As we make homes tighter, we need to provide ventilation, which costs energy. One way to reduce the energy impact of that ventilation is to use an air-to-air heat recovery system. A heat recovery ventilator (HRV) recovers sensible heat by exchanging heat between incoming and outgoing airstreams. An energy recovery ventilator (ERV) is similar to an HRV but also allows moisture to be exchanged.


ERVs make a lot of sense both in hot-humid climates and in cold climates. In the former they reduce the dehumidification load by keeping excess moisture out; in the latter they reduce the humidification load by keeping moisture in. Nevertheless, there are reasons why one may wish to be cautious in using ERVs.

ERVs do not make a lot of sense when you want to exhaust excess indoor moisture and replace it with drier outdoor air. Many codes (and ASHRAE Standard 62.2) require kitchen and/or bath exhaust to allow the removal of excess moisture. Running these exhausts through an ERV would recover this moisture and dump it back in house. Rarely is this what one wants to do. Yet there is a growing segment of building professionals who are using ERVs in exactly this way. It is not clear whether this use of an ERV meets the requirement of exhaust, but it does seem clear that it could cause moisture problems.

An even more disconcerting issue is the fact that some ERVs can “recover” formaldehyde in the same way that they recover water. Recent research has confirmed what many of us suspected—that there are hazardous concentrations of formaldehyde in many homes. While the ultimate solution may be source control, dilution ventilation is a key method of reducing indoor concentration. Having ERVs that recover formaldehyde represents a serious risk.

Because water and formaldehyde are reasonably similar chemically, it is not surprising that the mechanisms that would recover water could recover formaldehyde. Research has shown that specific materials (for example, certain desiccants and plastics) can do a good job of this. That is not to say, however, that all ERVs do, in fact, recover formaldehyde. Clever designs of materials, layers, coatings, membranes, and so forth could in theory make ERVs highly selective. There is, unfortunately, almost no data available on the performance of ERVs currently on the market with respect to formaldehyde (or other contaminants). Such test data is needed on the various ERVs in the marketplace. Unless one knows that formaldehyde is not a contaminant of concern, one should probably be cautious in using ERVs.

The yellow flag is out on energy recovery ventilators.

 

- Max Sherman


Max Sherman is a senior scientist in the Environmental Energy Technologies Division at Lawrence Berkeley National Laboratory and a frequent contributor to Home Energy.

Views: 61

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Michael Dunseith posted a photo

http://www.prattcenter.net/energy-champions-launch-party

Senator Kevin Parker poses with Pratt Center's Green Jobs Green New York Project Coordinator Elana…
49 minutes ago
Michael Dunseith posted a status
50 minutes ago
Rob Madden, Solar Home Broker posted a blog post

Phoenix 3rd Quarter Solar Resale Statistics Continue to Impress

Phoenix solar home sales were up during the third quarter of 2014, including the resale of homes…See More
17 hours ago
Everblue posted a status
"Green job alert! Energy Auditor in Baltimore, MD with Advanced Green Home Solutions. Check it out: http://bit.ly/1xhQuXO"
18 hours ago
Chris Clay replied to Isaiah Borel's discussion Blown Cellulose VS Blown Fiberglass in the Attic
"The Cold Climate Housing Research Center in Fairbanks, AK has alot of information about this…"
19 hours ago
Richard L. Sanderson replied to Bud Poll's discussion Inconsistant Local Authority
"Bud: I like the idea of a third party review board. My own experience in local government is that…"
yesterday
Matthew Lutz commented on Kaplan Clean Tech's blog post The Difference Between Home Inspection and Energy Auditing [Infographic]
"I would have to agree with Steve on this.  I am a Certified Energy Manager and have performed…"
yesterday
Matthew Lutz joined Diane Chojnowski's group
Thumbnail

Hall of Shame

In this group, members share an array of images from the field, showing the kinds of issues…See More
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service