Managing Humidity in the T@B 400

qhumberd

I’ve scanned a few threads on this and I ran across not many that mentioned stabilizing the temp and humidity levels in the camper on hot humid days followed by cooler but very humid nights. Our temp and humidity gauges are next to the bed, and I started noticing a big swing in humidity when the CoolCat had dropped the inside temp to the mid 70s. On the initial cool down the humidity meter would drop to 50% or lower, but when temperatures reach the thermostat set point, humidity would start to climb and depending on how long the compressor was off, could climb to 70-80%. This was a real issue at night, when temperatures inside would be 72 and relative humidity at 75%. It was just clammy feeling.

The comment by @rhyno was my ah ha moment

https://tab-rv.vanillacommunity.com/discussion/13887/running-both-air-con-alde-to-control-humidity

I just couldn’t figure out how so much humidity was being produced in the interior with the fan running low or high and compressor off. Even when no people were inside. So here is my thought. 

When running the CoolCat on fan AUTO mode, the fan stops when the inside reaches set temperature. Depending on how much heat gain happens, the unit will run every few minutes or even less frequently. Watching humidity now shows it stays at a comfortable 55% when outside is 80 and it is very humid.

I believe the constant fan mode is drawing outside air around the CoolCat and some gets pumped into the cabin with the fan running all the time, thus increasing the humidity in the cabin more than the intermittent compressor cycles can handle. Compressor can dry the leaked outside air when fan and compressor run together and turn off together.

This is a major improvement at night, when temperatures drop but humidity remains high. The fan running then  is just pumping moisture into the cabin but not raising the temperature enough to run the compressor. Therefore we are sleeping clammy.

We are driveway camping for a couple weeks now so I’ll get to check this further, but so far today cabin humidity has remained at 55% and temperature 75. It’s great. Fan AUTO mode seems the solution.

Other experience please comment.

rhyno

My thoughts re rising humidity when running fan on constantly vs Auto... I wonder if it may be due to the warmer temp when running fan only between AC cycles resulting in faster evaporation of the condensate from the unit. When that happens, the Cool Cat pumps more warm, humid air into the cabin. That's my guess. 

Now that we have a couple of summers under our belt, I'll add a couple more observations for maximizing AC performance:

1. If the AC has sun hitting it, you'll see a pretty big performance hit. We bought a 5 foot wide shade that attaches with suction cups near the roof above the AC, and we stake it out about 10 feet from the camper for when we camp with sun hitting the AC side. This gives it a little awning and seems to help. 

2. Putting a diverter on like below helps tremendously. The cool cat pulls fresh air in on either side, and exhausts ~150 degree F air from the middle. Breaking up these zones drops the intake temp by about 50 degrees, improving cooling. This especially helps when you camp in full sun.
https://tab-rv.vanillacommunity.com/discussion/comment/169392#Comment_169392
Here's my cowl, made from coroplast and attached with Velcro. 

Yoshi_TAB

Hi,  

During a recent trip to a high humidty area, I encountered the same humid conditions inside a 320 when the Air 8 AC  fan was set to run all the time and the compressor cycled off (when the set point was reached).   In between compressor cycles, I observed the humidity in the cabin rising (to the uncomfortable/clamy state).  When I made the change to only run the fan only with compressor cycles, the humidity noticeably  dropped and was much more comfortable in between compressor cycles.  I came to the conclusion that the moist air from our breath (the same reason you crack windows to avoid condensation) and the small amount of condensation moisture (left on evaporator) that did not drain and picked up by the recirculating air, was putting moisture in the air when the compressor was not on and the fan was running.

qhumberd

rhyno said:

My thoughts re rising humidity when running fan on constantly vs Auto... I wonder if it may be due to the warmer temp when running fan only between AC cycles resulting in faster evaporation of the condensate from the unit. When that happens, the Cool Cat pumps more warm, humid air into the cabin. That's my guess. 

Now that we have a couple of summers under our belt, I'll add a couple more observations for maximizing AC performance:

1. If the AC has sun hitting it, you'll see a pretty big performance hit. We bought a 5 foot wide shade that attaches with suction cups near the roof above the AC, and we stake it out about 10 feet from the camper for when we camp with sun hitting the AC side. This gives it a little awning and seems to help. 

2. Putting a diverter on like below helps tremendously. The cool cat pulls fresh air in on either side, and exhausts ~150 degree F air from the middle. Breaking up these zones drops the intake temp by about 50 degrees, improving cooling. This especially helps when you camp in full sun.
https://tab-rv.vanillacommunity.com/discussion/comment/169392#Comment_169392
Here's my cowl, made from coroplast and attached with Velcro. 

Thanks for your observations. This is clearly a great way to improve efficiency of the AC. As far as humidity in the cabin, we have been driveway camping for the last week using the AUTO setting and the humidity stays in the 50% range. Camper is in partial shade thru the day and the temperatures here are 90s with humidity very high.

What I am curious about is the air flow path of the CoolCat. I don't think I understand the design. Has anyone investigated this. To me it looks like the filter compartment is not that well sealed but I am not sure how the air is supposed to flow thru the unit over the two coils with the pan beneath. I just am observing that when my fan runs all the time that humid air is being drawn from somewhere and ends up in the cabin.  In my case it is clearly more than expired air.

Thanks

BrianZ

What happens with that cowl on when it rains?

Denny16

I would turn the cowl the other way round when rain is forecast.
cheers