Controlling humidity in the shop

[Blk88GT]

My shop is 2000sqft with in floor heat. I have a couple snowmobiles, my truck and a tractor that come out fairly regularly and need to be melted off when they come back in.

Once they've melted off, the humidity ends up in the 50-65% range. It normally sits around 30%. This normally wouldn't bother me but I hate seeing the moisture on my steel entrance door and some moisture on the windows.

How are you guys dealing with humidity in your buildings?

 

[pseudorealityx]

[coming from a warm humid climate guy...]

If you don't mind your heating bills going up a bit, add an exhaust fan and a powered intake louver on a timer. Have it ventilate the building for a few hours after you bring the truck/tractor in. The dry air circulating should pull most of the moisture out... but will obviously also cool the space. Hopefully with in-floor heat and otherwise good insulation, you'll have enough thermal mass that it should be able to heat up quickly once you close it back down.

That's the cheapest I can think of besides containing the area the vehicles melt onto, and using the wet vacuum, but that sounds like a hassle to me.

 

[Jackfre]

I would suggest that you check out the Tjernlund X changer. They make good products. The XC unit is listed as a basement ventilator, but it comes with a humidistat control. It would do well for you...I think

 

[Jackfre]

Forgot the link

http://www.tjernlund.com/xchanger_basement_fan.htm

 

[philjafo]

Umm how bout a dehumidifier, the ones you pic up at wally world are ****. Honeywell makes several sizes, Dr 65 would likely work very well for your application. It will remove up to 65 pints off moisture in 24 hours and uses about a third of the electricity that a portable 25 pint from the big box store. Has a good air filter too.

 

[stealman]

Is that just a fan or a heat recovery ventilator? My shop is very tight and I am finding condensation on the windows after a shower that wont go away until the windows are open for a while. I am thinking about adding a heat recovery ventilator. I dont know much about them though.

 

[A_Pmech]

Ventilating may or may not solve the problem depending on the dewpoint of the outside air and the temperature of objects in the building. Ventilating can actually make condensation issues worse if the dewpoint of the outside air is above the interior temperature of the building.

The only sure-fire solution is to heat the shop into the high 40's to low 50's and use a dehumidifier.

 

[philjafo]

http://www.forwardthinking.honeywell.com/products/dehumidification/dehumidification_products.html
This is a link to the dehumidifier I mentioned.

 

[the_saint]

Have you considered constructing an insulated plug? that could fit over the inlet of the fan? something that you could place over the fan inlet (inside the garage) when not in use?

It would be pretty easy to fashion some fasteners that would hold it in place 'airtight'. Would definitely be better than nothing, and would likely achieve your goals.

 

[Kevin C]

Ventilating may or may not solve the problem depending on the dewpoint of the outside air and the temperature of objects in the building. Ventilating can actually make condensation issues worse if the dewpoint of the outside air is above the interior temperature of the building.

The only sure-fire solution is to heat the shop into the high 40's to low 50's and use a dehumidifier.

Most dehumidifiers wont work in a shop thats 40°F. The issue is that the coils ice up. You need to find a unit specifically designed for cold room operation. They are out there.

Many standard units don't have a temperature sensor on the coils. If you run one in a cool room the next thing you know the cold side is iced up, the unit has no airflow and the compressor fails. This can happen in a 60°F room.

 

[xTonyCRx]

What solution did you choose? I'm having the same issue with my garage with radiant floors. I will be bring vehicles and snowmobiles covered in snow into the garage regularly so I will need to find a solution.

 

[pantera1]

Having this problem also

I keep the shop aroun 50-55, little warmer on weekends. Going to bring in the dehumidifier from the house and see how it does.

 

[Blk88GT]

I haven't done anything, I couldn't identify an affordable and effective solution.

 

[383 240z]

Have the same problem here. We got snow last week, warmed up to low 40's today. Little rain and my slab is SOAKED. ***** of it is if it goes below freezing tonight, I'll have a skating rink tomorrow. Keith

 

[maxjivi05]

With it cold outside open your garage door for a hour the humidity will disappear fast

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[383 240z]

I turned on a 4' barn fan with the doors shut. It will vent thru the open eaves. Don't want the wind blowing rain in. It should be dry before I get home tonight. Keith

 

[Randy in Maine]

My snowblower sits on a "tray" I picked up from Tractor Supply to hold melted snow in. I built a wooden "pallet" for it to be under. I just dump it outside as the snow melts.

I also have a 65 pint dehumidifier that I use as needed along with some fans to move air around inside.

 

[the_saint]

What temperature are you keeping the garage heated?

 

[The_Hun]

You guys can try this…Wizzvent I have one in my garage and so far its not bad… Not Perfect but pretty decent. I only get a little moisture beads where the garage door panels come together, slab is bone dry. I also am using radiant floor heat and heating 900sqft.

 

[70C-10]

Ventilating may or may not solve the problem depending on the dewpoint of the outside air and the temperature of objects in the building. Ventilating can actually make condensation issues worse if the dewpoint of the outside air is above the interior temperature of the building.

