Refrigeration - Evaporator vs. Holding Plate

[Richard Kollmann]

Originally Posted by savoir

I switch mine on/off manually. If I left it on auto it would cycle during the night and wake me up. The system is aligned with genset use so that it cannot accidentally drain the batteries. The system is separate fridge and freezer but I only use the freezer at sea.

The Original Post was mainly addressing small 12/24 volt refrigeration comparing conventional evaporators versus holding plates. On boats 40 ft and larger Eutectic evaporator plates are common with 1/2 HP compressors running once or twice a day for one hour.
Unfortunately any boat refrigerator compressor larger than 1/16 HP will require a very unfriendly water cooled condenser instead of discharging process heat inside boat.

[Richard Kollmann]

After reading all of the comments in this section you should be able to make a decision about what type evaporator is best for your boat’s ice box conversion refrigeration.

There are three different applications for energy storing eutectic plates in pleasure boat refrigeration. 1. Box size is too large for 12 volt refrigeration , 2. Boat’s onboard electric power grid is not sufficient enough to support 12 volt electrical refrigeration. 3. There is surplus electrical energy that can not be stored in batteries.

It is the compressor that produces the energy required each day to satisfy your refrigeration needs regardless of what type evaporator standard or eutectic energy storage tanks. The crutch that sales persons use to justify their claim that small compressor’s cycling too often is no longer applicable with variable speed small 12 volt compressors.
The comparison now between standard and eutectic evaporators is in their exterior thermo heat absorbing efficiency and how well the refrigerant coil inside eutectic plate is designed to quickly capture heat from plate’s exterior surface. There are a number of ways eutectic plate manufacturers transfer heat from plate exterior into the refrigerant coil inside plate avoiding the lower heat conducting ice formation on evaporator coils.

Gleaser Bay plates employed a spider web of mutable small tubing to reduce ice areas between plates surface and refrigerant coils.

Crosby and Grunert for years used Dole truck plates designed and for boat refrigeration. Their evaporator coils were attached inside plate to both front and back of plates.

SeaFrost added copper sheets to improve performance of their cast aluminum plates.

Technautics now is said to use a mutable fined evaporator coil inside their new plates.

Frigoboat plates in the past used a fined evaporators covering complete area inside their large plates.

The interior evaporator coil in plates for live aboard boats refrigeration are less expensive because eutectic solution does not need to be completely frozen each morning. These eutectic plates with plain copper tubing inside are designed to be used as 12 or 24 hour energy storage only when there is surplus energy from oversize mechanical or alternating current compressors are used for refrigeration.

Advantages and Disadvantages of standard evaporators versus Eutectic evaporators.

Standard roll bond aluminum thin evaporator plates

Uses very little box area.
Can allow box to have more than one temperature area, like drink cooler, refrigerator temps or freezer temps in one standard size box.
Box area temperature can be maintained stable as long as thermostat monitors evaporator temperature instead of box temperatures.
Box shaped aluminum bins evaporators add the ability for ice production and ice cream.
Fast temperature pull down when box is warm.
When it come to freezers luminum thin plates are better suited than eutectic as a good freezer needs the product surrounded as much as possible with evaporator.
Thin plate evaporators are not limited in reaching sub zero temperatures.
Aluminum thin plate evaporators are easily damaged and have an average life of 12 years in a live aboard boat.

Eutectic energy storing plates.

There a benefit from a properly designed eutectic plate on 12 volt refrigeration if there is a source of alternative electrical power from a generator, solar power or wind generator.
On pleasure boats eutectic plates generally waste space with little benefit.
These energy plate act as a rapid heat absorber when warn material is placed in box.
As to disadvantages you have read this very long thread and must decide that type evaporator is best for your application.
If you believe the eutectic energy plate is more energy efficient there is still a place in Heaven for all of us....

[RaymondR]

Hi Richard.

The design of the evaporator coils inside eutectic tanks is an issue I have been pondering on fairly consistently lately as I am approaching the time when I need to build the eutectic tank components if my fridge rebuild.

Nigel Calder wrote an article for Professional Boatbuilder titled Marine Refrigeration which addresses issues related to the various designs available at that time as you have done above.

