Author Topic: Archive 32  (Read 3297 times)

Richard

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Archive 32
« on: April 30, 2012, 04:14:32 pm »


Archive 32


leehaefele



Joined: 22 Dec 2005
Posts: 2    Posted: Sat Sep 23, 2006 4:18 pm    Post subject: Sea Frost
 

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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

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kollmann
Site Admin


Joined: 23 Jun 2004
Posts: 339
Location: Fort Lauderdale, Florida    Posted: Sat Sep 23, 2006 10:12 pm    Post subject: Sea frost performance
 

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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.
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R.L. Kollmann



seapr



Joined: 22 Sep 2006
Posts: 1    Posted: Fri Sep 22, 2006 3:22 am    Post subject: Technautics verus Frigoboat tradeoffs
 

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I recently purchased and read your book (which was very helpful). I also spoke with a number of vendors and looked into their websites and literature.
I have a 7 cubic foot icebox with the original adler barbour unit. I drilled some holes to check and the insulation (from 1982) varies from 3.5 inches in the bottom and side to about 2 inches on top. Its a hard brittle but dry insulation. I am modifying the icebox to add 2 inches of blue board to the inside and create a flat bottom reducing the size to between 4 and 5 cubic feet.
My cruising varies between 4-5 day trips in the New England to several months in the Bahamas/carribean so the usage and needs vary quite a bit.
I do not run the engine much except when needed. In New England when I'm not sailing the boat is at a slip with shore power.
At the moment I am leaning towards the Technautics or Frigoboat (keel cooled or air) units with cold plates.
I like the Frigoboat techtemp control which would make use of alternate or shore power whenever its available.
I'm interested in your opinions on the following pros and cons:
1. I've been told the Frigoboat cold plate uses a true eutectic solution at 14F while techautics uses an antifreeze type solution.
2. Your book indicates the technautics has a unique design that makes it very efficient.
3. The Frigoboat unit with Keel cooler would be silent and in some situations maybe more efficient and would avoid heat transmission into the boat. But I am concerned bout if there is a problem in cold water (45f) at times.

So my question is could you elaborate on your opinion of these tradeoffs? I do like the idea of using power to freeze the cold plate whenever its "free" like in the Frigoboat.
Thanks in advance for your response.
Alan

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kollmann
Site Admin


Joined: 23 Jun 2004
Posts: 339
Location: Fort Lauderdale, Florida    Posted: Sat Sep 23, 2006 12:43 am    Post subject: Selecting a Refrigeration System
 

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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.
_________________
R.L. Kollmann




billandbeaufort



Joined: 08 Aug 2006
Posts: 7
Location: Florida, USA    Posted: Wed Sep 20, 2006 3:03 pm    Post subject: Sea Frost - Holding Plate or Cold Plate?
 

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Mr. Kollman, I am considdering purchase of a Sea Frost "BD" unit with the "Bin" style evaperator. Sea Frost calls thier evaperators "Cold Plates" but they look just like a thin "Holding Plate". Are they a Holding Plate or some type of hybrid? They look like a Holding Plate in shape and size, also they have an expantion valve but looks like a cappilary tube leading to it! I have confidence in Sea Frost's reputation, so I'm quite sure it's a workable idea but just what is it? Thanks, Bill

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kollmann
Site Admin


Joined: 23 Jun 2004
Posts: 339
Location: Fort Lauderdale, Florida    Posted: Wed Sep 20, 2006 8:03 pm    Post subject: Sea Frost Cold Plates
 

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Sea Frost is an excellent company with great after sales support. The difference between Cold Plates and Holding plates is the holding plate has a liquid eutectic solution inside that freezes the cold plate does not have liquid inside. In the past when comparing the efficiency of the three types of evaporators, Thin aluminum plate, Cold plates and Eutectic holding plates the thin aluminum plate proved to be the most efficient because of its ability to transfer heat.

The problem with thin aluminum evaporators is they have a much shorter service life do to corrosion from the inside out and outside in and they are also easily damaged. Of the three metals used for refrigerator evaporators Copper, Aluminum and Stainless Steel, Copper has the better heat conductivity. Holding Plates are for storing energy and do not make efficient evaporators do to heat conductivity of partially frozen solution and conductivity of stainless steel.

