Fridge that uses little, if any, of your battery!

[Dsanduril]

Originally Posted by Dockhead

Why couldn't both technologies work together?

Storing cold when energy is abundant, in a nearly 100% efficient battery, seems like a decent idea to me. Then if you need cooling when energy is not abundant, you can take advantage of what you describe.

What am I missing?

I don’t think you’re missing anything, to me the question is if this is the best way of accomplishing the task? The compressor is the same but the eutectic plate takes up more space in the box, so there is either less usable cold volume or a larger overall refrigeration space compared with an evap. plate. Space is always at a premium on a boat.

With lithium battery chemistries you can probably come pretty darn close to the same efficiencies as eutectic heat storage, with the advantage that the stored energy in the battery is more universal.

For those reasons, to me there would have to be a very compelling use case. I can come up with a couple of scenarios where that might be the case, but in general I reach the opposite conclusion to the OP - putting the available energy into a good battery system beats holding it in a single-use device.

[BlackHeron]

A eutectic fridge may be less expensive than upgrading to lithium.

We run four GC-2 6v flooded lead-acid golf cart batteries with only 430AH capacity (actually only half of that because we don't go below 50% ever) as our house bank. Replacement cost is approximately $350 US. We have just 250w of solar and a Primus Air Breeze wind turbine that doesn't really contribute much unless it is very windy or cloudy. Usually the wind turbine sits automatically braked all day since the solar panels have pushed voltage up past the cutout voltage of the onboard turbine controller/regulator.

We have no trouble keeping our house bank charged and rarely see bank voltage of under 12.4v after a long windless winter's night. We are almost never in a marina (unless on a ball) or plugged-in and never in over three years of full-time cruising have we ever started the diesel engine to charge batteries.

During lockdown last spring we spent 4 months on the hook on Factory Creek at Lady's Island/Beaufort SC. The engine was never started that whole time. We sat in Vero this past winter nearly that long without running it either after installing our new fridge. We don't even have a generator, much less ever needed one. Our batteries are over 4 years old and performing like new.

We installed our Ozefridge in late December/January and have not seen any difference in our batteries other than we usually hit equalization charge an hour or two later than we used to on every sunny day (3-4 times/week) but we see the same voltage numbers in the morning after a windless night. Usually 12.5-12.6v or the occasional 12.4v if we have been running 3-4 of our Caframo fans all night or stayed up late watching streaming movies or heavy computing loads like video processing on our laptops.

If we had installed a conventional fridge that ran all night off & on as needed the morning voltage numbers would be much lower and the deeper discharge cycles on our batteries would be adding up much faster, shortening their lifespans until that awful time when we need to dig deep into our cruising kitty for the $350 to replace them.

Or instead of paying the extra $400 that the Ozefridge cost over a budget icebox conversion we could have upgraded to lithium batteries with all the BMS and high tech charging necessary and spent many thousands on that.

But whatever, keep thinking that a eutectic fridge is a "waste of money."

One other really nice feature of the Ozefridge is that you can have water-cooling for the compressor without a through-hull. This was our main reason for choosing this system. the eutectic holding plate was secondary to not having a through hull we couldn't ever shut off without turning the fridge off when we left the boat.

The cooling water is circulated from and back through the freshwater tank since the water-cooling lines in the condensor coil are food-grade. We have a built-in keel tank and the water is always against the fiberglass hull since the tank is integrated into the hull itself. The fractions of BTUs that get put into the tank aren't going to raise the temperature one tiny bit without heating the entire ocean. Even if we had a conventional water tank it wouldn't heat the water up more than a couple of degrees above ambient.

[Pegu Club]

Originally Posted by Boatguy30

Yes, the mighty Engel. They are extremely small therefore have a relatively low 24/hr consumption. It’s very easy to build a SYSTEM with a 2-3x box that will consume a comparable amount of energy as the 1.25” of insulation an Engel has is totally inadequate if actual efficiency is your goal.

