Dehumidify using the AC unit?

[A W Warn]

I've been pondering ways to dehumidify inside my trailer while it is in storage in Florida all summer. There are water/sewer/electric hookups 100% of the time. It is parked in the shade of a HUGE live oak tree.

At first I left a window and vent open so that there was cross ventilation. That did not work to keep things dry. Since then I have been using a combination of DampRid and kitty litter, keeping the windows and vents closed. This is better, keeping the trailer dryer and smelling fresher, but not great. I have considered a normal electric dehumidifier, but heat buildup inside the trailer would be excessive when it is 90F+ outside.

What I am considering now:
I changed the AC unit a few years ago and now have a Dometic CCC3 thermostat. It is programable, which would allow me to run the AC unit on a limited/timed basis to remove excess moisture while in storage.

I think there are 3 programable time periods, but not sure at this point how to set it up. I've got to spend more time reading the instructions.

I'm wondering if anyone else is doing this? I would like to know how long you run the AC unit per day and what temperature you set it on, etc? What happens if the power goes off for a day or so, does the thermostat retain the programing? I will be 700 miles north, so I can't check on it for months.

[HowieE]

You are not dealing with a timed function. You are dealing with humidity that fluctuates based on weather conditions so you want a humidistat rather than a thermostat or timed program to control humidity.

If you can rewire your AC to work off a humidistat then the AC will do the job just consider how low you want to go as the electric bill will be effected.

An Air King DH55 dehumidistat or equal should work. This is rated for 110 or 24 volt usage.

[A W Warn]

I'm not going to modify anything or add a humidistat.

Where I am in Florida there is high humidity every day. 60 to 100% is normal.

I don't mind running the AC unit a hour, or two, or three, per day, even if the humidity does not require moisture removal all of the time. If I run the AC I know condensation is being removed. A pint or two per day is all it would take.

I guess I could experiment by catching the condensate while I'm occupying the trailer. Right now it is in the mid 80's at 2:45 pm. I notice the AC unit is cycling on every 15-20 minutes then running a 10-15 minute each cycle. There is a fast drip for that run cycle. I'll measure now.

[crispyboy]

What about a standard 110 v dehumidifier or a free standing ac unit? Have the condensate drain dump into shower and let the grey water valve open to drain on the ground. May want to have someone check it 2x per month.

[A W Warn]

Over an hour today the AC unit removed about 3 ounces, at mid 80's and humidity with lower than normal humidity around 30-40%. I'll continue to monitor in differing conditions.

[A W Warn]

Originally Posted by crispyboy

What about a standard 110 v dehumidifier or a free standing ac unit? Have the condensate drain dump into shower and let the grey water valve open to drain on the ground. May want to have someone check it 2x per month.

An electric compressor type humidifier creates warm air/exhaust as it cools the condensing plate surface (just like the air conditioner exhausts warm air outside). In summer on 90 degree and higher days, I am concerned what heat buildup on the interior of the trailer would do to the vinyl ceiling, etc.

There is no one there during summer that I trust to have a key/enter/maintain anything in my trailer. There are good people there, just none I have that type of relationship with. All of my close friends with mechanical ability are snowbirds like me, gone all summer.

[A W Warn]

Originally Posted by A W Warn

<<snip>>now have a Dometic CCC3 thermostat. <<snip>>

typo - it is a CCC2 10 button.
It is not the 12 button CCC, does not have the de-humidify setting.

[JCWDCW]

If your AC will run without operational problems over your absence, then using the AC to dehumidify is workable. The first hour or so of running a House AC is mostly just removal of water vapor as each pound of water removed releases about 1000 BTU of energy back into the cooled air stream.Therefore, you absolutely need to seal the trailer completely; so no open vents or windows otherwise humidity just keeps pouring back in and the AC has to work harder (longer cycles). Lots of seasonal residents in Florida leave their AC running all summer while they return home to cooler climates. Otherwise the residence is full of mold when they return.

JCW

[jdalrymple]

Most of the "household" dehumidifiers have a built-in moisture sensor that would minimize run times.

I would prefer dryer over concern of inside temps. It is doubtful the dehumidifier would raise temps much when ambient is already in the 90s.



Regards,

JD

[Rocinante]

Hang on, you're not going to be living inside the trailer while in storage, so why do you care whether a dehumidifier warms up the interior? Compressor-based dehumidifiers work better when it's warm, right? So, it would be dry and warm inside. Sounds like a perfect resolution to your humidity concern. Worst case, you could also plug the dehumidifier into a properly rated timer so it only runs a few hours per day. Just be sure drain the dehumidifier into the grey tank via the shower, and you should be in pretty good shape.

I may be missing something obvious, but at the moment I don't see a problem with this approach.

<edit> Ah, now I see you're worried it could get so hot inside the trailer that stuff will peel off and so on. How about setting a timer so the dehumidifier runs at night? Then you could also run the air conditioner during the day via the programmable thermostat You'll have to check in on it from time to time, as you want to be sure both units don't try to run at the same time (popping breakers for sure).

