Refrigeration - Evaporator vs. Holding Plate

[Richard Kollmann]

Pete, Thanks for your opinions and you are correct eutectic plates refrigeration is not justified without alternative energy from sun wind or water generators. In mobile refrigeration there is no such thing as average conditions with proper insulated Boxes. Pete will you also agree that with 134a refrigerant and a zero degree F eutectic plate that a standard evaporator will reach temperatures lower than eutectic plate before reaching equilibrium?

[Typhoon]

Originally Posted by wsmurdoch

I can follow the argument that a freezing solution filled tank may be a better alternative to storing "cold" energy than a battery based on cost, weight, size, and usable life. But I can see a couple of detractors as well.

The tank is usually in the cold box using up room that could be used to store food (beer) or alternatively requiring a larger cold box with a greater outside surface area and thus greater "cold" loss. Is this additional "cold" loss included in the battery vs. freezing solution filled tank comparison?

I'll assume that a freezer is to be kept at 20F. I'll also assume that the economic temperature difference between the refrigerant in a flat plate evaporator and the air in the freezer is 15F. The required refrigerant temperature is thus 5F. Next, I'll assume that the economic temperature difference between the refrigerant and the freezing solution in a freezing solution filled tank is also 15F and that the temperature difference between the tank solution and the air in the freezer is also 15F. In this case the required refrigerant temperature is -10F. The capacity and the efficiency (COP) of the refrigeration system would be lower for an evaporator operating at -10F than an evaporator operating at 5F. Would this not favor using a battery instead of a freezing solution filled tank?

The accepted solution for a cold plate seems to be a propylene glycol - water mix richer in water than the eutectic (60v% PG). In that mixture starting at a temperature below the freezing point of water the first bit of the water freezes. The remaining liquid mixture then being richer in propylene glycol, the next bit of water then freezes at a little colder temperature. This continues until either the desired low temperature is reached or until the eutectic freezing point is reached. If the eutectic point (-60C, -76F) is not reached, only part of the water is frozen storing "cold" in its latent heat. The remainder of the "cold" is stored in the much smaller sensible heat of the remaining unfrozen propylene glycol and water. If the tank were filled with a true eutectic solution, it would all freeze at one temperature and store its "cold" in a smaller volume. Glacier Bay (https://www.boatdesign.net/attachmen...ucts-pdf.4216/) used to claim its TSS-8 and TSS+26 solutions were true eutectics. Does anyone know their composition?

Bill

This is our twin plate freezer set up in a 2.5 cubic foot deep freeze . Temperature is 0 degree F .

Regards John

www.coldeh.com

[CGirvan]

Originally Posted by OzePete

The key issues found as a result of that 60 day trial were:
Firstly the eutectic system operates at a far more efficient COP.


Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

Firstly thanks for sharing your data with the rest of us, I for one really appreciate it.

Regarding the above statement it seems like this is saying the eutectic system uses less power because it is more efficient. The question though is why is it more efficient or has a higher COP?. Sorry if this is a silly question.

[SV THIRD DAY]

Originally Posted by Richard Kollmann

will you also agree that with 134a refrigerant and a zero degree F eutectic plate that a standard evaporator will reach temperatures lower than eutectic plate before reaching equilibrium?

I don't know if Pete agrees, but I sure don't.
A 0-deg holding plate isn't 0-degs. That the temp that the Eutectic Solution freezes at. The actual holding plate temperate ranges from
-15 to -5 degs F depending on the thermostat settings. We have plenty of Zero deg F freezer boxes and have been doing it for what...50 years now.

But here is the perfect example.
I get an email this morning from a lady that just bought a boat with a CoolBlue Technautics unit in the stand along freezer. (yes we really do have 7 day a week customer support). So we exchange a few emails and her freezer box is only 14-degs F and she would like it colder. After a few questions, she has a 7CF Box with our standard single holding plate with 2" of 30yr old insulation. I explain the science to her and that given her box size and insulation that's about what I would expect. Heck that's actually quite good!

So when her friends at the dock and on internet chat rooms ask her if her holding plate freezer system is good, she will say:
"Well the handsome and intelligent customer service guy was great on a Sunday, but holding plates don't get down cold enough for me".

BINGO...that's how the dock and cruiser rumor mill game works with Cruising Gear. The system is working great (oh and it's 16yrs old) but in that application 14-degs F is as cold as it will get. It's not the Holding Plate that is the problem and can't get a 0-deg Box...it's the BOX. And what control do we have over that? Nada. But the Box and how the customer uses the system often reflects back on us. It's part of the marine industry game and after 50yrs at it we have seen it all. Even the guy that tried to use our system as an air condition unit for his aft cabin.....no joke....fun stuff this Marine Industry.

[a64pilot]

Originally Posted by CGirvan

Firstly thanks for sharing your data with the rest of us, I for one really appreciate it.

