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Old 10-22-16, 11:24 AM   #1
CrankyDoug
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Default Window Shaker (R410) to Heat Pump (R290)

I would like to replace the propane heater in my camper with a small heat pump. The current 5000 BTU window shakers are quiet and efficient but inevitably lose their R410 after about three years. If I could convert to R290 and replace the evap coil with another condenser, then install a reversing valve, I would have a heat pump.

Has anyone tried converting a R410 unit to R290? I'm having trouble finding a 5000 BTU R22 unit that isn't worn/rusted out. I would convert the existing rooftop unit but it is 13K BTU and the fan alone consumes 150-180W.

Doug

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Old 10-22-16, 02:33 PM   #2
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Look on freecycle, Craig's list, and ask around the neighborhood. It seems one out of five homes has an old, somewhat working window shaker or dehumidifier lurking in a dark place. Once people saw me resurrecting the dead, orphans began showing up out of nowhere. I'm not a hoarder, so i had to start refusing them.

Yes, R410a compressors can run R-290 but you lose capacity. The metering device has to be messed with as well. This has been discussed before here. R-134a can be used as well.
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Old 10-22-16, 03:08 PM   #3
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Yes, R410a compressors can run R-290 but you lose capacity. The metering device has to be messed with as well. This has been discussed before here. R-134a can be used as well.
What about the oil in R410 systems? Do I need to flush and change to mineral based oil?

I am interested in a specific R410 unit. I have two already and the dimensions are perfect. Otherwise I would look for an R22 unit. In any case I would scrap the cap tube and use a TXV.
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Old 10-22-16, 03:55 PM   #4
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No need to change the oil. It's the synthetic hfc refrigerants that aren't compatible with mineral oil.

I would look for a larger unit to modify, though. A 5kbtu compressor might only move 3kbtu after switching from 410a to 290. You might be surprised how much heat leaks out of rv's and campers when it's cold outside. I would really be tempted to hack the rooftop unit myself. Especially if it was out of warranty.
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Old 10-22-16, 08:40 PM   #5
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I would look for a larger unit to modify, though. A 5kbtu compressor might only move 3kbtu after switching from 410a to 290. You might be surprised how much heat leaks out of rv's and campers when it's cold outside. I would really be tempted to hack the rooftop unit myself. Especially if it was out of warranty.
Yep, spent my honeymoon in a 1949 camp trailer with a sheepherder stove for heat and cooking. In Idaho, in one of the coldest winters on record. Those memories are only good because they are behind me.

The purpose of snowbirding is to get away from the weather. The rooftop unit is not a good candidate because I am trying to stay under 500 watts. This thing was not designed for efficiency. The fan motor is big because it blows through undersized ceiling ducts - which also leak a lot. And the shroud is cracking which will cost $150 to replace.

Another option I'm considering is using the propane water heater for hydronic heating. I can get a circulation pump that uses about 20W making it suitable for off grid. The heat pump requires a generator or power pole. If I am at a campground with a hookup I can just use a $15 space heater.
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Old 10-23-16, 12:47 PM   #6
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OK, I'm lost here. You have some decision making to do. I would reach deep into your head, your heart, and your pocketbook, let them all duke it out in a safe place, and see who wins. The result will help you define your heating and cooling setup.

If your wallet wins, just go to wally world and buy a 15 dollar space heater. Use your existing propane furnace to heat on the road and the space heater when you can be on-grid. Propane is going to win hands down off-grid.

A hydronic radiator is most likely not going to be any more efficient than the furnace.

Any phase-change system that draws 500 watts or less isn't going to put any more heat out than the 15 dollar heater on high setting. When outdoor temperature droops, so does heat pump efficiency. A shiny, new coleman rooftop heat pump unit retails for around (only) 500 dollars, and draws the same power as the 15 dollar unit from the pole. However, it belts out at least twice as many btu's when it runs. Energy consumption may or may not be an economic factor when parked in a campground. However, it is safe to assume a manufactured unit will work well for at least a few years. Not so with anything improvised or homebrew.
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Old 10-23-16, 02:01 PM   #7
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What about a CHP setup? With good design and using the generator to run a heat pump, you can get more heat out of it than what the generator used for fuel.
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Old 10-26-16, 07:42 PM   #8
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Jeff is right. I've got too many conflicting ideas floating in an otherwise vacuous cranium. Here are the goals:

1. Reduce weight (the trailer is heavy)
2. Optimize some unknown balance between off-grid and on-grid.
3. Minimize off-grid generator time.
4. Minimize propane use.

The propane heater is horribly fuel inefficient and its fan will quickly flatten a battery bank. It is wasteful on-grid and practically useless off-grid. Most of the heat seems to go out the exhaust vent. Propane on the road runs upward of $6 a gallon.

Hydronic heating eliminates the fan. It is quiet and uses very little electricity. I have a friend that installed a hydronic system in a new motorhome in NY with remarkable results. Apparently they are common in RV's in his native Sweden.

I already have the water heater and I see no reason it can't do double duty. The batteries will easily handle the igniter and a circulation pump. I won't be drinking the water so bacteria isn't an issue.

I don't plan on roughing it in extreme weather. After all, who wants to travel two thousand miles just to sit in the trailer. Cold weather sucks and health issues ended my hot weather trekking long ago. 5000 BTU cooling is plenty for the places I'm going. I just thought it would be nice to have a reversible heat pump as long as I have air conditioning.

The Coleman on the roof is too big and incredibly noisy. It needs a 3.5KW genny just to start it. Even in a 98 degree Georgia summer it runs less than 50%. The window shaker starts and runs fine on my 1KW unit. If I drop the idea of a heat pump I will still go with the window shaker for AC.

I have friends that snowbird from Idaho 6-8 months a year. They rarely use the air conditioner, choosing instead to move with the weather.

Mike: I don't recall what CHP stands for.
EDIT: Answer - cogeneration heat pump. I suppose I should have googled it before asking.

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