Another look at Solar Powered refrigeration on sailboats

[newhaul]

Originally Posted by ramblinrod

Agreed, I think some get so caught up in "refrigerator efficiency" that they lose sight of "whole boat efficiency, functionality, comfort, and convenience".

Most boaters primary purpose of being out on the water is not to "achieve maximum fridge efficiency". It is to have fun and enjoy themselves. If monitoring the ice box temp religiously enhances that, a holding plate may be a good choice. If monitoring the ice box temp religiously draws from that, an evapourator based fridge may be a better choice.

we all know its about whole system efficiency balanced with cost and longevity .
Hence I'm installing ( on another of my boats) holding plate system with solar wind and Lfp batteries.

[newhaul]

Originally Posted by ramblinrod

No.

If the holding plate can't keep the food frozen as desired, between compressor run times, then technically, "the plate may be undersized for this application, for the system to meet design goals".

If the design goal, is to keep the ice box frozen under all cirmcumstances with least space consumed by the refrigeration system, lowest capital cost, and least ICE energy production specifically for refrigeration, evapourator plate refrigeration with sufficient battery capacity and renewable energy charging sources wins every time.

rod you remove your beloved ice and properly sized and installed holding plate systems will win every time .

[ramblinrod]

Originally Posted by newhaul

rod you remove your beloved ice and properly sized and installed holding plate systems will win every time .

Of course if one ignores valid design goal criteria, it may favour an alternate solution (to solve any problem), but that is a flawed argument.

In reality, maintaining ice and safe, frozen food, and not take up excessive ice box room, and not have to monitor ice box temp so religiously, and not strike up ICE energy production due to insufficient battery capacity, is a common set of design goals that the vast majority of my customers desire.

[newhaul]

Originally Posted by ramblinrod

Of course if one ignores valid design goal criteria, it may favour an alternate solution (to solve any problem), but that is a flawed argument.

In reality, the desire to maintain ice and safe, frozen food, and not take up excessive ice box room, and not have to monitor ice box temp so religiously, and not strike up ICE energy production due to insufficient battery capacity, is a common set of design goals for the vast majority of my customers.

really missed the mark there didn't ya ? ICE. ( infernal combustion engine ) for charging batteries that are low in the morning due to running your thin plate refer system all night.


I have installed every manner of refrigeration system and by far IMO the winner is holding plate with alternative energy . If running ICE Then it doesn't matter how many ah you use when the sun isn't shinning

[Richard Kollmann]

There are three reason batteries are more efficient in storing energy with solar powered small compressor refrigeration .
1 Even if there is excessive energy available from solar only an average of panels output 60 watts per hour are converted by compressor to heat removing Btu. To freeze a extra large eutectic tank of solution and keep it frozen the sun must be out more than the average of 6 hours per day.
I do not care what the charts here show the first one comparing standard evaporator against a Glvcol water eutectic plate claimed superior reduced power consumption of 1/3 of a amp per hour. And to say that today’s Danfoss BD variable speed compressors must cycle more than one and a half times per hour on a correctly designed system is just wrong and a poor choice of condensing unit on standard evaporator test.

2. To complete the phase change with a temperature equal to or lower than its melting point it takes time and energy. To shorten the time it takes to freeze a given liquid greater amounts of energy from a refrigeration compressor are needed to achieve temperatures far enough below the eutectic solutions phase change point. On lager systems we use 20 degrees below melting point. It would seem 7 degrees below phase change point is reasonable to freeze solution faster than heat load on box is absorbing heat from eutectic plate. When we increase the energy output of the compressors to reach lower temperatures than needed to freeze solution you get fewer Btu, a energy penalty over a standard evaporator.

3 Once the compressor converts energy to Btu the frozen ice to be stored is not free without extra losses. A eutectic ice tank can and will absorb heat as long as there is any solid ice left. The duration of ice melting will depend on the melting temperature eutectic point. Water ice melting point is above +32 F absorbing 144 Btu per pound. Eutectic tank ice for a refrigerated cooler is set to melt at +22 to +26 F degrees consuming approximately 144 Btu per pond, Refrigerator eutectic melting point will depend on size of box +12 to +22 degrees consuming approximately 144 Btu per pound. Eutectic solution melting point for either a medium temperature freezer or freezer spillover box using 134a refrigerant is generally zero to +6 degrees F still consuming again approximately only 144 Btu per pound. Depending on box size, box insulation and ambient air temperatures 10 pound of water ice might last 24 hrs while 10 pounds of zero degree eutectic solution may melt away in a few hours.
Because compressor cycle times on eutectic plates are increased by lower temperature eutectic melting points there is a tendency to use higher melting temperature plates and instead of holding plates use them as cycling plates as Glycol water does not have a true eutectic temperature range when melting like water ice.

