Mini split ductless

[motormitch]

I promise that I have read numerous threads hoping to find a clear answer(s) to my current situation before posting a new thread, but my clock is ticking so I will ask directly to experts.

I have a 70x55 shop with 18' walls and 2/12 roof pitch. It is a metal bolt up building. 3" insulation walls, 6" ceiling and the roll up doors (3 large ones) are Janus insulated doors. I live in Austin Texas and so cooling is a concern. This is a personal use shop for myself and a few close friends. It will be mostly idle during the workday/work week with heavy use on week ends and a few evenings during the week. I have a Mr. Slim ductless system in my three car garage at home and it performs wonderfully. However, I have 10' ceilings.

I would like to know if it is reasonable to use several separate ductless systems to cool (and a little heat in the winter) my shop. maybe (3) 2 or 2.5 ton units. There will be a living space that is 18'x28' taking up one corner on it's own system so I am looking at ~3300 sq.ft. I also plan to use large shop fans as long as I can till the heat gets too bad, but I will also have a paint booth and will need to get access to 75 degree temperatures for a while during painting.

Is this feasible?

 

[rquackenbush]

With those sizes and the number of mini-split units you're talking about, wouldn't it be easier / cheaper just to install one or two large regular units? That way you have the option of heating with gas, which should be cheaper than electric (especially if you have natural gas to the site).

 

[motormitch]

I don't have natural gas available and propane is as expensive here as electric which I have 350amp 3 phase available. Most estimates for traditional AC have been around 20K installed and I can pick up the 2 ton Mr. Slims for 2K each and install them myself. It really is very easy. I am worried about is the fact that they weren't designed for use in such and open air area.

 

[JakeKohl]

With those sizes and the number of mini-split units you're talking about, wouldn't it be easier / cheaper just to install one or two large regular units? That way you have the option of heating with gas, which should be cheaper than electric (especially if you have natural gas to the site).

Actually, with the efficiencies being experienced with the mini-splits, they're much more cost effective to heat with than fossil fuels...particularly if you live in a mild winter climate.

There is no reason that several of these units can't work together to cool the space. The fans you mention for the meantime, may help keep the temperature constant throughout.

 

[theoldwizard1]

You are thinking in the right direction, but I would check into a split system that has multiple heads. Most of the big names sell such units.

First, you need an expert to do a heating/cooling load analysis to figure out just how much cooling you need. If you do have to go to multiple individual units, someone smarter then me needs to figure out how to wire the thermostats.

 

[rquackenbush]

I don't have natural gas available and propane is as expensive here as electric which I have 350amp 3 phase available. Most estimates for traditional AC have been around 20K installed and I can pick up the 2 ton Mr. Slims for 2K each and install them myself. It really is very easy. I am worried about is the fact that they weren't designed for use in such and open air area.

Shoot - it sounds like you've already thought it through pretty well then. How easy are the Slims to install? I'm setting up a mini-man cave in the attic of the house that we're building - it's about 200 square feet.

 

[Jinks]

If you're lookin' at 3 24,000 BTU Mitsubishi inverter mini-splits it sounds to me like you're headed in the right direction. If you can get 'em for 2K each & are comfortable doin' your own install (you're right, it's easy) you should be set. I'd consider some good fans to circulate the air, & not expect much cooling if you open those big doors, but you knew that. $6000 initial cost, plus inverter technology will mean lower operating costs, & if one needs repair the others will provide some relief while it's being done. 20K in a ducted unit & a week in the heat when it breaks would be a bitter pill.

 

[Highbeam]

someone smarter then me needs to figure out how to wire the thermostats.

As I recall, these things all have internal thermostats so you won't have to do anything special. Put them up and turn them on.

They make higher tonnage units but the smaller ones are the most efficient.

 

[Charles (in GA)]

Look at it this way, you have a building with 77,962 cu.ft. in it. minus the living space of about 5,000 cu. ft. giving you about 73,000 cu ft you will be attempting to cool.

Your three car garage at home is very little larger than the living space in this building. Attempting to cool all of this will, no matter how you do it, cost a bunch of bucks in energy.

I don't really know how many mini splits it will take, but I'll bet its more than a couple or three, even large ones, I'll bet you could be looking at six to ten units to make a dent in the air temp.

