Ventilation assistance Los Angeles
I am working with a passive house consultant to remodel my current house to be energy efficient and from what I am reading on GBA, indoor air quality is much more important with tight air building enclosures. Our consultant says they do %100 Zehnder but very curious on the GBA communty’s thoughts on going with a more budget option (buying a $1-2k ERV and ducting with a manual JDS)
Our house will be single story, ~1800 sq ft in Los Angeles 2 miles from the ocean. I am concerned about the humidity with RH consistently in the 60-80% from the on coast fog. With outdoor temperatures so mild but humidity being so high, not sure how well an ERV will even work. Will I need a separate dehumidifier to top it off?
Right now, looking at
-Panasonics Intellibalance 100 cfm as my budget option (73% efficiency at 95F and 52 cfm)
-mid range Broan ERV200 TE (68% efficiency at 95 F and 64 cfm)
-Ultimate Air 200DX I haven’t been able to get in contact with them or can’t seem to find them sold either. (36% total effective recovery, 76% apparent sensible effectiveness @ 146 cfm)
Any help would be greatly appreciated as it seems I can’t trust the 10 HVAC contractors I interviewed for this project in Los Angeles.
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Replies
Hi John,
I'll let others comment on the specific ERVs you are considering, but I have a thought on the system as a whole. I think you know this, but an ERV will not lower humidity levels in your home. And if you are remodeling to Passive House levels of air tightness, your air conditioner won't likely handle your dehumidification needs either. You probably will need dedicated dehumidification. It might be worth listening to A Deep Dive Into Dehumidification. I good HVAC designer should be able to help you with all of this.
>" I think you know this, but an ERV will not lower humidity levels in your home. "
I think I know different. (Or maybe I'm just making it up as I go along... :-) )
The moisture return efficiency of an ERV core is d0wnright lousy compared to it's temperature return efficiency. Running an ERV in relatively dry-air soCal at ASHRAE 62.2. rates will very MUCH lower the humidity levels in the house, just not as quickly or deeply as running an HRV. That "...coastal fog..." zone in Los Angeles has an average dew point under 60F (pretty comfortable and healthy) even during the most humid weeks of July/August, more than 70% of the time during June or September:
https://weatherspark.com/m/1705/7/Average-Weather-in-July-in-Los-Angeles-California-United-States#Sections-Humidity
(Scroll it right & left using the side using the side arrows.)
So it only matters just how low an INDOOR realtive humidity you're targeting. A comfortable healthy 50% RH @ 75F corresponds to a dew point of 55F. (Play around with this tool for a bit: http://www.dpcalc.org/ ) That is the same dew point of 62F/80% RH outdoor air experienced on some foggy-dew AM on the water front.
The additional benefit of an ERV vs. HRV isn't really going to be "worth it" in this location, since the outdoor dew points will only rarely be sufficiently higher than normal indoor dew points, and it takes a pretty big difference to get even 50% moisture transfer out of it. In coastal Alabama where the outdoor dew points sometimes hit 80F there's a measurable (if still pretty small in the grand scheme) benefit to ERVs over HRVs, in soCal that benefit is so tiny that it's really "in the noise".
Yup, Dana's right, of course. I was recently reading an old post from Allison Bailes about folks attempting to use ERVs to dehumidify in hot humid climates in which he explained why that was not a wise approach and that a dehumidifier would be likely be necessary. But LA is not hot and humid, it's dry. Sorry for the confusion.
> but an ERV will not lower humidity levels
Be careful with "relative to what?" If you are using a HRV and replace it with an ERV, it often will lower humidity levels - from what you had previously.
Thanks Dana,
I guess humid is definately relative. Right now, it is cool but humid (80% RH with a Dew point of 65 F. We are close to LAX so we sleep with the windows shut. This doesn't seem "dry to me" and according to the weatherspark dew point of 65 F is "muggy". I attached a snapshot of weatherspark for my location and it is slightly more humid that LA as a whole. Nothing like 80 F dew points, I guess I can't complain.
I would like to have a 50% RH indoors.
So for example tonight, if it's 75 F inside, 50% RH inside, 75 F outside, 80% RH outside
and I assume 50% humidity recovery, does that mean the air coming into my house would be 65% RH?
I don't understand your comment - "Running an ERV in relatively dry-air soCal at ASHRAE 62.2. rates will very MUCH lower the humidity levels in the house, just not as quickly or deeply as running an HRV. "
How does the HRV lower my humidity if it doesn't transfer moisture?
If you are picky about indoor humidity, use a dehumidifier and a humidifier. Also note that there are interior sources of moisture - outdoor dew point does not predict indoor dew point.
> How does the HRV lower my humidity if it doesn't transfer moisture?
Another "relative to what" issue. It does transfer moisture from inside to out (or vice versa, depending on conditions). To a lesser extent, so does an ERV.
Thanks Brian! this video is loooong