Another look at Solar Powered refrigeration on sailboats

[missourisailor]

Originally Posted by OzePete

YES! The test was done with each system involved in maintaining cabinet temperature in sequence. Run periods of 10 days totalling two months in all.
As can be seen the cyclic system benefited greatly by 'inheriting thermal mass from the eutectic system. (See how much less the cyclic used on the first run day of each of its periods thanks to the eutectic system.) This was a great advantage to the thin plate system.
Click on chart to expand....

Attachment 185155



Please Note:
1> That testing was originally only for our internal research as we manufacture / market BOTH types. Buy whatever system.. your choice!
2> The results surprised us as said at the time, so we decided to make them available here.
3> The thin plate used had for greater surface are than the eutectic plate.
4> Many fail to consider that a eutectic plate is collecting heat 100% of the time regardless of whether the unit is running or not. The thin plate only collects heat while the refrigeration unit is running therefore has to then run considerably colder.
5> It is ONLY a eutectic system if it is engineered / controlled to run until the liquid eutectic mass is frozen (phase changed to a solid) Then remains off collecting heat until the eutectic mass has thawed.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

OzePete,
Thanks for taking the time to repost the results.
I'm having a bit of a time finding the old thread. Can you provide a link?

[missourisailor]

Originally Posted by missourisailor

OzePete,
Thanks for taking the time to repost the results.
I'm having a bit of a time finding the old thread. Can you provide a link?

Never mind.
I found it.

[missourisailor]

Originally Posted by OzePete

YES! The test was done with each system involved in maintaining cabinet temperature in sequence. Run periods of 10 days totalling two months in all.
As can be seen the cyclic system benefited greatly by 'inheriting thermal mass from the eutectic system. (See how much less the cyclic used on the first run day of each of its periods thanks to the eutectic system.) This was a great advantage to the thin plate system.
Click on chart to expand....

Attachment 185155



Please Note:
1> That testing was originally only for our internal research as we manufacture / market BOTH types. Buy whatever system.. your choice!
2> The results surprised us as said at the time, so we decided to make them available here.
3> The thin plate used had for greater surface are than the eutectic plate.
4> Many fail to consider that a eutectic plate is collecting heat 100% of the time regardless of whether the unit is running or not. The thin plate only collects heat while the refrigeration unit is running therefore has to then run considerably colder.
5> It is ONLY a eutectic system if it is engineered / controlled to run until the liquid eutectic mass is frozen (phase changed to a solid) Then remains off collecting heat until the eutectic mass has thawed.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

OzePete,
I did remember the previous thread correctly.
Your testing was done using a holding plate with TXV and a thin plate system with a restricted orifice.

We are not really comparing apples to apples.

I stand by my previous statement.

[a64pilot]

Originally Posted by OzePete

YES! The test was done with each system involved in maintaining cabinet temperature in sequence. Run periods of 10 days totalling two months in all.

As can be seen the cyclic system benefited greatly by 'inheriting thermal mass from the eutectic system. (See how much less the cyclic used on the first run day of each of its periods thanks to the eutectic system.) This was a great advantage to the thin plate system.

Click on chart to expand....



Attachment 185155







Please Note:



4> Many fail to consider that a eutectic plate is collecting heat 100% of the time regardless of whether the unit is running or not. The thin plate only collects heat while the refrigeration unit is running therefore has to then run considerably colder.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

That is likely the missing piece then, the “flywheel effect” if you don’t mind me misusing a term, smoothing out the spikes if you will.
However wouldn’t a freezer or fridge full of food to some extent replicate the effect?

Thank you for taking the time to explain things to us, I appreciate it.
I know it must be like trying to teach a pig to read a wrist watch

[Richard Kollmann]

Just to clear up another "feature!!! lol" comment the TE2 does not cause hunting on a BD35 compressor.

It is almost impossible to get TXV valve hunting with this small Danfoss compressor on a eutectic holding plate. It seems like to get a BD compressor to cause TXV hunting the evaporator would have to be very small for the size of compressor. Cyclical refrigerant fluctuation is common on large oversized compressor where there is excessive flow and a stabilized evaporator temperature.

A TXV has to be significantly oversized to cause superheat hunting do to variations in refrigerant flow. The TE2 valve may have with a warm evaporator an excessive full orifice opening allowing refrigerant flow as high as 1/9 of aTon, but the 600 btu coming from a BD35 compressor is sufficient enough to create necessary differential pressure across TXV. It should be understood that eutectic holding plate evaporator coils rarely have stabilized temperatures and flow like a standard evaporator.

Another point Cool Blue and Kollmann Marine both used the TE2 with 00 orifices on BD2.5 compressor holding plate systems. When Danfoss came out with the variable speed BD35 both companies changed to the smaller OX Danfoss orifice. Danfoss valve prices have increased so I do not know that size valves Technautics uses today.

[OzePete]

Originally Posted by missourisailor

OzePete,
I did remember the previous thread correctly.
Your testing was done using a holding plate with TXV and a thin plate system with a restricted orifice.

