How big should I go with a true HVAC.

[haugy]

Help me size my Heat/AC unit for a large shop. I've searched all kinds of threads, but couldn't find anything like what I'm going to ask.

I've got a 50x40x16. I'll be doing spray foam and then batts to really insulate it well. I'm also planning on having radiant floor heating.
So I was looking at my house HVAC with natural gas heat, and figured it's old, I'll put this at my shop, and upgrade the house with a new unit. But my house unit is only a 2-ton Trane.

That's not going to cool that much air space in my opinion. I plan to have a loft overlooking the shop where I will work (actual job work) with a desk, and the rest will be where I hang out, drink beer, watch movies, etc. The lower section will be all work. But I'm planning on running true duct just below the ceiling to help spread the air flow to the whole shop.

So I do want to be able to bring this thing down in temps. I'm thinking with the radiant floor and insulation, I should be able to easily heat up the shop, but cooling it in TN summer is HARD.

I used a calculator, but it can't do ceilings at 16', and it came out to 5-ton. That's a big sucker ($$$$$). While I believe in go big or go home, I also understand there is a science to sizing the AC and going too big can be bad.

Does anyone have any thoughts? Any advice?

 

[yeldogt]

How much foam .... ?

Windows and doors?

Will you be running the AC to maintain ... what's humidity like ?

 

[Yankeefarmer]

Several of us here have installed a Mr Cool Universal heat pump system. It comes in 2 versions, one is 2 or 3 tons, the other 4 or 5 tons. You choose capacity with DIP switches inside the unit. I did the 5 ton version for my 26x10x15 shop based on calculated heating requirements. I only started it up at the end of March, so it’ll get its first real world heating test this coming winter. 5 tons of cooling is way overkill for my building, especially since it naturally stayed below 75 degrees inside even on 90 degree plus days through August. What I found, though, despite what some people here will tell you, was that even being grossly oversized, it did reduce the humidity to tolerable levels. (I have data logs that show this.) I don’t doubt that I could achieve lower humidity levels with a smaller system that ran longer, but since I have a building that requires a cooling set point around 70 deg F just to turn on, I’d still be dealing with a system that would be off all night long, allowing humidity levels to rise. I will probably just get a dehumidifier for next summer.

My 5 ton system, all in, cost me a bit under $5k, as compared to a $14k quote from the HVAC company I use for things I won’t do myself. By using the Mr Cool No-vac line set, you get the full warranty even with a DIY install.

The only thing I can suggest to you on sizing is to consider your buildings exposure to sun, number of windows, and type of big doors and how often you expect to have them opened and closed. My building has only small windows, so not much solar gain through them, especially since they are shaded from the early sun by large trees (as is the east side of the building.) My temperature logs show just how quickly temperature (and humidity) rise when the doors are opened.

With a radiant floor, you probably don’t need the heating capacity of a heat pump, but that capability is essentially free with the system. It might even help you save a bit of money by maintaining a lower temperature in the cold months when unoccupied, and using the heat pump to warm it from say, 50 to 60 degrees when you are working out there.

Edited to add: I just realized that you plan to work from the building, so heating setback probably isn’t a consideration. But, life changes, so there’s still flexibility. And, if you need to work from the space, a backup heating system could be nice to have.

Hope this gives you food for thought.

 

[haugy]

How much foam .... ?

Windows and doors?

Will you be running the AC to maintain ... what's humidity like ?

1" on the walls, 2" on the ceiling. I used closed cell and batts on my last shop. Tightened it up, deadened the sound, and kept the air intrusion down. Use R19 batts on the walls.

No windows. But the entire front is ALL Doors. 14x14, 12x12, 16x12.

AC to maintain, yes. High humidity, and since a boat will be stored, that will be constantly pushed.

