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Old 28-07-2009, 13:42   #31
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Originally Posted by donradcliffe View Post
Now, if you want to maintain your foodbox at some minimum temperature, you will need the coolant to be at some lower temperature (Tcold). In a holdover system, you must transfer the heat from the coolant to the eutectic to the plate surface to the box, effectively insulating the coolant from the box and requiring a lower Tcold than a large evaporator. The holdover systems also cycle less often, which means that the Tcold must be even lower to maintain minimum box temperatures. The lower Tcold means a lower COP, given all else equal.
“must transfer the heat from the coolant to the eutectic to the plate surface to the box,”
I think this must read: must transfer the heat from the box to the plate surface to the eutectic to the coolant. If so this means unheated coolant returning to the compressor. I do not think this will happen in a gas expansion system, the gas will absorb all the heat that it can find in the “eutectic” and the eutectic will absorb all the heat that it can find until the box reach the cut out temperature. Anyway this does not happen on my system.
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Old 28-07-2009, 14:36   #32
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Originally Posted by donradcliffe View Post
If your main source of energy is solar, refrigeration that draws down the batteries at night will require about 25% more energy (to recharge the batteries) than refrigeration that runs during the day (when there is an excess of solar power).

From what I always have heard charge efficiency was around 80%. So I went searching and found this study by J. W. Stevens and G. P. Corey of Sandia National Laboratories concerning flooded lead acid batteries and charging efficiencies. IEEE Xplore - Login


They used a Trojan 30XHS battery deep cycle flooded battery.


According to their work charging a battery from 0 to 84% it is 91% but the incremental charging efficiency from 79% to 84% is only 55% and above 90% state of charge the charging efficiency is less than 50%. Since most cruisers try to stay in the 70% to 95% state of charge this is significant.

To me this would indicate that using the power from a solar array during the day (6 hours) to freeze a cold plate would be as effective as losing half of the energy storing it in a lead acid battery and using it later in a more efficient manner.
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Old 28-07-2009, 19:40   #33
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I have not experienced this so far. I must admit that I have a liquid trap.
240V compressor, 24V inverter and a good box insulation get you down to 20A/hrs (24V) in the tropics, with less weight, and an eutectic “brine” system. But then how reliable is an inverter?
The liquid flooding the evaporator only pertains to small prepackaged install yourself systems should you modify the system by adding a lot of volume on the high side such as increasing the condenser size or long runs to a keel cooler.
Obviously you have done something else, a liquid trap on the return line to protect the compressor.
Could you give us some details of your system.
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Old 29-07-2009, 13:03   #34
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Are they talking about batteries accepting less and less amps the closer they get to being "Full", or that, of the amps accepted, less and less actually get stored for future use?".

If it is the former, I would say that this is a well documented effect. If if is the latter, I would love to hear more comments on the subject.

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Quote:
Originally Posted by mesquaukee View Post
From what I always have heard charge efficiency was around 80%. So I went searching and found this study by J. W. Stevens and G. P. Corey of Sandia National Laboratories concerning flooded lead acid batteries and charging efficiencies. IEEE Xplore - Login


They used a Trojan 30XHS battery deep cycle flooded battery.


According to their work charging a battery from 0 to 84% it is 91% but the incremental charging efficiency from 79% to 84% is only 55% and above 90% state of charge the charging efficiency is less than 50%. Since most cruisers try to stay in the 70% to 95% state of charge this is significant.

To me this would indicate that using the power from a solar array during the day (6 hours) to freeze a cold plate would be as effective as losing half of the energy storing it in a lead acid battery and using it later in a more efficient manner.
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Old 29-07-2009, 13:41   #35
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Are they talking about batteries accepting less and less amps the closer they get to being "Full", or that, of the amps accepted, less and less actually get stored for future use?".

If it is the former, I would say that this is a well documented effect. If if is the latter, I would love to hear more comments on the subject.

Chris
What they are saying is from 79% 84% state of charge for 10 amps being put in only 5.5 amps can be taken out. The charge and discharge rates were both C/30 or 3.3 amps.

