Author Topic: Archive 19  (Read 3949 times)


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Archive 19
« on: May 03, 2012, 09:28:03 am »
Selecting a Refrigeration System
Before I get into your question of refrigeration let me give you my opinion on energy consumption and amount of insulation. Twenty five years ago I believed that to have a good ice box to convert to a refrigerator you needed six inches of insulation. After inspecting a boat refrigerator or to a day for 15 years I have a better understanding about refrigerator performance and how much insulation is really needed. Production boats under forty feet rarely have more than three inches of insulation and their iceboxes are generally smaller than 6 cubic feet. If two inches of additional insulation is added to these boxes I dont think the boat owner will realize a change in refrigerator performance unless its original insulation is over ten years old. The visual sign that refrigeration insulation is inadequate is when condensation forms on the insulation or the exterior of insulation is more than 5 degrees F colder than cabin ambient air. Good insulation with no moisture content and the correct refrigeration unit is what is important for a great refrigerator. If you plan on less than 120 watts (10 amp at 12 volts) of energy consumed per cubic foot per day for refrigerator or twice that for a freezer when selecting a refrigeration unit, the system wont be a good performing refrigerator if operated in tropical conditions. It is also important that the onboard power grid is sized to support refrigeration. Before selecting a refrigeration system it is important to decide on the level of refrigeration you want, a cooler, a refrigerator only, or a combination refrigerator freezer. The size of a box to be refrigerated, the planed cruising area and boxs desired operating temperature will dictate compressor Btu capacity. When selecting an evaporator or holding plate and expansion device they must match the compressors capacity. If a eutectic holding plate is selected as an evaporator the amount of its surface area is important as well as the freeze point of its solution. The surface area of a holding plate will determine how fast the energy will be transferred and the temperature of solution freeze point phase change will determine the refrigerated boxs temperature. A thin plate evaporator maintained by a capacity matched condensing unit at +12 degrees F can provide box temperatures much colder than a holding plate with a solution freeze point of +12 degrees. The purpose of a holding plates in a small cycling compressor system is to store surplus energy the same as energy is stored in a deep cycle battery. I looked at Frigoboats folder and checked their web sit and they no longer recommend holding plates, probably because it negates the advantages of their SSC Smart Speed Controllers performance and energy efficiencies. Frigoboats units do not offer auto start up or compressor speed up when electrical charging current is available. Isotherm does have holding plates and automatic speed up units but I do not recommend them for a 7 cubic foot box in a warm climate, plate is too small, SPU controller lacks the temperature range to freeze ice cubes in even a six cu ft box. See Isotherm test beginning on page 32 of 12/24 refrigerator volt manual. If you read the section on Water Cooled Condensers you will see why I do not recommend them for these small Danfoss compressors. The Frigoboat keel cooler does seem to perform well in warm and cool seawaters. My major concern with keel coolers and other seawater condensers is low voltage discharge from Danfoss compressors into the seawater requiring frequent zinc maintenance. If I were designing an icebox refrigeration conversion unit for a seven cu ft box to be operated in different cruising climates I would want a freezing compartment or some kind to make ice and extend the flavor/shelf life of a few food products. To achieve this objective the evaporators cooling effect needs to surround the frozen food. The evaporator or holding plates job is to remove heat from food product and box material, unless there is air movement around the box to carry heat to the evaporator device or the evaporator surrounds the product uneven or insufficient cooling will occur. There are few boat ice boxes that have room for air movement around the freezing section. In a seven cu ft combination box the only way to have a freezing section using holding plates is to have a spillover divider and two plates in freezer for even heat removal. Thin plate evaporators forming a bin or chamber offer the best solution for a small combination refrigerator freezer. RECOMMENDATION: My concern about your plan to cruising in the Caribbean is that the BD50 compressor or a larger 12 volt compressors may be over taxing your DC power system so I would recommend solar panels rated at 350 watts. For a refrigerator/freezer unit for your multi climate application I believe the Air cooled Capri 50 with SSC speed controller and model 340 B large 15 inch evaporator bin would be my first choice. If you do not believe a freezing area is needed then the Technautics Cool Blue unit with their large thin holding plate would be my second choice. I know of no automatic compressor start up devices but a small battery combiner can be used to close the thermostat contacts when a charging current is present, See drawing on Page 44 Charging Voltage Start Up.

