HRV/ERV Mix
The more I read about HRV and ERVs – the more I think that spending a bit extra up front and using BOTH is a better solution (costs aside). Here’s what I mean:
If we built a house with 3 bedrooms and 2.5 baths:
– A whole home ERV could be installed, with return ducts in the three bathrooms and kitchen and supply ducts in the bedrooms and living areas. This ERV would run 24×7.
– In the two bathrooms with showers, put in a smaller HRV with return ducting in the shower enclosure ceiling (I’m thinking something like a Fantech SH704) and supply ducting elsewhere in the same bathroom. This HRV would be installed on a timer or simple on-off switch like a typical bathroom fan.
This setup, the HRVs in the shower would exhaust more water vapor while someone is showering – exactly when the vapor is being created – while at the same time, then whole home ERV helps to keep moisture levels more moderated throughout the day.
Is this design (excluding the extra cost) a reasonable solution?
Also – lobbing this out – how do people handle vent hood ventilation? We often do a lot of cooking, so I would like to ensure the smells/smoke/etc doesn’t just recirculate within the home… but I read lots of stuff about NOT venting to the outside and it seems there isn’t a balanced kitchen ventilation system unless I’m missing something.
All this would be in the Portland, OR metro area.
Thanks in advance.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
This topic has come up a couple of times already.
My own testing as well as from other posters shows that the amount of humidity recovered from showers is so small that it barely budges the house humidity. Showers also tend to be short duration, even a long shower is short compared to a whole day.
If the ERV flow rate is small and you like steamy showers, a dedicated exhaust fan might be needed to properly clear the space.
To amplify this, the ERV moisture recovery rate is reduced at high airflow, as happens when the it's boosted for a shower.
I also note that the heat recovery rate is better when and fan energy lower when you run an oversized _RV system at low flow rate, so that makes an oversized system boosted for showers a better energy plan than a small ERV run at full or near full flow all the time with the boost coming from a separate system.
But for lacroixb, in the Portland OR area, I would think HRV would be a good choice. I don't know Portland specifically but in the general region of the countries, winters aren't so cold and you likely don't need ERV to avoid it getting too dry--I hear more complaints about wanting to get better drying, which, in the winter, is more effective with HRV. And that region also has the luxury of low summer humidity, so you don't need ERV to preserve low indoor humidity then either.
lacroixb,
The consensus here on GBA (confirmed by a search of "Kitchen Ventilation") is that you need some form of extraction at the source to get rid of the harmful particulates generated by cooking. Whether you also need make-up air depends on both the size of the fan, and the tightness of the house.
I agree with Malcolm about source control. Dilution is not the solution (generally). Especially if you cook at home frequently, I'd save money on a more standard _RV installation and put in a good kitchen exhaust system (hood, fan (not too big), and makeup air). There's a classic article at BSC (BSI-070 First Deal with the Manure) and many discussions here at GBA.
Not sure where you've read that it's a bad idea to vent kitchens to the outdoors, certainly not on GBA. Especially if you haven't converted to electric/induction yet.
Good for you to think about these things in advance.
If I were to spend lavishly on an unnecessary combined ERV/HRV system, I'd install both connected to the same set of ducts, and I'd have controls to manually or automatically run the HRV when the indoor humidity is higher than I want and the outdoor humidity is low, and run the ERV otherwise. And maybe run booth when I want a boost mode to temporarily get a high ventilation rate. It would be really hard to justify the expense for that.
Sounds like I may be overthinking it. Lol! It does sound like going with a larger central unit that runs on low, then boost to high for showers, is a very viable solution. It’s the intellectual part of me that thinks, “but it would be more efficient to only run extra ventilation in the bathroom where the shower is going”. While that may be a true statement, what I am hearing from folks here is that is overkill.
Panasonic does make a 40cfm HRV point of use unit that is $400-ish that could be put in each shower in lieu of a booster switch on a central unit. But maybe that $800 is better spent elsewhere? Like a kegerator?
The Panasonics I've seen are all ERV. I'd be interested in a $400 high quality 40 CFM HRV for another application if that's really avaible.
You are correct, The Panasonic is an ERV; I was getting this mixed up with some Fantech products that are lower CFM HRVs but this cost closer to $700.
Thanks for confirming, even though I was hoping you would tell me otherwise.