We are not really comparing apples to apples.

I stand by my previous statement.

Sorry MS, but you didn't remember the previous thread correctly.... In the test quoted BOTH systems were capillary fed NOT TXV.

(TX valves small enough to correctly service these micro systems don't exit! Some use the T2 with the OX orifice but it is still rated many times above that of the BD35 especially at low speed and low temperatures. They will work.. sort of.. but due to being grossly oversized 'Hunting occurs although some try to disguise this as compressor cooling!! )

So we WERE comparing apples with apples.

Perhaps instead of joining the anti-gravity chorus, it might be more productive to study the report specifically as it describes the two main reasons for such a huge difference in power efficiency.

If you can point to any deficiency (based on fact not rhetoric), or anything in that report that is unclear, please let me know and I will go through it with you taking on board your findings.

Cheers OzePete

[missourisailor]

Originally Posted by OzePete

Sorry MS, but you didn't remember the previous thread correctly.... In the test quoted BOTH systems were capillary fed NOT TXV.


Perhaps instead of joining the anti-gravity chorus, it might be more productive to study the report specifically as it describes the two main reasons for such a huge difference in power efficiency.

If you can point to any deficiency (based on fact not rhetoric), or anything in that report that is unclear, please let me know and I will go through it with you taking on board your findings.

Cheers OzePete

OzePete,
My sincerest apologies, I was wrong in thinking that your cold plate system used a TXV.
Yes, I agree that your tests were indeed comparing apples to apples.
At least for your two systems they are apples to apples.


When I first saw your test report, I was hoping my dreams had been answered, In that a true test was done comparing two identical systems. Both using TXV's with one having a holding plate. And the other a thin plate evap..


I now see that I was viewing it through rose colored glasses and skipping over details that would point other wise.



However, I do not share your view point on TXV or that no TXV is designed for these systems.
And I'm not just "joining the anti-gravity chorus".

It is from my own personal experiences with installing and maintaining both types of systems.
Way too many marine systems out there with TXV for them ALL to be oversized.


I also know that on a standard day, a orifice system will preform very satisfactory. But outside of a standard day, that is where the TXV shines.
And how many standard days do we have each year?
I believe your graphs show this as the CoE is dropping as the test goes on. Is the reason for the drop of CoE, because the room is heating up?!?!
Meaning the test environment is moving outside of the standard day envelope and now the orifice is operating out side of it's design criteria.



I do not have a engineering degree. Nor many decades worth of design, manufacturing and tech service, as you do.
I'm just the lowly mechanic with a trade school certificate, that is tasked with making these systems work, despite the best efforts of the engineers to do other wise.


Please don't misinterpret my thoughts or words.
I, in no way think that your products are inferior. In fact I really like your comp/cond layout and housing. I think that all the rest of the manufactures should take notice and learn from your design.
I just disagree with your view points on TXV.


We just have to agree to disagree and leave it at that.

[Q Xopa]

Originally Posted by a64pilot

That is likely the missing piece then, the “flywheel effect” if you don’t mind me misusing a term, smoothing out the spikes if you will.
However wouldn’t a freezer or fridge full of food to some extent replicate the effect?

Thank you for taking the time to explain things to us, I appreciate it.
I know it must be like trying to teach a pig to read a wrist watch

TXVs and Phase change aside.

Flywheel effect of Eutectic is part of the story.

The reason that can work so well is 'coldness' can be made and stored when energy is cheap, or free like Solar. No need to spend gasoline or diesel dollars to buy some cold.

Some of the Smart controllers do this too by making cold full tilt when there is an excess of power, ie Solar with batts topped off or the Alternators are producing when we are motoring.

Then when there isnt 'cheap' power available and cooling is required the compressor speed gets slowed down to to reduce its overall power consumption.

The other smallish advantage of Cold plates is the compressor doesnt have to start up as many times. There is obviously some extra current expended each time to overcome inertia to get a compressor going from stopped.

[john61ct]

If the evaporator fridge is starting up 117 times a day, and the holding plate type only once, the efficiency gains from just that factor are likely to be significant.

And if that one runtime is from relatively "free" energy, eutectic becomes a no brainer.

[a64pilot]

Originally Posted by john61ct

If the evaporator fridge is starting up 117 times a day, and the holding plate type only once, the efficiency gains from just that factor are likely to be significant.

And if that one runtime is from relatively "free" energy, eutectic becomes a no brainer.

117 times a Day is sort of way out there, the AEO module for instance wouldn’t allow that. If your cycling anything close to that then your temp set points are set way too close and or you have almost no insulation.
The once a day cycle for a cold plate isn’t very likely either.

Using my Engle and my cold plate as examples, I think the Engel cycles about once an hour, and my cold plate 3 or 4 times a day.

Now increase the Engle’s size and insulation to be the same as my fridge box and I’m sure it would cycle a lot less.

