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Community and Q&A

Most energy-efficient ERV?

Claire Anderson | Posted in Mechanicals on

I’m planning a net-zero energy home built from SIPs, and am trying to size my PV system accordingly. Unfortunately, I’m finding that the ERV that the home needs eats electrons with relish (one model, if run at the highest setting, will consume about 6 kWh per day if it runs continuously). That said, I don’t understand the workings of an ERV to know if it does run continuously or cycles, or what the average daily electricity consumption is. I’m hoping folks on this forum can share their insights.

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    If you're willing to use an HRV, the Fantech VHR704 draws between 35 and 40 watts.

    If you insist on an ERV, you should consider the UltimateAir RecoupAerator from Stirling Technology. It is equipped with ECM motors and is fairly efficient, especially at low speed (40 watts).

  2. James Riggins | | #2

    Third-Party Data on ComfoAir 350?
    I have also reached the point of HRV/ERV decision for our net-zero project in Colorado which requires 67 CFM under ASHRAE standards. After pouring over Home Ventilating Institute ratings for weeks I have come to Martin's oft-repeated conclusion-- for overall efficiency, the leader of the pack in the HVI tables is the UltimateAir RecoupAerator 200DX. On the other hand there is the only HRV Passive House-certified in the US, the Zehnder Comfoair 350.
    My problem is being able to make an apples-to-apples comparison. Zehnder products still do not show up in the HVI ratings. I have three documents from Zehnder that each show a different "efficiency," either 85, 90 or 95%, but without defining "efficiency" which has a very specific definition in the HVI tables. I've seen that some manufacturers throw out an Apparent Sensible Effectiveness number as "efficiency" instead of Sensible Recovery Efficiency. Depending on which Zehnder number I use, the Comfoair is either on par with Ultimatair or significantly out-performs it in overall energy performance.
    Does anyone have any actual Comfoair 350 performance data to validate the numbers in their literature?
    Jim Riggins

  3. mike | | #3

    i don't think 95% is possible w/ the zehnder.

    the brochure we have says 86-88%. i think the 'efficiency' percentage changes w/ volume of air and length of ducting.

  4. User avatar GBA Editor
    Martin Holladay | | #4

    It may not be one of your criteria -- but as far as I know the Zehnder products all cost considerably more than the RecoupAerator.

  5. Kevin Dickson | | #5

    the most efficient ERV per dollar is the single-point Panasonic at $280, with almost no ductwork needed.

  6. Aj Builder, Upstate NY Zone 6a | | #6

    Just talked to a zehnder rep, costs roughly $5,000 for all equipment, so a contractor might ask 1.5 to 2 times that for total install and warranty.

    Interesting note... the zehnder is able to be switched from an HRV to an ERV and back. One of the issues with high flow rates is low humidity levels in winter here in Upstate NY. My thinking at this point is that lowering the humidity lets the home occupants live more American carefree lifestyles! No yelling at the kids to use the fan when showering, and whoever is house chef can boil all the pasta they want with the lids properly off... How many times have I been told that one. (pasta should only be cooked lid free!...) not my rule by the way.

  7. Aj Builder, Upstate NY Zone 6a | | #7

    In winter conditions, Upstate NY, Zehnder reps says;

    HRV lowers humidity in home

    ERV transfers humidity

    Too high a flow rate may cause very low humidity issues.

    Also says the units are second generation technology and very high efficiency. A good man to have representing your company. I believe him.

    I forgot annual cost... oops... I think with filters and 40 watts per hour... $100 per year? $200 max... running at high rates

    filters are easy to change, washable, last a year or so.... change seasonally more often when heavy pollen etc is in the air. Seconds to change.

    Oh and they are adding an inline muffler section which supposedly makes system barely able to hear running.

    Good system for upscale home, not for small home, inexpensive home etc.

  8. James Riggins | | #8

    Thanks all for the responses.
    Martin, I do have the detailed price list from Zehnder, and yes, it is more expensive than the UltimateAir (which still is not inexpensive), but it has features you can't find in other units.
    Still, most bang for the buck, both initial and long term operating costs, appears to be the UltimateAir. Also, their optional EconoCool feature which bypasses heat exchange during cool night air, is a great feature for our passively cooled-only house, and would be a nice supplement to our "stack effect" nightime cooling. I'm also considering UltimateAir's optional water-to-air heat exchanger, running with our excess solar DHW capacity, as a preheater for the unit to keep it from going into defrost mode in the winter.

  9. Thorsten Chlupp | | #9

    Of course efficiency level of any HRV/ERV unit changes with many variables like temps, CFMs and installation...a pour install will require more flow, more CFM, higher wattage and so forth...which translate in a huge impact on installed effective recovery. Same goes for supply air temperature - with very cold temps efficiency goes down the drain when you need it the most. That's why preheating incoming air makes so much sense if it is done right in cold climates.
    The Ultimar Air has a high recovery rate at 81% effective but (32F/64CFM/49W/83% effective) uses more energy than the Zehnder - it's design is based on a rotating wheel which will freeze in very cold climates...a technology not practical for certain regions. In the right climate it seems like a great unit.
    The Zehnder ComfoAir 350 Passiv Haus certificate lists 84% effective recovery and 0.29Wh/m3 energy consumption...considerable more efficient then our US contenders in both recovery and especially in energy consumption. And getting a Passiv Haus certificate is very stringent - so there is no "efficiency" washing going on, this is the real effective efficiency of the unit. List price is $2195 for the unit which is about 1k more than the Venmar EKO (32F/64CFM/74% effective/26W) or Fantech 1505 (32F/65cfm/59% effective/72W) but IMO justifiable in regards to its superior efficiency ... Zehnder US is apparently getting a new HRV test unit with a certified 95% rating which they might start carrying in the next months - but I am sure it will come with its price tag.

  10. Anonymous | | #10

    Price of just unit... is way off full installed cost and a useless figure.

  11. Mark Saunto | | #11

    Regarding Thorsten Chlupp's comments: I would be interested in any practical and effective incoming air pre-heat strategies for HRV's. Earth tubes seam too problematic to me and I am wondering if a South facing wall mounted intake run vertically up the wall could collect enough heat energy on a cold sunny day to be effective at pre-heating. For our mixed climate it would then need to be shaded in the hot season so as to not add cooling load. What are the important design considerations?

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