on a boat.
comments to me.
This page updated:
May 2008
| Refrigeration on a boat. |
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Please send any comments to me. This page updated: May 2008 |
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Each type of refrigeration can be used with or without a "holding
plate" (aka "cold plate")
that is taken to a low temperature and then absorbs heat from the contents
of the refrigerator over the next day or so.
If there is no holding plate, the system must be "constant-cycling" (with a thermostat, running often, such as 3 minutes out of every 15) to maintain the temperature. Obviously constant-cycling doesn't make sense for engine-driven or genset-AC-powered systems. Rough rule of thumb: holding-plate system will take about 1/2 as much energy as a constant-cycling system. But a holding-plate system is more expensive and complex and doesn't run automatically. It seems to me that the type of refrigeration should be matched to the type of power source you will use. A high-power short-duration power source such as an engine or generator would work well with holding-plate refrigeration. A low-power long-duration power source such as solar panels or wind generator would work well with constant-cycling refrigeration. Dock AC power would work with either type of refrigeration. |
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Each type of refrigeration can use air-cooling
or water-cooling, or both, to transfer heat from the
outside of the system to the environment.
Water-cooling can be done either by pumping seawater through a heat-exchanger in the condensor, or by a keel cooler (metal outside the hull, connected to the condensor). Air-cooling is simpler and doesn't require through-hulls, but is less efficient (water conducts heat better than air, and the sea usually is cooler than the air near the refrigerator). Better to oversize your system (and pay a little extra), than to undersize it (and have to run it all the time). Rough rules of thumb: in tropics, refrigerator load is 600 BTU's per cubic foot, and freezer is double that. |
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Costs of maintaining a boat's refrigerator are skyrocketing due to recent changes in the
refrigerant industry and the lack of knowledge when servicing them. The ban on manufacturing R12
refrigerant has resulted in mistakes in how to service these units, costing many boaters hundreds
of dollars.
Here are some things boaters should know: Refrigerant 101: Refrigeration is the process of removing the heat from the evaporator in the refrigerated box and disposing of it to an area outside the box. The compressor circulates the heat to the condenser where it is transferred to another medium: air or seawater. It does not matter what type of a mechanical refrigerator you have; this is the basic principle of how it functions. Refrigerant 102: Most older boat refrigeration systems used Freon R12 refrigerant, except for low-temperature freezers which used R502. Both of these refrigerants can no longer be manufactured as they affect the ozone layer and global warming. If you determine that your unit needs R12, it is best to stay with that refrigerant. Yes, there is plenty of R12 out there but it just costs more. R12 is currently selling for $20 per small can on Ebay. Remember the final authorization to use alternative refrigerants or oil should come from the compressor manufacturer and no one else. The most-used 12/24 volt refrigerator compressor is the Danfoss. It is used by Adler Barbour and at least twelve other companies. The older Danfoss BD 2.5 compressors use Freon R12 refrigerant and mineral refrigerant oil. Refrigerant 134a was not approved for these compressors because of its inability to mix with mineral oil, and to change the oil to a compatible oil might destroy the insulation on the motor wiring. There is one blended refrigerant, 409a, that can be used as a replacement for R12 in BD2.5 compressors, but only in an emergency in cool climates. Warning: never mix refrigerants, and always vacuum out the old before inserting a substitute. Hermetically sealed compressors that are powered by alternating current (110 or 220 volt) may be filled with Alkylbenzene oil, which is compatible with HCFC component refrigerants. Blended refrigerant 409a is recommended as a replacement for R12 in systems where the compressor contains alylbenzene oil. Externally-driven compressors, engine-driven or those with large 12/24 volt motors, are being converted from Freon R12 to 134a refrigerant. This also includes changing to a compatible Poly Ester conversion oil. If you have one of these systems, contact the system manufacturer for their correct procedures before making this conversion. Don’t forget to clean the condenser coil annually on air/water cooled refrigerators when the system performance is in question. Nondestructive testing to determine refrigerant quantity is important to avoid contamination. You don’t need a mechanic to check out your boat's 12-volt refrigerator before your cruise. Turn the refrigerator on and after 30 minutes there should be frost covering the evaporator. Adler Barbour and other similar ice box conversion units supply a three-foot piece of insulated tubing to use on the lines just outside the box. In moderate temperatures and humidity three feet of insulation should be enough to prevent moisture on the lines outside the box. In hot humid climates, it is a good idea to insulate both tubes together in a single insulation tube outside the box all the way to the condensing unit. If the evaporator is not 100% covered with frost, the unit is low on refrigerant. It frost extends outside the box on the line back to the compressor then there is too much refrigerant in the system. Large refrigeration systems in boats generally have holding plates inside the refrigerated box that may take more than an hour to freeze. A touch of a finger on different parts of the system can tell if the system is working OK. On the line just before the plate is an expansion valve; by touching the outlet of this valve performance of the system can be determined. After about ten minutes the temperature of the outlet of the valve should be below +10 degrees F. If you place a finger on the valve outlet at this time your finger will almost stick to the valve indicating the system is probably OK. Systems with expansion valves generally have a sight-glass in the pressure liquid line after the condenser that will indicate refrigerant quantity, but you must know what it looks like when the system has the correct amount of refrigerant in it. To extend the life and obtain the best performance from your boat's refrigerator:
I provide a great deal of free boat refrigeration information on my website so be sure to check out the Forum and FAQ section. It you have one of the new efficient 12/24 volt compressors, the Slide Show will be of interest also. |
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Always look at the small-print specifications. "The above ratings are based
on cruising in areas where the seawater is not warmer than 72 degrees F
and the box must have medium size insulation."
