Conditioning with outdoor air
Hello Esteemed members of GBA.
I have a question regarding conditioning indoor air.
At night in my area the outdoor temperatures drop to a pretty nice low level (and we like it reasonably cool in the house)
However, the outdoor humidity levels are far lower than they are inside the house.
We do have whole house ducted AC, but it draws a lot of power to run.
Is there a middle ground using say, an ERV to draw in the cool outdoor air without losing a lot of humidity?
I figure and ERV would use less power than the AC unit?
I know the common response to using outdoor air to cool the home is to just “open a window” or to use a whole house fan but I don’t want to drop our indoor humidity to uncomfortable levels.
What are your ideas?
P.S. I’m located in Southern California, climate zone 3B (CA Climate Zone 10)
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Crontab,
What are your indoor conditions (temperature and relative humidity)?
What are typical outdoor conditions (temperature and relative humidity)?
Hey Martin!
I'm not sure the accuracy of the unit, but I use this to do my measurements:
https://www.amazon.com/AcuRite-02027A1-Temperature-Humidity-Forecaster/dp/B00GLDQFPY/
However, even if it's off it should be correct relative to itself?
Indoor we like to keep things around 70-72F at 35%-45% humidity.
It's rare that we can get into the 40% humidity range indoors, I need to do more air sealing to help with that.
This time of year it's starting to drop down to 50-55F at 7-10% humidity in the evenings.
The AC kicks on far far less than the summer, but it still does every now and then.
You could add high capacity, non-steam humidifiers and limit night air ventilation to say 100 CFM (no ERV when temp is beneficial). Both will add some cooling and the AC can efficiently handle any remainder.
Do maintain ASHRAE 62.2 ventilation levels.
Crontab,
The situation you describe -- Indoor relative humidity at about 30%, but occupants who like it higher -- is typical of winter in New England. I didn't realize that the same phenomenon happened in Southern California.
My first piece of advice: Are you sure you want higher indoor relative humidity? Most people do fine at 30% indoor RH, and running a humidifier can cause problems (or even mold and rot, although those last two are unlikely in California).
>"Indoor we like to keep things around 70-72F at 35%-45% humidity.
>
>It's rare that we can get into the 40% humidity range indoors, I need to do more air sealing to
>help with that.
>
>This time of year it's starting to drop down to 50-55F at 7-10% humidity in the evenings."
Taking the middle range, 40%RH@ 71F corresponds to a dew point of 46F, as your target humidity, which is only slightly above your average outdoor dew point in November in that location. Normal average outdoor humidity & temperature in zone 10 for the month of November is 55% RH @ 58F, which is a dew point of 42F.
https://www.pge.com/includes/docs/pdfs/about/edusafety/training/pec/toolbox/arch/climate/california_climate_zone_10.pdf
8% RH @ 52F corresponds to a dew point of about -3F. That is not a credible number for your location. The solid state sensors use in an AcuRite aren't usually very accurate near the humidity measurement extremes. If you want to calibrate the offset at those extremes, get a sling psychrometer and directly measure the wet bulb & dry bulb temperatures.
Right this second in nearby El Cajon the dew point is about +13F, which is still a LOT drier than the monthly average, largely due to the high winds coming off the deserts from the E & NE. In Santee it's +17F.