Regarding the above statement it seems like this is saying the eutectic system uses less power because it is more efficient. The question though is why is it more efficient or has a higher COP?. Sorry if this is a silly question.

That is exactly what he is saying or I misunderstand
https://en.m.wikipedia.org/wiki/Coef...of_performance

I don’t understand the statement, cause I can’t come up with a reason why, unless it’s something like the thermostat going off of evaporator temp, which would have it cycling a ridiculous number of time until equilibrium was reached.
I doubt that is the case though, but from what little I know about thermodynamics, a thin plate evaporator ought to be more efficient than a hold over plate as it cools the box directly and not through another medium.
However for a cruising Boat, I think a hold over plate superior as we can take advantage of its ability to get us through the night and keep the fridge cold when there is no Solar output.

I can only surmise that in his test, his cold plate design more more correctly matched to his system than his thin plate evaporator was, but that is just a pure guess.


On edit, if I understand Pete is comparing one of his systems to another of his systems, he sells both.
So this is not like someone intentionally setting up a test that will highlight the advantages of their product and testing theirs against a competitor.
If I understand Pete has no axe here to grind, this ought to be as honest as a test as we would see from a manufacturer.

Deepens my confusion

[Richard Kollmann]

Originally Posted by a64pilot

That is exactly what he is saying or I misunderstand
https://en.m.wikipedia.org/wiki/Coef...of_performance

I don’t understand the statement, cause I can’t come up with a reason why, unless it’s something like the thermostat going off of evaporator temp, which would have it cycling a ridiculous number of time until equilibrium was reached.
I doubt that is the case though, but from what little I know about thermodynamics, a thin plate evaporator ought to be more efficient than a hold over plate as it cools the box directly and not through another medium.
However for a cruising Boat, I think a hold over plate superior as we can take advantage of its ability to get us through the night and keep the fridge cold when there is no Solar output.

I can only surmise that in his test, his cold plate design more more correctly matched to his system than his thin plate evaporator was, but that is just a pure guess.


On edit, if I understand Pete is comparing one of his systems to another of his systems, he sells both.
So this is not like someone intentionally setting up a test that will highlight the advantages of their product and testing theirs against a competitor.
If I understand Pete has no axe here to grind, this ought to be as honest as a test as we would see from a manufacturer.

Deepens my confusion

Moderator, I am confused too, When discussing COP of compressors we know where the figures come from and they are understandable. In order to brag on Total System Coefficient Of Performance (SCOP) How does one come up with variables of (Qc) Heat removed from a refrigerated area by this type of refrigeration?

They both have good products, Why always the Smoke and Mirrors?

[missourisailor]

Originally Posted by a64pilot

Sorry, just back from inlaws House.
I see though that your questions were answered. The second plate will assist in your box temps being more stable, your electrical consumption will not vary appreciably.
However if I were in your shoes, I’d look at a bigger compressor, cause the second plate takes up a LOT of room in the box. I suspicion with only a 35 compressor that your box isn’t very big to start with, or it’s extremely well insulated for you to get by with a 50% duty cycle.
A bigger compressor of course takes no additional room in the box.
Your energy consumption will not change much with a bigger compressor either, increase some, but not a lot.

If you can freeze the food ahead of time, that helps tremendously. Most meat departments will freeze it for you to pick up next day if you ask.

Continuing to brain storm, if you now have a spill over, ideal is separating the box and having a separate fridge and freezer, second plate, second compressor, plus you have some redundancy in case of one breaking down. I like redundancy, an Engel is my backup.
I likely should have gone that route, but the $$$ scared me.

Just some more fodder...
You have a 38. I have a 35. So we basically have the same box. From the factory at least.

A PO split the box into 1/3 freezer and 2/3 fridge. With a spillover controlling the fridge,

The same PO installed 2" of blue foam on 5 of the freezer's sides (3 sides and top and bottom) The dividing wall between the freezer and fridge. is 1 1/2" thick. No interior insulation was added to the fridge section.

From the information that I have, This same PO also installed the Cool Blue at the same time.

When I got the boat, the freezer would run almost nonstop. Only shutting down for two to three, one hour periods during the night,

A significant amount of the heat loss, really heat intrusion, was coming into from the lid. After a total lid rebuild and going with digital temp contollers, I'm where I'm at now. A 50% duty cycle once the box is fully cooled.

Adding an additional hold over plate, the same size as whats in there now, on one of the other walls is very doable. But I'm concerned about the remaining usable space.
Maybe adding it as a shelf is a better option.

I don't know and hence why I said I need to measure before going any further.

Anyhow, just more info to muddy the waters.

