More on Refrigeration
I read Mr. Marchand’s comments about refrigeration systems [Mailport, December 2002] with some interest.I am not an expert in marine refrigerations systems, but I was a refrigeration engineer for 29 years and have six patents in this field, most having to do with conserving energy in domestic and commercial equipment. This experience leads me to disagree with Mr. Marchand’s assertions that both experience and theory deny the superiority of holding plates.
Mr. Marchand’s experience with two different boats and two different installations does not allow a fair comparison of the merits of the two systems. He says as much, attributing the difference in energy consumption to the difference in insulation.
Mr. Marchand’s assertions about the theoretical energy efficiency of holding plate systems compared to so-called “evaporator” systems neglects several major and critical factors. He has observed that the evaporator system will cycle many times per day while the holding plate system will only cycle a few times a day.Then he says “So what? the compressor is designed to do this.”
Indeed it is. However, the frequent cycling of the system, in fact, causes a very serious loss of efficiency in two ways. If the expansion device is a capillary tube, as most of these designs seem to be, during the off cycle, refrigerant from the condenser will migrate to the evaporator. While this might at first seem to continue the refrigeration process, in fact it begins the process of bringing heat from the condenser to the evaporator and refrigerated space.Initially, hot liquid comes into the evaporator, then hot gas comes in.This last condenses and introduces a major amount of heat into the evaporator.This heat gain occurs with each off cycle.The more off cycles, the more heat gain.
The second area where cycling causes a major inefficiency is in the start-up.Again in a capillary tube system, when the compressor starts after an off cycle, there is a fairly long period where the compressor draws a high current but does very little refrigeration. This loss phase is too complicated to describe in detail here, but can be explained by saying that a capillary tube system only works when a proper amount of refrigerant is in the condenser and also a proper amount is in the evaporator. At start-up too much is in the evaporator, too little is in the condenser. A large amount of time passes before the refrigerant is redistributed.During that period the system is very inefficient. In certain light-load conditions, as much as a third of the cycle can be lost in this way. Research done at Frigidaire Freezer division in the 1980s, when I was chief engineer there, suggested that these effects, which occur with each off cycle, can increase the energy consumption of a domestic refrigerator or freezer by 20% to 40%, depending on the rest of the box design and the normal cycling rate.
A system which employs a thermostatic expansion valve instead of a capillary tube will not exhibit this problem to anywhere near as great a degree. Still, the difference will always favor the system that does not cycle as much.
There are other considerations that will influence energy efficiency that Mr. Marchand did not mention in his list of factors.The most important of these is the saturated suction temperature of the evaporator (technically both of the systems he discusses have evaporators). The saturated suction temperature may be thought of as being the boiling point of the refrigerant.The higher this temperature, the less energy the system will use for the same net refrigerating effect.
Depending on the design of the holding plates, and the direct air cooling evaporator they are compared to, this could go either way, but since water freezes at around 32 degrees, I would expect most holding plate designs that use water will run 15 to 20 degrees below that, while most air cooling evaporators that do not use forced air from fans as part of the design will run colder yet, and so be less efficient. The use of antifreeze or eutectic solutions pull the saturated suction temperature of the holding plate down, but I suspect the majority of holding plate designs will still have higher saturation temperatures than direct air cooling evaporators and so be the more efficient.Direct air cooling evaporators that do not employ fans require quite low suction temperatures to drive the convection currents they need to function properly. There is no free lunch here.
-Jerry Powlas, Technical Editor
Good Old Boat magazine
———-
I would like to respond to David Marchand’s statement that, “there is no benefit to a holding plate system.” The total amount of energy used per day is not the only concern. There is the other question of when that energy is used. When motoring, it may not matter how much your refrigeration draws. When under sail or at anchor the battery drain is another matter altogether. You have no control over battery drain with an evaporator system because it must be left on to maintain temperature. A holding plate system can be turned off toeliminate battery drain for hours if desired without compromising foodsafety. My Technautics holding plate can maintain safe temperatures for24-48 hours while turned off, just like a block of ice. An evaporator cannot do that.
There are other factors that affect 12-volt refrigeration efficiency other than the compressor. All the components can impact energy efficiency. The only way to compare total energy use of two dissimilar systems is to test them in identical conditions. Unless Mr. Marchand has done that, he doesn’t really know whether his assumptions are correct.