... New Refrigeration Systems are not always more efficient. The ASU is a great enhancement to these refrigeration units where the compressor selected has a capacity somewhere in the mid range of the box's daily average heat load. The ASU's normal function is much like a car's automatic transmission by slowing the compressor down when high power is not needed. Slowing the compressor speed cuts current draw as much as half. Another advantage of the Auto Speed Up ( ASU ) is to override the controls when charging current is available to the battery buss. There is extensive testing of these speed controllers in my 12/24 Volt refrigeration manual with computer analysis profiles. The results of the Isotherm Model 4201 Magnum with ASU Showed poor results because the tropical heat load on the box was to much for the range of the system and ASU. On the other end, if the compressor at slow speed is too large for the box heat load excessive current will be used. If the system is to be used in warmer waters than the manufacturer's specification list, their figures must be adjusted to a new capacity and current draw. I use a simple rule: add 4 percent for each degree of warmer water, or subtract 2 percent for each degree F of cooler seawater. |
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| The most successful of the cruisers in my experience are using dual-coil holding plate refrigeration with dual compressors. One being engine-driven and the other electric, either 110 volt or 12 volt. The choice in electric is usually based on whether the vessel will be berthed a good deal of the time or has a generator in suite. I would say now a days most are going for 12-volt mainly because the new 12-volt compressors are getting a lot better than they used to be. You will find that most vessels in the forty-foot range do not have a generator, so they are using their engine to top off batteries for an hour or so anyway. The engine-driven compressor has a great deal more power than an electric compressor and will bring a holding plate down to temperature very quickly. |
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| 12-volt-powered refrigeration gives you the most flexibility. In port you can use a battery charger. You can use solar or wind and if the sun don't shine you can run the engine. |
| From Rob Dubin: for a DC refrigerator, get a smaller compressor motor rather than a bigger one. The batteries are much happier putting out small current for long periods rather than large current for short periods. |
| We also lived for ten and cruised for several years with a Dometic LPG fridge and loved it, except on passages where we were heeled over. After about 24 hours on a single tack it just stopped working. I thought about a gimbal, but it just got too large and tricky. Works great except for that and the fact that you need to vent some heat. [And you need to buy LPG.] |
| [A friend's] compressor is mounted on the boat with a belt to the engine. I think this stresses the engine mounts and pulls the engine out of alignment with the shaft because I can see it pulling the engine sideways, loosening the belt. I wouldn't install one in this manner. Insist they bracket the compressor properly to the ENGINE not the BOAT. |
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Among things that we specifically avoided based upon 1st-year experience: Engine-driven refrigerator (we were tired of being a slave to the boat; now we have a small and very efficient 12 volt / air-cooled system that came with boat which uses 55 amp-hrs/day). |
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First, I'm in favor of sailing with refrigeration and margaritas!
Some sailor types are also minimalists, not in favor of refers (but, they
usually like the margaritas).
I installed a SeaFrost system on my Tartan 37. It included both an engine driven compressor and a 12V compressor which ran from 110VAC via an inverter. It had a glycol solution which froze a holding metal block "plate" about the size of a block of ice. Two ice cube trays sat above the block and I could make ice cubes in 45 minutes. Very cool. The block would freeze meat, or whatever in one partitioned part of the ice box and refrigerated the other half of the box via holes in the partition. I could use 110VAC when at the dock, or engine when cruising underway or at anchor or 12VDC when necessary. I would recommend something similar. Glacier Bay also has a great system. You want holding plates and a freezer section that can drive a compressor from your engine via direct or a large 12VDC motor or 110VAC. ALL of the cruisers that we met with only 12VDC refers that ran from the batteries only, without holding plates - ran their batteries dead all the time. The goal is to freeze the plates in 45 minutes or less. That way the engine/genset can do the job without running too long and make a days worth of cold, re-charge the batts and hopefully make your daily water usage (if you have a water maker). Systems that just "trickle" all day to make cold, or electric, or water suck if you really seek cruising independence. |
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Our current boat had a Grunert engine-driven holding plate system, which
I've removed in favor of a super-efficient 12 VDC system using a keel
cooler from Frigoboat; VERY satisfied to date.
