Using basement air for cooling
Jacob_D
| Posted in Green Building Techniques on
Just had a heat pump water heater installed. Generally, the basement air is considerably cooler than the rest of the house. Now even more so. Is it worthwhile to stick an exhaust fan on the ceiling of the basement through to the first floor to suck that nice cool air up when it’s hot?
Edit: I’m guessing replacement air will be something to consider with this idea. So, maybe two fans one sending warm air down, the other sending cold air up? I’m new to green building concept, so I’m also guessing this might just be a bad idea altogether for reasons I’m not considering.
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Replies
I cut in a return duct on my forced air furnace return right above the basement slab level. I open it during the summer AC season and close it during the heating season. Why not mix the cooler air in when we need summer cooling. My heating guy looked a bit confused when he saw what I did but the added return duct is a standard 8"x12" and my basement level did not have enough returns to begin with. My summer cooling bills in Minneapolis are very low due to energy upgrades to the home and significant summer tree shading. I believe the mixing of the cool air above the basement slab also contributes to the low cooling costs. The basement slab is uninsulated so there is some Earth coupling.
Doug
The reason they call it "air conditioning" as opposed to "cooling" is that summer air needs to be dehumidified as well as cooled. Basements are actually problematic in the summer because they are cool and without dehumidification they tend to get moldy.
That said, heat pump water heaters also dehumidify as they cool, they're basically free air conditioning.
>"Basements are actually problematic in the summer because they are cool "
Yeah, so it seems the issue is not so much the basement air being brought into the upstairs (unless it's bad air quality), but the upstairs air (if higher dewpoint) being brought down and possibly increasing RH (which I suppose in turn would make the basement air poor quality).
But with continuous air flow, the basement could also become warmer, and so the RH could actually stabilize (or at least not get worse) (?). I am not sure on that last sentence, it will depend on the specifics.
I would at the very least monitor basement and upstairs temp and humidity to get a picture of what conditions are in the two scenarios (with and without powered air exchange).
I think the new fans you are preposing to use to move the basement air will heat to the air they move combined with the fact that the air they are moving contains more moisture will likely increase your power bills while lowering the upstairs comfort levels.
Walta
I just had a former client ask if they could or should do this with their near-Passive House home over a full basement, for the guest rooms that do not have air conditioning. The trick is to monitor the humidity levels to make sure they stay within a safe range. If your basement is insulated and air-sealed, circulating main-floor air down there will warm it up so once it reaches stasis there should be no problems. If your basement is currently cold you would initially have elevated humidity down there. If your basement is not insulated then the cooler temperatures and elevated humidity will continue to be a problem.
It may be a good idea to actually duct the cool air 10 feet away from your water heater, or to the opposite side of a basement partition (even a thick curtain). While the water heater is running it will create a cold zone close to the air intake and that decreases the efficiency of the unit.
I installed my unit in 2012 and I ducted it in 2020. Big difference, now I can run the unit in heat pump mode all winter.