Better Fresh Air Venting Plan
 

Okay, I have a dream, google is letting me down finding an off-the-shelf product to satisfy my dream and I'm asking here to see if someone has seen such a product before I just make it.

I want to have a exhaust fan controlled by 2 (two) humidistats. One inside, one outside. If the humidity inside is above the proper threshold AND higher than outside, the fan is allowed to run; if the humidity is higher outside than inside, it's not allowed to run (regardless of the humidity inside).

The fan can be switched on/off via a power switch, a/c, d/c, relay, I care not - the logic is all I'm after at this point... The logic is something I'm capable of doing but truly I'd just rather give someone else my money so I can enjoy a few beverages with the time I would put into scheming (not to say that the scheming time wouldn't involve some beverages, but you get the idea) ;)


Anyone run across such a device (or already-designed-schematic for such a device)?

http://www.auberins.com/index.php?ma...roducts_id=265

nvm that one will only detect inside...

Nope, never seen anything like it. But I don't see why you couldn't do something like that with an Arduino controller, a couple relays and 2 humidistats

can't say seen anything like your looking for put if the humidity is high in the house can't hurt to still vent it outside even if the outdoor rh is higher.

We're getting a little north for it but look into erv rather than just a hrv.

Why do you not want it to run if the humidity outside is higher than inside?

In theory, exhausting air from your house creates negative pressure which will draw air in from outside. If the end goal is to decrease humidity inside, that is counter-productive :)

If the humidity is higher outside, venting air from inside to out will draw more-humid air from the outside back in -- just making things worse ;)

If this is for a fish room which I assume you only need a small fan pushing 80 cfm to run a few minutes every couple hours I'd guess meaning it will take along time to get a negitive pressure in your house that will draw in the more humid air.

No different than turning on a bathroom fan when you shower every morning

putting my met training to use, you need to take in account a RH of 40% @ 20° is a different amount of water vapour than a RH of 40% @ 15° (@ 15° for a equal amount of water compared to 40%/20° your RH is up around 70%)

I had a problem with really high humidity in my sump area, as it's completely enclosed, and of course high humidity in the room - I wanted better CO2/O2 exchange through it due to pH fluctuation, so I added these fans to both sides:

http://www.jlaquatics.com/phpstore/s...t_ID=cv-sfan04

The humidity on the inside and outside thing is a little tough, and probably non-existent because it's not one of those problems a majority of people have.

They do come with a heat sensor, and the fan spins faster or slower depending on the amount of heat either inside, or outside the sump area. I have one on all the time with the fan drawing air into the sump depending on the temperature inside, and I have another that draws air out depending on the temperature outside the sump.

Not sure if that helps!

Yeah, not many likely have the 'issue' that I do. I have 49.5 square feet of surface area, yes, feet... I am working to cover some of them with some form of acrylic to limit the evaporation somewhat.

But, say if it's raining outside, I don't want to be drawing in more humid air ;)