I might peg to differ a bit, we run with two Firefly batteries, and two one hundred watt solar panels, augmented with an alternator when we motor, and have zero issue with sufficient power to run the fridge, and everything else, which granted is not as much in the way of demand as many other cruising boats, so it has been efficient enough to accommodate year round cruising, with no excessive load on our ability to generate electricity, so yeah, it is efficient. I guess if one is starved for power, because ones system is inadequate for ones amp hour draw... etc...

Fair winds,

[Richard Kollmann]

Originally Posted by Dockhead

Why couldn't both technologies work together?

Storing cold when energy is abundant, in a nearly 100% efficient battery, seems like a decent idea to me. Then if you need cooling when energy is not abundant, you can take advantage of what you describe.

What am I missing?

You are correct my sailboat had such a system (Hybrid) One HP compressor driven by engine run 15 minutes twice a day to freeze three eutectic plates and powering an 80 amp high output alternator. The highbrid part of system powering the same three eutectic plates was supported by a single BD2.5 Danfoss condensing unit.

[Dsanduril]

Originally Posted by BlackHeron

...If we had installed a conventional fridge that ran all night off & on as needed the morning voltage numbers would be much lower and the deeper discharge cycles on our batteries would be adding up much faster, shortening their lifespans until that awful time when we need to dig deep into our cruising kitty for the $350 to replace them...

The OP proposes a cyclic fridge that uses 29Ah/day. What’s that, 15-20Ah of additional overnight battery draw? Maybe 5% additional DoD? What does that mean in terms of battery life?

Does that mean 4 years battery life instead of 5? So fridge accounts for 20% of your battery replacement costs, or ~$70 every 4 years? Ignoring time value of money the “extra” $400 for a eutectic fridge has a payback term around 20 years?

[BlackHeron]

Granted we are an edge case on the fringe of the extremely basic minimalist bargain-priced low-usage high-efficiency but low-tech scale. But depth of discharge is everything when it comes to lead-acid batteries, especially sealed AGM where the battery costs can easily triple and even be 5-fold more than the cheap Sam's Club flooded golf cart batteries like ours. Depth of discharge's effect can't really be expressed in a linear equation as even a small increase creates progressively more life-eroding damage and shorter lifespans.



The eutectic system simply makes using the lowest-cost/cheapest battery alternatives more viable of an option, all other things being equal. But the numbers actually work better with AGMs that cost a lot more and are much more fragile than the basic dirt-cheap flooded batteries.

I have always chuckled at marine technologies that require mathematical payoffs far into the future to make them economically-viable with regards to their many-thousands of dollars in up-front costs. These costs are not just for the batteries themselves, but in precise high-tech and precise electronic charging systems and monitors to ensure the batteries don't go to an early grave. As if ANY electronic device on a boat can reasonably be expected to last 10+ years without failing, and causing cascading failures in other systems they were originally installed to protect.

IMHO anything that lasts the +/- 7 years of the well-cared for FLA battery (with a properly-designed charging system and with a capacity correctly sized for real-world everyday loads and minimal DoD) is doing extremely well.

The payback on Lithium has always amused me with the numbers they throw around in excess of 10-15 years. I've talked to many other cruisers who have smoked their lithium banks because of a small oversight, failure of essential "protective" charging electronics, or something as simple as a failing alternator that was putting out way too much unregulated voltage.


If everything goes right and that fancy lithium bank and associated charging/monitoring paraphernalia lasts the 10-15 years to the break even point there is the dirty little secret that most actual cruisers rarely stay cruising that long, or keep their boats that many years before selling out, trading up, trading sideways, or just loosing their boat to a storm or other natural or man-made disaster.

I think most folks investing $5-10k in a "better battery technology" are actually buying that "better battery technology" for the next owner in a few short years. Those that think that ANY upgrade to a cruising (or any other type) boat is going to yield anything close to a commensurate resale value a couple years or more down the road are fooling themselves in an even sillier way.

But, it's only money. Those of us who are making real full-time off-grid cruising life work on minimal budgets of around $2k/month are doing it not with a "better battery technology" that costs in excess of a half-years operating budget or more -but instead around one boat buck to implement. A Eutectic fridge is a friend to those of us who aren't living on a trust fund or borrowing against our life insurance to afford the "better battery technology" to make a $400 more costly eutectic fridge unnecessary.

