In message , Andy Wade
writes
On 16/10/2010 17:08, Mike Buckley wrote:

[...]
Assuming all that looks ok, and even if I'm quite a way off I've still
got another Kw+ before I need another heater, how do I calculate the
cost of the heater? I can easily do it per hour, but that assumes it's
on full blast all the time which it won't be - so how do you calculate
the cost based on partial use - is it even possible?

You can get an idea of the upper limit (continuous heating) by using
the concept of degree-days. Degree-day data is readily available for
the UK, see, for example,
http://www.vesma.com/ddd/ or
http://www.degreedays.net/.

The latter site allows you to set your own base temperature. Setting a
5 deg. base would give you the consumption for frost protection.

Add up your individual U*A products and ventilation heat requirement to
get an overall total heat demand in watts per kelvin of temperature
difference. Then multiply by the degree-days for any period - this
gives the consumption for the period in watt-days. Multiply by 24/1000
to convert to the more useful unit of kWh.


Thanks for the help everybody, very useful.

That degree days thing looks more accurate and it's very interesting but
I don't need that level of detail (and my u values aren't accurate
enough either). Stashed the info for bed time reading though.

--
Mike Buckley
RD350LC2
XJ900S