If you are using a real paint booth, I would look at an environmental system for it, separate from everything else.

Charles

 

[James-W]

I don't think the number of cubic feet matters all that much in this case because cool air falls and warm air rises. I am making an assumption that he will be working on the floor and that is the area he wants to cool. So the coolest air will be down by the floor and I would think 3 of the 2 ton units would be sufficient to keep the lower areas cool provided the doors aren't opened up. Now obviously if he wants to cool the upper areas as well, then it would require more cooling capacity. In any case, he should really consult with a cooling expert but just off-hand I tend to think that for just cooling the area down by the floor, he could get by with three 2 ton units. On the other hand it may be more efficient to get one 6 ton unit instead and run ducts to different areas of the shop. There again, he needs to do some checking into it to find out for sure.

 

[Bill1031]

If I had a shop that big, I would consider a split system on each end. Just 13 Seer because amount of use. Hang them to keep off floor. Run round duct for a supply with just a curved or (rat) seal tight and 6x12x8 boots and 6x12 register pointing at approx 45deg from main supply. Keep the returns up high again near AHUs. I would think your main concern is cooling in Austin. Wrap the round pipe with insulation, Your flavor. Just for condensation reasons. If you buy the units online or have a friend that is a contractor the basic units would run you about 3500 with linesets and basic tstats and the rest I would guess about another 2k max. Your labor! Just a thought!

 

[motormitch]

Shoot - it sounds like you've already thought it through pretty well then. How easy are the Slims to install? I'm setting up a mini-man cave in the attic of the house that we're building - it's about 200 square feet.

This Mr. Slim was super easy. The hardest part for me was getting a 3" hole through the wall since I had 4" of rock to go through. This is the process.

1- make a single 3" hole for the lines, drain and power (all pre-bundled together) to pass though out to the outside compressor.

2- screw up a mounting bracket that is super easy and then hang wall unit on bracket

3 - make pad for outside unit and place it on pad

4- wire up the outside power line to a 220V source

5 - connect all lines

6 - put batteries in remote and push button

I'm not kidding. The unit is precharged and ready to go.

 

[motormitch]

I don't think the number of cubic feet matters all that much in this case because cool air falls and warm air rises. I am making an assumption that he will be working on the floor and that is the area he wants to cool. So the coolest air will be down by the floor and I would think 3 of the 2 ton units would be sufficient to keep the lower areas cool provided the doors aren't opened up. Now obviously if he wants to cool the upper areas as well, then it would require more cooling capacity. In any case, he should really consult with a cooling expert but just off-hand I tend to think that for just cooling the area down by the floor, he could get by with three 2 ton units. On the other hand it may be more efficient to get one 6 ton unit instead and run ducts to different areas of the shop. There again, he needs to do some checking into it to find out for sure.

The cool air will certainly drop to the ground level where I will be working most of the time and in the winter I will likely just use a space heater in the area I am working unless I am having a group of people over on a bigger project or gathering. Two professionals have both spec-ed 7-8 tons needed, but then wanted 20-25K to do the job. Let's say I go with (4) 2 ton units and install them myself. That's 10K and I have 4 separate controllable zones. The big negatives that I see and worry about are as follows.

1 - I need to buy them on line so there won't really be a warranty. Read the fine print OK, so far my Mr. Slim has been rock solid

2 - Installation is all on me. OK, why did I build a big shop to do restorations if I am afraid of some like this?

3 - 4 separate systems with separate thermostats might be hard to balance

4 - Air movement will be a challenge. Ductless means the air intake and outlet are where the unit is. This is a BIG box so center air flow is going to be a challenge. Thoughts are to assist with shop fans

5 - This is not what these type of systems were designed for so am I thinking crazy since I can't seem to find anyone else who has done something this big with ductless?

 

[Jinks]

The cool air will certainly drop to the ground level where I will be working most of the time and in the winter I will likely just use a space heater in the area I am working unless I am having a group of people over on a bigger project or gathering. Two professionals have both spec-ed 7-8 tons needed, but then wanted 20-25K to do the job. Let's say I go with (4) 2 ton units and install them myself. That's 10K and I have 4 separate controllable zones. The big negatives that I see and worry about are as follows.

