Humidity! How to drop 20-30% in an hour.

When reading the last few posts, one thing occurred to me:

Your car uses the heat and cool process to control humidity in any weather, including getting the vapor off the inside of the windows when it rains. The engine's heat is waste heat anyway, by which I mean it is "free," but it lets the A/C dry the air in any weather to a nice, comfortable temperature.

And since vehicles are built very air-tight, there is essentially no other air coming in that didn't go through the heating/cooling process. It isn't uncommon to have air in your car that is very, very dry indeed, like under 30% relative. Ever notice how thirsty you can get during a long trip? As far as your respiratory system is concerned, you're in the desert.

pianotuna wrote:
There is no need to be cycling. Just turn on a small heat source while running the air conditioner. 500 watts is enough for my 28' class C.

Exactly what we were doing.

I can't recall if we used our 1500 watt electric heater on it's 1500 watt or 750 watt setting. Probably it's 1500 watt setting - since it has a temperature control, anyway, to modulate it's ON/OFF cycling as necessary to comply with what you set the temperature control at. Our 30 amp RV wiring can easily handle both the air conditioner and heater set on high at the same time. (We can even do this dry camping using the 4000 watt built-in generator.)

I'll mention again that I call this "a poor man's dehumidifier" for folks that already have a small electric heater in an RV with an air conditioner .... there's no need to buy a dehumidifier.

By the way, note that a "real dehumidifier" contains both a compressor and a heat pipe to warm the outgong dehumidified air - closely resembling the "poor man's method" of using a small heater in conjunction with an air conditioner. Here's a couple of links explaining how dehumidifiers work. In the first link ignore the drinking water portions and concentrate on the excellent explanation of how dehumidifiers work and when to use them:

http://alumni.stanford.edu/get/page/magazine/article/?article_id=29155

http://www.howstuffworks.com/dehumidifier1.htm

Hi Disk,

There is no need to be cycling. Just turn on a small heat source while running the air conditioner. 500 watts is enough for my 28' class C.

DiskDoctr wrote:
So next time you're out camping and it's crazy humid you can say to yourself, "I know it sounds crazy, but if I heat my camper to 80F then cool it with the A/C it will help with this cold, clammy feeling," Remember, you read it on the internet, so it MUST be true! :B

Great post Diskdoctr. I tried the heat/cool method several weeks ago on a rainy night when the outside temp was ~75 degrees and the inside RH was 75%+. I used a small electric heater on the low setting (~630 watts, 5.3 amps). The method worked but the 30 amp breaker tripped several times. We had the AC/TV/VCR on and with the convertor were close to the max – plus on a suspected worn out campground breaker.
I was on a mission to buy a small dehumidifier not only for the summer time but those times during the fall when the RH builds due to showers/rain/etc. Maybe I’ll continue to try this method and run an extension cord to the electrical post. Part of the problem with me sometimes is “too much information”…..maybe hiding the Temp/RH meter would help.

Thanks all for posting more in-depth explanations and ideas. All good info :)

As another said it better than I, "periodically heating then cooling" can really help reduce the humidity and increase the comfort in a camper on an exceptionally humid day.

So next time you're out camping and it's crazy humid you can say to yourself, "I know it sounds crazy, but if I heat my camper to 80F then cool it with the A/C it will help with this cold, clammy feeling," Remember, you read it on the internet, so it MUST be true! :B

Don't be a afraid to give it a shot. And post back to let us know if/how it worked out for you.

Another poster is also correct about heating items in the camper adding moisture. When we run the coffee maker (yes, I would have mocked that statement in my younger years as 'not really camping') we put it on top of the stove cover and make sure we run the external exhaust- and most of the time we remember to unlatch to outside cover ;)

Keep in mind that burning propane produces a tremendous amount of moisture and while properly installed furnaces/water heaters vent it outside the stove top and or oven do not. That little fan in your hood does not move a whole lot of air. When you do a lot of cooking you need to get outside air venting in, through and out of the trailer. :C

Of course an electric heater running inside an RV is also dry heat in that it does not introduce any additional moisture into the interior.

Our propane furnace, like most of them in late model motorhomes, only recirculates interior air so it too does not introduce any additional moisture into the interior.

