Do hvac systems run just to get humidity to a certain level?

[Hobby_Man22]

Cane into the shop and it's 75 degrees outside. It was 71 inside the shop but 83 percent humidity. The system ran for 39 minutes and got it to 69 degrees and 71 percent humidity. It got to the set temp of 69 and stayed running for about 10 more minutes before shutting off. The insulation is done so I'm trying to see if this is normal. I'll wait until it gets hotter then have the hvac company come back out and test the charge level I guess.

 

[yeldogt]

Your system is oversized ..... this was discussed in another thread with heat.

You have to have AC systems sized to the load ....otherwise they don't run long enough to remove the moisture. Removing humidity is done with long run times ... oversized systems cool the space too fast and have no time to remove the water.

That's why people use variable speed equipment and multi speed compressors .... or VS mini-splits.

75 degrees with low humidity is more conformable vs 68 with high

 

[Hobby_Man22]

Your system is oversized ..... this was discussed in another thread with heat.

You have to have AC systems sized to the load ....otherwise they don't run long enough to remove the moisture. Removing humidity is done with long run times ... oversized systems cool the space too fast and have no time to remove the water.

That's why people use variable speed equipment and multi speed compressors .... or VS mini-splits.

75 degrees with low humidity is more conformable vs 68 with high

Okay I've let it run now for a couple hours. Other than the initial run of 43 minutes straight after just turning it on it seems to be running 17 minutes on and about 7 to 8 minutes off before it cycles back on. How is that? I have it set at 69 in the shop and it's 80 outside right now. That's not bad then huh? I would think it would remain off a tad longer though. THIS IS THE FIRST TIME IVE TESTED IT IN COOL MODE WITH THE INSULATION INSTALLED. Without insulation it would run for like an hour cycle off then kick back on 3 minutes later.

 

[karoc]

If possible watch your temp on stat, once cycles off see what temp is then when it comes back on see what the temp is. You want your stat to be close to return air if possible, is it mounted on ext wall or interior wall. Where the wire penetrates wall into the stat there may be air being pulled in when unit is running causing it to cycle on/off due to that air. Just some thoughts, here in Tx its about 600sq ft per ton of air. Could be little more or little less

 

[Hobby_Man22]

If possible watch your temp on stat, once cycles off see what temp is then when it comes back on see what the temp is. You want your stat to be close to return air if possible, is it mounted on ext wall or interior wall. Where the wire penetrates wall into the stat there may be air being pulled in when unit is running causing it to cycle on/off due to that air. Just some thoughts, here in Tx its about 600sq ft per ton of air. Could be little more or little less

It's as close to it as you can get it. This t stat just stays at the set temp. Not sure if their is a setting to make it so its not so aggressive at keeping the set temp. The thermostat at home let's it drop down one degree then cuts off one degree above set temp if I remember right. Maybe this stat does the same thing and it just doesn't show that.

 

[67CarGuy]

Your system is oversized ..... this was discussed in another thread with heat.

You have to have AC systems sized to the load ....otherwise they don't run long enough to remove the moisture. Removing humidity is done with long run times ... oversized systems cool the space too fast and have no time to remove the water.

That's why people use variable speed equipment and multi speed compressors .... or VS mini-splits.

75 degrees with low humidity is more conformable vs 68 with high

Spot on. If your system allows it, can you run it in dehumidify only mode? If it's a basic system, probably not, but it can't hurt to check.

The first issue you're facing is relative humidity. If you can read a psychrometric chart, it may help to explain better than I can. Basically, warmer air can hold more moisture than cold air, so if you can allow your inside air temps to be higher, the *quantity* of moisture in the air can remain the same but the *percentage* of moisture in the air will decrease, resulting in it feeling "less humid".

The second issue you're facing is the source of the humidity. The insulation you've installed can do great things at slowing the transfer of heat from warmer to cooler, but if your building isn't appropriately air sealed, you can have R60 walls and ceilings and still spend $$$ on heating and cooling each year. What type of construction is your garage?

 

[Hobby_Man22]

Steel building. I went around and sealed up all the gaps with spray foam in a can. The two 10ft roll up doors aren't insulated yet cause I'm not sure how to. Other than radiant barrier, but that's going to look stupid having two silver doors.

 

[Showkey]

Higher end variable or multi stage unit not often used in shop is the solution.