Another important factor is ambient conditions. In the typical aft-cockpit sailboat with the engine under the cockpit sole, the temperaturein the sail locker and lazarette spaces can be affected by the engine heat. These spaces are often where the refrigeration compressor is mounted because people don’t want the noise and heat generation in theircabins. I measured the temperature in my boat in these areas. Afterrunning the engine for several hourson a hot July day on the ChesapeakeBay, I found the temperature reached 105-110 degrees and stayed therefor hours. I am unaware of any evaporator system that can functionproperly in such conditions; 95-100 degrees is usually tops for them.The Technautics system can and does. I know several boatowners whose evaporator systems run continuously in hot summer weather, using an enormous amount of battery power. They often have to open the cockpit locker lids at night to release the heat so their systems can catch up. On the hottest days my system runs for two hours three times a day.
The Technautics system is easier to install by one person. Because thetubing disconnects from both the compressor and plate, you don’t have to fully uncoil the whole length and, with the help of a second person,feed it through and then recoil the extra length again.
From examining many other brands, I concluded that the Technautics system was better made. It also carries a much longer warranty.
Of course, there are good reasons for choosing an evaporator system.They have a nice little freezer and are less expensive.
Many factors must be considered to make sure you make the right decision for you, your boat, and your sailing style. Some people think that the choice of a refrigeration system is the most difficult outfitting decision a boat owner can make.
-Mike Gellner
Galesville, MD
———-
The follow-up comments on your excellent survey report on 12V refrigeration systems leads me to believe that some may still have dated prejudices with respect to the performance of modern 12V refrigeration systems. Or possibly they are trying to rationalize thegreater expense of engine- driven and 110V systems.
I have previously had 110V and 12V cold plate systems and presently have a 12V system with “conventional” evaporator instead of the cold plate. My current systems’ performance far exceeds that of my previous installations. My current system consists of a 6-cubic-foot reefer with a Frigoboat 12V keel-cooled SSC Danfoss compressor and evaporator plate. My freezer is 4 cubic feet, with a Frigoboat 12V keel-cooled SSC Danfoss compressor with a horizontal box-type evaporator with door. Last summer in 86-degree water and 90-degree temperature around the box during the day, I had rock-hard ice cream in my box with a minus-20 degree temperature and a minus 5-10 degree temperature in the remainder of the freezer compartment. The compressor units are under a bunk and virually silent, with no heat.
The keel coolers did not suffer from excessive growth, as I feared at first. Routine hull cleaning every couple of months made this a non-issue. I have not gathered data on amperage usage, but by observing the control panel it appears that the freezer compressor runs on high speed about 60% of the time in summer and 30% of the time in winter. The reefer section runs about 50% less than the freezer. I also believe the evaporators distribute the cold better than the cold plates.
Based on my experience, I believe the 12V system with evaporator is the best choice for all but the largest systems. This is especially true with the large battery capacity and alternate battery charging choices available on most current cruising boats.
-Don Hey
Port Aransas, TX
———-
OK, Performance Ratios
Thanks for printing the formulas for the common performance ratios in the December issue. Even though familiar with these numbers, the last time I seriously compared boats it took me a search on the Web to find their exact definitions. In comparing designs, I also verified what you stated in your response, that some builders fudge the numbers by using genoa area instead of the 100% foretriangle area.Another common fudge is the use of a displacement figure for a bare boat without fuel, water and cruising supplies. While the builder can’t predict the added gear and supplies, the betters ones will give displacement with 1/2-full tanks.
Technically speaking, these ratios are not all dimensionless. Perhaps it would be more accurate to simply call them “performance ratios.” They are indeed very useful for comparing boats whatever they are called, but readers should be cautioned that such comparisons are only valid for boats of similar size. Any good book on yacht design will show that these ratios will be quite different for the average 75′ sailboat as compared to the average 25′ boat.
Keep up the good work.
-Craig Johnston
Portland, Oregon
———-
A Different Filter Test
I just finished reading your Deck-Fill Fuel Filter review [November 15, 2002], and have to agree that the West Marine unit is superb. The only fault I found is when the water level rises to the top of the center filter, the water will no longer be trapped in the filter. I realize that it takes an extreme amount of water to reach this level, but I was filtering some older five-gallon cans that didn’t have good seals and they had quite a bit of water in them.Nevertheless,it isamong the best values I ever received for the money spent, particular when compared to the “standard” Baja.
I first heard about the unit on the Hunter List on Sailnet. Someone hadinquired about fuel filters and having seen one listed in a West Marine sales flyer, I bought one and tested it. Below is my “test report.”
Materials required:
1 20-oz.Orange Strawberry Banana Burst (OSBB) flavor Tropicana Twister bottle (empty with cap).
1 20-oz.Kiwi Grape Combustion (KGC) flavor Tropicana Twisterbottle (empty with cap).
1 Standard Funnel.
1 Fuel Filter FunnelWest Marine Model WM-F8C #1933233.
1 Plastic cup stolen from the Grand Victoria Casino in Elgin, IL (directions available).
20 oz. reasonably clean diesel.
