Mini Splits in a large shop???

[Rob7181]

Not new, just been lurking for years!

Anyone using mini-split system in a large shop?

I have a 40x100x18 shop that I am thinking of putting mini-split system in.

I am looking to keep it 50-55* during the winter and knock some humidity down and keep it 78-80* in the summer. My last shop was 40x80x18 and I used older oil furnaces and they did ok, but with new inverter and hyper heat technology, I wanted to consider other options this time.

Thoughts/opinions are welcome.

 

[MrBalll]

That's a lot of shop for a mini split. I have a 30 x 25 x 14 and have a mini split. It does OK. I only ever turn it on hours before I plan to be in the garage and it keeps it comfortable enough for me.

I'd think with that size, and if it's not split into sections at all, you need at least three or four mini split units and maybe some portable units scattered around. But hopefully the experts will chime in and give better info to you.

 

[dsimatt]

I'd think you would need at least 3 units to come close to what you want, ducting would work a lot better imo.

 

[theoldwizard1]

First, where are you located ?
Second, what kind of building, how many windows, single/double glazed and what kind of insulation in the walls and ceiling ? Is this all one room ?

No first hand experience on that large of a building, but with a building that large I would recommend 2 mini-splits with 3 or possibly 4 interior units. One compressor would be installed along each of the long sides, in the center, feeding the interior units. They all can be slaved to one thermostat.

 

[justinjoyal]

You would need several units, and I have not seen mini-splits that you can set lower than ~62 degrees.

I would go with a ducted split system. Better air distribution, better filtration as well. More suited for a large shop.

You could also consider a rooftop unit.

 

[Rob7181]

The interior is totally finished. R-21 in the walls, with 3/4" plywood up 8' and white metal from 8'-18'. White metal ceiling with R-38 blown in. 8 double insulated windows, 6 on the southern facing 100' wall mounted at 12' up and 2 on the eastern facing wall at the same height.

I have 4 60" paddle fans down the center for pushing whatever heat back down and 2 3600 CFM louvered whole house fans in ceiling for helping to remove heat in the summer. Shop has 350 amps of dedicated electric service.

Have a tall motorhome and trailer down the northern side of the shop and a lift in the front of the southern wall.

I am fine with putting 4-5 interior units and 1 or 2 outside units in. Just wondering would they work well and would they eat me out of house and home with the electric bills.

 

[firebirdparts]

Climate is important. Pumping heat works well in North Carolina and not well in North Dakota.

 

[theoldwizard1]

You would need several units, and I have not seen mini-splits that you can set lower than ~62 degrees.

Not true ! Mitsubishi HyperHeat (and others) work down to below 0F !

I would go with a ducted split system. Better air distribution, better filtration as well. More suited for a large shop.

Ducting adds money and reduces efficiency. With multiple air handlers mounted on each wall distribution won't be a problem. About the only thing mini-splits don't do well is filter the air.

 

[theoldwizard1]

I am fine with putting 4-5 interior units and 1 or 2 outside units in. Just wondering would they work well and would they eat me out of house and home with the electric bills.

40' wide, you might need 3 on each side ! Actually, with all those fans, 2 on each side might be adequate.

Mini-split are probably the LOWEST cost of operation of any heating/cooling solution especially in the 30F-90F range. Mitsubishi HyperHeat efficiency does start to drop off around 10F, but it still makes heat !

Bonus. the interior air handlers can be installed with minimal disturbance to the interior walls.

 

[theoldwizard1]

Climate is important. Pumping heat works well in North Carolina and not well in North Dakota.

At -10F or -20F I sure would want a secondary heat source. Preferably one that could be run on a different fuel plus a small/medium size generator.

 

[justinjoyal]

Not true ! Mitsubishi HyperHeat (and others) work down to below 0F !





Ducting adds money and reduces efficiency. With multiple air handlers mounted on each wall distribution won't be a problem. About the only thing mini-splits don't do well is filter the air.

I think you got me wrong.

Im referring to the indoor temperature set point by the user, not the outside temp!

Ducting does reduce efficiency and cost money, but 3-4 heads also cost money, and then you have to keem them running good (clean filters, clean condensers, clean blowers, etc.)

