Using an AC as a dehumidifier

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Old 04-11-11, 05:46 AM
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Using an AC as a dehumidifier

Hey guys. This is probably a really dumb question but I'll ask it anyway. I know that on the cool cycle, an AC unit (whole house in my case) acts both to cool and dry the air. Will running just the fan cause the system to act as a dehumidifier if the compressor/condenser are not running?

I live in south Louisiana and the humidity here can be oppressive. Sometimes the temperature in the house will be set to something comfortable, but the humidity in the house can make that temperature uncomfortable. I'd like to be able to use my home automation system to sense when humidity levels are high and run the fan to remove some of the moisture in the air. Would running just the fan do this or will I need to drop the temperature set point to get the compressor/condenser running to achieve this?
 
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Old 04-11-11, 06:18 AM
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No...just running the fan will only move the humid air around. If you are right in the draft it may feel a bit cooler, but will still smell "musty".

Newer fancier units have a slow speed dehumidify function that works in conjunction with the smart thermostats. I believe that requires a variable speed fan (not just the typical multispeed). Don't think there's any way to retrofit to an older unit, though there may be a whole system dehumidifiers that can be installed.
 
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Old 04-11-11, 06:33 AM
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That's what I was afraid of. Oh well. Thanks for the info.
 
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Old 04-11-11, 07:32 PM
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you can actually build your own dehumidifier for around 25 bucks if you like. It wont cool the air much but it will take a few cups of water out of the air. What i did was fill a styrofoam cooler with ice and water, put a little water pump i bought at home depot for 12 dollars and a 1/4 inch copper line, comes in 10 or 30 feet and is found in either plumbing or near the refrigerators. i then attatch the copper line to the pump, some adapters may be required, mine is home made adapter. drop the pump in the cooler and then i wrap the copper line all over the front side of a box fan. turn on pump, turn on fan, medium speed. and place a bucket under the fan. the copper line will now have ice cold water running through it and should be very cold, the line will condensate like crazy and then just remove water when levels get high. oh ya and make sure that the ice cold water goes back into the cooler
 
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Old 04-12-11, 07:20 PM
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Sounds like u néed a dehumidifier.
 
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Old 04-12-11, 08:08 PM
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ender 227 it sounds like you have a little to much time on your hands.
 
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Old 04-13-11, 07:09 PM
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i wish i could take credit for the idea but i found it online. But that was last year, this year we are already booked solid for 2 weeks and I'll be lucky if I have any time on my hands
 
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Old 04-14-11, 09:32 AM
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Lightbulb Optimizing a system for dehumidification

Optimizing a system for dehumidification:

Undersize the condenser a little so it delivers much longer & considerably more runtime, even in more mild temp weather.

For a colder coil & more runtime, set blower for 350-cfm per/ton of cooling.

Buy a room temperature differential t-stat with a spread of 2 to 3-F; with half degree set-point increments.

Let the room temp rise to say, 78-F ON setting, then set the t-stat to a 3-F differential OFF, would be 75-F. If condenser is sized a little smaller for dehumidification it will do a fairly good job...
 

Last edited by HVAC RETIRED; 04-14-11 at 09:48 AM. Reason: Added clarification...
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Old 04-15-11, 04:24 AM
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Hvac makes some good points but a two stage system would take care of that. But I will add that any option is not a replacement for a dehumidifier
 
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