Several of us here have installed a Mr Cool Universal heat pump system. It comes in 2 versions, one is 2 or 3 tons, the other 4 or 5 tons. You choose capacity with DIP switches inside the unit. I did the 5 ton version for my 26x10x15 shop based on calculated heating requirements. I only started it up at the end of March, so it’ll get its first real world heating test this coming winter. 5 tons of cooling is way overkill for my building, especially since it naturally stayed below 75 degrees inside even on 90 degree plus days through August. What I found, though, despite what some people here will tell you, was that even being grossly oversized, it did reduce the humidity to tolerable levels. (I have data logs that show this.) I don’t doubt that I could achieve lower humidity levels with a smaller system that ran longer, but since I have a building that requires a cooling set point around 70 deg F just to turn on, I’d still be dealing with a system that would be off all night long, allowing humidity levels to rise. I will probably just get a dehumidifier for next summer.

My 5 ton system, all in, cost me a bit under $5k, as compared to a $14k quote from the HVAC company I use for things I won’t do myself. By using the Mr Cool No-vac line set, you get the full warranty even with a DIY install.

The only thing I can suggest to you on sizing is to consider your buildings exposure to sun, number of windows, and type of big doors and how often you expect to have them opened and closed. My building has only small windows, so not much solar gain through them, especially since they are shaded from the early sun by large trees (as is the east side of the building.) My temperature logs show just how quickly temperature (and humidity) rise when the doors are opened.

With a radiant floor, you probably don’t need the heating capacity of a heat pump, but that capability is essentially free with the system. It might even help you save a bit of money by maintaining a lower temperature in the cold months when unoccupied, and using the heat pump to warm it from say, 50 to 60 degrees when you are working out there.

Edited to add: I just realized that you plan to work from the building, so heating setback probably isn’t a consideration. But, life changes, so there’s still flexibility. And, if you need to work from the space, a backup heating system could be nice to have.

Hope this gives you food for thought.

I like the Mr. Cool Universals, but I'm having a Natural Gas line run out there. It's way more efficient than electric, and can power my boiler for the floor as well. As noted, I have big doors, and they will be opened when I come and go. So a few times a day at least.

Thanks for the input.

 

[Yankeefarmer]

With natural gas available, that’s the way to go for heat, no doubt about it.

 

[kj_mustang]

To really know, you need a Manual J calculation done. FYI as another data point, I have a 32 x 52 x 16 Pole building with a loft over half the building. The side with the loft is fully finished with sheetrock, 2" closed cell over walls and roof, then about 6" open cell spray over the roof so it meets R42 code, then I put R8 fiberglass blanket on the walls over the closed cell. I have 7 windows on that side that face south and I can cool it easily with 1.5 ton central ac, that is for about 1300 sq feet. The other half the building has the same spray foam but no fiberglass blanket. It has no AC right now but it stays reasonable as long as the garage doors stay closed. I have radiant for the whole building also.

 

[yeldogt]

I have never done the flash and batt that thin --- but, if that works in your area (the 1") fine. In colder climates you must condition the space after foam and while building out or you risk condensation problems. My flash and batt was about 2+ " and typical batt for 2x6 walls.

My well insulted 1700 sf space in PA can be cooled with 15k BTU's ...... my full foamed house in PA is over 4k and and only has 36k btu.

With ductwork going in --- I would build it out with zoning in mind. Make a zone for the loft area that will flood that area with cool air when needed and the lower when not. Are the doors at the far end or under the loft ?... often the area by the doors is the least critical area of a shop -- most are not working right by the doors. Who cares if it's a bit warmer .. they key is humidity anyway. If the doors are far from the loft all the ductwork can be under that area with a dump going out into the open area towards the door.

The reason I say to plan on zoning -- it's only a bit of extra duct work off the air handler to split the two levels. This allows some tweaking with manual dampers It's also available if you find it needs the addition of some zone valves. If it was me I would plan on zone valves and two thermostats --- don't oversize the unit and you can flood each area at will.

 

[Hobby_Man22]

If you stack two RMAX foam boards together that are R7 each do the values combine?

 

[BillK]

h,
My business unit is 30x60x16 It is in a building with other units on both sides so I consider it the same as being pretty well insulated ? The roof is a flat roof with about 6 inches of foam. My AC unit is a 5 ton and it is on the roof. The air handler hangs from the roof trusses and just has one long duct with holes punched in the sides. It does a good job. Kept up real well a month or so ago when we had a couple of weeks of high 90 degree temps.

