Fresh Water Cooling For Fridge

[Richard Kollmann]

I am always amazed when someone believes that using water as a refrigeration cooling medium on mobile systems of less than 1/6 horse power. Efficient refrigerant performance depends on liquid high pressure temperature control. If high pressure in a system powered by a BD size compressor is reduced to less than 100 psi or increased to above 115 psi by changes in water cooling temperature medium changes it will result in less than desirable performance. On large mobile water cooled systems heat disposal devices are designed into a system to control high pressure temperature ranges. Even if a water cooled refrigeration design ignores poor refrigerant flow control, what about the other unfriendly problems created by water cooling small units such as metal loss do to low voltage discharge corrosion and overall reliability?

[CGirvan]

Originally Posted by Richard Kollmann

If high pressure in a system powered by a BD size compressor is reduced to less than 100 psi or increased to above 115 psi by changes in water cooling temperature medium changes it will result in less than desirable performance.

Does this mean that you're condenser could potentially over cool the refrigerant. Is there such a thing as too much heat removal by the condenser?

[ColdEH]

Yes , if the system is a fixed orifice or a capillary system . Pressures in these small systems outside of there designed perimeters will impact the performance in a big way. These systems were designed to work in ambient temperatures of 72 degrees like inside your house . Put your beer fridge outside in your hot garage and watch how it does not work . Over cool your condenser in cold water , same effect . Pressures inside the system and the necessary pressure differential that is needed achieve good refrigeration will suffer and therefore efficiency will suffer .

All this can be avoided by using a thermostatic expansion valve to control refrigeration flow.

So don't use a fixed orifice or capillary system in a boat. As soon as your boat is no longer in a 72 degree environment your efficiency will suffer . So when it is hot outside and inside your boat, just when you need better refrigeration , you get less !!!

Don't wast your money , get a TXV system if your are heading into the tropics !!!

Regards



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[Richard Kollmann]

It is easy to see how someone who does not understand refrigerant flow might think a thermo expansion valve (TXV) could regulate flow better than a predetermined capillary tube sized for a small compressor system. Capillary tube refrigerant control device is not a fixed orifice it is sized to keep compressor within a flow range that protects compressor from exceeding manufacture installation application limits. The range of capillary tube refrigerant flow is much narrower than a TXV. The problem with TXV is I know of none that can limit high and low flow limits under changing climates to satisfy Danfoss BD compressor specs.

[ColdEH]

I am using Danfoss TN2 with an OX orifice in two of my systems with a BD35 compressors at low speed . Works just fine . A Danfoss tech rep recommended a TUA valve , stating that it is even better suited to the task then theTN2 valve . Both machines are running perfectly with very stable pressures in cool and hot weather . I'm sure the Coolblue systems have been using them for years and have had great success .

Regards




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[OzePete]

A few things here that I would like to comment on.
Firstly the use of capillary verses TX valve. There are approx. 60million domestic refrigerators built each year and nearly all are capillary and a great many, specially in developing countries, operate in varying environments some extreme. The issue with capillary throttling is that the required capillary orifice / length needed for optimum performance varies dramatically with a change of condensing temperature. (And other factors to a much lesser degree) For example an 80 watt system with -15c evaporator and 45C condenser would ideally use 3.18 Meters of 0.80 capillary but this would need to be nearly doubled if the condensing temperature reached 55C. Now altering the capillary size is not possible whereas a TX valve will vary its orifice opening to compensate somewhat but they have other issues.
At Ozefridge we use capillary and address the issue by maintaining our condenser temperature within desired parameters therefore providing optimum performance without the possibility of over or under condensing regardless of how hot or cold the environment is and without the need of a TX valve and receiver. Our system operates as follows to maintain a constant condensing temperature:
Upon a cycle start up the twin fans operate at half speed once the condenser temperature reaches 35C. This occurs quickly but avoids any possibility of over condensing as mentioned by an earlier poster. When / if the condenser temperature reaches 43C the fans switch to full speed and the one third amp water pump id powered on. The fans revert to slow and the pump is switched off once the condenser temp lowers to 38C. This maintains our condensing within our engineered range at all times.
(As a side issue we found that R134a used through a capillary without controlled condensing temperature, often builds a restriction at the capillary outlet!)

Regards water cooling: Our water cooling method complements the air cooling and the AW models can operate as either, and as described above the water function is controlled. Water cooling is the answer for those who have no well ventilated and dry area for the condensing unit, or those looking for optimum efficiency and performance specially in hotter environments. Absorption and dissipation rates of heat via water is far greater than air.

