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  1. #1
    Join Date
    Mar 2007
    Location
    Colorado Springs, CO
    Posts
    1,217

    Default HRV - Failure To Understand The Concept

    As I noted in another thread or two, I recently inspected a building that was once a Welcome Center for a developer and was later donated to a church and moved to its present location. (The property also included a Quanset hut.)

    Due to the large number of occupants during church services additional fresh air was required to maintain indoor air quality in this building. An HRV (Heat Recovery Ventilator) was installed to supply this fresh air.

    For those that are not familiar with HRVs (and the close cousin the ERV - Energy Recovery Ventilator), an HRV is essentially a heat exchanger that recovers heat that otherwise would be lost in the ventilation process. HRVs are usually 60% to 80% efficient. The air flow in equals the air flow out so the building is not pressurized or depressurized by the HRV.

    In a heating environment (such as Colorado) 60% to 80% of the heat in the inside air that is exhausted is picked up by the cooler outside air being brought into the building. The outside temperature here today was 30 degrees. With the indoor air at 70 degrees, after passing through the HRV the 30 degree outside air would be heated to somewhere around 55 or 60 degrees. The higher temperature of the fresh air will reduce the operating time of the furnace and reduce the utility bill.

    I do not typically inspect HRVs during a home inspection but I noticed something odd about the one in the church. The two registers in the room were fairly close together and I thought they might short circuit so I turned on the HRV to find out. One register should have been a supply and the other should have been an exhaust. I was surprised to find that both registers were blowing 30 degree air into the room. When I checked the two outside grilles they were both drawing air in.

    So, the HVAC contractor installed the HRV incorrectly. With both intakes located outside there is no exchange of heat. The HRV has now become a giant intake fan that delivers twice the intended CFM, pressurizes the building and causes a tremendous loss of energy while making the building very uncomfortable.

    The preacher said the HRV moved too much air and made the room cold in the winter. Now I think I understand why he said he didn't like to run the HRV.

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    Bruce Breedlove
    www.avaloninspection.com

  2. #2
    Join Date
    Mar 2007
    Location
    Chicago, IL
    Posts
    2,797

    Default Re: HRV - Failure To Understand The Concept

    Having installed an ERV in my own house (properly), I do have to say that at least on mine - where the intakes and exhausts were not clearly marked - I had to 2X and then 3X check to insure the hookup was correct.

    -----------

    BTW, if you encounter one of these at an inspection, and you intend to inspect it at all, check not only the internal filter elements but also the exterior intake, which if screened will clog quickely as a there *lot* of air in moving through it.

    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  3. #3
    Join Date
    Mar 2008
    Location
    southern ontario
    Posts
    130

    Default Re: HRV - Failure To Understand The Concept

    Might as well have had the furnace blowing straight outside, imagine that heating bill!!!


  4. #4
    Join Date
    Mar 2007
    Location
    Plano, Texas
    Posts
    4,170

    Default Re: HRV - Failure To Understand The Concept

    Good catch Bruce. Sometimes it is the simple things that get lost during an installation, the "can't see the forest for the trees" perspective issue.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

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