One large heatpump with a matched air handler/coil will perform very well and require less maintenance. Better filtration as well.

 

[ticklechicken]

Based on your good insulation and desire to only cool to 78-80°, I think you could get by with as little as 72k BTU of cooling. For your needs, the larger version of my system would work. For each of your 100' walls, I'd use a 3-zone outside unit which would drive three 12k indoor units. This is a really cheap option that will probably do what you want. Since you have the large ceiling fans, I think you can get by with only six indoor units.

I've never used mine for heating, so I don't know if it will meet your needs.

 

[dsimatt]

If you have access to NG then I'd say it's no brainer to go that route ducted, I love my mini split but unless it was the only option to put in your shop I'd go with something else.

 

[Rob7181]

Currently do not have any NG, Propane or oil on site. I am open to all options. Just seems that Mini Split efficiency is the cats meow and I would like to use that to my advantage.

 

[theoldwizard1]

If you have access to NG then I'd say it's no brainer to go that route ducted, I love my mini split but unless it was the only option to put in your shop I'd go with something else.

If you don't want A/C and you have NG at the building then I would agree with you.

 

[navycryppie]

My brother-in-law has a similar setup, still under construction. 40X74X16, fully finished on the inside, and is putting in two 3 ton (36K) mini splits this week. Won't have actual use data for a bit (no doors on yet), but that sizing was based on Pacific NW river valley climate and should keep it comfortable year round.

 

[Jackfre]

Not new, just been lurking for years!

Anyone using mini-split system in a large shop?

I have a 40x100x18 shop that I am thinking of putting mini-split system in.

I am looking to keep it 50-55* during the winter and knock some humidity down and keep it 78-80* in the summer. My last shop was 40x80x18 and I used older oil furnaces and they did ok, but with new inverter and hyper heat technology, I wanted to consider other options this time.

Thoughts/opinions are welcome.

Where do you live. With oil I am assuming the Greater Northeast. For 4000 with 18' ceilings the questions...how is this space to be used. Are large overhead doors opened/closed frequently? How is your insulation? Standard commercial sizing for cooling is 400 sq ft/ ton. In the NE residentially, I would regularly go to 600-700 sq ft/ton. Given the amount of cubes you may need some fans to push the heat down. As a guess, for that space I start with 4-36's. You could go hi-wall or suspended ceiling units.

 

[stm317]

Sounds like you'll end up with several pretty large units. I'm not an expert or industry insider, so this may be wrong, but I'm seeing prices around $2k per unit. I think you'll have 10k into mini splits, plus installation and they might still struggle with that much volume. I'd definitely run numbers compared to a traditional furnace/heat pump that would likely perform better, or at least give you the flexibility to set a wider range of temps.

 

[Rob7181]

Where do you live. With oil I am assuming the Greater Northeast. For 4000 with 18' ceilings the questions...how is this space to be used. Are large overhead doors opened/closed frequently? How is your insulation? Standard commercial sizing for cooling is 400 sq ft/ ton. In the NE residentially, I would regularly go to 600-700 sq ft/ton. Given the amount of cubes you may need some fans to push the heat down. As a guess, for that space I start with 4-36's. You could go hi-wall or suspended ceiling units.

I am in southern Maryland. The shop is for working on race cars and storing my motorhome and trailers. Two large overheads, each 16’x14’ that will not be opened often. Insulation is R-21 bats in the walls and R-38 blown above the metal ceiling liner.

Couple places I have talked to have suggested 60,000 btu multizone outdoor units with 3x24k indoor units.

Thoughts?

 

[terabitdan]

According to this calculator https://ag.purdue.edu/extension/renewable-energy/Documents/ON-Farm/heatcalc.xls only NG is a cheaper option to heat your shop than a mini-split.

$/MM BTU for NG @78% is $9.20, heat pump with a COP of 2.7 is $14.81, fuel oil is $37.17, electric resistance is $39.68 and propane $41.17.

From what I can see, smaller mini-splits have higher efficiency, I used a 48k unit specifications at 15 deg F, but more efficient units are readily available.




