Window AC dehumidifying question?

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  #1  
Old 07-18-14, 01:58 PM
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Window AC dehumidifying question?

There are times throughout the night that I feel clammy even though the temp is low enough. So basically i'm wondering what the best way to maximize the dehumidifying ability of the ac?

The room is small (~125 sq ft) and doesn't get much sun. I bought the smallest possible BTU unit , 5000 BTU, in hopes that the compressor would running often to remove the most humidity possible.

Its a model that slings the collected water onto the condenser coils to improve efficacy. I drilled 3 small holes in the plastic bottom to allow the water to drain just incase some of that water was getting back into the room somehow.

i used some sheet metal to divert the cold air upwards in hopes that it would leave the compressor on longer.

Maybe its the best I'll get but at night when I go to sleep its 72 and in the low 50's % humidity which is nice. But other times I'll wake up and feel clammy and the temp will be the same or lower and the humidity is 65%.

I almost feel like 5000 BTU is too much for this small room as the compressor does not stay on for long periods of time.

Also this is a cheap unit that the fan runs constantly. When the compressor turns off could the fan be blowing that much humidity back into the air from the evaporating coils?

Any idea on how to get the humidity into the mid 40's? I feel so much more comfortable when its around that.
 
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Old 07-18-14, 03:52 PM
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Most units have an economy setting where the compressor and fan go off together. That would reduce the humidity level.
 
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Old 07-18-14, 07:14 PM
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unfortunately this is a 99 dollar unit that doesn't have that feature. The fan stays on the whole time with this one. Do you think that option would significantly reduce the humidity in the room? Is it worth buying a 5000 btu unit with that feature?
 
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Old 07-19-14, 05:42 AM
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You can buy a 110 volt cool only thermostatic switch. Plug or wire the a/c into the switch and it will cycle the whole unit on/off which will help keep the humidity levels down.
 
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Old 07-19-14, 06:41 AM
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Thanks for the reply Tom. I was researching options like that last night for something that would shut off the fan off when the compressor shuts down.
I guess even something like this could work
Mechanical Thermostat | Digital Thermostat | Programmable
I even considered rewiring the dial controls inside the AC to get the fan to shut off with the compressor.

Does anyone know if the fan running while the compressor is off really adds a significant amount of moisture back into the air?
The way I visualize it is water condenses on the cold evaporator coils and drips down. Because it is tilted it goes out the drain hole to the outside of the ac unit. So when the condenser shuts off and the fan stays on the water left on the evaporator coils is blown back into the room. But how much water can actually be left on the coils?

Checked the temp and humidity a couple times last night.
72 degrees 58% humidity
73/62%
72/64%

Mid to low 60's humidity is just too much for me to feel comfortable at that temp.

Any other ideas beside having the fan turn off to lower humidity? Say the room is 80-85 degrees. When I turn on the ac it runs for ~30-45 mins to cool the room to 72 and the humidity drops to low 50's high 40's. But then the humidity slow climbs back up to the 60's even though the temp stays the same.

Thanks in advance for any further help
Jay
 
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Old 07-19-14, 07:07 AM
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Edit: sorry double posted
 
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Old 07-19-14, 12:06 PM
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Having the fan shut off with the compressor will not really affect the humidity.
You already figured out that the a/c needs to run continuously for the coil to maximize moisture removal.
In actual fact it might help slightly by circulating the air within the room causing the unit to cycle on sooner.

You could try running the unit at its lowest fan setting which will reduce the evap coil surface temperature and decrease the capacity slightly.
There is also a chance that your drilling holes in the casing caused a negative impact on the unit as the water being slung against the condenser is used to slightly lower the head pressure on the compressor.
 
  #8  
Old 07-19-14, 02:27 PM
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I agree with GregH regarding the holes. The water in the rear of the unit was definitely not your issue. It was designed to operate that way.
 
  #9  
Old 07-19-14, 03:50 PM
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Didn't see how the holes could do anything either. Easy fix as the holes are tiny and a little duct tape will close them right up.

Borrowed my parents 5000 btu with an energy save mode just to test out if the fan shutting off with the compressor will help at all. Its basically the exact same ac except with digital controls

Seems like a AC that less than 5000 btu woudl be ideal but don't think those exist.
 
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Old 07-19-14, 06:19 PM
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Well, there is a solution that would have a low cost to implement but not so cheap to operate.
In commercial applications where humidity control is critical, an a/c system is used to lower the temperature but when the temperature is satisfied but the humidity is still too high the dehumidification controls bring on an electric heating element that will prevent the temperature from dropping.

So, set the temperature on the a/c lower and plug in an electric heater!
Or, maybe get a dehumidifier.
 
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Old 07-20-14, 07:52 AM
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I use a LASKO Wind Machine 3300 floor type fan, with vertical adjustments, on a half-ton 6,000-Btuh to cool +650-sf 1st floor of my 1937 farm home. Less than half-ton upstairs for nighttime...

I'd try that type of fan to either be on a high bench to draw the cold discharge air away from the A/C or put it in the doorway & blow warm air from the other areas toward the A/C. That will dilute the air & should keep the A/C from short cycling as much.

Drilling the holes will usually not hurt anything (unless it is extremely hot outdoors) as it will just run a higher head pressure which (with most metering devices; non-TXV) could get the evaporator colder helping dehumidification some when temps are moderate outdoors.
 
  #12  
Old 07-20-14, 11:08 AM
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Thanks for the replies. Its was cool last night and will be cool again today so I'm not sure if the energy save mode will make a difference. I already have a diverter to try to push the cold air up higher to keep the compressor on longer. I have a box fan that I can put on the other side of the room to blow the warmer air towards the ac to see if it will stay on longer.

I actually tried a dehumidifier last week. It worked great but its way to loud and then there is the cost issue of operating the two machines. Once cooling one adding some heat back into the air.

I've see mini dehumidifiers advertized but don't think that would remove enough moisture in a day to notice a difference. Uses some type of thermo electric technology .
 
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