Another look at Solar Powered refrigeration on sailboats

[a64pilot]

Originally Posted by newhaul

well in the system I'm installing ( technautics) the plate I am looking at will be approx 12x24x1 is 288 cubic inches ( there are 1728 in a cf)

the solution is a mixture of food grade antifreeze and water. The plate inside as I am to understand looks more like a small radiator or transmission cooler.

(Don't know about other systems) and how they are built.

With my Lfp and 400 watts solar I will be able to run the fridge primarily off of the solar in the afternoons once the battery is fully charged.

You have an unusual holding plate it seems, this is their usual plates.
http://www.cruiserowaterandpower.com...ng_Plates.html
It’s interesting that is shows a dual plate configuration as well.
For my dual plate system it’s right at about 1 cu Ft. that is lost, but that still leaves me almost 14 cu Ft, so I don’t care, but some may.
I’ve not opened my plates of course, but would expect to see an off the shelf transmission cooler myself, as I think it would be nearly perfect to use.
Of course it’s unlikely that without a stupid amount of force that you could harm a cold plate, but many have ruined an aluminum thin plate evaporator by bending or poking a hole trying to knock off ice with something that has a sharp edge.

Richards point on condenser is important too, there are two sides of a heat pump and they are both equally important.
Remember 30 years ago a house heat pump would have the condenser on one side of the smallish box and it was about the size of a car radiator?
Well look at one now, it wraps completely around the unit and is much, much larger in surface area and they have some fancy fin types to remove heat too, losing as much heat as possible in your condenser will increase efficiency, just as much as absorbing as much heat as possible in your evaporator can.

This is where people try to show the obvious superiority of a water cooled condenser, except it’s been shown that it may seem to be an obvious advantage, that a very good air cooled is just as efficient under ordinary circumstances.

For that reason you’ll find that water cooled heat pumps aren’t as popular as they once were, and they are by no means a new thing either. My Father had one in 1960, I remember playing with the warm water that always flowed out as a kid.

[newhaul]

Originally Posted by a64pilot

You have an unusual holding plate it seems, this is their usual plates.
Boat Refrigeration Holding Plates | Cruise RO Water & Power
It’s interesting that is shows a dual plate configuration as well.
For my dual plate system it’s right at about 1 cu Ft. that is lost, but that still leaves me almost 14 cu Ft, so I don’t care, but some may.
I’ve not opened my plates of course, but would expect to see an off the shelf transmission cooler myself, as I think it would be nearly perfect to use.
Of course it’s unlikely that without a stupid amount of force that you could harm a cold plate, but many have ruined an aluminum thin plate evaporator by bending or poking a hole trying to knock off ice with something that has a sharp edge.

Richards point on condenser is important too, there are two sides of a heat pump and they are both equally important.
Remember 30 years ago a house heat pump would have the condenser on one side of the smallish box and it was about the size of a car radiator?
Well look at one now, it wraps completely around the unit and is much, much larger in surface area and they have some fancy fin types to remove heat too, losing as much heat as possible in your condenser will increase efficiency, just as much as absorbing as much heat as possible in your evaporator can.

This is where people try to show the obvious superiority of a water cooled condenser, except it’s been shown that it may seem to be an obvious advantage, that a very good air cooled is just as efficient under ordinary circumstances.

For that reason you’ll find that water cooled heat pumps aren’t as popular as they once were, and they are by no means a new thing either. My Father had one in 1960, I remember playing with the warm water that always flowed out as a kid.

yes small custom system that we are discussing building for my specific install . The standard is 2.5 inches thick. My install will give me 1.5 cf freezer and 3 cf of refer .


Now the issue of running a refrigerator directly off solar with no battery to stabilize the voltage that is delivered to the compressor . Well IMO a bad idea lack of stable power will cause irratic and damaging operation of the compressor .

Water cooled well it comes with its own set of issues

[newhaul]

Originally Posted by Q Xopa

Did I miss someine pushing the line that Cold plates create energy?

As for batteries storing energy more efficiently yes maybe.

However I would argue that if you can store 'free' energy, or energy that would have otherwise been wasted ie Solar when your batts are already topped off, I would be up for it.

Also if that inefficient energy storage, like Cold plates, was a lot cheaper and easier to maintain than batteries, I would also be sorely tempted.

as to the cold plate energy part Richard seems to always interject something into it implying someone has said that . ( I haven't seen it yet here .)
batteries are more efficient at storing energy yes .

