by ericmark »
Wed Jan 07, 2009 2:20 pm
Economy 7 is a tariff not a heating system when electricity used in a 7 hour slot is sold at a much reduced rate but electricity outside this time is more expensive.
For it to work energy needs to be stored and items like dish washers, washing machines and tumble driers need to run over night.
There are two main methods to store heat.
1) Heat up bricks with heavy iron content to around 1000 deg C and hold them in an insulated box with adjustable vents so heat gained at night can be released slowly through the day.
2) Heat up water in a large insulated container and circulate it when heat is required.
The first is cheaper to install but control is somewhat lacking and a smaller water heater is still required for domestic water anyway.
The second is far more controllable being able to store heat for a week if required but costs more to install.
For the latter there are also two types those which store the water at mains pressure and those which use a header tank. In both cases the shower can be run from mains pressure water but the type which stores water at mains pressure needs an annual inspection.
Of course electric showers are out and you need to used stored water for showers as during the day electric cost so much.
The old brick system with wife and children at home during the day may work OK although just before the power switches back on a night it tends to get cold just when you could really do with it getting warmer.
However the water system can nearly be switched completely off in the day and where all occupants of the house are at school or work it is a far better system.
Also the wet system can be combined with solar power so reducing the bill still more.
You must also consider noise and running washing machines, dish washers over night may be OK in a house where they are remote from bedrooms but starting up at 11 pm may not be best option!
I would expect Gas heating will be far cheaper than electric by time you include all the work required.
Also electric normally has a 100 amp limit and this is for 7 hours so total amount of power per day is 6.7Kw/Hours average but most gas heaters will be around the 27Kw/Hours for the smallest which means in any large house it will struggle to give enough heat using the Economy 7 and will require a boost. There are other systems I think there is an Economy 10 which gives a boost at some point during the day.
Also to work well you may need to change washer, drier, dish washer etc. to used the cheap power. So I think it may work out more expensive than gas to fit as well.
Normally it is only used where Gas is not available.