1 - I need to buy them on line so there won't really be a warranty. Read the fine print OK, so far my Mr. Slim has been rock solid

2 - Installation is all on me. OK, why did I build a big shop to do restorations if I am afraid of some like this?

3 - 4 separate systems with separate thermostats might be hard to balance

4 - Air movement will be a challenge. Ductless means the air intake and outlet are where the unit is. This is a BIG box so center air flow is going to be a challenge. Thoughts are to assist with shop fans

5 - This is not what these type of systems were designed for so am I thinking crazy since I can't seem to find anyone else who has done something this big with ductless?

I fell for the "professional" installation = warranty/better installation thing myself. After dealing with a dozen companies the most reasonable one sent Larry, Moe, & Curly to do my installation. They had to borrow some of my tools, & had obviously never installed one before. Now I don't know if I should hope I get some value out of the warranty, or just write the installation cost off as a loss. I would have done a better job on my own.

If it's possible I'd consider some ceiling fans for air movement. Shop fans will work, but moving the upper air will mix everything.

If you end up using 4 units you should be able to balance closely simply using placement of the air handlers. Remember, it's a shop area. You're not trying to cool it to 76 deg. & balance it like your house. I had a difficult time explaining to contractors that I was just looking to make WORK more comfortable, & that heat from that work, opening the door, etc. was going to keep it from being a living room environment.

 

[pseudorealityx]

Based on the size, is this a commercial property? If so, what's your plan to meet ventilation code requirements? Because a bunch of ductless splits aren't doing it.

Also, you need to define, "I have a paint booth and need 75 degree temperatures" a little more thoroughly. Do you have an area with some plastic drop clothes, or do you have a 'real' painting booth with massive exhaust?

If you have room for 4 condensing units, and the 'professionals' said 7-8 tons, I'd just use a packaged 7.5 ton packaged air conditioner with 2 compressors and duct it. Or a pair of 4 or 5 ton splits and duct those. I don't either option costing $20k, FWIW. That would at least allow you to get some ventilation air into the space.

With a huge box, you do NOT have 'controllable zones' because you can't confine the cool air to a single area.

If you're really stuck on the Mr. Slim's, get ceiling cassette style and hang them at 10-12' AFF in the center.

 

[theoldwizard1]

You are going to need a whole lot of ceiling fans !

 

[Charles (in GA)]

You are going to need a whole lot of ceiling fans !

Yes, the ceiling fans will be needed to help move the air around, since it is going to stay in the vicinity of the wall mounted mini splits and won't make it to the far side of the 55 ft wide building.

Problem is, as soon as the ceiling fans being circulating the air, that 73K cu/ft I mentioned, suddenly all needs to be cooled.

If you really want to cool the area, you are going to need to do it "right" and use, as others have noted, more conventional A/C or heat pump or A/C and gas furnace units with ducts, like you see in Walmarts or big box stores or other locations with high roofs and open structures. Look UP when you go to the store, or out to eat and see what is there, it isn't mini splits, its ducts with outlets fitted in the sides pointing down at a 45° angle blowing that air throughout the building.

The other issue is, as already noted, what is the paint booth? a real, OSHA approved metal paint booth with lighting, ventilation, filters, etc, or some clear poly suspended from a frame with some box fans drawing air out of it?

Charles

 

[motormitch]

The paint booth is a real OSHA approved system, but is not metal. It is the coolest thing I have ever seen and one of the best kept secrets I have ever seen when it comes to paint technology for space restricted businesses like body shops in cites where space is a premium. It is a PVC fire rate vinyl retractable enclosure that has everything, including the exhaust chamber on casters making it portable to different parts of the shop and saving 80% of the space when not is use and collapsed.

There is a video of the booth in action on thier landing page at www.duroair.com

Here are the ratings
Compliance
CSA SPE-1000 Model Code for the Field Evaluation of Electrical Equipment
NFPA 33 Standard Spray Application using flammable or combustible materials
NFPA 17 Standard for dry chemical extinguishing systems
NFPA 701 Standard methods of fire tests for flame propagation of textiles and films
OHSA O.Reg 851 – 63 Industrial establishments – Ignition or Explosive
OHSA O.Reg 851 -65 Dust – Ignition or Explosive
OHSA O.Reg 213 Construction Projects (5.12 Fire Code – Spray Operation)
OSHA 29CFR – 1910.107 Spray Finishing using flammable and combustible material
OSHA 29CFR – 1910.94 Ventilation
EPA 40CFR – Part 63.11173 Spray Finishing Requirements

 

[DefSport]

The paint booth might require some ventilation even with the filters, which will up your AC capacity significantly.

