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Community and Q&A

Data on Pre-Heater Energy Consumption of ERV

abaerlo | Posted in Mechanicals on

We’re building a passive house in climate zone 6 (eastern Canada). We’re considering several ERVs for ventilation including a Zehnder Q450, Renewaire EV200, Panasonic IntelliBalance 200, and VanEE G2400. I like the idea of avoiding recirculation when it gets cold but it’s hard to find good data on actual energy consumption when the electric pre-heater is on? Has anyone monitored this over time? I found several references/articles, most from a decade ago, but the numbers seem to vary widely. Trying to get a sense of how much energy this would actual use. From what I’ve read, this is generally only required when it’s below -10 C (14F)? Thanks!

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  1. charlie_sullivan | | #1

    I have some data on electricity consumption in my house with some of the loads factored out, such that it's possible to look at it and manually identify the Zehnder preheat. With sufficient work, it would be possible to tease out what's going on there, in combination with weather records. But I haven't tried to work on it.

    1. abaerlo | | #3

      Are you in a relatively cold region? I assume you have the electric pre-heater (not the glycol loop)? Just trying to get a sense if this would add hundreds of kWh over a typical winter or be relatively insignificant overall.

      1. charlie_sullivan | | #6

        I'm also in Zone 6, in NH. I've got a busy week this week but can try to dig something out next week.

        1. abaerlo | | #8

          That would be great, thank you!

  2. Expert Member
    Akos | | #2

    Unless you are using something like a geo loop to pre-heat, a pre-heater is a waste of energy. Since the HRV/ERV is a passive heat exchanger, any energy you put into the intake gets sent right back out. Depending on the efficiency of the core, the COP is around 0.1.

    Even with a geo loop, if you look at heat delivered to the house and pumping costs, the COP is not that great.

    I'm relatively cold climate on the north end of Zone 5, the amount of time my ERV spends in defrost is so small, that I would not worry about it. I haven't fully wrapped my head around the energy needs during recirc defrost, but I don't think it uses any on net basis. Any heat taken out of the house to defrost the core was captured from the exhaust which caused the core to frost up in the first place.

    1. abaerlo | | #5

      It's a bit counterintuitive but I see what you mean. The temperature difference between incoming/outgoing air is reduced with a pre-heater so less outgoing heat is recovered. I guess what I'm trying to understand is how frequently is the pre-heater required? I've read it just turns on a few minutes every hour to prevent frost buildup. For other people, though, it seems to use a lot of energy overall.

      Do you have any recommendations? It looks like the Renewaire ERVs somehow avoid frosting problems? They claim they don't require a pre-heater or need to recirculate except under 'extreme conditions', whatever that means?

      1. Expert Member
        Akos | | #15

        For cost and efficiency, you can beat the Panasonic IB100. Their larger unit is a bit too expensive, at which point there are many options with similar or better performance.

        The Renewaire ERVs use a cross flow core which is much less prone to frost built up than a counter flow core. If they say the unit is fine in your climate, I can't see any reason not to use it.

        Cross flow cores are lower efficiency but they don't charge all that much more for a big unit. This lets you run a way oversized unit at very low flow rates at which point their efficiency is pretty decent.

        1. abaerlo | | #16

          I think the Panasonic IB100 is a bit small for us. The IB200 is pricey, not far off from the Zehnder (at least locally) but I guess it wouldn't need a pre-heater. The VanEE G2400 seems similar to the Panasonic price/performance wise although seems to require a bit less recirculation at lower temperatures.

          The Renewaire EV Premium L seems to have very good efficiency for the air flow we need. I'm waiting to hear back from them to see if it would work in our climate (without a pre-heater).

    2. charlie_sullivan | | #9

      To add to this, if you had an issue with loss of ventilation from the defrost cycle, a better solution would be to use a larger unit, normally running on low speed (where efficiency is higher) and boost the speed by 20% if it's spending 20% of the time in defrost mode.

      I think the best use of the geo loop is to run it in the winter only when needed to avoid frost, and in the summer, run it whenever the outdoor dew point is significantly above the ground loop temperature, to get some dehumidification of the incoming air, and to recover the ground temperature going into winter. But it's an expensive solution.

      1. abaerlo | | #10

        It seems like that could be built into 'defrost mode' (boost when it's enabled)?

