Refrigeration - Evaporator vs. Holding Plate

[daletournier]

Originally Posted by kmacdonald

Of course you are correct. Just about any test or research can be manipulated or designed to show exactly what the person doing the test or paying for the test wants it to show. IMHO that is exactly what was done. If anyone thinks a properly designed eutectic system is 100% more efficient than a properly designed evaporator system, god help them.

You do realise you just called a reputable professional a liar that has manipulated data? Poor show.

[RaymondR]

Originally Posted by kmacdonald

Of course you are correct. Just about any test or research can be manipulated or designed to show exactly what the person doing the test or paying for the test wants it to show. IMHO that is exactly what was done. If anyone thinks a properly designed eutectic system is 100% more efficient than a properly designed evaporator system, god help them.

I don't think Ozepete is manipulating the research.

Once one opts for the solar panel generation of electrical power and battery storage usage rationalization by time shifting the most intense period of usage into the time period of most intense period of electrical power generation so as to minimize the wear and tear on the storage devices is a logical progression.

It appears that what they have done in their experiment is fix the variables between the two systems by installing both options in the same insulated enclosure so that they operate under the same conditions then run a number of experiments on each mode whilst recording the power consumptions of each.

To me this appears to comply with the requirements of the scientific method wherein hypothesis is confirmed or not by experiment. Consequently I tend to the opinion that unless one also carries out a similar experiment which produces contrary results one should be a little restrained in one's criticism.

My own experience with a comparison of the two systems occurred accidentally when I rebuilt my on-board fridge as a sort of cold air circulation system and condensation collected in the bottom of the box because it did not have a drain. Noticing that it was cycling less often I installed a timer to exploit the holdover at night and found that my batteries were still at almost full voltage in the mornings and fully charged again by mid morning.

The system in my new boat is a cold plate constant cycling system and it's really pissing me off to know that it is daily cycling my expensive batteries to where their usable life is probably being halved. At the completion of this years winter cruising season one of my high priority projects is going to be to convert my fridge to the eutectic system and install a timer to ensure the load/generation cycle makes best use of the available power generation. I will probably go to the trouble of installing two eutectic tanks in my rather large box and another compressor/condenser unit to provide system redundancy.

[Typhoon]

We have an 7 cubic foot fridge and a 2.5 cubic foot deep freezer running at zero Fahrenheit in separate boxes . 10 ah a day on the fridge 17 ah a day in the freezer . In hot weather this increases to 12 and 20 ah due to more heat getting into the boxes . Batteries can handle this . Add solar and you have free refrigeration. The boxes are well insulated with good seals. I never give the systems thought . It just runs.

How well are your temperatures controlled in your holding plate systems ,

Regards John

[kmacdonald]

Originally Posted by daletournier

You do realise you just called a reputable professional a liar that has manipulated data? Poor show.

The physics don't lie.

[kmacdonald]

Originally Posted by sailcrazy

Quote:
Originally Posted by kmacdonald View Post
Of course you are correct. Just about any test or research can be manipulated or designed to show exactly what the person doing the test or paying for the test wants it to show. IMHO that is exactly what was done. If anyone thinks a properly designed eutectic system is 100% more efficient than a properly designed evaporator system, god help them.

what a great statement.....posted without a grain of proof or data to support it! IF you such proof, lets see it. If not, .....my BS flag just went up.

I have a new engine designed to run on salt water. I'm giving them away to the first 100 takers. Would you like one?

[Richard Kollmann]

Originally Posted by missourisailor

Richard,
You kinda answered my question with out answering it.

So let me pose the question another way.
With a Bd35 compressor running on 134A, what is a realistic low freezer and/or Evap Temp?

I do not know how to answer your questions because there are too many variables about your box and ambient temperature are not known.

I do know + 4 to +10 degrees F on a pleasure boat freezer will keep frozen food for six weeks without any noticeable taste changes.

If your thermostat is designed for a freezer and senses evaporator plate temperature when set full cold evaporator temperature should be near -15 degrees F. It is your thermostat that determines how cold evaporator gets. If compressor never reaches a low enough temp to trip thermostat then you will know there of a limit for your system.

As far as the lowest box temperature, This will be determined by heat loading in box, insulation, ambient air and water temperatures also air infiltration from lid or door seals. The difference in temperature between evaporator and box is usually more than 15 degree F.

If your first test if thermostat stopped compressor and you would like to know how cold the box or evaporator will get bypass thermostat letting compressor run continuously for eight hours.

[missourisailor]

Originally Posted by Richard Kollmann

I do not know how to answer your questions because there are too many variables about your box and ambient temperature are not known.

I know that I left a lot of info out. But with your statement that small compressors running on R134A, don't have enough Hp to create enough vacuum to get below -16F, kind of threw me. I know my holding plate evap is reaching -10F with a box temp of around -5F. I was just wondering if I'm at the edge of the envelope sort of speak.

Originally Posted by Richard Kollmann

I do know + 4 to +10 degrees F on a pleasure boat freezer will keep frozen food for six weeks without any noticeable taste changes.

I just like rock hard ice cream!
Also I like to reload ice cube trays with out having the box temp go nuts.

Originally Posted by Richard Kollmann

If your thermostat is designed for a freezer and senses evaporator plate temperature when set full cold evaporator temperature should be near -15 degrees F. It is your thermostat that determines how cold evaporator gets. If compressor never reaches a low enough temp to trip thermostat then you will know there of a limit for your system.

The stat is the determination for compressor cycles.
I have set it to -15F and after a very long time, it did start to cycle again.
But the duty cycle almost doubled.
Right now at -10F plate temp., I have just over a 50% duty cycle.

Originally Posted by Richard Kollmann

As far as the lowest box temperature, This will be determined by heat loading in box, insulation, ambient air and water temperatures also air infiltration from lid or door seals. The difference in temperature between evaporator and box is usually more than 15 degree F.

Fully understand and totally agree.
I do have a known insulation problem. But if I can maintain my daily power consumption of around 75~80 Ah's, I'm okay with the insulation as it is.
Of course I'm only talking about the freezer's use age. Not the whole boat.

Originally Posted by Richard Kollmann

If your first test if thermostat stopped compressor and you would like to know how cold the box or evaporator will get bypass thermostat letting compressor run continuously for eight hours.

Like I previously said, the stat is shutting down the compressor. But it is a holding plate system, so the stat is reading plate temp..
A separate temp probe/indicator is used for box temp monitoring.

[Richard Kollmann]

Originally Posted by missourisailor

I know that I left a lot of info out. But with your statement that small compressors running on R134A, don't have enough Hp to create enough vacuum to get below -16F, kind of threw me. I know my holding plate evap is reaching -10F with a box temp of around -5F. I was just wondering if I'm at the edge of the envelope sort of speak.



I just like rock hard ice cream!
Also I like to reload ice cube trays with out having the box temp go nuts.



The stat is the determination for compressor cycles.
I have set it to -15F and after a very long time, it did start to cycle again.
But the duty cycle almost doubled.
Right now at -10F plate temp., I have just over a 50% duty cycle.



Fully understand and totally agree.
I do have a known insulation problem. But if I can maintain my daily power consumption of around 75~80 Ah's, I'm okay with the insulation as it is.
Of course I'm only talking about the freezer's use age. Not the whole boat.



Like I previously said, the stat is shutting down the compressor. But it is a holding plate system, so the stat is reading plate temp..
A separate temp probe/indicator is used for box temp monitoring.

missourisailor, Out of hundreds of discussions about pleasure boat refrigerator freezers it is rare to hear of performance as good as yours. Your holding plate's performance and power consumption are exceptional. Most of my comments on freezers deal with high temperature freezers from +15 to +27 degrees F. If government standards require transportation of frozen foods to be maintained below +22 degrees F and temperature drift with holding plates it is easy to see why food quality in boat freezers changes fast. I usually end most of my responses by saying, If evaporator plates do not surround frozen food as much as possible frozen product should be rotated in box weekly.

We should be asking you questions and not answering yours.

[transmitterdan]

Originally Posted by john61ct

Are you saying that for my application there's no point using fluid with a lower freezing point? Doesn't the fact it changes phase at a lower temp make its cooling effect last longer?

Not really. The amount of energy required to change phase from frozen to liquid is not greatly affected by the actual freezing point temp. It is affected by the volume but not so much the actual freezing temperature. In fact, I think most solutions need less energy than pure water to effect a change in phase (frozen to liquid). But we use solutions because we need less than 0C freezer temps.
And compressors are more efficient the less delta T they have to work against. So a much lower freezing point of the solution than necessary means the system is working a higher delta T to ambient and will be inherently less efficient.

[SV THIRD DAY]

Originally Posted by missourisailor

An interesting point that I had not thought of.




So if we have a box temp of -5F and a holding plate temp of -10F, what ratio of Glycol/water?

Don't go with a higher concentration of glycol....stick with 1/3 glycol and 2/3 water for best results.

[john61ct]

Sorry for crosstalking polar tubes, but too late now I guess.

So I'm now inferring for that use case,

I'm not buying extra cooling time there by going in with lower-melting-point frozen tubes, so

I may as well use plain water wrt the coolbox-melting part of the cycle,

and in fact will gain efficiency on the freezing stage by doing so.

Does that actually make sense to the gurus here? I'm very skeptical, but physics can be non-intuitive.

[missourisailor]

Originally Posted by Richard Kollmann

missourisailor, Out of hundreds of discussions about pleasure boat refrigerator freezers it is rare to hear of performance as good as yours. Your holding plate's performance and power consumption are exceptional. Most of my comments on freezers deal with high temperature freezers from +15 to +27 degrees F. If government standards require transportation of frozen foods to be maintained below +22 degrees F and temperature drift with holding plates it is easy to see why food quality in boat freezers changes fast. I usually end most of my responses by saying, If evaporator plates do not surround frozen food as much as possible frozen product should be rotated in box weekly.

We should be asking you questions and not answering yours.

Richard,
Thanks for the kind words.
But my fridge/freezer really pisses me off!!
For the exact reason I highlighted above.

I can see if our sailing/cruising consisted of weeks or months from land based supplies where I would have a good to very good setup. One time loading then frozen until needed.

But as coastal sailors, we tend to load up when ever we come ashore. Which is usually every three to five days.

When we load the "high temp" frozen food into the freezer, the system goes nuts trying to bring the temp down. Usually it will run nonstop for 36 to 48 hours until the stat shuts it down.
Honestly this is really no big deal because our house bank can handle the load. But it drives me nuts when it is not cycling.

IMHO I think the driving cause for this long cool down time is directly related to the surface area of the holdover plate. Small surface area equals less BTU transfer.

Pete's test showed that with an empty box, the holding plate system is more efficient. But if a half full box was brought down to temp, then more items added and the system was allowed to recover. I would bet that the results would swap. At least until it recovered.

Most holding plates just don't have the surface area that the thin plates have. At least not the ones I've seen.

[Typhoon]

Not only that but holding plates are usually made of stainless , a very poor conductor of heat.

It all adds up .

Regards John

[savoir]

Originally Posted by Exile

Sorry to read this, and completely inconsistent with my experience over the past 11 years with my Seafrost 110v system. Mine is the 'Shore Assist 3' fwiw, but they also make a higher capacity 110v unit that looks better suited for boats with large generators. Quality of the original installation and amount of usage are obviously big factors which may explain our different experiences. But like you, if mine starts giving me a lot of trouble I will also likely replace with a 12v BD unit. If for no other reason then less reliance on running my diesel generator when away from the dock.

This is my compressor. I would recommend it to anyone with a large motor boat or someone who never goes away from the dock for longer than a weekend. The compressor burns a staggering 500w which is out of the question for most sailboats.
DC5000

[newhaul]

Originally Posted by missourisailor

Richard,
Thanks for the kind words.
But my fridge/freezer really pisses me off!!
For the exact reason I highlighted above.

I can see if our sailing/cruising consisted of weeks or months from land based supplies where I would have a good to very good setup. One time loading then frozen until needed.

But as coastal sailors, we tend to load up when ever we come ashore. Which is usually every three to five days.

When we load the "high temp" frozen food into the freezer, the system goes nuts trying to bring the temp down. Usually it will run nonstop for 36 to 48 hours until the stat shuts it down.
Honestly this is really no big deal because our house bank can handle the load. But it drives me nuts when it is not cycling.

IMHO I think the driving cause for this long cool down time is directly related to the surface area of the holdover plate. Small surface area equals less BTU transfer.

Pete's test showed that with an empty box, the holding plate system is more efficient. But if a half full box was brought down to temp, then more items added and the system was allowed to recover. I would bet that the results would swap. At least until it recovered.

Most holding plates just don't have the surface area that the thin plates have. At least not the ones I've seen.

the plate on the la ruina is 13x24x2.5 stainless steel so about 5 sq ft of surface area and if memory serves the last evaporation plate unit I installed was about the same but only 3/8 inch thick aluminum.