The reason I had holding plates on last boat and will on this one is this.
My battery bank 100ah Lfp costs about 450 a holding plate costs about a grand.
I have 400 watts solar and 400 wind . Once bank is fully charged the excess power can be stored in the holding plate.
My battery bank would need to be almost 3 times the size it is now to run a thin plate system .
Life expectancy is this my batteries approx 3,000 to 5,000 cycles . (Estimated to be 15 to 25 years. ) we don't know just how long Lfp will last in our type of installation and usages )
could be well in excess of 30 years.
Holding plate they are SS so they have a life expectancy of forever.
With thin plate evap system my battery cycle would likely double therefore cutting the expected life in half . ( replacement of 1300 worth of batteries ) every 7 to 10 years ( Estimated.) .

[Frankly]

Have not read every single word on this rather long discussion but don't believe this has been mentioned as a simple possibility.

Standard IP 32 (12 CUFT if I remember correctly), improved door and top insulation. 15 YO AB BD50 air cooled condenser (condenser in outside ventilated compartment). Mechanical thermostat with toggle switch to add resistor when necessary. Spillover fan that operates with compressor. Normally runs @2000 RPM but can switch to high speed when we add a bunch of new load.

Just sitting (not opening the box) in 90 degree Summer temp usage is about 40AH per 24 hrs. Normal cruising open/ close and adding beer the number will typically move up to 60AH per 24 hours. Not earth shattering in efficiency but pretty cheap and simple.

In the phase change efficiency business you need to define efficiency. Phase change gives volumetric efficiency vice just cold stone, electrical efficiency a different kettle of fish.

Frankly

[newhaul]

Originally Posted by Frankly

Have not read every single word on this rather long discussion but don't believe this has been mentioned as a simple possibility.

Standard IP 32 (12 CUFT if I remember correctly), improved door and top insulation. 15 YO AB BD50 air cooled condenser (condenser in outside ventilated compartment). Mechanical thermostat with toggle switch to add resistor when necessary. Spillover fan that operates with compressor. Normally runs @2000 RPM but can switch to high speed when we add a bunch of new load.

Just sitting (not opening the box) in 90 degree Summer temp usage is about 40AH per 24 hrs. Normal cruising open/ close and adding beer the number will typically move up to 60AH per 24 hours. Not earth shattering in efficiency but pretty cheap and simple.

In the phase change efficiency business you need to define efficiency. Phase change gives volumetric efficiency vice just cold stone, electrical efficiency a different kettle of fish.

Frankly

question is you state 40ah but not where that comes from . Is it directly off the solar? is it just off your batteries ? Or is it a mixture? And if so what ratio is solar and battery?

The answers to which will tie your post into the Germaine of the topic of the thread .

[Q Xopa]

Originally Posted by newhaul

as to the cold plate energy part Richard seems to always interject something into it implying someone has said that . ( I haven't seen it yet here .)
batteries are more efficient at storing energy yes .

The reason I had holding plates on last boat and will on this one is this.
My battery bank 100ah Lfp costs about 450 a holding plate costs about a grand.
I have 400 watts solar and 400 wind . Once bank is fully charged the excess power can be stored in the holding plate.
My battery bank would need to be almost 3 times the size it is now to run a thin plate system .
Life expectancy is this my batteries approx 3,000 to 5,000 cycles . (Estimated to be 15 to 25 years. ) we don't know just how long Lfp will last in our type of installation and usages )
could be well in excess of 30 years.
Holding plate they are SS so they have a life expectancy of forever.
With thin plate evap system my battery cycle would likely double therefore cutting the expected life in half . ( replacement of 1300 worth of batteries ) every 7 to 10 years ( Estimated.) .

Sounds good, I like your reasoning.

That idea of using solar to freeze your cold plate sounds good. It almost sounds like fr.... eeer, ooops nearly used thr 'f' word. I mean 'utilizing previously wasted solar energy'. And less cycle life battery cycles.[emoji106]

[Q Xopa]

Originally Posted by valhalla360

Nope, I don't but I can tell you with certainty...there is no such thing as "free power". Several of the posts from various posters talk about free power.

As most already have a solar/battery bank system, you need to break out the incremental costs to buy and maintain it compared to the incremental costs to buy and maintain a solar/cold plate system to get a true comparison.

Personally, had a cold plate on the last boat...didn't care for it, so unless there is a major benefit that can be shown, I going steer away from them on future boats.

Any more clues than "you didnt care for it". Its not much to go on.
Maybe it froze you lettice? Left the icecream soft? Sucked your batteries down? Or maybe the chemistry just wasnt there?

