HVAC for 40x60x16 red iron building?

[Codyboy]

Hi. Looking for recommendations and trying to decide on the size of HVAC I'll need.

As the title says, it's a 40x60 with 16' eave height and a 5/12 roof. It's all one big open space except for a small 4x10 shower/ toilet bathroom.
It will be insulated with 2" of closed cell spray foam on the walls and roof.

I thought about a mini split but I didn't think it would distribute the air efficiently.

I'm thinking of an Alpine/Blueridge 48,000 BTU high efficiency heat pump. https://www.alpinehomeair.com/produ...r-handler-complete-systems/blueridge/bmah4816

The guy I talked to at Alpine suggested 8 tons! Sounded like an upsell to me. But I know nothing about HVAC.

I am planning to run a single fabric duct down the middle . The duct sock place recommended a 14" should be sufficient for the 1600 CFM the air handler puts out. It is variable speed also.

I think the biggest problem will be the large rollup doors. Two 14x14 and two 12x14 (insulated). Two man doors and three double pane windows .

The work in the shop will be woodworking, metal working and general auto working. Only me in there and not a full shop full of workers . Just me and my hobbies.

 

[ratflinger]

You need a Manual J to determine the AC size. Contractors spitting numbers are not someone you want to use. There are Manual J programs on the web. For a small fee they are quite accurate.

 

[ericm]

You need a Manual J to determine the AC size. Contractors spitting numbers are not someone you want to use. There are Manual J programs on the web. For a small fee they are quite accurate.

Loadcalc.net has a free one. With some practice I was able to get reasonably close to value the fancy SW the HVAC company doing my new house got. Some of that inaccuracy may have been due to my simplifying the somewhat complex house shape. A shop is a lot simpler shape.

But be sure you put something in every field that is appropriate for your building. It doesn't check. If you miss some the number will be low.

 

[PoorUB]

If you were in North Dakota I would stuff a 100,000 BTU 80% unit heater in that place and not even worry about it.
Texas? You can get by with less as you will never see -20F. I don't thing a 48,000 will cool it on the hot days. Maybe 60,000 BTU for cooling. Maybe put in two 36,000 BTU units. 8 tons? I find that hard to believe!

You could install a 48,000 BTU unit and if it doesn't keep up in the 110F days add another unit, maybe 24,000 - 36,000 BTU.

 

[danski0224]

You need a Manual J to determine the AC size. Contractors spitting numbers are not someone you want to use. There are Manual J programs on the web. For a small fee they are quite accurate.

Blasphemy.

 

[PoorUB]

You need a Manual J to determine the AC size. Contractors spitting numbers are not someone you want to use. There are Manual J programs on the web. For a small fee they are quite accurate.

And if you don't know what you are doing you can get some really crazy numbers. We have seen it here before where a guy builds a 1,000 sqft shop, goes to an online heat loss calculator and comes up with 100,000 BTU to heat it, when 45,000 will do it.

 

[My Old Tools]

My red iron shop is 30x40x12 with 6/12 pitch, 7 large windows, 12x12 insulated door, so about half your size. I put a 36k MrCool in the center of the 40 foot wall. It's overkill. It covers the shop well from 9 feet down, where it's mounted. I have 12 inches of insulation on my roof that helps a lot. It will spend most of the first two days sucking humidity out, then it will just idle along. I would think about a couple of 24-36k mini splits.

 

[Codyboy]

Loadcalc.net has a free one. With some practice I was able to get reasonably close to value the fancy SW the HVAC company doing my new house got. Some of that inaccuracy may have been due to my simplifying the somewhat complex house shape. A shop is a lot simpler shape.

But be sure you put something in every field that is appropriate for your building. It doesn't check. If you miss some the number will be low.

I filled out the info as best I could but no idea if I did correctly.

39467 cooling btu and 44562 btu for heat.

Even reading the directions , two or three times some of it made no sense.
It asked for linear foot of the slab? Well it's a rectangle. I put 60.

2400 sq ft, estimated 48000 for the cu ft. (2400×20)

No selection for metal siding so I used the (siding or stucco selection).

Doors I just went with metal due to the large rollups . The man doors are fiberglass and insulated (no selection for that or to differentiate types of doors)

 

[danski0224]

Linear foot of slab is the perimeter length of the slab on grade.

 

[Codyboy]

Linear foot of slab is the perimeter length of the slab on grade.

Ok gotcha. Changed that to 200. No change on BTUs.
I also increased the cu ft to 55000 from 48000 and it only added about 300 BTUs.

