Syzygy Sailing

I built this:

Out of this:

I read Nigel Calder’s “Refrigeration for Pleasureboats” three times, I read Richard Kollman’s forum on marine refrigeration, and I spoke with Marcus a few times (a fellow cruiser-friend in the marina).  Marcus is lending me his top-quality, indispensable refrigeration tools (much thanks to Marcus!), and also turned me on to RParts, where I ordered all my stuff.  I learned how to “sweat” copper tubing (i.e. silver soldering copper), how to form flare fittings, how to use a refrigeration gauge set, the detailed principles behind refrigeration, and I built my own refrigeration system.  I’m pretty proud of this 1.5′ x 1.5′ x 1′ cube of refrigeration goodness–it’s hard to believe that a month ago I didn’t understand how this thing worked, and now I’ve built my own out of parts.  It’s not making anything cold yet, but I pressure tested it yesterday and to my immense satisfaction and relief I have no leaks!  (that’s huge–to find and fix a leak would have been a nightmare)

Refrigeration is a lot more interesting once you understand how it works.  You don’t want to hear the details, but I have admin access on this blog so I’m going to tell you all about it.

—————————————————————————————————————————

A refrigerator works by moving heat from one place to another.  It does not “create” cold.  Heat is removed from the icebox and deposited at the “hotbox” (that’s my own term, it will be helpful for the discussion).  On our boat, the hotbox happens to be the storage space under the quarterberth; for your fridge at home, the hotbox is just the space behind the fridge.

On each side of the circuit there is a heat exchanger.  The heat exchanger transfers heat from the air to the refrigerant in the icebox, and from the refrigerant back to the air in the hotbox.  The heat exchanger in the icebox is called the evaporator; the heat exchanger in the hotbox is called the condenser.

The refrigerant is the medium that moves the heat around the circuit.  If the refrigerant was simply pushed around in a circle, it would not be inclined to transfer heat out of the cool icebox into the warm hotbox–that would be trying to push the heat uphill, so to speak.  The key is to pressurize the refrigerant, using a compressor.  When the refrigerant is compressed, it warms up; when it de-compresses (expands) it gets cold.  The refrigerant comes out of the icebox medium-warm.  The compressor pressurizes the refrigerant, which heats it up.  Then the pressurized refrigerant passes through the condenser–which looks like a mini car radiator–and as the refrigerant passes through the condenser its heat is transferred to the air (just like your car radiator, in fact).  The refrigerant returns to the icebox at a mediumish temperature, but this time it’s pressurized.  At the icebox, the refrigerant is allowed to expand–which causes it to get cold.  The cold refrigerant sucks up heat as it passes through the evaporator.  Then the process is repeated.  Good diagram.

There’s one more principle at work: phase changes.  If you just pumped a liquid around in circles, from the evaporator to the condenser to the evaporator to the condenser, etc, then you might be able to remove a small amount of heat from the icebox and dump it at the condenser.  However, you can’t suck up much heat just by warming up a liquid and then cooling it off.  The real way to suck up heat and drop it off elsewhere is to use a PHASE CHANGE to your advantage.  The phase change is the key to the whole process.

Consider heating a quart of water in a pot on the stove.  It takes 320 BTU of energy to heat that water from 33 degrees F to 211 degrees–320 BTU to change the temperature of the water by 178 degrees.  Then, to heat that water only 2 more degrees, from just 211 degrees to 213 degrees, it takes 1934 BTU!  Because at 212 degrees, the H2O changes from water to steam; this is the phase change.  During the entire process of converting water to steam, you keep dumping in large quantities of energy and the temperature stays the same–all the energy goes into the conversion from liquid to gas.  The message is that the energy required to do a phase change from water to steam is WAY GREATER than the energy required to change the temperature of the water itself.

In refrigeration, we store our heat as a phase change of the refrigerant in order to efficiently transfer it from the icebox to the hotbox.  We don’t use water though, because we want the phase change to take place around the 20 degrees F in our refrigerator (not very helpful to us for it to take place at 212 degrees).  We use refrigerant specially formulated to undergo the phase change near freezing (in our case, R134a).

We pump a liquid to the evaporator, and then let it expand into a gas; that expansion to a gas sucks huge amounts of heat out of the box.  Then back at the compressor we compress the gas, which heats it up (essentially exchanging “pressure energy” for heat).  Then we send it through the condenser, where the the hot gas dumps off all its heat and turns back into a liquid (condenses!) in the process.  Then we sent the liquid back to the evaporator, where it turns into a gas again . . . and so on.  The refrigerant goes to the icebox as a liquid, but it returns as a gas; the phase changes that happens in the icebox and the hotbox are the primary means of temporarily storing the heat in the refrigerant for transfer from one location to another.

