Cold plate cooling down too slowly?

[BluJu]

Hi all,

My boat is equipped with an E-Z cold 12-V air/water cooled cold-plate refrigeration system (model EK 12CPAW). 25-30 yr old system.
The cold plate is located in the freezer box. Cold air spills over to the adjacent fridge box via a small opening. The cold plate is roughly 16x11x3 in. Typical draw from the compressor is about 5.8 amp.

Lately I've been running the fridge to track performances as I was already suspicious something was off last summer. I turned on the unit yesterday morning, both boxes were at about 12 deg C; 13 hrs later, the freezer was at 2 and the fridge 9 C; this morning (after 24 hrs), the freezer box was at -7 and the fridge at 4 C (as cold as I've ever gotten it to be). At that point I was getting average plate temp reading around -16 C, but surprisingly the plate did NOT look to be uniformly frozen. I turned the unit off f and within 5 hrs, the temp came up to -2 and 6. It was about 24 deg C inside the boat. I ran the unit again for 2 hrs and only got the freezer box to go down by 1 deg C.

After that lengthy background info, here are the questions:

1) I feel it should not take that much time to reach the final temp. Is it correct?

2) If so, could I be low on R134? Last summer I had a refrigeration technician come inspect the unit. He said we were a bit low on R134 (pressure test) and topped It up

3) Could a low R134 level explain the fact that the plate did look to be uniformly frozen after 24hr of running? by that I mean the plate surface temp varied between areas by at least 5 deg. or is it normal?

4) What is the "life expectancy" of such units? The former (only) owner mostly sailed in the summer months. I've had the boat for 2 yrs and have not used the fridge much so I can't imagine that the compressor has a huge number of hours.

5) I'm getting ready for 1-2 yr cruise with wife and 2 young kids. We'll need a reliable refrigeration system and I've been contemplating replacing the system . Mostly because I think the plate may not be large enough to keep the fridge near 3-4 deg and the freezer <-5 C without running too often, which defeats the purpose of the cold plate. Based on the dimensions above and assuming a system working properly, does that make?

Looking forward to hear your advice/comments!
thanks.

[Richard Kollmann]

Bluju, Unfortunately many manufacturers of pleasure boat refrigeration experiment away from the more simple proven designs. I hear frequently from boaters with basic refrigeration systems that are 25 to 30 years old but not any of the overly complicated models like E Z Cold machines can last that long.
Your Questions
1) I feel it should not take that much time to reach the final temp. Is it correct?
A. There are a few items that can change over time that affect performance of that refrigeration unit, Moisture in insulation do to out gas aging, Loss of eutectic solution in holding plate, loss of refrigerant or moisture in refrigerant. There have been more than a few E Z Cold units destroyed by Seawater condenser failures. E Z Cold also had an extra tan colored small wired box for Compressor speed up control after 1995 that can retard performance.
2) If so, could I be low on R134? Last summer I had a refrigeration technician come inspect the unit. He said we were a bit low on R134 (pressure test) and topped It up.
A. It is normal for a service tech to say he added refrigerant, What else can he say when he does not know how to answer a poor performance problem. I do not know the size of your icebox or the ambient temperatures or that compressor you have BD 35 Or BD 50 during your test. With your holding plate containing near 19 pounds of warm eutectic solution the compressor needs to run more than 9 hours just to freeze holding plate solid. The way to see if that stainless steel plate is frozen solid is tap on it when warm and again when frozen with a large coin. When warm sound is a metal sound when frozen sound is a dead solid sound. The time it takes to freeze plate is only half the compressor running time required, heat must also be removed at the same time from box and surrounding insulation. Testing performance the fist day will not provide a realistic performance review.
3) 3) Could a low R134 level explain the fact that the plate did look to be uniformly frozen after 24hr of running? by that I mean the plate surface temp varied between areas by at least 5 deg. or is it normal?
A. When a holding plate is placed in freezer area of box its eutectic freeze point is generally as low as – 18 degrees C. Because most manufacturers use a Food Grade Gycol there will be a temperature variances over time between top and bottom of plate caused by eutectic solution separation. Refrigeration volume in systems with holding plates is hard to confirm. Knowing compressor size and speed along with amp draw will confirm reasonable correct refrigerant charge. A little low on refrigerant is always better that too much refrigerant.
4) What is the "life expectancy" of such units? The former (only) owner mostly sailed in the summer months. I've had the boat for 2 yrs and have not used the fridge much so I can't imagine that the compressor has a huge number of hours.

ANSWER When an air cooled basic system is correctly installed the compressor seems to last forever. Fan service life is I believe to be 7000 hours. A properly designed holding plate should last the life of the boat. I would avoid systems using line connectors with O rings as a final seal like those used on E Z Cold machines. The major problem with Danfoss compressors is their electronic control module’s failure rate if not connected to clean electrical power and protected from excessive heat. Water cooling these small compressors compromises reliability and reduces service life to less than five years on a live aboard boat

5) I am getting ready for 1-2 yr cruise with wife and 2 young kids. We'll need a reliable refrigeration system and I've been contemplating replacing the system . Mostly because I think the plate may not be large enough to keep the fridge near 3-4 deg and the freezer <-5 C without running too often, which defeats the purpose of the cold plate. Based on the dimensions above and assuming a system working properly, does that make?

ANSWER Unless You have alternative surplus energy from Solar or Wind holding plates are less efficient space wise and energy wise. I agree that it is wise to replace the existing refrigeration system. I recommend you take time to select the best system for your needs. Be watchful of sales people at boat shows that say their unit is better than someone else’s unit. They are also the people when unit does not satisfy your needs will say you need more insulation.