[Frankly]

Originally Posted by newhaul

question is you state 40ah but not where that comes from . Is it directly off the solar? is it just off your batteries ? Or is it a mixture? And if so what ratio is solar and battery?

The answers to which will tie your post into the Germaine of the topic of the thread .

FF to date (diesel and shore power). I am drilling holes in my solar mounts for 200 watts as we speak. My hope is that this will take care of the frig (minimal opening during the Summer sitting docksides) with no/ minimal help from shore power.

The reasoning might be of interest because it is pretty "out of left field".

Cbreeze sits at a dock right behind my house. There used to be several tall trees to compete for Summer lightning, but Michael ran the table. That mast is sitting out there like a sore thumb. Yacht getting hit will be a enough grief, not interested in involving my house. Shore power feed and submerged well pump share a conduit. My plan is to cutter loose.

Frankly

[RaymondR]

The Efficiency Myth.

It is being stated and restated that batteries are a more efficient method of storing energy than eutectic fluids.

The energy conversions involved are:

In the case of constant cycling with evaporator plates. 1 The light photons are converted to electrical current in the solar panels. 2 The electricity is used to sustain a reversible electrochemical process which charges the battery. 3 The electrochemical process reverses to run the refrigeration compressing and condensing unit.

In the case of the eutectic system. 1 The light photons are converted into electrical current. 2 The electrical current is used to run a refrigeration compressing and condensing unit.

It appears to me that we are missing two processes in the second option, the first conversion from current to electrochemical and the second from electrochemical to current.

Assuming Azopete's companies tests were valid, they showed twice the power use for the same heat energy transfer end end with the evaporator plate than the eutectic tank.

I'd hazard a guess that if one could factor in the electrochemical conversions the power usage with batteries could increase to three or even four times from photon impact to heat energy extraction.

[ramblinrod]

Originally Posted by RaymondR

The Efficiency Myth.

It is being stated and restated that batteries are a more efficient method of storing energy than eutectic fluids.

The energy conversions involved are:

In the case of constant cycling with evaporator plates. 1 The light photons are converted to electrical current in the solar panels. 2 The electricity is used to sustain a reversible electrochemical process which charges the battery. 3 The electrochemical process reverses to run the refrigeration compressing and condensing unit.

In the case of the eutectic system. 1 The light photons are converted into electrical current. 2 The electrical current is used to run a refrigeration compressing and condensing unit.

It appears to me that we are missing two processes in the second option, the first conversion from current to electrochemical and the second from electrochemical to current.

Assuming Azopete's companies tests were valid, they showed twice the power use for the same heat energy transfer end end with the evaporator plate than the eutectic tank.

I'd hazard a guess that if one could factor in the electrochemical conversions the power usage with batteries could increase to three or even four times from photon impact to heat energy extraction.

But But But...When the solar is connected to batteries is connected to the compressor, the current produced by the solar panels is fed directly to the compressor, and the electrochemical process of the batteries is not involved at all in running the compressor.

The batteries are only really involved:

A: When they need to be charged (due to any discharge reason).

B: They are discharged (due to any load.)

If there is sufficient solar to run the compressor, the compressor does not draw any energy from the batteries.

So the net result is virtually identical, with respect to efficiency, when batteries are present or not.

The only difference is, if the system demands energy beyond what solar is providing, if charged batteries are present, they meet demand.

If no batteries are present, and compressor needs to run, another source of energy (ICE generated for example) is necessary, else the fridge is most definitely going to heat up.

Addendum: The other difference is, if the refrigerator system (including all contents) can hold enough energy to prevent the compressor coming on when solar is not present, then battery use can be avoided. This is no different between holding or evapourator plates, other than the holding plate can store energy (just like the ice cubes, and all other thermal mass, including phase change lunch box coolers if desired) in the evapourator plate based fridge.

[a64pilot]

I believe Solar powered refrigeration on sailboats is a title that leads to a little misunderstanding.
Yes there are modules that are made that will operate in very variable voltages, I believe these are intended to run from Solar alone.
However I doubt seriously that is what is found in marine refrigeration, surely almost everyone of us has a battery bank, and many recharge that bank with Solar.

I’d just guess that the use for a pure Solar powered fridge is some kind of portable unit maybe that the weight and size of a battery bank is undesirable?
In truth I don’t understand why anyone would want such a thing, surely a small Li-Po bank would be better to have for some kind of portable fridge, I’m thinking something like maybe Dr’s without borders or similar may have in Africa or something similar?

