# Energy cost Calculation check please .

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

1. ### scotjimlandFunsterLife 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 oh:

thanks

jim

2. ### Landy loverFunsterLife Member

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I only just managed to catch that before it went over mine
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 ??? Therefore if the ambient temperature is low you will be burning fuel for no return

3. ### lebesset

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

approx of course as quality varies

4. ### scotjimlandFunsterLife 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. ### scotjimlandFunsterLife Member

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

jim

6. ### Tony Lee

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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

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Over my head !!!! I still cant figure ouot how a flame can make something cold

8. ### TerryFunsterLife Member

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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:
terry

9. ### Boo

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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

Boo

10. ### scotjimlandFunsterLife 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

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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.

12. ### scotjimlandFunsterLife 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. ### keithFunster

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

One site in Spain charges €5 a night.

14. ### johnsandywhite

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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

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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

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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

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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

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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. ### scotjimlandFunsterLife Member

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Hi Braunston,

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

jim