Hvac for new shop... any ideas?

[Jared1982]

I’m in the process of putting the finishing touches on my new shop. It’s 40x64x12.5 tall pole barn with 6-8” of open cell foam in the walls and about 8” on the roof deck. My question is what size of heat pump do I need to heat and cool this building? I don’t want it over sized as it would short cycle during the summer months and no dehumidify . Any ideas? Thanks


Sent from my iPhone using Tapatalk

 

[Balor]

https://www.theseverngroup.com/how-to-size-your-hvac-unit/

 

[theoldwizard1]

... open cell foam ...

Open cell foam is also called a sponge ! It will hold water. If it hold water, it can mold.

 

[ericm]

https://www.theseverngroup.com/how-to-size-your-hvac-unit/

They really want to sell big air conditioners don't they! That calculator says I need a 9 ton AC for my house. It's hitting the target temps with a 3 ton. The 4.5 ton before it was too big.

 

[Jim greengo]

I'd say somewhere between 5-6 tons without seeing your building.

 

[SeniorCitizen]

Being warm air rises, with 12.5 walls, I believe you'll find the shop much easier to cool than heat.

 

[bdog]

I just installed a 5 ton in my 50x50x14 and it works great on heating it. It will be a few months before I can say how the cooling performs.

 

[kj_mustang]

Only way to know is with a Manual J calculation. Windows, doors amount of insulation, ceilings all affect what a building needs. I had a couple HVAC pros quote me 3 ton AC only unit for half my 32 x 52 spray foamed building. Sq. footage was about 1,500 since it was 2 floors. Told them to go away. Finally got one that came in and did the calculation and installed a 1.5 ton unit. Works great and doesn't run much.

 

[PWC Repair]

I'd go with a 4 ton with inverter compresoor. You're insulated pretty good. Of course it depends on how warm or cool you are going to keep your shop too. I'm heating my 30x48x12 with 16,000 BTU. Yes, it works fine even though everybody says it shouldn't. I'm just below the Missouri line and have 3" foam board insulating mine. It's all in the last page of my build thread below.

 

[dcg9381]

Open cell foam is also called a sponge ! It will hold water. If it hold water, it can mold.

And we still use it in residential construction here all the time.
I agree - if you have a leak, this type of insulation is not ideal. Neither is bat, cellulose, or perhaps anything other than closed cell foam.

I have a 2400 sqft building in the south. I cool it with 2 x 24K BTU units. This was less expensive than a 36K unit and it also allows me to run one unit when the temperature isn't that nuts. Solves the "multi-head" problem too...

My insulation is about 1/2 of what you're installing. Our summers are more extreme, but your winters are more extreme.

Inverter units are less sensitive to short cycle than traditional heat pumps - I get called out on this - I mean LESS sensitive as they can throttle back.

One concern for you is in really cold weather heat pumps decrease in capacity, so take that into consideration.

 

[mygarageone]

The main purpose of an ac unit is to dehumidify the air and then cool it , over sizing a Ac unit is not the way to do anything . Because it will cool the building before it gets the humidity out , leaving you with l a cool humid building , you want cool dry air . Get a proper heat load calculation before doing anything . Bigger is not better when it comes to heating and cooling products .

 

[SeniorCitizen]

Old school says moisture is removed before the temperature can change, whether cooling or heating, so how does a oversized unit cool if it can't remove moisture?

 

[yeldogt]

https://www.theseverngroup.com/how-to-size-your-hvac-unit/

That's going to way oversize for spray foam

 

[yeldogt]

Open cell foam is also called a sponge ! It will hold water. If it hold water, it can mold.

Open will not hold water like a sponge -- it will always flow if the foam is too thin. Made thicker it wills top any air movement -- w/o movement ther si no real flow.

The mold or moisture problem is caused when the foam is too thin and does not stop flow -- this can move and condense on the underside of the roof deck

 

[yeldogt]

In a well insulated building -- IE: spray and no leaks -- good windows and doors. 1k sf per ton is easy to achieve. More with a LEEd building. That's why mini splits work in those structures.

the old rule of thumb could be as bad a 1T per 400sf

 

[mygarageone]

Old school says moisture is removed before the temperature can change, whether cooling or heating, so how does a oversized unit cool if it can't remove moisture?

The problem is , it will cool but won’t dehumidify as it should seen it happen many times.
The major problem with a house with lots of glass , over coming solar gain and yet keeping the AC system properly sized .

 

[Innovate1]

Old school says moisture is removed before the temperature can change, whether cooling or heating, so how does a oversized unit cool if it can't remove moisture?

If the unit is oversized it only runs for short cycles because it cools the air quickly. Because of the short cycles it only condenses a small amount of water out of the air. The smaller unit runs longer and condenses water out of the air the whole time it is running.

It's a well known issue with oversizing AC. Our area has very humid summers so it is important to get the right size. It will run more of the time which is exactly what you need to reduce humidity.

 

[yeldogt]

I bought a big old house years ago with oversized R12 York equipment -- those units would make ice. When it was 105 outside they would keep the house as cold as I wanted ... and since it was so hot out they ran enough to remove the humidity .....the rest of the time we often had the house at 70 or lower to keep them running long enough to remove the humidity.

As the house was restored and upgraded with better windows and insulation ...the units were replaced. The house is now more comfortable at many degrees higher w/ much lower interior humidity.

W/ low humidity 75 can be very comfortable vs 70 when humidity is not managed

 

[Sanmiam]

The problem is , it will cool but won’t dehumidify as it should seen it happen many times.
The major problem with a house with lots of glass , over coming solar gain and yet keeping the AC system properly sized .

This is very true of traditional split systems, but minisplit runs on a variable basis. If you have a 24KBTU unit/head, there are typically 3 different calls for heat/AC meaning the system can run at 9, 18, 24 (these are examples and vary between manufacturers). In summary, removing humidity/short cycling is less of an issue with mini-splits as the units themselves adjust to allow for the longest run times possible within the confines of the hardware capabilities.

This is in stark contrast to a split system which is basically an on/off button.