Controlled Ventilation

One foundational principle of building high-performance homes is to minimize airflow through all six “sides” of a building’s enclosure, encompassing foundation, walls, and roof. It’s a surprisingly difficult goal to reach and distinctly different from conventionally built houses whose oxygen supply and indoor air quality relies at least partially on the structure’s tendency to “breathe” in a haphazard way.

All Things Stale and Odorful

No, breathing in this sense isn’t the normal respiration we instinctively picture, with lungs extracting oxygen for the bloodstream and expelling carbon dioxide. But the cracks and hidden openings of a conventional home do allow the random exchange of air between indoors and outdoors—ensuring that its occupants will never suffocate, but also wasting energy and making the living environment uncomfortable.

The looseness of conventional construction allows so much air exchange that it helps avoid the potential buildup of indoor pollutants—at the cost of energy and comfort. 

In high-performance homes, an effective air control layer can dramatically shrink the overall surface area of the combined openings in a typical house’s enclosure. While this reduction offers enormous advantages for saving energy and keeping occupants comfortable, it has the side effect of containing the moisture, gases, and particulates that human beings generate.

Yet getting the advantages of airtight construction without the self-evident disadvantages is possible. With the use of controlled ventilation technologies, high-performance homes can be havens of comfort and paragons of energy efficiency while supplying their occupants with a continuous stream of fresh air.

Estuary of Energy Conservation

In the natural world, an estuary is a place where fresh water and salt water mix—like the mouth of a river where it meets an ocean. In high-performance construction, the estuary between stale indoor air and fresh outdoor air is an energy recovery ventilator (ERV) or heat recovery ventilator (HRV).

The important difference between these devices and a seaside estuary is that the two streams of vapor meeting in an ERV/HRV don’t actually blend together—but much of the energy they contain does transfer, thanks to the reliable laws of physics.

Both devices create a bidirectional flow that exhausts stale air from a house while bringing fresh air in from outside. But crossing those streams through a heat-exchanging “core” at the heart of these devices is what makes such systems into far more than just two fan-driven, air-circulating pipes in the wall.

You experience the basic principle of heat exchange every time you wrap cold fingers around a cup of coffee: Through conduction, the hot coffee heats the cup it’s in, which in turn warms your fingers and (along with help from the surrounding ambient air) cools the beverage.

In the same way, a heat exchanger in an ERV/HRV effectively transfers energy between the ingoing and outgoing streams of air as they pass through a series of small-diameter tubes and closely-spaced surfaces that can both absorb and radiate heat. On a winter day, the cold air coming in from outside functions like your fingers reacting to the stale but warm “coffee” of interior air headed outside—with the heat exchanger functioning as the cup that prevents the two entities from physically contacting each other.

All the while, ERVs and HRVs filter both the incoming and outgoing air to reduce the intake of dust and other particulates while protecting the heat-exchange core itself.

The Humidity Factor

While both ERVs and HRVs can transfer heat without mixing airstreams, ERVs can do an additional trick: transferring moisture between the crossed incoming and outgoing airstreams. The key is its so-called “enthalpy exchanger,” a specially engineered membrane that lets a high-performance home in a pronounced four-season climate preserve much of its interior humidity level when it’s cold and dry outside. The same membrane can also reduce the humidity of air entering the house through the system during the hot and humid days of summer.

Taking the Bypass

Low and Continuous

A key tenet of successful controlled ventilation is to keep the air exchange volume low and the flow continuous. After all, domestic life is constantly introducing a varying stream of impurities into the indoor air. A well-designed controlled ventilation system quietly, automatically, and continuously rises to the challenge of removing these irritants, odors, and toxins without the effort or even awareness of the occupants. 

Helping you Breathe

Houses that “breathe” through cracks and openings are uneconomical to own, uncomfortable to live in, and likely to expose occupants to things they don’t want to inhale. Through the use of sophisticated controlled ventilation systems, high-performance homes maximize the advantages of airtight construction without the drawbacks. 

Controlled ventilation via ERVs and HRVs could be viewed as a technology to help your house itself “inhale” and “exhale” in a well-managed, energy-efficient way. But in the end its real triumph is to help the people who live there to breathe better.

Claims about a home’s performance are easy to make, but going the extra mile to get a home certified by a recognized third party provides transparency, consistency and trust. It helps us create buildings that are better for the environment and those that inhabit them.