Two thoughts: Do you REALLY want a refrigeration system that relies on running that very expensive diesel at extended idle to make it work? And if you are looking at 12 VDC systems, remember that almost all manufacturers build their system around the same Danfoss compressors. |
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Our last three "cruising" boats had different systems:
Alberg: Ice Box. Pros: Always plenty of ice for cool drinks. About as simple as it gets. Cons: Everything is always wet. Need for ice every couple days. Clogs in drain are a real pain. No ability to keep frozen food frozen (short of dry ice, which wasn't practical for us). Vertical stacking storage is a pain. Beneteau: 12-volt air-cooled. Pros: Loved it, low energy drain. Small freezer compartment could keep a steak or two frozen and make small quantity of ice. Never had a problem with it. Cons: Not enough ice production for 4 people. Freezer too small for serious frozen storage. Vertical storage still a bit of a pain, but side racks made it easier. Gemini: Propane. Pros: Larger box. Door allows access to everything quickly without digging. Freezer good for our frozen needs and making ice. Even living aboard full-time and using the grill and stove almost every night, we use one 20-lb propane bottle [about $18] once a month. Very cold. Cons: We have a multi-hull; I understand that propane fridges like to be level. The heat generated goes to the cockpit, which is nice on a cool morning, but on a hot day it's not welcome. Other notes: Purists may scoff at a unit with a door, but our system is so cold, it's not an issue; we monitor it with an external thermometer and it really isn't an issue. If I used more than one bottle of propane a month, I might think otherwise. Ease of access makes all the difference. We still have a cooler in the cockpit. With a family of four, it's not realistic to keep everything in the fridge. So we'll put in a couple of bags of ice (which we use for our drinks) all our drinks and any veggies that want to be cool but take up a lot of space (lettuce, broccoli, etc). If it was just my wife and I, we could easily live with just the fridge. I really like having a big old pile of ice around. A coke in a big tall glass of ice tastes FAR better to me than one straight out of the can. Same for lemonade. We have one of those Coleman "five day" coolers. Keep in mind, our needs are those of coastal cruisers; we shop once a week and have a diet very much the same as we have on land. An "ideal" system for a coastal cruiser with a family is going to be different than the "ideal" system for a single-handed long-range cruiser. |
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| ... use flare fittings instead of compression fittings. Either fitting will work. The downside of the compression fittings is that they can only be tightened a fixed amount until the ferrule gets crimped onto the tube. The flare fittings can be tightened until the threads get stripped off. |
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We didn't notice it too much on our SSB, but it was bad on our VHF, even if
we weren't receiving or transmitting it had a hum. It was noticeable by the
people who were receiving our VHF transmissions as well.
I put a large filter from Radio Shack that was intended for a stereo in a car on the VHF power input and it helped a lot. If I could have found one that would have handled the amperage I would have installed one on the SSB and Fridge as well, but we were in Key West about to leave for the Bahamas when we went looking for something to fix it and that was all we found. I don't recall now what all I did to convince myself that the interference was all coming in on the power line and not the antenna, but I do recall that I was pretty sure that was how it was affecting it and the filter verified it. The Adler Barbour unit uses a crude inverter to run the compressor and I expect that it is just a noisy unit. I would expect that some shielding and a lot of filtering, both at the compressor and the unit being affected, would be the only cure. By the way, ours is about 5 years old and I have no idea if it has Danfoss parts or not. |
| Insurance companies seem to be increasingly nervous of propane devices in boats which can/are left unattended. Our new-to-us-boat has a propane/AC freezer on the boat deck. Both insurance agents we have talked to indicated that insurance companies would most likely deny coverage if the freezer unit was inside the boat. They don't want any propane devices which are not "attended" to. |
| Mr. Kollmann's earlier book was a wealth of information - the systems I built from it have given top-notch service now for about 10 years BUT. Don't purchase his water-cooled condensers. They are badly designed. All three that I purchased from him failed in the same way. Freon erosion from the entry tube cuts through the water jacket in about 2 to 3 years, allowing salt water into your freon system. ... Although he was very responsive and helpful while I was building the system and purchasing parts, he never responded to any of my reports about the condenser failures so beware. |
| Have had lousy luck with our fullsized Norcold fridge. It is AC/DC autoswitch and I can tell you it sucks a battery down right now. We also had to totally replace the fridge when it was three years old (total compressor failure). |
| I also had one of the full size nevercolds and it proved true to its name. The compressor was replaced three times and you know how expensive that can be. I ended up cutting the whole unit out with a saws-all and putting it in the dumpster because the boat cabinetry was built around it. This is one company I will never support again for refrigeration. Now I'm getting along well with a 110 VAC 3.3 approx cube fridge running off a separate inverter and a couple 4d's. |
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I just want to put in a word here in defense of Norcold. I installed one of
their icebox conversion units on my last boat, and it ran 24/7 flawlessly for 5
years, and was still running when I sold the boat. I installed another one a
friend's boat, and his experience was identical. I chose this brand because
they have a lower power consumption and are much cheaper than Adler Barbour. At
that time - about 1994 - the whole kit cost about $400.
Another advantage was the ability to run on both AC and DC, and switching automatically to AC when available. Actually, as previously stated here, the compressor runs on 24 VAC, which is provided from 110 VAC via a transformer and from 12VDC via an inverter and another winding in the transformer. The AC powered hermetically sealed design is probably the most reliable and maintenance-free type of compressor - this type is used in almost all domestic refrigerators and air-conditioners, and these devices often run 20 years or more without maintenance. |
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We have a Grunert air- and water-cooled frig. It has worked flawlessly since
I installed it in 1997.