Refrigeration is by far the single largest energy sink on a cruising sailboat.  In the average residential home, refrigeration is 5% of the energy bill–not an insignificant amount. One site says that the average fridge uses ~$8 of electricity per month, depending on how big, what kind, and where you live.  The efficiency of the refrigeration system depends very strongly on the refrigerant dumping off heat as it passes through the condenser.  Most systems use air-cooled condensers (I put in both air-cooled and water-cooled condensers–the air-cooled is the radiator-looking thing in the picture above; the water-cooled is the black circle of tubing on the top of the apparatus).  If the air-cooled condenser is located in a cool spot with good air-flow, this heat dump can happen very effectively; if the condenser is located in a hot spot with stagnant air, or even worse in the hot engine room, then the refrigeration cycle’s efficiency plummets.  Meaning that the fridge runs much longer, and consumes much more power.  Moral: the quickest improvement you can make to reduce your energy needs on a sailboat is to improve the air circulation around the refrigeration condenser.

You can do the same for your fridge at home: just pull the fridge away from the wall an extra inch, and you’ll greatly increase the air-circulation around the condenser, improving the efficiency.  Avoid shoving plastic or paper bags between the wall and the fridge for storage–that’s not helping out your fridge, or your electrical bill.  Even better, use a vacuum to clean off the condenser tubing on the back of the fridge–that gunk kills the condenser’s ability to dump heat.

To document our energy budget, let’s start with the sources of our power. 

1. Sun: Solar Panels
Planned installation: two kyocera KC 85 panels mounted on top of the dodger, currently available at Wholesale Solar for $410 each.  They are 85W panels, and can be expected to output an average of 20Ah each, so 40Ah each day from solar.  Naturally, these numbers vary wildly depending on how sunny it is, how high the sun is in the sky, and whether our mainsail is blocking the sun from hitting them. 
daily contribution: 40Ah

2. Wind: Wind Generator
Planned installation: KISS wind generator, recommended by cruisers for its simplicity, quietness, and low startup speeds.  Cost: $995, not including the mounting of it.  Wind generators provide a decent amount of power in winds over 10 knots, and plenty of power when the wind is 15knots or above, but almost nothing below 10 knots.  So it is hard to estimate how much energy we’ll get from them on average.  The output curve of the KISS claims ~4A @ 5 knots (I’m skeptical) and 10A at 15 knots.  Let’s use a ballpark estimate of 4A for 10 hours a day average.
daily contribution: 40Ah

3. Water: Tow Generator
We own a tow generator that came with the boat–I do not know what brand it is or anything about it (there are no markings of any kind).  It mounts to the port toe-rail, and a 100ft line is tied to a propeller on a weighty shaft that drags behind the boat.  The propeller rotates, twisting the line, which then turns the generator.  From the various things I’ve read all over the internet, I expect it will produce 6 A at 6 knots of sailing speed, and in doing so slow down the boat by half a knot.  It’s difficult to estimate how fast we will be sailing on average–we’ll probably average right around 6 knots when we are sailing, so on passage we would derive 144Ah a day, but we’ll only sail on average one of three days, so call it another 40Ah a day.
daily contribution: 40Ah

Total clean energy sources: 120Ah per day

4. Diesel fuel: Engine Alternator
We have a "Silver Bullet" 165A alternator mounted on the engine.  After breaking the mounting bracket twice, the previous owners turned it down to a maximum output of ~110A.  This is considered a "high-output" alternator (stock alternators are 65A) and will produce the remainder of whatever our daily deficit ends up being, thereby balancing our energy budget.

Those of you out there who have more accurate estimates of daily production for the above sources, please share!

The Amp-hour, Ah for short, is the currency of energy on the boat.  Every electrical device on the boat has an amperage rating; multiply the amperage rating by the number of hours it runs, and you get the Amp-hours that it consumed.  The stereo, for example, consumes 0.5 amps.  If I listen to music for 3 hours, I have used 1.5 Ah of energy.  Our battery capacity is currently about 130Ah (we will replace and upgrade the batteries before we depart).  So I could listen to music for 260 hours straight without recharging our batteries.

The electrical panel on the boat has both an ammeter and an amp-hour counter.  We can use the ammeter to determine the precise amperage of any device on the boat, and the amp-hour counter tracks exactly how much energy we have stored in the batteries.  At any point in time we can immediately measure the effect of turning something off.  When we open the icebox to get a cold beer, half of the time it will cause the refrigeration compressor to kick on for cooling: the ammeter shows the spike in energy usage.  In this sense, the energy cost of even the simplest conveniences is noted on a digital readout.

Everyone loves to talk about lights, to compare the energy efficiency of various lights.    We have three different types of overhead light on the boat: incandescent, compact fluorescent, and LED.  These are the same choices that we have for home use.  On the boat, we have measured exactly how much energy each uses.  The incandescent uses 1.5A, the fluorescent .75A (on the brightest setting), and the LED .05A.  The incandescent uses 30 times more energy than the LED.  In our world, that means we could use the LED for 30 times longer than the incandescent before we use up our batteries. 

