Semi conditioned crawlspace?
Ytsehoos
| Posted in Mechanicals on
https://www.jlconline.com/how-to/hvac/simple-fresh-air-for-tight-houses_o
I read the above article and thought it may present an affordable, easy solution for fresh air. I’m building in CZ -4A and could do a similar setup in my (conditioned) crawlspace.
Any foreseeable complications? Concerns about condensation?
Thanks for the input!
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Replies
Brian,
Q. "Any foreseeable complications? "
A. A few. This approach appears to require an air handler that operates for 24 hours a day -- an approach that uses a lot of electricity (depending on the power draw of the air handler fan, of course).
Another potential problem: If the conditioned attic is insulated with spray polyurethane foam, building codes forbid any air exchange via ductwork between the attic and the rooms below unless the foam insulation is covered with 1/2-inch gypsum drywall. For more information on this latter problem, see "High Humidity in Unvented Conditioned Attics."
This ventilation approach does not include any heat recovery. In that way, it resembles an exhaust-only ventilation system. Heating the ventilation air during the winter, and cooling the ventilation air during the summer, requires more energy than is needed when ventilating with an HRV or ERV.
"Semi-conditioned" often means that warm/moist air is cooled but not dehumidified - this can create a mold risk.
Fair points.
So, in considering an ERV; do they replace bath fans (when a duct is installed there) or would a bath fan still need to be used?
Brian,
Q. "In considering an ERV; do they replace bath fans (when a duct is installed there) or would a bath fan still need to be used?"
A. For a thorough discussion of that question, see this article: "Does a Home with an HRV Also Need Bath Fans?"
If the ductwork is appropriately sized, they work quite well as a replacement for exhaust fans. The only issue with using an ERV for an exhaust fan is they recycle the moisture from your showers. So if you have any problems with high humidity and you take lots of showers, an ERV can exacerbate that.
The moisture recovery on an ERV isn't enough to make a huge difference in the showering scenario. At ANSI/AHRI conditions the moisture recovered is still no more than about 50%. At super-high humidity levels the recovered amount is less. The moisture transfer rate capacity isn't unbounded, and the percentage recovered from very high nearly saturated bathroom air is small compared to the published numbers from testing at more average indoor & outdoor conditions.