I have recently purchased a new portable air conditioning unit. For some reason when I am using it the RH increases rapidly. The exhaust pipe goes through the wall and appears to have a good seal. The BTU’s seem to be suitable for the room size. Does anyone have any suggestions on what the issue could be?
Why is the portable air conditioning unit increasing relative humidity
air-conditioning
Related Solutions
I have seen outside units whose paint has faded and become chalky-looking after several years of service. I suppose waxing it might prevent or delay this, but I agree with Doresoom that the benefit is really going to be mainly cosmetic.
You could build a wood frame that fits in the window with an interior hole large enough to accommodate the AC unit. This also has the advantage that you won't have to hold the window open, while juggling the unit into place. You can install the light weight frame, then slide the unit into place.
I built one when I lived on the second floor of an apartment building, because I was always afraid I would drop the unit out the window while installing it. I used foam tape around the exterior and interior of the frame, to make sure I got a good seal around the window and AC unit.
For a unit that only vents through the window (not sits in it), you could build a smaller frame with a port to allow the vent to pass through. Filling the interior of the frame with Lexan will reduce the amount of wasted window space.
(You could always use smaller lumber for your frame, if you want it to have a lower profile. The frame size in the image is just an example, to illustrate the idea).
Best Answer
The amount of water vapor that air can hold depends on the termperature. Warm air can hold more moisture than cold. The relative humidity is the amount of moisture in the air compared with the maximum that it could hold at that temperature.
If you rapidly cool the air, then the relative humidity will go up, even if the total amount of moisture stays the same.
Air conditioners condense moisture from the air. In a portable unit, there is probably a tank that needs to be emptied from time to time. But it may take some time for enough water to condense out to make up for the temperature drop.