DIYbanter - View Single Post - Ever wondered why your gas bill is so high?

Andy Wade

wrote:

The conversion factor is an average, depending on when the meter
reading took place. It will take into account the varying chemical
composition of the gas and a deemed temperature at which it is
delivered (the meter measures volume, not mass, which would be better).

There are actually up to *four* "conversion factors" which are now being
confused in this thread:

1. Imperial to metric conversion: since 1992 all gas bills have been
based on usage in cubic metres. As most gas meters still read in
"units" of a hundred cubic foot the metered consumption (difference
between the "current" and "previous" readings) is multiplied by 2.83
to convert to cubic metres. This conversion factor is constant, and
clearly does not apply if you have a metric meter, which reads
directly in m^3.

2. The volume conversion factor or VCF. This is a constant multiplier
with a value of 1.02264 and is an adjustment for temperature and
pressure. The VCF was first introduced during 1997 along with a
corresponding reduction in the gas price. I'd be interested if
anyone knows the detailed reasons for its introduction, but its
existence seems to be an admission that metered gas volumes had
previously been slightly low - presumably because the temperature
and pressure at which meters are calibrated don't quite match actual
supply conditions.

3. The calorific value. This is the energy content of the gas and is
the only factor which varies from bill to bill. The value used is
a legal "declared" value of the fuel's gross calorific value (GCV)
in units of megajoules (MJ) per cubic metre.

4. Conversion from megajoules to kilowatt-hours. Gas is priced in
kilowatt-hours (kWh) so the calculated energy consumption is next
divided by 3.6 to convert from MJ to kWh.

So, for an imperial meter, the billing calculation is essentially

charge = (current - previous) * 2.83 * 1.02264 * GCV * price / 3.6

or, for a metric meter,

charge = (current - previous) * 1.02264 * GCV * price / 3.6

then add VAT at 5%.

--
Andy