mini split for moisture control?

[sierradmax]

I left my detached garage unattended over the summer months and came home to notice some of my tools developed surface rust and any cloth/vinyl developed some mold. The garage inside of the garage was completed this past winter so this was my first summer experience. The garage is mostly secluded by tall trees so sunlight barely ever hits it.

My initial thought was a dehumidifier but after doing some research, I see mini splits have heating & cooling. My concern is if using a mini-split, during summer months, that the temperature of the garage will remain low enough for the unit to not turn on as frequent, and draw the moisture out of the garage.

 

[Jackfre]

Not enough info to advise. How big is the space? Is it insulated? Good windows/doors? I was very impressed with the dehu feature of the mini-split in my MA home.

 

[soob]

Mini splits are not the best for moisture control. Most mini splits don't have programmable thermostats, and relative humidity is the highest during the coolest part of the day. Plus, cooling the air raises the relative humidity.

Dehumidifiers actually raise the indoor temperature and are triggered by a humidistat rather than a thermostat so they only run when they're needed.

 

[sierradmax]

RI, 30x30 detached with 12' ceilings. Fully insulated, drywalled, etc.

 

[theoldwizard1]

Talk to an HVAC person about hooking up a humidistat to run in parallel to your thermostat on a mini-split. That is what kept my Dad's place in FL from getting moldy, 6 months of the year. At 30x30, you may need 2 air handler in opposite corners.

 

[PoorOwner]

the AC is for temperature control, not moisture control, the moisture removal is really a side effect of dropping the temperature. Once the heat load is removed the humidity will also stop being removed, in fact it would increase a bit as the fans run low speed over the moist coils.

 

[Doozer75]

Air conditioning was originally invented to control humidity, not temperature. Willis Carrier in Buffalo NY invented it. Cooling was the side effect. You have it backwards. Know your history.
--Doozer

 

[yeldogt]

Look into getting a "real" dehumidifier ..... I use a Santa Fe compact in my studio.

In the spring and fall when it's not very warm the AC does not run long enough to remove the humidity -- same in the summer when I'm not there. Can happen in the winter when I'm not there and the heat is low.

Type needed depends on the humidity load. Humidity level/size of space. The small consumer units (with the included tank) can't keep up and run 24/7 in large spaces or where high humidity is encountered. The more powerful units can remove lots of water and dry a space -- they also do it using less electricity.

 

[Trey T]

Lowering the temperature will ALWAYS have the potential of moisture removal, it doesn't matter the method you use (atmospheric pressure is assumed constant). Now, the rate of moisture removal is dependent on the equipment.

I'm willing to bet that minisplit (w/ bulkhead or cassette) can't remove moisture at the same rate conventional split system, simply because of the location of the return air. The return air should be further away from the supply air to effectively pull moisture from the furthest point of the room.

It's one of the reason why when guys on here recommend a single 2ton minisplit unit and I tell y'all to use more than one - well, here's a good reason, guy, to have good moisture control!!!

 

[Jackfre]

I was stunned when I put in my first mini-split in my MA home years ago. It was a 12k unit and ran about a steady steam of water out of the drain line. It did an excellent job on de-humidification. My Fujitsu had a "Dry" mode on the remote that was designed specifically for dehu purposes. Essentially, what the Dry mode does is keep the coil cool to maximize dehumidification without overcooling. It worked very well in MA and will as well in RI. Don't oversize it.

 

[yeldogt]

I was stunned when I put in my first mini-split in my MA home years ago. It was a 12k unit and ran about a steady steam of water out of the drain line. It did an excellent job on de-humidification. My Fujitsu had a "Dry" mode on the remote that was designed specifically for dehu purposes. Essentially, what the Dry mode does is keep the coil cool to maximize dehumidification without overcooling. It worked very well in MA and will as well in RI. Don't oversize it.

I find this to be the case in the house -- it does not work as well in my studio. Maybe I have more humidity -- not using the mini as often. It drops the temp too low .. OP may have better results.

If the Op is getting a mini for AC and heat -- he should wait to get the dehumidifier

 

[PoorOwner]

My understanding is that the mini split dry mode runs the compressor on full for a few minutes and then turn off. Potentially this can be hard on the compressor in the long run.

As inefficient as it sounds. I never seen an air conditioned space have rust developing.
Moisture in the air is one thing but it is when the temp swing happens that the condensation forms a film on the metal surface causing the rust. With air conditioning you get some moisture control and the temp swings are minimized. Seems like a win win situation?

 

[Warrenator]

The inverter models of mini-splits are super efficient because they run continuously, speeding up and slowing down the compressor as needed, rather than starting and stopping like a conventional unit. The inrush of current to start the compressor gets expensive when it happens 20 or 30 times a day. If I recall correctly from when I was shopping for one, the small ones use about 100 watts in cruise mode, same as an old school light bulb.