There are a number of good reasons to use eutectic energy storage plates but efficiency and stable temperature control are not the best reasons.

[ramblinrod]

Originally Posted by newhaul

really missed the mark there didn't ya ?

Nope.
Disrespectful.
Balance of post ignored.

[newhaul]

Originally Posted by Richard Kollmann

There are three reason batteries are more efficient in storing energy with solar powered small compressor refrigeration .
1 Even if there is excessive energy available from solar only an average of panels output 60 watts per hour are converted by compressor to heat removing Btu. To freeze a extra large eutectic tank of solution and keep it frozen the sun must be out more than the average of 6 hours per day.
I do not care what the charts here show the first one comparing standard evaporator against a Glvcol water eutectic plate claimed superior reduced power consumption of 1/3 of a amp per hour. And to say that today’s Danfoss BD variable speed compressors must cycle more than one and a half times per hour on a correctly designed system is just wrong and a poor choice of condensing unit on standard evaporator test.

2. To complete the phase change with a temperature equal to or lower than its melting point it takes time and energy. To shorten the time it takes to freeze a given liquid greater amounts of energy from a refrigeration compressor are needed to achieve temperatures far enough below the eutectic solutions phase change point. On lager systems we use 20 degrees below melting point. It would seem 7 degrees below phase change point is reasonable to freeze solution faster than heat load on box is absorbing heat from eutectic plate. When we increase the energy output of the compressors to reach lower temperatures than needed to freeze solution you get fewer Btu, a energy penalty over a standard evaporator.

3 Once the compressor converts energy to Btu the frozen ice to be stored is not free without extra losses. A eutectic ice tank can and will absorb heat as long as there is any solid ice left. The duration of ice melting will depend on the melting temperature eutectic point. Water ice melting point is above +32 F absorbing 144 Btu per pound. Eutectic tank ice for a refrigerated cooler is set to melt at +22 to +26 F degrees consuming approximately 144 Btu per pond, Refrigerator eutectic melting point will depend on size of box +12 to +22 degrees consuming approximately 144 Btu per pound. Eutectic solution melting point for either a medium temperature freezer or freezer spillover box using 134a refrigerant is generally zero to +6 degrees F still consuming again approximately only 144 Btu per pound. Depending on box size, box insulation and ambient air temperatures 10 pound of water ice might last 24 hrs while 10 pounds of zero degree eutectic solution may melt away in a few hours.
Because compressor cycle times on eutectic plates are increased by lower temperature eutectic melting points there is a tendency to use higher melting temperature plates and instead of holding plates use them as cycling plates as Glycol water does not have a true eutectic temperature range when melting like water ice.

There are a number of good reasons to use eutectic energy storage plates but efficiency and stable temperature control are not the best reasons.

then there is the all important elephant in the room.
Insulation . The better it is the better any refer system will work.
My newest build will have an estimated R45 insulation. So should be great with the holding plate . ( spill over system)

[ramblinrod]

Originally Posted by newhaul

then there is the all important elephant in the room.
Insulation . The better it is the better any refer system will work.
My newest build will have an estimated R45 insulation. So should be great with the holding plate . ( spill over system)

That is is a flawed argument.

My position is that improved insulation may help improve fridge performance of any technology. So do good seals, and avoiding frequent or long duration opening, or inserting a large warm mass when desired compressor running energy is not abundant.

While increasing insulation can be beneficial, this does suffer from diminishing returns. At some point, the amount of energy efficiency gained, is not worth the additional insulation and box capacity consumption.

If additional measures reduce a fraction of energy consumption, when there is already ample energy production and storage via desirable technologies, meh.

[newhaul]

Originally Posted by ramblinrod

That is is a flawed argument.

My position is that improved insulation may help improve fridge performance of any technology. So do good seals, and avoiding frequent or long duration opening, or inserting a large warm mass when desired compressor running energy is not abundant.

