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Old 29-10-2004, 17:33   #46
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Wheels the type of refrigeration you have is called absorption refigeration and is the one of the most inefficient systems.They power hungery,slow cooling and need to be on the level to work.Compressor type refrigeration is hard to beat for efficiency either electric or shaft driven or both.On our system we have both engine driven which is a rotary car airconditioning compressor and an 12v compresser piped into the one system we run which ever compressor is appropiate at the time. 8inches of insullation and large heavy holding plate makes it very efficient and cost me approximately $1500aud parts only no labour costs. Regards greg
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Old 29-10-2004, 18:41   #47
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Well, Alan ... look's like we're in the same boat ... so to speak! This Origo unit also has a heating coil, for the ammonia gas based system ... will start looking for something more effecient, that fit's, that I can afford ... but for the time being, this is OK. Big difference is the expense .. what with my situation working in a chandlery that deals in new & used merchandise ... shouldn't cost me more than a couple hundred US dollars.

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Old 29-10-2004, 20:59   #48
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ArrHa. Absorbtion refrigeration. I thought it would be cool because it had no moving parts. Oh well. I think the inefficient part has to be just the heating element. As I have the fridge thermostat turned right down to 2.5 and it goes to 8. If I turn it up, it not only makes my icecream in the freezer box like a block of granite, it freezes everything in the fridge solid as well. So why on earth don't they build a thermostat on the heating element as this part runs all the time. In fact, it would be easy for me to make a circuit that would cycle the heater as the fridge cycles. So what problem would I introduce if I did so?? I don't think time heating the element from cold would be an issue, as the box is hardly going to thaw out in a minute or two. Any idea's anybody? What am I missing?
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Old 30-10-2004, 02:43   #49
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The ting most people miss is in the depth of the insulation. You need at least 6" of good insulation for the freezer and 4" for the fridge. More is better.
You also need to use a water cooled system rather than air, cause in a hot clime, the air is hot, and thus the poor system has to work overtime to achieve any cooling, whereas the water is normally quite a bit cooler. On a cat, make sure you have the cooler between the hulls, as the water there when at anchor in zero current is normally cooler.
If you have the space, the same evaporator can be used for both the fridge and the freezer thus reducing power consumption. You build the plate into the freezer end, and use a small computer fan to suck some cold air into the fridge section through a small hole in the insulation.
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Old 30-10-2004, 08:03   #50
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Wheels you would run into all types of problems if you upset the element heating intensity. I try to explain how the system works.Absorption refrigeration uses ammonia as a coolant, and uses water,ammonia hydrogen gas to keep the ammonia cycling through the system. Heat from a heat source (element,gas flame)heats the generator the generator contains a mixture of ammonia and water the mixture heats up till the ammonia boils.The boiling mixture flows to the separator the water and ammonia separate, the ammonia gas flows upward and through the condenser(the condenser has the fins and gets warm) and lets the ammonia gas to dissipate heat condensing into liquid. The liquid ammonia then enters the evaporator where it mixes with hydrogen gas and evaporates causing temperatures cool in the refrigerator.Hydrogen and ammonia gas flow to the absorber where water has flowed from the separator all mix together the water and ammonia forms a solution and the hydrogen is released and flows back to evaperator.The water and ammonia enters the generator again and repeats the cycle. The heat intensity is what controls your refrigeration temperature. Greg
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Old 30-10-2004, 13:37   #51
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Arrr I see. Thanks Greg. That is a very cool system in most respects. Apart from it not being a good system for a boat, I could see many potential situations of making a very efficient fridge system via other potential heat sources if you are on land.

So if I may ask another question. The systems others and yourself are discribing, sound like they are all engine run systems. Is this correct?. Or do you have/is there an electrical means of running your compressor when not running the engine? Or what would ones suggest as a good electrical compressor system. Open to all suggestions and advice.
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Old 30-10-2004, 13:50   #52
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Or what would ones suggest as a good electrical compressor system.
12 Volt air cooled works for me.

The water cooled ones are slightly more efficient as noted above, but have other problems..More hoses, more potential leaks, salt water on sensitive components and so on.

Holding plate systems are also slightly more efficient.