At above 90% state of charge for 10 amps going in you only are able to recover 4.5 amps.
I would presume the "missing" amps heat the battery, spilt water into hydrogen and oxygen, etc.
One would think this would show up on the battery monitors but then they reset themselves at a preset voltage. It would be interesting to set this voltage so high it could not reset and see what would happen after 10 or so charge cycles.

I am digging around for other info on the subject.
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Old 30-07-2009, 07:43   #36
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Originally Posted by mesquaukee View Post
According to their work charging a battery from 0 to 84% it is 91% but the incremental charging efficiency from 79% to 84% is only 55% and above 90% state of charge the charging efficiency is less than 50%. Since most cruisers try to stay in the 70% to 95% state of charge this is significant.
In which unit Ah or Wh?

Efficiency in Ah = quantity of electricity returned during the discharge / quantity of electricity supplied during the charge.
Up to 0.9 for a battery in good condition.

Efficiency in Wh = energy returned during the discharge / energy supplied during the charge
This vary between 0.7 and 0.8
The average discharge voltage being lower than the average charging voltage, the efficiency is always greater in Ah than in Wh.
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Old 30-07-2009, 09:03   #37
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Could you give us some details of your system.
Liquid trap I think it is called an accumulator your side of the world.

The condenser, home made of recycle material, has it will be said in OZ&NZ, looks like sh.t but it work fine. It is shown without the fans. The shape is “oval in plan and conic in elevation” open at the bottom for natural airflow from the bilge, the coil is staggered, the pipe work show the trap. So far I did not have any problem with oil migrating into the trap.
A description of the electrical system can be seen in the thread. Battery Management System
More details can be supplied if required.
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Old 30-07-2009, 13:08   #38
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Quote:
Originally Posted by chala View Post
In which unit Ah or Wh?

Efficiency in Ah = quantity of electricity returned during the discharge / quantity of electricity supplied during the charge.
Up to 0.9 for a battery in good condition.

Efficiency in Wh = energy returned during the discharge / energy supplied during the charge
This vary between 0.7 and 0.8
The average discharge voltage being lower than the average charging voltage, the efficiency is always greater in Ah than in Wh.
Amps are the units they are using. you are right for the charge from an empty battery up to 95% charged it is 0.9 or 90%. What they are saving is the incremental charge from say
50% to 60% it is 90%
60% to 70% it is 88%
70% to 80% it is 80% (10 amps in 8 out
80% to 90% it is 55% (10 amps in 5.5 amps out)
90% to 95% it is less than 50%.

I found some other studies and design data for solar panel battery systems but I haven't had time to study them yet.
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Old 30-07-2009, 13:13   #39
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Liquid trap I think it is called an accumulator your side of the world.

The condenser, home made of recycle material, has it will be said in OZ&NZ, looks like sh.t but it work fine. It is shown without the fans. The shape is “oval in plan and conic in elevation” open at the bottom for natural airflow from the bilge, the coil is staggered, the pipe work show the trap. So far I did not have any problem with oil migrating into the trap.
A description of the electrical system can be seen in the thread. Battery Management System
More details can be supplied if required.
Your right looks like ****!
More details please.
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Old 31-07-2009, 16:34   #40
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The Danfoss BD50 is not all that efficient compared to other compressors according to Danfoss itself.
To level the playing field I am quoting COP for ASHRAE LBP conditions for an evaporation temperature of -10C or 14F. Obviously in actual use there will be differences due to subcooling of the liquid, etc. The essential point is these are the numbers are for exactly the same conditions
TTY5F 1.87……………...………20%
NTX5.7FK 2.21…………………42%
NTX5.2FK 2.17…………………39%
BD150F 1.88 @ 2000 rpm..20%
..............1.85 @ 2500……….19%
.............1.82 @ 3000……….17%
..............1.73 @ 4000……….11%
BD50 1.66 @ 2000 rpm......6.4%
.........1.62 @ 2500……....….3.8%
..........1.61 @ 3000…....….…3.2%
..........1.56 @ 3500..............0%
From the Brazilian website where the Tecumseh THA1340YXA is manufactured the COP is 1.73 again greater than the BD50F at any speed.