Good article on the AC system deficiencies when it comes to humidity:

https://aristair.com/blog/hvac-humidity-control-5-reasons-your-ac-is-ineffective/

 

[justinjoyal]

Sounds like the typical oversized system...

Maybe you could have the blower slowed down to remove more moisture. Get a tech !

 

[larry4406]

Sounds like the typical oversized system...

Maybe you could have the blower slowed down to remove more moisture. Get a tech !

I had an oversized unit in my last garage. Similar issue with high humidity yet temp set point was made. My air handler had jumper positions so I could lower the fan speed while in AC mode (it was factory set at high). This resulted in longer run times for me and better humidity removal. I was warned it might cause the coil to freeze up but this did not occur; maybe I was lucky and my unit was not super sized but just enough larger than needed?

 

[metlmunchr]

How much ductwork is attached to the air handler on supply side and return side? A picture would be useful.

A 5 ton air handler will typically do 2000 cfm @ 1/2" external static. Without adequate static, the same unit can do 2500 cfm or more, and in the process it keeps the coil temperature too high to achieve dehumidification. At the same time, since not much capacity is going toward removing the latent load, it will pull the space temp down fast as all capacity is directed to sensible load.

A simple check would be to measure the temperature drop across the ahu. Using a known good thermometer, check the inlet and outlet temperatures at the unit. The drop should be in the 20°F range. If less, the unit could be handling too much air (or the system could be undercharged). If the system has minimal ductwork, as is often the case with systems in open areas like this, my bet would be on too much air.

If the fan motor is a standard multi-speed PSC, changing the motor speed is as simple as moving the cooling speed connector at the molex connector near the fan motor. If the motor is the ECM type, you'd need the installation instructions to see how to change speed.

Also, any time I ever installed a system in this type building, it was necessary to let the ahu fan run continuously as opposed to cycling it with the condensing unit to maintain the best comfort conditions in the space.

If this is a relatively new installation, typically within the last year, all the above would normally be the responsibility of the installer to provide a properly functioning system under the warranty.

 

[LS6 Tommy]

HVAC systems basically remove around 80% Sensible and 20% Latent heat. Since the thermostat only reads Sensible heat, an oversized system only runs long enough to remove the Sensible heat.

Tommy

 

[Hobby_Man22]

How much ductwork is attached to the air handler on supply side and return side? A picture would be useful.

A 5 ton air handler will typically do 2000 cfm @ 1/2" external static. Without adequate static, the same unit can do 2500 cfm or more, and in the process it keeps the coil temperature too high to achieve dehumidification. At the same time, since not much capacity is going toward removing the latent load, it will pull the space temp down fast as all capacity is directed to sensible load.

A simple check would be to measure the temperature drop across the ahu. Using a known good thermometer, check the inlet and outlet temperatures at the unit. The drop should be in the 20°F range. If less, the unit could be handling too much air (or the system could be undercharged). If the system has minimal ductwork, as is often the case with systems in open areas like this, my bet would be on too much air.

If the fan motor is a standard multi-speed PSC, changing the motor speed is as simple as moving the cooling speed connector at the molex connector near the fan motor. If the motor is the ECM type, you'd need the installation instructions to see how to change speed.

Also, any time I ever installed a system in this type building, it was necessary to let the ahu fan run continuously as opposed to cycling it with the condensing unit to maintain the best comfort conditions in the space.

If this is a relatively new installation, typically within the last year, all the above would normally be the responsibility of the installer to provide a properly functioning system under the warranty.

Also I don't HVAC the shop unless i'm inside.

 

[Terry D]

Is this a mini split or a conventional system. Pictures would help. Is there duct work. What size is the system. How big is your shop.

 

[Bert_]

Also I don't HVAC the shop unless i'm inside.

If you only run it when you're out there then you just have to accept worse performance.

Lots of people turn it off when they're not using it but you can't expect it to act the same as if it was kept at a constant temperature.

 

[Showkey]

If you only run it when you're out there then you just have to accept worse performance.

Lots of people turn it off when they're not using it but you can't expect it to act the same as if it was kept at a constant temperature.

This ^^^^^^^^^^^^^times 10

There’s no free lunch. You either control the indoor climate or NOT.

You can not expect humidity control if you don’t control the temperature, air exchange rate all the time. Part time HVAC a is not going to work is any climate ............especially in Texas with heat and humidity.

Same goes to cold winter climate 20-30* one day, 60* the next creates all sorts of problems not to mention maybe not even cost effective in the long run.