Replies

1. 
   mjezzi | Jul 21, 2019 10:21pm | #1

   I think I answered my own question

   “The myth that HRVs are preferred in northern areas is based on a freezing problem that ERVs experienced twenty years ago. This problem has long since been corrected, with current models featuring updated technology. However, some still use this outdated claim as a misleading justification. The HRV industry survives on this misinformation.”

   https://www.ultimateair.com/blog/bid/85515/energy-recovery-ventilation-or-heat-recovery-ventilation

2. GBA Editor
   Martin Holladay | Jul 22, 2019 07:52am | #2

   Mike,
   For more information, see this article: "Preventing Frost Buildup in HRVs and ERVs."

3. 
   Trevor_Lambert | Jul 22, 2019 08:35am | #3

   An ERV passes some of the moisture from the the more humid stream to the less humid stream. So in winter, some of the moisture in the outgoing air will be returned back to the house. This is contrast to an HRV, where the moisture in the house goes directly outside and is replaced by whatever is in the incoming air.

   I find UltimateAir's comment puzzling. The HRV industry and the ERV industry are essentially the same industry. Almost all the manufacturers produce both types. UltimateAir is the rare exception that only produces ERVs. Both ERV and HRV cores can potentially freeze up in cold weather, and various frost prevention strategies are included with both types.

4. 
   Jon_R | Jul 22, 2019 08:57am | #4

   > Do ERVs help retain moisture

   Quite possibly too much, leading to Winter moisture problems.

   If you can accurately estimate your moisture load and outdoor conditions, then you can calculate which will be better from a humidity standpoint. An HRV may be better in a cold climate with a tight house.

   If it's close, I'd use an HRV. There aren't good alternatives for reducing Winter indoor humidity below ~45%.

1. 
   mjezzi | Jul 22, 2019 10:21am | #5

   Do ERVs allow you to set the desired humidity level? In winter, 40% would be ideal compared to 20%.

1. 
   Trevor_Lambert | Jul 22, 2019 10:41am | #6

   They do not. The Q600 is a new model, but if it's like previous Zehnder units you can swap out the core, changing it from an ERV to an HRV and vice versa.

2. 
   charlie_sullivan | Jul 22, 2019 12:43pm | #7

   With either ERV or HRV, you can control the amount of run time or the speed to have an influence on humidity. I've heard of systems that are cycled on and off by a humidistat, but it's more efficient to run it continuously at low speed.

   The problem might be that with an HRV in the dead of winter, the run time might be too low to get enough ventilation, if you target a fairly high humidity. On the flip side, in shoulder seasons in some climates, it can be hard to get enough moisture removal using an ERV, when the outdoor dew point isn't all that low. You end up running the ERV on high all the time and not getting the humidity down as you'd want to, while wasting energy and making it noisy.

   In your climate, the latter problem might never occur, so you might want an ERV. It does depend on how much moisture you generate: number of people, style of cooking, shower setup and usage, etc. So it's hard to predict.

   A nice thing about Zehnder is the swappable core, which means you can change it out if you guessed wrong about which will work best for you. We own both cores, and use the HRV in the fall and early winter, when the house has a little more moisture in it than we want coming out of summer, and then switch to ERV for the late winter when it's getting a little dryer than we'd like. Summer is definitely ERV to keep the spikes in outdoor humidity from coming inside, so I usually leave the ERV in through spring.

1. 
   Jon_R | Jul 22, 2019 12:57pm | #8

   Charlie has a good approach. Now if it could just be automated so it can switch much more often. At a price that creates a reasonable payback.