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    • CommentAuthorRobinB
    • CommentTimeJul 10th 2012
     
    I like it Mike!
    I always put any food I take from the freezer at the top of the fridge to defrost hoping for a similar trickle-down effect. I tend not to "cook from frozen" and move stuff from freezer to fridge top shelf in the morning for the evening, thinking I'm also saving on heating/cooking time too. I have absolutely no idea if it does any good really.
    • CommentAuthorSeret
    • CommentTimeJul 10th 2012
     
    It's bound to do some good. Similarly keeping your fridge full of food will help, if only because you lose less "cold" when you open the door and all the cold air falls out on the floor.
    • CommentAuthorEd Davies
    • CommentTimeJul 10th 2012
     
    Bringing ice into the house cools the house. If your fridge runs less your heating runs more. Obviously, heating energy (gas, wood, whatever) is usually cheaper than cooling energy (electricity) but still the whole thing seems pretty marginal to me once that's subtracted.

    Arguably, it'd make sense to do the opposite. Make some ice in the freezer then put it outside to melt. Rinse and repeat. Sort of an improvised air-source heat pump.
  1.  
    Mmm,
    I think what you are saying is that anything that comes in with a different temperature up or down from the house ambient in theory would push the house temp slightly in that direction? eventually.
    Therfore, if i place ice from out side in my fridge, the fridge is slightly colder by that amount thus being warmed more by the ambient (as the heat will want to go towards the cooler) and the compressor is operating less giving off slightly less heat (to the house) so overall there is a net decrease in heat(temp?) in the house. Its a case of tipping that energy balance in one or other direction.
    As to being marginal well there has been lots of discussion on this site about thermal break of a key lock on the front door so I think we'll still want to debate it. At high levels of thermal performance yes it may/may not contribute in one way but at everyday levels perhaps not measurable.

    So assuming I put 2 x 2kg of solid ice from out side (no input energy required) into my fridge every morning at 9am whats happens and why?????

    In my case I cant fill 2 lit drinks bottles and leave them out becuase a) dont use them, b) uses water (no cost - I have my own) but, c) my borehole water supply is pumped so for every lit there is x seconds of elec driven pump cost.

    Cheers
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 10th 2012
     
    Posted By: Mike (Up North)So assuming I put 2 x 2kg of solid ice from out side (no input energy required) into my fridge every morning at 9am whats happens and why?????

    What temperature where they at in the solid phase and did they make it to the liquid phase.
    Either way, they will cool your house by the amount of energy they absorb as I suspect that you throw the water/ice down the sink/outside.
    SHC of Ice is 2.11 J.kg^-1.K^-1
    Air is 1 J.kg^-1.K^-1
  2.  
    Ok so this means the only way to improve fridge performance (a fairly common consideration) is to add insulation in an appropriate manner. Helping the condenser cool is ok but there is an off set with regard to the heat from the motor.

    Cheers
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 10th 2012
     
    The heat from the motor/compressor is usually used to auto-defrost (that that little hole in the bottom of fridge is for).
    Opening and closing the door less would help, as would not having it 'on' when in use a lot. So say that the morning flurry of fridge activity is between 7 and 8AM, get a timer to turn it off then and see what happens. Not applicable in my house as I work from home, so used spasmodically and stochastically all day long.
    •  
      CommentAuthorJSHarris
    • CommentTimeJul 10th 2012
     
    Interesting point about the use of ice. Ed's right, if you look on the house as a closed system, with a fridge in it, then bringing anything into that closed system that needs its temperature increasing will use more energy.
    • CommentAuthorSeret
    • CommentTimeJul 10th 2012 edited
     
    Sure, but if you expand the system even further you've got one box trying to warm itself above ambient, with another box inside that trying to cool itself below ambient. You're using energy to heat air, then more energy to cool the heated air.

    So as ST says, try not to open the door. But if you do, minimising the volume of energy-rich warm air you have to cool after you shut the door will improve your overall efficiency. So what you want to fill your fridge with isn't so much low-temperature things, but high volume ones.

    The lesson: Keep your cotton wool balls in the fridge.
    •  
      CommentAuthorJSHarris
    • CommentTimeJul 10th 2012 edited
     
    <blockquote><cite>Posted By: Seret</cite>The lesson: Keep your cotton wool balls in the fridge.</blockquote>

    I wish this forum had a "memorable quotes" section............ :bigsmile:
    • CommentAuthorEd Davies
    • CommentTimeJul 10th 2012
     
    The latent heat of fusion of water is 334 kJ/kg so 4 kg of ice will contribute 1.376 MJ of cooling as it melts. That's about 0.382 kWh. If the fridge's cooling COP is 2 (remember that cooling COPs are typically one less than heating COPs because the waste heat from the pump doesn't help) that'll save you less than 0.2 kWh.

    Warming the ice to its melting point and warming the resulting water to fridge temperatures will make very little extra contribution.

    I think the best thing is if you can arrange for the fridge to do its cooling when electricity is cheap, e.g., at night if on-grid and when available from the source rather than from a battery if off-grid.
    • CommentAuthorTimber
    • CommentTimeJul 10th 2012
     
    Interesting thoughts going on here.

    I know in the summer, when we have extended periods of warm weather my old fridge used to struggle to keep cool. Pulling it out a bit definately helped (subjectively) as there was more air movement. I am temped to add a pair of fans to my current fridge and freezer for use in the summer to help improve the performance. In thoery the lower the temp difference between the hot and cold side of the pump the better the efficiency of the system. But I would only bother doing this in the summer.

    Surely all of the 'cold room' larder setups end up causing a conflict of detailing in a high efficieny house. I.e. cold room need a decent door between it and the habbitable space. Also thermal bridging is likely to be a problem too. Surely using a decent A rated (or better) fridge and freezer result in less hasstle, and perhaps a less compromised building design in the long run?
  3.  
    Yes i have pondered the conflict of the internal cold room. As usual there is a balance to be found.
    •  
      CommentAuthorjoe90
    • CommentTimeJul 12th 2012
     
    I proposed a cold larder on the other fridge thread but mine will be outside the house envelope,(part of the garage/workshop) and its door will be into the boot room (also outside the envelope) with another door into the house and a third to the outside(the boot room acts as an airlock to the back door) so thermal bridges should be minimal.
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