I installed the water-cooling plumbing (new thru hull too), but the tiny sea water circulation pump makes too much noise. In my infinite wisdom I "hard mounted" it to fiberglass and it makes the boat roar. Powerful little pump. That's one of my projects - to find a softer mount for it. ... |
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We have had excellent service from our Engel reefers (one as reefer, one as
freezer) and they have our highest recommendation.
The one used as a freezer a few months ago began having problems starting. It would take several tries, running for only 3.5 seconds, before it would stay running. [The distributor] replaced the machinery on the spot and the trouble disappeared. We highly recommend the Engel. Our two units, both MT-45's, have been in operation for almost two years and we are very happy with them. The one used as a freezer (simply the coldest setting on the thermostat) keeps ice cream hard and makes ice cubes daily. [later] ... My Engel reefer used about 1.8 amps when I measured it some time ago. The unit set to 0 deg F for use as a freezer pulls 2.6 amps. The freezer runs almost all the time so it might use as much as 60 amp/hours per day. I guess the reefer uses about 20-25 amp/hours per day depending on the ambient temp. I recommend the Engel, but contact the Engel distributor, for the latest in his line of portable reefer units, the state-of-the-art is in rapid development. My main complaint about the Engel is the insulation. The series is designed to operate having an unlimited supply of electricity and is not as efficient as would be a unit with more or higher R-value insulation. Perhaps there is available a unit with more insulation that would fit your space. I thought of adding insulation to the Engels, even have it on board, but never found the round-tuit needed ... The more insulation, the less electricity required, but the less room for food available for a given outside dimension. There are some vacuum panels that claim high R values that might be of value on a portable unit. Within the next year, I may be replacing my Engel's with SunDanzer units which have 4.3" of insulation. They have 4x the interior space and take about the same amp/hours. ... > the Engel can sit out in the hot summer sun with a temp > (I measured it) of 125 deg F on its 'skin' and be > zero deg. F inside with only 18 AH per day consumption. I find the above statement hard to believe. 18 AH/day is 9 hours of operation out of 24 for a duty cycle of .36. It was on 36% of the time. Our Engel freezer, set to zero F, in the galley, used more like 50 AH/day and operated almost continuously in the summer. I have used two Engel units for about two years, one as a refrigerator and one as a freezer. They pulled about two amps each when running. These were the 1.4 Cu/Ft units. Early on I put an hour meter on one of them and made some guesses as to AH used. My final conclusion was that both together used about 75 AH in the summertime with ambient temps around 90F, somewhat less in winter with the ambients around 70F. Their main drawback for us was that the insulation is around one inch and they were small, 1.4 Cu/Ft. They seem to be designed for use in a motor vehicle with a plentiful supply of 12 to 24 volts where portability was important. However, they were well designed by a German, solidly built by the Japs, and worked very well even considering the AH useage for their size. The were also self-contained, trouble-free, and sold quickly when I moved up to my present Sundanzer units. Our current units, called "Sundanzer" are made in Sweden by Electrolux specifically for off-grid use. They are around 5 Cu/Ft, pull about 2 amps, and use the same amount of AH because the insulation is 4.3 inches thick. We love them but they are a bit large for most boats. [later] ... I have aboard a Sundanzer refrigerator and a Sundanzer freezer. They are made by Electrolux for folks who live with solar panels, as I do. They are 6 cu/ft, air-cooled, self-contained, 12 volt, 25 watt, quiet, maintenance-free and wonderful. |
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Used the BIG Engel before and agree not enough insulation thickness or
quality - we are in the BVI's sheesh even the water temp is over 90 deg.
I would much rather have something 'good' than an almost works option ... |
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The Engels use some type of 'sling' type compressor that doesn't eat much
power. I've had my 45 running 24x7x6years - no issues, the 45 uses about 2
amps. I've thought many times about getting another, lose the case and
install into the two deep iceboxes, but take a nap and forget the idea as I
have a large investment into SeaFrost holding plates, which by the way make
a lot of very large ice cubes!
Just a side note that Engel did at one time offer up the 45 without the case as a 'built-in'. Don't see that it is offered any longer. |
| The Engel guts are removable as a unit without disconnecting any tubing. |
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Re: a 12-volt freezer:
The Engel 45 is a top-loading cabinet unit that is AC/DC and will provide the results you are looking for. This unit is air-cooled and adds about one half the amount of heat to the cabin as a crew member would. The idea of water-cooling is not practical or reliable enough for these small units. I tested most of the new small 12-volt refrigeration systems for my new book and here are a few of the Engel 45 performance figures: These tests were performed in a 24-hour controlled environment 78.5° to 81.2° F. in still air except for the unit's cooling fan. As a day-use cooler at 46.9° F. the average amp per hour was 0.45 amps. As a high temp. Freezer at 21.2° F. the average amp per hour was 2.78 amps. As a low temp. Freezer at -2.65° F. the average amp per hour was 2.56 amps. The amazing figure in the test as a low temp. unit, with a 82° drop in temperature the outside cabinet skin temperature only dropped five degrees. |
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As for the energy consumption you are giving, something isn't right here. Based on the number you
give, and the way you state the test results, for the "average" refrigerator draw (.46 amps/hr.) I
assume that you are taking the total energy consumed and dividing it by the test hours. Indeed, to
do anything else would be useless for comparing to other systems as it is the total amount of
energy used per day that matters.)