While increasing insulation can be beneficial, this does suffer from diminishing returns. At some point, the amount of energy efficiency gained, is not worth the additional insulation and box capacity consumption.

If additional measures reduce a fraction of energy consumption, when there is already ample energy production and storage via desirable technologies, meh.

how is improving insulation a flawed argument ? Then in the next sentence you say exactly what I said .
And what are my diminishing returns? 3 inches of foil lined Cryogel on the outside of the existing box means no loss of capacity .

[ramblinrod]

Originally Posted by newhaul

how is improving insulation a flawed argument ? Then in the next sentence you say exactly what I said .
And what are my diminishing returns? 3 inches of foil lined Cryogel on the outside of the existing box means no loss of capacity .

I doubt any more effort on my part will be fruitful. Higher priorities await.

[hellosailor]

There could be a somewhat rational and objective way to quantify "this is too much insulation". Given that the space aboard any boat is limited, and that every cubic foot of space can only be traded for some other purpose, never really created or added, you could say:
If the added insulation occupies more cubic feet of space than a BATTERY which could run the system to provide more cooling than the insulation gains...
That's excessive and wasted insulation, and it would be more effective to add a battery.

Unsaid assumption of course, there's also got to be a power source for that battery but there's often a way to bump up a charging source. Not always--but that's one possible way to measure "excess" insulation.

And of course, once the insulation hits the hull, no more can be added anyway. There will be limits as to where it can be added in any case, unless you're designing from scratch.

What buys more condensor off time? A cubic foot of magic insulation, or a cubic foot of lithium battery?(G)

[newhaul]

Originally Posted by hellosailor

There could be a somewhat rational and objective way to quantify "this is too much insulation". Given that the space aboard any boat is limited, and that every cubic foot of space can only be traded for some other purpose, never really created or added, you could say:
If the added insulation occupies more cubic feet of space than a BATTERY which could run the system to provide more cooling than the insulation gains...
That's excessive and wasted insulation, and it would be more effective to add a battery.

Unsaid assumption of course, there's also got to be a power source for that battery but there's often a way to bump up a charging source. Not always--but that's one possible way to measure "excess" insulation.

And of course, once the insulation hits the hull, no more can be added anyway. There will be limits as to where it can be added in any case, unless you're designing from scratch.

What buys more condensor off time? A cubic foot of magic insulation, or a cubic foot of lithium battery?(G)

insulation is cheaper.

[hellosailor]

Insulation is cheaper than batteries, sure.
But insulation is MORE EXPENSIVE if it occupies more cubic feet, and you don't have more cubic feet to fill. Then the insulation requires a bigger boat, or new carpentry for the new cooler box, and the battery may become much cheaper than the carpentry or the cubic feet--which only come with a new boat attached.

[ramblinrod]

Originally Posted by hellosailor

There could be a somewhat rational and objective way to quantify "this is too much insulation". Given that the space aboard any boat is limited, and that every cubic foot of space can only be traded for some other purpose, never really created or added, you could say:
If the added insulation occupies more cubic feet of space than a BATTERY which could run the system to provide more cooling than the insulation gains...
That's excessive and wasted insulation, and it would be more effective to add a battery.

Unsaid assumption of course, there's also got to be a power source for that battery but there's often a way to bump up a charging source. Not always--but that's one possible way to measure "excess" insulation.

And of course, once the insulation hits the hull, no more can be added anyway. There will be limits as to where it can be added in any case, unless you're designing from scratch.

What buys more condensor off time? A cubic foot of magic insulation, or a cubic foot of lithium battery?(G)

The following statements are always true:

1. Everything on a boat is a compromise.

2. Any solution to a problem necessarily creates another problem.

That one may consider the new problem "more desirable", another may not.

[newhaul]

Originally Posted by hellosailor

Insulation is cheaper than batteries, sure.
But insulation is MORE EXPENSIVE if it occupies more cubic feet, and you don't have more cubic feet to fill. Then the insulation requires a bigger boat, or new carpentry for the new cooler box, and the battery may become much cheaper than the carpentry or the cubic feet--which only come with a new boat attached.

yes insulation does reach a point where you run out of space and that's where my 3 inches of insulation gets me to . Max space used outside of my ice box .
If I was using any other insulating material I could not get much in the way of r value.
My statement was in reply to a specific posters response to me

Where in I was wondering how max insulation was not a valid way to reduce refrigeration system running time.