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Old 05-23-2011, 01:31 AM   #1
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Running AC and Dehumidifier


I live in Maryland in an 800 sq ft condo.

Last summer, I had a new 18000 BTU thru-the-wall A/C installed. When it is fairly hot outside, it does a great job cooling and an OKish job of dehumidifying.

However, when it is 70-75 and rainy or sticky, it cools very rapidly and leaves the air feeling clammy and humid. I hate humid. I understand that this is because the compressor is not running long enough to dehumidify. I have tried adjusting it to low with no success.

The other day, I got a 50 pint Frigidaire portable dehumidifier. It is doing a terrific job and has removed gallons of water from the air. I run the AC along with it on low at 75 degrees or so. (Used to have to put it at 72 to get any kind of dryness.)

All was well Ė after 10 yrs in this swamp I was finally cool AND dry. That is, until a friend said I should never run a dehumidifier AND AC at same time. He said itís making both work harder and that my AC is wrong size. Maybe AC is wrong size, but since I picked it out, I donít think itís going anywhere.

Q: Am I violating some law of nature or HVAC by running both? Any ramifications of which I am unaware??

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Old 05-23-2011, 01:46 AM   #2
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Running AC and Dehumidifier


How did you try and slow down the compressor? I think you may mean blower motor fan speed.

The longer the system runs and on lower blower speed the better it will dehumidify. 1.5 ton system sounds about right. With a a bigger system then it will not run as long as it will reach set point (desired temperature) quicker and thus not dehumidify properly as it won't have the chance, resulting in possible mold and mildew.

Of course the size all depends on your heat loss but without knowing that I think 1.5 is fine.

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Old 05-23-2011, 02:10 AM   #3
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Running AC and Dehumidifier


Thanks - I thought I had sized it right. I used an online calculator that took into consideration many variables.

It just won't run very long when it is in the 70s outside even with the fan speed set to low...
I am loving the dehumidifier - Is there any harm in running it at the same time??

Important point, my electrical is included in condo fee, so I don't pay a bill directly.
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Old 05-23-2011, 02:23 AM   #4
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Running AC and Dehumidifier


Quote:
Originally Posted by mscrankypants View Post
Thanks - I thought I had sized it right. I used an online calculator that took into consideration many variables.

It just won't run very long when it is in the 70s outside even with the fan speed set to low...
I am loving the dehumidifier - Is there any harm in running it at the same time??

Important point, my electrical is included in condo fee, so I don't pay a bill directly.
Not that I'm aware of, no.

http://www.dri-eaz.com/VAULT/DoACsDehu.html

Thermostat
Never set the thermostat so the temperature drops too low, either for the comfort of occupants, or to retard the rate of evaporation. Our goal when using the air conditioner for restorative drying is to have the unit in operation as much as possible. If the logistics are right, setting the thermostat a little lower than normal will help. Running dehumidifiers will help keep the temperature elevated. Also, placing a dehumidifier near the thermostat will help keep that area warm which in turn will "fool" the system into thinking that the building is warmer than it actually is. The result is dryer air in less time because you have the advantage of running both the air conditioner and dehumidifiers at the same time.
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Old 05-23-2011, 02:28 AM   #5
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Running AC and Dehumidifier


Thanks Doc!
I appreciate your help

It seems like the two are getting along for now.
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Old 05-23-2011, 02:29 AM   #6
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Running AC and Dehumidifier


This is a very common dehumidifer. You set the desired humidity level and the desired temperature on one thermostat and each system, the actual air conditioner and the individual dehumidfier, can run in conjunction with each other, no harm, or when the desired set point is reached and if it's still above desired humidity level only the dehumidifer runs, and vice versa.

http://blog.aprilaire.com/blog/clean...tioner-working
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Old 05-23-2011, 02:31 AM   #7
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Running AC and Dehumidifier


Quote:
Originally Posted by mscrankypants View Post
Thanks Doc!
I appreciate your help

It seems like the two are getting along for now.

You're welcome.
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Old 05-23-2011, 05:19 AM   #8
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Running AC and Dehumidifier


Many houses have whole house dehumidifiers that run at the same time the A/C runs. No harm in running both at the same time.

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