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Fridge efficiency

Discussion in 'Photovoltaics' started by Starbase, Jul 27, 2004.

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  1. Starbase

    Starbase Guest

    Hi all,

    I am plumbing my fridge freezer in to run off solar power through my studer
    12 volt 1.2 kW sinewave inverter, in the interests of efficiency I am
    thinking that glueing aluminium fins onto the fridge motor with thermal
    epoxy will increase efficeincy as the motor runs quite hot. (Perhaps even
    enclosing the fins and adding some form of chimney to promote air flow over
    the fins and motor casing, or even a small computer fan).

    Am I right in this assumption or is the system set up to expect and work
    better with this heat, pressures generated inside etc.

    P.S. I can't quite justify the buying of a more efficient fridge freezer, at
    least not just yet.

    Regards to the group

  2. If you are talking about solar powered RE, you can't afford _not_ to
    upgrade your fridge/freezer if it's not already the most efficient one
    available. You'll save the cost of the fridge just in buying fewer
  3. SQLit

    SQLit Guest

    Do not forget that starting current can be 6 times FLA. Make sure your
    inverter can handle the inrush.
  4. Starbase

    Starbase Guest

    You are of course right, and this will be addressed in due course, however
    this is a hobby rather than a necessity as we are grid connected (in the UK)
    so I
    make progress when and where I can with all my equipment being secondhand,
    (repaired) or home made, except my battery bank (4 x 125 amp/hr 12 volt
    elecsol batteries). It is all one big learning curve and I am learning from
    the group/experience. Currently I do not have enough capacity to run the
    fridge freezer
    24/7 from solar alone (pulls 90 watts (estimated 60% duty cycle warm summers
    day) plus
    inefficiencies in conversion etc, with a 170 watt peak output array not
    ideally aligned, (upgrades/more panels pending)) so am testing an automatic
    change over circuit using comparator based voltage sensing circuit driving a
    double pole relay as I am not happy about the level of discharge the
    inverter will allow the batteries to drop to before cutting out. I think it
    is important to struggle with what I have for a while, at least until "the
    paymaster" is a little more educated and sympathetic towards my RE efforts

    Thanks for replying

  5. Starbase

    Starbase Guest

    Thankyou, yes I did consider this, the fridge/freezer pulls aprox 90 watts
    when the motor is running normally so I can guess at worst 6 - 750 watts or
    so start up power which is well within the 1.2kW (sustained) output of the
    inverter, under normal operation the inverter is not even worked enough to
    bring on the fan (and I have mounted it for maximum ventilation) so I
    currently have plenty of capacity there and I am at an early stage of my RE
    education. I hold the view that I always try never to exceed 75% capacity of
    rated spec as have a tight budget and can't affort to stress components
    (especially my batteries).

    Thanks for your input

  6. Where abouts ?

    Cheers, J/. (Derbyshire)
  7. If the thermal epoxy is in thick layers you may find it's not very
    thermally conductive. These things usually work best in very thin
    layers between flat surfaces.

    Point an old computer fan directly at the case compressor or the
    'radiator' ?

    Chimney sounds good, but how compact would it be ?

    Heat pump efficiency will improve if the hot / output side is cooled

    Not sure if it's worth trying to cool the compressor housing though ?

    Cheers, J/.
  8. In message <%5ANc.995$>, Starbase

    If you want a response to your emails I probably need your real email
    address. Do you want to email it to me ?

    Cheers, J/.
  9. ....

    It might be cheaper to simply get some foam board and add it to
    the outside of the fridge. More insulation would mean less heat
    leakage and therefor less compressor run time. Just don't cover
    the coils or block the air flow around them. You also have to
    be careful with the foam as it's flammable. You'll want something
    better than the cheap white stuff. Look for the kind of stuff
    they make floats out of. You might also want to cover it to
    keep it from getting easily torn up and/or igniting.

  10. Starbase

    Starbase Guest

    ----- Original Message -----
    From: "John Beardmore" <>
    Sent: Tuesday, July 27, 2004 11:32 PM
    Subject: Re: Fridge efficiency

    Agreed, the epoxy contains a very high quantity of silver and is designed
    for thermal heat transfere,
    I like to thrash my computers (while remaining stable, floating point
    calculations etc) and use it on
    various componets North Bridge, RAM etc to help with overclocking stability.
    There is enough space, I guess it is just balencing the effort with the
    possible return, but heck it is not
    a proper hobby unless you are willing to go to extremes.
    Good point, possibly a good case for adding more surface area to the
    existing grill and using a little
    forced air. The trouble is doing comparative testing in our changable

    Thanks for the tips

  11. Starbase

    Starbase Guest

    Sorry I meant to send the response to the group and have an un-usable
    default e-mail in case of just such an error, for the group the missing
    resoponse is;

    ----- Original Message -----
    From: "John Beardmore" <>
    Sent: Tuesday, July 27, 2004 11:20 PM
    Subject: Re: Fridge efficiency

    Cleveland, Middlesbrough, so obviously wind power is on the agenda but first
    want to get the solar side sorted and decide wether I should get another
    load of
    batteries while these ones are still new as I do not have as much time as I
    like for playing, due to this impediment called a job.


  12. Starbase

    Starbase Guest

    Many thanks for these helpful remarks, I do have to find out exactly how
    this fridge/freezer works and am prepared to make some mods to test out the
    theory. One frustrating thing living in the UK is that we hardly ever have
    two days the same for comparative results (it is also constantly in use), as
    well as my enthusiasm for change not quite being shared by "the boss". My
    first mods will be some limited outer (and possibly interier) insulation,
    better air flow to the compressor and radiator with the possibility of
    bringing cooler air up from under the kitchen's wooden floor. I am currently
    taking temperature measurements of internal and external temps, what I think
    I also need is some form of hour run meter connected to the compressor
    circuit to guage the changes as I am at work far too many hours in the week.

  13. Starbase

    Starbase Guest

    Many thanks for that idea, as I don't have a spare 240 volt clock, but do
    have a real irritating 3 volt clock, I will wire the power through a 240
    volt realay. I already think the compressor runs way way to much even though
    it is summer. I am looking at newer fridge freezers already but it will
    still be good to see what can be done.

    PS two fridge compressors connected in series does make a pretty cheap
    vacuum pump.
  14. mikell

    mikell Guest

    Some of the new fridges do run 12+ hours but the compressors are small so
    the efficiency is good. We (Whirlpool) just introduced a stove that has a
    refrigerated oven!!! You can program it to chill up to 12 hours before it
    starts cooking. Or you can hide the good stuff from your guest during a

  15. Andy Baker

    Andy Baker Guest

    There are documented cases of people using fridge compressors to pump down
    certain types of lasers. Especially good units come out of air conditioners,
    as they are (though probably not always) of the rotary vane type. They tend
    to last a long time since most of the gasses they pump are very dry and very

  16. If you liberate the [H]CFCs !

    Cheers, J/.
  17. Starbase

    Starbase Guest

    Unfortunately I work on a housing estate where dumped, vandalised fridge
    freezers (and more) are ten a penny :-(
    Plenty of bike frames too which make good bearings for a savinous turbine
    (future project).

    Global warming, symtom of a throw away society?
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