New a/c for shop.... not impressed

[wade_660]

Hey guys. Just got a new a/c unit in my shop and it doesn’t seem to get the job done. I have a 36x40 garage with spray foam insulation in the ceiling and fiberglass in the walls. I have good windows, insulated doors, and had skylights but I covered them up recently.

I wanted a big mini split but was talked out of it by my hvac guy (several of them actually). I still think that would have been my best bet.

My situation: I turn the unit down to 75 the night before so it will be cool in the morning. I go in the next morning and it’s 75. I will bump it down to say 72 and it will never get below 75. It will run all day nonstop and as the day gets hotter, the temp will slowly go up in the shop. I’ve only ran the unit a time or two but have honestly never heard it shut off on its own.

I’m worried I was sold an undersized unit although I know nothing about it. Any info would be awesome

Seems like I remember the box saying it was a 36k btu unit


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[mikec35]

Do you have plans to install a ceiling? Without one you have a lot of extra space to cool.

 

[Trey T]

Do you know which evap/blower do you have?

2ton: BVA-24WN1-M18

3ton: BVA-36WN1-M18B

That condensor is rated 2-3ton capacity, based on the paired evaporator/blower, and it can throttle the refrigerant flow (25% -110% load capacity).

You can get an idea of the capacity by checking the power consumption (amp reading). The LRA is rated for 18.5A; @ 3ton and given time of the day, you'll see it run anywhere from 10-18A.

 

[larry_g]

Where in the world are you? What are your outside temps these days? Is your garage door insulated? Is the door being hit by sunlight most of the day? Is the air coming from the system as cold as it should be? Does the air move enough to circulate to the floor and back up? Any shade on the building or is it in full sun all day.

All these questions play into the you getting the best answers you can. Without good data we can only guess. What works in my area and location may not work for you.

lg
no neat sig line

 

[Lonnies Performance]

Where are you located & what are the outdoor conditions (temp & humidity) during the time of insufficient cooling? Also how tall are your walls?

 

[justinjoyal]

What size is the main supply duct?

What kind of return do you have?

Is the air handler in a conditionned space?

What is it we see in the 2nd picture? Whats the flex duct for? And that branch box or whatever that is, some kind of plenum or what? Can’t really tell from the picture.

 

[wade_660]

Sorry about being so vague. I thought I was covering all of the bases. I’m in central Georgia. It’s super hot and humid and this shop sits in full sun all day. The walls are 10’ high, then add for the space above the ceiling. I don’t have intentions on adding a ceiling, I should have instead of the foam insulation honestly. I would have rather had the heat overhead and just cooled the space under the ceiling. I will look when I get home to see which blower I have. And yes the doors are insulated.


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[danski0224]

A load calculation will tell you the answers.

If no one did that, then oopsie.

Foam can be improperly installed, and you won't get the claimed R value.

 

[8mpg]

How much foam do you have? Something isnt right. Im in Texas with a 2000sqft shop and my MrCool 24k unit is holding my shop at 72*f when I want it to. I have 6" ceiling and 3.5" open cell walls for insulation.

Check the air temp coming out of the ducting with a cheap IR thermometer.

 

[themiller]

What is the temp of return air and what is the temp of air coming out of the vents?

1400+ sq ft on 3tons is borderline low in my non-expert opinion for 72 degree temps when outside is in the high 80/low 90s with humidity. I am not an expert, but I have purchased A/C in 4 different houses over the last 20 years in the Midwest and one out here... AND I just saw you had 10' ceilings + attic space. hahaha yeah right on 2-3 tons.

I would get the professional back and not let him off the hook. I wouldn't go any smaller than 4T for 1400 sq ft in your zone and would probably end up with 5T, especially if you want ever open the doors during the day and/or pull a hot car in.

My next house will have one or two steps above whatever is "recommended". Those of us that like our environment at 68-72 degrees seem to be regularly disappointed with the calculations.

The last time I had a professional heat calc - the "professional" didn't seem to understand that an oven makes heat and that having a wife who likes to use the oven on the hottest of days was something to plan for, not argue about. Just a caution to not take their word as gospel and to do a little critical thinking for yourself.

 

[danski0224]

My next house will have one or two steps above whatever is "recommended". Those of us that like our environment at 68-72 degrees seem to be regularly disappointed with the calculations.

The last time I had a professional heat calc - the "professional" didn't seem to understand that an oven makes heat and that having a wife who likes to use the oven on the hottest of days was something to plan for, not argue about. Just a caution to not take their word as gospel and to do a little critical thinking for yourself.

Your desired temperature range is well outside of what is considered "normal" for a residential AC load calculation and gets into de-rating equipment to size it properly. Indoor design is 77*F.

I always ask what the desired temperature is.

Same goes for cooking and entertainment. That stuff can be factored in- for the most part.

