Mini-Split, Dehumidifier ??

[DSWalker]

Just got a digital temp and humidity gauge for the shop. My Pioneer Mini-Split unit has a 'DRY' setting to dehumidify, but when I run it on that mode it will drop the temp into the low 60's! I haven't tried it often, once this winter and then again last week when the humidity seemed really high inside. I went out the next morning and the walk thru door was condensing water everywhere on the outside because it had cooled so much inside.

Is that normal for the dry setting? Does the temp gauge setting not generally work when on the dry mode?

Just curious. Humidity is running in the high 60's inside the shop. Building is very well insulated. I might go in/out 1-2x's a day, so shouldn't be letting in a lot of humidity.

Just curious how others work. I know mini splits aren't known for their humidity control.

 

[redknife]

My shop mini-split didn’t “over-cool” on the dehumidify mode. The temp stayed as set. In theory it slowed down the cooling to extract more moisture (per hvac guys). That said, dehumidify didn’t seem to make a practical difference in RH vs cooling mode. I ran a separate dehumidifier.

 

[junquecol]

In the early AM, dew point was most likely higher than shop temperature, thus condensation. Several days this past week, dew points have been over 70. As soon as sun comes up, temp rises and dew point lowers, thus no condensation during the day. Condensation is why you can't paint bridges at night.

 

[gmakra]

What they are attempting to do is lower the air temp below the dew point.
True dehumidification will actually use both heat and refrigeration.
Industry standard for comfort and humidity is generally 72 degrees and 40-60 percent relative humidity.

 

[KenOfCary]

I don't have a mini split (but would like to install one eventually for the heat) but my basement shop has a separate dehumidifier. It has started coming on the last month or so - I keep it set at 50 and it does a good job keeping the humidity at or close to that. If I have to open the garage doors for any length of time it works a lot harder.

 

[Tarhead]

Dehumidifiers work by blowing room air over cold coils. Water vapor condenses into liquid water and it drips to a collector or in your case a drain. Most inside/portable units produce more net heat to compress the refrigerant and operate the fan than they produce cold air. With a mini split or regular permanent A/C units most of the heat produced is vented to the outside and the resulting cold dry air is blown inside.

 

[redknife]

David, are you able to get your eyes on the manal? I will say that the American Standard customer manual was shorter than light switch instructions. Installer? (Doesn’t sound right to go that far off temp setting)

 

[Jeff]

No specific answers to your questions but this calculator may help. Play around with any 2 of the 3 sliders to see the effect on the 3rd one.

We've had dew points in the 70-74 degree range over the last 2 weeks so it's been really soggy.

http://www.dpcalc.org

What does the mini-split do in just the AC mode instead of DRY?

 

[Mike Wilkins]

I only have a window AC unit in my shop. I just run it while in the shop; maybe start an hour before to cool down the interior before working inside. My humidity gauge shows a noticeable drop in % after running for a while. I am thinking it is just the AC function that is
moving the humidity down.

 

[Skymaster]

A/c in normal function cool and DE HUMIDIFYS drier air feels cooler at room temp than humid. every a/c has a drain because of that function

 

[DSWalker]

What does the mini-split do in just the AC mode instead of DRY?

It is cooling w/o any issue. Just had a high humidity level. When I use the DRY function is will freeze you out!

I found my owners manual this morning and am going to reread, and then possibly reach out the MFG. I really don't think it should be dropping the temp so low when in the dry mode.

Thanks for all the comments and information.

 

[Jeff]

It is cooling w/o any issue. Just had a high humidity level. When I use the DRY function is will freeze you out!

Did you measure the humidity level while it was just in the cooling mode? I think that several responses here suggest that the cooling mode should be adequate to lower the humidity as well as cool. What were you expecting as drastically reduced humidity levels?

 

[DSWalker]

Did you measure the humidity level while it was just in the cooling mode? I think that several responses here suggest that the cooling mode should be adequate to lower the humidity as well as cool. What were you expecting as drastically reduced humidity levels?

Just running the AC humidity will be in the high 60's to low 70's at times with the temp set on 73-75.

I just called the MFG and they said DRY mode will drop the temp into the low 60's, so that does match what I'm seeing. Although in the owners manual it clearly says you can set the Temp when in the dry mode. I pointed this out and he said it must be a printing error.

Most literature on mini splits does say they are not the best dehumidifiers, and several members here say they run a separate dehumidifier with their Mini-splits. I guess I just have to determine what is an acceptable level for humidity for me. The unit has barely moved my electric bill... maybe $15-20 a month. Really don't want to run the electric bill up with another unit running all the time.