One of the things I'm curious about is the return circulation of oil to the compressor. The standard thinking on this aspect was that one needed a return velocity of between 1,200 - 1,500 fpm to achieve this successfully. Obviously on the multi tube arrangements used to get a better distribution of cooling effect in the eutectic tank these velocities would not be achieved.

The question I have is do the multi tube arrangements rely upon the agitation resulting from the boil off of liquid refrigerant to transport oil back into the single tube return line to return it to the compressor?

[SV THIRD DAY]

Look at the CAD drawing of the inside of our holding plates on page 11 of the manual:
We Transfer manual link: https://we.tl/t-nof0ugJo1k

This is how Technautics has ALWAYS been making their holding plates since 1968, the oldest marine refrigeration company in existence.

So when Richard K either doesn't know this and makes statements like:


"Technautics now is said to use a mutable fined evaporator coil inside their new plates."

You have to ask yourself, what else has been going on for 53 years in the marine refrigeration business that he doesn't know about?

[Richard Kollmann]

Rich, I reported the facts I can confirm in the eutectic plates I listed only those that I cut open and inspected. Yes I am aware Technautics is 50 years in business. Their Coolblue machine maybe the most energy efficient eutectic plate small 12 volt refrigeration, when installed in a matching capacity insulated box. I myself spent nearly 40 years manufacturing eutectic plate systems with the first prototype plate system on wheels in 1963.

[OzeLouie]

Originally Posted by SV THIRD DAY

Look at the CAD drawing of the inside of our holding plates on page 11 of the manual:
We Transfer manual link: https://we.tl/t-nof0ugJo1k

This is how Technautics has ALWAYS been making their holding plates since 1968, the oldest marine refrigeration company in existence.

So when Richard K either doesn't know this and makes statements like:


"Technautics now is said to use a mutable fined evaporator coil inside their new plates."

You have to ask yourself, what else has been going on for 53 years in the marine refrigeration business that he doesn't know about?

Yes and thanks SV Third Day, we members sure do. This topic has seen over 46,000 reads so obviously of great interest to members, members seeking real data, test results, factual info and on topic discussion as you and we often present, not more puffery, self glorification or mis-information.

So to assist the majority wanting to understand, here is a description of how Eutectic refrigeration expectations are computed, and confirmation that 12vdc systems can and do operate marine cabinets very economically and successfully.
I will keep this basic for those with little understanding of the fundamentals.

First we need to establish a couple of facts:

A: Heat load. A cabinet to be refrigerated can easily have it's 'Heat load' calculated. This takes into account things like capacity, temp to maintain, temp of the environment, insulation properties etc etc. The Heat load is quoted as WATTS of heat related to hourly or more usually to daily (24 hrs) and what must be extracted to maintain cabinet temp. Without firstly establishing the heat load using this industry method, all else is guesswork.

B: Specific heat. This is the amount of heat in watts to warm or cool a medium that is not phase changing. Water between 0C and 100C requires one watt of heat added to warm one litre of water by one degree centigrade and conversely needs one watt removed per litre to lower the temp by one degree.... simple Cyclic systems rely on specific heat computations.

C: Latent heat. This is the amount of heat in watts required to 'phase change' a litre of water to a frozen mass or the amount of heat in watts that the frozen mass absorbs as it 'phase changes back to a liquid. It requires 93 Watts to phase change a litre of water!!! (that is 93 times more thermal energy is involved in the phase change than a change of 1C otherwise!!) (Note: the latent heat factor for a typical fridge temp glycol / water mix is approx 80 watts per litre, not 93 as for pure water) Eutectic systems rely on Latent heat benefits and heat storage computations.

And understanding these facts are essential in appreciating why eutectic refrigeration can be so advantages specially when the power supply is often limited at best or erratic.
A system that doesn't freeze then thaw on each cycle is not a eutectic system!