You can do some of these same calculations for your own home.  The currency of electricity in the domestic house is the kilowatt-hour (kWh), and every device has a wattage rating.  Our amp-hour is your kilowatt-hour.  To find the number of kWh consumed, multiply the wattage of the device by the hours it runs, and divide it by 1000.    A 100 watt lightbulb, left on for 5 hours, will consume 500 watt-hours; divide that by 1000 gives you 0.5 kWh.  The average cost of a kWh in california is 12 cents (US average is 11 cents), so it costs 6 cents to leave that lightbulb on for 5 hours.  Thus we come to the real reason why people aren’t doing more to save energy and to reduce carbon emissions: on land, POLLUTING IS CHEAP.  People can talk all they want, but realistically they aren’t going to change unless it directly affects them, and energy is just too cheap for people to notice the cost savings. 

Let’s compare home to boat.  With a single conversion factor we can convert home energy measured in kWh to sailboat energy measured in Ah. You may be surprised: 1kWh = 83Ah.  The moral of that story is that it takes a whole lot of amp-hours to make a single kilowatt-hour.  Our new batteries will hold about 500Ah, and a kWh costs 12 cents, so with a little calculation you can figure out that the value of the energy stored in our fully charged batteries is $0.72.  Yeah. 72 cents.

The purchase cost of those batteries is over $1100, but the value of the energy they store, fully charged, is less than a dollar–that’s the sailboat for you!  Remember those SAT analogies?  Here’s the sailing version:

land life :: sailboat life
73 cents :: 1,100 dollars

So, energy is not cheap on the boat.  Energy is cheap on land and there’s no incentive to reduce consumption–hence the polluting nature of our modern society.  But on the boat, we will spend $1200 on batteries for storage, $1100 on a wind generator, $1200 on solar panels, and we already own a $1000 tow generator.  And even with all this money spent on energy creation, and carefully counting every amp-hour made and used, we will probably still have to run our engine occasionally to make up an energy deficit–and that will cost us in the price of diesel fuel.  As a result, on the sailboat we are motivated to monitor energy usage in a realistic, practical way, and we are directly rewarded for saving energy.  And this is only one of many reasons why sailboat life motivates us to live SIMPLY and to live CLEANLY.

 The front cover of the March National Geographic Magazine is titled "Saving Energy: It Starts at Home".  The article follows a few families trying to track and reduce their carbon emissions, by measuring and reducing their energy usage.  The article describes how these families have a hard time figuring out how much energy they are actually using, where it’s all going, and what techniques can legitimately alter their consumption. 

On the sailboat, we can instantly measure the energy savings of any flip of any switch.  I got fired up reading the article, because I realized that we have so much more real information and feedback to offer.  The sailboat is a miniature model of a self-sufficient society, complete with energy creation, storage, and consumption, and it’s all on a scale that can be measured and monitored and understood.  We make our own electricity and we store it in batteries.  And we can track every bit of energy that we make and every bit that we consume. 

Moreover, when we are out in the middle of an ocean, tracking our energy usage will not be some leisure exercise without consequence, as it was in the Nat Geo article.  If we don’t make enough energy with our few sources, or if we use too much energy with lights or the radio or any number of other devices, then the important systems on our boat will turn off.  Our lights will go out, our navigation instruments will go dead, we won’t even be able to start the engine.  Sure, we can always keep moving–provided there is wind–but we would be loathe to do so without such basic safety items requirements as nav lights at night, a radio for emergency communications, or a gps for navigation.  Keeping track of our energy usage will become a crucially important aspect of daily existence–not a mere exercise for the purpose of writing a magazine article.

—Future installments of the Energy Accountability series will describe the details of our electrical system and our efforts to balance our energy budget—stay tuned

I grew up on a farm, and all my life my father has been bashing gasoline engines and lauding diesels. He wouldn’t buy any vehicle that wasn’t a diesel, and we had two 1,500 gallon diesel tanks around by the barns–one for on-road vehicles and one for the tractors. As a result, I grew up plugging the diesel suburban into an extension cord in the winter, and waiting to start the car until the glowplugs–whatever the hell they were–warmed up the engine. Meanwhile, in their gasoline vehicles, my friends could fill up at any gas station and accelerate from 0-60 in something significantly less than the 30 seconds it took in the suburban. I wrote off my father’s opinion as old-fashioned, ultra-conservative, non-progressive, and wrote off our diesel vehicles as too loud, too much work, and too slow.

I’m home now, back around my dad, and back into the diesel debate.

Never in a million years would I have guessed that one day I would know how to sail (?), that I would own a sailboat (!?) and that the sailboat happens to CONTAIN A DIESEL ENGINE (!?!). And never ever ever would I have guessed that one day I would agree with my father about the benefits of diesel engines. Don’t be mistaken: I have done my own research and come to my very own, independent conclusions. They just happen to be the same conclusions as my dad’s.

Continue reading “Home for Christmas (or: diesel vs gas)”