Mini Splits in large pole barn??

[kkinney]

I'm in the process of building a 60'X108'X16'tall pole barn to house my shop and storage for my antique tractor collection. 5" of non-insulated concrete floor. Two insulated man doors. Two insulated overhead doors, 20'X14' and 16'X14'. No windows. Walls and roof have 4" of open cell foam insulation sprayed on house wrap. Metal siding on the inside and outside of walls.
I live in Southern Indiana, where it gets hot and humid in the summer and can be fairly cold in the winter. Is it realistic to heat and cool this building using mini splits? I've been looking at MrCool. How do I calculate the number and size of the units needed?
Thanks.
Keith

 

[dcg9381]

Keith, I've got a smaller building 40x60x16 in Texas. It's cooled by 2 x 24K Daikin units. 2-3" foam insulation. Non-insulated big *** roll up doors (3). Definitely lower insulation levels than yours.

Sure, you can do a 6K building with mini splits. Your building is probably better than mine. The answer to HVAC questions is typically "run a manual J calculation" - but my answer is find similar buildings in similar climates, hopefully with similar insulation and adjust to that design.

We found that single larger mini-splits were more economical than larger multi-head mini-splits. Where you put them DOES matter.

You can definitely cool that building in Indiana with mini-splits. Where I'd use caution is take a look at the cold-weather (below 30) performance of Mr.Cool - many of these units are not worth a **** in cold weather - their BTU capacity drops quickly after 30 degrees - think like half or less the heat capacity they have otherwise. You'll need units designed to function in the cold. We supplement the few very cold days we get with ventless propane (not good for humid climates) as our units are not great in cold weather... So either get hyper heat units or design for supplimental vented heat in the winter.

 

[kkinney]

Keith, I've got a smaller building 40x60x16 in Texas. It's cooled by 2 x 24K Daikin units. 2-3" foam insulation. Non-insulated big *** roll up doors (3). Definitely lower insulation levels than yours.

Sure, you can do a 6K building with mini splits. Your building is probably better than mine. The answer to HVAC questions is typically "run a manual J calculation" - but my answer is find similar buildings in similar climates, hopefully with similar insulation and adjust to that design.

We found that single larger mini-splits were more economical than larger multi-head mini-splits. Where you put them DOES matter.

You can definitely cool that building in Indiana with mini-splits. Where I'd use caution is take a look at the cold-weather (below 30) performance of Mr.Cool - many of these units are not worth a **** in cold weather - their BTU capacity drops quickly after 30 degrees - think like half or less the heat capacity they have otherwise. You'll need units designed to function in the cold. We supplement the few very cold days we get with ventless propane (not good for humid climates) as our units are not great in cold weather... So either get hyper heat units or design for supplimental vented heat in the winter.

Thanks for the reply. I'm not too worried about the heating as much as the cooling. We have a lot of heat days in the mid-90's with 95% humidity. Our really cold days are not that frequent.

I tried to do a J calculation but it was much better suited to a house than a barn.

How do you determine where to place the units?

 

[dcg9381]

How do you determine where to place the units?

They tend to cool the area in front of them best. For us, we had "living space" in our shop - so most of the focused cooling went in that area, even though the entire building is "open". It's not as much of an issue if your building is open and you install large fans to move the air around.

I get that you're mainly concerned about cooling... Trust me, in Texas, that's 98% of my concern. I just wanted you to know that Mr.Cool may perform with a fractional heating capacity when it's really cold (I haven't actually looked at the performance curve) - just be prepared to have supplemental heat if you're using units that don't do great below 30. In 2021 (great freeze) - our building dropped below 50 degrees and we were living in it at the time. Not pleasant. Adding propane solved that problem for us. I just used "portable" 100 lb tanks outside the building... but your climate is colder.

I get it on manual J. There is napkin math. I'm cooling 2400 sqft with 48k in a hotter climate. Scale that out. Honestly, I wasn't sure if we needed 48k or more... So I simply put electrical drops in for additional units in case 2 of them didn't get the job done.

 

[fitter30]

This might help

How Many BTUs Does It Take to Heat a Garage?

Keep scrolling to use our easy & free BTU calculator When a garage is ice-cold in the wintertime, it can be hard on your vehicles and anything else that you store in there. Furthermore, you may want to use that area for a home workshop or laundry room, as an extension of...

www.newair.com

 

[American Locomotive]

Another important factor: What are your target temperatures?

