Constructing New Fridge / Freezer Boxes

[s/v Jedi]

Hi Giovanni,

If I would build it today, I would do it exactly the same. The energy consumption is dependent on box volume, insulation, weather conditions and on how much warm stuff is put in to cool, NOT on which model Frigoboat. Choose the Frigoboat components on alculated maximum cooling needed and switch to bigger unit when the math shows close to max. With smaller unit. For example: the BD50 has 5 speeds and will be better efficiency on low speed than a BD35 maxed out.

ciao!
Nick.

[olliric]

Originally Posted by s/v Jedi

Hi Giovanni,

If I would build it today, I would do it exactly the same. The energy consumption is dependent on box volume, insulation, weather conditions and on how much warm stuff is put in to cool, NOT on which model Frigoboat. Choose the Frigoboat components on alculated maximum cooling needed and switch to bigger unit when the math shows close to max. With smaller unit. For example: the BD50 has 5 speeds and will be better efficiency on low speed than a BD35 maxed out.

ciao!
Nick.

Hi Nick
Good to hear from you and thanks for the feedback. I think my boxes sizes are on the borderline between the BD50 and BD35 compressors or F160 or F200 evaporators and either could work. In the attached links there is a test that that shows that the BD35 could be a better choice. The BD50 has 25% greater capacity but it comes with a 40% increase in consumption.
I'll wait till the Italian Frigoboat are back from the holidays and see what they say. By the way, which evaporators did you use? I can't make it out from the pics.
How is your system doing when it comes to evaporator frosting? How often do you defrost in the tropics?
Here in Malaysia my home fridge needs defrosting every few days which is a major PIA. The ice in on the evaporator insulate it and it keeps the compressor going all the time.
I am thinking of installing a foil heater in the space between the evaporator and the box wall. Frigoboat has a thermostat with defrost function that can control it.
I have worked on walk in large refrigeration plants and they all have defrosting system. Without it the plants don't work well and it is impossible to reach very low temps (-20 or lower)
In my case the energy loss for defrosting is not a problem as at mid day I will have plenty of spare energy from solar. Even if I did not I could defrost any time I motor.
I don't understand why Frigoboat or others don't offer defrosting kits.
Cheers
Giovanni

http://www.veco-na.com/images/Fridge...eb_reprint.pdf
http://www.veco-na.com/images/Green_...ge_edition.pdf

[senormechanico]

I use a 1500 watt heat gun. It only takes a minute or two.

[olliric]

Yes, that is a simple way to go about it and the gun can be handy for other uses. The drawback is that you have to empty/refill the cell every time. Where do you sail and how often do you need to defrost? The frequency of defrost is key. I would not mind using the gun once a month but if I need to do it every 3 days then it would be a pain.
Cheers

[senormechanico]

When we were in Mexico (different boat with a cold plate) we defrosted about once a month.
This boat has an evaporator plate and we went almost a month in the Canadian Gulf Islands and Jervis inlet. Daily temps were in the mid 80's.
Fridge worked wonderfully after the Aerogel rebuild. Freezer near zero f. (held ice cream rock hard) and box about 40 F. It used about 30aH daily.

[olliric]

I guess in the tropics with a plate evaporator defrosting should be done every one or two weeks. I guess I could defrost with a heat gun and move the food from one cell to the other. I may build a gutter under the plate evaporator so I can direct and collect the water in some kind of collecting pot. Still, I wish they made they made a defrosting upgrade kit.

[ColdEH]

Vacuum Panels have dropped in price making them a more viable option . http://www.sealedair.com/ Custom sizes , $10 to $15 a square foot . They do have a minimum order of $1000

At that price I can do my fridge and freezer . With spares.

Regards

[Neptune's Gear]

Hi Guys, good thread about a really important issue for cruisers! For my 2c I'd really recomend for the tropics a water cooled system. Perferably a fresh water cooled system like these Here. There is a bit about my experience with them on the link on that page. Briefly though, we have a very large fridge and freezer (290ltrs each) and ONE of these units cooled BOTH cabinets. Yes, one can do both fridge and freezer! We had Ice Cream on the equator, and without a genset or huge solar panels. It really is a great system!
Nice Job on your build Nick!
Cheers
Matt

[downunder]

Matt,

what do you do to fresh water cool the ozfridge unit.