 

[ericm]

I filled out the info as best I could but no idea if I did correctly.

39467 cooling btu and 44562 btu for heat.

Even reading the directions , two or three times some of it made no sense.
It asked for linear foot of the slab? Well it's a rectangle. I put 60.

Linear is around the perimiter. That's 200'. Slabs lose most of their heat around the edges.

2400 sq ft, estimated 48000 for the cu ft. (2400×20)

20 is pretty close. With a 16' wall the peak is 20*(5/12) or 8.33. Divide that in two since it's a triangle, so it'd be 4.16.

No selection for metal siding so I used the (siding or stucco selection).

That's what I think is most appropriate for metal siding too.

Doors I just went with metal due to the large rollups . The man doors are fiberglass and insulated (no selection for that or to differentiate types of doors)

Rollups will be leaky so down grade the building air tightness some.

You set the door type on the first page of the calculator then use those on the second page.

Make sure to save the Manual J result and then run Manual S on it to get the recommended equipment size.

Also adjust the heating and cooling temps to what you think is appropriate. Since I'm usually moving around in the shop it doesn't need to be as warm as the house, and I'm ok with it not being as cool in the summer.

 

[dcg9381]

Hi. Looking for recommendations and trying to decide on the size of HVAC I'll need.

As the title says, it's a 40x60 with 16' eave height and a 5/12 roof. It's all one big open space except for a small 4x10 shower/ toilet bathroom.
It will be insulated with 2" of closed cell spray foam on the walls and roof.

I thought about a mini split but I didn't think it would distribute the air efficiently.

I have a 40x60x14 in the same state.
A big portion of HVAC calc will be how you insulate it.

I use 2 x 24K BTU Daikin mini-splits. You're right that they are pretty "directional". You can get around this by adding a Big *** Fan or similar.

I'd say that 48k is a little "light" in the HVAC department for summer use, but I have R12 insulation (foam).. I have lived in my building for 18 months, so it worked as long as we kept the HVAC on. But if you're only in there "sometimes" and want to bring the temp down, you might want to go with a little more... Those manual J calcs are for residential and assume that you keep the building at temperature. I don't cool my building unless I'm going to be using it.

Ductless are less particular about over-capacity than traditional AC. You could do both.

Main reason I went ductless was that I could install it myself... All in cost under $3k.

Buying seals for the roll up doors will help some, but they are still big *** holes in the building. Hopefully yours are better than mine.. Mine rattle like death traps in the wind.

 

[strength_and_power]

I got nothing to add but I am interested in what you end up doing and how it works out as I have a similar sized shop in Texas as well.
I’ve seen in commercial spaces on long duct runs, the duct size reduces the further out it is, may be something to think about/ look into. Adding some fans to keep the air stirred up may of benefit as well.

 

[My Old Tools]

Even though the ductless minis are directional, it surprised me how comfortable the shop was even outside the flow area. The cool air spreads along the floor and the warm humid air gets sucked in up high. It creates a natural circulation. Just like in a house, you don't need to stand under a duct. The air will stratify at the level of the unit. That's a good thing as you don't need to condition the entire volume of air. My loft area stays pretty warm in the summer, but not hot. In winter, I uee a fan the drive the heat down. For me, getting the humidity out was the biggest benefit.

 

[Codyboy]

I got nothing to add but I am interested in what you end up doing and how it works out as I have a similar sized shop in Texas as well.
I’ve seen in commercial spaces on long duct runs, the duct size reduces the further out it is, may be something to think about/ look into. Adding some fans to keep the air stirred up may of benefit as well.

I will be installing this myself. I will have to get a tech to braze the lines and evacuate them.
I wasn't going to have to braze the line set on the one i linked in the OP. But they ran out of that model for the air handler which had flared fittings.
So they set me up with the same evaporator but the blower is a goodman unit and I had to piece them together.
This evaporator doesn't have the flared fittings and neither does the lineset they sent.

I am going to hang the AH on the wall about 10ft to the bottom (ought to be fun). This is so when I build the loft area it will already be in place.

I think the 48000 btu will be fine except for the most extreme days .

