A Breath of Fresh Air: Energy and Heat Recovery Ventilators

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Residential Energy Recovery Ventilator (ERVs) and Heat Recovery Ventilators (HRVs) are efficient mechanical ventilation systems that bring fresh air into and remove stale air from a home to improve indoor air quality. Since indoor air is typically several times more polluted than outdoor air, ventilation is certainly beneficial.

An ERV typically transfers heat and moisture (which helps control humidity levels) , while an HRV only transfers heat. ERVs are especially recommended in climates where mechanical means of cooling is significant.

HRVs and ERVs are usually designed as ducted whole-house systems, but some small window or wall mounted units are also available. Both types include a heat exchanger, one or more fans to push air through the machine, and some controls. The heat exchange units are typically installed in an attic, crawlspace, or storage/utility area, often adjacent to air handlers.

Toolbase.org explains how it works: “After passing through the heat exchanger, the warmed or cooled fresh air goes through the HVAC air handler, or may be sent directly to various rooms. Stale air from return ducts pre-conditions the incoming flow before exiting. Systems in various sizes and configurations are available to automatically maintain 0.35 air changes per hour, the rate usually recommended to maintain good air quality. Many systems include filters to further control contaminants that would otherwise re-circulate through the home.

Conventional fan and vent assemblies for bathrooms and kitchens, often required by code, may allow significant energy losses. An HRV system can incorporate small, separately switched booster fans in these rooms to control moisture or heat.”

HRV systems generally cost between $700 and $2,000 installed by qualified HVAC contractors. ERVs will cost more.  Simple systems that utilize your existing ductwork will be more cost-effective to install, operate, and maintain than complex systems. Last night on ‘Renovation Nation’, a homeowner doing a major green renovation of an older home, installed a $500 ERV system (himself) that uses only 22 watts of electricity to run!

According to the U.S. Department of Energy, “Energy recovery ventilation systems provide a controlled way of ventilating a home while minimizing energy loss. They reduce the costs of heating ventilated air in the winter by transferring heat from the warm inside air being exhausted to the fresh (but cold) supply air. In the summer, the inside air cools the warmer supply air to reduce ventilation cooling costs.”

Sources: University of Minnesota Extension

Tag(s): Energy, Green Building, Greening the Home

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