Mitsubishi A/C for the Shop

[Mark Duksta]

Hello Everyone,

I'm considering a Mistsubishi Mr. Slim ductless A/C to cool my 480 sqft garage workshop with 10 foot ceilings.

Most of the BTU calculators online recommend a 18K BTU A/C. Mitsubishi offers a 16K and a 22K BTU unit. I want to buy the 22K BTU, but I don't want to over size the unit.

Are any of you cooling your workshops with a Mr. Slim? What size and how many square feet?

Mark

[Jim Bell]

My shop is 480 squ ft and insulated. My 18,000 btu a/c is busy on extremely hot days with lights on and equipment running. I live in Fl. My advice is go with the 22,000 btu unit. Mine is not a Mitsubishi. I couldn't bring myself to spend the money.

[Mark Duksta]

Thank you Jim. The last thing I want to do is spend a bunch of money and still be hot.

Mark

[Tyler Purcell]

I don't have one in my shop, but I have a Mr. Slim in my living room that does an amazing job. The room is about 480 square feet as well and the place is ice cold within 5 minutes of the unit being turned on. I'd have to find you the exact specs on it, however.

[Jeff Kerr]

You may want to get some advice from a HVAC pro. I think I remember reading somewhere that it is not good to oversize.

The reason I remember is that if the unit is too big then the unit cycles on and off often which is not efficient. the smaller would run longer.

Clear as mud.

[Randy Denby]

You will be oversized by 4000 btu's according to the calculations? Or one third of a ton. Did the calculations allow for physical work being done in the tempered space? I know you'll have quite abit of machinery , possibly refrigerators etc that can put a load on it. Also, depends on insulation etc...All this to say, I'd err on the high side, which in actuality is not that much oversized...BTW the mitsubishi is a good unit. I just hate that this is becoming one more area we are loosing industry in tho. (My wife works at Carrier so I'm biased a little)
Randy
Air-Tech

[Joe Jensen]

You will be oversized by 4000 btu's according to the calculations? Or one third of a ton. Did the calculations allow for physical work being done in the tempered space? I know you'll have quite abit of machinery , possibly refrigerators etc that can put a load on it. Also, depends on insulation etc...All this to say, I'd err on the high side, which in actuality is not that much oversized...BTW the mitsubishi is a good unit. I just hate that this is becoming one more area we are loosing industry in tho. (My wife works at Carrier so I'm biased a little)
Randy
Air-Tech

Randy, I'm considering something similar. Does Carrier offer anything similar? I'm pretty amazed by the SEER ratings on the Asian split units. Are those real ratings?...joe

[Al Willits]

Can't help ya for sizing as here in Minn its about 12,000 btus for every 600 sq ft, if I remember right.
But you make want to consider whether your gonna keep the shop at a lower temp, or just turn it on when ya use it, smaller size will work better if you keep the room air conditioned, as it will reduce humidity better, but a smaller unit may not cool quick enough to reduce temps down, if you start the unit just when you use it.

If your not gonna keep the room cooler, I'd really lean to wards oversizing, if the unit has several fan speeds, use the high speed to get the temps down a bit then reduce fan speed to help drop the humidity.
Last I remember, it takes about a 1,000 btu's to remove one pint of water, that's cooling power that's being used for humidity removal and not cooling.
So the more humidity you have the longer the unit will run before your notice a temp drop.
So over sizing will normally lean to wards cool humid air, but with useage on demand, you'll probably have to deal with it.

I normally shy away from oversizing, but in your case I think it'd be a wise move, as heat load in the building will probably be a bit higher than normal.

