Energy cost Calculation check please .

Discussion in 'Motorhome Chat' started by scotjimland, Aug 20, 2009.

  1. scotjimland

    scotjimland Funster Life Member

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    I'm trying to determine the cheapest method of running my fridge .. electric or LPG , for the sake of the calculation I'm assuming the fridge is equally efficient on either fuel..

    So, using these two costs ..

    A kw unit of electricity costs 15p

    1lt of LPG costs 50p

    How many kw do you get from 1 lt of LPG

    1kw h = 3412 btu

    1lt LPG = 25,248 btu = 7.4 kw

    so, 1kw of LPG cost 50p div 7.4 = 6.75 p

    If this is correct it is cheaper to run on LPG

    Can someone verify ? my head hurts :Doh:

    thanks

    jim
     
  2. Landy lover

    Landy lover Funster

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    I only just managed to catch that before it went over mine:Eeek:
    If your figures are right then yes it is BUT have you taken into consideration that when running on electric there will be no consumption when the temperature is achieved but when its running on gas there will always be a pilot light on burning away ???:RollEyes: Therefore if the ambient temperature is low you will be burning fuel for no return
     
  3. lebesset

    lebesset Read Only Funster

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    1litre of diesel will produce 10Kw/hr
    1 litre lpg 7Kw/hr

    approx of course as quality varies
     
  4. scotjimland

    scotjimland Funster Life Member

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    Hi , thanks for that ..

    The Dometic fridge I have doesn't have a pilot, it has electronic ignition, once temp is reached the flame goes off then re ignites when demanded.. so no losses there..

    The reason I'm checking is because we are on metered leccy .. it's a domestic size fridge with a freezer and it does use a lot of energy ..

    jim
     
    Last edited: Aug 20, 2009
  5. scotjimland

    scotjimland Funster Life Member

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    thats close to the figure I used .. of 7.4 , thanks for confirming

    jim
     
  6. Tony Lee

    Tony Lee Read Only Funster

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    Difficult to make that sort of comparison because it ignores how efficiently the fuel is used within the appliance itself. A lot of the energy derived from gas just goes up the flue

    The fridge manufacturer should be able to give the consumption in grams per hour and you have the electricity use per hour, so assuming it would use either fuel for the same time each day (probably not true either) then you can do a comparison.
     
  7. 6pm Cowboy

    6pm Cowboy Read Only Funster

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    Over my head !!!! I still cant figure ouot how a flame can make something cold :Rofl1::Rofl1:
     
  8. Terry

    Terry Funster

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    Hi Jim I remember this from a couple of months ago :thumb:
    The easiest way of finding it out is buy a small bottle of gas and see how long the fridge works for using gas :thumb: You already know how much leccy you use--- I think it was around £3 plus a day --- then you have to factor in the actual price you pay for gas not the bottled variety :thumb::Rofl1:
    terry
     
  9. Boo

    Boo Read Only Funster

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    In my Winnie handbook it says that running the fridge on gas is more economical as it burns hotter and so less gas is needed to get it to temp, it also advises using gas initially when first switching fridge on before a trip for the same reason :Smile:

    Boo
     
  10. scotjimland

    scotjimland Funster Life Member

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    Hi Boo

    I would agree it runs better on gas .. and by my calculation cheaper than metered leccy but as Tony pointed out some of the heat is lost through the roof vent ...if I factor in a loss of 25% .. it still works out cheaper.

    Prior to metered leccy we hardly used any LPG, hot water, fridge, space heating, cooking all on electric.. now we use about 6 -7 kg LPG per week, about £1 per day


    jim

    jim
     
  11. johnsandywhite

    johnsandywhite Read Only Funster

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    :Cool: In Spain, our Newmar uses an 11kg bottle every 2.5 weeks (mas o minus) running the reefer, cooking and the odd heating. Averages out over the year. Because in Summer it uses more for the reefer, in Winter it uses more for heating. :Wink:
     
  12. scotjimland

    scotjimland Funster Life Member

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    Hi John

    I guess you use the camp showers .. an option we don't have.. so that would explain why we use a bit more ..

    jim
     
  13. keith

    keith Funster

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    Thanks for this thread Jim. I have often wondered about this myself with more sites starting to meter the electric.

    It demonstrates how over charged we are for EHU if we pay per night.

    One site in Spain charges €5 a night. :Eeek:
     
  14. johnsandywhite

    johnsandywhite Read Only Funster

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    :Sad: That is quite true. By meter it varies between 25 and 39 cents/KW. Cost 55 Euros for 1 month for reefer etc. It now costs us and average of 5 Euros. Then again, we have Solar power. :thumb:

    You are right Jim, we use the super showers on the camp. Then again, when we were Wild-camping we didn't really use much more. We used Solar to boil kettles and had bucket baths. We still, when using the showers, get wet, lather up, wash hair and then rinse off. Use perhaps a gallon of water. :thumb:
     
  15. Tony Lee

    Tony Lee Read Only Funster

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    This may give a bit of an idea. Taken from the specs for a Dometic RM4601
    Electric Input: 240V - 325 Watts. 12V - 215 Watts. 18 Amps, Gas Input 20 g/hr

    If the figures are correct then even leisure gas could well work out cheaper than electricity for this particular fridge.
     
  16. acdcdave

    acdcdave Funster

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    Gas versus electric cost

    Jim

    I haven't checked your numbers, but I did a similar comparison for domestic oil versus electric for water heating last year. Despite being almost 100% efficient in its operation, electricity was still significantly more expensive despite the very high oil price at the time. So your result feels good to me.

    Cheers, ACDCDAVE
     
  17. pieterv

    pieterv Read Only Funster

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    Realistically, when using an electric only fridge it will be a compressor fridge. Gas/electric will be absorber. The former are much more energy efficient.

    Have a look at Engel or Waeco compressor fridges to get a feel for their energy consumption. On holiday in Marocco, we could have a compressor fridge running in a Land Rover on a 85Ah battery, whilst driving every day. An absorber fridge would have emptied the battery overnight.

    Pieter
     
  18. Braunston

    Braunston Read Only Funster

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    Hi,

    Is the Gas thermostatically controlled as some older fridges were not they just relied on the size of the jet to control the cooling,
     
  19. scotjimland

    scotjimland Funster Life Member

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    Hi Braunston,

    yes, the thermostat controls the temperature by turning the flame on and off..

    jim
     
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