A/C and heat suggestions needed

[tallfreak]

I am located in Memphis, TN and I just finished my 40x60x12 pole barn and had 2 inches of closed cell foam sprayed on all walls and roof. I have no windows and 1 12x12 RUD insulated with 2 layers of mylar and bubble insulation and 1 walk door. Both doors face south. The shop is fairly well shaded on the east and west.

I will have 4 ceiling fans to help bring the heat back down in the winter. I am planning on having a full size fridge and probably a chest freezer at some point. I will occasionally be running a car inside the shop and I am building an exhaust extraction system to connect to the tailpipe. I'm not sure what cfm yet.

I want to be able to leave the ac set to 80 in the summer and probably 50 in the winter and turn it on about 30 minutes before I am going to be in there to get it comfortable.

I have talked to several locals about it. My building contractor said 2 ton ac would be plenty, my insulation guy said no more than 4 ton, and the place that boards my dogs uses a 40x40x14 steel building with vinyl backed fiberglass insulation (I think r-10) with a 4 ton unit. It stays cold in there even with 30+ barking dogs. The owner works in the commercial ac business and said I need 7 tons.

I was planning on getting a Goodman packaged unit 5 ton heat pump, but if my insulation guy is right it wont run long enough to pull the humidity out.

We get maybe 2 weeks of 20 degree weather in the worst winters. I dont mind having to supplement with a propane or other fuel heater a few nights a year, but I dont want to run a gas line to the shop unless absolutely necessary.

I have tried several online calculators, but they aren't designed for a workshop. But they tell me about 4.5 tons.

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[tallfreak]

Or should I go with mini splits?

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[fitter30]

Package unit- seer is 13/14 would need either a metal or fabric supply duct to distribute the air. Minis would have have two systems, would have extra expense of wiring two units, more efficient 18+ seer, tighter temperature / humidity control do to the variable refrigerant compressors. Minis negatives units get dirty quicker because their filters are not that good and harder to clean. No heat during defrost mode. Be sure to check with your electric company for any rebates

 

[LS6 Tommy]

Mini splits for 2400 square with a 12' ceiling? 2 tons? No way. I'm at 1.5 tons for just the first floor (>900 square feet) of my Cape Cod, in a much cooler climate. You're looking at probably between 4.5 and 6 tons. Mini splits aren't going to be as comfortable as a package unit. They don't move anywhere as much air nor do they distribute it anywhere near as evenly as a package unit.

Tommy

 

[MUDFORD]

If you were to get a Goodman 5 ton, Get the square (M) series. It's 2 stages of cooling and heating even in the basic 14 seer. You can have it run a 67% for 10 minutes before it kicks into high.

 

[tallfreak]

I like the efficiency of mini split systems for sure. I am doing the electrical and install myself and I dont mind a little maintenance. Its not a wood shop so at least I wont have that much dust. How many cfm does a typical 2 ton mini split run? I cant find any specs.

It doesnt have to be a packaged unit either, but I'd prefer to not have a split system hanging from my ceiling.

I have checked on the rebates. $100 per ton on >16 seer and $125 per ton on >18 seer.

$550 >15 seer, $750 >16 seer, and $1000 on >18 seer central heat pumps. The problem is packaged units are about 14 seer.

I am leaning towards 2 4 ton 20.5 seer mini splits one on each end of the shop. Its sealed very well and I have fans to bring the heat down off the ceiling.

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[LS6 Tommy]

2T in a high ambient area like Tennesse would probably be around 1000 CFM. A typical 2T minisplit moves about 600 CFM.

Tommy

 

[tallfreak]

How many cfm is recommended for my application?

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[LS6 Tommy]

How many cfm is recommended for my application?

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It doesn't go by "application". Rule of thumb is 400 CFM/ton residential, 500 CFM/ton commercial or high ambient location. I personally would consider a garage a commercial app.

The best thing you could do before getting quotes is have Manual J load calculation done. That would avoid ridiculous guesses of two tons, like your one contractor gave you.

If you did the (2) 4T mini splits, would you get 4 zone (4 indoor units for each 4T outdoor unit) systems? That may work pretty well, but would involve a lot of piping and use a lot of wall space.
Tommy

 

[HotrodHR]

It doesn't go by "application". Rule of thumb is 400 CFM/ton residential, 500 CFM/ton commercial or high ambient location. I personally would consider a garage a commercial app.

The best thing you could do before getting quotes is have Manual J load calculation done. That would avoid ridiculous guesses of two tons, like your one contractor gave you.

If you did the (2) 4T mini splits, would you get 4 zone (4 indoor units for each 4T outdoor unit) systems? That may work pretty well, but would involve a lot of piping and use a lot of wall space.
Tommy

You mention "a lot of piping and wall space." Compared to HVAC heat pump system I would not consider that "a lot." I probably say it's about the same amount of work... mini split- exterior units connected via line sets to interior units, plus dedicated power or traditional units connected air handler, dedicated power, plus ducting.

 

[LS6 Tommy]

You mention "a lot of piping and wall space." Compared to HVAC heat pump system I would not consider that "a lot." I probably say it's about the same amount of work... mini split- exterior units connected via line sets to interior units, plus dedicated power or traditional units connected air handler, dedicated power, plus ducting.

(2) four zone mini splits have (8) wall mounted indoor units, (7) more sets of piping and electric than a regular split system and (8) times the piping of a package unit. They all need dedicated power. None of them "plug in".

Tommy

 

[tallfreak]

I ran 2 free load calculations with free programs and got about the same each time.

45k heating btu
28k cooling btu
0.804 SHR
1000 cfm

I'm thinking for as cheap as mini splits are I can get 2 2ton single zone units and if I need more I can get another one and still be cheaper than 5 ton packaged unit.



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