Cheers

[Neptune's Gear]

The unit has a small heat exchanger built in. So it takes water from the fresh water tank, runs it thru the heat exchanger, and puts it back in the tank. No thru hulls, no corrosion issues, really simple. Because water is a much more efficient heat sink than air, the water temp in the tank rises hardly at all. In our case less than 1 deg c.
I really can't praise these units enough!
Matt

[GreenHeaven]

Originally Posted by s/v Jedi

Terry,

I have been where you are now, taking 3 months to build three new boxes in 2005. This is what I discovered and how I did it:

First, reset your brain, purge all your current thoughts about the project, just while reading the rest of this post. After that, compare and make your decision.

My first discovery was that vacuum panels were not going to happen. Even the Rparts panels (which are way cheaper) were still outrageously expensive. I could afford it but realized I was not crazy enough to spend that much money on this. VIP's were quoted at $7,800.- to get the idea.

So, what I want to say is that it is much better to have a smaller box with more insulation than the other way around. If you plan to sail into the tropics and not run a genset hours each day, design a fridge with 4" foam and a freezer with 6". A 6 cubic feet box with a BD50 compressor unit will run about 20 minutes each hour, a duty cycle of 1:3. This is for both freezer and fridge because the freezer has more insulation and is opened less.

Start with the selection of foam. Use pure refrigeration foam, 2" and/or 4" thick, no reflective coatings or plastic lining or whatever, because you are going to have several layers and you don't want anything in there that conducts heat better than the foam. Use expanding spray-foam as the adhesive.

Now, you have to make a rectangular outer box where you can put the foam in. When the space for the box isn't rectangular at all, like against the hull, use 1/8" plywood, some 1"x1" battens and a tacker to create the biggest possible rectangular box. You will remove it later, so nothing fancy. Use the 1"x1" battens for the corners but also for plenty supports/struts inside the box to keep it in shape. So, give the box a bottom but no top.

Next, use spray glue to put plastic foil on the outside of this wooden box, except the bottom of course (can't reach it). Use epoxy and roller and brush to coat the inside of the space around the box (like the side of the hull, inside of front-cabinet wall, etc.) Let the epoxy gel to the "very sticky" phase and use it at that moment as the adhesive for aliminium foil, which you put in with the shiny side out (shiny side facing the hull). The epoxy and foil are the moisture barrier and the radiation barrier.

Next, measure one outside of the box (largest measurement) and cut a piece of foam. Parts, like the bottom edge, will need to be tapered. This is easy, use a bread knife and a surform rasp. You can get it to fit pretty quick and every panel will be faster. Spray some expanding foam on the bottom edge (or just into the space down there) and put the panel in. Use masking tape at the top to hold it against the plywood. Keep going on until all is filled up. After that, remove the plywood and plastic foil.

You are now left with a big hole where the bottom should be. You can use sheet-foam or pour 2-component liquid expanding foam (but go slow, 1 mixed cup at a time). Use the surform rasp (after fully cured) to shape it when pouring went a bit out of hand.

Now is the time to decide on minimum isolation thickness and interior volume. I would advise a maximum of 6 cubic feet interior. You make it smaller by putting in more panels on the sides and bottom.

Next is the lining. Easy but time consuming when you want it to look pretty. Start with a sheet (or half sheet, do the math and jigsaw puzzle on paper first) of 3/8" marine plywood. Put it on a level bench or A-frames. Using a black permanent (thin point) marker, draw out all the panels you need for the inner lining. Make the bottom piece the full size so that the walls stand on the bottom.
Don't use the existing edges of the sheet (stay a half inch away from them) anddon't cut yet! Vacuum it.

Drape the lightest fiberglass cloth over the whole panel (in 1 piece) and cut it so that a couple of inches hang over the sides, like a table-cloth. Now start mixing batches of epoxy resin + fast hardener. Pour the first batch (6 pumps if using West System is a good start) in the center of the sheet and use a plastic spreader to spread it. It must become completely transparent without trapped air. This is really easy. Works all the way to the edges and ignore the overhang. Let cure until gelled (still sticky) and add another coat. If the spreader becomes difficult to use, switch to a roller. Continue this process (start in the morning) until the cloth is completely under the epoxy. Let cure for 24 hours; it'll look like a varnished panel and the cloth is only visible at the overhangs.

Cut away the overhang with a sharp knife and smooth it with very course sandpaper (don't cut yourself on the edges, very sharp). Turn the panel over. Use brush and roller to coat the backside and edges with epoxy (fast hardener again). Let fully cure. Dry-sand (wood fibers come up after first layer of epoxy) and coat again. Let fully cure.

Turn panel over again and wet sand it (with orbital sander). Hose it wet and sand; rinse with hose and look how the water flows over the panel: look for any "rapids". This is where you must sand more. Stop sanding when you hit the fiberglass. This is where you decide how pretty the end result must be. You can roll on more layers of epoxy or decide it's good enough.

