Heat Recovery Units

 

Heat recovery ventilation systems allow R-2000 homes to maintain high indoor air quality without excessive additional energy costs.

As shown in the diagram below, a heat recovery ventilator (HRV) consists of two separate air-handling systems – one collects and exhausts stale indoor air; the other draws in outdoor air and distributes it throughout the home.

Life inside today's tight home generates both moisture and pollutants

  

While necessity may be the mother of invention, it's increasing costs that spawn efficiency.Before the '70s, we happily cranked up the thermostat when the house felt chilly. Once heating costs went through the roof, though, we all put on sweaters and started looking for ways to save. And, with up to 40 percent of our heating dollar going to air infiltration--otherwise known as drafts--sealing the place up began to seem like the best defense against high heating bills.

Over a period of time, older homes began to sport new, tight windows and doors, insulation and vapor-barrier improvements, modern siding, and caulk for every crack through which air might pass. New homes left the drawing board designed to be tight, and builders became familiar with the new materials and skills needed to meet market demand and updated regulations. Homes were finally becoming thermally efficient. What some began to wonder, though, was whether they were habitable.

It turns out that those heat-robbing drafts had a role in the ecosystem of the home--they provided fresh air to breathe. Without realizing it, builders before the energy crisis had been installing an effective, albeit haphazard, ventilation system. If you could afford the heating bills, it worked.

 

Why Ventilate?
Life inside today's tight home generates both moisture and pollutants. The moisture comes from cooking, washing, showers and breathing. At excessive levels, moisture condenses on windows and can cause structural deterioration. Areas of excessive moisture are also breeding grounds for mold, mildew, fungi, dust mites and bacteria. You know you have a problem if you find moisture collecting on your windows, or if you notice black spots on walls. These unsightly spots indicate mildew growth. Mold spores and dust easily become airborne and circulate freely throughout the house, possibly causing a range of symptoms and allergic reactions.

Heat Recovery
At the core of an HRV is the heat transfer module. Both the exhaust and outdoor air streams pass through the module, and the heat from the exhaust air is used to pre-heat the outdoor air stream. Only the heat is transferred; the two air streams remain physically separate. Typically, an HRV is able to recover 70 to 80 percent of the heat from the exhaust air and transfer it to the incoming air. This dramatically reduces the energy needed to heat outdoor air to a comfortable temperature.

Air Exchange
The HRV system installed in an R-2000 home can change all the air in the house over a three-hour period. Most HRVs are also equipped with automatic humidity sensors that increase the ventilation rate when needed - for instance, when you use the shower. Exhaust air is normally collected from the kitchen and bathroom areas, where most moisture and odours are created.