[a64pilot]

I have been thinking and have one possible answer, although this is just thinking.
I believe that if you want to keep fridge temp say Exactly at 40f, then the large thermal mass of a cold plate of course works very well and dampens the temp swings very well, back to it being like a flywheel.
However I’m under the impression that with a thin plate evaporator that you set the thermostat with several degrees, as in maybe 5 degrees between on and off set points, to keep excessive cycling down?

Or maybe the test was run with an empty box, no thermal mass in a box with a thin plate evaporator would make temps rise pretty quickly, resulting in excessively short compressor cycles?
Maybe the thermostat settings were identical, which of course would make sense in order to keep the test as identical as possible? However one would assume that with a thin plate design, you would allow larger temp swings between compressor on and off settings?

Only thing I can think of to explain the large drop in cop is excessively short cycling of the compressor?

If the boxes were full or half full of food, I assume the cycling would be much less?

However I am certain that there was no “shenanigans” here, I’m sure it was as dead equal of a test as was reasonably possible, just trying to explain the outcome is all

[a64pilot]

Originally Posted by missourisailor

Just some more fodder...
You have a 38. I have a 35. So we basically have the same box. From the factory at least.

A PO split the box into 1/3 freezer and 2/3 fridge. With a spillover controlling the fridge,

The same PO installed 2" of blue foam on 5 of the freezer's sides (3 sides and top and bottom) The dividing wall between the freezer and fridge. is 1 1/2" thick. No interior insulation was added to the fridge section.

From the information that I have, This same PO also installed the Cool Blue at the same time.

When I got the boat, the freezer would run almost nonstop. Only shutting down for two to three, one hour periods during the night,

A significant amount of the heat loss, really heat intrusion, was coming into from the lid. After a total lid rebuild and going with digital temp contollers, I'm where I'm at now. A 50% duty cycle once the box is fully cooled.

Adding an additional hold over plate, the same size as whats in there now, on one of the other walls is very doable. But I'm concerned about the remaining usable space.
Maybe adding it as a shelf is a better option.

I don't know and hence why I said I need to measure before going any further.

Anyhow, just more info to muddy the waters.

I’m spit 50/50, with no additional insulation.
I need to add it, just other things keep popping up and getting in the way.
I have dual cold plates in my freezer, one against the wall near the engine, the other in the wall towards the bow.
In my opinion I have plenty of room, but you would have to move your dividing wall to put the second plate if you do it like I did, move it just enough so that the plate barely fits and that is real close to 50/50.

My dividing wall is just one layer of the blue board, but both sides faced with thin fiberglass that is used inside of cargo aircraft to cover the walls. I wish I had a source for it, thin, strong and lightweight.
I cut two 2” holes to allow air to flow, but leave both of them covered and that works perfect to keep freezer single digit, and fridge just above freezing. I like it when my beer light,y freezes when I open it, that is just right
I have no idea of my duty cycle, but know it’s high, if I add insulation it’ll come down of course. I have a sweating issue on the top of the fridge now that is annoying, but demonstrates on the lack of insulation.
I told Rich when he designed/ built it, that I wanted excess cooling, don’t worry about energy consumption, I’d figure out how to power it.

However after is has been on for a few days, it actually is meager on the power, pulls about 5 amps it seems. My assumption is then that it’s running on low speed only.

[OzePete]

Originally Posted by CGirvan

Firstly thanks for sharing your data with the rest of us, I for one really appreciate it.

Regarding the above statement it seems like this is saying the eutectic system uses less power because it is more efficient. The question though is why is it more efficient or has a higher COP?. Sorry if this is a silly question.

Thanks CG, this is not a silly question at all. The COP is a very important factor in determining efficiency yet even many refrigeration people don't understand it or choose to ignore it because it is factual/ physics and often proves some of their rhetoric wrong!

So I shall try to explain: (Simply put)
The COP (Co-efficiency of Performance) is a factor that indicates how many watts of heat a refrigeration system or compressor can remove for each wall of electrical energy consumed. (Like how many miles per gallon! MPG) And like MPG, the COP varies considerably depending on how it is operating.

The COP varies mostly due to the systems evaporator operation temperature and to a much lesser degree, the compressor speed. Any compressor manufacturers data indicates the COP on a scale usually from say a COP of 2.23 at a 0C evaporator down to a COP of 1.07 at a -30C evaporator.
Therefore a system while the evaporator is at 0C, removes a massive 2.23 watts of heat for every watt of electrical energy consumed (w/w), yet the same equipment only removes 1.07 watts (w/w) while operating at -30C.

In the trial reported here at the 'Commercial Posts' forum, the eutectic evaporator was averaged at -7C (COP 1.85) while the cyclic evaporator temperature was averaged at -23C (COP 1.25)
Or simply put the Cyclic evaporator system having to operate at a much lower temperature consumed 48% more energy for the same result due to the difference in operation COP alone.