Now for a practical example:

1: Assume a 140 litre top opening cabinet with 75mm thickness insulation (r15) maintaining cabinet / product temp of +2 to +4C while operating in a 35C environment. This cabinet would require an average of approx 24 watts per hour or 480 watts per 24 Hours, to be removed so that cabinet temperature is maintained. (heat load)

2: Using a 5.5 litre eutectic plate we can establish that it can accept and 'store' 440 watts of thermal energy for each freeze / thaw cycle approx the total for one 24 hr day! (5.5 x 80 watts)

3: Using a 3.5cc refrigeration unit with an hourly heat extraction ability that averages 125 watts per hour, the refreeze would require a long single four hour run per day to refreeze the eutectic medium!
Or using less capacity refrigeration units as follows

Compressor ... Secop Secop Secop Ozefridge
Model number > BD35 BD50 BD80 BE90
Compressor Capacity > 2.0cc 2.5cc 3.0cc 3.5cc
Rating in watts/hr> 67.3 85.1 108.1 125.9 (All data extracted from manufacturers publications)
Time for single duty> 7.0+ 6.0+ 5.0+ 4.0+ (Hours of ONE long run per day!)

As can be seen any of the 12.00VDC refrigeration systems are capable of operating as a eutectic system in reasonably hot environments and usually requiring only one long run cycle. Interestingly all systems used similar power input to maintain the cabinets needs.
This example assumes that the system is correctly engineered and that the cabinet's heat load has been correctly estimated and not just guessed!

Now having hopefully explained the eutectic system calculations, phase change and thermal storage made possible by the relatively massive storage made possible by phase change (Latent heat), lets go one step further and look at how although requiring less power compared to other system types, due to usually just one run required per day it is possible to at all but remove any battery consumption, here is why:

Having concluded that usually only one long run per 24 hours is required, and if the system is equipped to perform this one long cycle automatically (ECO2) when abundant power is available therefore powered direct from the power source. ( gen set, solar, wind etc after batteries are topped up and excess power would otherwise be wasted) And bingo virtually no battery drain!!

I hope this info helps those interested to understand eutectic and look forward to responding to any genuine ideas or questions. After all we are covid 19 locked down here in 'Fort Oz' and its bloody boring!

[RaymondR]

That's a very good explanation Ozylou.

[wsmurdoch]

QUOTE=OzeLouie;3466564]
B: Specific heat. This is the amount of heat in watts to warm or cool a medium that is not phase changing. Water between 0C and 100C requires one watt of heat added to warm one litre of water by one degree centigrade and conversely needs one watt removed per litre to lower the temp by one degree.... simple Cyclic systems rely on specific heat computations.

C: Latent heat. This is the amount of heat in watts required to 'phase change' a litre of water to a frozen mass or the amount of heat in watts that the frozen mass absorbs as it 'phase changes back to a liquid. It requires 93 Watts to phase change a litre of water!!! (that is 93 times more thermal energy is involved in the phase change than a change of 1C otherwise!!) (Note: the latent heat factor for a typical fridge temp glycol / water mix is approx 80 watts per litre, not 93 as for pure water) Eutectic systems rely on Latent heat benefits and heat storage computations.[/QUOTE]

As has been pointed out earlier, these are not the correct units. The specific heat of water (the sensible heat) is 4184 J/kg-°C or 1 cal/g-°C or 1 Cal/kg-°C or 1 BTU/lb-°F. The heat of fusion of water (the latent heat of freezing) is 333,550 J/kg or 79.7 cal/g or 79.7 Cal/kg or 144 BTU/lb. Watts are not an amount of energy, watts are an amount of energy flowing in a period of time. An amount of heat is expressed in joules, small calories, large calories, or BTUs.

And, between 0°C and 100°C it requires not one watt but one Calorie to heat a liter (about a kg) of water 1°C.

From all appearances you and your company have a good product; well made and a commercial success. You have documented testing that show an unexpected superiority of your holding plate refrigeration system over your previous aluminum evaporator plate system. Your misstatements like those above detract from your efforts to market your product. I urge you to contact the mechanical engineering department at the University of Sidney, at the University of New South Wales, or at RMIT and to ask them about assistance through their industrial outreach service. I am sure that they could help you better evaluate the results of your testing and perhaps further improve your product. They could also guide you more in rigorously describing the benefits of your holding plate refrigeration system. This sort of industry assistance to small and growing firms (along with education and research) is a primary focus of all engineering schools.

[newhaul]

Originally Posted by OzeLouie

Yes and thanks SV Third Day, we members sure do. This topic has seen over 46,000 reads so obviously of great interest to members, members seeking real data, test results, factual info and on topic discussion as you and we often present, not more puffery, self glorification or mis-information.