        I have looked into the geo loop. It would cost $5k CAD plus installation. It's a huge investment, supposedly the pump is very efficient, though.

  3. Jon_Lawrence | | #4

    I have a Q600 with the integrated pre-heater which is designed to keep the core from freezing as opposed to trying to raise the temperature of the supply air like the glycol loop. It turns on at somewhere below 20F and as I recall it draws about 1kw.

    1. abaerlo | | #7

      Apparently Zehnder offers both an integrated and, more powerful, external pre-heater, depending on the climate. Do you know how often it's on during the winter? Can you even tell when it's on, other than higher energy consumption?

      1. Jon_Lawrence | | #11

        If you cycle through the menus on the LCD display on the unit to "Frost Protection State Preheater" it will tell me how much power it is currently drawing. My total energy consumption YTD is 227 kWh, but I can't tell how much of that was from the pre-heater. We had a pretty mild winter this year and I remember waking up only a few times and noticing my energy use overnight was higher than I expected. I was able to confirm it was caused by the pre-heater because it was still on when I woke up and I could see the power draw.

        Zehnder has pretty good tech support. You could give them a call and they should be able to give you an exact answer as opposed to my recollection.

        1. abaerlo | | #12

          Thanks for the info! That seems very efficient if it includes both the fan and pre-heater energy consumption (~50 watts).

          1. Expert Member
            Akos | | #14

            New Jersey is a relatively mild place, it doesn't get bellow 20F much of the time. Even when it does, the delta T the heater needs to provide is pretty small.

            In zone 6 you'll spend much more time bellow 20F and will need much higher temperature lift from the heater. My gut feel is that it will add up quick.

            You can big the temperature data from a local weather station, should be a straight forward calculation to see how much heat is required to bring the intake up to 20F.

            For example if, around me there are about 250 degree days base 20F.

            Assuming 100CFM, that means I would use:

            250*24*100*1.08=6.48 Therm or 190kWh. Not crazy high but something.

          2. Jon_Lawrence | | #17

            Like Akos said NJ is relatively mild compared to Zone 6 and we had a relatively mild winter compared to normal this year. The pre-heater probably ran maybe 10 times this past winter and usually just for a few hours in the early morning hours.

            I found the spec sheet for the Q450 and it says power consumption with/without pre-heater is 250w/2240w. Those sound like max because my 600 draws around 50w on low and 100w on medium and 200w on high, without pre-heater.


          3. abaerlo | | #18

            Akos - Thanks, this is very helpful. It looks like we have 194 degree days base 20F here so I get 191 kWh (@130 CFM). I guess this is less than I expected although not insignificant. Given the Zehnder uses less energy for the fans, though, it's actually pretty comparable overall to the other options.

            Jonathan - Got it, thanks! Are you happy with the Q600 otherwise?

  4. boxfactory | | #13

    Perhaps my question will be comparing apples to oranges, but how would the Zehnder pre heat compare to the CERV, and it’s built in ability to heat (and cool) incoming air?

    I believe the CERV also has a ground loop, would there be any major differences as compared to the Zehnder ground loop?


  5. Jon_Lawrence | | #19

    Yes, I am happy with it. I typically run it on low as that is all need to keep my CO2 levels below 500. I installed it myself and it is relatively easy to do. You will need to get the option box if you have more than 1 bathroom. The boost function works well when cooking or showering. The filters need to be changed twice a year and that will cost you $60. Otherwise it is pretty much set it and forget it.

    1. abaerlo | | #20

      Ok, thanks, good to know. I also like the 'bypass' feature and it seems like they are much quieter than other units (important in a well sealed house).

      1. Jon_Lawrence | | #21

        The bypass feature will probably work better for you than for me. In my case, the colder evening and early morning temps in the summer were times of higher humidity so the bypass function actually increased my humidity levels. I spoke to my guy at Zehnder about it and he said they have been pushing HQ to update the software to factor humidity as well as temperature when determining when to active bypass mode. The unit currently measure humidity of both incoming and outgoing air, but it is just for informational purposes at this point. Apparently humidity is not an issue is Switzerland in the summertime.

        1. abaerlo | | #22

          Good point, I hadn't thought about that. Humidity generally isn't a big issue where we are but there are a few uncomfortable days each year.

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