What's the best modern freezer unit?

[Paul L]

Originally Posted by Terra Nova

Reefer/freezers that I have built with Frigoboat keel coolers have used about 1 amp/hour. This should not require any special generator or watermaker gymnastics.

24 amp- hrs per day total for freezer/reefer in the tropics? Seems too good to be true.

[skipmac]

Originally Posted by Terra Nova

Reefer/freezers that I have built with Frigoboat keel coolers have used about 1 amp/hour. This should not require any special generator or watermaker gymnastics.

My Frigoboat air cooled model used a max of 58 amp hours in 24 hours, mid summer in Florida, +/- 95 degrees every day. At that I had to keep turning the thermostat warmer to keep from freezing the bottom of the fridge section.


Have to say 24 amp hours in a day is way lower than any usage I have ever heard unless it was a very small box.

[Terra Nova]

That difference is likely due to the increased efficiency of the keel cooler.

[Jolly Roger]

I examined a Norcross unit with an L shaped evaporator plate yesterday at West marine. I can’t even wangle it thought the lid and turn it to mount on the side of the box. Anyway, they told me I would need two L shaped evaporators to keep my box frozen and they would come pre-joined from the factory, so I have no chance with that.
Nor can I use one of the long flat evaporators and try to bend it inside the box.
½” thick holding plates take longer to freeze, but once there stay frozen longer with the power off. We will loose ¾” on each side, but that can’t be helped.
I’m talking to Sea Frost, who offer integrated systems and custom plates, along with the newest more powerful Danfoss BDX compressor. Their plates are screwed to the insides of the box, then the pipes fed through into the box and connected in situ.
It should come together next month, so I’ll let everyone know.

[a64pilot]

OK think of a cold plate as a flywheel for an engine, it has the ability to absorb quite a bit of heat by the fluid inside of it changing from a solid to a liquid, then the compressor comes on of course and runs until the liquid is frozen again.
If there is any difference in efficiency, it's because the compressor on a cold plate system isn't "short cycling", it runs for far longer when it's on, but is off for far longer as well.
Think of it like your water pump, without an accumulator, the pump cycles on and off frequently, a cold plate is like this accumulator.
A large amount of food or your favorite beverage will accomplish much the same thing.
I'm sure he is in contact with the manufacturer in specifying dual cold plates, need to be as you won't only one expansion valve, fixed orifice, whatever this unit uses.
You of course also have to have enough condensor to handle both cool plates, condensor and evaporators withing limits need to be sized to work together.

[a64pilot]

If an air cooled unit is properly designed, a keel cooler is no more efficient, but then of course a keel cooler has to have it's components properly matched as well.
Only theoretical difference would be the fan draw on the air cooled unit as a keel cooled unit has no fan or pump to move the cooling medium over the condensor, so I'm sort of contradicting myself. I guess I should say a keel cooler should only be very slightly more efficient

[Paul L]

Originally Posted by Terra Nova

That difference is likely due to the increased efficiency of the keel cooler.

I assume you aren't measuring in 90*F water. What's the approx air and water temp?

[colemj]

Originally Posted by Paul L

I assume you aren't measuring in 90*F water. What's the approx air and water temp?

And box size.

Mark

[skipmac]

Originally Posted by colemj

And box size.

Mark

Yes, box size does have just a little impact on daily power usage.

[CarlF]

As suggested. You'll get the most efficiency bang-for-the-buck from insulation. Even expensive insulation.

Look first at VIP (vacuum insulated panels). These are only 1" thick but are more than 6" of foam. They won't last forever but probably longer than the rest of the refrigeration system (e.g. 10+ years) You also shouldn't drive a screw through them. Easiest thing is just to build a thin wood frame box around the panel and then a white plastic cover that faces the freezer. You'll find some threads on this site who bought from NanoPore. They said that there's a $1000 order minimum - expensive but less than the other parts of your refrigeration.
NanoPore Incorporated

The next option is Aerogel. Twice the R value of foam. I bought some off Ebay. Easy to use. 1/2" thick that you can cut with scissors. 3" = 6" foam. Make up a stack of layers and wrap in plastic sheeting to keep out moisture. Then tape it in place with a cover.

The best idea might be to use a mix. 6" foam at the bottom. VIP's on the sides. And Aerogel to fill in any odd areas. Since you already have 3" of foam you only need 1.5" of Aerogel.

Get rid of the drain. Your home freezer doesn't have a drain. You lose a lot of cold down that uninsulated pipe.

Consider magnetic door gaskets. Air leaks will undo the benefits of the best insulation.

And finally, I don't understand the technical issues but my Frigoboat keel cooler seems to use much less energy than my old air cooled system. I respect other's concerns about Frigoboat but I've loved the system.

[Terra Nova]

I can't remember box size on those. But they were large boxes that could be run as freezers or reefers. Top loading. Stainless steel liners. Water temp ~65*. Air temp ~80*. Keel cooled is much more efficient. 4" minimum insulation plus vapor barrier.

[colemj]

Originally Posted by Terra Nova

I can't remember box size on those. But they were large boxes that could be run as freezers or reefers. Top loading. Stainless steel liners. Water temp ~65*. Air temp ~80*. Keel cooled is much more efficient. 4" minimum insulation plus vapor barrier.

When we lived in 65* water and 80* air, our large spillover reefer/freezer combination with a single air-cooled DB50 used ~30Ahr/day. If we were to operate both boxes as only a reefer, then it would have used less.

I don't think the keel cooler is more efficient than a properly installed air-cooled unit. It certainly isn't at 90* water and 90* air temps.

Where keel-cooling gets this reputation for efficiency is from comparisons to improperly installing air-cooled systems. Compressors are often installed in engine rooms or tight, no airflow compartments - where they operate very inefficiently if air-cooled, but just fine if keel-cooled. They are then forgotten and their air-cooling fins clogged up with dust and debris, making things even worse.

Mark

[Jolly Roger]

It has been about two months since my last post on this thread which I started by asking how to convert an existing ice box into a freezer. Since then I have been hard at work doing tests and adding extra insulation to the existing ice box, and finally installing equipment.
I decided on a 12 volt, air cooled system and sent drawings to four suppliers, asking for recommendations, specifications and prices. One didn’t reply at all, another was so difficult to drag a price out of I gave up. Finally I choose Sea Frost, who were the most helpful. They could supply all the equipment, along with custom sized holding plates.
This all took time, a lot of work, and money, but I now have a fine three cubic foot freezer in my boat and the wife is delighted.
Thanks for everyone’s advice and help.

[skipmac]

Congrats on the new freezer.

Have you got a figure on the power use yet? Of course it's been pretty cool in north FL lately so maybe not a really good test.

[Jolly Roger]

I finally got round to writing an article about the conversion of my ice box to a freezer, and posted it on my boat website.
Anyone interested in doing the same thing, or the members who kindly helped me with this project, can read the final result here:

FREEZER
We are delighted with the result and haven’t bought a bag of ice since.