The key to all systems however are the insulation in the boxes.
Get that right first, then install the rest of the system

Good luck
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Old 30-10-2004, 15:45   #53
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As i said i have both piped up together and works very well but as csy said insulation is everything mine 8 inches thick but if as a friggy labour cost me nicks. There is a very good danfoss Compressors models BD50 or BD35 they are available in 12 or 24volt and draw 5 to 12 amps depending on what you vary their out put to by adding a resistor to terminals provided.When shore power is available you run it through an adaptor. Greg
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Old 30-10-2004, 15:59   #54
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Thanks CSY and Greg. Thats what I need, some makes and models.
The 12V conversion is no prob. All my lighting is 12V and runs off a "big mother of a" transformer when connected to shore power.
As I said earlier, the freezer and fridge boxes are already there and have 4" insulation around them. Umm maybe 3" around the fridge. The fridge has one of those stupid "Pelter" devices on it now. Mate, and you think the absorbtion thing is heavey on power.
The only thing I presume, is the original builder of the boat put the insulation around ALL side's and the bottom of both. One would presume, but you know the saying. Presumption is the mother of all stuff ups (and other versions).
The only other problem is the freezer box is in a different part of the boat to the fridge box. Plus because of the design of having a lid at the top instead of a front opening door, the ability to open and having everything displayed infront of you isn't as nice. But I suppose you just have to loose a few creature comforts when cruising.
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Old 30-10-2004, 16:20   #55
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Top opening fridge and freezers are a lot more efficient than front opening ones. I should have warned you that those compressors with 43% trade discount are$700 aud. Greg
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Old 31-10-2004, 04:40   #56
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Wheels, would really recommend starting again for the best efficiency. You could probably get away with th 3" insulation for a fridge, but better with more, and totally inadequate for a freezer. remember that the greater the depth of insulation the less the compressor has to run, thus the less power consumed.

Top loading is the ideal as you dont loose so much cool when getting anything from the fridge/freezer.

Seperate fridge and freezer will nearly double your consumption, ason a combined unit, you only need the single compresor and plate, plus a small computer fan to drag some of the cold air through a gap in the insulation between the freezer and the fridge section.

Realise that it may not be possible to co-locate the Fridge and Freezer, but this is the optimum solution.

Personal ambition is to be able to operate at the hook or in transit without having to run the engine to generate power.
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Old 31-10-2004, 08:11   #57
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Due to space and a desire for simplicity, I will be changing over to an air cooled electric unit (sometime in the future) ... so what's the deal on insulation there? Insulate top, bottom & sides, but not the rear? Would like to hear opinions on what's the best insulation to use.

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Old 31-10-2004, 11:25   #58
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I would strongly advise not to go for an air cooled system. This is very inefficient by comparison with the keel cooled system. The water temperature is normally going to be a lot cooler than the air temperature!. The keel cooler does require a hole through the bottom of the boat, but then the unit seals the hole and does not transfer saltwater into the boat:

There are two big advantages of this over the more orthodox water cooled system, the lack of a pump to pump sea water up to the evaporator, (and hence no jammed sea cock and less power requirement), and the fact that there is no hole in the bottom to worry about. The more orthodox water cooled system looks like:
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Old 31-10-2004, 13:46   #59
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I don't doubt for one minute that you are right about the effeciency of the keel cooled refrigerator ... however ... My current fridge is only 2.4 cubic feet (holds a case of beer ) and that's adequete for me .. at that small size, I can afford somewhat less effeciency than someone requiring a much larger unit. Cost also becomes a determining factor ... I can afford a couple hundred bucks and a days labor & stay on track to depart this time next year. If I had to go to the much, much more expensive & complex system ... I wouldn't be leaving when I want to. By the way .. as for water temp VS air temp ... here locally, the water temp stays above air temp for months at a time. Had a neighbor who's A/C was acting up ... came to find out that the 92* water temperature (yes that's right .. 92*!!) wasn't cooling his condenser ... plumbed it to the local water supply at the dock ... and the problem went away.

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Old 31-10-2004, 14:42   #60
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Wow! thats warm water. You must really struggle with Fogs huh?
Our sea temp is around 12C att he mo. It got down to 7C in the winter. Thats cold for us. But we are seeing a progressive rise now. But even so, around here, a temp of 18C is getting about tops. Sorry I am using C, I have no idea how to make that F.
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