On Refrigerators and Cold Beer
19 05 2011 Posted by Daniel
Ah, refrigeration. If soap is the yardstick of civilization, refrigeration is a reference standard of the First World and all that connotes. And, like a First World mindset, refrigeration or the lack thereof evokes strong emotions when discussed by sailors. Many sailors, even modern-day long distance ones like Jessica Watson, eschew “the fridge” for its space consumption, energy demands, and perceived unreliability, being willing to put up with a lack of cold beverages and food as the price of simplicity and self-sufficiency. Others, particularly those from larger cities in the U.S. and increasingly Europe, view a refrigerator aboard a boat as an absolute necessity and fundamental human right, up there with pressurized hot water, daily showers, in-mast reefing, and powered winches. While I’ve been aware of these differing views, I’d not paid too much attention to the differing viewpoints; my mind had been made up for me in the form of a boat which fortuitously came with a working fridge. Little did I know how quickly this would change.
Queue The Introspection
A few days ago, after a thoroughly exhausting overnight regatta [in which my valiant crewmates and I utterly vanquished our faster and professionally-crewed opponents aboard more “modern” race craft], I returned to my full-keeled, slightly chubby but solid and faithful ketch-rigged cruiser to find that I had suddenly been transported to the Second World. Or maybe even the Third, depending on how close to Manhattan you take your survey.
In short, my fridge had completely died. Given up the ghost. Gone to Davy Jones’ Locker. Rode the final wave. You get the picture.
Let’s skip the troubleshooting I went through, the initial diagnosis, the attempts to revive said device, and even the final “I’ve done all I can let’s contact the pros” phone call. The latter of which, fortunately, ended up being to an honest guy who sold me straight without having to make a “boat call”. The upshot is that I am currently without a refrigeration device with which to ensure optimum beer drinkability. (I should note that the Prime Directive of all refrigerators — indeed their very raison d’être — is to keep beer at proper temperature. This temperature varies by culture but is nearly always cooler than typical spring, summer, and early autumn outdoor temperatures in most cruising zones. Hence the fridge. Freezers on the other hand are for two things: ice for mixed drinks, and ice cream — both of which are for keeping the ladies happy. Its simply fortuitous that I also happen to like ice cream and iced mixed beverages upon occasion.) And despite my efforts to temper my First World upbringing with the sensibility attained with my Third World humanitarian aid experiences, I began to view this as a Serious Problem. Maybe consuming all of the beer before it got warm had something to do with that. Of course, I could have just gone out and bought a 20-lb sack of ice, but after all that beer, it wasn’t the first thing that came to mind.
Upon waking up the next afternoon, and after considering the usual questions, those being “how much would it cost to get a replacement for my unit” ($1500 + labor), “how much are competing units” ($1000-$3000 depending on quality), and “how much of a pain is this going to be” (a lot), I began to regain my sanity and start thinking outside the box.
The question then became “do I even need a fridge”. And so I started diving into the subject, both conceptually and investigatorially. I thought about what I was giving up, what I was gaining, and what I wanted. I thought about cost, failure modes, and expectations. I thought about paying for convenience, sustainability, energy efficiency. The ideas of waste, manufacturing and shipping, raw material usage, and consumerism crossed my mind. And so, I started thinking about where the line was between getting a fridge and not getting one. If I were to get one, it would have to last for an extremely long time. It would have to be made of materials that were largely recyclable, minimize use of plastics, be exceptionally efficient, and provide maximum utility. In short, I wasn’t about to buy a cheap piece of crap, if I bought one at all, and it would have to show some kind of exceptional durability, re-use potential, and extreme energy efficiency to make the cut. If I was going to have a fridge, it would have to earn its keep.
Anatomy of a Boat Fridge
The usual boat fridge is essentially a cabinet, framed on the back side by the rounded shape of the hull, and on the other sides typically by marine plywood which forms both the fridge cabinet as well as serving as a bulkhead or a component of other interior woodwoork. Heavy insulation is applied to the inside of this cabinet - sometimes taking the form of fancy vacuum panels or aerogel inserts, and sometimes simple styrofoam board, cut and laid in by hand. The mechanism of refrigeration, that is to say the compressor, expansion and condenser coils, and thermostat control circuit, are separated into various components, with the evaporator (the “cold” coils) placed inside the cabinet1 and the compressor and condenser (the “hot” coils”) placed outside the cabinet, usually in the engine compartment or some other remote location out of the way. When the unit runs, the evaporator coils in the cabinet get cold, often below freezing, and cool the air in the cabinet, as well as usually creating ice in specially designed trays attached directly to cold plates on the coils.
To put it more directly, the refrigerator is a complicated system that is built into the boat structure, connected by intricate piping, and insulated during the design and building phase of the actual boat’s interior. It is the exact opposite of the appliance which you find in a modern home, where the cabinet, insulation, and refrigeration mechanics are all integrated into one cohesively integral unit which can be transported and moved about at will. Boat owners like the “built-in” approach because it often provides the maximum refrigeration storage space. But what it does not provide is a well-matched refrigeration system and thoroughly optimized insulation - in short, its usually highly inefficient. Expensive boats with well-engineered refrigerators have fantastic efficiency - and well they should: a typical high-end “reefer” on such a boat often represents $3000 or more worth of investment. But the problem remains: when they break, and they will all break at some point, it usually means replacement of the entire mechanical system, which often requires serious carpentry. On my boat, though, the existing cabinet is so poorly insulated as to be nearly a joke - even in relatively mild 26.5 C (80F) weather my fridge compressor was working hard and consuming a lot of power to keep a cool temperature (power is in short supply on my boat when it is not at a dock, as it runs on batteries which are charged by solar or wind power). If I were to refit a new unit, regardless of its mechanical efficiency, the cabinet would need upgrading too.