Next: The big difference in evaporator temperatures and therefore COP / efficiency is due to two key factors..
1> The cyclic system only refrigerates (removes heat) during a compressor run period and therefore has to remove cabinet heat at that time, and this is in short run periods therefore a lower plate temperature is needed whereas the eutectic system is absorbing heat constantly.
2> The cyclic plate's evaporator is relying on removing heat directly from the cabinets air (while the compressor runs) and has to run much colder as heat transfer from air is many times less efficient than transfer from a liquid. The eutectic evaporator is removing heat from a liquid and therefore much more efficiently.

The issue of efficiency related to different system COP's is indisputable, but now watch the usual suspects try to re-invent physics!

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[OzePete]

Originally Posted by SV THIRD DAY

I don't know if Pete agrees, but I sure don't.
A 0-deg holding plate isn't 0-degs. That the temp that the Eutectic Solution freezes at. The actual holding plate temperate ranges from
-15 to -5 degs F depending on the thermostat settings. We have plenty of Zero deg F freezer boxes and have been doing it for what...50 years now.

But here is the perfect example.
I get an email this morning from a lady that just bought a boat with a CoolBlue Technautics unit in the stand along freezer. (yes we really do have 7 day a week customer support). So we exchange a few emails and her freezer box is only 14-degs F and she would like it colder. After a few questions, she has a 7CF Box with our standard single holding plate with 2" of 30yr old insulation. I explain the science to her and that given her box size and insulation that's about what I would expect. Heck that's actually quite good!

So when her friends at the dock and on internet chat rooms ask her if her holding plate freezer system is good, she will say:
"Well the handsome and intelligent customer service guy was great on a Sunday, but holding plates don't get down cold enough for me".

BINGO...that's how the dock and cruiser rumor mill game works with Cruising Gear. The system is working great (oh and it's 16yrs old) but in that application 14-degs F is as cold as it will get. It's not the Holding Plate that is the problem and can't get a 0-deg Box...it's the BOX. And what control do we have over that? Nada. But the Box and how the customer uses the system often reflects back on us. It's part of the marine industry game and after 50yrs at it we have seen it all. Even the guy that tried to use our system as an air condition unit for his aft cabin.....no joke....fun stuff this Marine Industry.

Cheers Rich,
NO, like you, I don't agree with that poster's comments at all. He totally twist what was said but hey, whats new. At least we didn't get a lifes resume this time!
I just don't reply to such waffle any more, besides there are far too many genuine posters here looking for service help, factual data, ideas or system advise to waste time responding to that nonsense.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[newhaul]

Ozepete question for a 1.5 c.f. Freezer with 3.5 c.f. Spill fridge. 12v 400 watts solar 400 watts wind . R25 (aerogel)
What size holding plates ?

[SV THIRD DAY]

That sounds like one of Pete's (or mine) standard size hold over plates, since we are both using the same Eutectic Tank.

[Richard Kollmann]

Pete I still did not get an answer to my question. When discussing COP of compressors we know where the figures come from and they are understandable. In order to brag on Total System Coefficient Of Performance (SCOP) How does one come up with variables of (Qc) Heat removed from a refrigerated area by this type of refrigeration?

Why always the Smoke and Mirrors? Just fill in the blanks on the SCOP formula and tell us what measuring device did you use to determined watts of heat removed.

[OzePete]

Originally Posted by Richard Kollmann

Pete I still did not get an answer to my question. When discussing COP of compressors we know where the figures come from and they are understandable. In order to brag on Total System Coefficient Of Performance (SCOP) How does one come up with variables of (Qc) Heat removed from a refrigerated area by this type of refrigeration?

Why always the Smoke and Mirrors? Just fill in the blanks on the SCOP formula and tell us what measuring device did you use to determined watts of heat removed.

Oh my apologies Richard, my bad, I thought you would have understood COP and the application of that factor as derived from the compressor manufacturers data, and the systems pressure at the time.
So let me help you out here: (Click on pic to expand)



This is a 'cut and paste' from Secop's data relevant to the BD50.
Now knowing the suction pressure / temperature of your system, (You can read this using an R134a compound gauge, its fairly simple) then look across where the black arrow indicates and you can witness the different COP factors relative to the suction (evaporator) temperature above.
It really is simple Richard.

And by the way, look across from the red arrow and notice that Secop (was Danfoss) quote all their data at a 55C or a PSIG high side pressure very much greater than your often and wrongly stated 120 PSI max. Perhaps they and everyone else involved in refrigeration is wrong and you are correct, it is possible. lol

Richard I have responded to your request and enlightened you here to which I am sure you are undoubtedly most grateful, so maybe could reciprocate by explaining to us as to why you stick by your incorrect advice that high side pressure should not exceed 120PSIG which is absolute nonsense. Some factual data to support your miracle 120 PSIG would help, not just more puffery from what someone may have told you once upon a time!.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems