Archive for the 'Refrigeration' Category

Refrigeration

I (Jon) finished these jobs variously on March 15th.

The refrigerator was malfunctioning in some unknown way. It was exhibiting signs of electrical issues and of having moisture in the refrigerant lines.

To deal with the electrical issue, I checked all of the connections from the fuse panel to the switch in the fridge. All seemed to be reading fine. I pulled the switch off inside the fridge, fiddled with the electrical connections, and that was about it. I’m not sure if I actually did anything but electrical problems have since gone away.

Concerning moisture in the lines, we have suspected that we have a pinhole leak in the system. The pinhole was perhaps caused by one of the drawers in the frig not being locked in place and then when the boat was rocking back and forth, the drawer could have hit the evaporator plate.  However, other evidence suggested that there was not in fact a leak. The refrigerant would normally leak out when the icebox temperature rose to room temperature, for example when the top was opened for a couple of hours to clean it out.  However, I went to the States for a month and when I came back the plate frosted over perfectly. Nothing was particularly clear.

I vacuumed down the system for hours and hours to try and draw moisture out. This did not seem to help. But as the electrical system was simultaneously acting up during all this, I can’t be sure what the problem was.

I then had a bitch of a time finding more coolant as we were running out. In Australia, you are not allowed to work on your own refrigerant systems. Nobody does, so you can’t buy coolant. The coolant we did have came from Mexico and the tops of the cans were different than the tap we had. I had to spend a week just trying to find a way to usefully open the cans. The fridge topped off a month of hellish frustration at Australia and work on the boat.  Oh, you also aren’t allowed to import to boat to sell it here in Australia if it has a refrigeration system that uses liquid/gaseous refrigerant and can be worked on by you. You either have to pay thousands of dollars to get a certificate stating you are a refrigerant mechanic, or declare that its not a refrigeration system, just an icebox that you fill with ice. Australia is obscenely heavily regulated. Finally, another boat blessedly gave me some of their refrigerant so I could continue this process.

Since nothing else seemed to be working, I took Matt’s suggestion and tried patching the leak. Kollman talks about using JB Weld to patch tiny holes. Matt said I should go with thickened West System epoxy, as he thought that Kollman wouldn’t have much experience with epoxy and that it might be better.

So I cleaned the whole thing with acetone, roughed up the area around the possible pin-hole leak, taking off the paint in the process, re-acetoned it, and then put on a larger than necessary splotch of thickened epoxy. I couldn’t make it very smooth and pretty looking, since there wasn’t anything to level it and I just needed a blob of it on one spot.

Finally, I did a long, long, long, vacuum down.

The fridge has worked perfectly for the last three months and undergone multiple complete warm-ups to room temperature. The electrical seems fine and it doesn’t seem to be leaking refrigerant or have moisture in the system. So I’m pretty happy that I was able to get the fridge back to running perfectly.

 

Built storage shelves for icebox

It quickly became clear that a wide open, deep icebox is extremely difficult to use efficiently–you spend all of your time rummaging through a stack of food, or have to remove everything to get what you want, or discover that containers have tipped over and spilled their contents.

I decided to built boxes out of acrylic, using the jigsaw to cut the pieces, the sander to take off the sharp edges, and the methylene chloride toxic stuff to weld it all together.

This is a process that I have used a couple of times now on the boat for working with acrylic, I believe I explained more of the details earlier.  Some of the details worth mentioning: cutting the acrylic with the jigsaw is frustrating, but doable with care and patience.  I use the wood scrolling blades; the metal blades seem to get gummed up and stall.  The blade just melts a path through the acrylic, which re-seals itself in places after you pass.  So then you have to go over the same cut a second time to free it up.  The blades get super hot and eventually snap, so you need quite a few of them.  There are special blades designed for cutting acrylic, but honestly I can’t tell the difference between them and the wood blades–perhaps they’re a bit more heat-resistant.

The methylene chloride is a nasty solvent, extremely volatile (evaporates very quickly), and very thin.  A respirator and good ventilation is a must, or you will surely kill brain cells.  The deal is that the methylene chloride melts the acrylic, which then rebonds as the solvent evaporates; the result is literally a weld–continuous acrylic–rather than a glue job.  It is important to get the surfaces as flush as possible along the entire length of the seam, which can be difficult when cutting with a jigsaw.  Because the solvent doesn’t fill in any gaps whatsoever; so only the areas where the surfaces directly touch will contribute to the strength of the bond.

There is a trick for applying the methylene chloride.   You use a little plastic bottle with a syringe cap.  You squeeze out the air in the plastic bottle, invert it and stick it into the container of methylene chloride, then let go and it will suck up into the plastic container.  You don’t need very much.  The you use the same method for applying: hold the syringe bottle upright, squeeze out a decent amount of air, then let go and invert the bottle.  While the bottle is sucking air, no solvent will come out even though it’s inverted.  Then you take the syringe and run it down the seam you’re welding, squeezing the bottle slightly to let the solvent drain out.  You will have 10 seconds or more to apply the solvent before the container refills with air and starts to leak out.

It’s best to clamp the two pieces of acrylic together.  But, if you have a second person and steady hands, you can sometimes just hold the two pieces together while you weld them; it should only take about 45 seconds for the bond to set.

It was a challenging problem, to figure out how to build the boxes such that they would fit down in the icebox.  At least one of the boxes I had to finish assembling inside the icebox–so that one will never come out without breaking it apart.  I put all of the boxes on rails–I used strips of starboard for this, nice and slick–so they slide back underneath the inaccessible sides of the box.  And I was paranoid about the box banging on the evaporator plate and damaging it, so I put extra effort into making blocks and stops that would prevent the acrylic from touching the evaporator plate.  After our first sail I discovered that I also needed to come up with a way to prevent the boxes from sliding back and forth while the boat rocked, so I used some cotter pins with keeper cords–works like a charm.  All in all, a very successful project.  No space is wasted and the system is easy to use.  It took a damn long time, but what’s new.

Refrigeration, pt 5 (FINAL)

Pt 1
Pt 2
Pt 3
Pt 4

I installed gauges in the countertop above the icebox: a thermometer (convenient to have one outside the fridge so you don’t have to open the box to check), a green LED that lights up whenever the compressor is running, a red LED to show faults, and an hourmeter to use in measuring the duty cycle.

Here is the wiring diagram for my system:

IceboxWiring

Also, here is a pdf for the Danfoss BD50F_compressor.

I did not install the plumbing or the pump for the water-cooled condenser–I’m going to wait to buy that stuff until hotter climates (other projects take priority).  Up in the bay area the air-cooled condenser is more than adequate, and more efficient than running the water-cooled condenser anyway.

The whole box is painted with two coats of Primekote and two coats of Perfection.

The icebox has stayed 32-38 for the past three weeks, so it’s working well.  We have been having some issues with the compressor short-cycling (coming on for two minutes, going off for three, back on, etc).  The situation started to worry me when we started getting the intermittent fault code of three red blinks: indicating “rotor blocked or pressure differential too high”.  I speculate that the compressor was trying to turn on again too quickly–before the pressure differential had sufficient time to equalize through the evaporator plate.  My research on kollman’s forum and the rparts forum tells me that the short-cycling is a result of too much of the thermostat sensor touching the evaporator plate.  I have pulled all but an inch of the sensor tubing off of the plate, coiled up a few inches away from it.  It seems to be working better, but I haven’t got a trustworthy data set yet to be sure.  Aside from that, the box is totally finished:

Refrigeration, pt4

Pt 1
Pt 2
Pt 3

Built a platform and mounted the compressor, and built/faired the lid for the box.  Glued down formica laminate, then painted with two coats of Primekote, sanding in between.  Almost finished, just have to put on the two coats of Interlux Perfection, mount a ring pull in the lid, then seal down the hinges and run a bead of caulk around the countertop.

Refrigeration, pt 3

Pt 1
Pt 2

I built this:

And I pressure tested it using Marcus’s tank of argon and refrigeration gauges (thanks Marcus!), and I have NO LEAKS.  It was a very exciting moment for me, I’m not going to lie, I was really proud.

Next step: fabricate mounting platform for it, wire it up, then vacuum down the system and charge it up.

I’m working long days (paid work I mean) for a few months though, so I don’t have much time to work on boat stuff.

refrigeration, pt 2 (building a compressor kit)

refrigeration pt 1

To recap: initially I was going to buy an Adler-Barbour Cold Machine, hook everything up, and be done with it.  After talking to Marcus, I decided to order all the parts from Rparts.com and build my own.

I ordered the 1M kit, which uses an air-cooled condenser and the Danfoss BD50 compressor, and comes with a small evaporator box.  Extra things I bought beyond what comes with the 1M kit: the small evaporator box is both too small capacity-wise and doesn’t fit well in our icebox, so I also purchased a large flat-plate evaporator, unbent, and we’re going to bend it ourselves (they wouldn’t switch out the small box for a large flat plate, but they gave me a 20% discount on the extra one, so I got it for $80).  I wanted to have both air- and water-cooled condensers, so I bought a water-cooled condenser which I am going to figure out how to mount and plumb in somewhere.  I bought a 40 amp relay to use for powering the water circulation pump, and an analog thermometer to mount outside the icebox.

The excellently written manual for the 1M kit is here.

It all arrived today.  It felt sort of like christmas, unpacking the boxes and discovering all of the parts.  I took photos of all the stuff spread out on the floor.  Below the black foam tubing are the extra parts beyond the 1M kit (and the white flat plate evaporator on the right).

There are a whole lot of parts for me to put together!  And I won’t be able to start on it for at least another two weeks.

Refrigeration, pt 1

We’re in the process of redoing the refrigeration.  Unlike other posts, in which the job is already completed and I give a very brief recap, I’m putting down my notes and choices while currently working on this project.

Our compressor was kicking on and off erratically for a period of probably 6 months after we started using the boat.  Each time it stopped working, jonny would lose a bunch of food that went bad in the icebox, and then he would have to clean it out when it started smelling, etc.  Finally we gave up and Jonny has been living without refrigeration for 6 months now. Also, I decided from my research that the insulation in our box was inadequate: 1) it’s 30 years old (it deteriorates big time in r-value) 2) there was 1.5″ on the top and 3″ on the rest of the box; there should be at least 4″.

At first we made minor attempts to figure out what was wrong with the old system.  I wasn’t going to participate in that attempt though, because I was convinced that we would need a whole new system regardless and I didn’t want to sink any time into messing with the old one.  If I was going to go at it full bore, I wanted us to do it right: first reinsulate the box, then replace the whole refrigeration setup.  Jon and Jonny were not psyched about this idea–justifiably so, because it represented a collosal amount of work and a couple thousand dollars–and weren’t ready to pull the trigger on a new system.  I didn’t try to persuade them, I just said that I would let them take care of repairing the old compressor, then.  🙂

In April I started tackling it.  I drew up detailed plans for the box and a list of steps, so that we could move as efficiently as possible once we started.  I decided on 4″ all around of Blueboard–an extruded polystyrene made by Dow–for our insulation.  Blueboard doesn’t have the highest R value of all the insulations available, but it is the most impervious to moisture and that means that after just a year or two it might be outperforming your other choices (lots of people use polyisocyanurate foam–commonly available at home depot, it looks like yellow foam with a foil backing–it absorbs moisture pretty readily!).  The only place within 50 miles that sells the blueboard is Pacific Supply in South San Francisco, and the Dow representative I talked to told me that their west coast machine only makes boards 2′ wide. The design of the lid is the hardest part.  You want it to ideally have the following features: double gaskets (top lip and bottom lip), flush mounted in the counter, minimal gap all around, angled front surface so it will open without jamming, easy to clean pretty finished surface.  Since you build the box from the bottom up, it can be tricky to get the interior of the box and the countertop to be perfectly spaced for the exact thickness lid, etc.  There are many ways of building it–the easiest is to buy a premade one for ~$500, from Glacier Bay for example.

Initially I knew nothing about how the refrigeration system worked, and I decided to buy an Adler-Barbour Cold Machine and evaporator plate, which come precharged with refrigerant and ready to go, and just hook them up and be done with it.  The total cost would be about $1300, and it could be installed in a day.  I was all ready to buy it when I ran into Marcus on the dock and stopped by to check out his new system.  Marcus was also in the process of rebuilding his whole refrigeration setup, including reinsulating (with vacuum panels!) two iceboxes, and building two compressor setups from parts himself.  He purchased all the specialized refrigeration tools necessary to do the work himself, including a vacuum pump.  Talking to him I was daunted by the amount of work and complication it represented, and in my mind I was still saying to myself “hell with that! I’m buying the adler-barbour!”  But Marcus suggested that I take a look at a website called rparts to at least see if there was a cheaper option for me.

I checked out rparts, looked at their do-it-yourself kits, looked at the list of parts contained in the kits, looked at the price ($800), and decided that maybe I would learn how to do refrigeration after all. So I downloaded the installation manual for the 1M kit they sell, and using the manual and the rparts website and Kollman’s forum I sat down with Calder’s refrigeration book (which I had already read twice, without much illumination) and figured it all out finally.  With the right combination of resources, each section of Calder’s book was now like a lightbulb going on.  It was gratifying to finally understand an area which had previously seemed so baffling to me. I am extremely indebted to Marcus for inadvertantly convincing me to learn it and do it myself.  “Do it ourselves” is our modus operandi for everything else on the boat, and it was out of character for me to want to simply pay money for a setup and not have to think about it or understand it or put in ridiculous amounts of time and labor for its installation.

I started by dorking out with Calder’s refrigeration book, and measured our box to calculate the surface area and thereby estimate the heat loss, in order to size the refrigeration capacity appropriately.  Here is my diagram:

IceboxAreaCalculation

You can think of the refrigeration system as a closed circuit of refrigerant with two heat exchangers: the heat exchanger in the icebox is the “evaporator”; the heat exchanger mounted with the compressor is the “condenser”.  The compressor itself is a just a refrigerant pump; it is the block ovoid shape easy to recognize in most pictures.

There are two common types of evaporators: the “evaporator plate” and the “holding plate”.  The evaporator plate is the simplest, cheapest, most maintenance free of evaporators.  It is a roll bond aluminum plate–“roll bond” describes the manufacturing process–that contains a network of channels through which the refrigerant passes.  Inside the icebox, the refrigerant passes through the plate and makes it cold, and then the plate cools the air around it in the box (which is why the plate must have space on all sides of it, so that all of the surface is working to cool the box rather than just one side).  The holding plate is actually an evaporator immersed in a specialized fluid (a “eutectic” fluid).  The refrigerant passing through the evaporator freezes the eutectic fluid, and then over a number of hours the eutectic fluid keeps the box cold.  Essentially the holding plate is a big reservoir for holding the cold, just like a big block of ice.  With a roll-bond evaporator plate, the compressor comes on and off more frequently, for shorter periods of time.  With a holding plate, the compressor comes on much less frequently (perhaps as little as once a day) but runs for a long time to completely freeze the eutectic fluid.  Which is better?  Entirely depends on your system, and there is continued debate.

There are two common types of condensers: air-cooled and water-cooled.  The air-cooled condenser is a series of fins (not unlike a car radiator) through which a length of the refrigerant tubing runs, and usually there is a fan to blow air over the apparatus.  The hot refrigerant passes through this and hopefully cools off in the process.  Obviously this is more likely to happen if the air temperature where the condenser is located isn’t 120 degrees (if it is you’re totally screwed).  The water-cooled condenser is more like the heat exchanger on the diesel engine: it circulates seawater to cool a length of refrigerant tubing.  There are a couple different models, “tube in a tube” and “shell type”, take a look at the offerings on the Rparts website.  There are a few more exotic water-cooled solutions out there; the “keel cooler” is a design that takes the refrigerant to the ocean instead of bringing the seawater to the refrigerant.  My favorite is the tube in a tube type (maybe because Calder seems partial to those).  The refrigerant goes through the center tube, and an electric motor pulls water from the ocean and pumps it through the outer tube and then back out of the boat. Air-cooled condensers are simple and require power to run a fan (~.2A).  Water-cooled condensers are more complicated because they require plumbing seawater from a through-hull and back out, and require power to run a pump (~1.5A).  The water-cooled condensers are much more effective at efficiently removing heat from the refrigerant, but until the air temperature gets really hot, the additional power required to run the water pump outweigh the efficiency gains in heat transfer.  The cutoff point of efficiency is debated (and different for every installation).  Calder thinks that water-cooled is essential for a functioning system in the tropics, Kollman is completely against water-cooled because of the increased complexity, expense, and failure rate.

A refrigeration system is a heat pump–it moves heat from the evaporator to the condensers, sucking heat out of the icebox and dumping it off at the condenser.  If you just pumped a liquid around in circles, from the evaporator to the condenser to the evaporator to the condenser, etc, then you would indeed remove some 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. Consider a quart of water on the stove.  It takes 320 BTU of energy to heat that water from 33 degrees F to 211 degrees.  Then, to heat that water from 211 degrees to 213 degrees, it takes 1934 BTU.  At 212, the H2O changes from water to steam, and during that entire process 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 energy required to do a phase change from water to steam is way greater than the energy required to change the temperature. So we use that phase change to make refrigeration possible.  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 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 turns back into a liquid and dumps off all its heat in the process.  Then we sent the liquid back to the evaporator, where it turns into a gas again . . .

Once I decided that I was going to buy the kit and parts from Rparts and build my own system, I was free to design a system that includes both condensers:  air-cooled for cooler climates and water-cooled for when it gets really hot.  To alleviate Kollman’s concerns about the water-cooling, which I take seriously, I am going to take precautions against galvanic corrosion of the water-cooled condenser by electrically isolating it, and I’m going to wire in a PWM circuit so that I can turn down the power consumption of the water pump.

Jonny and I ripped out the old box in one day–the entire thing.  The next day I picked up 18 sheets of 2’x4′ Blueboard 2″ thick from Pacific Supply.  We lined the inside with a layer of aluminum foil, used spray adhesive to stick it in place.  I taped the seams with metal tape.  Then we made a huge mess cutting up the foam with the Dozuki saw–pretty easy and quick actually–and pieced most of the insulation in place. We bought two thin sheets of plywood and glassed over them with a few layers of fiberglass, then faired them smooth with quikfair, cut them to fit, and built a box inside the insulation.  Jonny glued all the edges together with fillets of thickened epoxy, then we sanded them fair, and painted the inside of the box with two layers of Primekote, an epoxy primer.

That’s as far as we’ve got.  I ordered the refrigeration parts from Rparts, and we need to wait to put the evaporator into the box before we put the lid on it and build the hatch for it.  So we’re probably 30% done with the job.