12vdc Refrigeration Confusion

[SailVanora]

I'm going to replace my ancient, but still functioning, Adler Barbour 12V refrigeration. Being thorough, I've discussed options with fellow sailors, manufacturer reps, and others. And everyone, of course, has a different opinion. The simplest option, it seems, would be to replace the current unit with a new AB. Then there are those who claim the newer holding plate refers are better and more efficient. The fact that the AB on my boat has lasted for twenty years is certainly a testimonial. I live aboard and the refer is on 24/7 here in the Pacific Northwest. I have cruising plans for South, but not for several years yet. So is it evaporator or holding plate, air or water cooling, AB, Norcold, Isotherm or Technautics?

[Vasco]

I have had both holdover plate and evaporator type 12v fridges. Right now my favourite is the AB. I have a top opening freezer with an evaporator and a front loading fridge which spills over from the freezer. Just one compressor. Works very well. It's air cooled and works fine in the Bahamas where I cruise.

[Pblais]

Ab fridges use the Dafoos compressor and it still is quite popular even after all these years. Both our boats had them and they both lasted about 17 years. We were unfortunate to see the death of both of them.

If you don't get to the tropics the differences in the sytems are less apparent since the ambient temperature difference is what forces the more difficult challenges with keeping cold or frozen food.

based on the threads I've read and expeinces we have had the AB isn't a bad choice for price and longevity. Some of the other systems build on the AB frisdge with variations. IsoTerm uses the same compressor but uses a diffeent heat exchanger and a differreent electrical controller. Isotherm in this way shows some neat inovations with the galley sink through hull replaced with an insert that sloshes water to help exchange off the waste heat instead of the air cooled apporach. They also used some elctrical connections to force the compressor on while the engine is running to use more alternator power. They seem to have made the system more battery efficient with less noise but at a price.

If you had to do the cheapest smart thing I would try to add as much insullation as you can add and go with the AB system. I've had AB cold plates and evaporators and came away liking the cold plates better. They seemed less fragile but they take a bounce better as when you open the lid the plates buffer the heat loss better than the evaporator. The better sytems cost a lot more and if you need to store more cubic feet then you may do better with them. If you need a seperate freezer then that is more complicated as well.

I guess I would ask what you didn't like about your AB system before? If they are installed well there is almost nothing that can be fixed and generally do last about 17 years. I would like to think I could out sail one.

[SailVanora]

There was not much about the AB refer that I didn't like, though it does cycle on often and I can't really keep anything frozen in the evaporator unit. Guess there is no "perfect" system, just darn good ones. Do you know anything about Technautics?

[Vasco]

I can keep ice cream frozen in my freezer (AB). That's the usual test. We make ice cubes too. There may be a problem with insulation with your unit. I might add that my box is not that well insulated but I can still keep ice cream frozen. I got a lot of loss from poor seals but have fixed that. My top doors are only about 1 1/2" so there's loss there even though I put a sheet of closed cell foam over it.

[Pblais]

I can keep ice cream frozen in my freezer (AB). That's the usual test.

Ultimate test I would say. Quit while you are ahead, pass go, pay $200 (no free lunch on a boat).

[CSY Man]

Do you know anything about Technautics?

I do...

Had a Technautics Cool Blue for 7 years. Got 8500 hours on the compressor.

Very efficient, never a problem, alaways works and we have hard frozen icecream in the freezer...-20 degrees C..

Got the upgraded 2.5 Inch cold plate and some other mods that increased efficiency..Do a search on this here bulletin board and more details are available.

Highly recommended.

[Richard Kollmann]

Did the people you talk to about what refrigeration to purchase inform you of the following:

• If you are satisfied with your present refrigeration system’s performance in the Pacific Northwest most replacement systems may take twice as much energy a day when operated in the tropics.
• New systems are only more efficient than similar old systems if compressor speed and all system components are a matched set.
• If box temperature is maintained at the same continuous temperature Holding Plates are not as efficient as conventional Evaporators.
• If a holding plate’s surface area is not large enough to handle capacity of compressor’s rate of heat transfer it will reduce box temperature rate change.
• What makes the evaporator system more efficient is compressor’s efficiency can be changed to match heat load conditions day and night, winter summer by changing compressors speed. One question to ask fellow boaters and sales people is how would the system you are recommending compensate for box heat load changes?
• If someone says a new unit will cycle more often that generally means compressor is not running efficiently.
• Through hull condenser coils require frequent cleaning especially if used as sink drains. How can this be avoided?
• Twelve volt refrigeration will perform properly only if boat’s electrical grid is sufficient enough to satisfy owner’s refrigeration needs. Another question you should be asked is, Do you want a cooler, refrigerator, a high temp freezer or a log temp freezer? This will determine the system and options you may want.

There are many 12 volt systems to chose from with each having a number of component options. To help people select the correct 12 refrigeration system for their pleasure boat I suggest you either read my 12/24 volt book or watch the slide show on my web site. The slide show should provide sufficient information to make your equipment selection, if not post your questions on my web refrigeration forum and I will respond.

[Extemporaneous]

I have read that the Danfoss BD 35 and the BD 50 compressors are the same physical size on the exterior but yet the BD 50 provides 3100 more BTU's in 24hrs.
Can someone tell me the difference?
Is there a way to increase the output of a BD 35 to become a BD 50?

Thanks,
Extemp.

[RBEmerson]

Nigel Calder went through the question in a recent Ocean Navigator. He came down in favor of constant cycle systems (e.g., A-B) after having been inclined towards holding plate systems in the past. The impression I came away with is it's still really a coin toss where the deciding factor is the cost of the system (including installation) more than the base technology.