And then, just as this project started looking enormously overwhelming, I was reminded of a concept that changed everything.
Enter the Mobile Fridge
I’d known about mobile refrigeration units since I was a teenager in the Boy Scouts. 4x4 camping, expeditions, and humanitarian aid projects often equipped themselves with vehicular refrigerators - highly efficient integrated units with DC power supplies, high-tech insulation, and modest but acceptable internal space. Hell, a lot of fellow sailors on smaller boats had them. I’d somehow never thought about them on a larger boat - namely “my boat” - because mine had a built in fridge. But while I was researching boat refrigeration, I stumbled upon an old post on Boat Bits that reminded me how sane of an idea it was. The kicker isn’t just efficiency, as important as that is, its long-term reliability. Boat fridge units are notoriously unreliable and inefficient, often requiring the engine to be run to generate enough power (or in extreme cases to even produce refrigeration power at all!). In the hotter climes its not uncommon for them to be breaking down within months of the last repair due to high duty cycles and thermal overload. But these mobile units were designed specifically for these harsher environments, with insulation and refrigeration mechanics well matched to each other and designed purposely to deliver 100% performance in blistering 43.5 C (110F) heat while consuming a very modest power draw suitable for solar or small vehicle power. The Boat Bits article specifically mentioned some Aussies who had excellent and highly reliable self-contained fridges aboard.2 And I just so happened to have a fantastic magazine at hand which reviewed the most revered of these units worldwide: Overland Journal.
After reading the Overland Journal refrigeration reviews and doing a vast amount of online research, I’ve made my decision as to the unit I’m getting. Here’s a hint: it has both a fridge and a freezer compartment. Its pretty small but that is fine by me. And it consumes a running average of only 0.83 Amps at 12.6 volts in 32.8 C (91F) heat3, 4. Ridiculously efficient, legendary reliability, and an installed base the world over.
But to find out exactly which unit, you’ll have to wait. There’s a cabinet to demolish and some carpentry work to do before my new fridge has a home. But trust me, when she’s in place, you’ll hear about it.
Footnotes:
1 For you refrigeration geeks, I am deliberately simplifying the description and omitting discussion of cold plates, engine-driven refrigeration compressors, etc…
2 In the same article, Bob at Boat Bits also mentioned a Stirling Cycle driven refrigerator made by Coleman and co-branded by Tropikool, but it seems as though that model isn’t available any longer. Available power data suggests that the fridge I am buying now is equal or more efficient in terms of power (though not in cost, sadly) and has similar expected longevity (e.g. it should outlive me).
3Doing the power calculations, that means that in a typical region of the world with only 4.2 average hours of peak sun per day, a 70W solar panel and decent storage battery can keep up with the fridge’s power needs.
A more thorough discussion on refrigeration and power consumption would take a full article or two, but here is a quick and dirty summary of the basic concepts. Let’s say a fridge benchmarks at 0.83 Amps average @ 12.6 V and 33 C (92 F). That equals 10.46 Watts average consumption, 24 hours a day. Solar panels are rated at peak power output under normal temperature, so they need to be derated to include the fact that hot days make them produce less power, as well as the fact that during the day the sun is not always shining at maximum brightness. To compensate for the first is a bit complex, but a typical derating of 10% for higher temperatures is usually a good rule of thumb, and 20% can be used in extreme situations. To compensate for the amount of actual sun you get in a given region is also complicated but typical values for a given region can be found. For instance, a broad portion of the US in the midwest and southeast gets 4.2 equivalent peak hours of sunlight per day, which is another way of saying that if you add up all the sunlight you get from sunup to sundown it approximately equals 4.2 hours of direct overhead noontime sunlight, which is what your panel is generally rated at. Putting these values together gives us 0.83 A x 24 hours = 19.94 Ah total use during the day. 19.94 Ah / 4.2 peak hours = 4.74 peak amps the solar panel will need to produce. 4.74 A x 12.6 Volts = 59.82 peak watts the panel will need to produce, at minimum. Factoring in a 10% derating gives us 66.5W, call it 70W to take care of some other small inefficiencies. That will handle this fridge in typical heat throughout a day. Remember, though the fridge is rated at 91F, a blistering hot day is usually still significantly cooler at night when the solar panel is not producing any power. The averaging of the power draw versus the solar power production means that even in extreme cases, a significant increase in panel power is not necessarily required. In fact, even in an area with extensive cloud cover and rainfall, factors which reduce the panel’s power production, much more than a doubling of panel capacity (along with a suitable storage battery) is not needed as the temperatures are also reduced when the cloud cover and rain are present, reducing the fridge’s demand on the power supply commensurate with the reduction in power production. Again, these are oversimplifications, but they are suitable for beginning calculations and introducing the basic concepts in self-sufficient refrigeration and power generations. Technologies such as these are critical in introducing both the luxury and life-saving abilities of refrigeration to remote communities without solid infrastructure, and reliable and well engineered equipment is, in the long run, more affordable and less wasteful of resources.
4 I happen to (currently) have 2x135W solar panels, or nearly 4x the average estimated need for this fridge. I powered that much up because it was only 2x what my last fridge drew. That’s how serious the difference in efficiency is here.
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