Refrigerator / freezer

[Portager]

I thought I'd address a less controversial topic, the refrigerator and freezer.

For the entry level O-1 we need to keep the cost as low as possible, so I am thinking of an ice box instead of a refrigerator and a salt ice box instead of a freezer. The ice would be contained in conductive containers which could be built of thin plastic, cooper/nickel, stainless steel or aluminum. These ice boxes could be designed to be upgradeable to a refrigerator and freezer at a later date by installing evaporators or cold plates. Of course we will design O-1 with the refrigeration system and allow the builder to leave it out until later.

Refrigerator / freezer access: Access is usually through the top or a front door. I would like to suggest an alternative. The refrigerator and freezer would be Siamese twined together (to minimize insulated surface area) in an over/under arrangement with the opening to the front, but instead of a door there would be a drawer. The front of the drawer would seal to the front of the enclosure like a conventional refrigerator door. This would provide the confinement advantage of top access although not quite as energy efficient with the accessibility of front access.

Obviously the refrigeration system should be 12 volt DC, but we need to decide if the condenser should be air or liquid cooled. Liquid cooling is usually 25% more efficient than air cooling because the water is cooler than air and a much better conductor. To use liquid cooling you either need a source of raw water or a keel cooler. I'd like to see a keel cooler designed into the hull.

Cheers;
Mike Schooley

[Willallison]

.... I was really hoping someone else might address this - I hate coming across as an argumentative spoiler - or a nuisance!:(
Mike, your idea certainly has merit - I like the draw idea - ensuring that it seals adequately would be the only concern. It would allow for a fairly deep unit in which access to the rear is easy.
I also like the idea of designing for the kiss approach - for many an ice box would be the most appropriate solution.
But (it had to come....) I have some reservations about the keel cooler. Whilst it's true that liquid cooling is the most efficient option, a keel-cooler would probably result in a custom built system.
Anything protruding from the hull surface (as keel coolers generally do in order to maximise their efficiency) creates drag, is prone to damage - especially when trailering and adds complexity to the system. I think this is another area where builders should be able to make their own choice on which system suits them best. Lets face it, if you bought plans for a boat and didn't like the refrigeration system specified, you'd change it to suit your needs and the availability of the various choices.
I think the most important consideration here is to ensure that we allow enough space for the unit so that it incorporates decent insulation.

I would personally go for an off the shelf cooling system. It means you are covered by warranty, you can be confident in its integrity and efficiency and chances are it will be superior in every way to something I could build myself.
I like the Isotherm systems http://www.isotherm.com/ ) Any of their smaller systems would make sense - they offer both air and self-pumping liquid cooled models and freezers for those who need them.

[Portager]

Originally posted by Willallison
.... I was really hoping someone else might address this - I hate coming across as an argumentative spoiler - or a nuisance!:(

I feel the same way some times. I'm glad you like the drawer idea and the KISS approach of just using ice.

I have some reservations about the keel cooler. Whilst it's true that liquid cooling is the most efficient option, a keel-cooler would probably result in a custom built system.

Keep in mind that we are not talking about the huge keel coolers like commercial boats use for their main engines. I'm thinking about something comparable to the Frigoboat keel cooler http://www.frigoboat.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=frigoboat&Product_Code=PN+E50361&Category_Code=keelcooled only flush fitting. For the aluminum hull it would be an aluminum channel about 12" to 18" (300 mm to 450 mm) long and 1" (25 mm) wide, welded to the inside of the hull. I was hoping that we could come up with a cleaver solution for the composite hull. Maybe increase the surface area to account for the thermal conductive of GRP and bond a section of square tubing onto the inside of the hull?

Anything protruding from the hull surface (as keel coolers generally do in order to maximize their efficiency) creates drag, is prone to damage - especially when trailering and adds complexity to the system. I think this is another area where builders should be able to make their own choice on which system suits them best. Lets face it, if you bought plans for a boat and didn't like the refrigeration system specified, you'd change it to suit your needs and the availability of the various choices.

I think the keel cooler should be flush mounted and ideally internal like on metal hulls. It would be much easier for the builder to leave the keel cooler out and use the air cooled option than to add it in himself.

I think the most important consideration here is to ensure that we allow enough space for the unit so that it incorporates decent insulation.

I've got that covered. http://www.411web.com/R/REFRIGERATIONPARTSSOLUTION/ has very good prices on Vacuum Super-Insulation Panels (VIPs). Look under "Box Building" for insulation. This is the best insulation available and the prices are coming down. It is R28 per inch and $24 per square foot with a $48 minimum. As a worst case example, 3 foot cube would be $1,296 but it would be equivalent to 4" to 5" (100 mm to 125 mm) of Urethane foam.