On the other hand, if your "average" does include the total run time then you need to double-check your test setup as there is no way that the system has lower total energy consumption at -2.65F than it does at 21.2F. |
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The tests I have done on the Engel 45 are correct and they did prove the value of this inexpensive
Refrigerator/Freezer. The reason the Engel performs so well is it is not a conversion unit, it has
a wrap around evaporator, and the components are a matched set for the boxes heat load.
I ran a series of tests using a cycle counter, Data logger, computer print outs to plot performance along with an amp-hour meter. If you check my figures against the manufacturer’s figures you may find their figures are better than mine. Average amperes per hour times 24 equals the daily amp-hours consumed. Cooler 0.45 x 24 = 10.8, Refrigerator 0.91 x 24 = 21.8, High Temp. Freezer 1.47 x 24 = 35.3 and a Low temp. Freezer 2.56 x 24 = 57.5. Of the two hundred tests I have conducted in the last three years for my book, the ones I did on the Engel 45 were the most impressive. But like most items sold in the marine environment this unit is not salt water proof. |
| Not to belabor the point, but your previous post claimed 2.78 amp/hr average for the high temp freezer and 2.56 for the low temp freezer. Also, what is the interior volume of this box? |
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The 24 hour High Temp Freezer Test on the Engel logged 35.3 amp-hrs maintaining the box
temperature at 21.2° F. and divided by 24 equals 1.4708 average amps used per hour. Bill was
looking for a two cu. ft. freezer the Engel 45 quart is 1.5 cu. ft. Engel does have a larger 65
Quart model.
These Swing compressors have produced a better COP on smaller boxes than the larger Danfoss DB2.5. The newer BD 35 at its slow speed should approach the same COP of the 60 watt Swing compressor. Just when we think the new variable speed Danfoss compressors are the answer to all of our small 12 volt conversion designs, I hear of a more efficient variable speed Rotary compressor to be available soon. The new Rotary is reported to have 30% higher capacity than the BD 50 and a 20% better COP rating. If you need more information on these units go to Engel's web site. There are several other manufacturers of these self-contained units. If you recommend them as a low temperature freezer make sure the box insulation and the system is rated for the low temperatures. |
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The tests I
have been running are controlled in a static air area with a stable temperature control. I monitor
each test with temperature data-loggers, cycle meter amp-hr meter, run time hour meter and total
time clock. Three years ago I started evaluating some of the wild claims about boat refrigeration
and box insulation. To do this I obtained many of the various manufacturer’s systems without their
knowledge. After hundreds of tests, I documented the results of what works and what doesn’t.
In my new book on 12/24 volt refrigeration, there are a series of six evaluations of the Engel 45 refrigerator. Each test compares ambient air temperature against exterior box temperature to evaluate insulation quality. As to your question about condenser cooling, any air-cooled unit must draw air from one area and dispose of the super heated air to another area to be efficient. The refrigerator test listed with a power consumption of 16.1 amp-hrs per day was conducted with an ambient temperature of 81°F. and an average exterior box temperature of 77° F. As to using it for a freezer with the thermostat set to full cold, it should outperform any unit that does not have a full wraparound four-sided evaporator. As a low-temperature freezer with an average ambient temperature of 80.4°F, it consumed 57.5 amp-hrs per day running on 12 volts, with an exterior box temperature of 74.5°. With a delta-T of 6 degrees this is within an expectable range to prevent condensation on box exterior. There are several manufacturers of these portable boxes and I am not saying it is the best. What I am saying is that it does exactly what Engel says it will do. There is no question that if any of these cabinet units were placed in the sun their efficiency would be affected. With seasonal changes or when cruising areas change, the seawater temperature has a major affect on cabin air temperature and refrigerator performance. I use a simple formula to adjust power consumption of air-cooled units located below deck. As the seawater temperature increases, add 4% for each degree F. of temperature rise or reduce the power consumed by 2% for each degree of temperature drop. An example of the same boat’s power consumption in California could be 50% of what the same boat would use in July in Southern Florida. |
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Using an Engel 35 right now and keeping it up with a 32-watt flexible solar panel on the fridge
setting using a 27 AGM battery. Only issue I have with the device is that it rusts as we keep it
under the companionway on our Corair 31 trimaran and can not prevent water from splashing it. The
rust is on the outside so not really an issue.
