ERV Capacity for High Humidity
LandonW
| Posted in Mechanicals on
I live in a humid climate and I am looking to add a ventilation system that is designed to handle a household that takes long hot showers. The problem I run into is all the recommendations tend to be for an ERV system with the potential for a boost mode in the bathrooms.
I am concerned though that the humidity load from the outdoor air and the long showers basically would not be the best pairing with an ERV. After reading a number of posts on GBA it appears people’s experiences with similar configurations are mixed at best.
Is there a better way to approach this issue?
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Replies
I am wondering about this also
Without knowing more specifics, shoot-from-hip solution is ERV and a dehumidification system. In a cold climate you can often get away with just an HRV but that's not advisable in a humid climate.
I live in a humid climate and the baths are ventilated with Panasonic Whisper Quiet Exhaust fans. The ERV system is completely separate. I have some concern running the exhaust fans in the baths makes the house go negative, however I'm not sure how to verify that. The house is tight (supposedly between 1.1-2 ACH/50).
One thing about the Panasonic Exhaust fans is they are not wired like most fans, and they don't come with very good instructions. I had to call Panasonic, and even after writing down what they said, the electrician did not believe me because the wiring is so unusual, so he had me call them again so he could hear it direct from them...
An ERV can easily clear a steamy hot bathroom as long as the pickup is sized correctly. You are probably looking at around a 100CFM pickup, which means most ERVs can only do a single bathroom, maybe one more smaller one.
A while back was curious how much difference in humidity it makes to have the ERV run in the bathroom. My setup has a 100 CFM ERV with a 30cfm pickup in the bathroom. I installed temperature and humidity sensors in the house, the ERV stale air pickup and the fresh air supply to the house. After a shower, the humidity in the stale air pickup went up a bit, the fresh air supply and the house didn't budge at all. I don't note down the exact numbers as they were so low that it is within noise. Overall, showers only last for a small fraction of the day, I would not worry about and ERV recycling shower humidity to the house.
As a side note the 30CFM pickup is fine for most showers, but I still run an 80CFM bathroom exhaust fan which is definitely needed after spicy chili night.
Part of how this works is that when the ERV is in "boost" mode (a high flow rate per unit area of heat exchanger), the moisture "recovery" efficiency goes down. Also, there's some delay for the moisture to get absorbed by the membrane and released into the other air flow.
In any case I think it's fine to clear bathroom humidity through the ERV without much concern about that reflecting that humidity back into the supply.
Note also that a more-enclosed shower stall will emit less humidity and be more comfortable for people who like long hot showers.
"Note also that a more-enclosed shower stall will emit less humidity and be more comfortable for people who like long hot showers."
That is a good point.
Where is your preferred pickup location in the bathroom with a more enclosed shower?
What are your thoughts on ERV sizing?
Do you try to size conservatively or oversize some and adjust run time?
Had a discussion with the Panasonic Northeast representative about this: they recommend separate bath fans besides ERV.
In case of bath fans and kitchen range exhaust: a makeup air system would be necessary.
Can someone share their experience, please?