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[theoldwizard1]

According to this calculator https://ag.purdue.edu/extension/renewable-energy/Documents/ON-Farm/heatcalc.xls only NG is a cheaper option to heat your shop than a mini-split.

Nice to see formal confirmation of what I have always said !

Bonus with any heat pump is it also does cooling (A/C).

 

[dsimatt]

If you don't want A/C and you have NG at the building then I would agree with you.

There are a lot of variables we don't know but up by us heat is a necessity and AC is a luxury, also if there is going to be a lot of dust from working in there I wouldn't want to put the expensive head units in there.

I would put a mini split in my garage but if the OP goes that route in his shop I'll be interested to hear how well it works for him.

 

[Rob7181]

I hate to take a $10K gamble on it working.

I am glad to see efficiency wise, that it's a smart choice. No NG near me, so that is not even an option.

The environment is not what I would consider a dusty/dirty environment. Occasional welding, cutting with a torch or cutoff wheel. I will try to make a conscious effort to keep dusty tasks outside.

I have spoken to several contractors and they have offered two solutions:

One is to put a 60,000BTU muli-zone outdoor unit and three 24,000BTU wall units in.

The other option is two 36,000BTU outdoor units with one indoor 36,000 unit per outdoor.

Which would you do and why?

 

[Radix2]

You have not commented on the point made above about inside temperature setpoint.

My Gree hyperheat style unit can only be set down to 61degrees minimum for heat. If this is not acceptable, be sure to verify that any units you are looking at can be set to maintain heat at tge 50-55 degrees you want.

The 61 degree limit is the only thing I don't like about my unit since it is in a building that is not used all the time. The instruction manual talks about a lower setpoint being possible, but the software in the unit I have does not support it. So I don't know if it is an across the board limitation for these minisplits or not. Also I assume you will want a hyperheat style unit to make sure it does well under winter conditions in MD.

 

[Rob7181]

I will check and see if the models specified go below 61*. With the efficiency that much better than oil (which I am used to) maybe I can afford to keep it 61* as long as I keep my paddle fans blowing the heat down from the ceiling.

Several contractors have indicated I did not need the hyper heat option????

 

[terabitdan]

I plugged your shop size into my heat loss calculator. Obviously this is just a swag. In Maryland the design temp is 15 deg, so rise is 61-15 or 48 deg. Uninsulated floor with 8 tight windows and one large garage door. That’s probably understating your actual.

But you would need 42000 BTUh based on those assumptions. If it drops to 5 deg outside and you only get to 50 deg inside, seems like that’s not a problem.

Of course, A/C may need more or less.

3 indoor units will give better distribution in the shop, and can be staggered with the right controls. They also provide a lower minimum heat output.


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[dsimatt]

I understand the cost risk, I figured the prices would be a lot more than $10k for the systems you have been talking about.

Myself I do like redundancy so of the 2 options you have stated would go with the 2 separate mini splits over the single outdoor unit so if one breaks then you have the other to try to limp along. I was looking around the shop at work today and it is somewhat similar sized to what you have and just don't think i'd be confident in having 2 head units trying to control temps in there.

My mini split in my house is a hyper heat model, the guy said for around here the normal one would do ok except for when it got really cold but again with redundancy if my main heat is going to go out chances are it will be during one of the coldest days when its working the most.

I guess it comes down to how cold does it normally get to by you, will you have stuff stored there that can't freeze without damage so that you need the capabilities of heating even in extreme cold....having the hyper heat is nice but it comes with a pretty good price jump.

 

[ticklechicken]

I understand the cost risk, I figured the prices would be a lot more than $10k for the systems you have been talking about.

Myself I do like redundancy so of the 2 options you have stated would go with the 2 separate mini splits over the single outdoor unit so if one breaks then you have the other to try to limp along. I was looking around the shop at work today and it is somewhat similar sized to what you have and just don't think i'd be confident in having 2 head units trying to control temps in there.

The system I recommended was about $4500 total. It has two outside units so it's redundant. With 6 interior heads, it would equalize temps throughout the shop.

 

[Rob7181]

I like the redundancy. What brand are you using/suggesting? How big of a building are you using your system in? I see you are in Florida, what temp are you cooling it to and how bad of an electric bill are you experiencing in the summer with them.

