants that are present along their paths of entry to the home. This can include dust and allergens from inside the walls, VOCs and solvents from the garage, or post-combustion products from chimneys and exhaust vents.
Balanced ventilation systems seek to address this problem by using a second fan system to bring enough air into the home to offset the air being exhausted. This solves the problem of air entering the home through uncontrolled pathways, but leaves the issue of that air being unconditioned. This is where heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) come in. These systems pass the incoming and outgoing airstreams through a heat exchanger, transferring much of the energy in the outgoing air to the incoming air. ERV’s also allow the transfer of water vapor between the airstreams, while HRV’s do not. In addition to allowing the conservation of the energy inside our buildings, this approach also allows us to filter all the incoming air as it enters the home.
Combined with good air sealing techniques, this approach allows us a great deal of control over the air inside the home, which has several advantages. First, we can carefully control the humidity inside the home. This increases the comfort and well-being of occupants, but it also extends the life of the building. Not only does drier air help preserve the components of the home, but maintaining correct indoor humidity levels helps dry the building out in case it starts to absorb moisture for any reason.
Well designed balanced ventilation systems also improve indoor air quality in the home, reducing levels of carbon dioxide, carbon monoxide, VOC’s, and other pollutants. Many homes, even those being built today, concentrate these pollutants to unhealthy levels. These pollutants have been linked to decreased cognitive function, poor sleep quality, asthma, cancer, and other negative effects. Well designed homes with good ventilation systems ameliorate all of these effects.
Unfortunately, changing weather patterns have complicated this simple solution for those of us living in the Pacific Northwest and other areas. Massive wildfires in the summer sometimes invert the air quality dynamic, polluting the outdoor air with smoke that we certainly do not want to bring into our homes. The good news is that balanced ventilation systems can be designed with specialty filtration systems to reduce or eliminate smoke particles and any other pollutants in the incoming air stream.
Balanced ventilation systems have a long history of use in commercial and industrial applications, but including them on residential projects is a newer phenomenon. Many residential designers, builders, and HVAC installers are unfamiliar with them. At Balance Construction Consulting, our staff has been on the cutting edge of the implementation of balanced ventilation systems in residential applications for nearly a decade. You can rely on us to guide you to balanced ventilation and indoor air quality solutions that work for your project and your budget.