[Dockhead]

Originally Posted by BlackHeron

Granted we are an edge case on the fringe of the extremely basic minimalist bargain-priced low-usage high-efficiency but low-tech scale. But depth of discharge is everything when it comes to lead-acid batteries, especially sealed AGM where the battery costs can easily triple and even be 5-fold more than the cheap Sam's Club flooded golf cart batteries like ours. Depth of discharge's effect can't really be expressed in a linear equation as even a small increase creates progressively more life-eroding damage and shorter lifespans.

The eutectic system simply makes using the lowest-cost/cheapest battery alternatives more viable of an option, all other things being equal. But the numbers actually work better with AGMs that cost a lot more and are much more fragile than the basic dirt-cheap flooded batteries.

I have always chuckled at marine technologies that require mathematical payoffs far into the future to make them economically-viable with regards to their many-thousands of dollars in up-front costs. These costs are not just for the batteries themselves, but in precise high-tech and precise electronic charging systems and monitors to ensure the batteries don't go to an early grave. As if ANY electronic device on a boat can reasonably be expected to last 10+ years without failing, and causing cascading failures in other systems they were originally installed to protect.

IMHO anything that lasts the +/- 7 years of the well-cared for FLA battery (with a properly-designed charging system and with a capacity correctly sized for real-world everyday loads and minimal DoD) is doing extremely well.

The payback on Lithium has always amused me with the numbers they throw around in excess of 10-15 years. I've talked to many other cruisers who have smoked their lithium banks because of a small oversight, failure of essential "protective" charging electronics, or something as simple as a failing alternator that was putting out way too much unregulated voltage.


If everything goes right and that fancy lithium bank and associated charging/monitoring paraphernalia lasts the 10-15 years to the break even point there is the dirty little secret that most actual cruisers rarely stay cruising that long, or keep their boats that many years before selling out, trading up, trading sideways, or just loosing their boat to a storm or other natural or man-made disaster.

I think most folks investing $5-10k in a "better battery technology" are actually buying that "better battery technology" for the next owner in a few short years. Those that think that ANY upgrade to a cruising (or any other type) boat is going to yield anything close to a commensurate resale value a couple years or more down the road are fooling themselves in an even sillier way.

But, it's only money. Those of us who are making real full-time off-grid cruising life work on minimal budgets of around $2k/month are doing it not with a "better battery technology" that costs in excess of a half-years operating budget or more -but instead around one boat buck to implement. A Eutectic fridge is a friend to those of us who aren't living on a trust fund or borrowing against our life insurance to afford the "better battery technology" to make a $400 more costly eutectic fridge unnecessary.

Thread drift, but I almost went to lithium last year and did a lot of work crunching numbers. They come out better than you seem to think. The payback is pretty quick for full time cruisers who cycle their batteries most days. And that's including the not insignificant cost of converting the boat's electrical system to take prismatic cells.



But this is neither here nor there. If for $400 you can have a "thermal battery" which replaces x Ah of battery capacity of whatever type, and moreover lasts 20 years -- why not?

[Jammer]

Originally Posted by Dockhead

Why couldn't both technologies work together?

Storing cold when energy is abundant, in a nearly 100% efficient battery, seems like a decent idea to me. Then if you need cooling when energy is not abundant, you can take advantage of what you describe.

What am I missing?

The eutectic plates and their control systems add cost and complexity and reduce the amount of available space for cold food. Turn back the years to before solar power, before lithium batteries, before inverters, before Danfoss 12v compressors -- in that era, people used engine-driven compressors and eutectic plates, and ran the engine once a day. Or in a few cases used propane-powered or kerosene-powered absorption (ammonia cycle) fridges. Or, in many cases, ice, purchased ashore.



I lived in that era, and though not cruising I spent some time living in several off grid / alternative energy homes, and refrigeration was a huge problem compared to today. One of them made ice runs every other day to a friend's house that was on-grid, where he froze 5 gallon buckets of water.