So to assist the majority wanting to understand, here is a description of how Eutectic refrigeration expectations are computed, and confirmation that 12vdc systems can and do operate marine cabinets very economically and successfully.
I will keep this basic for those with little understanding of the fundamentals.

First we need to establish a couple of facts:

A: Heat load. A cabinet to be refrigerated can easily have it's 'Heat load' calculated. This takes into account things like capacity, temp to maintain, temp of the environment, insulation properties etc etc. The Heat load is quoted as WATTS of heat related to hourly or more usually to daily (24 hrs) and what must be extracted to maintain cabinet temp. Without firstly establishing the heat load using this industry method, all else is guesswork.

B: Specific heat. This is the amount of heat in watts to warm or cool a medium that is not phase changing. Water between 0C and 100C requires one watt of heat added to warm one litre of water by one degree centigrade and conversely needs one watt removed per litre to lower the temp by one degree.... simple Cyclic systems rely on specific heat computations.

C: Latent heat. This is the amount of heat in watts required to 'phase change' a litre of water to a frozen mass or the amount of heat in watts that the frozen mass absorbs as it 'phase changes back to a liquid. It requires 93 Watts to phase change a litre of water!!! (that is 93 times more thermal energy is involved in the phase change than a change of 1C otherwise!!) (Note: the latent heat factor for a typical fridge temp glycol / water mix is approx 80 watts per litre, not 93 as for pure water) Eutectic systems rely on Latent heat benefits and heat storage computations.

And understanding these facts are essential in appreciating why eutectic refrigeration can be so advantages specially when the power supply is often limited at best or erratic.
A system that doesn't freeze then thaw on each cycle is not a eutectic system!

Now for a practical example:

1: Assume a 140 litre top opening cabinet with 75mm thickness insulation (r15) maintaining cabinet / product temp of +2 to +4C while operating in a 35C environment. This cabinet would require an average of approx 24 watts per hour or 480 watts per 24 Hours, to be removed so that cabinet temperature is maintained. (heat load)

2: Using a 5.5 litre eutectic plate we can establish that it can accept and 'store' 440 watts of thermal energy for each freeze / thaw cycle approx the total for one 24 hr day! (5.5 x 80 watts)

3: Using a 3.5cc refrigeration unit with an hourly heat extraction ability that averages 125 watts per hour, the refreeze would require a long single four hour run per day to refreeze the eutectic medium!
Or using less capacity refrigeration units as follows

Compressor ... Secop Secop Secop Ozefridge
Model number > BD35 BD50 BD80 BE90
Compressor Capacity > 2.0cc 2.5cc 3.0cc 3.5cc
Rating in watts/hr> 67.3 85.1 108.1 125.9 (All data extracted from manufacturers publications)
Time for single duty> 7.0+ 6.0+ 5.0+ 4.0+ (Hours of ONE long run per day!)

As can be seen any of the 12.00VDC refrigeration systems are capable of operating as a eutectic system in reasonably hot environments and usually requiring only one long run cycle. Interestingly all systems used similar power input to maintain the cabinets needs.
This example assumes that the system is correctly engineered and that the cabinet's heat load has been correctly estimated and not just guessed!

Now having hopefully explained the eutectic system calculations, phase change and thermal storage made possible by the relatively massive storage made possible by phase change (Latent heat), lets go one step further and look at how although requiring less power compared to other system types, due to usually just one run required per day it is possible to at all but remove any battery consumption, here is why:

Having concluded that usually only one long run per 24 hours is required, and if the system is equipped to perform this one long cycle automatically (ECO2) when abundant power is available therefore powered direct from the power source. ( gen set, solar, wind etc after batteries are topped up and excess power would otherwise be wasted) And bingo virtually no battery drain!!

I hope this info helps those interested to understand eutectic and look forward to responding to any genuine ideas or questions. After all we are covid 19 locked down here in 'Fort Oz' and its bloody boring!

This should help you correct any errors in your post.

https://www.convertunits.com/from/wa...ories+per+hour

You can view more details on each measurement unit: watt or calories per hour The SI derived unit for power is the watt. 1 watt is equal to 859.84522785899 calories per hour. Note that rounding errors may occur, so always check the results.