Then don’t forget if you have that 4 cu Ft box that keeps being brought up, and your cold plate takes up 1.5 cu Ft, then you only have 2.5 cu ft of usable box space. Those are mythical numbers by the way, I don’t know how many cu Ft a typical cold plate is
There is no free lunch, an efficient evaporator system is possible as is an efficient capillary system, just I’d suspect the TXV can accommodate more variables and is more flexible and that many times a cold plate is indeed more efficient, but you do lose a lot of box space to one.
My box is 14.5 cu Ft, losing a couple of cu Ft doesn’t bother me, but to some it may.

[valhalla360]

Originally Posted by john61ct

If the evaporator fridge is starting up 117 times a day, and the holding plate type only once, the efficiency gains from just that factor are likely to be significant.

And if that one runtime is from relatively "free" energy, eutectic becomes a no brainer.

Where is this free energy coming from?

You need an energy storage system with both systems...it's just a battery vs holding plate storing the energy. Both require the box, insulation, compressor, etc...but the cold plate trades battery for cold plate. You can take that same "free" energy and put it in a battery for later use.

Efficiency might be better but we've reached the point where it's not hard to run a compressor based fridge on a typical cruising boat.

[a64pilot]

Originally Posted by Q Xopa

TXVs and Phase change aside.

Flywheel effect of Eutectic is part of the story.

The reason that can work so well is 'coldness' can be made and stored when energy is cheap, or free like Solar. No need to spend gasoline or diesel dollars to buy some cold.

Some of the Smart controllers do this too by making cold full tilt when there is an excess of power, ie Solar with batts topped off or the Alternators are producing when we are motoring.

Then when there isnt 'cheap' power available and cooling is required the compressor speed gets slowed down to to reduce its overall power consumption.

The other smallish advantage of Cold plates is the compressor doesnt have to start up as many times. There is obviously some extra current expended each time to overcome inertia to get a compressor going from stopped.

I had one of those smart controllers, it worked off of voltage that you could adjust voltage points.
In order to prevent voltage sag from messing with it, it only looked at voltage at turn on, if it was above your set point, then it enabled a lower temp setting to extend run time on Solar. It would also change thermostat wiring resistance to run the compressor at its max speed.
It had to only look at voltage at turn on because your voltage when the compressor is on is less than off, so if it didn’t then it would trip back and forth with voltage sag from turning the compressor on.
Then factor in the long cycle times of a cold plate system and it’s very likely that you wouldn’t go into the lower set point until towards the end of the Solar day, and run well into the hours of not Solar, just the opposite of the desired outcome.
Final coffin nail was my system and many cold plate systems run the compressor at max speed, so you can’t make it run faster than max anyway.

However it seems to be a great system for a thin evaporator refrigerator as it had automatic defrost etc., just didn’t work with my cold plate.

Your likely better off with a simple timer if you want to do the save excess energy trick. But to really accomplish that, you need a compressor that is big enough to completely refreeze the cold plate in less than 5 hours, and a cold plate that is big enough so that it can maintain temp in the box for the remaining 19 hours.
Reason is that you only have about 5 hours of usable Solar per day, that isn’t excess Solar, that is much less.

Very few if any systems can in just a few hours provide enough cooling to maintain box temp for 19 or more hours, so while it is definitely a possibility, I doubt many systems are capable of it, likely because if they are not operated off of Solar primarily, then they due to compressor size being so large aren’t an efficient system, and who wants an inefficient system?

Engine driven cold plate systems were this way I’m sure, a big ole compressor that could freeze down a big plate fast.

[valhalla360]

Originally Posted by a64pilot

Reason is that you only have about 5 hours of usable Solar per day, that isn’t excess Solar, that is much less.

Very few if any systems can in just a few hours provide enough cooling to maintain box temp for 19 or more hours, so while it is definitely a possibility, I doubt many systems are capable of it, likely because if they are not operated off of Solar primarily, then they due to compressor size being so large aren’t an efficient system, and who wants an inefficient system?

Engine driven cold plate systems were this way I’m sure, a big ole compressor that could freeze down a big plate fast.

I think back in the day when many cruisers charged by running the engine an hour or two per day, cold plate systems made sense. The battery bank couldn't accept as much power as the motor could generate, so you went a bit smaller on the alternator and put in an engine driven compressor to use up some of the excess power that was available from the motor that was already running...this is actually much closer to "free" power as the incremental amount of fuel used was negligible.

With modern solar charging over many hours and modern compressor based fridges that are drastically more efficient compared to 20-30yrs ago, there just isn't the advantage to using an exotic system.

[a64pilot]

I guess I’m playing both sides of the fence, cause I don’t see what is exotic about a tank full of largely water. All a cold plate system is, is a thin plate evaporator placed into a water tank.
Only true downside I see is loss of box space.

[john61ct]

This thread is (was) about enabling refrigeration from solar without batteries.

Yes, once you are using batteries to store energy produced, eutectic storage requires a certain set of circumstances to make the increased efficiency worth the extra cost and lost space.