Placing Dehumidifier in Cold/Warm Space for Optimal Condensate Flow

[randomjuice]

Hi. I purchased a dehumidifier in order to prevent condensation on aluminum windows in one area of my home. My home is comprised of two spaces: a warm space (20-22°C) and a cold space (<16°C). The door separating these spaces must remain slightly open for several hours of the day/night, so they share the same air. Consider absolute humidity is the same in both spaces and the relative humidity in this region stays above 70% consistently.

In order to achieve the higest flow of water condensate, should the dehumidifier be placed in the cold area (low temp, high HR) or the warm area (warm temp, lower HR but >70%)?

 

[.Scott]

Assuming equal dew points, it will work more efficiently in the low temperature area. Water will condense out of the air quicker with the cooler air.

 

[randomjuice]

Thank you

 

[russ_watters]

Hi. I purchased a dehumidifier in order to prevent condensation on aluminum windows in one area of my home. My home is comprised of two spaces: a warm space (20-22°C) and a cold space (<16°C). The door separating these spaces must remain slightly open for several hours of the day/night, so they share the same air. Consider absolute humidity is the same in both spaces and the relative humidity in this region stays above 70% consistently.

In order to achieve the higest flow of water condensate, should the dehumidifier be placed in the cold area (low temp, high HR) or the warm area (warm temp, lower HR but >70%)?

Assuming equal dew points, it will work more efficiently in the low temperature area. Water will condense out of the air quicker with the cooler air.

Whoa, not so fast. The correct room to put the dehumidifier in is generally the room where the condensation is happening! (which should be the warmer room)

...but this scenario does not make much sense. Is the warmer room open to outside? Is the door open or closed when the condensation happens? At what outside temperature does the 70% RH occur?

16C and saturated is the same absolute humidity as 22C at 70% RH. If the warmer room is at ambient, how does the cooler room get cooler?

 

[jim hardy]

Assuming equal dew points, it will work more efficiently in the low temperature area. Water will condense out of the air quicker with the cooler air.

That's an interesting thought.
Carnot efficiency is indeed favored by lower exhaust temperature

the closer Th and Tc the smaller the denominator

So if by 'efficiency' one means pints of water condensed per kilowatt-hour of electricity consumed
that's the right answer
at least until dewpoint gets down to the usable limit of whatever refrigerant is inside the dehumidifier.

Just check it occasionally for ice on the cold coil

In order to achieve the higest flow of water condensate, should the dehumidifier be placed in the cold area (low temp, high HR) or the warm area (warm temp, lower HR but >70%)?

That'd be an interesting experiment for our DIY thread -
one could catch and measure a couple days worth of condensate
and one of these $20 gizmos would tabulate the kwh used (i see they have got even cheaper since i last looked)

i found one laying in the mud at my junkyard. It looked so rough they just gave it to me.
I washed it out and now don't know how i ever got along without one.
To borrow a phrase from Red Green - it's "The Hobbyist's Secret Weapon "

old jim

 

[Tom.G]

In order to achieve the higest flow of water condensate, should the dehumidifier be placed in the cold area (low temp, high HR) or the warm area (warm temp, lower HR but >70%)?

For example, at 80°F and 60% RH the http://www.santa-fe-products.com/santa-fe-classic/ removes 110 pints per day. At real-world conditions of 60°F and 60% RH the Santa Fe Classic removes 60 pints per day—conditions where conventional units may not remove any moisture at all!
from: https://www.santa-fe-products.com/dehumidifiers-why-low-temperature-operation-is-important/

This would indicate best results by placing the dehumidifier in the higher temperature room, if there is enough air circulation to the cold room to adequately reduce its humidity.

The reason the above states that at 60°F "... conventional units may not remove any moisture at all!" is that the cooling coils tend to ice up at lower ambient temperatures. Units rated for lower ambient conditions use a higher airflow thru the coils. This tends to make the low temperature units noiser. Some (many?) models detect icing and shut off the cooling until the ice melts.

For actual energy usage, my 70pint per day unit is rated 2.0L/kWH. (don't you love mixed units )

Another thing to watch out for is can you clean the coils and water collection area of dirt and mildew. My Fridgidaire - made by Electrolux - has the water drip area under the coil completely non-accessible. After about 1000Hrs of runtime two of three drain passages were completely clogged with a jelly-like mass, fortunately the third drain was clear. Once I managed to remove the plastic cabinet, I discovered that the drip pan was the first item in the construction. There was no way to get at it without a TOTAL disassembly. It took several hours of pouring in Vinegar and flushing with water to clean the thing. If that happens again, the beast is going to the trash heap!

So keep maintenance in mind when shopping.

Cheers,
Tom

 

[256bits]

The correct room to put the dehumidifier in is generally the room where the condensation is happening! (which should be the warmer room)

I was going to write that down, and I looked back that you already had.

In any event, it takes way more energy to remove the latent heat, than to cool the air to the dew point ( and beyond since the coils have to be at a lower temperature to remove any appreciable amount of moisture ).

 

[jim hardy]

So keep maintenance in mind when shopping.

of course this old maintenance man agrees wholeheartedly.

I discovered that the drip pan was the first item in the construction. There was no way to get at it without a TOTAL disassembly.

i wager the fan is held on with a left hand thread too, as in my Vornado room air filter.

Anyhow
at 60F and 60% RH the dewpoint is 46°F
https://www.calculator.net/dew-poin...dewpointunit=fahrenheit&humidity=60&x=80&y=14
at 60F and dewpoint of 32F,, RH is 34%
i'd aim a design at minimum coil temperature of 35 to 40F so as to preclude icing. and accept that RH numbers at low ambients won't look very impressive ..

I dislike the unit RH , much prefer to think in dewpoint.