But if you're just looking to hit high 70's or maybe 80 after running the units a few hours (assuming it's not 100 deg F in there at 2 PM in July and you fire it up) I'd say 6 tons would easily do it if the insulation is the typical steel building stuff at that thickness.

8 tons will cool it down quicker and help keep it from going really far away from the setpoint when you put a big heat load on it (opening the door, pulling in a hot car etc.). It will take at least a few hours to get things cool when it's all hot inside, but I'm guessing you know that. 6 tons will likely run almost flat out on the hotter parts of the year to keep mid 70's, but I still think it'll do it if you let them cool it down in the morning. Remember, you're just trying to slightly drop the temperature of already cooled air, that's why you can get by with much less AC than you'd think with good insulation all around in a large structure. Skimp on insulation and you need huge AC capacity to keep a say 20-25 deg F delta.

 

[pseudorealityx]

The paint booth is a real OSHA approved system, but is not metal. It is the coolest thing I have ever seen and one of the best kept secrets I have ever seen when it comes to paint technology for space restricted businesses like body shops in cites where space is a premium. It is a PVC fire rate vinyl retractable enclosure that has everything, including the exhaust chamber on casters making it portable to different parts of the shop and saving 80% of the space when not is use and collapsed.

There is a video of the booth in action on thier landing page at www.duroair.com

Here are the ratings
Compliance
CSA SPE-1000 Model Code for the Field Evaluation of Electrical Equipment
NFPA 33 Standard Spray Application using flammable or combustible materials
NFPA 17 Standard for dry chemical extinguishing systems
NFPA 701 Standard methods of fire tests for flame propagation of textiles and films
OHSA O.Reg 851 – 63 Industrial establishments – Ignition or Explosive
OHSA O.Reg 851 -65 Dust – Ignition or Explosive
OHSA O.Reg 213 Construction Projects (5.12 Fire Code – Spray Operation)
OSHA 29CFR – 1910.107 Spray Finishing using flammable and combustible material
OSHA 29CFR – 1910.94 Ventilation
EPA 40CFR – Part 63.11173 Spray Finishing Requirements

You know when they're talking about the "exhaust fans" in your video....

Capturing "particulate" is not the problem... it's the vapors. That's why you exhaust the air OUT OF THE BUILDING. IE, you need to provide make up air to counter that. Which means, since you said you need it to be 75 degrees, you need a LOT of air conditioning, and it's expensive air conditioning. It's even more expensive if you're concerned with humidity, which you should be in Austin.

 

[motormitch]

You know when they're talking about the "exhaust fans" in your video....

Capturing "particulate" is not the problem... it's the vapors. That's why you exhaust the air OUT OF THE BUILDING. IE, you need to provide make up air to counter that. Which means, since you said you need it to be 75 degrees, you need a LOT of air conditioning, and it's expensive air conditioning. It's even more expensive if you're concerned with humidity, which you should be in Austin.

I understand and will only be painting a few times a month so I will be able to allow the AC to catch up between coats. I am leaning toward to a more traditional industrial AC. Know I need to understand the different pro and con of a fully packaged system or standard split system.

 

[pseudorealityx]

The paint booth is a real OSHA approved system, but is not metal. It is the coolest thing I have ever seen and one of the best kept secrets I have ever seen when it comes to paint technology for space restricted businesses like body shops in cites where space is a premium. It is a PVC fire rate vinyl retractable enclosure that has everything, including the exhaust chamber on casters making it portable to different parts of the shop and saving 80% of the space when not is use and collapsed.

