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Preheat/ temper incoming air for HRV

MtLarry | Posted in General Questions on

I live in zone 6a and was wondering if it is feasible to incorporate a GAHT system to temper the incoming air for an HRV.  For those unfamiliar with what a GAHT is check out:

The system is quite simple and inexpensive,   excavation being the most costly part of the project. But I  own my own excavator and this project is something I can do myself as I am building my new house next year…

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  1. Tim_O | | #1

    This appears to be another approach at earthtubes. It probably works fine for a greenhouse. I wouldn't do it in a house. If you want to DIY it, a small water to air direct system in the intake of an HRV/ERV would probably make sense. As soon as you start buying premade systems, the payoff is non existent. They only save a little bit of energy.

  2. MtLarry | | #2

    I am less concerned with saving energy as I am not wanting to deal with a frosted core on my HRV when it is 0° F.

    The water/ air on the inlet sounds promising. That seems like it would be something fairly simple to DIY. I'm already planning on a radiant floor heat system so to tap into that would not be too difficult. The tricky part would be to preheat the incoming air just enough to keep the core from frosting up without heating it too much which defeats the purpose of the HRV in the first place

    1. Tim_O | | #3

      You could pair it into the radiant system, but it would be best served on the distribution end of the HRV. I agree, you don't want to heat it up to room temperature.
      If I'm not mistaken, most HRVs just reverse the airflow temporarily to defrost the core. Other than Zhender which relies on preheated air only. Either way, I don't think there is anything to deal with, it's just a matter of energy usage to clear it up. Or have you had other issues?

  3. DennisWood | | #4

    Rather than adding the expense of preheating, I'd look at a more efficient ERV. I would take a look at the RenewAire Premium L. It has a very large core, that does not require much for defrost (they suggest no defrost for most situations) and is at around 88% efficient at ~60 CFM. I've been staring at HRV instrumented data for over a year now and I don't feel that a preheat system makes a lot of sense, unless you're in a much colder climate zone.

    Zehnder does have a preheat system offering which uses a brine ground loop and inline exchanger. If you look at data with respect to running costs though, (there are a few whitepapers out there on this topic) again you'd need to be looking a colder climate zone for this to make sense.

  4. Expert Member


    It's very similar to the method used by several house in William Shurcliffe's book from the early 1980s, except they used rock storage in the crawlspace, rather than soil.

    With enough tinkering they can work to provide some supplement heat, but like earth tubes I'd be very cautious about having the fresh air supply for a house run though an underground pipe where it isn't possible to insure it is clean and free of contaminants.

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