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Old 07-14-2014, 01:20 AM   #31
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Originally Posted by rbryan4 View Post
It's quite surprising that with the new compressor technology, the ac/dc fridges are far more power efficient than the 3-way fridges when running on DC.
I think any reasonable compressor-based refrigerator would be more efficient than an absorption-cycle unit (which has the same efficiency regardless of the heat source). As far as I know, the only reason absorption refrigeration is used in small sizes is that it will run on heat, when a mechanical drive (such as an electric motor) is not available. In an RV outside of a serviced site, it is a real advantage to be able to run on easily produced heat instead even a smaller amount of expensive-to-obtain electricity.
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Old 07-14-2014, 02:01 AM   #32
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I think any reasonable compressor-based refrigerator would be more efficient than an absorption-cycle unit (which has the same efficiency regardless of the heat source). As far as I know, the only reason absorption refrigeration is used in small sizes is that it will run on heat, when a mechanical drive (such as an electric motor) is not available. In an RV outside of a serviced site, it is a real advantage to be able to run on easily produced heat instead even a smaller amount of expensive-to-obtain electricity.
All true. I was pointing out that the newer compressors are much more energy efficient than even 5 or 10 years ago. I am really thinking about the possibility of ac/dc instead of the absorption unit. We don't intend to do much dry camping, and when we do, the dual batts and solar might just give us the power we need.
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Old 07-14-2014, 02:17 AM   #33
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Originally Posted by Brian B-P View Post

In an RV outside of a serviced site, it is a real advantage to be able to run on easily produced heat instead even a smaller amount of expensive-to-obtain electricity.
Although it's now not only less expensive-to-obtain electricity but easier to get electricity. In the South Pacific and before solar cells were a viable option I had something called a ""Wind Bugger" wind generator. It had a prop much larger than many other brands. The price you paid, aside from the bucks to buy it, was that it sounded like a Cessna taxiing on your deck 24/7 and often wasn't generating as much as solar cells do now.

I wonder, in 10 years if temperature extremes become the norm, will absorption type units be entirely replaced with DC compressor units?

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Old 08-16-2014, 07:15 PM   #34
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Another good web page giving some general info on why the manufacturer is now using compressor based fridges instead of the absorption type. The idea is certainly not new, and it's becoming more and more accepted, as solar prices go down, and the fridges become more efficient:

Why Advanced RV Uses Compressor Fridges - Advanced-RV
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Old 09-29-2014, 12:49 PM   #35
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The absorption versus compressor question came up again in one of the Dometic 8XXX threads (New Fridge Topic: A Different Approach, post #67), and I am responding to it here...

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Okay. If the compressor refers are so much better, why aren't they used instead of the Dometics?

... Is there a downside to compressor units that would explain why they are not the standard?
The compressor makes some noise, but personally I doubt that's a big issue for most people.

The significant reason that compressor-based refrigerators are not common is that - unlike absorption-type refrigerators - they cannot run on a propane flame. That has large implications to power supply, especially when camping without services, and is the fundamental reason for the dominance of absorption refrigerators in RVs of all types.

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Is there a cost issue? Will the Nova Kool fit through the door?
Both types (absorption, and DC-powered compressor-based appliances optimized for mobile use) are relatively expensive compared to home refrigerators; I doubt the cost difference is the determining factor in popularity.
Both types are available in a variety of sizes, and the compressor types are probably a bit less bulky for the same usable interior volume, so I'm sure that package size is not an issue for compressor-based units.
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Old 09-29-2014, 12:58 PM   #36
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Thank you, Brian, for your response. I will keep an eye on this thread.
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Old 09-29-2014, 04:48 PM   #37
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In my truck camper I'm currently running an Engel 12v compressor frig, model SR70 which is a 60qt built-in unit with front door loading. I did install an extra matching 12v battery, solar charge controller and have about 54watt of folding solar panel.

Looking at the same manufacturer and the same volume units, the performance curves for the Engel 60qt SR70 and the 60qt MT60 top load unit are noticeably different. Both units use a 1 to 5 dial for temperature setting with 5 being the coldest. What is surprising is with the same ambient air temp and same temp setting the front load unit will run more often than the top load unit at steady state (door/lid is closed and not being opened and unit is down to holding temperature)

In terms of the batteries lasting to me the main question is whether or not you are also running your furnace as it has a 12v fan. The frig and furnace fan run the battery down quicker.