The flip side is that if every contingency is allowed for, then the AC system is grossly oversized for the other 98% of the season.

Then there are the complaints of being cool and clammy.

And then the customer doesn't want to pay for a multi-stage system that is flexible enough to meet the demands, nor is the existing ductwork capable of dealing with the required airflow... and then the ductwork is too small for the low end of the output.

People want the flexibility of a medium pressure commercial system with a duct loop, individual VAV boxes and thermostats, and a freq drive on the chiller....

 

[themiller]

Your desired temperature range is well outside of what is considered "normal" for a residential AC load calculation and gets into de-rating equipment to size it properly. Indoor design is 77*F.

I always ask what the desired temperature is...

My point exactly - and probably one aspect of why the OP is unhappy. I’m glad you ask the customer - can I ask how you mathematically arrive at a new size/number? If I told you I wanted it 67 degrees instead of 77 for example...

 

[wade_660]

Thanks for the replies guys. I climbed up in the ceiling and got this pic. looks like this is for a 3 ton

Someone asked about the insulated duct. I didn’t mention it before because I didn’t think it was important. That duct is going to a separate 12x24 room that does have a ceiling. The install is not completely finished. The one room and the big side of the shop will have separate zones. It’s just running as one big room as of now. Looks like the returns on the air handler are wide open as of now so any returned air will be coming from the ceiling, which is technically air conditioned but warmer than below. I can tell you anything you want to know about a traffic signal but hvac is something I know nothing about. I was told to run this unit as it sits and they’d be back to finish after vacation.


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[Tracs]

Duct work job looks like ****. Should have used T's where they wanted drops, then had proper diffusers on the end of them.

 

[firebirdparts]

This is about as hot as it's going to get, so you're not too far off where you want to be. I think you should verify how much cooling you are getting, the best you can, and I think you could use more foam in the roof. It might be interesting to measure some indoor surface temperatures and see how the wall insulation compares to the roof insulation.

 

[Trey T]

Everyone need to hold on until the the tech finish with the installation

Keep an eye on the final air return location(s) to promote circulation to maximize the capacity. This system WILL NOT push 3ton if the loading is not there. It’s a cool but weird system

 

[LS6 Tommy]

Duct work job looks like ****. Should have used T's where they wanted drops, then had proper diffusers on the end of them.

No sealer on the joints either, but as the OP says, the installer isn't done yet.

I'd sheet rock and insulate the ceiling and run those ducts to proper diffusers.

Tommy

 

[8mpg]

What is the temp of return air and what is the temp of air coming out of the vents?

1400+ sq ft on 3tons is borderline low in my non-expert opinion for 72 degree temps when outside is in the high 80/low 90s with humidity. I am not an expert, but I have purchased A/C in 4 different houses over the last 20 years in the Midwest and one out here... AND I just saw you had 10' ceilings + attic space. hahaha yeah right on 2-3 tons.

I would get the professional back and not let him off the hook. I wouldn't go any smaller than 4T for 1400 sq ft in your zone and would probably end up with 5T, especially if you want ever open the doors during the day and/or pull a hot car in.

My next house will have one or two steps above whatever is "recommended". Those of us that like our environment at 68-72 degrees seem to be regularly disappointed with the calculations.

The last time I had a professional heat calc - the "professional" didn't seem to understand that an oven makes heat and that having a wife who likes to use the oven on the hottest of days was something to plan for, not argue about. Just a caution to not take their word as gospel and to do a little critical thinking for yourself.

Youre thought is old school mentality...and even then, a little heavy. Old mentality was 500sqft per ton of a/c (Im talking Texas). There is no reason his building should need more than that which he is at. Newer buildings with spray foam and that are air sealed better are reaching 700-1000sqft per ton. My house for example is 2100sqft and I have a 2.5 ton in Texas and it is more than enough. I have a 2 ton on my 2000sqft shop and its more than enough.

That 3 ton should be more than enough to cool properly. I wonder if its low on coolant, has a leak, etc.

 

[wade_660]

For what it’s worth I have a 4 ton unit on my house that’s 3000 sqft with 4 zones. It has foam insulation with about 13’ of space above the 9 and 11’ ceilings. It could have easily been a two story house. The unit seems perfect in there, and I think that’s what I’m trying to compare the shop to. I’ll sit on my hands and wait for the install to be finished before I worry. Is the consensus that a mini split would outperform this unit? I was looking at a 48k btu with three heads. One for small room and two larger ones for big part of shop.


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[bonneyman]

Yeah, if the install isn't done - and the installer signed off on it - then we're just shooting burritos into the air.

 

[thymer]

duct work does look a bit small. I used a 5 ton unit for a 60x40x16 inside dimension, stick build, insulated and dry walled. It just plugs into a airsock running at the ceiling the 60' length. Keeps it nice and chilly in the summer and warm in the winter. I got mine from ************************ I think and cost less than 100 bucks for the whole thing.