Al

[Randy Denby]

Randy, I'm considering something similar. Does Carrier offer anything similar? I'm pretty amazed by the SEER ratings on the Asian split units. Are those real ratings?...joe

Some manufacturers go by EER instead of SEER. SEER stands for "standard energy efficiency ratio"...as you can probably guess, they did this to standardize cuz manufacturers were stretching the ratios a bit....kind of like sears and their horsepower ratings. If its rated at SEER, then it should be believable, but being asian, who knows. I'm not sure if they have to follow our standards or not. ...sorry. And Carrier doesnt make a mini-split that I know of, unless they rebadge someone else's unit. I've heard good things about the Mitsubishi tho I've never installed one. The only thing I would be concerned with in a woodshop is dust control. I would want the capability to run oversized filtration so I could use a finer filter media without restricting airflow. With a regular unit, no problem as the filter is field installed and you can install the size you want. ( filter grill) But with these, you are basically restricted to the built in filter.

[Howard Acheson]

You may want to get some advice from a HVAC pro. I think I remember reading somewhere that it is not good to oversize.

The reason I remember is that if the unit is too big then the unit cycles on and off often which is not efficient. the smaller would run longer.

Clear as mud.

Correct. In addition, if the unit does not run long enough it does not dry the air to the optimum relative humidity.

[Mark Duksta]

Thanks for the replies everyone.

I've been researching this for some time now. I know that there a lot of variables that go into sizing the unit, insulation, heat producing machinery, etc. I understand the problem with over-sizing the unit.

I'd like to hear from those of us that have a set up like I'm considering. I know Jim (above) said he has an 18,000 BTU A/C in a shop like mine. His advice is to go with the larger unit.

Apparently the Mitsubishi has a variable speed fan. I think I could run it on low speed if I need the unit to run for longer periods.

Thanks again for replies.

Mark

[Kyle Kraft]

I agree with the don't oversize the unit mantra. The builder put a 3 ton ac unit on my 1800 sq. ft. house, and it would pull temperature in a matter of minutes so it never ran long enough to dehumidify.

After much research and letter writing, I got the HVAC contractor to swap out the 3 ton for a 2 ton, and it works soooooo much better.

[Al Willits]

Mark, you never said, or I missed, whether you were going to run this unit all the time, or just when needed, that will tell you how to go.

The problems with over sizing a unit is under the assumtion your going to keep the unit running.
You put a undersized unit in a shop and come out when its 98 degree's out and in, your gonna wait many hours to get cool.

Trust me on this one, I do work in the HVAC field..
imho

Al

[Mark Duksta]

Al,

My workshop is in a two car garage. It's dedicated to be a wood shop, but I'll only use it on week nights and weekends. During the week I may go out there two or three times a week in the evening. During the weekend I'll be out there for longer periods. I don't see the unit running 24/7.

I have to store stuff out there like my kids bicycle, and yard tools. I know she'll want to open the door.

Also, The blower will be mounted in the corner of the garage, not centered on a wall which would be optimal.

Mark

[Gary Tenney]

Concerning the SEER ratings, check and see if the ones with the higher ratings have Variable compressors. I know that Fujitsu make a model that does. When the heat load is low the compressor runs at better efficiency but more continuously. I cant remember if it is a variable frequency drive for compressor speed, or variable vanes in the compressor. Most likely variable speed. Anyhow, it keeps the compressor from cycling on and off which is a less efficient control and makes it more analogous. Probably gives longer compressor motor life as well. Anyhow, that is how the SEER ratings become so much higher on those models. I wanted to put one in my shop, but it is a square log construction and I hate putting holes in those logs so I just opted for a window unit that comes out in Winter time. Good Luck!

[Peter Elliott]

Mark,

I am in the same situation as your shop. But more geared towards a shop than other family items, thanks to a new shed, etc.

Just wondering what others have put in. I just looked around and boy the Mitsubishi is a little "salty".

Without starting a new thread, just wondering what other brands or options.

I once saw a picture of a regular window ac unit mounted on a stand with a drip pan.

I like the idea of a ductless system, I already have gas heat and need a/c only.

[Gary Tenney]

Let me correct myself! It is Sanyo that makes the Variable speed compressor units. Their units seem a bit more pricey though! Anyhow, I suspect with this technology, installing an over-rated unit would not be a dis-advantage anymore since on/off cycling should be minimum.

[Mark Duksta]

Mark,

I am in the same situation as your shop. But more geared towards a shop than other family items, thanks to a new shed, etc.