[savoir]

If it's any help, my holding plate system takes around 12 - 15 hours to get down to temperature with the box empty and around 30 - 35 hours with the box full.

Holding plates are just the best. I run mine 1 hour in 12. If I had children opening the lid all the time that would probably be around 45 minutes per 6 hours.

[Olddan1943]

Do you have a fan inside the freezer and fridge?
If not, give serious consideration to installing them. They will make the units more efficient.

[BluJu]

Richard,

thanks for this detailed answer. I've got plenty of power supply (240 W solar panel and a good wind generator), so I'm not worried about that. The box dimensions are as follows: Freezer: 1x1.5x2 ft; Fridge: 2x1.5x1.75 ft. So a little over 8 cubic feet of space. I'll have to check on the compressor model, but its draw when running is between 5.5 and 5.8 amps. I've never seen it outside of that range.

I will track performance of the system over a longer period. However, assuming that the temps I observed after the 25 hr initial cooling period reached their minimum in each boxes, I'm surprised not to have seen much decrease in temperature when I turned the unit back on ~5 hrs later and ran it for 2.5 hr. I thought/hoped that a 1-hr run time would freeze the holding plate again (though I'll do the coin test to verify next time) and bring the temps back at their minimum.

As far as a replacement system, if I stick with holding plates, I would go for a larger plate or a dual plate system. Any recommendations for/against these options?

Oddan1943: I'm going cruising for 3 weeks starting next week and was absolutely planning on experimenting with a small fan to help circulating air in the boxes.

[Olddan1943]

BluJu, on my Nordavn I had a cold plate freezer. It had a 12vt pancake fan inside the box. Of course the fan did not work. I replace it and discovered I could fit inside the box.
The fan I used was a 12 computer pancake fan. It was identical to the fan I removed.

[a64pilot]

I believe I would replace just the compressor and condenser and keep the existing cold plates and save a bundle of money and work.
I know Cool Blue will use existing plates, I am sure they are not the only one. The plates don't wear.
Cold plates are less efficient because basically your freezing the solution and it's keeping the box cold, most efficient to cool the box directly. Cold plates are sort of like making ice to put into an ice box. However they are good for their hold over ability, for people with a lot of solar they can be run continuously during hours of solar output and not run over night, shifting energy consumption to the times when there is an excess, total consumption is more, but it's consumed when there is an excess so there is a savings.
Placing a fan inside the box may even out the temps in the box, but it's not going to increase efficiency of the system. I have a tiny fan in my fridge section, it takes only a tiny fan only a very small movement of air is needed.

Water cooling looks good on paper, but we don't sail paper boats. Long term it's a fail in the real world

[Richard Kollmann]

Bluju, When I recommended you replace the complete E Z Cold system this included the holding plates. When seawater enters the refrigerant circuit as has been my experience with four of these E Z Cold units the plates and all tubing must be replaced. Before E Z Cold went out of business they replaced compressor and condenser under warrantee without solving the contamination problems. E Z Cold’s seawater condenser failures first show up as a very slow loss of refrigerant, then next poor cooling. Finally compressor rotor locks up. I discussed this problem with then president of EZ Cold who felt these condenser leaks were isolated cases. Five years ago when there were more condensers failing they were replaced with a large what seem to be a homemade PBC pipe condensers. Because of the earlier problems with Condenser leaks I advised owners of this system to use air cooling only.

Bluju, It is always important to have open air areas in a refrigerated box for air to naturally tumble over food. Adding a small fan can improve box low temperatures by as much as six degrees F. See my web site section on FANS.

[topmast]

I fastened a small computer fan to a length of aluminium flex hose (big electrical cable stuff) Sucked cold from under cold plate and dumped at top far corner. Made a huge difference and the Hagen Das appreciated it.

[savoir]

Mmmmmmm Haagen Dazs

[BluJu]

Originally Posted by Richard Kollmann

Bluju, When I recommended you replace the complete E Z Cold system this included the holding plates. When seawater enters the refrigerant circuit as has been my experience with four of these E Z Cold units the plates and all tubing must be replaced. Before E Z Cold went out of business they replaced compressor and condenser under warrantee without solving the contamination problems. E Z Cold’s seawater condenser failures first show up as a very slow loss of refrigerant, then next poor cooling. Finally compressor rotor locks up. I discussed this problem with then president of EZ Cold who felt these condenser leaks were isolated cases. Five years ago when there were more condensers failing they were replaced with a large what seem to be a homemade PBC pipe condensers. Because of the earlier problems with Condenser leaks I advised owners of this system to use air cooling only.

Bluju, It is always important to have open air areas in a refrigerated box for air to naturally tumble over food. Adding a small fan can improve box low temperatures by as much as six degrees F. See my web site section on FANS.

Thanks again Richard. The symptoms you describe seem to fit what I observe with my unit. I had no idea seawater cooling was an issue in the long run. I'm pretty sure at this point that I'm losing refrigerant somewhere. I may try to locate the leak over the next few weeks when we go cruise but I'm set on replacing the whole system next winter/spring.

[Richard Kollmann]

The problem with that condenser is there a spot inside condenser where the cupro nickel seawater tube is too close to outer refrigerant tube concentrating the low voltage discharge to only one spot. Over time a micro size hole opens up letting out a very small amount of refrigerant in a month. In time this small hole will get larger. Because this leak is in the high pressure side damage to complete system is not done until all refrigerant pressure has leaked out allowing water to inter refrigerant side of condenser.

If you want to determine if loss of refrigerant is inside condenser remove water hoses from condenser and place balloons on condenser water tube. Using only air cooled fan condenser see if after a few days flat balloons start to open up.
Warning open water hoses can sink boats so shut off pump and plug open hoses.