As far as compressor noise that was not as much of an issue as the compressor running causing other things to vibrate. Once I tracked those things down I was able to sleep with the noise. Example, my standard two burner stove has a cover with side screens and the compressor running would cause the cover/side screens to vibrate. Don't really know if the vibration issue was my particular frig or my particular installation.

Long ago the compressor frigs ran on a pure refrigerant plus oil for the compressor. Now the refrigerants are a blend and the oil is blended. The old rule of thumb used to be don't run the frig if the air temp is below 50degF due to problems getting the oil to return to the compressor. Don't know if that is still true.

Remember both propane and 12v compressor frigs absorb heat into their evaporators from inside their frig boxes and reject that heat through their condensors. The 12v compressor frig rejects that heat to the inside of the camper or trailer while the propane frig rejects that heat outside the camper or trailer.

It seems unfortunate to be faced with these issues when you just want something that works. The 12v compressor will work but you have to have enough battery and solar wattage to recharge. The trailer carries enough propane to run the propane frig but will the frig work the way it is supposed to.
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Old 09-29-2014, 04:55 PM   #38
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...
Remember both propane and 12v compressor frigs absorb heat into their evaporators from inside their frig boxes and reject that heat through their condensors. The 12v compressor frig rejects that heat to the inside of the camper or trailer while the propane frig rejects that heat outside the camper or trailer.
...
The venting depends on the unit - many/some (?) (including the Nova Cool 6800) vent out the back. I think the Nk6800 will vent fine using the existing venting.
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Old 09-29-2014, 05:38 PM   #39
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In my truck camper I'm currently running an Engel 12v compressor frig, model SR70 which is a 60qt built-in unit with front door loading. I did install an extra matching 12v battery, solar charge controller and have about 54watt of folding solar panel.

Looking at the same manufacturer and the same volume units, the performance curves for the Engel 60qt SR70 and the 60qt MT60 top load unit are noticeably different. Both units use a 1 to 5 dial for temperature setting with 5 being the coldest. What is surprising is with the same ambient air temp and same temp setting the front load unit will run more often than the top load unit at steady state (door/lid is closed and not being opened and unit is down to holding temperature)

In terms of the batteries lasting to me the main question is whether or not you are also running your furnace as it has a 12v fan. The frig and furnace fan run the battery down quicker.

As far as compressor noise that was not as much of an issue as the compressor running causing other things to vibrate. Once I tracked those things down I was able to sleep with the noise. Example, my standard two burner stove has a cover with side screens and the compressor running would cause the cover/side screens to vibrate. Don't really know if the vibration issue was my particular frig or my particular installation.

Long ago the compressor frigs ran on a pure refrigerant plus oil for the compressor. Now the refrigerants are a blend and the oil is blended. The old rule of thumb used to be don't run the frig if the air temp is below 50degF due to problems getting the oil to return to the compressor. Don't know if that is still true.

Remember both propane and 12v compressor frigs absorb heat into their evaporators from inside their frig boxes and reject that heat through their condensors. The 12v compressor frig rejects that heat to the inside of the camper or trailer while the propane frig rejects that heat outside the camper or trailer.

It seems unfortunate to be faced with these issues when you just want something that works. The 12v compressor will work but you have to have enough battery and solar wattage to recharge. The trailer carries enough propane to run the propane frig but will the frig work the way it is supposed to.
Some good points. The top load units are always more efficient than their front loading counterparts, mainly because cold air sinks. Engel doesn't make a fridge of sufficient size for the Escape trailers, at least the last time I checked. One thing about venting: compressor fridges that are "self venting" are designed to vent to the interior cabin, but they do make some that vent to the outside as well.
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Old 09-29-2014, 07:05 PM   #40
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On the venting I didn't see the official Nova Kool installation instructions. I did see mention for one of their big dual compressor models that talked about external ventilation.

Heat transfer is driven or governed by temperature difference. Remember when the Norcold person told Reace that if the trailer inside temperature was above 80degF (say due to 95deg outside air temp) you should run the AC unit. Knocking the inside trailer temp down to say 72 would lessen the heat transfer to the inside of the frig box. For rejecting heat from the condenser at a given temperature and given air flow you will reject more heat into 72deg air than say 95deg air.

Anyway I'd go by what Nova Kool says in their instructions.
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