Just wondering what others have put in. I just looked around and boy the Mitsubishi is a little "salty".

Without starting a new thread, just wondering what other brands or options.

I once saw a picture of a regular window ac unit mounted on a stand with a drip pan.

I like the idea of a ductless system, I already have gas heat and need a/c only.

Peter,

I was considering the 18,000 BTU Sanyo. It seems to have some good reviews. At least what reviews I can find. The Mitsubishi seems to have been around for quite a while. It seems to be a proven product.

What do you mean by "Salty"?

Mark

[Randy Denby]

Mark, Check with a local A/C guy there in Austin. One factor alot of people over look is what happens when you need parts? I'm not pushing the mitsubishi, but it was one, if not the first , marketed thru a wholesale house here in east texas around 1988. I believe they have an outlet there as well. Baker Distributing.
Could be other wholesalers selling the sanyo, etc. so this is just a heads up.
Also, Al is right on about the sizing. If its not 24/7 you'll need a little more make-up capacity.Normally, the closer the unit is to actual load (design temp, heat load conditions) the better for humidity control. But, since you've got to cool all that space, walls, machinery, etc. down fairly quick better to err on the side of a "little" to much. Especially since living in Austin, 104 is pretty common during the summer....a little warmer than design temp of 99. Good luck

[Kevin Herber]

Mark - I am in Round Rock. Here is what I did in my condo garage:

http://www.sawmillcreek.org/showthread.php?t=20193

I've been using this for a couple summers now and am very happy with it.

-- Kevin

[Mark Duksta]

Kevin,

I remember your post. Great idea. I sent you a PM back then asking you who did the A/C work for you. I lost your e-mail. Do you remember who did the work for you?

How big is your garage? How long does it take your garage to cool down?

Mark

[Randy Denby]

Well......foot! Carrier does make a mini-split. Learn something everyday!!

[Kevin Herber]

The mounting piece was built by Stiller Hitches. I bought the unit from Darling AC. I assembled everything. Darling came back and evacuated and charged the system. He also did he electric hook up. I could have done the electric myself. Rather than hard wiring I put a plug on it with a flexible cord. That way I can store it when not in use. I can't say I got a great deal from Darling, but I don't think it was a bad one either considering the Carrier stickers on it. I think you pay a premium for those :D .

My garage is a standard 20 x 20. Faces south. When I bought the place I had them put in a factory insulated door cuz I anticipated doing this.

I usually use it over the weekend. I put the car out on Friday evening after dark. Let the hot air inside escape for a few minutes, then set everything up. All toll, about 15 minutes from the time I put the car out till I'm buttoned up. I'm as cool as I want by the next morning. I usually set the temp to 70.

In the pics, see the padded mat on the floor in front of the machine? I cut that into strips as a gap filler under the door. Works great. Although the door is up about 1/2 inch from fully closed, I see very little light around the door when I go in with the lights off. That is only in a couple places and I am not concerned over it.

Overall, I don't know how to get a better portable system to work. As I said a few times, I am very happy with this.

-- Kevin

[Al Willits]

Al,

My workshop is in a two car garage. It's dedicated to be a wood shop, but I'll only use it on week nights and weekends. During the week I may go out there two or three times a week in the evening. During the weekend I'll be out there for longer periods. I don't see the unit running 24/7.

I have to store stuff out there like my kids bicycle, and yard tools. I know she'll want to open the door.

Also, The blower will be mounted in the corner of the garage, not centered on a wall which would be optimal.

Mark



Go with the larger unit, nothing worse than waiting all day for a shop to cool down, your not that much over sized anyway.
Cool damp is still better than hot damp in my thinking.
Also consider you shouldn't have the humidity adders like showers, cooking and people like a house does.

Also make sure you keep the coils clean, I did a furnace/AC set up for a guy once who had a paint booth, and used a large metal box with filters on three sides to supply air to the unit, used standard 16x20" filters and he'd change them whenever they got dirty.

I'd think some sort of prefilter in a wood shop would be a must.

Al