PDA

View Full Version : Humidity and dehumidifiers.



fahrner
06-30-2010, 10:38 AM
My shop is 4000 cu. ft.
The average relative humidity in the shop is around 58% +/- 5%.
My desire is to lower and maintain the RH to ~45%. I know that temperature and dew point are also a factor. So lets say my average temperature in the shop is 68 degrees F.
Dehumidifiers are specified in pints in a 24 hour period. One can find dehumidifiers that claim to remove 70 pints of water in 24 hours for under $200.00.
It seems to me that there must be a mathematical way to determine how many pints of water need to be removed in this environment to reach the desired level and maintain it. I understand that there are other factors such as leakage to the outside real world but it would be nice to get something in the ballpark short of simple trial and error.
Just trying to make an informed decision. Any help for a more scientific approach?

thistle3585
06-30-2010, 03:07 PM
Get a dehumidifier with a digital display and let it do all the math. I would just make sure it is big enough for the space. My first one was too small and seemed to run non-stop which probably meant I was never getting it to the humidity level I desired. It also required more maintenance because it was always running. You might try calling Rick Turner. I think he's in SC, so he could help you out.

Moore Bettah Ukuleles
06-30-2010, 05:22 PM
You might want to think of dropping a wall and sectioning off your shop. Many lutherie shop have a "dirty" room and a "clean" room under the same roof. The dirty room is where the rough work is done and the stationary tools are located. There's no real need to keep the climate controlled in this room. The clean room is where the instrument lives and where the actual building takes place. My clean room (building room) is only about 120 square feet and in it I have both a Sears dehumidifier and a in-window 9000 BTU air conditioning unit. Average humidity here can range between 65% and 85%. The dehumidifier has to work most of the time to suck the moisture out of this room. I don't use it much because it puts off a lot of heat. I use the A/C instead; it does a better job of removing the moisture and it keeps the temperature comfortable.
No matter what you do you need to prepare your building or your room properly otherwise your machines are going to be working overtime. This could mean sealing a concrete floor, plugging up any drafts and wrapping everything with Tyvek or something similar.
Sorry I can't help you with the math except for I would take any manufacture's claim and divide it in half!

fahrner
07-01-2010, 08:08 AM
Get a dehumidifier with a digital display and let it do all the math. I would just make sure it is big enough for the space. My first one was too small and seemed to run non-stop which probably meant I was never getting it to the humidity level I desired. It also required more maintenance because it was always running. You might try calling Rick Turner. I think he's in SC, so he could help you out.
Thanks for the comments Andrew. That's exactly what I'm trying to avoid is getting one too small.
What size did you end up with and how big is your space that you are trying to control?

fahrner
07-01-2010, 08:27 AM
You might want to think of dropping a wall and sectioning off your shop. Many lutherie shop have a "dirty" room and a "clean" room under the same roof. The dirty room is where the rough work is done and the stationary tools are located. There's no real need to keep the climate controlled in this room. The clean room is where the instrument lives and where the actual building takes place. My clean room (building room) is only about 120 square feet and in it I have both a Sears dehumidifier and a in-window 9000 BTU air conditioning unit. Average humidity here can range between 65% and 85%. The dehumidifier has to work most of the time to suck the moisture out of this room. I don't use it much because it puts off a lot of heat. I use the A/C instead; it does a better job of removing the moisture and it keeps the temperature comfortable.
No matter what you do you need to prepare your building or your room properly otherwise your machines are going to be working overtime. This could mean sealing a concrete floor, plugging up any drafts and wrapping everything with Tyvek or something similar.
Sorry I can't help you with the math except for I would take any manufacture's claim and divide it in half!
Thanks Chuck. The shop is a two car garage that is part of the house and the floor is sealed so four of the six sides are well buffered. The layout has simply evolved over the past 25 years.... when I brought in something new, I simply made space for it. Albeit a monumental task, would be great to move everything out and start over with a thought out layout to include a partition area that is RH controlled. Would still be faced with the same question though. The manufacturers sites I've checked so far typically provide some kind of table that talks about room size in terms of 'small', 'medium' and 'large' and then the RH in terms of 'damp', 'wet' and 'very wet'. I could deal with the room size vagaries but struggle with their RH descriptions. I may just end up with a closet or cabinet as we discussed a while back. Perhaps with a cookie sheet of desiccant that I bake once a week.

Moore Bettah Ukuleles
07-01-2010, 10:34 AM
I still feel that even the largest dehumidifier you can buy will be overburdened if you are not able to seal the room off pretty well. I don't know how you would seal a garage door. Then again, if you're talking about lowering the RH by just a few points you'll probably be OK. Still, I'd buy a big one. I've measured the pints extracted on my dehumidifiers and it doesn't come close to the manufacturers claims.

thistle3585
07-01-2010, 11:02 AM
The reason you want to go larger than what is recommended is because of the room contents. Its easy to control an empty space, but once you add stuff to the space it complicates things. You'd be surprised how much moisture can be trapped in a full dust collector bag, or that favorite couch you have in the corner to take your afternoon siesta, or the six logs that the neighbor brought over to see if you could use them to make him a dulcimer. When you dry out the air then the moisture is going to be pulled out of those things too. When it comes down to it, the most important number is the 7% +/- that you are trying to control.

Steve vanPelt
07-01-2010, 11:07 AM
Hi Fred,

I went through this search last winter when the RH is 100%, give or take, and cold. My shop takes up about half of a 40 X 40 steel building that is not sealed too well at all. This year it gets a section sealed off and climate controlled. After going through all the reviews, I settled on this dehumidifier from this company. http://www.allergybuyersclubshopping.com/danby-premiere-ddr7009ee-70-pint-low-temperature-dehumidifiers.html?itemId=2352 .

Seems that many dehumidifiers don't work well when it's cold unless they're designed to. This one is supposed to be good down to about 40 degrees. Even with the poorly sealed shop it managed to knock the RH down 20 - 30%, depending on temp. I am confident that in the new smaller, better sealed space it will keep the RH to where ever I set it.

Good luck with your search, and please let us know how it turns out.

Steve