Note we have minimal other power use but if we did I am sure the panel would not keep up. Overall I am very happy with the unit and would highly recommend. |
| I almost went with the Frigoboat but was reluctant to cut another below-the-waterline hole in the hull. I discovered the Isotherm unit which, in most respects, is identical (including price) to the Frigoboat. The big difference is I didn't have to cut another hole. The Isotherm unit is also keel-cooled but they developed a "cooler" incorporated into a thru-hull which replaces an existing through hull. I already had a thru-hull for the galley sink drain (2" or 2-1/2" I think) and the Isotherm is a direct replacement. With the Isotherm thru-hull the sink still drains through that fitting but the heat from the refrigerator system is still dissipated. |
| This is the system I use. I am very satisfied with it. You do have to increase the size of the hole in the hull though. |
| John, it probably varies boat to boat. In my case it was a direct replacement. The only modification was that I had to cut the drain hose to shorten it. The Isotherm thru-hull is a few inches taller than the standard one. |
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Air-cooling versus water-cooling:
I attended a seminar on refrigeration at last year's SSCA Gam. The water-cooling did not perform better until compressor was more than 1/6 HP. Until then, the pump consumed more than the gain. THEN, the instructor advised to DO ANYTHING POSSIBLE TO NOT SALTWATER COOL. He has had many early failures due to corrosion, all total losses. Several things that improve performance: Using a cold plate instead of an evaporator, improves efficiency due to keeping refrigerant at 15F instead of colder, major difference in energy use. Variable speed compressor, smart, voltage-sensitive controls that cool extra when engine or battery charger is on. The keel-cooler in a drain seemed like a good idea, but, it may not cool well in a totally calm anchorage; also, be sure to change its zinc. |
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The TropiKool 40 runs continuously; it does not
cycle on/off as do conventional compressors. The Electronic Control Module
modulates cooler performance to match the current heat load of the box being
cooled. This modulation is in the form of shortening the piston stroke of
the cooler; this then decreases the power required during low load periods.
Under the Cruising World benchmark criteria, the TropiKool 40 consumes 18 amp/hrs per 24 hour period. Power consumption at 95 degrees F ambient, a R28 value, and a 40 degree F box temperature, the TropiKool 40 consumes 36 amp/hrs per 24 hour period. The continuous operation of the cooler enables the system to maintain a constant box temperature of +/- 3 degrees of selected temperature. |
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How to test insulating quality of your icebox, summarized and derived from "This Old Boat" by Don Casey, with some additions from "The Boatowners Mechanical and Electrical Manual" by Nigel Calder:
"Refrigeration for Pleasureboats" by Nigel Calder shows how to calculate heat leakage while designing an icebox, from its surface area and insulation thickness. It assumes top-loading, closed-cell foam insulation, and no air leaks. Paraphrased from "The Boatowners Mechanical and Electrical Manual" by Nigel Calder and "Refrigeration for Pleasureboats" by Nigel Calder:
From John Branch on the Morgan mailing list:
From Bob Lucas on the Morgan mailing list:
From Dan / SunDial on the SailNet liveaboard-list:
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| I have the Kollman book. It was the basis of acquiring equipment to install mechanical refrigeration in the future. I have found from talking to other vessel owners that the Kollman equipment is fair to average but that customer service is poor. I have no personal experience at this time. ... |
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> is a "holding plate" the equivalent of those blue plastic packs > you can buy to freeze at home and then put in a cooler ? Adding frozen blue packs would increase your "holdover". ... The blue plastic packs contain an anti-freeze solution. Unlike ice, they will warm up as they thaw. Most American-manufactured holding plates do the same. Some holding plates behave like ice and stay the same temperature as they freeze and thaw. This is desirable because it results in more stable box temperatures and results in the food lasting longer. |
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If you're water-cooled, you need a brushless pump or
you'll be replacing pumps all the time.
... A standard 12V pump will die in a couple of months. I know, I went through several of them. The solution is a March model 893-09. It is a brushless, submersible (I don't submerge it) impeller-type, NOT self-priming, so it has to go below the waterline. My pump has been on my reefer for 3 1/2 years, only shut down to defrost. I think the cost is around $150, but it's money well spent. |
| DO NOT purchase the March pumps that have the water-cooling feature that is fed by the pump itself. It is guaranteed to self-destruct. There are a couple of pipes that divert a little of the water through the pump motor for cooling. A really dumb idea. The first time the inlet or strainer is blocked up, the water flow stops and the pump motor cooling stops allowing the pump to overheat and self-destruct. |
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> I have a 15-year-old Iceberg water-cooled freezer/refrigerator > system in my Swan. It appears to power two large holding plates > in the freezer box (approximately 18 cu ft), this shares a common > wall and cools the fridge box (approximately 12 cu ft) as > well as a smaller holding plate for a small day fridge > (approximately 8 cu ft). > > The compressor and evaporator finally gave up the ghost > this season and I am attempting to figure out how to > upgrade the entire system since it also used the older > and now banned CFC's. What complicated this system is > that the compressor could either run off a clutched pulley > when the engine was going or off an electric motor when > my 230v 50hz generator ran. So where do I begin? > I obviously need all the upstream stuff to drive the > holding plates, but how do I figure out what and how much HP? The holding plates are your evaporators. I would recommend trying to replace the condenser and compressor, and keep your system as close to its designed specs as possible. The condenser is easier to chose than the compressor. To be of more help I need a better description of the compressor (and condenser). Obviously, it is belt driven, but can you find any labels or tags that may have some manufacturer info on it? Or a physical description, including shape, size, material (aluminum, steel), and pulley sizes (both engine and compressor). Can you tell how many cylinders it has? Can you find any photos on our website that look similar? It isn't that the refrigerant is banned, it's that the refrigerants are very expensive, and harmful to the ozone. There is a good supply of recycled R12 available, but it is way expensive, and there are many interim "drop in" replacements that work very well. The 12 volt compressors that we offer really are too small to do what you want to do, which is freeze two large freezer plates (probably plumbed in series). We do have compressors that will work, and condensers as well. Does your system have a water pump, and what does the condenser look like? What are the water connection sizes, and the refrigerant connection sizes? |