The idea of directly using the power being produced by solar panels and frost over a cold plate is attractive. It removes all the problems with batteries, maintenance, energy losses etc.
The cold plates produced by a variety of suppliers freeze at -8F. They suggest that temperature as then the compartment will be no warmer than 4F. To freeze this cold plate we need a evaporation temp of -10 to -15 for the BD50. The capacity is 260 to 300 BTU/hr, for 6 hours we can only store 1, 560 to 1,800 BTU, this is approximately 2/3 of the capacity of the cold plates that come with these install yourself packages.
The typical cruisers need of 3,000 to 5,000 BTU. The rest 50% to 66% has to supplied from the batteries. Obviously the BD50 is too small.
We would need a compressor that can move heat at a rate of 500 to 850 BTU/hr. Danfoss makes the NTX5.2FK, moves 650 BTU/hr using .84 amps at 110 volts or 9.5 amps input to an inverter. A larger compressor is the NTX7.3FK, moves 950 BTU/hr at 11.8 amps (110 volts). All of these compressors have a higher energy efficiency than the BD50.

Still working at confirming those efficiency losses of batteries at the top 30% of charge (previous posts)

FF8.5GX http://de.refrignet.danfoss.com/TechnicalInfo/Literature/Manuals/06/FF85GX_R134a_115V_60Hz_07-03_Cd43d522.pdf
TTY5F http://de.refrignet.danfoss.com/TechnicalInfo/Literature/Manuals/06/TTY5F_R134a_115V_60Hz_01-04_Cd42v522.pdf
NTX5.7FK http://de.refrignet.danfoss.com/TechnicalInfo/Literature/Manuals/06/NTX57FK_R134a_115V_60Hz_07-03_Ch43l322.pdf
NTX5.2FK http://de.refrignet.danfoss.com/TechnicalInfo/Literature/Manuals/06/NTX52FK_R134a_115V_60Hz_07-03_Ch43k322.pdf
BD150F http://de.refrignet.danfoss.com/TechnicalInfo/Literature/Manuals/06/BD150F_R134a_220V_50-60Hz_10-02_Ch42a102.pdf
BD50F
http://de.refrignet.danfoss.com/TechnicalInfo/Literature/Manuals/06/bd50f_r134a_12-24vdc_01-2008_ed100m322.pdf
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Old 02-08-2009, 03:08   #41
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Your right looks like ****!
More details please.
Not to often someone tell me that I am right, at least it will please some CF members who do not like shinny things.

Mesquaukee, here are some data taken some years ago during an Australian winter in the tropics, a pleasant day with low humidity 25% min., and ambient average temperature of 26C (78.8F)
Compressor was supplied by shore power 240V nominal 0.8A.
Fans 12V dc current 0.22A * 2, ex Amstrad computer. Switching the fans on will bring the high side down by 8C at start up.

Time ..... box temp. Low side .....High side......High side .......Ambient
C/F............C/F.........C/F........no fans C/F.....with fans C/F......C/F
10.54..... 26.6/79.88............................................. ..........28.5/83.3
11.02..... 1.3/34.4.....................59/138.2.........................28.5/83.3
11.11......-2.0/28.4......................................51/123.8......28.5/83.3
11.14......-3.6/25.52.....................................50/122........29.0/84.2
11.16......-4.4/39.92.....................................49/120.2......29.3/84.74

The base load was and is still made of 5 * .75 = 3.75 l of brine at 5% table salt and of 4 * .85 = 3.4 kg of Ice Bricks of unknown eutectic solution. I think the solution must be only water at 144Btu/lb heat of fusion because the bricks swell. I have not been able to find yet the heat of fusion for the above brine.
The change of state when cooling occurred at around -20C/-4F
.............-19.8/-4.18.........-28.5/-19.3.......49/120.2.......36.1/96.98
.............-21.0/-5.8...........-29.0/84.2........45/113..........30.9/87.62
I hope the above did not confuse you too much.

