40X80X14 Building AC help

[built408]

New 40x80x14 tall metal building. Has 2" of closed cell spray foam on the roof, and 1" on the walls. Has 3 12x12 insulated doors that have an R value of 20. I have a 200 sq ft office which is part of that which will have a separate mini split. So 3000 sq ft total.

Would a 5 ton unit work or will I need more? I've had ac guys tell me yes, and some say i need 10 tons.

I don't need 70 degrees in the middle of the day, 80 would be just fine. But i'm in Texas where is gets 100+ during the summer.

 

[dcg9381]

40x60x16 in Texas, 4 tons does it for me. My insulation is a little better, but my doors are larger and non-insulated. I accomplish it with 2 x 2 ton ductless systems. For your use, I'd start with 3 (depending on layout of your building).... If you're doing a ducted system, have them run a real load calculation and show you the results. You shouldn't be seeing swings of 5 to 10 tons...And note that a single ducted system is much more size critical.

The "other" thing that comes to mind is how you use the building. Normally, we use ours on weekends and don't keep it cooled 5 out of 7 days. So the HVAC systems need to be able to "catch up" in a few hours...

 

[Black Oak]

In Texas , I'd say you need better insulation , no matter what you decide to do . Just my two cents .

 

[mattlikesbikes]

We just put up 2" CCF on all exterior surface and will still follow up with batts on the exterior walls. That is in addition to a radiant barrier layer between the foam and metal. I can't imagine any less on the walls than 2".

That said, we are in the same boat, weekend place. So if I have to run the units a little longer on those two days a week, so be it.

I would make sure your units have some type of wifi connectivity, so you can turn them on remotely. We had a weekend place with a wifi window unit that we put a geofence on, so when I got within 80 miles of it (so clearly on my way) it would turn on.

 

[built408]

In Texas , I'd say you need better insulation , no matter what you decide to do . Just my two cents .

This is what 5 spray foam companies recommended. What better option would you give?

 

[mattlikesbikes]

This is what 5 spray foam companies recommended. What better option would you give?

All three of my foam companies recommended the full 2" on the walls as well as ceiling.

That said, only one then recommended additional batts in the sunny side wall. The other two thought their 2"CCF would be enough.

I asked about 1.5" on the walls and all three said it just wasn't enough.

This is in the Canyon Lake/San Marcos area.

 

[nadogail]

You will find that more insulation will lower your air conditioning operating costs.

 

[ticklechicken]

4 tons should be enough for your goals. If you're still unsure, you could consider adding 2 separate 2 ton mini splits and trying that out for the summer. If you end up wanting more cooling, you can add another one.

 

[Black Oak]

One inch of closed cell foam for the walls of a metal building , IN TEXAS , I can't believe will be enough . Some BTU's will get thru - warming the space . Go touch the metal on any metal shed near you . It will burn your hand . Do you have the budget to add more insulation ?

 

[jvitez]

Definitely need more wall insulation. Can you add batts? The best would be Roxul mineral wool as it sheds water unlike fibreglass. I'm thinking about your Texas humidity.

 

[Jim greengo]

With those high ceilings I think youd beat a 5 ton system to death.
Are you planning a split/forced air system on mini splits?

 

[PWC Repair]

5 tons will be enough to keep it cool until above 90 outside. A metal 40x80.......in the sun......in Texas........that's 8 tons of cooling bud.

 

[babylou]

I owned a small factory 4000 sf with 15 ft eave in Houston until last year. The machinery produced very little heat since they were cooled with external water chillers. We were insulated and 10.5 tons of mini split AC. In August we wished we had 12 tons.

Get at least 7.5 tons. Prefer 10 tons. There's not that much cost differential to upgrade tonnage. Labor is basically the same and usually half the cost,

 

[Black Oak]

Is this a pole barn or all steel ? I think steps could have been taken on both methods , but would have meant more $$ spent . At this stage , I'd add the "batts" for sure . What is your budget for the AC equipment ?

 

[built408]

This is a steel building. I don't want mini splits. Either a packaged unit or traditional split system. I'm leaning towards 2 4 ton units.

Really don't want to add more insulation. I'd rather spend the money on more a/c.

 

[built408]

Visited a buddy's shop today that is the exact size as mine, except 12' tall. Has 2 un-insulated doors and not sure of size. Building is about 20 years old and has the old chicken wire insulation. He has 1 5 ton unit and it keeps his cool pretty well. He said it its 105 outside, about 80 is as cold as it will get. But thats perfectly fine with me.

 

[Novamania]

I'm in the "more insulation" camp. Not sure what your energy costs are but think about it this way. Right now you have a fixed cost of what insulation will be. Over the years your energy costs will increase. It won't take long for you to recover the insulation cost in reduced energy bills.

 

[jeepxj]

need way more insulation unless you like spending money on electricity forever.