 

[brownbagg]

my house is 1200 sq ft and i got 4 tons, but that another story, usually 20 degrees different from outside is damn good.

 

[u3b3rg33k]

I'd wait to see how things are when it's finished. that system auto-modulates to hold an evaporator / vapor line temp i believe, so if the indoor unit isn't providing enough heat to the evaporator, the outlet temp wont drop, the ODU will simply modulate down. it probably doesn't have the AHU side dialed in yet.

per this: https://www.winstelcontrols.com/customer/docs/SKUDocs/IDS_Quick_Start_Guide_20February2018.pdf
it has 85 stages of capacity modulation.

https://resource.bakerdist.com/is/c...1m18m_article_1470385935659_en_ii.pdf?fmt=pdf

Section 15 System operation and Troubleshooting
1. Control Logic Description
● The variable speed system adopts the same 24VAC control as any conventional Heat Pump.
● The compressor’s speed is controlled based on coil pressures monitored by pressure transducer.
To insure stable and adequate capacity, the compressor speed will modulate relative to evaporator pressure during cooling operation and relative to condensing pressure during heating operation.
The target pressure can auto-matically adjust based on compressor operation so optimal capacity can be achieved.
Target pressure can manually be adjusted (SW4) to achieve improved dehumidification and capacity demands

2. Sensors (Thermistors/Pressure Transducer)
● T3 = Outdoor Coil Temperature (Table 1) o High/Low temperature protection
o Outdoor fan control (cooling mode) o Defrost control (heating mode)
o Ambient Temperature forecast
● T4 = Ambient Temperature (Table 1)
o Operating condition permission
o Defrosting condition permission
o Outdoor fan control (heating mode)
● T5 = Compressor Discharge Temperature (Table 2)
o High/Low temperature protection
o Electronic Expansion Valve (EXV) control (ODU)
● TF = IPM Radiator Temperature) (Table 2) o Inverter High Temperature Protection
● Pressure transducer (Table 3)
o Operating speed control
o Electronic Expansion Valve (EXV) control (ODU) o High pressure protection (heating mode)
o Low pressure protection (cooling mode)

as above the ODU has dip switch settings for accelerated cooling/ other settings.
here's the manual: https://resource.bakerdist.com/is/c...1m18m_article_1470385935659_en_ss.pdf?fmt=pdf

fwiw it's been 80s-90s and humid here lately and my poorly insulated house with worse ductwork has been holding setpoint with a 2 ton system.

 

[themiller]

Youre thought is old school mentality...and even then, a little heavy. Old mentality was 500sqft per ton of a/c (Im talking Texas). There is no reason his building should need more than that which he is at. Newer buildings with spray foam and that are air sealed better are reaching 700-1000sqft per ton. My house for example is 2100sqft and I have a 2.5 ton in Texas and it is more than enough. I have a 2 ton on my 2000sqft shop and its more than enough.

That 3 ton should be more than enough to cool properly. I wonder if its low on coolant, has a leak, etc.

No - my mentality is math, science, personal experience, and reading the fine print as opposed to "rule of thumb".

OP wants low 70's. Commonly accepted design from the actual pro's (as has shown up in this thread) is 77 or 75. You stated in another thread that you keep your system at 76...

Generally speaking GA is more humid than TX. If you plopped your house down in GA you would need a bigger system.

 

[danski0224]

OP wants low 70's. Commonly accepted design from the actual pro's (as has shown up in this thread) is 77 or 75. You stated in another thread that you keep your system at 76...

The industry standard (cooling season) is 77*F indoor temperature for the USA (possibly North America). The manufacturers published specifications are for an indoor design of 77*F.

Going below that number requires additional steps to ensure proper equipment sizing, beyond the load calculation. The system may not remove enough humidity during normal operation.

There are also people that have improperly sized systems that do not remove enough humidity that set the thermostat lower to provide an improved feeling of "cool". Homes with lots of air leakage will also overwhelm the dehumidification abilities of a residential AC system (unsealed ductwork in an attic is a good one for this).

Multi-stage condensers (2 or more) and variable speed drive blowers can really help.

I wouldn't take on a job where the homeowner insisted on a 68-70*F cooling setpoint without a signed waiver that excluded comfort with the exception of meeting the desired thermostat setpoint.

 

[themiller]

...

I wouldn't take on a job where the homeowner insisted on a 68-70*F cooling setpoint without a signed waiver that excluded comfort with the exception of meeting the desired thermostat setpoint.