We have a Grunert AR-50 12V holding plate system that's worked well for 10+ years, with repairs limited to replacing a thermostat (the capillary tube chafed through), motor brushes, and, just this year, a crankshaft seal. Concurrent with that repair we replaced the R-12 (ozone-hostile) refrigerant with R-409a. We'll keep the unit until it fails.

However, I've looked at possible replacements and, frankly, find more hot air and hype than solid information to base a choice on. IMHO, take the names of the units you like, put 'em on pieces of paper and tape them to the wall. Toss a dart while blindfolded and go with the name closest to the dart.

[Richard Kollmann]

Both the BD35 and BD50 compressors are variable speed with maximum speed of 3500 rpm. The BD35’s cylinder has a displacement of 2.00 cubic CM and the larger BD50 has a cylinder displacement of 2.50 cubic CM. The best energy efficiency of both compressors is when they are run at slower speeds.

At max rpm the BD35’s output is controlled and limited by system design and components selected. The size of evaporator and its expansion device along with temperatures inside and outside will reduce daily Btu output.

Exemp, I do not know what you are attempting to do but it is a fact that these new variable speed compressors can under the right conditions reduce daily power consumption by as much as 50%.

[svcattales]

Originally Posted by Richard Kollmann

Did the people you talk to about what refrigeration to purchase inform you of the following:

• If you are satisfied with your present refrigeration system’s performance in the Pacific Northwest most replacement systems may take twice as much energy a day when operated in the tropics.
• New systems are only more efficient than similar old systems if compressor speed and all system components are a matched set.
• If box temperature is maintained at the same continuous temperature Holding Plates are not as efficient as conventional Evaporators.
• If a holding plate’s surface area is not large enough to handle capacity of compressor’s rate of heat transfer it will reduce box temperature rate change.
• What makes the evaporator system more efficient is compressor’s efficiency can be changed to match heat load conditions day and night, winter summer by changing compressors speed. One question to ask fellow boaters and sales people is how would the system you are recommending compensate for box heat load changes?
• If someone says a new unit will cycle more often that generally means compressor is not running efficiently.
• Through hull condenser coils require frequent cleaning especially if used as sink drains. How can this be avoided?
• Twelve volt refrigeration will perform properly only if boat’s electrical grid is sufficient enough to satisfy owner’s refrigeration needs. Another question you should be asked is, Do you want a cooler, refrigerator, a high temp freezer or a log temp freezer? This will determine the system and options you may want.

There are many 12 volt systems to chose from with each having a number of component options. To help people select the correct 12 refrigeration system for their pleasure boat I suggest you either read my 12/24 volt book or watch the slide show on my web site. The slide show should provide sufficient information to make your equipment selection, if not post your questions on my web refrigeration forum and I will respond.

What he said! I bought Richard's book before installing a new system and I believe he is "the authority" on boat refrigerations systems. He will cut through the hype of all the vendors and tell you what "bells and whistles" you really need. He will also answer questions on his website.

Kollmann Marine Home: http://kollmann-marine.com/
Technical Forum: http://www.kollmann-marine.com/phpBB/

[Extemporaneous]

Hi Richard.
My previous question was more one of curiosity.

I would like to run something else by you and the rest of the group though.
Would it make sense to have both a cold plate and a condenser in the same refrigerator? That way when you have and abundance of power (presuming that happens), say at high noon or when you have to run your engine anyway, or......, you could bring your cold plate down to temperature and at other times use your condenser to supplement the cold plate. I'm thinking that the best would be if you could run this configuration with a single compressor that would perhaps change the compressor speed and output location depending on which of the two devices is being cooled. However I doubt the valves or controls for such a system are available for sailors. Assuming they are not, I'm thinking that besides the initial cost and also assuming there are fairly regular times of excess power this may still make sense even if one had to have two separate compressors.
What do you think?

P.S. Richard, I was over to your site and found it very informative.
Extemp.

Originally Posted by Richard Kollmann

Both the BD35 and BD50 compressors are variable speed with maximum speed of 3500 rpm. The BD35’s cylinder has a displacement of 2.00 cubic CM and the larger BD50 has a cylinder displacement of 2.50 cubic CM. The best energy efficiency of both compressors is when they are run at slower speeds.

At max rpm the BD35’s output is controlled and limited by system design and components selected. The size of evaporator and its expansion device along with temperatures inside and outside will reduce daily Btu output.

Exemp, I do not know what you are attempting to do but it is a fact that these new variable speed compressors can under the right conditions reduce daily power consumption by as much as 50%.

[Richard Kollmann]

The condenser is located outside the refrigerated area where it condenses the high pressure gas to a liquid by removing its process heat. A holding plate is a form of evaporator and is less efficient than a standard thin plate evaporator because it is not as good of a heat conductor as the evaporator. Eutectic solution holding plates are only used to store surplus energy the same as a battery. Surplus energy for holding plates must come from a very large compressor, one half HP or larger, or from extended hours of alternative electrical power wind or solar for use in runing a small refrigeration compressor.

Selecting the correct equipment and compressor speeds for 12 volt refrigeration is the key to good performance and energy efficiency. Poor equipment selection could mean you will receive only 30 Btu of cooling for each amp-hr consumed.

[Talbot]

Originally Posted by Richard Kollmann

Variable speed condensers

I was aware of the variable speed capability, however, is it possible to set the system up with one of the new condensors such that in the day time (and thus hotter), it is possible that the unit automatically selects a higher speed?