Home Improvement Asked on May 25, 2021
My HVAC unit in the bedroom seems to increase humidity when turned on. I live in the tropics so humidity is 50-80% on average. Even if its 55% outside turning aircon on it seems to reach a level around 70% and stay there. We don’t lower the temp that much. from 30C down to 26C.
The unit is oversized but my understanding is that might make it ineffective at dehumidifying but shouldn’t increase humidity right?
The unit does have a cool mode vs a dry mode. Cool mode the fan doesn’t turn off even if the fan is set too low. Dry mode can reduce humidity < 60% but it reduced the temp to 22C regardless of the temp setting which is too cold for us.
The outside compressor is 10M+ from the bedroom so I worry the pipes aren’t sealed as they are old. The compressor and aircon are new though.
I did recently buy a seperate dehumidifier (rated at 15L). When the dehumidifier is turned on when the aircon is it will produce a lot of water (about 5L from 9pm-7am) but the humidity doesn’t go much below 70. In fact it might start at 60 and end up at 70 in the morning.
We also have a air-filter which is effective at removing outside PM2.5 during the night at a low airflow setting which makes me think the room is reasonably sealed from the outside. We do have an ensuite bathroom but we’ve blocked the ventilation holes between in the door inbetween.
Whats going on? Is there anything I can fix on the aircon unit, for example is it problems with leaks in the pipes?
For an A/C unit to reduce the % of relative humidity in your home a properly sized A/C unit coupled with a dehumidifier must run a long time to decrease that humidity. When the A/C unit is first turned on, it begins to cool the room temperature which may actually increase the relative humidity. Just because the room temperature is reduced does not mean that the humidity has also been reduced. It usually takes a long time to reduce the % of relative humidity, that is why you should set the temperature and let the unit run 24/7. Remember, every thing in that room is at the same approximate relative humidity and temperature, (floor surfaces, furniture, etc).If you look up or search for the explanation of relative humidity you will get a good understanding of the term and how it is derived. After the units have run a couple days the % of relative humidity is still excessive then I would look for sources of the excessive humidity, say a leaking pipe, a wall opening, or a source of moisture.
Answered by d.george on May 25, 2021
In my limited experience, most homes in the tropics are not particularly well air sealed. So, air moves from inside to outside easily, even with the doors and windows closed.
As such, when your A/C is running, it may well be that you are getting a great deal of outside air inside, and a great deal of inside air is moving outside - so when you bring in outside air and cool it, the humidity rises (since the water content remains the same, but the capacity of the air to hold water is reduced.) If the building/room is not sealed well enough to slow that air exchange enough that dehumidifying the air in the room is meaningful, you're just dehumidifying the air passing through, and more humidity is coming in with the fresh air flowing in.
Answered by Ecnerwal on May 25, 2021
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