As a customer I’ve signed that. First was for my mother, 16 years she was happy with the system. Sales guy swore up and down that 4 tons was overkill and she’d hate it. I knew my mother better than him. She loved it until the day she moved out as she could come home in the middle of the day, turn it on, and the house would be cool in 20 minutes, all while opening and closing the door to unload the car or whatnot. Her set point was 67. 912sq ft 1950s ranch.

 

[u3b3rg33k]

As a customer I’ve signed that. First was for my mother, 16 years she was happy with the system. Sales guy swore up and down that 4 tons was overkill and she’d hate it. I knew my mother better than him. She loved it until the day she moved out as she could come home in the middle of the day, turn it on, and the house would be cool in 20 minutes, all while opening and closing the door to unload the car or whatnot. Her set point was 67. 912sq ft 1950s ranch.

that'd be a perfect setup for a 4 ton 2 stage. stage 1 would at least be close to reasonably sized.

 

[yeldogt]

my house is 1200 sq ft and i got 4 tons, but that another story, usually 20 degrees different from outside is damn good.

wow .. that must leak

 

[yeldogt]

No - my mentality is math, science, personal experience, and reading the fine print as opposed to "rule of thumb".

OP wants low 70's. Commonly accepted design from the actual pro's (as has shown up in this thread) is 77 or 75. You stated in another thread that you keep your system at 76...

Generally speaking GA is more humid than TX. If you plopped your house down in GA you would need a bigger system.

In PA with full closed cell foam I have done 1000sf per ton with no issues and outside temps at 100. I have a 3T 5 speed unit doing my 2500 sf beach house .. it was 94 Tuesday ... very high humidity.

The newer systems eliminated humidity ..... high humidity at 70 feels warm vs 73 at 40%

 

[8mpg]

In PA with full closed cell foam I have done 1000sf per ton with no issues and outside temps at 100. I have a 3T 5 speed unit doing my 2500 sf beach house .. it was 94 Tuesday ... very high humidity.

The newer systems eliminated humidity ..... high humidity at 70 feels warm vs 73 at 40%

He has the science behind him... no sense in arguing.

 

[yeldogt]

He has the science behind him... no sense in arguing.

The 3T replaced an older 4T York R12 unit. I hated to see it go as it never gave me any trouble .. and would make ice. But, it was always oversized using the 500sf or so per ton formula .. it was less of an issue prior to a lot of insulation work. But, spray foam and other measures made it worse and even adding about 500sf did not help -- it was still too big to get the humidity out when it was not extremely hot.

People seem to think a unit is great when it will drop a house down in 20min -- that's fine if you want to have AC that way. Most people want continual comfort -- my units are never off. We may raise the temps up .. but the units are always running for and if humidity is around. On really hot days where you are going to have solar gain, keeping the inside temps at say 72 is now the norm .. on mild days it's often 73 or 74. With the old system it was always on 70 .. and sometimes lower if the humidity was bad.

The five speed is on 1 this morning -- a really nice mild morning w/ some humidity. What's surprising to me is how cold the small amount of air flowing through the system -- the new systems eliminate humidity. I guess in areas of the country with little or no humidity things could be different -- but if you have humidity oversizing is not advantageous.

 

[My Old Tools]

my house is 1200 sq ft and i got 4 tons, but that another story, usually 20 degrees different from outside is damn good.

I don't know a single person in Texas that would be happy with a 20 degree difference when it's 107 outside.

 

[rebelranger]

Yes something is wrong. Get an thermal camera to see what is going on with the building.

I have a 4ton trane worth 4 zones covering a 5300sqft th story home that works no matter the temp in south missouri. I paid a pretty penny but I was very picky.

3ton for sub 1400sqft should be plenty.

 

[brewchief]

Without knowing a lot more details it's hard to do a real good load calc but running some quick numbers I'm coming up with a need for about 18k btus.

I'm wondering if it's more of a duct design problem then anything.

 

[RAM2940]

Without the difusers on the ductwork, your just blowing the cold air straight down to the ground.

 

[themiller]

Update from OP?

 

[PWC Repair]

Even with the insulation, in your area, you are undersized. That shop should have had 4 tons. You can contact your local HVAC city or state inspector and they will come out and check it out.

 

[MrSurly]

I don't know a single person in Texas that would be happy with a 20 degree difference when it's 107 outside.

Can I get an AMEN. We've finally cooled down to 99* today after 107* a few days ago capping two weeks of 100s. And , no, it's NOT a dry heat.

Both my old house (1900sf/3t) and the new shop (1200sf/2t) are undersized, both are adequate at 95 ambient, 74 indoors; both will slip at 105 amb to 80~83.

 

[LS6 Tommy]

my house is 1200 sq ft and i got 4 tons, but that another story, usually 20 degrees different from outside is damn good.

The 20° difference rule of thumb is measured between the return and the supply air temps, not indoor and outdoor temps.

Tommy

 

[u3b3rg33k]

where'd OP go?