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Community and Q&A

Device that switches between ERV and HRV?

PrairieBurner | Posted in Mechanicals on

We live in a 1910 craftsman style bungalow in very northern Illinois (climate zone border 5a/6b) that has undergone some VERY heavy insulation/airsealing retrofits. Now as the weather gets cooler and the air dryer, the inside RH stays VERY high all winter.

We are thinking about getting an HRV or ERV as a remedy. But aren’t sure which to purchase. (I’ve read extensively the blogs/Q&A on here [and elsewhere] regarding them).

The issue is our climate. I would like to preserve the low RH air in the summer when the A/C is on and the outside air is EXTREMELY humid so that would mean an ERV. But, in the winter, we’d like to lower the RH so an HRV would be the way to go.

Does anyone know of a product that you can switch between ERV/HRV modes? (perhaps exhaust only too?)

Thanks!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    David,
    Research shows that (in spite of what ERV manufacturers tell you) an ERV has very little effect on the indoor RH during the summer. The solution to high indoor RH during the summer is an air conditioner (in some cases, supplemented by a dehumidifier), not ventilation. In fact, during hot humid weather, the less you ventilate, the better.

    So get an HRV.

    For more information on these issues, see HRV or ERV?

  2. PrairieBurner | | #2

    Thanks for the response Martin. I understand an A/C (and/or dehumidifier) is the solution to lowering the RH during a summer. My question about an ERV in the summer is to preserve the low RH that has be lowered BY the A/C.

    In hot, humid weather when the house is all closed up with the A/C on isn't ventilation just as necessary as in the winter when the house is all closed up?

  3. PrairieBurner | | #3

    I guess my original question still remains: Is there a product that you can switch between ERV/HRV modes? (perhaps exhaust only too?)

  4. GBA Editor
    Martin Holladay | | #4

    David,
    As far as I know, there is no appliance that can perform as both an HRV and an ERV.

    I'm pretty sure that you need an HRV. During the summer, an ERV would transfer some of the incoming moisture in the ventilation stream to the exhaust air stream. But the amount of moisture being transferred isn't a huge amount. If you have an HRV, and you are ventilating at a normal rate, your air conditioner should easily be able to handle the required moisture removal.

    And yes, most tight houses need ventilation during the summer. But many ventilation systems are improperly commissioned, and end up over-ventilating. So it's a good idea to experiment with different ventilation rates to make sure that you aren't over-ventilating.

  5. PrairieBurner | | #5

    Ok makes sense, HRV it is! Thanks for your responses!

    Is there an HRV that can also do exhaust only for the shoulder seasons?

  6. charlie_sullivan | | #6

    Zehnder has swappable cores, and is very nice otherwise, e.g., low fan energy consumption, and an easy-to-install duct system. They used to only have HRV, but now have both available. Their systems are expensive.

    Even though an A/C can handle the extra moisture an HRV brings in, it's true that the A/C doesn't need to work as hard with ERV. Whether it's worth the extra cost of buying a second core, I'm not sure.

    Zehnder also has a bypass mode, which might be what you wanted for shoulder season. It still has balanced intake and exhaust, but no heat exchange between the flows.

    Martin's suggestion of using minimal ventilation in summer of course helps regardless of whether you use ERV or HRV.

  7. GBA Editor
    Martin Holladay | | #7

    Charlie,
    Thanks for sharing the information about Zehnder's swappable cores.

  8. GBA Editor
    Martin Holladay | | #8

    Andrew,
    Thanks. I appreciate the input of the GBA community.

    For more information on the Air Pohoda, see New Green Building Products — May 2014.

    If you are broadening your consideration of ventilating devices to include devices that have a compressor, you might be interested in considering the CERV. For more information on the CERV, see A Balanced Ventilation System With a Built-In Heat Pump.

  9. user-1081937 | | #9

    AIr Pohoda has an adjustable ERV, you set the RH and the air flow changes directions when the core become moist to reintroduce it into the incoming air stream, or it can act like a regular HRV. It has some cooling potential in summer via the evaporation of the condensed moisture on the core. Not sure how well it will work in a more humid environment, they had to adjust some of the settings due to saturation issues.

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