Same load as above but in summer season (wet) ambient average temperature 31C, (87.8F).
Tuesday Start 9.22 box temp. -4.0C/24.8F
Stop 12.01 -21.5C/ -6.7F run time 2.39

Wed. Start 9.56 box temp. -4.8C/23.36F
Stop 11.56 -18.7C/ -1.66F run time 2.00

Thu. Start 10.16 box temp -1.6C/29.12F
Stop 12.45 -19.1C/-2.38 run time 2.29

Running the freezer for 2 ˝ hours a day is sufficient to maintain the box at this temperature range. Spreading the run time over the day keeps the range lower. The budget for cooking and charging the battery on our boat (37 feet) using the inboard 5kW generator, no LPG on board, is 2 hours or 4 liters of diesel. The demand on the battery is only for ˝ hour. If using the main engine for motoring, there is no demand on the battery and the box can be brought colder than the minimum –21C/5.8F.
Sorry, above time does not include the making of ice and I have never heard of cocktail being cooled by “ice brick”

When adding equipment to a boat, in general people do not take into consideration the weight of the equipment to be added. A conventional eutectic system does weigh more than few eutectic “bricks” and is not removable. An “Esky” cooled by Eutectic bricks taken from the freezer can be used as a refrigerator.

Before trying to make the bilge pump more efficient it is better to try to reduce the leaks into the boat. The same applies for a refrigeration system. A well-insulated box takes a fair amount of space. On our boat it is part of an L shape chart table incorporated at the design stage of the boat.

The calculated COP of this system is 2.
On any system I like to have Gauges permanently installed. They let you know how the system behaves, when to switch off the fans for adjusting the back pressure and when to switch on the inverter (balanced pressure), and make recharging easier even though I often use current (A) to charge systems.

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Since space is restricted for the mounting of solar panels
Be also aware that any rigid Bimini or arch with or without solar panels can affect the steerage of a vessel in a storm.

Mesquaukee your “Colibri” and Fahrenheit make for long editing.

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90% to 95% it is less than 50%.
I will try to explain in another post my understanding of this 50%
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Old 02-08-2009, 10:54   #42
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The change of state when cooling occurred at around -20C/-4F
.............-19.8/-4.18.........-28.5/-19.3.......49/120.2.......36.1/96.98
.............-21.0/-5.8...........-29.0/84.2........45/113..........30.9/87.62
......................................-29.0/84.2 should have read -29.0/-20.2.

the post did not like my tabs and made a mess, editing took more than 30 min and I got quicked out.
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Old 02-08-2009, 11:06   #43
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Sams club 3.2 refrigerator $139 1.2amps
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Old 02-08-2009, 15:03   #44
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Mea culpa my bad silly me, I'm so bad with numbers
That's a 4.3 cu ft refrigerator I've got

I keep asking why 12v is more efficient than 110v and no one's answering. And if it is, why don't we run everything on 12v, or 220 as they do in Europe?

I do agree that if you're on a small boat, fewer batteries are better and a 1 cu ft freezer will require less electricity than a 7 cu ft unit and that perfectly engineered small systems are best run by 12v, but they cost thousands of dollars and what you get is 1 cu ft. Or in the case of an Engel, 2 cu ft in a cute little case you can sit around and admire.
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Old 02-08-2009, 18:25   #45
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Mea culpa my bad silly me, I'm so bad with numbers
That's a 4.3 cu ft refrigerator I've got

I keep asking why 12v is more efficient than 110v and no one's answering. And if it is, why don't we run everything on 12v, or 220 as they do in Europe?

I do agree that if you're on a small boat, fewer batteries are better and a 1 cu ft freezer will require less electricity than a 7 cu ft unit and that perfectly engineered small systems are best run by 12v, but they cost thousands of dollars and what you get is 1 cu ft. Or in the case of an Engel, 2 cu ft in a cute little case you can sit around and admire.

The typical 110 volt household fridge, freezer or bar fridge has very little insulation (1-2 inches) in comparison to a built in fridge or freezer in a cruising boat (3-6 inches(. That is what makes household equipment “inefficient”, it has all to do with the insulation.


If you could take a household fridge or freezer and add insulation to it that would help however where do you add it. A lot of fridges and freezers use the exterior skin as the condensor. The other problem is the front opening door, the cold air dumps out when you open it, very bad. Also the gasket, that magnetic thing is very thin and has a considerable length, it leaks heat.



A 12 volt system is no more efficient than a 110 volt system. Those 12 volt dc compressor are not a direct current motor, there is a control module which is an inverter producing 3 phase current for the motor. A dc motor needs brushes, the arcing would break down the refrigerant.



The efficiency of 12 volt systems is basically all about insulation.



Does that answer your question?
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