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Old 02-11-2012, 07:47 PM   #1
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Heat pump efficiency

We got our new 25 FB Flying Cloud back from the dealer yesterday where they fixed some small issues and also addressed an issue with the ccc that has not worked right since new. Yesterday when we brought the unit home I turned on the CCC in the heatpump mode set the temp on 68 (about 44 outside). After running all night in the heatpump mode without much outside temp change the best I could do was about 59 degrees as an inside temp.
I'm an engineer and know how heatpumps work and lose efficency as outside air becomes colder.
I did some calculations and based on what I came up the heatpump should have acheived an inside temp of 68 degrees.
Am I losing that much heat? I hope not.
I would like to know if this is a common problem at these (outside) temps or maybe I need a freon charge on my heatpump/AC unit and it is not running at peak.

Best
Dan
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Old 02-11-2012, 09:37 PM   #2
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Dan,

You might be correct that your Penguin heat pump may be low on charge, but there is no practical way to re-charge your roof unit. These appliances are hermetically sealed at the factory and do NOT have process valves on them. They were never designed to be re-charged.

That said, DO NOT believe anyone who tells you otherwise. I have seen several units lately that had one piercing valve on the high side line and was supposedly re-charged. NOT! The re-charge did not last very long, as piercing valves leak soon after they are put in place. Piercing valves are designed for temporary use to evacuate a system prior to replacing a compressor or other major component and should them be replaced with a soldered-in Schrader valve. Actually, there should be 2 valves in place.....one for the high side and one for the low side.

Doing this type of repair is no longer cost effective, as all roof units have been designed to be replaced if they have leaked refrigerant. Your Dometic unit has a 2 year factory warranty. You should have the amp draw at the compressor checked by a competent factory authorized Dometic dealer to see if it is operating to specifications.

If your unit exhibits lower than specified amp draw at the compressor, you have probably lost refrigerant and your unit should be replaced....NOT RE-CHARGED!!!
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Old 02-11-2012, 09:47 PM   #3
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Quote:
Originally Posted by danlehosky
We got our new 25 FB Flying Cloud back from the dealer yesterday where they fixed some small issues and also addressed an issue with the ccc that has not worked right since new. Yesterday when we brought the unit home I turned on the CCC in the heatpump mode set the temp on 68 (about 44 outside). After running all night in the heatpump mode without much outside temp change the best I could do was about 59 degrees as an inside temp.
I'm an engineer and know how heatpumps work and lose efficency as outside air becomes colder.
I did some calculations and based on what I came up the heatpump should have acheived an inside temp of 68 degrees.
Am I losing that much heat? I hope not.
I would like to know if this is a common problem at these (outside) temps or maybe I need a freon charge on my heatpump/AC unit and it is not running at peak.

Best
Dan
Doesn't sound right to me. The original 15k Penguin on my 2011 failed within the first week, and it was September before the unit was replaced. The next trip out in October we tested the heat pump and had no problem bringing the temperature up to 20 degrees when the outside temp was around 5. That's Celsius, btw.
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Old 02-11-2012, 11:37 PM   #4
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We just used our Heat Pump (in an '05 Classic) while on a trip to Port Townsend. The HP was able to warm the trailer to the set 73 deg. The outside temperature was in the low 40's and it was breezy. It doesn't sound like yours is working correctly.

By the way, we live in Kingston... Maybe we will be seing you around the great PNW!!
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Old 02-12-2012, 12:03 AM   #5
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We used ours into November before I winterized it for the season. My experience is that the heat pump will maintain the inside at the 70° set point on the CCC down to about 30° outside when the CCC automatically switches to furnace mode. I have the 13.5K model in a 27FB. It does sound like they need to replace that for you under warranty.
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Old 02-12-2012, 12:04 PM   #6
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Oh well, back to the Dealer again.
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Old 02-12-2012, 12:42 PM   #7
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You can use a thermometer to find out the temperature of the air that is coming out of the unit's vents at various outside temps. This information can be useful when the dealer tells you everything is ok—that will be what they do first. You can look at the manufacturer's website for info about the unit and what temps are supposed to be in A/C and heat pump mode and compare them with what you get.

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Old 02-12-2012, 12:57 PM   #8
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Most heat pump systems have heater strips as well. Most systems use the heat pump to preheat the air and the heater strips to finish the job. When the unit goes into defrost it reverses the cycle and blows out cold air to defrost the condenser on the outside. When this happens you are using the heater strips full time. Since there may not be enough power, the RV units may work differently. I expect they compressor is turned off and stays that way until the outside temperature gets above a certain value.