Sea Frost
I am about to return to my boat (38' Leopard catamaran 1999) which is in charter in BVI. It has Sea Frost system with 2 plates 5/8" thick described as thermal clay in 3.7 cu ft freezer with spillover to 3.7 cu ft fridge, all top loading with single door. I gave them recommendations from you on repairs before, will see if outcome is any good when I get there in November. When I bought boat, return line had frost all the way to compressor, would this damage compressor (BD3F) giving poor performance? If I replace compressor, what model should be installed? Fan:The fan in this draws fresh air via 4" hose from cabin feeding back of condenser where it is impossible to clean. I could reverse fan but then air would get preheated from passing over compressor, should I upgrade fan, reverse it? What should the condensor temperature be? What about case temperture of compressor, is this important? Lee Haefele

Sea frost performance
Liquid returning to compressor can cause mechanical failure where compressor will no longer function or it can damage the reed valves to reduce refrigerant pressure. Danfoss BD compressors are low torque units with an electronic current limiting feature that should protect the compressor before damage is done. My best guess is that the compressor is OK. The BD3F compressor was the first BD compressor to use 134a refrigerant and its Btu output was the same as the Freon 12 BD2.5 made famous by Adler Barbour. If your BD3F system were efficient using Danfoss and my own figures to maintain both boxes to desired temperature in tropical conditions the compressor would run 22 hours per day. My worst case design concept for daily compressor running of this fixed speed compressor would be 12 hours per day. I do not know if your refrigerated boxes are in the upper area or in the lower hull where the warmer seawater effect is there 24 hours per day. Regardless where the boxes are the present system lacks the cooling capacity to handle both boxes. Changing just the condensing unit to one with more capacity like a BD50 adding 42% more output may not produce desired results because the cold plates may not be able to handle the needed 6700 Btu energy transfer in 12 hours. The best answer to your problem is to get the present unit working properly for the freezer and buy a second complete system for refrigerator. I have to assume the person that sized your system lives in California or north of Latitude 30 N, with no plans for tropical cruising. I believe Sea Frost uses a pressure regulating expansion device on their Thermo Clay cold plates, if so I may have earlier given you the wrong advice. Frost on the return line of a BD compressor system with a capillary tube expansion device would indicate too much refrigerant in system. Frost on the return line of a BD compressor system with a constant pressure expansion is caused by improper valve suction pressure adjustment. Before returning to the boat you should contact Sea Frost and ask them for the correct setting for the expansion valve. This valve has a plastic cover easily removed with your fingers. Inside the valve is a spring loaded adjusting tube with vertical numbers on it. These numbers represent the refrigerant pressure setting in the evaporator someone may have change the factory setting allowing too much refrigerant to flow through. I would not change the direction of airflow from the fan reversing it will only cause unit to run warmer. You must find a way the check the condenser to see it is not restricted with dirt and hair. The temperature of condenser and compressor is directly related to the work being done and how well the condenser and fan are removing the heat. This temperature could be as high as 135 degrees and over time can shorten the life of a compressor and its electrical module.

Hi, the boat is located at the Miami Yacht Club, in Miami FL, (of course), next to Parrot Jungle Island. The tech. replaced the old Freon with HFC134A, or R134A. These are apparently friendly to the environment. We called him when we noticed that the unit was barely refrigerating. His diagnostic/intervention was to drain the Freon and recharge with the 134A. I believe he may have OVERcharged the system. Possibly that letting some 134A out would help. Or course, I am open to your knowledgeable advice. Thanks,

Tripping Circuit Breaker
Miami is too far for me to go these days I live in Ft. Lauderdale, so I will try to provide help here on the forum. 134a is not a friendly refrigerant to convert to unless the conversion is compatible to the system being converted and the conversion is done properly. The best procedure to follow when converting a mechanical compressor like you have is to: Remove as much of the old mineral oil as possible from the system and then replace the old oil with Polyester conversion oil. It is recommended that the filter dryer also be replaced. Before adding the new 134a refrigerant it is important to evacuate the complete system with a refrigeration vacuum pump to remove air, all of old refrigerant and moisture. Mineral oil does not mix well with 134a refrigerant thats why ester oil is requires with 134a refrigerant. The miscibility of oil and refrigerant is important as this mixture is what cools and lubricates the compressor. Many refrigeration mechanics take short cuts in converting from R12 to 134a by adding ester oil on top of old mineral oil and removing R12 and adding 134a, there are times when this seems to work and others when the compressor locks up do to lack of oil. If the compressor can be turned by hand just after the breaker trips then I would think the system is over charged. You indicate the unit runs for 35 seconds is their good water flow through the condenser as this could cause a motor overload. Without knowing what type servicing valves you have I do not know how to advise on the removal of a small amount of refrigerant. Any refrigerant removed must be taken out of the suction service valve when unit is turned off this can be dangerous unless you know what you are doing. Venting to the air is also not legal.