 

[BurtEggley]

it isn't just the temperature. Air exchange to the outside can be a big one. If you were in coastal San Diego, you would need very little AC, in SE Texas you need to remove water from the air when the humidity in summer is 90%. But if you are comfortable at 80F and just a little lower humidity, a smaller AC is needed than if you want to be 74F and 45% humidity. You have the foot print of a 4800 sq ft home. Meaning, with 16' ceilings, and not inner walls, you have as much or more cubic air feet as a 2400 sq ft house - although your walls and roof are the same as a 2400 sq ft house more or less. Here, when it is 106F+ it takes 3 tons to keep up with the heat coming into this 1400 sq ft house. Making matters worse, we have time of day pricing so we have to super cool the house before the higher priced power that comes in the late afternoon, right at a time when heat soak is coming thru the walls and ceilings. More insulation here just delays the heat soak when we are that hot because it will be 100F sometimes still at midnight. My instinct, based on my parents living on the gulf, and my family being southern in ancestry, tells me that while the 8 ton suggestion probably was a bit high, the guy may have guessed you'd open the big doors, and then want the temp and humidity back down for the benefit of the shop equipment. It is also going to depend on how many lights are on in that shop during the day, how much equipment is running, how many times you go in and out the door(s), and if you have skylights etc.. If you just Google how many tons do I need for commercial shop space, it will tell you that the industry rule of thumb is one ton per 400- 600 square feet. You 2400 \ 400 is six tons. The guy may have been thinking that with two four ton systems you could run one most of the time, and the second one would only come on if needed, where with two three ton units both would be running most of the time.

 

[Donka22]

Hi. Looking for recommendations and trying to decide on the size of HVAC I'll need.

As the title says, it's a 40x60 with 16' eave height and a 5/12 roof. It's all one big open space except for a small 4x10 shower/ toilet bathroom.
It will be insulated with 2" of closed cell spray foam on the walls and roof.

I thought about a mini split but I didn't think it would distribute the air efficiently.

I'm thinking of an Alpine/Blueridge 48,000 BTU high efficiency heat pump. https://www.alpinehomeair.com/produ...r-handler-complete-systems/blueridge/bmah4816

The guy I talked to at Alpine suggested 8 tons! Sounded like an upsell to me. But I know nothing about HVAC.

I am planning to run a single fabric duct down the middle . The duct sock place recommended a 14" should be sufficient for the 1600 CFM the air handler puts out. It is variable speed also.

I think the biggest problem will be the large rollup doors. Two 14x14 and two 12x14 (insulated). Two man doors and three double pane windows .

The work in the shop will be woodworking, metal working and general auto working. Only me in there and not a full shop full of workers . Just me and my hobbies.

May be worth your while to pay an Civil Engineer a fee to determine the heat load of your building. There is Roof, Wall insulation calcs (R-?) , Air infiltration, Floor heat loss/ load. Slab infiltration. South facing glass, windows, Doors, Etc. All of this stuff adds up, and ive seen ,even home builders guess wrong and undersize the HVAC and forever pay for remediation,. Thats worse case. 2" spray foam may not be enough, is it about R6? 2400 square feet will need about 5 tons.

There is a online tool used by architects and Civil Permit offices called Comcheck. Its on the IBC building code site somewhere. You can get R values and Get a CLF (Constant Load Factor) for the building. This is all geared toward a HOME or commercial building , you are not living in the garage, Er. or are you? You can still get a estimate of the BTUs needed to Heat and cool, and go from there.

I have Building Code and HVAC Engineering experience, but just not Civil. I do not think a Mini split would work well. They are for compact areas, and dont have the airflow. A split system and gas furnace would be a better setup.

 

[Donka22]

I filled out the info as best I could but no idea if I did correctly.

39467 cooling btu and 44562 btu for heat.

Even reading the directions , two or three times some of it made no sense.
It asked for linear foot of the slab? Well it's a rectangle. I put 60.

2400 sq ft, estimated 48000 for the cu ft. (2400×20)

No selection for metal siding so I used the (siding or stucco selection).

Doors I just went with metal due to the large rollups . The man doors are fiberglass and insulated (no selection for that or to differentiate types of doors)

This is handy. Ive have experience with IBC code compliance, and a few things are missed in the selections. The Construction of "tight" isnt the best for a metal shop. This means air infiltration, ex: a home has masonry, or siding, fiberglass R-13, vapor barrier, sheathing and then drywall and sealer/paint. A metal wall will leak air. The slab "perimeter" is for slab infiltration loss. The biggies are the roll ups. Wood roll up doors will be better , tighter seams, but still have leakage. Also need U-factor for windows, penetrations, vents, and non insulated areas over a few s.f. , they add up. Not to mention equipment (motor) heat loss (3.41 btu/watt), how musch is in there? Im guessing minimum 5 tons w/forced air ventilation.