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Community and Q&A

HRV strategy

rshuman | Posted in Energy Efficiency and Durability on

I’m looking for some insight into how I might go about ‘deploying’ HRV units to combat moisture issues in my house. I think I have captured the options through Martin’s ventilation article from 2017, a couple other items on GBA, and searching the web. For my house (~1888 ft2 on three levels (walkout basement, first and second floors)) in Zone 6A (Lubec, ME), it seems to come down to the Micra 60 and 150 and the Lunos e2, eGo, and Nexxt. The Panasonic WhisperComfort Spot can’t handle the low temperatures in 6A; the TwinFresh RA/RW1-50-2 are ERVs (I want to get rid of moisture not recover it); and the Zehnder ComfoAir 70 is no longer distributed in the US.

The Micra 60 and 150 move 18/27/35 and 35/53/71 cfm of air, respectively. The Lunos e2 and eGo move 9/18/22 and 3/12 cfm, respectively, while the Nexxt moves 8.8-53 cfm. My 2 bdrm house appears to be quite tight so if I assume, as a starting point, that I need to supply something on the order of 40-60 cfm then I would need 1 or 2 Micra 60s, a couple pair of Lunos e2, or a single Micra 150 or Lunos Nexxt from strictly a capacity standpoint. The eGo doesn’t seem to be worth considering because of its low capacity.

It isn’t clear to me how to factor in the effects of house geometry (i.e., air mixing/circulation) in selecting suitable units and distributing them throughout the house. About half of the 656 ft2 basement is open, the remainder is divided into a utility room and two other rooms. Doors are usually, or can be, left open. The 656 ft2 first floor is wide open except for a 80 ft2 bathroom. The 576 ft2 second floor has a bathroom and two bedrooms.

The humidity issues (as evidenced by window condensation) are greatest in the bedrooms, esp. if doors are kept closed but even if they are left open (no doubt ‘helped’ along by the fact that I do not actively heat the second floor); condensation lessens but is  still quite evident on the first floor and is usually light in the basement. Indoor RHs are never lower than 48-50% anywhere in the house.

I would appreciate hearing ideas people might have about placement strategies of the various units. I want to maximize effectiveness while trying to keep the overall cost in check. If people have experience with the various units listed above I would also appreciate informal reviews of the choices facing me.



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  1. GBA Editor
    Martin Holladay | | #1

    It sounds like this is an existing house, not a new house that is under construction. Is that correct?

    The best HRV system includes ducts that pull stale air from bathrooms (and sometimes the kitchen -- although never from the range hood), and that deliver fresh air to the bedrooms and living room (and in your case, perhaps the basement). Ideally, you will install the necessary ducts, and box the ducts in as necessary.

  2. rshuman | | #2

    Hi Martin,

    The house does indeed exist already, all but eliminating the opportunity to design and implement an efficient ducted system.

    If I assume there will be relatively little communication from floor to floor, I would probably need to deploy an HRV on each floor. I suspect whatever unit I placed on the first floor would do the trick because it is essentially one big room. The cut up nature of the upstairs (i.e., small landing, bathroom and two bedrooms) may beg for a unit in each bedroom which I would like to avoid given the cost of things like the Lunos e2. From a condensation standpoint, the basement seems to be better off although the RH is still 48-50% at best so that level might not be my first priority.

    On the other hand, if I can 'expect' some communication between floors than there may be an opportunity to purchase fewer units and achieve the necessary ventilation. Throwing another variable into the discussion, I could supplement the ventilation with (periodic/random/regular/whatever) dehumidification, although the ventilation units are likely more efficient from an energy usage standpoint.

    As far as the units themselves, I have seen extremely limited customer reviews of the MIcra units and they are middling at best, but that might not mean much. As far as I know, the Lunos e2 is a viable unit. In passing, although I mentioned the Lunos Nexxt as a potential candidate, it may not be as a 475 representative told me yesterday that they carry them but only for larger orders (and 1-2 units doesn't seem to qualify as such ;-)).

  3. charlie_sullivan | | #3

    As I understand it, the Twinfresh and Lunos units are the same technology, and as a result, both provided limited moisture recovery. The decision to call Lunos HRV and Twinfresh ERV may be more a marketing decision than a reflection of different moisture recovery levels. But I haven't attempted to dig into their data to see.

    For shoulder seasons during what you want to get some heating, and the outdoor air moisture content is not yet all that low, dehumidifiers can be an good choice. you not only get the waste heat generated by their inefficiency delivered to the space you are heating, but you also get the heat of vaporization of the water you condensed delivered as heat. So that can have a decent COP as a heater, and the dehumidification is a bonus.

    But a dehumidifier only removes water vapor; the advantage of ventilation is that it also removes CO2 and other pollutants.

    My subjective experience is that humidity equalizes between rooms better than temperature, absent major issues such as a wet basement or a bathroom lacking exhaust. But of course if you can locate exhaust in kitchens and bathrooms that's preferred.

    One more comment is that although you seem to be assuming that a ducted system is not feasible, the Zehnder ducting system uses smooth-wall tubing that fits in a 2x4 wall cavity and that can make it feasible where you thought it was not.

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