I currently have a conventional dehumidifier in my very well insulated and sealed 36 x 60 shop in rainy Oregon. Keeps the humidity down below 50 percent no problem. But it does make quite a racket, and probably uses more power than a small mini-split.... I think I will be getting a mini-split with a dehumidify setting instead. That has the added benefit of heating and cooling the shop too.

The tools that were stored outside in the barn got quite rusty over the last couple months. Inside the shop stuff is clean as a whistle.

 

[Jackfre]

I find this to be the case in the house -- it does not work as well in my studio. Maybe I have more humidity -- not using the mini as often. It drops the temp too low .. OP may have better results.

If the Op is getting a mini for AC and heat -- he should wait to get the dehumidifier

Do you run the studio full time or do you only run it when you are going to be out there. If run in the on/off you are always chasing the mass of the building. A lot of the better mini-splits are featuring wireless controls so you can anticipate if you are going to be using the space and call up the unit to get a head start on the temp. In the on/off you are always chasing the mass of the building.

 

[zmaxmotorsports]

Air conditioning was originally invented to control humidity, not temperature. Willis Carrier in Buffalo NY invented it. Cooling was the side effect. You have it backwards. Know your history.
--Doozer

 

[LS6 Tommy]

I'll just say that since I installed my 18k Fujitsu Halcyon in my basement and set it to "Dry" my dehumidifier has not cycled once. It used to cycle about every 10 minutes... Oh, also I see almost no difference in my electrical bill with the Fujitsu running on "dry" as compared to not running the dehumidifier at all. The dehumidifier used to pull about 7A continuously when it ran.

Tommy

 

[Lelandwelds]

My 2 ton Mitsubishi removes a measured 7 gallons per day per unit. It almost never shuts off. It just ramps the pump up and down as needed. The evaporator stays constantly cool enough to dehumidify. It has every electronic programming gizmo a japanese marketer could dream up.

You can get as small a unit as you want. But, there are much more expensive humidifier which still work by refrigeration and include exterior air makeup or "tempering".

If I knew about it then, I would have bought something more conventional with a Coupland digital scroll in it. I hate cleaning my cheesy little filters.

 

[LS6 Tommy]

Air conditioning was originally invented to control humidity, not temperature. Willis Carrier in Buffalo NY invented it. Cooling was the side effect. You have it backwards. Know your history.
--Doozer

Carrier is not the inventor of air conditioning itself, he invented the first "modern" electro-mechanical air conditioner and as you mentioned, it was used for process control in a printing company.
Benjamin Franklin and John Hadley experimented with evaporative cooling. Michael Faraday and others worked with compression technology for coolong in the 1820s. In the 1840's, Dr. John Gorrie basically invented actual "air conditioning" by using his patented ice making equipment to make ice which he then used to cool the air for patients in his hospital and got a patent for his ice making equipment in 1850. James Harrison had a patent for the first vapor compression refrigeration machine (same exact process we use today) as far back as the 1850s.

I had to look a few details up to refresh, but it's all stuff we used to teach at LTI...

Tommy

 

[Doozer75]

Like ! ! !

-Doozer

 

[soob]

the AC is for temperature control, not moisture control, the moisture removal is really a side effect of dropping the temperature. Once the heat load is removed the humidity will also stop being removed, in fact it would increase a bit as the fans run low speed over the moist coils.

Air conditioning was originally invented to control humidity, not temperature. Willis Carrier in Buffalo NY invented it. Cooling was the side effect. You have it backwards. Know your history.
--Doozer

His post wasn't a statement about history; it was a (correct) statement about what modern air conditioners are actually intended to do.

Yes, they remove moisture, but since the condenser is located outside, they also drop the temperature. Dropping the temperature increases relative humidity. If the condenser is located inside, like it is on a dehumidifier, the net effect is to warm the air inside which lowers relative humidity.

There's also the fact that relative humidity is highest during the coolest part of the day (that's why dew/frost form late at night). That's the time dehumidification is needed the most and the time air conditioners won't be running.

 

[firebirdparts]

Exactly. This should be obvious, but I guess it's not.

If you want dehumidification, dehumidifiers will do more of it for less money. Simple. The mini-spit will also do heating and cooling, which is a wonderful invention, for much more money. If you spend more money, you could get heating and cooling occasionally when you want it. It's a win either way.

It don't see how really obvious things like this get debated. To the OP, your original concern was spot on. If the environment or internal heat sources didn't supply heat to a building, then air conditioning would not provide any dehumidification at all. That should be obvious, but again, I am sure somebody will say it's totally wrong.