Refrigeration - Evaporator vs. Holding Plate

[alansmith]

Rorzech, would u expound why u prefer a 110v refridge through an inverter. I know Sailorchic also replaced her refridge with a dorm style refridge and it is cheap and sips juice. Is there a certain brand / model u can recommend. Thanks for sharing your knowledge

[Sandero]

I am not an expert. I did "build" a Grunnert engine drive holdover plate "freezer"system about 25 yrs ago and it has worked rather flawlessly since then. Why did I go engine drive?

Reality is that I will and do run the diesel every day when cruising. It does multiple things

recharges via a smart regulator and high output alternator the 2-8D AGM house bank
makes hot water for wash up and showers
Powers the compressor for the refer / freezer

During engine run time I will be:

anchoring and using the windlass... which is a large amp drawer
running the inverter and vacuuming
using the high seas radio which uses lots of amps
entering, leaving or maneuvering around the anchorage... or going to and from the gas dock

I choose a freezer eutectic because for passages I fill the "ice box" with frozen food and pre pared meals ready to eat by quickie cooking. For regular cruising the freezer plate is the cold area in the box... which where things like butter, milk and drinks live. On the other side are fruit and veggies and so on. Frozen items live next to the plate slowly defrost and are consumed

My system uses insignificant electrical energy. For passages I add a cooler with ice.

The system is pretty quick. In an hr the plate is solid ice at freezer temps,

I can add cooling... drop the temp whenever I run the engine which in reality is more often than expected... turn on the refer as needed.

The install was not easy... but I did it as a novice with no experience in these things. It's worked for me and I would not change. It may not work for other boats and cruiser's needs.

[john61ct]

Can these holdover plates work with the energy-efficient Danfoss type compressors?

Or do they need their own type? Only interested in 12V. . .

[Rorzech]

It doesn't really matter to me what brand cuz most of the compressors are made in the same place. As long as it is newer than 2000 it will be high efficient. 120 V gives me a better choice of wire size. Todays good inverters have very efficient power conversion. 120V fridges are cheap and plentiful compared to 12V fridges. This is just my personal preference of course.Do what ever works for you.

[a64pilot]

Originally Posted by john61ct

Can these holdover plates work with the energy-efficient Danfoss type compressors?

Or do they need their own type? Only interested in 12V. . .

A cold plate, or hold over plate is nothing but a tank filled with a solution that freezes, think giant blue ice, you know the stuff you buy for a cooler.
The cold plate is just an energy storage medium, likely best use for one is to store excess energy so that in times of no energy available it can carry you over, for example is you have Solar, during the day you can set ten thermostat so that the compressor runs continuously and gets very cold, than over night turn it off and repeat next day, this allows you to get by with a small house bank. Type of compressor is irrelevant really, a cold plate is just a flywheel so to speak. It can help with overall efficiency as it can extend compressor run times, and off time, meaning far fewer cycles, like a flywheel.
One very good one that uses a Danfoss type compressor is Cool Blue, sold by a vendor here on CF, however I think it would bust your budget.
From a cost perspective it's just not possible to best a good efficient 120 VAC fridge run off of an inverter, and they are not all that inefficient as you might think either.
More than anything else insulation determines efficiency, super insulate a box and even with an inefficient refrigeration system, you will have an efficient fridge, super efficient refrigeration system, but poor insulation, and the compressor will run 100% of the time and it will be tough to stay cold and it will use a lot of energy.

[a64pilot]

It's the phase change of water from a solid to a liquid that absorbs so much energy, it's why ice keeps things cold for so long. Think of how long plastic cubes kept in your freezer would keep a drink cold as opposed to ice cubes to see my point, a cold plate is one big giant ice cube

[Richard Kollmann]

John61, you need to understand the actual performance facts about refrigeration components as they relate to pleasure boat refrigeration. Your question “Can these holdover plates work with the energy-efficient Danfoss type compressors?”, Is not easily answered because of boat’s onboard power grid limits, what your desired box temperatures will be, and your planed cruising climates. Once box and evaporator/holding plate are at operating temperature there is little energy consumption difference between evaporator and holding plates. The only purpose of a eutectic holding plate is to store surplus energy when it is available. In the case of these BD compressors there usually is no surplus energy unless alternative energy from wind, solar, or shore power is present. One hour of compressor running time with correct size standard evaporator can provide refrigerator type box temperatures. Depending on size and surface area of a holding plate it may take 5 to 24 hours for box temperature to reach desired temperature.


Danfoss BD80 variable speed compressor equipped with AEO control module in this thread will become energy efficient only after thermostat stops and restarts compressor several times.
Danfoss BD35 and BD50 compressors with standard control modules are much more efficient when manually programmed to operate at slow speeds.
The object of newly designed compressors is to improve energy consumption matching volumetric efficiency (System Coefficient Of Performance) to a complete system balance.

Each of the above Danfoss BD compressors must have a condenser capable disposing maximum process heat into a controlled cooling medium regardless of climate conditions. Danfoss only recognizes fan air condenser cooled systems in there application engineering data.