 

[Tarhead]

Could the mini split unit be oversized for the space? That would explain the high humidity because it is not running long enough to circulate the air. If you can control the fan speed I would run it on the lowest setting. Keeping the humidity level where you have it will definitely create a mold/mildew problem.

 

[DSWalker]

Could the mini split unit be oversized for the space? That would explain the high humidity because it is not running long enough to circulate the air. If you can control the fan speed I would run it on the lowest setting. Keeping the humidity level where you have it will definitely create a mold/mildew problem.

Hmmm... I have a 17 SEER 18,000 BTU unit. Was looking at the 12,000 BTU and got up sold by the MFG when I bought it. They said the 12k would work, but the 18k would work much better and cost difference was less than $200, so I went for it. I'm sure there is an on-line calculator out there somewhere I could try. I have 576 sq ft. 24'x24' with 9.5' ceiling height. R-30 in walls and ceiling + the thin insulation wrap directly behind the metal siding and roof to prevent moisture. So it is well insulated.

Not sure if the temp gauge on the unit is off, but I had it set on 75 last night and it was 70 degrees inside this morning. Trying to get this regulated is frustrating. Maybe getting a separate dehumidifier is going to be the best option. With the building being well insulated and climate controlled, maybe it won't run up the electric bill.

 

[Jeff]

David,

Your mini-split is oversized for 576 sq. ft. even with 9.5' ceilings. Maybe a case of more is not better but it's already done.

A 12,000-14,000 BTU unit would have probably been sufficient.

https://www.sylvane.com/mini-split-air-conditioner-buying-guide.html

 

[gmakra]

Do you have a timer setting on your thermostat? If you do turn it off the timer and just let the unit run since dehumidification is time over temperature.
Do you have any kind of make up air coming from the outside?
How tight is the shop is there much air infiltration??
In other words set it and forget about it.

General rule of thumb is 1 ton of air for every 500 sq feet, but that can drop to below 300 sq ft per ton depending on insulation, solar gains, windows so you probably ok on sizing.
And if your wondering were a ton of refrigeration effect comes from it is from the cooling effect one ton of ice gives over a 24 hour period or 12,000 BTUs per hour.
And that was figured out by a young mechanical engineer name Willis Carrier who around 1900 was hired to figure a way to dehumidify a print shop because the paper was sticking together.
He came up with mechanical refrigeration to dehumidify and it wasn't applied for human comfort till the late 1930s.

 

[Mrfixit71]

I have a well insulated, tight shop with climate control. I also have a dehumidifier set at 50% and does not run enough to make a noticeable difference in my electric bill. It runs more in the spring and fall when the temperatures don't require heating or air conditioning, but it's humid. Once you get the humidity in the shop under control, your AC should minimize the run time for the dehumidifier, although as mentioned already, with the oversized AC unit, the AC unit won't do as effective a job of dehumidifying. To me, not having to deal with rusting tools (by controlling humidity) is worth the small additional cost of running the dehumidifier.

 

[DSWalker]

Do you have a timer setting on your thermostat? If you do turn it off the timer and just let the unit run since dehumidification is time over temperature.
Do you have any kind of make up air coming from the outside?
How tight is the shop is there much air infiltration??
In other words set it and forget about it.

Do you have a timer setting on your thermostat? If you do turn it off the timer and just let the unit run since dehumidification is time over temperature. There is a timer, but I let it run 24/7
Do you have any kind of make up air coming from the outside? Not intentionally. Open/close door 2-4 times a day.
How tight is the shop is there much air infiltration?? The shop is pretty tight. Metal building. It has the thin roll of insulation all around, then the r-30 in walls and ceiling, then black plastic as interior vapor barrier. Has 2 double pane insulated windows, 1 insulated walk thru door, and one insulated garage door. The garage door is the least insulated part of the building and typical 'sealing' around the door, so I'm sure there is some leakage there. It is on the east side of building and has a carport in front, so no direct sunlight hitting it.

In other words set it and forget about it.

I had the unit thermostat setting at 74 yesterday and fan at 'auto'. Indoor temp was 70 and humidity was in mid 50's. So that was good. Last night I set the fan on the low speed and temp remained the same, but humidity level was up a little over 60. I put the fan back on 'auto' this AM and will see what I have tonight.

I guess I just need to dial it in. If humidity keeps bouncing around I'll go with a dehumidifier.

 

[gmakra]

40 to 60% relative humidity is considered industry standard is considered industry standard also if you're doing woodwork you want to have the wood acclimated to the humidity that you're going to be in.