Help when you need it
I had hoped that my 12/24 Boat refrigeration Manual would answer all questions about the smaller icebox conversion refrigeration systems and the Do It Yourself Boat Refrigeration book would provided information needed to support the larger mechanical systems. From the 1960s through the 1980s there were very few variation in the systems used for small pleasure boat refrigeration. With the unwelcome changes in refrigerants, improved DC power grids onboard boats and more efficient refrigerator equipment, no book can answer all questions. For twenty years I have helped boaters over the phone or by mail today the internet is a far better and less expensive way to communicate. I have a slide show on this web site titled What Works and What Doesnt to aid in the selection of refrigeration for a boat. This forum is the best place to ask for refrigeration help as it is much easier to track those follow up questions than e mail. If you must send e mail please send previous communications.

Getting an Adler/Barbour Crosby going
To - happy - owners of an Adler/Barbour Crosby 12-volt refigerator: After a professional recharge, our fridge now functions this way: 30 seconds at a time, before tripping at 35 amps. It used to start at 30 amps, then work down to 10, as it got "momentum", and then just keep on colding. On the 'technician's recommendation, wiring has been upgraded to a larger gauge; breaker has been replaced with new one. Yet, this behavior persists. Hesitate to call same tech on this job, and he has cornered the market on older Adler/Barbour units. Currently reading lots of fridge literature. Maybe someone can share some expertise? Thank you,

Where is the boat located? Do you know the type of refrigerant this mechanic put into the system? What was the problem indication before you call the mechanic?

Best place for excess tubing
My brother just replaced his BD 2.5 w/ a new AB BD 50 cold machine and small verticle evaporator after a leak and 15 years .The guy that installed the new system coiled all extra tubing and stuck the coil behind the evaporator inside the box. The unit works well in the NW where you wear ski cloths in August. I am about to install my own unit (AB Bd 50 cold machine w/ lg verticle evap)and question putting that excess tubing inside the box as my cruising ground is the Sea of Cortez each spring. I have a nice place to put excess just out side the box .What is the best place and should I insulate any of the tubing and how far away from the box is ideal for the condensing unit.Thanks Buz Branch PS ,just got your 12volt refrig book and it is great)

Extra Refrigerant Tubing
The extra refrigerant tubing from your AB BD50 system should be coiled outside the box anywhere that is convenient. The first three feet of tubing outside the refrigerated area should be insulated to eliminate unwanted condensation outside the box. I generally coil the extra tubing in an eight to ten inch coil near the compressor. A good length of tubing ten to fifteen feet long outside the box can prevent liquid slugging of compressor on some installations. As long as the tubing provided is long enough place the condensing unit where you can. The important thing to remember about the location of condensing unit is it needs ambient air not superheated air. The air that passes through the condenser coil should not pass through it again. Your new Adler Barbour thermostat has a paper decal on it listing the compressor speed resistor setting, read pages 28 through 36 for information on this subject.

Waeco BD-50 intermittent on /off cooling
I have a new Waeco BD-50 with a VD-15 air circulating evaporator. The unit will not maintain a narrow band of temperature, but comes on/ off unreliably, sometimes after the unit reaches 45 degrees or more and off all night . It is a new installation. The wiring to it is new and consists of 10 ft of 10 guage tinned copper with a 15 amp breaker inline. I have replaced the control module with no effect. The problem happens at the dock with battery charger on and two 27 size batteries fully charged. I have replaced the thermostat with no effect. The thermostat capilliary tube is sent down between finning of evaporator and up again as done originally. The 6ft copper line to compressor is iced to within 1 ft of compressor. It is drawing about 8 amps on start up and 5 amps when running. The unit is in the freezer side of box about 4 sq ft with a divider of 1-1/2 " R-5 foam. The boat is the north with cooler temperatures and a large volume of air around compressor.