Worst case, count on the AC to dehumidify. Set it for something like 80 degrees, maybe? That would keep it relatively cool and dry inside. However, we agree you'd need to close vents, etc. to keep the humidity from pouring back in every night.

No matter which method you choose, you will want to visit periodically to clean air filters, make sure everything's going according to plan, etc.
</edit>

[HowieE]

The average household dehumidifier is probably 1/10 to capacity of your AC. The AC is designed to offset temperature with dehumidification a secondary function.This would mean the AC would be running on low humidity days while the temperature is above the set point.

If you have sewer I would suggest placing a household unit in the kitchen sink and cracking the gray water valve to drain the water. Some owners put the dehumidifier in the shower but the circulation throughout the trailer is very poor in this configuration.


As mentioned above the amount of effort you put into sealing the trailer will be critical.

[Rocinante]

Agreed, shower positioning is sub-optimal for air circulation, but any self-respecting dehumidifier that will actually keep the trailer dry is going to need a bit of space and will need to sit on the floor or maybe in the shower. It's a conundrum wrapped in a riddle, clouded by an enigma.

[HowieE]

I accept the fact that you are not interesting in modifying you AC but others reading this thread with the same question might want to consider this.

The question that will remain unanswered is the duty cycle of what ever path one takes. A house hold dehumidifier has far less capacity than the trailer AC. Using a house hold dehumidifer will greatly increase the duty cycle and may even take it to 100%. In that case you have not reached your desired set point and mild due may be the result. Running the AC against a temperature setting also will not guarantee you have reached the desired humidity before the set temperature setting.

My original suggestion of installing a humidistat will allow you to run the AC only when needed and assuming reach the desired humidity level.

The installation is just the connection of 2 wires across the current thermostat wires. By setting the thermostat and humidistat this would allow you to run the AC against a temperature set point, a humidity set point, or both.

Interested can see the typical wiring diagram at the bottom of this page. Just consider one of the units as the thermostat and the other as the humidistat wired in parallel.

http://www.airkinglimited.com/instructions/DH55IO.pdf

[Bill M.]

Interesting discussion for me. I also leave a Airstream sitting under a big live oak tree in Florida. We tried several things that did not work. Then we bought a dehumidifier at Lowes. We leave it sitting on the kitchen counter with a drain into the sink. And the gray valve is open and plumbed with a solid pipe to the drain. This method has worked fairly well for us for 3 years now. I know several of our neighbors in the park units leave the AC running all summer. I would worry about the AC drain stopping up from mold and the unit dripping on the floor and in the wall. Ours leaks a little when we are there running it.

Our unit is older, does not have the vinyl ceiling, and sat in Florida under a different oak tree for 18 years before we bought it. So anything that was going to be damaged by heat or humidity is long done in.

I guess the opportunity is here to buy some equipment and actually take some measurements of what happens. You could actually monitor and run the AC remotely, I expect. But I am probably too lazy. We get there early in the day and just deal with whatever problems we have. Costs us a day in a motel on the way to do the early arrival time. Tree limbs falling on it twice, once making an unseen hole in the roof. And leaks,

[GammaDog]

We live a bit east of you in Indian River County. When not traveling, I park the Airstream at either our house or our son’s. Both have 30 amp outlets for the trailer. In either place I set the AC to 80 degrees while in storage in the summer. On the worst days the condensate flows in a continuous stream while the AC is running. In the winter I leave both fantastic fans open with one set to run at about 80 degrees. So far, no mold issues or humidity damage.

[A W Warn]

Originally Posted by HowieE

I accept the fact that you are not interesting in modifying you AC but others reading this thread with the same question might want to consider this.

The question that will remain unanswered is the duty cycle of what ever path one takes. A house hold dehumidifier has far less capacity than the trailer AC. Using a house hold dehumidifer will greatly increase the duty cycle and may even take it to 100%. In that case you have not reached your desired set point and mild due may be the result. Running the AC against a temperature setting also will not guarantee you have reached the desired humidity before the set temperature setting.

My original suggestion of installing a humidistat will allow you to run the AC only when needed and assuming reach the desired humidity level.

The installation is just the connection of 2 wires across the current thermostat wires. By setting the thermostat and humidistat this would allow you to run the AC against a temperature set point, a humidity set point, or both.

Interested can see the typical wiring diagram at the bottom of this page. Just consider one of the units as the thermostat and the other as the humidistat wired in parallel.

http://www.airkinglimited.com/instructions/DH55IO.pdf

To add to the above: Dometic now makes a 12 button CCC thermostat. It has one button that is a "dehumidify" setting, and the CCC is programable for multiple times and modes. It is not plug and play to older model heat pumps or air conditioners. It requires the new thermostat, a new circuit board, and a reset of the dip-switches. For me this mod is too expensive to consider.

[Tater]

I run a regular household dehumidifier in ours when needed during the summer. I got one with a pump built in for water removal. I just pumped it into the sink. Heat was not an issue inside the trailer as the heating/cooling of the dehumidifier made the temperature feel like lower than outside. Running the A/C should work fine and when I've done that I just set the temperature at 80 for the main unit. In reality, it is probably good for the A/C to run some during the summer while you are away just to keep the system in good operating order which would be better than just setting idle for months IMO. So, my recommendation, program the A/C like you planned for a few hours daily at a high temperature and I believe you will be fine.