I would personally go for an off the shelf cooling system. It means you are covered by warranty, you can be confident in its integrity and efficiency and chances are it will be superior in every way to something I could build myself.
I like the Isotherm systems http://www.isotherm.com/ ) Any of their smaller systems would make sense - they offer both air and self-pumping liquid cooled models and freezers for those who need them.

RPARTS will sell you the complete system in pieces, provide advice and warranty the complete system. If you don't feel qualified to solder cooper fittings you could hire a professional installer. If the system is designed by an engineer with a thermodynamics background (I know of one who is willing to help :)) and defined in the plans you could be confident of superior performance. The Isotherm self-pumping cooler has had problems with fouling and when there is very little boat motion. These conditions are rare but it can cause the system to overheat, run continuously and fail prematurely. I would recommend an air cooled condenser in parallel with a temperature activated fan.

Cheers;
Mike Schooley

[Polarity]

I just had a long and fruitless search for a Peltier effect unit that I saw at a boat show about 7 years ago ( the principle is here :http://www.mse.berkeley.edu/classes/matsci102/F01reports/thermoelectric.pdf ) Whilst solid state refrigeration is around in chiller boxes (I have one, cost about 25$, plug it in, It kept stuff cold but would not bring it down if you see what I mean - as long as I put cold beer in it it was great!)
I digress. The thing I am on about had a huge semiconductor plate about 25mm (1") thick and a foot across. You embeded it in the bottom of your hull outside and used a huge copper strap to connect it to the fridge plate. That was it, it just got cold, the cold went up the copper strap, the beer got cold. Seemed like a great invention to me.. so where is it??

Paul

[Portager]

Peltier cooling/heating devices suffer from extremely low efficiency (9% to 11% if memory serves me right) and relatively high sensitivity to shock. We use then in some sensitive electronics where we need to get rid of heat and we don't care about power draw, but off batteries they can really such the juice. I think the one you are looking for may no longer be available or may not be advertised on the web. I looked into getting one to use in my car when we were on long trips. I determined it could drain my car battery in less than 8 hours in a hot car. I figured it would be OK as long as I was driving but I would have to remember to unplug it every time we stopped or :(. We decided against it.

I think the cable going to the heat sink plate might have been part of the Peltier cooler impressed current loop, but I think we could utilize the principle. If we had some non-corroding thermally conductive (NCTC) rods embedded in the hull and welded to a coolant tube inside the hull the heat would be conducted through the NCTC rods into the water. I would use Bronze, Cupronickel or Titanium (if I could steal it) because it is virtually corrosion proof and a good thermal conductor. The hull could be fabricated around the keel cooler or installed after curing. Holes could be drilled for the rods and then filled with epoxy around then.

Whatcha think?

Cheers;
Mike Schooley

[Willallison]

The Isotherm self-pumping cooler has had problems with fouling and when there is very little boat motion. These conditions are rare but it can cause the system to overheat, run continuously and fail prematurely. I would recommend an air cooled condenser in parallel with a temperature activated fan.

This is the 'mark 2' version of the self-pumping unit. As I understand it, the earlier models did have problems with clogging - whether they've fixed it, I have no idea, but I would assume so......
My father installed an Isotherm ASU (air cooled) unit in the ice box of their 36ft 'trawler' a few years back (the ice box serverd us well for about 20yrs...). It is a very clever little unit - when extra power is available (via engines, shore power, generator, whatever) it draws more and rapidly freezes the holding plate. At other times it 'throttles back' to ensure minimum battery drain. If insufficient battery power is available, the unit switches off altogether - not great for your food, but better than being unable to start an engine....

For the aluminum hull it would be an aluminum channel about 12" to 18" (300 mm to 450 mm) long and 1" (25 mm) wide, welded to the inside of the hull. I was hoping that we could come up with a cleaver solution for the composite hull. Maybe increase the surface area to account for the thermal conductive of GRP and bond a section of square tubing onto the inside of the hull?

I can see it working on the aluminium hull - heat (or cold) transfers quite well thru alloy. Someone will have to come up with something clever for the composite hull though......and then, is the gain in efficiency of using liquid cooling going to be offset by the loss of efficiency of having to cool thru the hull surface - and even after all that, is any gain going to be worth the complexity? For some perhaps, so I guess it is worth examining further.....

[Portager]

Your are correct about the complexity and efficiency trade-offs. I think it requires a cleaver solution from someone who is more familiar with fiberglass fabrication techniques that I am. I was hoping that buy discussing it somebody might get a cleaver idea. It would be a shame to restrict such an elegant solution to only aluminum boats (although Portager, being an aluminum hull, will benefit from internal keel coolers:))

Cheers;
Mike Schooley