The question for today, given that we have various electrical storage alternatives that are 80%-90% efficient, and that are cost effective, safe, and practical on board, is whether the eutectic systems offer enough advantages to offset the fridge space they take up and the cost and fiddling around they entail.

[Boatguy30]

To keep on drifting the guy currently sailing his 13’ boat from New Caledonia to Reunion island non stop had both batteries “fail” 2 days after leaving New Cal. Can’t imagine those were lead acids! But can’t ask as he now has no comms for another 2 months or so.

I have had Nova Kool custom evaporators in 3 boats know. Simple cap tube system. Only way to make it more efficient would be a tx valve instead of the cap tube. But I can hear the refrigerant still bubbling away a few minutes after shutdown. Hard to beat that kinda of efficiency.

I have 2x 190 watt panels 2 GC2 Trojans, run GPS Pelagic tiller pilot and fridge freezer/ 2 boxes/ 3 plates. No engine charging and a 20 amp battery charger on a Honda EU1000 that has gotten maybe 30 hours run time in 7 years.

But hey, I’m sure buying all the most expensive stuff is much better

[RaymondR]

Ozefridge fabricated a test bed with which they could collect data on the comparitive efficiencies between plate evaporator and eutectic tank systems. One of the more interesting facts identified by the series of tests carried out.

Not only were there significant electrical storage life extension benefits in not deeply cycling batteries overnight but the eutectic system displayed almost a halving of the electrical power consumption of the evaporator system. This significant increase in efficiency was attributed to the difference in electrical power usage between a system which has one start up per day versus the constant cycling system which may have multiple start ups per hour.

Dockhead has introduced a very significant factor to the discussion, the difference in perceived benefits between the permanent live aboards, who spend a high proportion of their aboard times away from shore power and weekend users, whose vessels spend most of their time connected to shore power with their battery chargers connected to the electrical grid most of the time.

I am in the process of rebuilding my fridge from a plate evaporator type into a eutectic tank type. I tend to like DIY projects and experimentation anyway but I found that it was cheaper for me to build eutectic tanks than to purchase evaporator plates. Consequently I tend to the opinion that the installation costs difference, even had I to purchase the eutectic tanks, between plates and tanks is not significant within the overall cost of the project.

As to the space and weight requirements of the two systems in my case I am reducing the volume of the refrigerator, which was originally designed as an ice box, so this is not a negative factor and in a 40" boat neither is the extra weight.

[rgleason]

We've had an Ozifridge system since 2003 and would not change it other than add insulation. We are on a mooring, have a very small amount of solar to recharge 2 T-105 Trojan FLA. We use engine run time to cool the fridge at full Danfoss power, then finish cooling at the more efficient low speed when we start sailing.

This system has been reliable and worked for years. It uses the water tank to help cool as well,, intended for very warm days and warmer climates,, however we turn on the small water pump when the engine is running to speed up the drawdown..

Even when we get lithium Batts (not much room for these on this small boat, still considering where to put then) and a bigger alternator,, I would not change this system significantly.

I've corresponded occasionally with Ozifridge and they have always been very helpful, reading the results of my tests and suggesting things to improve performance.

I am considering upgrades to insulation using aerolite.

I've found a eutectic system to be essential and cannot imagine operation without it.

[BlackHeron]

Originally Posted by rgleason

This system has been reliable and worked for years. It uses the water tank to help cool as well,, intended for very warm days and warmer climates,, however we turn on the small water pump when the engine is running to speed up the drawdown..

How did you wire this? Do you use a manual transfer switch or a relay? I don't suppose you would want to accidentally backfeed power into the pump contacts of the controller board on the compressor/condensor unit.

[OzeLouie]

Fridge and power:
There is a lot of cruiser interest in powering up fridges, but sadly after starting this thread it was disappointing to see that some posts following indicate that the fundamentals of eutectic refrigeration are not understood.
My OP may have been clumsy and along with the confusion caused by those still stuck in the Imperial system of weights and measures, may have contributed to the thread being confusing and side tracked.
As there is so much cruisers want to explore about this subject I shall start again and hope to better explain in a simpler manner using metric weights and measures! Although I stand by the OP for those who can follow and appreciate those who added to the thread with actual experiences, discussion and ideas on the subject.
And for those who wish to respond, please remember most cruisers are not rocket scientists so let’s keep it simple!

