refrigeration gas or elec

Discussion in 'Multihulls' started by taezow, Sep 14, 2010.

  1. CatBuilder

    CatBuilder Previous Member

    He has a trimaran. Should stay relatively level.

    Movement past the maximum angle of operation, then back again doesn't matter on these refrigerators. It's the average of the angle over time (say, half an hour) that matters.
     
  2. jonr
    Joined: Sep 2008
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    jonr Senior Member

    50% cycling is going to be variable between units. Some can have a more powerful compressor that runs 25% and some can run 60% - both with the same ambient temperature, efficiency and amp hours/day.
     
  3. cavalier mk2
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    cavalier mk2 Senior Member

    I was reading an old Hiscock book and I wondered if anyone still makes kerosene (paraffin) powered refrigerators? How do they compare?
     
  4. taezow
    Joined: Jul 2009
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    taezow Junior Member

    What is wrong or bad with gas?

    Where I'm putting the fridge is in an area that hangs over the water. It could be vented so if it did have a gas leak it would go over board not into the hull.

    The tri only heals about 10*, so it would be very easy to gimbel the fridge for this, if it was even needed.

    A small propane tank weighs about the same as an extra battery. I could use a small camp propane bottle to run the fridge when I get the main bottle filled.


    Thanks
     
  5. cavalier mk2
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    cavalier mk2 Senior Member

    Propane is fine as long as it is well vented. Having the set up in the wing means no explosion hazard. I use a kerosene stove/oven because it is lighter than a stove/oven plus a propane tank. Now ifwe stopped baking and eating those pizzas I could lose the oven......
     
  6. CatBuilder

    CatBuilder Previous Member

    There are some problems, then.


    10 deg heel is more than allowed for the gas models. Iirc, it is 2 or 3 degrees max.

    Also, a small propane tank won't last long. I get 3 weeks or so out of a 30lb tank, continuous use.



     
  7. taezow
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    taezow Junior Member

    Cat builder,

    How big is your frig
     
  8. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hi Guys,

    I agree with CDK, the fridge sounds about right. The 2,8A drawed would only be drawed when the fridge is over temperature. It would be off the rest of the time

    Since so many people asked me about solar powered things I put a page up to explain how is what, have a look at it here

    http://www.fanie.cambs.net/Solar/Solar.html

    Though solar is expensive and unefficient, I would prefer it over gass in this case because if you install the correct solar setup it would be maintenance free. You will have to refill the gass every now and again.

    I can also say the danfoss compressor motors used in the fridges nowadays is very efficient, at 2.8A for a few hours daily is very acceptable consumption.

    The time the fridge motor work is also a function of how much you are in and out of the fridge all the time.

    One thing that works for us of course is at night when there is no sun it is also a bit cooler, so the fridge keeps it's temperature that bit better.
     
  9. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    I would agree with Richard here, you have to check your location and how much sun you have there. A solar panel would never be too powerfull.
     
  10. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Re gas operated fridges -
    It would work well on a boat. The two things that affects the fridge's performance is the angla at which the flame burns up and the angle of the pipes that does the heat exchange when the fridge is tilted.

    If the boat is tilted at an angle most of the time the it's going to be a problem, but last time I checked most boats were pretty level most of the time. I have also seen a thing you make that keeps items upright all the time, it swings on a hinge so even if the mono leans the fridge goes level. It should have a damper though, other wise it's called s swing and not a leveller :D
     
  11. Bglad
    Joined: May 2010
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    Bglad Senior Member

    I am curious about propane refirgerators so did a little reading and came across this:

    http://www.multihullsmag.com/magazine/articles/propane article.htm

    Properly maintained a propane refrigerator is likely a reliable device but kept in a locker basically outside I don't see how the igniter mechanism and other components don't begin corroding and causing problems.

    The propane refrigerator I had in my travel trailer never did work right even after the cooling unit was replaced. Replacement of the cooling unit seemed to be the only option because getting the ammonia refrigerant charge just right seemed to be beyond the service guys ability.

