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Old 12-05-2018, 23:37   #16
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Re: A simple refrigeration economiser tip!

Hi OzePete,
Recommendations implemented!
Thanks again for your advice. The fridge performance is greatly improved. I used about 30ml of water in the probe bottle. Thermostat set points ended up being 2.7C & 3.7C which translated to 0C to 4C for cabinet air temperature.
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Here are the before and after test results

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Power consumption substantially improved with more consistent box temps. A thing of beauty!
Iím also expecting a few less cycles/day with the fridge and freezer fully loaded.
All the Best,
Neal
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Old 13-05-2018, 00:27   #17
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Re: A simple refrigeration economiser tip!

Quote:
Originally Posted by sailor_ed View Post
OzePete

In the US on our eBay I find an ITC 1000 temp sensor/controller that seems to be similar to the controller you mention but the 12V units are all listed as 12VAC 50/60 Hz. Would I be able to use / adapt one of these? I would like to exit the stone age!
My apologies Sailor Ed, I didn't notice your question... Yes that should be fine, the digital controllers often refer to the supply being 12VAC but they are OK for 12VDC.
IF you get or have one that is 110VAC or 240VAC then you simply need to slide off the controller case cover and by-pass the tiny transformer. It will be obvious once you remove the cover.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems
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Old 13-05-2018, 00:30   #18
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Re: A simple refrigeration economiser tip!

Quote:
Originally Posted by rvlandlubber View Post
Hi OzePete,
Recommendations implemented!
Thanks again for your advice. The fridge performance is greatly improved. I used about 30ml of water in the probe bottle. Thermostat set points ended up being 2.7C & 3.7C which translated to 0C to 4C for cabinet air temperature.
Attachment 169700

Here are the before and after test results

Attachment 169704

Attachment 169705

Power consumption substantially improved with more consistent box temps. A thing of beauty!
Iím also expecting a few less cycles/day with the fridge and freezer fully loaded.
All the Best,
Neal
Thanks for the heads up Neal, but I can see you didn't get to position that fridge where recommended!! What? wouldn't it fit?

Cheers OzePete
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Old 13-05-2018, 02:18   #19
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Re: A simple refrigeration economiser tip!

My Vitrifrigo fridge/freezer runs on 110v when on shore power, and 12v when on battery power. Which digital temp sensor will work in both modes?
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Old 13-05-2018, 05:08   #20
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Re: A simple refrigeration economiser tip!

Quote:
Originally Posted by BozSail View Post
My Vitrifrigo fridge/freezer runs on 110v when on shore power, and 12v when on battery power. Which digital temp sensor will work in both modes?
If your fridge uses a 110VAC compressor then use the 110VAC controller. To check this read the label on the compressor itself.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems
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Old 13-05-2018, 05:47   #21
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Re: A simple refrigeration economiser tip!

As a previous poster suggested, using a small cabinet circulation fan will improve refrigeration performance, efficiency and product temperature pull down. But is is critical that the cabinet is well sealed as using a cabinet fan with any air leaks can more than negate any benefit. Check cabinet seals by placing a strong torch inside the cabinet on a dark night, any leaks will be exposed. Suggest a very very soft sponge for a seal, not domestic fridge door material.

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Old 13-05-2018, 06:48   #22
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Re: A simple refrigeration economiser tip!

Heat leaks into a box, cold doesn't leak out. A well sealed empty box will use same energy as box filled with water bottles.
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Old 13-05-2018, 07:29   #23
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A simple refrigeration economiser tip!

Quote:
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Heat leaks into a box, cold doesn't leak out. A well sealed empty box will use same energy as box filled with water bottles.


Your correct in that heat leaks in, in fact ďcoldĒ isnít even a thing, itís only the lack of heat.
I try to explain it like this, there is no such thing as dark, dark is only the absence of light, if dark were a thing, then we could likely build a dark projector, like a flash light. That makes sense to most people.

However with the fridge being full of food, the food has mass, a lot of mass. You have to add enough heat to this considerable mass to raise the temp to the thermostat turn on set point. Of course you then have to remove a lot of heat to drop the temp back down to the turn off point, so you end up with few, but longer run time cycles. The amount of heat removed is the same though, your correct there, however by increasing the cycle on and off times your making the compressor operate more efficiently, so while the heat removed is exactly the same amount, your using less power to remove it. Remember these things donít create heat, they move it, so therefore they can move more heat than they consume doing so.
If there were no food and only air, the air has very little mass and not much heat is required to raise the temp to the thermostat set point, so your cycles are shorter but more frequent.

Think of a pot on your stove, if itís empty, it will get hot very fast, fill it with water and of course it takes a long time to get hot, reason is of course your now having to raise the temp of the mass of water not just the pot.

RE using water ice as an eutectic fluid in your freezer. This will work as long as your allowing the ice to melt and refreeze, which of course means your constantly thawing your freezer.
If the ice never melts, itís still thermal mass, but you donít get the huge absorption of heat required to phase change the water from ice to water.

I think most of us donít actually phase change our cold plates. I know I rarely do, mine almost always stay frozen cause I want the set point to stay lower than the freezing point of the fluid, itís only when I consciously turn off my compressor after sundown and then back on in the morning that I may be using them as they are designed.
However there is a whole lot of mass in those plates, and just this mass of course helps increase cycle on times.
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Old 15-05-2018, 06:09   #24
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Re: A simple refrigeration economiser tip!

Quote:
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Heat leaks into a box, cold doesn't leak out. A well sealed empty box will use same energy as box filled with water bottles.
This assumes a perfect seal as well as perfect insulation, so while it's true in theory it is not true in practice. Insulation is not perfect and the door is opened with varying frequency. For those of us that live aboard, that's at least several times per day.

As A64 pointed out, the more thermal mass there is in a refrigerator, the slower the transfer of energy. Air has low mass and is highly fluid. Open the door and warm air rushes in and cold air rushes out. On a basic level, the less air in the box the lower the transfer of energy from simple air exchange. Beyond that, the more thermal mass in the fridge the the lower the overall energy exchange each time you open the door.

The result is more stable temperature holding and ultimately less energy usage to maintain a given temperature range. A test of this is pretty simple. Empty your freezer and run it a few days, opening it a few times a day for 10 seconds or whatever. Observe the temperature change over time and the energy used to maintain a desired temperature. Then fill the freezer with bags of ice and repeat. You'll see a significant difference.
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Old 15-05-2018, 06:32   #25
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A simple refrigeration economiser tip!

Small point.
Ignoring the air exchange thing, the increased mass does not slow the heat transfer down, it still occurs at the same rate, just it takes longer for the temp to increase due to the increased mass.
Freezer full and freezer empty, the rate heat transfers is the same, meaning over a set period there is the same heat gain.
However a full freezer or fridge will be more efficient due to the increased time between compressor cycling. A full freezer with a thin plate evaporator is similar to a cold plate, hopefully no phase change of course
The only thing that influences heat gain significantly that I can think of is insulation.
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