Is 5 ton a/c enough for me?

[Dave Carney]

I have 2000 square feet, 14 foot ceilings, but at any one time, no more than 1575 square feet would be climate controlled, due to an insulated interior room that I can close off. Ceiling will be r44, walls will be R19. Interior walls and ceiling will be steel. Three 12x12 insulated overhead doors, 2 insulated service doors, two insulated glass windows.

It gets hot here....today 108 tomorrow 110, but most years we have 10 days or so over 100. I want enough performance to take the interior temp down from hot (110 - 116 degrees) down to 75 in no more than two hours. This may be an unrealistic goal, given a heat soaked concrete slab, etc, I'm not sure. I don't have 3 phase power so this limits me, I think, to a 5 ton max unit or using 2 units, which I really don't want to do. The insulation is not done yet but that's the next step. If a radiant barrier would make enough difference, I could do that but, i'm not interested if it's not cost effective. Looking for ideas. I'm thinking the 5 ton will not be enough.

 

[W-Cummins]

1500 sq ft, and 5 tons, well insulated are you trying to make a meat locker??

I have 5 tons in my building and it knocks about 20 deg off ( about 3x the whole volume of yours)


BTW I like the foil stuff and have it in my roof. I think it really helps cut the heat transfer. I don't think it helps much in the winter but it cuts the heat from the roof.
William...

 

[Dave Carney]

Thanks, not a meat locker necessarily but I do want to effectivley handle the big delta, 30-40 degrees change or so in relatively short order....right now, I have a 4 ton unit in my home, which is about 1900 sq ft plus a full basement, and this week, which is incredibly hot.... it runs non stop from about noon to 10pm, just to maintain the 75 degrees, and the house has 40% 10' ceilings, and 60% 8' ceilings, R38, R19, low e windows.

Did you put your foil stuff right up against the roofing? I keep getting conflicting reports on where to install it. I have a metal roof so I don't have to worry about roofing material getting too hot.

 

[W-Cummins]

Sounds like the 4 tons for you house is sized just right. It's cooling about 3800 sq feet, and on the hotest days runs full out to do it. The problem with over sizing the unit is that yes it will cool it off fast ( good) but then it will short cycle (Bad).

I have the foil (double bubble, double foil) right up under the steel. The only thing I did to install it was poke 1000's of holes in it with the "perforator 2003 <TM>" ( took about 25, 2 3/4" nails and sharpened them on the grinder and then installed them in slightly under sized drilled holes in a 2x2 and attached a "T" handle to it). Then after the fiberglass insulation was put down, and the foil over placed it. I went along and poked the holes in the foil so that moisture could pass through, and I would have only one vapor barrier.

William...

 

[neblinc]

So did you put unfaced insulation against the steel, then the foil stuff or vice versa?
I need to decide on how I am going to insulate my shop.

In your build thread it looks like you have a white blanket type insulation and then a second layer?

Randy

 

[W-Cummins]

So did you put unfaced insulation against the steel, then the foil stuff or vice versa?
I need to decide on how I am going to insulate my shop.

In your build thread it looks like you have a white blanket type insulation and then a second layer?

Randy

not to hijack the thread but

The package from top to bottom (so far)
(big part of the shop)
steel, foil, 4" fiberglass r-13 wmp-50 faced
(Small part )
Steel, Foil, 4" fiberglass wmp-50, 8.5" R-25 unfaced, steel liner panel

William....

 

[Dave Carney]

No way. Can't afford to heat and cool it even to that temp when it's not being used. Seems like a complete waste of money and an invitation for pests. It's essentially a weekend shop until retirement. But I would like to be able to handle the big delta for those unexpected times.

With 3 12x12 overhead doors (R4), and the pole type construction, I'm thinking 5 tons won't be anywhere close to too much. I'll have a load calc done but because I'm watching for deals now, it's important just to know whether or not 5 tons is enough, because if it isn't, that changes everything. $$$$$$