[A W Warn]

Originally Posted by Bill M.

Interesting discussion for me. I also leave a Airstream sitting under a big live oak tree in Florida. We tried several things that did not work. Then we bought a dehumidifier at Lowes. We leave it sitting on the kitchen counter with a drain into the sink. And the gray valve is open and plumbed with a solid pipe to the drain. This method has worked fairly well for us for 3 years now. I know several of our neighbors in the park units leave the AC running all summer. I would worry about the AC drain stopping up from mold and the unit dripping on the floor and in the wall. Ours leaks a little when we are there running it.

Our unit is older, does not have the vinyl ceiling, and sat in Florida under a different oak tree for 18 years before we bought it. So anything that was going to be damaged by heat or humidity is long done in.

I guess the opportunity is here to buy some equipment and actually take some measurements of what happens. You could actually monitor and run the AC remotely, I expect. But I am probably too lazy. We get there early in the day and just deal with whatever problems we have. Costs us a day in a motel on the way to do the early arrival time. Tree limbs falling on it twice, once making an unseen hole in the roof. And leaks,

Originally Posted by Tater

I run a regular household dehumidifier in ours when needed during the summer. I got one with a pump built in for water removal. I just pumped it into the sink. Heat was not an issue inside the trailer as the heating/cooling of the dehumidifier made the temperature feel like lower than outside. Running the A/C should work fine and when I've done that I just set the temperature at 80 for the main unit. In reality, it is probably good for the A/C to run some during the summer while you are away just to keep the system in good operating order which would be better than just setting idle for months IMO. So, my recommendation, program the A/C like you planned for a few hours daily at a high temperature and I believe you will be fine.

Ok, you've got me thinking. Your situation is very similar to mine. I'm re-considering this option. I could purchase one and giving it a test run when it gets hot next spring, the end of March when it gets in the 90's. I think a 30 pint unit will do the job and the size will allow it to set on the kitchen counter right beside the sink for drainage. Leaving the dump valve open and sewer connected is ok.

I replaced the AC unit a couple years ago. I removed the pan and added the drip cups. If the drain line gets stopped up, the condensate will overflow the cups the run onto the roof, not inside.

Still considering this no cost option also;
I could use the AC, in the afternoons when it is hot inside the trailer. I've re-read the instructions to the CCC2. It is programable, which would allow me to run any mode, any temperature, any time duration, twice per day. If the power is interrupted, the programming will be retained, according to the manual.

I measured how much water was removed running the AC yesterday and today. Today late afternoon for a one hour duration, mid 80's ~60% humidity, about 4 ounces. Yesterday mid 80's ~40% humidity, about 3 ounces. The thermostat set at 76F the AC unit was running 3 to 4 cycles per hour. If I set the temperature to a lower setting, the run time would increase, additional moisture removed.

I agree - everything will be sealed tightly.

I replaced the window and door gaskets about 6 months ago, they are tight. Skylights are Maxim, no leaks. Both Fantastic fans have new lids, no leaks. The bath vent has a cover and lid, so no water entry there. I plan on resealing the beltlines this season. The trailer is water tight, except for one nagging leak in a tail light, which I plan to reseal in the next few days. I purchase all new marker lights last year and will install them this winter, resealing the penetrations beneath them. I inspect and reseal all caulk joints as needed spring and fall.

The rear access hatch door is a little loose in the frame and the fridge vent/louver lets air in. There could be some improvement there.

[Jekerrville]

High technology.

Ponder this. Purchase a large bag of cedar shavings. Place on a big trash bag in the AS.

With a long blade knife, stab into the cedar shavings bag about 20 openings so to maximize surface area exposed to the inside air of the cabin.

Close off all vents and seal all windows. Include all vents over cook surfaces and openings around access doors and ports for power, sewer or fresh water.

At this point the trailer should be ready to be locked up.

There are no bugs that will tackle cedar shavings. This includes ants, silver fish, roaches and MOLD.

The cedar will evacuate many times its volume of humidity and bonds it to its surface. The cedar oil in the chips have an affinity for free vapor water.

When you return to your trailer, open up and air out to a dry, pleasant, no stale oder vehicle. Sack up the cedar chip bag and discard.

Under a big oak tree, in shade and not direct sun, I don’t believe the interior temp will be above ambient by a degree or two.

Nothing to check, dump out drain or plug in.

Works at the ranching operations on the gulf coast.

But, each to his own.

All the best.

[A W Warn]

Where do you get the material? Is it the pet bedding/red cedar shavings, like those available at wallyworld?

If it is kiln dried I can understand wood absorbing moisture. If not would it not already be moist from being exposed to the normal humidity?

The sun does warm the trailer. Morning sun directly hits the hitch end of the trailer. After 10 am until early afternoon dappled sun is on the curb side of the trailer. The rest of the day the trailer is in solid shade. That morning sun does warm the trailer substantially while I am in the trailer during winter. I suppose it is even more during the summer.

ps:
My trailer has a cedar lined closet. We still have the occasional ant and lizard come inside.