AC size recommendation

[fifth]

My shop is 41x32, roughly 1,300sf and 14' tall ceiling. Its 2x6 construction, insulated with R19 in the walls and blown-in R38.

I installed a 3ton unit and it will cool the shop to 80 degrees at night and the morning but can't hold temp as the day gets warmer. It will run constantly, 24 hours a day. I had to up the temp in the afternoons from 80 to 90 degrees so that it starts cycling on and off. If I open the RV door for any more then a few minutes to pull a car in, the unit struggles to get the temp back down.

What size unit would you recommend?

Phoenix @ 110 degree summers

 

[Laucker]

My shop is 41x32, roughly 1,300sf and 14' tall ceiling. Its 2x6 construction, insulated with R19 in the walls and blown-in R38.

I installed a 3ton unit and it will cool the shop to 80 degrees at night and the morning but can't hold temp as the day gets warmer. It will run constantly, 24 hours a day. I had to up the temp in the afternoons from 80 to 90 degrees so that it starts cycling on and off. If I open the RV door for any more then a few minutes to pull a car in, the unit struggles to get the temp back down.

What size unit would you recommend?

Phoenix @ 110 degree summers

While not running detailed load calc I would roughly estimate 4 tons of capacity would be sufficent if not more depending upon how the sun hits the building and specific details on building construction. You are in AZ so low humidity so your latent/sensible heat load is probably fairly close. So you have blown R19 in the walls and R38 in the ceiling?

 

[fifth]

Fiber glass in the walls, and the eco friendly stuff blown in on the ceiling. How much more power draw is there from a 4 ton unit compared to a 5 ton unit?

 

[SuperD]

Just wondering how hot the car is that you move in there? Engine and transmission at 195* F not even counting exhaust and engine block plus transmisson. If the car is in the sun, at 90*f then you are trying to cool down 3400 pounds of plastic and steel.
Have you considered a swamp cooler, I think the humidity in Arizona is low enough that it will work very well there.

 

[redxiii75159]

My shop is 41x32, roughly 1,300sf and 14' tall ceiling. Its 2x6 construction, insulated with R19 in the walls and blown-in R38.

I installed a 3ton unit and it will cool the shop to 80 degrees at night and the morning but can't hold temp as the day gets warmer. It will run constantly, 24 hours a day. I had to up the temp in the afternoons from 80 to 90 degrees so that it starts cycling on and off. If I open the RV door for any more then a few minutes to pull a car in, the unit struggles to get the temp back down.

What size unit would you recommend?

Phoenix @ 110 degree summers

What up boss. You have a 41x32 which is 1312 sqf. Because is a main floorand you have a 14 foot ceilings you need 45360 btu is what should aim for. Hope this helps dont know how to convert to tons sorry.

Sent from my LGMS210 using Tapatalk

 

[Rockhead261]

How to calculate HVAC BTU requirement

18,368 ft/3 and a desired 40-degree drop with average insulation will require 53,696 BTU/h (4.5 ton). Since there is no such thing as a 4.5 ton unit, go with a 5.

Keep in mind, average insulation.

 

[rattle_snake]

My shop is 41x32, roughly 1,300sf and 14' tall ceiling. Its 2x6 construction, insulated with R19 in the walls and blown-in R38.

I installed a 3ton unit and it will cool the shop to 80 degrees at night and the morning but can't hold temp as the day gets warmer. It will run constantly, 24 hours a day. I had to up the temp in the afternoons from 80 to 90 degrees so that it starts cycling on and off. If I open the RV door for any more then a few minutes to pull a car in, the unit struggles to get the temp back down.

What size unit would you recommend?

Phoenix @ 110 degree summers

I have same size building, same insulation, same AC size, and in same location. Mine has no problem keeping 80F, units cycle or run on low even when 110+.

3 tons can drop 10 degrees in an hour. Opening door is no issue.
I have 2x, 1.5T Daikin mini spits that use only 20-30$ per month.

I think something is wrong with your system, 3 tons should be more than enough. What type is is? What is temp split? need more info.

