These systems use the exactly the same compressor as does the Mexicolder. Even water cooled systems are less efficient as the energy used to power the pump takes more from the system than it gives....An ever increasing entropy.
The disavantage is that when you are hauled for bottom work you lose all your refrigeration.
The alarming defect in the system is that in tropical waters the keel cooling plate and or associated through hull fitting is too small to efficiently remove heat from the hot condensing refrigerant gas.
This is evidenced by simply measuring the temperature of the liquid refrigerant after it exits the condenser/keel cooler, this enthalpy curve allows us to determine ho much energy is lost due to the FACT that small through hull condensers offered on several off the shelf systems are very inefficient in tropical waters.
If the liquid refigerant temperature is significantly higher than ambient air or water temperature then you have a huge inefficiency built into the system as when the above ambient liquid refrigerant vapourizes it is heavily taxed by reducing it's temperature using the "latent heat of vapourization of HFC 134a", which was supposedly going to be used to take heat from the evaporator. If this is too technical for you, just trust me it follows the second law of thermodynamics.
The fact....is that in 20 plus years of using the Danfoss BD series compressors these are the only failures I have seen. Here is an example
Read the third blog entry down from the top Refrigeration 101 and 102
The retrofit involves installing a double air condenser within the system.
My client jokingly failed to see how this would use less energy than the static keel cooler as the fans pull 0.34 amps. Let's say this guy is no dummy and is well versed in engineering. A year later I returned to retrofit his second system as he had spent a year monitoring the retro system and this was the icing on the cake (pun intended). It used considerably less energy.
I will try and get the results directly from him to prove this fact so keep an eye on this space.
Well here it is from the horses mouth..so to speak:
Hi Mike- I read you blog and found much useful information, good job. Regarding the retrofit you did on my boat, Sandpiper, an island packet 420. You may recall when I purchased the boat it had a stock refrigerator/freezer with two separate compressors using keel coolers. In southern California, my home waters, these operated well because the water temperature is quite low, typically between 55 and 65 deg F. However when I took the boat to Mexico the time to cool down became noticeably longer. The first problems occurred with the freezer when the copper tubing connection to the keel cooler corroded through with resulting loss of coolant. Because these connections to the keel coolers are necessarily located in the bilge areas they are prone to salt water immersion and can easily corrode. The keel cooler manufacturer did not offer any solution other than to replace the cooler plate. The quoted cost to haul the boat and replace the keel cooler plate was around $5,000. Lucky for me your solution, to replace all seals and fittings with a fully welded system and to use a large volume Mexicolder fan instead of keel cooling was only a small fraction of the cost compared to replacing the keel cooler. In the two years since this was done I have had only good experiences with the air cooled system. Running side by side with the refrigerator system (still keel cooled) it was easy to see the differences. The freezer ran for half the time of the refrigerator and used approximately 30 A-hr per day. In the summer heat, the outside water often reached into the 80-90 deg range and the refrigerator compressor ran almost continuously. Based upon this experience I elected to have the refrigerator system also converted to air-cooling and since then the total drain for both systems is approximately 60 A-hr per day. As a bonus I no longer worry about corrosion of cooper tubing in the bilges. Best regards, Ed Staples S/V Sandpiper
It would seem that some smart advertising and business types have sold cruising sailors down the road on these systems? If that is the case at this miniscule end of "heat transfer pumps" It makes me shiver to think as to where big industry is and how much precious energy is being wasted on this planet?
I rest my case