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Old 10-27-2015, 06:12 PM   #1
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New AS, heat pump pushing out high humidity?

I have a new 2015 30' with the ducted air. It's fantastic for AC operation.
The dealer and I tested all the functions when I picked it up, but last night was the first time I really field-tested the heat pump function under real conditions.
Here's what happened. In 10 minutes of operation, I first started to smell something like hot solvents and engine grease from the vents. Then the air got quite warm (a good thing) while the smell continued. Very humid air came from the vents. Condensation formed on all aluminum wall surfaces. My internal hygrometer measured an 11% rise in humidity in 10 minutes. So I shut it off and used the Fantastic vents to get the humidity and solvent odor out of the cabin, and slept with an electric blanket and a vent open.

I thought that heat pumps were supposed to remove humidity? That's what others have told me. Is what I experienced normal? Would it eventually have started pushing out dryer air? What am I missing?

External temps were only low 60s. Humidity started out at 70% and went to 81% in 10 minutes.

thanks!
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Old 10-27-2015, 06:25 PM   #2
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New AS, heat pump pushing out high humidity?

The unit is new. So the first time you use it, it has to burn off all the manufacturing solvents that they used. Just like a new stove that smokes the first time.

The condensate on the walls is normal. Cold walls and warm air equals condensate.

The heat pump will sound different that the AC. There is a defrost cycle that runs to defrost the outside coils. You can read about the system cycles in the Domeic thermostat owners manual. By the way in the auto setting the furnace does not come on until 30 degrees. The only time your tanks are heated is when the furnace is on. 30 degrees is fine. I know water freezes at 32 but there should be enough residual heat in the trailer to not get worried about it.

I found I like the dump valve open when I use the heat pump. It blows straight down and drives the colder air up to the pump.
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Old 10-27-2015, 06:27 PM   #3
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Quote:
Originally Posted by lbdesign View Post
I thought that heat pumps were supposed to remove humidity? That's what others have told me. Is what I experienced normal? Would it eventually have started pushing out dryer air? What am I missing?
Condensation happens when a surface is colder than the dew point of the air around it. Just like a glass of iced tea "sweats" when the glass is cool and the air is warm and humid.

Now, assuming that the amount of water vapor in the air remains the same, as the air temperature goes up the humidity of the air should go down. The fact that your Airstream's relative humidity is going up at the same time the temperature of the air is going up tells me that you're getting more water vapor into the air from somewhere.

My guess is, there was some water had previously collected at a low point in the ductwork, and as warm air started blowing through, that water evaporated and entered the air— which then condensed on the cooler surfaces of your aluminum interior walls.

So the trick now would be to track down where water got into the ductwork.
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Old 10-27-2015, 06:31 PM   #4
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Had you been using the AC prior to testing the heat pump? There could have been icing on the coils.
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Old 10-27-2015, 06:46 PM   #5
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Thanks all!
It's a transitional season here in SoCal, so I used the AC for a few hours during the afternoon, ending around 4pm. The system was off, then I turned the heat pump on experimentally around 1am. So it was off for 8 or 9 hours before I tried the HP function. So I'd assume the coils were fine, but there may have been moisture elsewhere?
I can try running it longer to see if the water vapor "burns off" over time and turns dryer again, when I have more time to let it run and measure the results.

(I figure the smell will eventually go away, but it was unpleasant.)

I am accustomed to condensation on the walls when they are colder than the room air, but this was so rapid and so pronounced that I "pulled the plug" immediately, not wanting to encourage any mildew or rot to start.
I own a portable dehumidifier from my last AS, but was hoping to be able to avoid using it —*at least when using the heat pump.

If HP heat is less pleasant than straight electric heat, I will go back to an electric ceramic warmer, or maybe pay through the nose for a Dyson.
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Old 10-28-2015, 12:04 AM   #6
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Another test: If I run just the fan, the air coming from the ducts has the same humidity as the interior -- there doesn't seem to be any moisture being added just from circulating air through the system.
It's not cold enough yet to test the heat function again, but I'll take measurements!
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Old 10-28-2015, 11:52 AM   #7
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We can share our experience with you as to humidity and the heat pump.