About the wet sanding: only use the machine when the hose is away and excess water is off the panel. Use a double-insulated sander, which is every modern one I think (label on sander states that with 2 square symbols, one inside the other).

Now you cut the panels. The lines drawn on the wood are as clear as before the epoxy and glass went on.

Put the panels in the box, using very little spray foam (just couple of dots) to hold them in place and immediately put some struts in to force the walls onto the foam. Don't put the top on yet. Use angle to check it is as straight as you want and don't worry about some small openings where they meet. Use thickened epoxy to put fillets in. I used Coloidal Silica to peanutbutter consistency and those West System fillable caulking tubes for a quick job.
Now you have the best excuse in the world for buying the Fein Multimaster tool. You can get sanding attachments to sand the fillets to perfection. Alternatively, use a short piece of hose with sandpaper around it but I ended up with RSI from that job.

Sand everything incl. the underside of the top. Now you can paint it, the top still off the box. I used Awlgrip which is safe (but still not food grade may be) after cure. Don't use white paint with lead.

Now, drill the holes for freon lines. The connectors of the evaporator determine the size. Mine just fit through a 1-1/4" thin-wall PVC pipe. Use PVC pipe, it's the moisture barrier at the most important spot because the freon lines will create condensation. I used a 10" long 1/4" drill bit to drill a pilot hole through the whole lot first. Next was the hole-saw from both sides. I used the PVC pipe itself to cut away the foam. Make the pipe 1/4" too long so that each end stick out 1/8". Use silicone sealant to close the gap around the pipe... do this good, absolutely watertight.

Install evaporator, sensors etc. as the top is still off so easy access. I installed compressors and everything at this phase and tested the system to be sure all the equipment was good. Afterthat, I used silicone sealant to put the top on (don't use stronger, silicone is tough enough and leaves hope to get it off later, if ever needed).

Now, you hopefully didn't forget room for the insulation at the top I hope. Put the sheets on, level the surface with batten and surform rasp. Now, stab the bread knife in what you think is the center of the opening and start cutting to a side. Cut the opening out. Epoxy brush/roller the foam and aluminium again. Should look like a spacecraft part now. Fit collar, lid and counter top, ready!

Some detail photo's attached.

cheers,
Nick.

This was a lot of work to write up. thank you for that, but I am afraid I just could not follow it and once lost, its a road map that relies on previous steps.
Perhaps you could give a simple overview of what all this detail is trying to accomplish?

Also Im not understanding how expanding foam is NOT going to force the panels apart as it expands.
I dont knopw what vaccum means in the context of this build. Are you doing vaccum layups in fibreglass

The problem with US based projects like this is that outside of the US, none of these options are available. Its building merchant expanded polystyrene on nothing
I dont even know if expanding foam is available here or if it sticks to polystyrene?
Where to get aluminim foil??
I presume we are not talking about the cooking grade stuff cos thats gonna last 5 mins inside my fridge )

Apply it to the outside as water barrier and reflect radiation

polystyrene is a water barrier, so confused there
reflect what radiation? are we talking about radiated energy of heat, or cosmis rays or something else?

I am also not clear if there should be a small air gap between the insulation and the hull to prevent the sun heated hull from transmitting heat to the insulation directly. I am thinking of a 1cm air gap to promote the cooler air from the bilge to flow up as the hull heats the air.

Finally could you summarize the math in the book you read. Cannot find it here. No amazon or fed ex deliveries )

[GreenHeaven]

also, what is the R value of expanding foam?

[s/v Jedi]

Vacuum panels are a form of insulation panels that are very good, just like a thermos to keep coffee hot.

Expanding foam is sold in every place that sells building materials. It’s used around window frames etc.

Aluminium foil is sold in every place that sells kitchen supplies. It’s used to wrap food in.

I’m not sure where in the world you are so I can’t really advice where to go.

[GreenHeaven]

Originally Posted by Neptune's Gear

The unit has a small heat exchanger built in. So it takes water from the fresh water tank, runs it thru the heat exchanger, and puts it back in the tank. No thru hulls, no corrosion issues, really simple. Because water is a much more efficient heat sink than air, the water temp in the tank rises hardly at all. In our case less than 1 deg c.
I really can't praise these units enough!
Matt

That is a great idea! and the water tank can dissipate heat slowly through the hull.

I occasionally run out of water tho. How does it handle that situation?

[wholybee]

Originally Posted by GreenHeaven

also, what is the R value of expanding foam?

5-6 per inch. It is a closed cell polyurethane and performs as polyurethane panels. At least if you use the correct expending foam.