I manufactured Cold Plates at one time mechanically bonding copper evaporator coil to a stainless steel cover plate limiting the heat transfer to only the areas where there was contact. Today I understand that Sea Frost and others are using highly efficient heat sink gels to conduct heat from refrigerant copper tubing to stainless plate.

I have not tested Sea Frost Bin or Cold plate evaporators but I see no reason not to recommend them. They have used the Pressure Regulated expansion device instead of capillary tubes for at least twenty years on their small 110 volt units. These fixed pressure expansion devices provide a fixed evaporator pressure which results in a given evaporator temperature.
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R.L. Kollmann




pegasusmc



Joined: 01 Apr 2006
Posts: 2    Posted: Sat Apr 01, 2006 4:56 am    Post subject: insulation inside box
 

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I am about to add Armaflex 1" to the inside of my box on an Irwin 37 CC built in 1982. There is an old FRIGABAR unit installed that runs about 80% of the time. The Armaflex is a closed cell foam used to cover A/C duct, it is very flexable so will follow the hull on one side. I realize the R 3.57 is not a lot and can lamanate another piece if needed. If 1" does well I probably will line the inside with Ventureclad sheet to give the box inside a white or foil finish to prevent moisture getting to the foam and add a reflective finish instead of the black foam.

I plan to cut paper pattern(s) for the sides and top, cut the Armaflex from the pattern and attach to inside the box with Armaflex 520. I plan to do wet seams in corners and edges.

Comments/suggestions would be appreciated. Blue board is not very flexable and about the same R-value. Armaflex is very moisture resistant and is not suposed to support mold growth when wet.

I am full time live aboard Melbourne FL and do the Bahamas so warm water nearly year round. I have 2 120 Watt solar panels and a Windbugger with a Balmar 110 Amp alternator to charge golfcart batteries 4 for the house and 2 for cranking. Each system has its own smart regulator.

PEGASUSMC

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kollmann
Site Admin


Joined: 23 Jun 2004
Posts: 339
Location: Fort Lauderdale, Florida    Posted: Sat Apr 01, 2006 7:41 pm    Post subject: Pipe Insulation for Refrigerator
 

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Frigabar and similar Danfoss condensing units in 1982 lacked air cooling capacity to be efficient in warm climates. If you will enclose the fan with a shroud so that all of its intake air must be drawn through the coil and replace the fan with a 80 to 100 CFM volume fan the compressor run time will be greatly reduced.

I have seen tube type insulation used in large chilled water air conditioning systems but these systems work at a much lower delta T than would be experienced in boat refrigeration. I would contact Armaflex and ask them two questions; which of their flexible insulation products do they recommend for a Refrigerator or freezer? And since the exterior membrane is only on the outside will the ends need to be sealed some how?

I am afraid that my knowledge of the various types of insulation is limited to my own experience and those of boaters reporting problems with their refrigerated boxes. We all know that the amount of water in the air, humidity, will separate from the air on a cooler object when its surface temperature reaches its saturated dew point. A glass of ice water or a refrigerators exterior will collect moisture if the surface temperature is above the dew point. I believe that when the insulation keeps exterior skin of a boats refrigerated box within four degrees with a 90 degrees F ambient cabin air temperature, that amount of insulation is adequate.

All insulation manufacturers list their products R value in the dry state almost no moisture content. Closed cell is a term used indicating each cell containing gas is surrounded by a water resistant membrane. Urethane insulations are defined as closed cell but have a faster rate of aging allowing moisture to enter cells. After insulating gas leaks out and moisture inters that cell, energy efficiency is lost. To help extend the life of urethane insulation a envelope of sealed plastic can be used. One can only guess how long urethane will be effective in a boats box, my belief is it looses 50% of its R valve in 20 years if not in direct sunlight. Extruded polystyrene products like DOWs Blue Board have a far greater resistance to moisture intrusion than urethane but have a lower R value.
_________________
R.L. Kollmann
Author of DIY Refrigeration & 12-24 Volt Refrigeration