By Rick Reynolds.
No, this is not about cooling your jets by blowing off steam. This is, however, about being bottled up inside, at least when it comes to our indoor air. In short, this post is about ventilation science for health and comfort, especially as it pertains to the tight, energy-efficient homes being built today.
Every day, every adult takes in more air by weight than any other substance. At rest, this daily air intake amounts to 388 cubic feet per person. At 0.08 lbs per cubic foot, this tips the scales at 31 lbs. By contrast, with a quart of water (32 ounces) weighing in at two pounds, one would need to drink more than 15 quarts of water per day to knock the air we breathe from its weighty position at the top of consumables.
And while we spend most of our time at home (and on average, 90% of our time indoors), few people understand how the indoor air that they breathe affects them or, perhaps more importantly, how they can affect it. So while many of us think nothing of conditioning our water, fewer pay attention to conditioning indoor air quality.
It’s important to note that the so-called “fresh air” we associate with outdoor air can be, in fact, anything but fresh. So despite what our parents told us, throwing open the windows, even weather permitting, is often not the answer.
Whether we live in the city or the country, outdoor air can carry poisonous gasses, chemicals, and particulates (think pollution), as well as allergens (think pollen, dust mites), excessive or inadequate moisture levels (think relative humidity), and undesirable thermal energy (think temperature)—all of which requires mitigation to ensure a healthy, comfortable, and energy-efficient indoor environment.
Additionally, with indoor air, household pollutants like carbon dioxide, carbon monoxide, methane, VOCs (volatile organic compounds), smoke, dust, mold spores, and even radiation in the form of radon, can build up and must all be exhausted with minimal energy loss, in order to promote health and maintain optimal temperature and relative humidity year-round.
In today’s new high-performance houses, mechanical ventilation is essential, since to achieve their extraordinary energy efficiency, they must be highly insulated and tightly sealed; in some cases to within 0.6 air changes per hour (ACH) at 50 PASCALs of pressure. In these houses, balanced ventilation systems work for the whole house (not just kitchens and bathrooms) to exchange stale indoor air with conditioned, filtered outdoor air while, at the same time, reclaiming its thermal energy and managing its moisture levels.
HRV (Heat Recovery Ventilation) systems transfer heat through a sealed heat exchanger. In winter, the cooler incoming air is pre-warmed by the warmer outgoing (exhaust) air. Conversely, in summer, the hotter incoming air is cooled by the cooler outgoing air. Since the two air masses never mix, relative humidity is little affected, so humidification and dehumidification systems may need to be deployed to promote year-round comfort.
ERV (Energy Recovery Ventilation) systems transfer both heat and moisture in an energy exchanger. Since moisture contains some energy, these units can raise efficiency levels while helping to control relative humidity. In winter, when outdoor air is typically drier, the ERV systems can help maintain comfortable humidity levels by holding onto some of the moisture in the exhaust air. And in summer, when outdoor air is typically more humid, ERVs can lower relative humidity somewhat. However, in regions experiencing high levels of humidity, an added dehumidification system may be necessary to maintain a comfortable level of humidity.
With the combination of a tight, well-insulated building envelope and a high-quality ventilation system eliminating drafts and cold/hot spots, they not only promote health and comfort, but also help to eliminate moisture problems that can damage roofs, walls, and foundations.
In sum, it’s clear that venting, at least of the mechanical kind, does promote health. Modern, high-efficiency ventilation systems help to maintain the extraordinary energy efficiency of high-performance homes, while ensuring they’re the healthiest, quietest, most comfortable indoor environments available. And those are a lot of concerns to get off one’s chest.
To learn more about healthy, high-performance indoor environments, go to www.bensonwood.com