 

[dsimatt]

The system I recommended was about $4500 total. It has two outside units so it's redundant. With 6 interior heads, it would equalize temps throughout the shop.

What brand is that, I'm running mitsubishi hyper heat so I know it cost is pretty the highest of all the brands.

I agree 6 units would do a lot better job then just 2 big heads, my question is even as efficient as they are how many can you run before you are less efficient than say a normal system?

 

[PurdueSD]

I just put put a 5 ton Bryant multi unit in my new shop. It has 2 2ton heads in the 42x60 portion on the 60 foot wall. I have another 1 ton head unit in the lean to. Im impressed so far. The 62 degree min was a surprise that the damn HVAC company kinda screwed me on. I told em i wanted to keep the shop 55/60 and they said no prob. Its ok though, i'm still happy. its only been down to about 30 here so far, but circulation has been fine even with my glass OHDs. I cant comment on how they'll be in the colder months, but the efficient down past 0 degrees and no strip heat was a big plus for me since i'm all electric. Theres more pics in my build thread if you're interested.

My building is really airtight, r19 walls r50 ceiling and 1.5 foam under slab. My glass is insulated but theres a bunch of it.

View media item 75003

 

[Jackfre]

Given the build quality I would start with two 3 ton units. One of the advantages of the mini-splits is that you can add easily as you define the hot or cold spots. You are in a fairly moderate climate and while your design temp is 15* typical weather is at design temp less than 1/2 of 1% of the hours requiring heat. So...what type race cars are you working on?

 

[ticklechicken]

I like the redundancy. What brand are you using/suggesting? How big of a building are you using your system in? I see you are in Florida, what temp are you cooling it to and how bad of an electric bill are you experiencing in the summer with them.

What brand is that, I'm running mitsubishi hyper heat so I know it cost is pretty the highest of all the brands.

I agree 6 units would do a lot better job then just 2 big heads, my question is even as efficient as they are how many can you run before you are less efficient than say a normal system?

My suggestion was in post #12. I'll copy it here:

Based on your good insulation and desire to only cool to 78-80°, I think you could get by with as little as 72k BTU of cooling. For your needs, the larger version of my system would work. For each of your 100' walls, I'd use a 3-zone outside unit which would drive three 12k indoor units. This is a really cheap option that will probably do what you want. Since you have the large ceiling fans, I think you can get by with only six indoor units.

I've never used mine for heating, so I don't know if it will meet your needs.

I only run my mini splits a few nights a week and most of the weekend, so I don't have a good cost estimate. My shop is on it's own meter and the bill is $20-$24 per month. The a/c can't cost that much.

 

[pcampbell]

4000 sq ft... and how much insulation?

I use a single mini split Fujitsu 15RLS3H to heat my 1800 sq ft house, but it is well insulated.

 

[Rob7181]

Perdue,

Awesome build thread. I think we may be brothers from another mother, as you would be surprised at the similarities of our buildings. I am not sure where you are but my current motorhome came from a buddy in New Palestine, IN.

My last was 40x80x18 with a 15’ liento down the 80’ side. 2 14tx16w rollups on opposing gable ends (pull through) Liento was open to allow me to pull four tractors and backhoe in and out easily.

The new one is 40x104x18 with the same size doors. This time with high bay track. The 15’ liento runs the 104’ length, but I put 4 14’ sliders, one on each end and two 32’ from each end wall on the sides.

Insulation is R-21 in the walls, R-38 blown in the ceiling and the doors as I said are R-19.

Wish I knew how to post a pic. Use to use photobucket, now what?

Race cars now are a low 7 second dragster and a high 7 second tube chassis 85 Camaro.

 

[Rob7181]

Well the cost estimates have come in. The best one so far is 3 30k BTU Mitsubishi M series units installed for $11.5k.

Good deal? Will they work and do what I want?

 

[handymancanfixit]

I have a 30x50x10 stick built garage with 3 garage doors, 2 walk doors and 4 windows. I installed a MrCool 36k DIY heat pump system and could not be happier. Cool in the summer and warm in the winter and the cost is very low.