| Usually, refrigerator holding plates are around 24-26 degrees F, and freezer holding plates are around 0 degrees F. It is important to go several degrees below this temp to assure that the plates are as frozen as you can get them. |
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> I found that I didn't have enough insulation by drilling > 1/8" holes through the bulkheads and probing with a coat hanger. > This worked well but I found I only have from 1-1/2 to 3" > of foam. Also a lot of empty space on all 4 sides > including 7" under the bottom. > > Since I can't get into that space, I intend to inject that > spray foam (hardware store) to fill all the dead space, it > will greatly increase the total volume of foam. Question: > will it hurt that the foam will adhere to the 3/4 ply > bulkheads and the fiberglass hull? I hate to be the bearer of bad news, but you have a problem which is going to be much more difficult to correct than you are now thinking. You are correct in that you will indeed increase the amount of foam by filling in all the gaps with spray foam. What you are not considering is that in 6 months to a year (of constant refrigerator use) you will end up with a lot of very wet foam which will make you wish you hadn't touched it. It is not correct that "closed cell foam" does not absorb water. You must have some air circulation around the foam to prevent moisture buildup. The only way to really solve the problem is to rip out the box and completely rebuild it. If you are not up for that big of a task - don't do a thing. ... Keep in mind that all of the information you are getting from various foam manufacturers applies to "normal" installations in a land-based application - not boats. The only conventional foam you are going to find that does not have a water absorption problem in boats is an extruded (not expanded) polystyrene. The moisture passes directly through the cell walls so the fact that a foam is "closed cell" does not solve the problem. ... Without having any clue about water absorption and condensation, I did what you want to do on an older Hunter. Bought cans of foam at Home Depot and squirted foam into neatly spaced holes, thinking that when it came out of an adjacent hole, I could move to the next empty hole. Did so. Then to my horror, watched interior of box bulge inward up to 1 1/2" in the middle of the sides and on the bottom. Shelves would no longer fit, etc. Had to drill more, bigger holes in woodwork surrounding box and slowly dig out extra foam. Even so, each summer, the foam expanded a bit more. What a pain! Box got colder, though. Caution! Caution. ... Be careful when using expandable foams. Read the can for the expansion ratio and compare this to the volume you intend to use it in. These foams can and will exert a large amount of pressure if there is nowhere to go! |
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> Can buy refrig flare-fittings at hardware store ? No, the flare connections for refrigeration are a different specification. They are "wrot" brass, and are stronger than the standard hardware ones. We sell fittings on our web site. |
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[To recharge a refrigerator that has no charging valves on it, after fixing the leak:]
You can buy bolt-on line-piercing charging valves. Any refrigeration parts store should have them. Example: Supco "Bullet 3-In-1 Line Tap Valve" |
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Re: DIY Kit Experience - it works!
I assembled System 1 but made it water-cooled. I read the Calder book, tried to make sense of the calculations and decided, with some help from the Forum, to go for it. I would like to thank the Forum Tech, the Frigoboat guy on the forum and Alan, below, for their advise and help. I have a stainless box (3 cuft freezer + 4 cuft refer, front loading) built into my 45' Catamaran with a lot of nice maple cabinetry, so I decided to use it. Not the ideal but it was already there and someone spent a lot of $ on the box. My timing was a bit off since I did most everything before the DIY systems, and instructions, appeared on the site. I am happy to report that the system works well, I learned a lot and saved some money in the process. Having read through the new instruction manuals and compared the recommended way with the ways I used, I conclude there are a lot of ways that work. Fortunately, I did not make any serious mistakes. Below are some observations that might help others. 1. I used the Aeroquip Quick Disconnects. This allowed me to pressure-test (120 PSI and soap bubbles) to find leaks (one solder pinhole and a few flares that needed tightening), disconnect the pieces and take them to a service shop (Swedish Marine in SF Bay Area) for evacuation and charging. I then installed the system, connected the components and fired it up. The service guy, Alan, at Swedish Marine was one of the original founders of RParts! He offered many words of wisdom as we evacuated and charged my system. 2. I found the high-temp silver solder (brazing) to be easier to work with. It came with the flux on the rods and flowed much better for me. The danger I learned is that the fittings, like the RParts water cooled condenser, are brazed. I used a heat sink like a wet rag and sheet metal to deflect the heat from the torch. For the disconnects, I placed then in a bowl of water that covered the brass but left the copper uncovered. This way the end of the fitting was a couple of inches from the brass part that houses the rubber seals. Both worked well in that the plastic covering on the condenser was not affected and the discoloration on the disconnect only got halfway to the brass component of the disconnect. 3. I got a controller from Frigoboat for the BD50 that allows me to set the RPM from 2500 to 3500. Without the controller the compressor runs at 2500, I am told. 4. RParts is a web-based company. They do not hold your hand, answer questions or otherwise operate as a normal retail store. Hey, it's their business model and they can run the company the way they want. The Forum answers most questions from what I can see, but there is no one to call at RParts for help. They do get you the parts. I ordered the disconnects on the web at about 4 PM PDT with overninght delivery. At 9 AM the next morning the UPS truck was at my door. Great service. ... |
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I recommend pressure for leak testing. Vacuum testing isn't adequate, as vacuum pressure is less
than 15 psig, and since it is sucking, it is quite possible the leak won't show up due to flux,
grease or other debris plugging the hole during suction. An internal pressure of 150 psig supplied
by nitrogen or CO2 will be much more effective for finding leaks. Soap bubbles are a good way of
finding leaks, also watch for a pressure drop over several days. Some of the nitrogen or CO2 will
go into solution with the oil, especially with a temperature drop, but this should be less than 3
to 5 psig per day, and will usually stabilize after the first day. If the temperature doesn't
drop, the pressurizing gas won't go into solution as readily.