 

[fifth]

The brand is Day and Night

 

[danski0224]

My shop is 41x32, roughly 1,300sf and 14' tall ceiling. Its 2x6 construction, insulated with R19 in the walls and blown-in R38.

I installed a 3ton unit and it will cool the shop to 80 degrees at night and the morning but can't hold temp as the day gets warmer. It will run constantly, 24 hours a day. I had to up the temp in the afternoons from 80 to 90 degrees so that it starts cycling on and off. If I open the RV door for any more then a few minutes to pull a car in, the unit struggles to get the temp back down.

What size unit would you recommend?

Phoenix @ 110 degree summers

You need to pay for a load calculation, whether it is done by someone else or you buy/rent software. Any other course of action is a waste of time and money.

Once this is done, then you will know whether or not your installed equipment is adequate, or not.

If the load calc says that your equipment meets design requirements, then there is something wrong with the equipment, the installation, the ductwork, or the building.

An AC system can appear to work (make cold air to the layperson), but is operating at significantly reduced capacity due to a metering device problem, incorrect fan speed, improper refrigerant charge, mismatched coil and there's a few more. These issues cannot be found without proper diagnostics of the equipment and the ductwork.

One thing I can say with virtual certainty is that your ductwork (probably flex in your area) is undersized for what you have now. Installing a bigger AC unit and retaining the same ductwork will not fix the problem.

 

[fifth]

One thing I can say with virtual certainty is that your ductwork (probably flex in your area) is undersized for what you have now. Installing a bigger AC unit and retaining the same ductwork will not fix the problem.

I hope the duct work is the correct sizing... 18" return duct and six 8" lex lines coming off the main distribution box.

I have scheduled an appointment to have my setup reviewed by a professional.

 

[danski0224]

Nope.

 

[LS6 Tommy]

What up boss. You have a 41x32 which is 1312 sqf. Because is a main floorand you have a 14 foot ceilings you need 45360 btu is what should aim for. Hope this helps dont know how to convert to tons sorry.

Sent from my LGMS210 using Tapatalk

You can figure out the Btu requirement, but you don't know how to convert it to tonnage?

Divide by 12,000, which is 3.78.

Fifth, I would suggest you get a manual J calculation done. It's the most accurate way to do it.

Tommy

 

[fifth]

Interestingly enough .. The company recommend two 2ton mini splits

 

[rattle_snake]

Interestingly enough .. The company recommend two 2ton mini splits

How old is your existing system? If it's new I wouldn't spend a pile of $ to start over. What is the temp split? pressures?

No duct loss on a ductless mini, so you get the rated BTU. Perhaps your 3T only delivers 2 or so though ducts.

 

[danski0224]

Interestingly enough .. The company recommend two 2ton mini splits

But, did they do a load calculation?

 

[fifth]

But, did they do a load calculation?

Nope, it wasn’t something they do.

 

[fifth]

20 degree split.. 80 degree in and 60 degree out

 

[danski0224]

Nope, it wasn’t something they do.

Then how do they size equipment properly?

Call around until you find someone that does.

 

[rattle_snake]

20 degree split.. 80 degree in and 60 degree out

That sounds about right.

Do you have lots of windows?
Are the overhead door(s) insulated?

Can you visually inspect the ductwork? perhaps one or more has failed and your attic is getting the BTUs instead.

 

[rattle_snake]

FYI, one of my mini's had a leak, so I have been running with just one 1.5T unit for awhile, in the hottest part of the year. It does just fine by itself and can easily reach set point.

I don't see how OP needs more than 3T. Must have really ****** ductwork.

 

[fifth]

I’m wondering if it’s just a crappy unit... don’t get me wrong, it works.. 110 outside and inside will be 80-83 but unit runs all day.

 

[Jim greengo]

So what style of 3 ton unit are you using does it have ductwork ran through out the shop?

 

[fifth]

So what style of 3 ton unit are you using does it have ductwork ran through out the shop?

Split system, I have six separate ducts that branch off the main collector. I believe they are 8” ducts.