[Richard Kollmann]

It seem the current assumption is the heat energy consumed in melting ice is equal to the energy needed to produce the lower temperature eutectic ice?

[OzeLouie]

Originally Posted by newhaul

This should help you correct any errors in your post.

https://www.convertunits.com/from/wa...ories+per+hour

You can view more details on each measurement unit: watt or calories per hour The SI derived unit for power is the watt. 1 watt is equal to 859.84522785899 calories per hour. Note that rounding errors may occur, so always check the results.

Thanks Bill and Newhaul, appreciate your constructive replies and suggestions which I will explore.
In trying to get a message across and keep it simple yet with the correct outcome, I opted to take some terminology liberties, liberties to simplify which don’t affect the outcome. Either calculation method provides a similar outcome.

My post stated “I will keep this basic for those with little understanding of the fundamentals.”
Watts to BTU…… https://www.advancedconverter.com/un...o-btu-per-hour

My aim was to address the mass of misinformation regards eutectic refrigeration particularly explaining / indicating the different properties of specific and latent heat in an attempt to show where there are ‘energy storage benefits.
Also to prove that unsupported claims suggesting the inability of the common micro systems to operate effectively as eutectic systems, are incorrect.
The resulting outcomes I stated are correct.

When referring to cabinet heat load, system ratings, all RAC’s, compressor ratings, FDC,s condensers, COP etc. we now use the term ‘watts of heat’. (In most of the world)

We have produced an interactive ‘Heat load, Power consumption and Duty cycle’ estimating tool which we check every system for ‘suitability of proposed use’ prior to supply and to date we have not had one end user indicate that the estimate was inaccurate.

The end result is what matters and in an industry that is lacking of accurate information, providing a method of determining if a proposed system is ‘fit for purpose’ surely is the greater issue.
BTW apart from my 4 year refrigeration apprenticeship, I completed Engineering via RMIT! (Second in group! So the others were obviously not very bright, )

[OzeLouie]

Originally Posted by Richard Kollmann

It seem the current assumption is the heat energy consumed in melting ice is equal to the energy needed to produce the lower temperature eutectic ice?

Please explain. Are you referring to the amount of heat to be removed to phase change liquid to a solid (ice) compared to the amount of heat required to thaw the solid mass back to a liquid?

[newhaul]

Originally Posted by Richard Kollmann

It seem the current assumption is the heat energy consumed in melting ice is equal to the energy needed to produce the lower temperature eutectic ice?

Explain what the difference is in the energy consumed in either melting or freezing the same fluid regardless of what that fluid is.

[RaymondR]

"As has been pointed out earlier, these are not the correct units. The specific heat of water (the sensible heat) is 4184 J/kg-°C or 1 cal/g-°C or 1 Cal/kg-°C or 1 BTU/lb-°F. The heat of fusion of water (the latent heat of freezing) is 333,550 J/kg or 79.7 cal/g or 79.7 Cal/kg or 144 BTU/lb. Watts are not an amount of energy, watts are an amount of energy flowing in a period of time. An amount of heat is expressed in joules, small calories, large calories, or BTUs."

We would not have these problems if we stuck to BTUs and Ions or fractions of and leave the Watts for electrical definitions.

[OzeLouie]

Originally Posted by RaymondR

"As has been pointed out earlier, these are not the correct units. The specific heat of water (the sensible heat) is 4184 J/kg-°C or 1 cal/g-°C or 1 Cal/kg-°C or 1 BTU/lb-°F. The heat of fusion of water (the latent heat of freezing) is 333,550 J/kg or 79.7 cal/g or 79.7 Cal/kg or 144 BTU/lb. Watts are not an amount of energy, watts are an amount of energy flowing in a period of time. An amount of heat is expressed in joules, small calories, large calories, or BTUs."

We would not have these problems if we stuck to BTUs and Ions or fractions of and leave the Watts for electrical definitions.

Oh come on Raymond, do you also want to go back to 'pounds, shillings, pence',......... 'ounces, pounds',........... 'inches, feet, yards, miles' etc ect.? The imperial system is a nightmare, with all of its crazy interacting factors. Decimal weights and measures are a God send.