I hope you hoping to keep 76 in the summer, and 62 in the winter? Or 62 in the summer and 76 in the winter?

 

[PoorUB]

This might help

How Many BTUs Does It Take to Heat a Garage?

Keep scrolling to use our easy & free BTU calculator When a garage is ice-cold in the wintertime, it can be hard on your vehicles and anything else that you store in there. Furthermore, you may want to use that area for a home workshop or laundry room, as an extension of...

www.newair.com

That calculator is way off. It tells me I need 75,000 BTU tp heat my shop that heats easily on 45,000 BTU and would most likely heat on 30,000BTU. IMO, it is roughly two times high.

 

[PoorUB]

I ran the numbers quickly and in my opinion you will need around 200,000 BTU to cool it. Of course, to some degree this is a wild *** guess, but I think it is fairly close.

You could always install maybe 150,000 BTU, run it and see what happens and add more units as necessary.

Another thing, it doing multiple units, go with wired remotes. Wireless remotes tend to fight each other.

You might consider the MrCool unit with an air handler and electric heat strips, seems to me it will go to 5 tons. Put in a couple of them, and add a third if necessary.

Keep in mind that you will need "hyper heat" moldels or what ever MrCool calls them to get any heat out of them in below zero temps.

By the way, the fore mentioned calculator says 800,000 BTU, Laughable!

I worked for a company that had a 10,000 sqft building, 16 foot sidewalls and scissor truss roof the peak inside was something like 25 feet. We heated it on North Dakota on 250,000 BTU and cooled it with 25 tons, or 300,000BTU.

 

[kkinney]

Thanks for all the help guys! I did the calculations too, and it also showed 800,000 plus btu's. To get even close would be pushing $25,000. I'm afraid I have champaign tastes on a beer budget.
Keith

 

[mogandave]

I like mini-splits (I have 7 from 12-36K BTU) but if I had a pole-barn or shop I could frame openings in I would just use window/motel units mounted high.

 

[PoorUB]

Thanks for all the help guys! I did the calculations too, and it also showed 800,000 plus btu's. To get even close would be pushing $25,000. I'm afraid I have champaign tastes on a beer budget.
Keith

Trust me, those calculations are about twice of the real world.

I bet three of these would do it.
MrCool Universal

 

[olytdi]

That calculator is on crack...told me I needed 1.5 million BTU for my 36x36 shop.

 

[huggi]

In general 36000 btu systems are made for 1800sf, I'm assuming this is for a house. A pole barn, with ceilings close to twice as high I'd guestimate 36000 btu for ~ 1200sf. If it were me I'd probably run 4 x 36000 btu units with extra wiring if additional units are needed. Looks like the cheapest units on Amazon are about $2200 each (so $8800 for your system)

36000 BTU Mini Split Air Conditioner - Heat Pump - SENL/36CD https://www.amazon.com/dp/B09TCQTV1N/?tag=atomicindus08-20

 

[jblnut]

Y'all may call BS but I kept my farm shop comfortable this past summer with a 5 or 6k el'cheapo window unit from WallyWorld. It ran almost nonstop from noon-midnight but kept it near 70f with low enough humidity that you felt really nice working in there. No sweating just walking from one end to the other like the year prior.

Shop is 54x72x18 and is very well insulated.

Doing some math on the 10f drop in temp that occurs in the 350gal of water in my outdoor boiler in the 10min cycles the in floor pumps run the shop took on average 18,500btus/hr to heat and it averaged 10F with a slight wind today. Maybe my math is wrong

Anywhooooo ..... If it's well insulated just taking the humidity out will help a tremendous amount and it shouldn't take much to heat.

Good luck and post pics of that tractor collection sometime !!

 

[mogandave]

Y'all may call BS but I kept my farm shop comfortable this past summer with a 5 or 6k el'cheapo window unit from WallyWorld. It ran almost nonstop from noon-midnight but kept it near 70f with low enough humidity that you felt really nice working in there. No sweating just walking from one end to the other like the year prior.

Shop is 54x72x18 and is very well insulated.

Doing some math on the 10f drop in temp that occurs in the 350gal of water in my outdoor boiler in the 10min cycles the in floor pumps run the shop took on average 18,500btus/hr to heat and it averaged 10F with a slight wind today. Maybe my math is wrong

Anywhooooo ..... If it's well insulated just taking the humidity out will help a tremendous amount and it shouldn't take much to heat.