There is a video of the booth in action on thier landing page at www.duroair.com

Here are the ratings
Compliance
CSA SPE-1000 Model Code for the Field Evaluation of Electrical Equipment
NFPA 33 Standard Spray Application using flammable or combustible materials
NFPA 17 Standard for dry chemical extinguishing systems
NFPA 701 Standard methods of fire tests for flame propagation of textiles and films
OHSA O.Reg 851 – 63 Industrial establishments – Ignition or Explosive
OHSA O.Reg 851 -65 Dust – Ignition or Explosive
OHSA O.Reg 213 Construction Projects (5.12 Fire Code – Spray Operation)
OSHA 29CFR – 1910.107 Spray Finishing using flammable and combustible material
OSHA 29CFR – 1910.94 Ventilation
EPA 40CFR – Part 63.11173 Spray Finishing Requirements

I understand and will only be painting a few times a month so I will be able to allow the AC to catch up between coats. I am leaning toward to a more traditional industrial AC. Know I need to understand the different pro and con of a fully packaged system or standard split system.

Ok, so you don't really need 75 degrees while you're painting. That's what I figured, but you gotta push a bit to get the real answers sometimes.

Packaged unit pros: everything in one place, typically more options available from the factory, less refrigerant volume, economizer is easier to deal with, only 1 electrical feed. If using gas heat, then fewer concerns with venting. Ventilation is easier to handle.

Split system pros: Smaller footprint, allows you to put condensing side/compressors away from where you need air. Smaller penetrations to exterior wall/roof.

If the roof can carry the load, a rooftop on the top of your building with concentric supply/returns would work rather nicely, and from the interior, be a very clean install. To get even better air distribution, use (2) ~4 ton units, at roughly the 1/3 and 2/3 dimensions of the rectangle.

Concentrics are something like this...

http://www.micrometl.com/concentrics.aspx

 

[JakeKohl]

The paint booth is a real OSHA approved system, but is not metal. It is the coolest thing I have ever seen and one of the best kept secrets I have ever seen when it comes to paint technology for space restricted businesses like body shops in cites where space is a premium. It is a PVC fire rate vinyl retractable enclosure that has everything, including the exhaust chamber on casters making it portable to different parts of the shop and saving 80% of the space when not is use and collapsed.

There is a video of the booth in action on thier landing page at www.duroair.com

...

That is a really neat system...but I must admit, I was a little disappointed when the speaker introduced Kelly to "tell us more" and the camera panned over.

 

[motormitch]

That is a really neat system...but I must admit, I was a little disappointed when the speaker introduced Kelly to "tell us more" and the camera panned over.

That's soooo funny because I thought the exact same thing.

 

[whatuusay1]

I vote minisplit! I love mine

 

[motormitch]

Well, It's done. For the main shop I went with two 5-ton packaged units and I went with a a 2 ton dual head ductless system for the finished living space. One head unit for the bathroom and one for the kitchen/living room. I love the whole setup. The living space can be a meat locker on the hottest days and I am able to get the shop to 70 degrees when it is 107 outside.

 

[theoldwizard1]

Well, It's done. For the main shop I went with two 5-ton packaged units and I went with a a 2 ton dual head ductless system for the finished living space. One head unit for the bathroom and one for the kitchen/living room. I love the whole setup. The living space can be a meat locker on the hottest days and I am able to get the shop to 70 degrees when it is 107 outside.

This is the real bonus of multiple mini-splits ! Heat/cooling only the space you need will cut your energy bills.

Curious as to what brand you choose ? Several manufacturers allow multiple interior "heads" (typically 2 or 4) that operate independently.

 

[motormitch]

I went with Mitsubishi Mr. Slim. This is the second time I used them and I can't say enough good things. I love them.....

My outside packaged unit are Goodman and I know that is viewed as cheap, but they are working great and have the same warranty as the premium brands.

 

[WakonTonka]

This Mr. Slim was super easy. The hardest part for me was getting a 3" hole through the wall since I had 4" of rock to go through. This is the process.

1- make a single 3" hole for the lines, drain and power (all pre-bundled together) to pass though out to the outside compressor.

2- screw up a mounting bracket that is super easy and then hang wall unit on bracket

3 - make pad for outside unit and place it on pad

4- wire up the outside power line to a 220V source

5 - connect all lines

6 - put batteries in remote and push button

I'm not kidding. The unit is precharged and ready to go.

Might I add, #5A- pull a vacuum in the lines before releasing the freon