 

[haugy]

I have never done the flash and batt that thin --- but, if that works in your area (the 1") fine. In colder climates you must condition the space after foam and while building out or you risk condensation problems. My flash and batt was about 2+ " and typical batt for 2x6 walls.

My well insulted 1700 sf space in PA can be cooled with 15k BTU's ...... my full foamed house in PA is over 4k and and only has 36k btu.

With ductwork going in --- I would build it out with zoning in mind. Make a zone for the loft area that will flood that area with cool air when needed and the lower when not. Are the doors at the far end or under the loft ?... often the area by the doors is the least critical area of a shop -- most are not working right by the doors. Who cares if it's a bit warmer .. they key is humidity anyway. If the doors are far from the loft all the ductwork can be under that area with a dump going out into the open area towards the door.

The reason I say to plan on zoning -- it's only a bit of extra duct work off the air handler to split the two levels. This allows some tweaking with manual dampers It's also available if you find it needs the addition of some zone valves. If it was me I would plan on zone valves and two thermostats --- don't oversize the unit and you can flood each area at will.

The flash and batt at 1" worked well here in TN. I only had a window AC and a hanging electric Dayton heater and it kept it tolerable with no insulation in the ceiling.

I do plan on using dampers to adjust the flow of air from below ceiling in summer, to below loft in winter.
Thanks!

h,
My business unit is 30x60x16 It is in a building with other units on both sides so I consider it the same as being pretty well insulated ? The roof is a flat roof with about 6 inches of foam. My AC unit is a 5 ton and it is on the roof. The air handler hangs from the roof trusses and just has one long duct with holes punched in the sides. It does a good job. Kept up real well a month or so ago when we had a couple of weeks of high 90 degree temps.

Good info, thanks! My friend had his engineering firm do a calculation based on my R-values and air space and thinks a 4-ton will do the job without worrying about short cycling. I'm still skeptical, but he mad a good point. I'd rather have a 4-ton run consistently longer, than a 5-ton going on and off and killing it after 4-years.

 

[yeldogt]

The flash and batt at 1" worked well here in TN. I only had a window AC and a hanging electric Dayton heater and it kept it tolerable with no insulation in the ceiling.

I do plan on using dampers to adjust the flow of air from below ceiling in summer, to below loft in winter.
Thanks!


Good info, thanks! My friend had his engineering firm do a calculation based on my R-values and air space and thinks a 4-ton will do the job without worrying about short cycling. I'm still skeptical, but he mad a good point. I'd rather have a 4-ton run consistently longer, than a 5-ton going on and off and killing it after 4-years.

As I mentioned above ....my 1700sf space in PA can be cooled with 15k BTUs on 95 degree days .. at that temp all week.

My house is over 4k and it's fine with 36k .. that's a house with windows and doors and levels. It hit the highest speed one day at 2pm when the temp was 99 degrees and the inside was 71.

You are trying to cool 2000sf with 4T ..... 48K ......... Using your thinking my house should have 8T of cooling .... not 3T.

Make sure you do a proper load using the foam -- and proper r values. That same house as the smallest Viessmann boiler for the heat -- Net around 60k and it's never hit high.

The need to oversize is really about recovery and how you want to take car of the space. AC in a humid climate ... you have to run the unit enough to knock down the bulk of the humidity or it requires too much capacity and that capacity works against you.

I don't see how a foamed building will need 1T per 500sf. Have you checked the cost to do more foam and skip the batts ...... The project after the one with flash and batt did not cost out doing that way as the foam cost had come down. I normally do full batt on the inside walls and ceiling of my projects so it's not that we don't have the batts around. Both reg fiberglass and the rockwool

 

[danski0224]

There are independent contractors that just do load calculations and duct design. They can be found with an online search.

By independent, I mean that they do not sell or install HVAC equipment.

Last time I had one done, it was less than $500 and I had to provide a drawing.

If this is too much money to get the correct answers for your build, you might want to scale the project back until doing it correctly is affordable.

 

[FMB4]

So I was looking at my house HVAC with natural gas heat, and figured it's old, I'll put this at my shop...

Not worth the trouble imo.

 

[danski0224]

Not worth the trouble imo.

Of course not, much better to guess.