Cold air doesn't hold humidity like warm air does. I don't understand, is there a difference between humidity & dew point ?

 

[maxjivi05]

Humidity is the amount of grains of water in the air the ratio is the amount in the air vs that can be in the air. Dew Point is the point the air can't hold moisture anymore so you get moisture everywhere causing a huge issue.

If it's cold outside there isn't much humidity in the air because it can't hold that many grains therefore if you open windows or doors or exchange air with vents and fans it'll remove the moisture in the garage and solve your issue. If it's summer time this don't work unless there is less humidity in the air.

I do this work for a living drying out structures and in the winter you can dry faster and easier.

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[Blk88GT]

I heat the shop to 50-55F (11.5C for us Canadians)

Can anyone comment if the Honeywell DR65 can be installed without a furnace? Just hang from the ceiling and let it run? It looks like it can but any feedback from people who use it would be appreciated!

http://yourhome.honeywell.com/home/Products/Dehumidifiers/Whole-House-65-Pint/

It's -30c outside and I've got 68% humidity in the shop after melting off my snowmobiles and tractor. The condensation on my windows and man door is pretty bad. I don't want this to continue.

 

[cos]

Hi Been following this discussion. Busted Knuckles is dead on his advice. Best way I think, keep inside temps 5 degrees warmer than outside temps. Problem is you need a differential thermostat. I have not found one that is under $300. No cheap way to do it.

 

[Blk88GT]

I think you might have the wrong thread....

5 degrees warmer than outside is still way too F'in cold

 

[pseudorealityx]

With the shop at 50 degrees F, a standard dehumidifier isn't going to do anything, since your dew point is below the temperature of the dehumidifier coil.

For that temperature, you need dry air, and the only way you're going to get that is to ventilate.

Using a normal 'house' dehumidifier for a 50 degree space is similar to saying you want to cool your building from 90 to 70 degrees using 75 degree air. Doesn't matter how much 75 degree air you you.... you'll never get below 75 degrees in that building.

 

[Blk88GT]

What temperature would you recommend? I can go up slightly but it gets expensive!

 

[pseudorealityx]

What temperature would you recommend? I can go up slightly but it gets expensive!

I wouldn't keep it at a higher temperature long term.

I'd ventilate it via the way I said in the first response to your thread.

Exhaust fan on a timer + make up air louver (powers open when fan energizes, powers shut when exhaust fan powers down). You could probably just a gravity damper with a counterweight too, but it will probably bit a bit drafty in comparison.

 

[cos]

Hi BLK88gt I thought I was commenting on the problem a fellow has with humidity in a storage container over on general forum, sorry for that.I reread this discussion and most of the comments good. Like some mentioned before, get things as dry as possible. Hose snow off with warm water then us leaf blower before you bring in if is above freezing. Your shop will have to act as a giant clothes dryer. Cold dry air in, add heat, warm moist air out.

 

[jvitez]

-30C prairie air heated to +10C will be close to Sahara desert dry, ie perfect for reducing the relative humidity inside your shop. I don't think any fancy dehumidifier will work nearly as well as plain old ventilation.

Your two options are plain ventilation, ie barn fan with make up air as pseudorealityx explained, or an HRV. The HRV will cost more to install but partially heat up the make up air. I'd figure out the air changes/hour you need to drop the humidity, then see what barn fans vs HRV's are available at what prices for that cfm and take it from there.

 

[Blk88GT]

I'm not opposed to installing an HRV, but I'd like to keep as much heat as possible in the building. The costs between an HRV and the dehumidifier are a wash.

The Honeywell unit shows a minimum operating temp of 56 degrees (13.3C) and I could deal with that. I'm waiting for a price back from my local HVAC supplier (2 days so far, ugh)

 

[pseudorealityx]

I'm not opposed to installing an HRV, but I'd like to keep as much heat as possible in the building. The costs between an HRV and the dehumidifier are a wash.

The Honeywell unit shows a minimum operating temp of 56 degrees (13.3C) and I could deal with that. I'm waiting for a price back from my local HVAC supplier (2 days so far, ugh)

Can you provide a link for the HRV you're looking at?

My *guess* is that it's not enough airflow to really dry out the space quickly. Is it doing sensible or sensible + latent heat transfer?

There's quite a bit more electrical use as well with an HRV. Typically, they have 2 or 3 electric motors, depending on the type. You also need to duct them.

I really don't think an HRV is going to pay for itself. Especially since you already have good insulation and radiant heat.

Is there a particular reason you're against the numerous recommendations of adding an exhaust fan on a timer?

 

[Blk88GT]

I wasn't looking at a particular HRV, I was looking at the dehumidifier posted earlier:

http://yourhome.honeywell.com/home/Products/Dehumidifiers/Whole-House-65-Pint/

I looked briefly to find a somewhat weather tight exhaust fan and I'm convinced they don't exist at the residential homeowner level.

I'd rather install an HRV than I would an exhaust fan. Have you ever exchanged air in a building when it's -35c outside and you're trying to work in there? At least the HRV could warm the incoming air.....

I'm not trying to be difficult, I'm trying to find the best solution to my problem without letting all the heat out of my building.