8 oz clear water.
Exactly 1 handful of dirt, carefully measured.
Procedure:
1.Fill Grand Victoria plastic cup to the top of the blue diamond shape.
2.Placestandard funnelinto the KGC Twister bottle (after removing cap).
3. Pour water from Grand Victoria plastic cup into the KGC Twister bottle.
4. Fill KGC Twister bottle to the end of the spiralindentwith diesel fuel.
5. Replace cap and shake violently for 10 seconds.
6. Wait for3 minutes, staring at the interesting mix you’ve made as the water and diesel slowly separate.
7.Remove cap and add the carefullymeasured handful of dirt to the KGC Twister bottle.
8. Replace cap and slowly mix, don’t shake.
9. Wait 2 more minutesstaring at the horrible mess you’ve made as the water and diesel slowly separate while thinking, “Do I really want to pour this stuff in my brand new $21.74 (+tax, on sale) filter?”
10. Remove cap and place your brand new $21.74 (+tax, on sale) filterin the OSBB Twister bottle.
11. Take deep gulp and pour the horrible messthrough your brand new $21.74(+tax, on sale) filter into theOSBB Twister bottle.
12. Watch in amazement as only clear (well, red-dyed, but that is different)diesel appears in the OSBB Twister bottle.
13. Slowly rock the funnel to allow the remaining diesel to pass through the filter.
14. Place the standard funnel back into the Grand Victoria plastic cup.
15. Pourremaining contents of the filterinto Grand Victoria plastic cup.
16. Watch in amazement again as the level of water in the Grand Victoria plastic cup returns to its location at the top of the blue diamond shapealong with thesome of dirt added in step 7 with less than 1/8″ of diesel floating on top.
17.Stare at the indescribable concoctionremaining in your brand new $21.74 (+tax, on sale) filter thinking “Now how do I clean up this mess?”
18. Get out the hose.
19. Fill the filter until water suddenly starts pouringthrough the end ofyour brand new $21.74 (+tax, on sale) filter thinking “Uh-oh, now Ive broken it!”
20. Realize with relief that the water is coming out because the level has reached the top of the filter assembly cap.
Conclusions:
1. Darn thing works pretty well for $21.74 (+tax, on sale).
2. I really don’t want to see the inside of my fuel tank if it looks anything like the mess in steps 7 and 8.
3. The operating instructions on the filter are more in depth than those that came with myYanmar.
3. (Seriously) If your diesel has a lot of water be very careful that the water level doesn’t reach the top of the filter assembly or it will pour directly into the tank.
-Bruce Sobut
Via e-mail
———-
Mr. Funnel
As one of the many companies that actively market the fuel filter shown in your December issue as the West Marine WM-F8C, I was very pleased to see your evaluation. It should, however, be known that the filter is not so much a West Marine development as the product of a company known as “Mr. Funnel,” based in Alaska, which developed the filter for transferring aviation fuel to bush pilots in the north. Mr. Funnel is available through a number of distributors, including ourselves, and is available in both the “electrically conductive” model carried by West Marine, and an even less expensive non-conductive model which is fine for diesel.
Whatever the name and source, it is an excellent product and should be part of every cruiser’s fueling procedure as the first line of defense against water and contamination in their fuel system. Congratulations on a good review.
-Bradd Wilson, Cruising Solutions
Boca Raton, FL
We received two other admonishing letters on this subject. Apologies to Smart Tech and their distributors. We hadn’t heard about Mr. Funnel. Now we have. Thanks.
———-
Rigging Cutters
This is my first ever letter to Mailport, but after reading your article on rigging cutters I am finally moved to raise a voice in protest. I know the article was published over a year ago [November 15, 2001], but we are in the fourth year of our circumnavigation and magazines, even PS, reach us after much delay, and even after that they get read whenever Murphy allows us some time for reading.
To the point: Felco C-16 Cable Cutters for $350! Wow, are the cutting edges made of kryptonium, the aluminum handles studded with diamonds? Surely they also include preferred stock in the company.
Any US hardware store will sell you a good cable cutter for under $100. I bought one from Tractor Supply some eight years ago for under $50. It has been aboard ever since, sprayed with WD40, and is in fine shape after being used regularly on everything from anchor chain, 1×19, 7×19, and Dyform wire.
We met Nick Nicholson in Opua, NZ, and I can see him buying one of these expensive gizmos to fit in with the decor on Calypso, but for the rest us commoners, wouldn’t a tool from Sears be good enough?
I like your magazine, being a lifetime subscriber, and this is meant to be constructive. Best wishes.
-H.A. Cserny, M.D.
S/V Gold Eagle, Turkey