To clarify a few things:
We all know supply of electrical energy on board for cruisers is often erratic at best with storage needed for periods when solar, wind or whatever is not available. This is usually by battery storage but this thread talks about a possible option when adding refrigeration.
The metric measure of heat as in cabinet heat load calculations, compressor output, COP etc is in watts (was BTU’s in the Imperial system)
Approx. one watt of heat has to be removed to lower the temperature of one litre of water by one degree centigrade. (Sensible heat)
Approx. 93 watts of heat has to be removed to lower (through phase change) one litre of water from a liquid to a solid frozen mass (Latent heat)
To phase change that litre to ice involves the refrigeration unit removing 93 watts of heat, while consuming electrical energy at a rate that is determined by its operating COP. (see later) Having phase changed the water to ice the unit shuts off and that ice can now absorb approx. 93 watts of heat per litre as it thaws while maintaining cabinet temperature. EUTECTIC REFRIGERATION!

Using water as a eutectic medium is not ideal as it’s phase change temperature of 0C is not cold enough and phase changing pure water to ice can cause damage to the host container due to hydraulic action. There-fore water usually has salt or glycol added to lower the phase change temperature and allow expansion while still fluid. This reduces that heat factor to approx. 85 watts per litre for fridges phase changing at approx. minus 5C and less again for freezers.

The OP project: (Reducing demand on batteries)
The eutectic tank contained 5.1 litres which required a minimum of 433 watts of heat, being the daily heat load, to be removed to phase change the medium from a thawed liquid back to a solid. This required a minimum of one long run of at least 3hrs 25minutes of system run time for a 3.5cc refrigeration system with condenser temperature control.
There-fore if there is *abundant power available by say midday, the system starts automatically to do its long refrigeration cycle, and in the case described, the only run cycle for the 24 hr. period and possible without any use of stored battery power. The cabinet temperature is maintained there after by the heat absorbed as the frozen mass thaws. (*Abundant power is energy from solar, wind etc that may otherwise be wasted once batteries are charged)

System efficiency: (Eutectic is also far more efficient because: )
A eutectic system is refrigerating, absorbing cabinet / product heat 100% of the time weather compressor is on it’s long run cycle or not, while a cyclic system only absorbs heat while the unit is running say 25% of the time. This allows the eutectic system to do its job without having to operate at the very low temperatures that the cyclic needs to when running. Typically the eutectic system for this project would see the system run at a minimum of minus 10C while the cyclic would need to operate down to minus 23C to enable the required refrigeration in the shorter periods.

COP:
The COP of a refrigeration system refers to the number of watts of heat removed for each watt of electrical energy consumed and is indicated as w/w (coefficient of performance) The more watts of heat removed per watt of power consumed, the better. This is the industry recognized method of evaluating efficiency.
This is where the first operational power saving originates from. The cyclic system with a -23C evaporator has a poor COP of 1.01 while the eutectic system with a -10C evaporator has a COP of 1.41. (Both at the same RPM)
The second power saving is due to the eutectic only needing one or two start ups per day instead of up to 40 per day although todays ‘soft start’ MDM’s have reduced start-up loses considerably.
The above simply establishes the considerable power efficiency advantage of the eutectic system compared to a cyclic system in normal circumstances.

Conclusion:
If abundant power is available then the eutectic system not only benefits as a system with a lower consumption rate to achieve the same cabinet temperature, but its daily consumption can be part or totally from the power source when power is abundant and not from the batteries!

Hard subject to describe so I hope this helps.

[rgleason]

We asked Ozifridge to provide the controls on a 6' harness and asked for some special switches to turn on/off the pump and another tooverride the controls and run at full power.
I have the wiring diagrams and can post later when I get access to them.

[rgleason]

All of these controls are incorporated and automatic in ozifridge controls. Now when the voltage goes above a certain setting the ozifridge may turn on at high speed depending on where in the thaw eutectic cycle. There are other bewer optimizing controls with a new system, but we are quite accustomed to doing this more manually.