 

[pseudorealityx]

Yeah, notice the change in performance based on temperature in that dehumidifier. It loses half it's capacity going from 80 degrees to 70 degrees. Another loses half again from 70 degree air to 60 degree air. At 55 or whatever you plan keeping it at, it's going to reduce even further, likely to ~12-16 pints/DAY. That's 1 cup of water per hour.

https://customer.honeywell.com/resources/techlit/TechLitDocuments/68-0000s/68-3079.pdf

HRV is certainly going to work better than a dehumidifier.




This is a good read, or at least skim it...

http://www.greenbuildingadvisor.com...st+ventilation+v.+ERV+Report+-+Semmelhack.pdf

Basically, ventilation only (exhaust fan) is likely more cost effective over time. Even including the increase in heating load on your HVAC system. Much less fan operating costs, and first cost.

I agree that exchanging a lot of -35 degree air is going to cool down the air in a hurry, your radiant floor system should be able to make up for most of that. It's a LOT more thermal mass than just air. And radiant heat doesn't care much about the air temperature as far as it's effectiveness towards occupants. This would a totally different story if you were using a standard furnace to heat the shop via hot air.

 

[Chetter]

I heat with a Bigg Maxx 45000btu heater and I also use a low temp dehumidifier that I picked up and I have it set for 50% humidity. My garage stays much drier when I started using it and I keep my t-stat at 50* 24/7 unless I am out there working. My truck and the wife's car are parked in there every day and when they are snow covered and melt off then I will go out empty the dehumidifier once a day and I also use an old shop vac to pick any standing water. I have been heating my garage for the past 4 years and using the dehumidifier last year and now this year as well.

 

[xTonyCRx]

As I posted earlier in this thread I had big humidity problems with my radiant floor heating the garage to 60 degrees. In the winter. The snow from the cars and snowmobile would melt and evaporate completely fogging my windows. A dehumidifier just couldn't keep up. I even tried running two residential units.

Over the summer I picked up a used hrv and installed it. It works great. Using the humidistat it only exchanges as much as needed to keep humidity down then will shut off.


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[JCByrd24]

TonyCR's experience is inline with the advice I would give. Psychrometrics tells you two things that are really the same. Cold air can't hold as much moisture as warm air and warm air with the same absolute has less relative humidity. As such, you want two things, a warmer shop, and to bring in some of that dry cold outside air inside. As has been discussed a dehumidifier won't work as well in a cooler shop and doesn't take advantage of the dry dry outside air. Straight ventilation will work but not nearly as well as an HRV for the following reasons. Straight ventilation (bathroom or other fan) will **** heated air out of the building and therefore **** cold air into the building. The hole idea of the HRV is to exchange the heat from the air you **** out to the air you put in. An ERV will also exchange moisture, so you don't want that. So with the HRV you will pull wet air out, take whatever heat you can out of it, and preheat the super dry air from outside some, lowering its relative humidity even further. HRVs can be bought with super efficient electric motor (most now only have 1 not two or three) and will definitely use less power than a big ventilation fan. Also, it will save you a bunch of "reheating cost". For a garage, you don't really need to do much ducting either and it should be very simple. If run constantly I do believe it's true that like a heat pump they can frost up especially if it's cooler, but this is the job they are designed to do.

 

[XS29L9B]

Does this really work?

http://wizzvent.com/index.php/wizzvent

 

[DEnd]

Does this really work?

http://wizzvent.com/index.php/wizzvent

Yeah, it's basically a 75 cfm exhaust fan, and there are bath fans in that range for a bit less probably. If you don't mind the fan being a bit louder you can get one in that CFM range for much less (like 1/4 the price less). I doubt it is explosion proof, so I see no reason to get it over a bath fan.

 

[DEnd]

I'm not trying to be difficult, I'm trying to find the best solution to my problem without letting all the heat out of my building.

You are already letting all of the heat out of your building (just at a really slow rate).

Seriously though, the performance hit of a exhaust fan is really minor. it takes 0.018 BTU per cubic foot of air for each degree of temperature rise. Lets say you are at -35ºF and are raising the temp to 65ºF, a 100ºF temp rise. That is 1.8 BTU per cubic foot of air. If you have 12' ceilings and are exchanging the air at 0.35 air changes per hour that works out to 15,120 BTU per hour. Here's the thing though, you won't actually use that much as the negative pressure will depower the stack effect slowing the air exfiltration you currently have through your roof. Your actual BTU/hr increase will basically be that minus a good part of the current air exchange (due to the stack effect) rate BTU/hr requirement. I'd bet your actual increase is below 12,000 BTU/hr, and probably closer to 10,000 BTU/hr.

 

[XS29L9B]

Yeah, it's basically a 75 cfm exhaust fan, and there are bath fans in that range for a bit less probably. If you don't mind the fan being a bit louder you can get one in that CFM range for much less (like 1/4 the price less). I doubt it is explosion proof, so I see no reason to get it over a bath fan.

What about the controller for humidity though, doesn't the bigger buck unit cycle, or is it on all the time?

Thanks for your input