View Full Version : Does using a dehumidifier increase evaporation?
moppy
01/19/2014, 12:30 AM
Anyone know?
It seems like it does.
I have it set to 55% and it has removed the excess moisture from the windows but it seems like I am having more evaporation now...
Reefer54
01/19/2014, 12:36 AM
It probably will induce more evap. That's kind of the point of dehumidifiers...remove moisture from the air....thus, if a tank really only evaporates at a consistant rate until the moisture in the air and the (barometric...) pressure equalise, then when removing moisture from the air, the two will not equalise without more evap, considering that evap is a substantial contributor to the humidity in your home....
thats how my brain would go about it, though i live in the mountains, and my evap goes up in the winter, when i use dry heat to heat my home....
Triggercdog
01/19/2014, 12:42 AM
+1....I agree with reefer54....I know a little about dehumidification (I own an a/c business here in swfl)....a dehumidifier will cause you to evaporate more water from your tank...
moppy
01/19/2014, 01:24 AM
Is there a better way to reduce the moisture level in a room with a large fish tank then?
Mine's a 200 gallon tank.
fishysteve
01/19/2014, 02:30 AM
I'd like to know that too. I spent an hour today bleaching the mildew off my window sills.
ridetheducati
01/19/2014, 08:01 AM
Improve air exchange and circulation.
fifthtoe
01/19/2014, 08:38 AM
I'm thinking that anything done to reduce moisture will in turn increase evaporation to an extent. Unless you are able to reduce evaporation from the source. I don't know of ways to reduce evaporation other than covering stuff up; which will probably reduce aeration of your tank.
dkeller_nc
01/19/2014, 09:01 AM
I can answer this authoritatively. Absolutely - running a dehumidifier will increase evaporation from a reef tank.
From a thermodynamics point of view, evaporation is driven by three things: the temperature difference between the body of water and the surrounding air, air movement over the body of water, and the relative humidity of the air moving over the water.
The last item is what I think you're asking about. The relative humidity of air is a percentage measurement of the degree of saturation of that air with water vapor at the air's temperature. If a body of water is the exact same temperature as the air in contact with it, and the air is at 100% R.H., then no water will evaporate from the body of water, regardless of how quickly that air is moving across it.
However, in practice, even if the air in the room is at 100% R.H., water will still evaporate from reef tank if the temperature of the water in the tank is significantly above the air temperature in the room because the tank water will heat the air, and the warmer the air is, the more water vapor it will hold (referred to as "absolute humidity" by engineers). So air that starts out at say, 68 degrees F at 100% R.H. is heated to 78 deg F and now has a R.H. of 70%, and the reef tank water will now evaporate into that under-saturated air.
From the standpoint of practical considerations, you generally have 4 solutions to overly-humid air in the tank room, and possible mold/mildew issues:
1) Leave doors open and/or run the HVAC fan on a frequent basis to mix the tank room air with the air in the rest of the house. That will have the effect of raising the humidity throughout the house, but that's typically a good thing in the dead of winter.
2) Purposefully evacuate the air from the tank room with a small kitchen-hood type fan. This can even be done with a computer fan and a dryer vent penetration through the wall. This method has the drawback of pulling the make-up air through cracks under and around outside doors and windows, and in cold climates, increases heating costs.
3) Install an air exchanger. These units are similar to solution #2 in that they draw in outside air to vent the tank room, but they use the out-going air to heat the incoming, thus saving significant energy in cold climates.
4) Run a dehumidifier in the tank room. Presuming air movement over the tank water is kept to minimum, the dehumidifier will keep the tank room air at a comfortable RH, though it will increase evaporation from the tank to some extent.
biecacka
01/19/2014, 09:58 AM
So should I stop running my ceiling fan over my tank in the winter?
Corey
ca1ore
01/19/2014, 10:31 AM
Anything that reduces the humidity level in your fish-room, whether better outside air circulation, a dehumifiier, A/C, etc., will increase the rate at which water evaporates from your tank. In warm climates with low humidity, evaporative coolers work on this principle, but they only function efficiently to an ambient humidity level of about 50% because any higher than that and water doesn't evaporate quickly enough to be useful at cooling the air - same principle in your fish-room.
If you have a reasonable ATO system, not sure why this would be a problem. A very humid room creates all sorts of problems, from mold and mildew to quicker rusting of metal, etc. I absolutely run an AC/dehumidifier in my sump room from about May through September. Higher ATO frequency also allow me to get more kalk into the system.
dkeller_nc
01/19/2014, 10:47 AM
So should I stop running my ceiling fan over my tank in the winter?
Corey
Presuming you don't need it for cooling (such as if you had really intense MH fixtures), and aren't trying to increase the evaporation rate, such as if you were trying to get more kalkwasser into the tank for Ca/Alk purposes.
TropicalTANK
01/11/2016, 04:40 PM
I have the opposite issue myself, Im wondering if you can advise me. I have a 3000 Litre tropical fish tank, Im having alot of evaporation which id like to reduce. Im thinking about installing a "Heat pump air conditioing system" This will heat the room ambiant to match the tank temperature (26c).
I noticed in your post (linked above) you said three things effect evaporation, temperature difference between the body of water and the surrounding air, air movement over the body of water, and the relative humidity of the air moving over the water.
my understanding is this air will be "sensibly" heated to no moisture will be added thus decreasing the relative humidty meaning this warmer air could now hold more water vapour.
my question is will this decrease evaporation overall as the water temp and air temps will match? Or will it actaully have the oposite effect and increase water evaporation from my tank due to the RH being lower?
Thanks for your time!
It really is appreciated!
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