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Metal bldg A/C setup

jespo27

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Apr 19, 2022
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6
I have a stand alone 30 x 40 metal building with 30 amp service for my rv that I am going to insulate with closed foam insulation. I am trying to determine the best method to install an ac unit. Was looking at stand alone 24k btu solar powered minisplit ac unit or should I do some kind of solar/ inverter/ battery setup? I would not be doing any evening work. So ac at night would not be necessary. I live in Las Vegas, on 5 acres, ground mount prefered and sunlight is abundant. Maybe Will Prowse would like to do a start to finish youtube video? 🤔
 
I have a stand alone 30 x 40 metal building with 30 amp service for my rv that I am going to insulate with closed foam insulation. I am trying to determine the best method to install an ac unit. Was looking at stand alone 24k btu solar powered minisplit ac unit or should I do some kind of solar/ inverter/ battery setup? I would not be doing any evening work. So ac at night would not be necessary. I live in Las Vegas, on 5 acres, ground mount prefered and sunlight is abundant. Maybe Will Prowse would like to do a start to finish youtube video? 🤔
massive temp swings will cause condensation inside anything that cools off... this includes your electronics. i suggest if you are going to cool it down, keep it reasonably cool the whole time.
 
Thanks Bruce, will do as you advise. Hopefully the closed cell foam will mitigate some condensation.
Thanks again
 
What is the night time temperature in Las Vegas? What temperature are you shooting for inside? You might need battery backup for the night time.
 
Night temp in vegas summer can be 95 - 100 degrees. I would not be doing any work in bldg at nite. I also have 30 amp service in bldg .
During day 80 degrees would be a lot better than 95. Possibly a 24k btu run from solar only during day and a 12k btu 110volt to keep temp steady in evening till sun starts powering the 24k btu system? just trying to get some options and suggestions.
Thanks
 
massive temp swings will cause condensation inside anything that cools off...
The dew point in Las Vegas is generally very low. Right now it is 58 F which is close to the max they ever see.

Condensation will not occur until you get below the dew point. If the AC is set to 70 F or higher, condensation in Las Vegas will never be an issue.

This assumes there is no significant source of moisture inside the building (like gardening), open water, etc).

Mike C.
 
thanks... no gardening, open water, fountains :) in bldg. In June, July August hot as hades in Vegas. non insulated bldg , outside temp 110 degrees = 122 degrees inside. that's why shooting 2 inch closed cell foam on entire inside, walls and ceiling. virtually no humidity in Vegas. as they say. it's a dry heat! but hot is HOT. Sig solar has solar mini for around $3k. and 110v mini online for around $800.
 
Night temp in vegas summer can be 95 - 100 degrees. I would not be doing any work in bldg at nite. I also have 30 amp service in bldg .
During day 80 degrees would be a lot better than 95. Possibly a 24k btu run from solar only during day and a 12k btu 110volt to keep temp steady in evening till sun starts powering the 24k btu system? just trying to get some options and suggestions.
Thanks
Having grid power is a big benefit
I think the solar EG4 mini split from Signature Solar is a hybrid, it can automatically run off grid power when the sun is not strong enough or gone completely
 
The 24kbtu utilizes solar and 220v which I do not have at bldg. Would have to run that on only solar and utilize a second 12k btu mini hybrid running on pv and 120v.
Going with inverter and battery that puts out 220v to power the 24k btu hybrid seems mighty expensive. I do not have ability to run a 220v feed to bldg as distance makes that option impractical. I could go inverter 230v/ battery and then just use the single 24k btu mini. but I think the 2 mini splits may be less expensive.
 
outside temp 110 degrees = 122 degrees inside. that's why shooting 2 inch closed cell foam on entire inside, walls and ceiling.
Something to be aware of in metal buildings is that they are often built without any thermal breaks from outside skin to inside structure. You can spray foam on the interior side of the skin, but the girts and purlins will carry the outside heat into the structural metal. This basically bypasses the foam insulation to a large degree.

To add thermal breaks after the fact is usually infeasible. You can spray not only the interior skins, but around the structural parts, but that often doesn't work well, makes the foam easily knock off, and makes attaching things to the building hard. Lastly, you can build an interior skin thermally broken from the structure and then spray on that.

Don't get your hopes up too much for how effective this will be. You might find a foil radiant barrier might do as well as the spray foam for this reason.

You might consider painting the roof and maybe the southern wall as brilliant white as you can.

Mike C.
 
You might consider painting the roof and maybe the southern wall as brilliant white as you can.

Mike C.
this right here is the biggest part of the equation that you can cheaply (relatively speaking) do yourself.

The other one is if it is a new construction, spec insulated steel siding. it already has an insulation layer on the steel and other then the actual protrusions through it (screws, bolts etc.) thermal conduction is much, much lower. (they may not have this in the US, not sure.) here it is a foam layer attached to the steel that you then put in place and the structural steel (girts and purlins) all touches insulation only. only the attachement bolts go through the foam and actually touch the steel siding or roofing.
 
this right here is the biggest part of the equation that you can cheaply (relatively speaking) do yourself.

The other one is if it is a new construction, spec insulated steel siding. it already has an insulation layer on the steel and other then the actual protrusions through it (screws, bolts etc.) thermal conduction is much, much lower. (they may not have this in the US, not sure.) here it is a foam layer attached to the steel that you then put in place and the structural steel (girts and purlins) all touches insulation only. only the attachement bolts go through the foam and actually touch the steel siding or roofing.
This stuff has started to be widely used here for roofing the only issue being most builders have no clue here, so the insulation tends to be left exposed so critters and sunshine slowly eat into it.
 
This stuff has started to be widely used here for roofing the only issue being most builders have no clue here, so the insulation tends to be left exposed so critters and sunshine slowly eat into it.
yeah I have it on the roof of my shop to prevent a bunch of condensation build up in the wet months, but if you use it for a living structure it makes a pretty big difference in transferred heat as well.
 

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