Cheers..
Pete

[ColdEH]

Originally Posted by OzePete

A few things here that I would like to comment on.
Firstly the use of capillary verses TX valve. There are approx. 60million domestic refrigerators built each year and nearly all are capillary and a great many, specially in developing countries, operate in varying environments some extreme. The issue with capillary throttling is that the required capillary orifice / length needed for optimum performance varies dramatically with a change of condensing temperature. (And other factors to a much lesser degree) For example an 80 watt system with -15c evaporator and 45C condenser would ideally use 3.18 Meters of 0.80 capillary but this would need to be nearly doubled if the condensing temperature reached 55C. Now altering the capillary size is not possible whereas a TX valve will vary its orifice opening to compensate somewhat but they have other issues.
At Ozefridge we use capillary and address the issue by maintaining our condenser temperature within desired parameters therefore providing optimum performance without the possibility of over or under condensing regardless of how hot or cold the environment is and without the need of a TX valve and receiver. Our system operates as follows to maintain a constant condensing temperature:
Upon a cycle start up the twin fans operate at half speed once the condenser temperature reaches 35C. This occurs quickly but avoids any possibility of over condensing as mentioned by an earlier poster. When / if the condenser temperature reaches 43C the fans switch to full speed and the one third amp water pump id powered on. The fans revert to slow and the pump is switched off once the condenser temp lowers to 38C. This maintains our condensing within our engineered range at all times.
(As a side issue we found that R134a used through a capillary without controlled condensing temperature, often builds a restriction at the capillary outlet!)

Regards water cooling: Our water cooling method complements the air cooling and the AW models can operate as either, and as described above the water function is controlled. Water cooling is the answer for those who have no well ventilated and dry area for the condensing unit, or those looking for optimum efficiency and performance specially in hotter environments. Absorption and dissipation rates of heat via water is far greater than air.

Cheers..
Pete

I just saw your post , let me get this straight , you have added water cooling to your system that is electronically controlled to over come the problem with high condensing temperatures which impact the bubble length of your cap tube and impact the efficiency of your system ? Sorry for the run on sentence.

Regards

[MIRELOS]

the Indel-Webasto system that I have is water cooled, three compressors, three pumps; however unless you are in pristine waters the filters get clogged very quickly so I added one small water tank for one of the pumps and that works great but to put all three pumps on a fresh water system i would need a very large tank or draw from my fresh water supply (250 gal), we don't use the water for drinking so it's ok, but my problem is how to return the water to the tank.

[chouliha]

Originally Posted by MIRELOS

the Indel-Webasto system that I have is water cooled, three compressors, three pumps; however unless you are in pristine waters the filters get clogged very quickly so I added one small water tank for one of the pumps and that works great but to put all three pumps on a fresh water system i would need a very large tank or draw from my fresh water supply (250 gal), we don't use the water for drinking so it's ok, but my problem is how to return the water to the tank.

We return the fresh water into our water tank by Teeing into the Fill hose. Others have tee'd into a vent. Once the systems cycles a bit there is no reason that the water would not be potable.

Chuck



www.jacarandajourney.com

[OzePete]

Originally Posted by typhoon

I just saw your post , let me get this straight , you have added water cooling to your system that is electronically controlled to over come the problem with high condensing temperatures which impact the bubble length of your cap tube and impact the efficiency of your system ? Sorry for the run on sentence.

Regards

Hi Typhoon. I'm not sure if your post is a question or a statement!
Perhaps you might explain further what you are stating or wish to know.
Then I can address your post properly because at this stage I am not sure what you are saying or asking!
Cheers, OzePete

[ColdEH]

It was sort of both . It seems like a lot of trouble to control codenser temperatures . Introducing electronics and water cooling is adding a lot of failure points . Why not just increase the size of the condenser and use a thermostatic valve ?

Regards


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[OzePete]

Hi Typhoon, apologies for delay in getting back.
To answer the second part of your post first:
Ozefridge have an air cooled only model A480 condensing unit and an air / water cooled model AW480. The A480 has a cupro - nickel piped triple pass condenser with a total fin area of 1205 square inches. This cross finned condenser with it's twin fans has unequaled heat dissipation ability therefore there is no issue regards increasing the condenser. It is controlled to prevent over condensing not under condensing, and to obtain optimum performance under all conditions.. Next you suggest using a TX valve in lieu of maintaining a controlled condenser as if a TX valve will some how compensate for an inadequate condenser!! Quite the contrary. (If you need I will explain why) Besides TX valves, specially fixed with flare nuts, can be a major pain in the butt!
As explained in an earlier post, capillary and TX systems suffer efficiency losses once the condensing temperatures are outside engineered parameters.
To address this is simple. The Ozefridge system uses a water proof dual digital controller. One stage cycles the compressor on demand like most others also do. The second stage controls the fans (+pump on AW480) on/ off to maintain the required condenser parameters. This is simple and trouble free unlike other 'open to atmosphere' controllers which I agree can be troublesome.
The AW480 air / water cooled system is used when unit location is where air movement would be restricted or maximum performance and efficiency in extreme conditions is required. The AW480 has its condenser controlled the same as the air only unit.
Another advantage of the dual controller is that the condenser temperature can be read by simply pressing a button.

[ColdEH]

Hey Pete .

Interesting ,Still have a few questions about your design, maybe im just a little slow but you have an aircooled system using a Cupronickel heat exchanger ? Why not use an all copper fin and tube condenser the thermal conductivity of Cupronickel is 17 and pure copper is 223 (Btu/(hr oF ft)).Plus if you go to a TEV you can use an condenser of any size you want and increase subcooling . You would not have to worry about water condenser corrosion if you just stay with an aircooled system . I agree with efficiency loss due to hi condenser temps , and low (if you are using a cap tube ) TXV systems can not have to much subcooling at least when we are in the tropics .
How is your compressor controled ? Evap temps or box temps. I understand that a TXV valve will not help in an under condennsing state , you always need subcooled liquid at the TXV .

Regards