Good luck and post pics of that tractor collection sometime !!

Yeah, people love the splits, but they're not really as cost effective as the old "window" units.

There's a reason why most every hotel in the US uses them...

 

[PoorUB]

Y'all may call BS but I kept my farm shop comfortable this past summer with a 5 or 6k el'cheapo window unit from WallyWorld. It ran almost nonstop from noon-midnight but kept it near 70f with low enough humidity that you felt really nice working in there. No sweating just walking from one end to the other like the year prior.

Shop is 54x72x18 and is very well insulated.

Doing some math on the 10f drop in temp that occurs in the 350gal of water in my outdoor boiler in the 10min cycles the in floor pumps run the shop took on average 18,500btus/hr to heat and it averaged 10F with a slight wind today. Maybe my math is wrong

Anywhooooo ..... If it's well insulated just taking the humidity out will help a tremendous amount and it shouldn't take much to heat.

Good luck and post pics of that tractor collection sometime !!

Good insulation does wonders!

I keep harping about heater or air conditioner sizing. People want to heat or cool with 100 BTU per sqft when sometimes as low as 20-25 BTU per sqft will do it.

I am honestly surprised the 6,000 BTU would keep nearly 4,000 sqft cool. Did it actually stay near set point, or did it climb a few degrees but keep the humidity down?

Humidity is the big thing. Often I have been working in the driveway. then decide I need to close up the shop and turn on the AC. A half hour later it is pleasant and I am no longer sweating, but the temp hasn't dropped. An hour later it is nice and cool.

 

[mogandave]

Good insulation does wonders!

I keep harping about heater or air conditioner sizing. People want to heat or cool with 100 BTU per sqft when sometimes as low as 20-25 BTU per sqft will do it.

I am honestly surprised the 6,000 BTU would keep nearly 4,000 sqft cool. Did it actually stay near set point, or did it climb a few degrees but keep the humidity down?

Humidity is the big thing. Often I have been working in the driveway. then decide I need to close up the shop and turn on the AC. A half hour later it is pleasant and I am no longer sweating, but the temp hasn't dropped. An hour later it is nice and cool.

I don't understand people installing multiple mini-splits, particularly the wall units in a big open area. The beauty of splits is that they're ductless. If you have an open area, ducts really aren't much of an issue.

If one really wants mini-splits, the cassettes are much better than wall units in large open areas.

 

[jblnut]

Good insulation does wonders!

I keep harping about heater or air conditioner sizing. People want to heat or cool with 100 BTU per sqft when sometimes as low as 20-25 BTU per sqft will do it.

I am honestly surprised the 6,000 BTU would keep nearly 4,000 sqft cool. Did it actually stay near set point, or did it climb a few degrees but keep the humidity down?

Humidity is the big thing. Often I have been working in the driveway. then decide I need to close up the shop and turn on the AC. A half hour later it is pleasant and I am no longer sweating, but the temp hasn't dropped. An hour later it is nice and cool.

I had a TempStick in there to watch what was going on and the temp would climb a few degrees from noon - dark but the humidity would stay fairly flat. The AC unit only has a Hi/Lo fan settings and a knob that goes 1-6 for temp so I don't known what it was set at for sure but it kept it 70f ish in there.

I ran a dehumidifier the summer prior and it worked sort of but sucked power and created heat. This little AC used 400ish watts when running compared to the 1,100w the dehumidifier used. I even built a nice window plug deal out of that spendy plastic 3/4" plywood stuff so it'd look nice and last forever.

 

[American Locomotive]

Are you trying to keep this place cool and cozy like a museum, or just trying to cut the humidity and take a bit of the edge off? (Like, keep it 76-78 in the summer?)

Yeah, people love the splits, but they're not really as cost effective as the old "window" units.

There's a reason why most every hotel in the US uses them...

They use those PTAC units because they are an extremely cheap way (relatively speaking) to allow per-room temperature control.

There's also a reason why nearly every Hotel also has a system in place that overrides the room thermostat/PTAC unit thermostat after a certain time (usually 11-12 at night) - they're horribly inefficient and absolutely plow power.

 

[75gmck25]

The other reason hotels use PTACs is that they are very quick to swap out. I believe they just unplug it and slide it out of the housing, kind of like a big file drawer.

If a hotel keeps a few spares, maintenance can swap out the unit in just a few minutes. and that room is now back in business.