I interpreted the main idea of the OP's original post as: "Hey, we can both remove moisture in our RV using it's air conditioner - while at the same time not having to cool it too much to remove this moisture - by periodically heating the RV in between air conditioning sessions."

We do the same thing by running electric heat and air conditioning at the same time with both control settings just about right so as to make and keep the interior both dry and at a comfortable temperature, regardless of the outside temperature and humidity.

Ironically, the part of my post that has been re-posted over and over was not directed at the idea of heating and cooling simultaneously, which as others . . . and I . . . acknowledge, will work. It was directed to a post in which it was stated that propane heat is a 'dry' heat.

As a former HVAC professional, I used to hear people make such comments; that somehow, heating with a fossil fuel heater has magical properties that help to dry the air, more so than other means of heating. Not so, and doubly so in a trailer, as trailers use outside air to combust and vent it directly to the outside. Inside and outside air do not mix in this system, which would be called "high efficiency" in a stick home.

The "well, but" to this is that low efficiency furnaces in some homes DO use inside air for combustion, which of course must be replaced with outside air. In the winter, when you bring outside air in, no matter how humid, when it warms the air becomes very dry in a relative sense. So burning a fossil fuel can be drying, but only because of the process of combusting inside air and replacing it.

How relevant is the effect? This is right out of the charts: if you bring 20 degree, 100% humid air into the home and warm that air to 70 degrees, the humidity (relative to temperature) is 14%. Very, very dry. Desert air is generally considered to be 25%, for comparison. Imagine what happens with zero degree air brought in and heated! My chart doesn't even go below 20 degrees, but it would be single-digit humidity.

So, OP, I never disagreed with your post. In the same situation as you described, I'd do what you did: run heat and air at the same time. It works, and as I said, some office buildings use it year around. My earlier posts were directed to only those who frequently run into cool temperature, high humidity conditions that are best dealt with by other means. In my opinion, that is.

K3WE wrote:
Now, does the camping world need to change our ways and start running both the heat and AC every time it gets a little humid???...

Well ... yes - sometimes.

(By the way I misspoke in my posts earlier. What I do to reduce humidity in our RV when it's only marginally warm outside but real moist outside is to run both the RV's air conditioner and an electric heater at the same time - NOT the RV's air conditioner and the RV's propane furnace at the same time.)

Here's the macro situation in the past under which we ran both a heater and an air conditioner at the same time to stay comfortable:

1) We were touring the Deep South and Southeast in July and August under special circumstances that gave us no choice ... I recommend that no one EVER DO THIS in an RV this time of the year.

2) It was a temporary RV experience (10 weeks only), so we did not want to invest in a stand-alone quality dehumidifier (which can cost almost as much as an air conditioner) just for this trip.

3) Energy efficiency was of no concern for the short time periods that we had to run both an electric heater and the air conditioner to be comfortable in super-humid but not overly hot evening or nighttime conditions.

Under the three criteria above, our use of both an electric heater and the RV's air conditioner at the same time was what I called "a poor man's RV dehumidifier". I called it this because we already had the electric heater and the air conditioner - so why spend the additional money to buy a dehumidifier?

Also FWIW, most dehumidifiers have a water tank that has to be emptied periodically. Using my poor man's RV dehumidifier setup, there was no water tank to bother with, as the water was removed by the air conditioner and drained automatically outside the RV. ;)

DiskDoctr wrote:
...No need to get upset over it :S...

Ok Disk Doc...I saw you and another poster going back and forth and saw you using ALL caps while disputing the word "remove" and specifically not acknoledging that you were using an RH meter to make your case.

It seems that you do get it- and thanks.

On another subject- yeah, it is my opinion that you may (emphasis on "may") be a bit over the top in having the heater and the AC fighting each other.

If you really need to remove humidity in a camper (where almost none of us have formal dehumidifier sitting around), your method definately works...zero argument.

Now, does the camping world need to change our ways and start running both the heat and AC every time it gets a little humid???...I'll stand by my point that chosing a comfortable temp and letting the weather and camper gradually stabilize is cheaper and easier...

Now- as to the question if YOU really needed to remove humidity or could have just let things work out more gradually- yes, I wasn't there and am not in a good position to make that call.