Evaporators come in many shapes and BTU sizes to allow application engineer it select correct size to match compressor’s Btu range to a particular refrigerated box.

Eutectic Holding plates have some type of evaporator refrigerator coil inside to freeze a liquid or solid to cause a phase change to occur. The temperature where this eutectic phase change happens is determined by percent of material mix. Eutectic plate mix for refrigerators temperature is 22 to 26 degrees F, Freezer eutectic phase point is zero to +10 degrees F. To achieve a complete phase change inside eutectic plates they must reach a temperature 20 degrees below eutectic phase change point.

[sailorboy1]

Within extreme limits, I don't really care how efficient my freezer/frig is. What I want is it to keep things frozen and/or cold! I have a standard BD50 system and I'm not sure it has turned off at all the past 8 months. But since it has never caused a power issue I don't care.

[john61ct]

If available space or weather limit solar production and you want to minimize genny runs, efficiency becomes important.

I did some good research on the rationale for holding plates, and am now thinking a freezer-only unit.

This would obviously be for freezing food, some ice and "poor man's holding plate", rotating seawater "polar tubes" into a large well-insulated passive ice box. Which would get stocked from the freezer at most once a day with current food and cold drinks.

[SV THIRD DAY]

Originally Posted by john61ct

Can these holdover plates work with the energy-efficient Danfoss type compressors?

Or do they need their own type? Only interested in 12V. . .

Yep...that's the type of system we have been making for years.
12v DC compressor running a Holding plate in the Box.
Here's a link to download the manual and check them out.
http://www.cruiserowaterandpower.com...anual_2015.pdf

We have been making holding plate systems since 1968 and they all started out as engine driven, then AC (or dual AC and engine drive). But once the advent of the efficient 12v compressors hit the market that changed everything and now we do lots of engine driven or AC to 12v conversions. Since the 12v compressors are coming on based on the thermostat there isn't the need like in the old days for the Holding plates to be huge to handle the BTU's the long intervals between engine runs.

Here's a graph showing the compressors runs for a 24hr window.
You see the compressor turned on 4 times the lower data is for an evaporation system that turn on/off about 130 times in that same test box over 24hrs. Which compressor do you think is using less energy and working less for long life? (same box size 7CF and same ambient temp 70-degs with R30 insulation)

These two Data Sets also do a nice job of showing the difference between TXV/Holding plate systems and Critical Orifice Evaporator Systems.





Cheers

[JanetGroene]

Since your needs are limited, consider getting an icemaker and portable ice chests This gives you flexibility in using chilling only as needed, where needed, in amounts needed. Or just make ice cubes for drinks. http://amzn.to/2vrLuoZ
Hard ice chests come in handy as a work surface or seat; the padded ones are easily stowed or used as pillows.

[john61ct]

They only hold a tiny amount at a time, which immediately starts to melt, would be a lot of work to try to fill a cooler.

Plus very fussy, break down quickly if you're not meticulous about cleaning, counteracting mineral buildup etc.

And I prefer to not deal with food in meltwater, the dry sealed polar tubes are lots cleaner, and say a 2" diameter, won't melt for days in a good cooler.

[a64pilot]

Making ice to keep things cold is significantly less efficient, however it can be much cheaper, however it's less efficient and not much less money than a dorm fridge.
Most efficient will be something ala the Cold Blue, however It's likely to bust that budget, but is likely the best long term solution.

I'm prejudiced however as I have a Cold Blue system myself.
I believe unless mistaken it's not so much the cold plates that lead to the Cold Blue's efficiency, but the variable orifice expansion valve as opposed to a fixed orifice. I believe the variable orifice allows the system to adjust to differing conditions, like when you toss in 10 lbs of meat to freeze or add a case of beer to the fridge.
Power consumption figure etc are interesting on a sealed box that is at equilibrium at the beginning of the test, but are not real world.
Of course I know of no standard test that exists systems can be fairly tested against each other. To a great extent you can only go by the testimonials of other cruisers.
I do know however that if you have a system go down like I did on Labor Day weekend and you call Rich, he answers, cause that happened to me.
Not sure how many companies you can say that about.

[missourisailor]

Originally Posted by a64pilot

I believe unless mistaken it's not so much the cold plates that lead to the Cold Blue's efficiency, but the variable orifice expansion valve as opposed to a fixed orifice. I believe the variable orifice allows the system to adjust to differing conditions, like when you toss in 10 lbs of meat to freeze or add a case of beer to the fridge.

I'll also have to agree with A64, that the Expansion valve is head and shoulders above the fixed orifice/capillary tube systems.

Also remember that the Cool Blue system has a larger condenser than most other marine systems.

As far as which is better, holding plate over thin plate, it would be most interesting to see which one is more efficient, if both are equipt with expansion valves,

[john61ct]

Rich stated in past threads he reckoned the efficiency would be close to equivalent if the evaporator unit incorporated the TXV, much larger condenser and oversized drier/receiver.

The advantage then would be just a few starts per day vs 150+: startup current, plus lower wear and tear, neither being that significant.

The holding plate being more robust is another advantage, if you've ever poked a hole in the thin aluminum scraping ice.