Dyes work well, but the system usually has to be run for a while before the dye will show up, and once the dye gets spread around, it can be hard to pinpoint the leak. |
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We might be replacing our refrigeration system. Currently we have an older Grunert AR-50 DC
system. We're starting to have some problems, and the guys at Cay Electronics are saying that we
might just be better off replacing the system, as ours now is about 16 years old.
Cay has offered a reasonably decent deal just to swap out a new Grunert system for the old, which would keep the existing plates, etc. They are recommending, however, that we consider the SeaFrost BD system which is both air and water cooled, so it has a little bit more flexibility. |
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Before you decide on a replacement refrigeration system, review the slide show on my web site. If
you are to replace the compressor and keep the holding plates, make sure the compressor's output is
equal to the old unit's capacity. If the tubing in the holding plate is 1/2 OD then a 1/2 HP is the
minimum size replacement compressor. If the boat has a generator onboard or has spent time
connected to shore power I would also replace the seawater condenser.
Sixteen years is not an old Grunert unless the boat was used as a full-time live-aboard or has water damage. One comment, there is no such thing as a bulletproof boat refrigeration system. Grunert, Frigoboat, Crosby, Adler Barbour, Technautics, Sea Frost all have excellent systems. The trick is to select the correct system for your application. If part of the box is to be a freezer and you plan on cruising in the tropics, sixteen year old insulation will have lost much of its insulation qualities. ... All closed-cell foam insulation breaks down over time, allowing the trapped insulating gas bubbles in the cells to escape and be replaced with air containing moisture. Polyurethane ridged and spray foams are the most common foams used in refrigerators. What percentage of an insulation's R value is lost in ten years or twenty years is not something manufacturers would want to make available. I have heard the figure of 15 years used as the service life of closed-cell foam insulation, but not from any credible study. From my own experience there is two inches of spray foam in my 21 year old boat's refrigerated box. I see no measurable change in heat gain over the years but this observation means very little . So I still feel it necessary to point out the fact that insulation does age and become less effective over time. It is also my opinion that only boats with low-temperature freezers cruising in the tropics, need to be overly concerned about replacing dry old refrigerator insulation. If insulation is found to be wet then it must be replaced. |
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I have always felt "ripped-off" by the prices that "marine" fridges command.
We bought a domestic underbar refrigerator. It is modern, made with the latest insulation material, clean, white, and has natty little racks that the women in my life love. It has a small freezer compartment up at the top, and all the goodies in the door too. It came with a 220v 90w motor, and a 220v 15 watt courtesy light. I got a Danfoss BD 35F compressor and a 15w 24v lightbulb, and fitted them. It starts about 3x per hour for 7-10 minutes and consumes 2.3 amps at 24v including the fan. The charge is 47 grams of R134a. It has a concealed condenser using the case for radiation. We are thrilled with it. The fridge cost 149 Euros and at that price I can afford to replace it every 2 years for the next 8 and still won't be close to the ridiculous overpriced madness that we are subjected to. Most of the compressors are made in the same place regardless of the brand name anyway. |
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| Best book I ever saw on troubleshooting R12 systems was a Sam's manual on Automotive Air Conditioning by K. L. McDonald. Doesn't cover anything marine, but the principles still hold. |
| Moisture on the outside of a refrigerator indicates the insulation is poor. Moisture inside a refrigerator indicates moist air is infiltrating into the box. Any time an object is ten degrees colder than the air, moisture will collect on the object. Moisture always collects on the refrigerant evaporator and forms frost in a refrigerator. Trying to eliminating evaporator frost by insulating it is not the answer. Keeping moisture out of the box is the answer. |
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Air-cooled refrigerator:
Touch the cooling coil on back. Where it comes out of compressor, and probably goes to the top of the coil, it should be almost too hot to touch. At the other end, probably at the bottom, it may still be warm but you can touch it. If you can touch it everywhere, needs Freon. |
| A refrigeration engineer told me that the air in the fridge or freezer doesn't really hold that much cold. When you open the door the impact has more to do with the entry of moist air, not the loss of "cold air". We see this especially in freezers and the ice buildup due to the moisture in the air that enters the freezer. |
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