The first time we used our heat pump, we immediately noticed condensation on the ceiling and an odor as you described. I turned it off just as you did.

Several days later I decided to use it again and on this occasion it worked properly without condensation except it had a noisy rattle. We didn't use it again until we returned from our trip and visited CANAM for service.

Service tech's removed a bird nest from under the cover of the AC/HP. Since then we have used the HP many times (ducting makes this much quieter than our previous AS) and have not had a condensation issue whatsoever. Works just as it should!
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Old 11-04-2015, 12:58 AM   #8
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After a few moist tries, I'm now getting "normal" air out of the vents during HP operation. Whatever humidity was in there must have evaporated away. I like it now!
So my experience seems to match cbrittan's. And thank you cbrittan for your experience (and no birds' nests here!)
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Old 11-04-2015, 07:15 AM   #9
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In A/C mode, the inside coil condenses moisture that drips into a collection tray where most drains away to the outside though a tube in the street side wall that is used in most Airstreams. The fins also retain some condensation. How much is up there? I could guess that 1/2 cup or more could be retained if the trailer was parked so that the street side was slightly elevated including what hasn't dripped from the coils after the unit cycled off.

In H/P mode, the condensation now occurs in the outside coils in the form of frost due to the lower outdoor air temperatures and that now requires a regular defrost cycle. On startup, any condensation remaining inside from an earlier A/C cycle will be driven off by the heated inside coil. An initial spike in the inside humidity could be expected on those days when the A/C is run during the day and the H/P at night. There is nowhere for this added humidity to go except to condense on windows and cooler inside metal surfaces. This phenomena is likely prevalent near the coast and may not even be noticed in the high deserts.

I like to keep a couple of the vents open to permit humidity to escape that we can't help but generate in the closed confines of our trailer. Running an exhaust fan when the H/P is initially operated if a noticeable bump in humidity is observed should be helpful. Closing the vents may be desired as the night gets colder.

As previously noted, the paints and adhesives in new equipment often produce an odor when first operated to running temperatures. It shouldn't be toxic but could be harmful to those with breathing concerns and is unpleasant in any case. If the dealership can't take the time to allow everything to burn in before delivery, they could advise new buyers to do it at home before that 1st night out where you think you're getting gassed.
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Old 11-30-2015, 05:48 PM   #10
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First time we turned the furnace on we set off the smoke alarms. If you have not used it yet recommend you open a window and not the door. Exhaust on mine for the furnace is right next to the door. Let it run for several minutes to get the smell out. Our heat pump also causes the inside to sweat when first used. Leave it on and within a few minutes you will see it start to dry out.
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Old 12-01-2015, 02:01 AM   #11
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Thanks everyone. After the initial 2 cycles of high humidity, it has been running dry, and running well, ever since. It's kind of odd to have a heat source up high, since heat rises, but it's nice to have that option when plugged in.
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Old 12-01-2015, 01:07 PM   #12
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Since some of the new models feature quiet ducted air in the ceiling, it would be nice if they could include a vane in the there that would direct the output in H/P mode to a duct maybe in the corner of the closet that would tee into the furnace ductwork delivering most or some of the warm air to the floor area.
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Old 12-01-2015, 08:25 PM   #13
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Silver Goose, that would be brilliant! They do not consider full timers or serious winter campers in the design. Admittedly, it would add weight and expense to do so.
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Old 12-02-2015, 06:46 AM   #14
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Our ducted A/C and H/P work exactly as they should.

It didn't take us long to discover how we could improve the distribution of both cold air from the A/C and heat from the H/P by using a small diameter fan (25$) which sits on the floor silently moving air all the time. This helps by mixing the interior air as cold air naturally falls to the floor and warm air rises to the ceiling just as we would expect.

Under normal circumstances the cooled/heated air inside our AS is generally the same temperature at most any spot and we never suffer from hot or cold corners that get little circulation.

Works perfectly for us and much cheaper than AS could engineer and install a built-in system. Easy to keep clean (collects dog hair) and move if necessary!
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