    If you built a well insulated box with cold plates in the exterior locker how much energy would you need to keep it frozen once it was pulled down? How much more reliable would it be, easier to have serviced and less likely to try and blow you up or make you stay asleep indefinitely?

    I like propane stoves and grills and could live with an instant-on water heater that I could run when I need it but I think the refrigerators are trouble on a boat and not all that good in an RV.
     
  12. jonr
    Joined: Sep 2008
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    jonr Senior Member

    Some say that the most efficient refrigerators use the Masterflux compressor by Tecumseh. But the COP figures I've seen are poor - would be interesting to see a comparison to Danfoss.

    Storing the heat in phase change materials make far more sense than batteries to me - for solar or for running a generator.
     
  13. CatBuilder

    CatBuilder Previous Member

    It's larger than yours. I have this one:


    [​IMG]

    http://www.pplmotorhomes.com/parts/rv-refrigerators/norcold-refrigerator-n641.htm


    A 30# propane tank will run it for approximately 3 to 3.5 weeks. It is not to be confused with the DC only model you are looking at which uses an entirely different refrigeration system. I would be concerned with possible corrosion of the igniter on the gas refrigerators over time, but they swap out very easily.

    Heel angle is about 3 degrees max for long periods of time on a gas adsorbtion refrigerator. You can tip the refrigerators beyond that for short periods of time, but staying on a point of sail at 10 degrees for an hour will start to cause problems both for the flame (it rises against gravity, so if you tip it the flame will miss the thing it's supposed to heat) and for the movement of the ammonia refrigerant inside the system. There can be build ups that cause damage to the refrigerator if it's tipped at 10 degrees for an extended period of time.

    So... I would go with the DC refrigerator based on your actual heel angle. You can get away with these in catamarans quite often and in power boats like trawlers, but if you're heeled past 3 degrees, best to go with the DC only model.

    These are not installed in a way that CO is an issue, so that is never a problem.

    I would agree with Fanie's posts too, in that the main drawback is restocking the gas for the refrigerator. Do you enjoy going to get propane when the time comes? Is it easy to refill? Do you want to carry a 30# propane tank to and from the boat? Those are the main issues when you are considering propane, even with a gimbal.

    Solar is completely maintenance free (until something breaks), so there is a nice bit of convenience there. I have owned both types of systems and prefer the solar, though the propane is less expensive.

    To figure out how much solar you need, don't look at refrigerators and solar panels. Look at your entire boat's electrical consumption in amp hours, including the refrigerator. Add up the worst case electrical usage day in amp hours. You'll come up with 100 amp hours or something like this.

    Now, decide how many days reserve you'd like to be able to run on a day with no power inputted to the batteries. 1 day? 2 days?

    I'll assume 2 days.

    So if you want to use 100 amp hours of power on your boat (this includes your refrigerator) and you want to be able to do that for 2 days without any power generation, you'll need 400AH of batteries. Why? You can't discharge a standard wet cell battery past 50% without damage. So, you need a 400AH bank if you need 100AH per day and want to have a 2 day reserve. That makes sure your battery bank is right sized.

    Now, look at how to keep those batteries topped off with solar panels (is this the only charging source?). I'll assume solar is your only source. An easy "rough estimate" to get from Watts on your solar panel to find out the number of amps it will deliver per day, on average, for an average weather condition is: SolarPanelWatts x .3 = AH Delivered Daily

    On my last boat I had 2(qty) 120 Watt panels. By the formula, they put out .3 x 240 = 72AH daily. Not enough to keep up with a 100AH daily need, but it was enough for my last boat, running a built in, top loading, refrigerator/freezer, computer and odds and ends at anchor 24/7/365.

    It's better to have a touch more electrical capacity than you need, because there are always the odd cloudy weeks or a breakdown or something where the little bit of extra comes in handy.

    Hope this post helps.
     
  14. apex1

    apex1 Guest

    No, the Danfoss is the best at present.

    The cold plate storage is not new, and it is a sensible addition but not a perfect solution as standalone.

    Regards
    Richard
     

  15. yipster
    Joined: Oct 2002
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    yipster designer

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