I still think that you can have all kinds of super efficient gizmos etc., but it’s insulation that is the real way to efficiency, once temps are stabilized in a fridge, 100% of the power that is used is due to heat gain thru the insulation.
Cut that heat gain in half, and you cut power consumption in half.
Of course that ignores the inevitable opening of the fridge and putting something in that isn’t cold, so it’s not a true statement, but it is likely the one thing that you can control that will make the most difference in efficiency.

[ramblinrod]

PS, I have sold, installed, owned, used, serviced, both holding plate and evapourator plate type ice box conversions.

It is more difficult to keep ice in holding plate versions with insufficient battery capacity, which may result in frozen food unthawing before it was needed.

To avoid this, one would need to monitor their ice box temp religiously, and start ICE power generation whenever it came up to high set-point (which will be often if one is trying to keep things frozen instead of just cool).

I find that most fans of holding plates, are those who don't care so much about freezing and keeping frozen.

This is very dangerous when it comes to frozen foods that may be repeatedly thawed and re-frozen due to compressor run cycles that are just too far apart, and can lead to food poisoning.

I sell and install marine refrigeration systems on rec boats from 25 to 50 ft.

I advise the pros and cons of each type. The vast majority are evapourator plate based. Yes, I am biased, but for good reason.

When considering which type, consider all of the pros and cons, and don't be swayed by alchemy and fan boys.

Including that energy stored in a holding plate, can be used for one reason and one reason only (refrigeration), whereas energy stored in a battery can be used to satisfy any electrical need, including operating safety equipment when needed which can be higher priority than refrigeration.

So if one wishes to increase "energy storage" on their vessel, I recommend increasing batteries, not holding plate.

[newhaul]

Originally Posted by ramblinrod

PS, I have sold, installed, owned, used, serviced, both holding plate and evapourator plate type ice box conversions.

It is more difficult to keep ice in holding plate versions with insufficient battery capacity, which may result in frozen food unthawing before it was needed.

To avoid this, one would need to monitor their ice box temp religiously, and start ICE power generation whenever it came up to high set-point (which will be often if one is trying to keep things frozen instead of just cool).

I find that most fans of holding plates, are those who don't care so much about freezing and keeping frozen.

This is very dangerous when it comes to frozen foods that may be repeatedly thawed and re-frozen due to compressor run cycles that are just too far apart, and can lead to food poisoning.

I sell and install marine refrigeration systems on rec boats from 25 to 50 ft.

I advise the pros and cons of each type. The vast majority are evapourator plate based. Yes, I am biased, but for good reason.

When considering which type, consider all of the pros and cons, and don't be swayed by alchemy and fan boys.

Including that energy stored in a holding plate, can be used for one reason and one reason only (refrigeration), whereas energy stored in a battery can be used to satisfy any electrical need, including operating safety equipment when needed which can be higher priority than refrigeration.

So if one wishes to increase "energy storage" on their vessel, I recommend increasing batteries, not holding plate.

what brand of holding plate systems do you sell ? Sounds like they are very undersized for the installation. I have never had any issues such as you describe with technautics systems that are properly sized for the box.

[ramblinrod]

Originally Posted by a64pilot

I believe Solar powered refrigeration on sailboats is a title that leads to a little misunderstanding.
Yes there are modules that are made that will operate in very variable voltages, I believe these are intended to run from Solar alone.
However I doubt seriously that is what is found in marine refrigeration, surely almost everyone of us has a battery bank, and many recharge that bank with Solar.

I’d just guess that the use for a pure Solar powered fridge is some kind of portable unit maybe that the weight and size of a battery bank is undesirable?
In truth I don’t understand why anyone would want such a thing, surely a small Li-Po bank would be better to have for some kind of portable fridge, I’m thinking something like maybe Dr’s without borders or similar may have in Africa or something similar?

I still think that you can have all kinds of super efficient gizmos etc., but it’s insulation that is the real way to efficiency, once temps are stabilized in a fridge, 100% of the power that is used is due to heat gain thru the insulation.
Cut that heat gain in half, and you cut power consumption in half.
Of course that ignores the inevitable opening of the fridge and putting something in that isn’t cold, so it’s not a true statement, but it is likely the one thing that you can control that will make the most difference in efficiency.

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.

[ramblinrod]

Originally Posted by newhaul

Sounds like they are very undersized for the installation.

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.

The last sentence of post # 117 is extremely pertinent in all refrigeration cases.