Perry
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Old 02-12-2012, 01:07 PM   #9
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Quote:
Originally Posted by perryg114 View Post
Most heat pump systems have heater strips as well. Most systems use the heat pump to preheat the air and the heater strips to finish the job. When the unit goes into defrost it reverses the cycle and blows out cold air to defrost the condenser on the outside. When this happens you are using the heater strips full time. Since there may not be enough power, the RV units may work differently. I expect they compressor is turned off and stays that way until the outside temperature gets above a certain value.

Perry
RV heat pumps are not built like residential units. ALL RV roof units have a single compressor and the traditional evaporator (indoor coil) and condenser (outdoor coil) when operating on the A/C setting. The evaporator gets cold and vents cool air into the trailer and the condenser is hot and exhausts the hot air outside.

On heat pump mode, the flow of refrigerant is reversed by means of a solenoid controlled reversing valve the switches the operation of the coils; the indoor coil becomes the condenser and the outdoor coil becomes the evaporator, thus blowing warm air from the hot condenser into the trailer and the cooler air to the outside. RV heat pumps loose their effectiveness at around 40*F ambient temps.

There are NO heat strips in an RV heat pump. Some roof units do have a heat strip for mild air warming, but these units are solely air conditioners with an auxiliary resistance heating strip and are NOT heat pumps.
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Old 02-12-2012, 05:44 PM   #10
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The AC with the heat strips should do just as good of a job at 40F as a heat pump then. The heater strips are probably good for around 6000BTU of heat. The heat pump I am sure can do better than that at say 55F but when you get in the 30's it is pretty much worthless and will start to freeze up. I would rather have an AC with heat strips. If the camp ground is paying for the electricity why worry about a marginal increase in efficiency that you get from a heat pump. The heat strips will give you some heat to reduce propane usage at lower temps. The heat pump won't do much at all. If the humidity is high a heat pump can turn into a block of ice at relatively warm temperatures say in the 50's.

At 44F his heat pump is not very efficient. If it is raining and 44F it will freeze up and not heat at all.


Perry
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Old 02-12-2012, 05:55 PM   #11
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The heat pump and fan is noisy and inefficient. We use a ceramic heater which does a pretty good job. They are cheap and also use the CG's electricity. It also means less wear on the A/C and they are really expensive to replace.

More recent Airstreams have a thermostat that automatically turns off the heat pump at around 28 or 30˚ and turns on the furnace to keep the water tanks warm. That is the one advantage of the heat pump, but if the forecast is for temps down that low, or near that, or by late evening the temps are dropping quickly, you can just turn on the furnace and set the thermostat (in ours it is in the bedroom) to 50˚or so and use the ceramic heater in the main cabin. I usually wake up in the middle of the night and check the temps and make any adjustments necessary.

A sensor near the water tanks that could be set to turn on the furnace when the temp there gets into the low 30's would be a good thing.

Gene
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Old 02-13-2012, 12:42 AM   #12
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All, first off thanks for the replies and advise. I did some temp differential checks today. It was about 50 drgrees out and the warmest air temp measurment I could record was about 62 degrees. I also did an amp load test and the compressor is only drawing a little over 10 amps at start up. I will get back to you guys after I talk to the dealer tomorrow. They are new so they should I would think want to be cooperative. Anyway I know way more about how this system works than he does so if he starts to BS me I can take care of that. They also did a screen repair and left the window latches open which I didn't see until about 10 miles away at 60mph with the window flapping in the wind. I will always do my own walkthru after any maintanance no matter who does it. Lesson learned. Our unit has no heat strips. I love this forum so many good people and such good information. I hope to see all of you guys on the road.
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Old 02-13-2012, 01:18 PM   #13
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Glad to read you didn't loose a window. One of the latches on ours was loose and fell open after we left the dealership. A 100 miles away we stopped for lunch and the window was gone. Enough wind was getting in to distort the window enough to make it dissolve; possibly a passing truck could have exerted enough force to shatter it. Make sure the adjustment nut on the latches are all set to keep the latches tight and closed.

Gene
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Old 02-13-2012, 03:09 PM   #14
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Up North here I think the lack of AC use may have more to do with a possible failure than any thing else. I have found that the heat pump actually gets more use than the AC itself. Comes in very handy keeping things cozy above 40 degrees, hasn't been a problem keeping the interior at 68 degrees, our max on either mode.
Anything lower and the Polonis comes out, usually when on the pad. The furnace takes over when on a trip.
I try to cycle the AC regularly here at home, just to keep things up and running.
Heat pump has been a worthwhile option for us.

Bob
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