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karstranger

High humidity w/new Trane XL16i air conditioner (heatpump)

karstranger
13 years ago

I live in hot and humid North Florida. This past November, we put up a new modular home and had the local A/C dealer install a Trane heat pump. During this summer, my indoor humidity is usually around 65% and I didn't realize this was a problem until my wife just noticed mold growing on some of the (ceiling) vents.

I called the dealer out and he tested the humidity with some type of wet-bulb device and said sure enough that it was 65% and that is what I should expect indoors in this climate. That seems like hogwash to me based on this forum and any other source I find on the web. I would expect that about 50 - 55% humidity level would be desired.

I went up into the attic and checked that there were no leaks to the individual vents or from the plenum. And, this new modular house really is sealed up well with nice windows and door gaskets - I do not think outside air intrusion is my problem.

This is a variable speed air handler with a two-stage compressor, and a humidity smart thermostat. I basically understand that an oversized compressor unit can cool too fast to remove sufficient humidity, but I think mine is sized about right, and here is the data:

Heated/cooled square footage: 2010 sq. ft.

Rated tonage of A/C: 3 tons

Model# of air handler: 4TEE3F40B1000A

Model# of compressor: XL-16i 4TWX6036B1000AA

Model# of thermostat: TCONT803AS32DAA Touch Screen with Dehumidification Control Comfort Controls

(I see a "4" at the beginning of the compressor model number - I hope that does not mean a 4 ton unit(!))

As with all Florida modular homes, a state agency analyzed the heat/cool requirements examining the windows' size and type, and installed insulation. They came up with an A/C tonnage requirement of 2.8 tons.

I just found out that if I make the air handler run at fast speed by turning down the temperature, in an hour the humidity has dropped from 67% to 54% (and is still dropping).

In reading the manual, the thermostat appears to have been correctly set to 55% internal humidity. And now I know why I have always had to set the thermostat to 80 deg. to actually get 77 deg. internal temperature. The humidity sensor is trying to cool down more in order to satisfy it's humidity setting. But for me, it never gets there because it can't drop the temp by more than 3 degrees from the main temperature setting, and basically the air handler runs at slow speed most of the time especially at night.

For some reason, the slower speed of air handler does not seem to remove sufficient humidity. I almost want to disable the adjustable speed function and just have it come on full-blast.

Any ideas, please? Thanks.

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