under garage & house ventilation
I’m about to put out for design comment and bid a residential home in northern Illinois. The plan calls for unheated storage below the garage. The architect has included in the HVAC specs a air exchanger for the leaving space and also a dehumidifier for the storage area. Homes in the area that have under-garage storage seem to have moisture problems in the storage space. There’s two ideas I’d like to put out for comment.
My first take was I’drather have a exhaust fan w/ humidistat exchange air in the storage space (much like an attic fan) so that I don’t need to pay to run a dehumidifier. Then I thought…why not combine the air exchange concept with the need to move air through the storage space. Instead of exhausting living space air to the outside, I’d only exhaust air from the storage space via the exhaust fan, but I’d pull the storage space’s replacement air from the living space (via vent). I’dpush make-up air for the living space from the outside via a fan, but after running it through ducting in the storage space (sort of a giant heat/cold sink depending on the season). If I figure correctly, regardless of the season the living space would be drier than the storage space air so that even if its warmer than the storage space, moisture would still be reduced.
The second idea revolves around running the make-up air through a buried-in-the-ground pipe first. Seems like years ago it was touted as sort of a ‘natural’ heat exchanger to mitigate the incomming air temp. But I haven’t heard of anyone doing it now…so am wondering if it was one of those good-on-paper ideas that just don’t have the payback.
Thanks for taking the time to read the post.
Jeff
Replies
I think your idea of running the exhaust vent of the house through the storage area is a good one, though the question would be whether it would be enough ventilation (in terms of average CFM) to dehumidify the storage area. Even without the air from the house, it's definitely better (cheaper) to ventilate than run a dehumidifier, except perhaps when it's bitter cold outside.
Re the make-up-air-through-the-ground idea, the problem is that eventually the ground gets as cold as the incoming air. Probably works better in theory than in practice, as you suggest. And anyway, a good heat exchanger for the vent system will adequately temper the incoming air.
(On second thought, there could be a problem with venting air from the house into the storage area in deep winter, depending on conditions. If the house air is 30% humidity and 70F, and the temp in the storage area is 40F, the humidity will hit 90%, meaning you'd have condensation on anything stored in the area.)
Dan,
Thanks for the replies. Sounds like I'll spec an house-to-storage-to-outside exhaust system for the summer AND spec some pvc pipe foundation penetrations so I can place a dehumidifier in the storage area if it proves necessary. In the winter I hope the relatively dry and constant low temp will keep the storage dry. In the spring/fall when we have large swings in temp from day to night, I think the house conditioned air might be just as good as good of make-up as the outside air.
Jeff