Increase in calorific value of Gas

oldtrout

As it's so complicated, I've previously accepted that the calculations made for converting gas usage into kWh were what they were and fixed.

However, I have a spreadsheet set up with all these calculations included. As I'm on a fixed tariff until April, I did not expect my own figures to differ from that on my latest dual fuel bill.

It's the gas. Admittedly it's only about 40p difference on a 60 day bill period, but it did not reconcile.

Noticed why ... it's an increase in the calorific value from 39.2 to 39.4.

Anyone know what that's all about?

ollski

I think suppliers use an average as the calorific value of gas changes constantly.

[Deleted User]

Your gas meter measures the volume of gas you use, but the price you pay is for the energy it contains. Calorific value is the amount of energy per unit volume that enables them to calculate your energy consumption from the meter reading. The units are MJ/m^3 (megajoules per cubic metre).

It doesn't matter to you, because if the CV of the gas changes the boiler will simply burn more or less according to what it takes to heat the home. The amount of gas required to heat your home is measured in terms of the energy it contains, and the amount you're billed for is also measured in terms of energy content.

The volume of gas is dependent on temperature and pressure, so If you look at your bill you will see a number called the volume conversion factor which compensates for the difference in average T&P between your location and the lab conditions under which the CV was measured. If you're at lower altitude or cooler weather than those figures assume then you're winning a little bit of free gas, if it's higher or hotter then you're losing a little bit to the winners. If you are interested, you can write and ask for the details of your volume conversion factor. They'll tell you what mean temperature and altitude or atmospheric pressure they're using to calculate your bill.

Your bill calculation is simple enough. Starting with the volume read off the meter, it's first converted to metric if your meter is in cubic feet. Then you just multiply by the CV, then the VCF, and last you divide by 3.6 to convert from MJ to kWh.

DragonQ

Yeah CV changes slightly all the time. Nothing to be concerned about, jack_pott's explanation is sound.

molerat

If you are really interested go here http://marketinformation.natgrid.co.uk/gas/DataItemExplorer.aspx and you can find your CV for any given day. I use this to accurately calculate my bills but I wish they had an average between dates figure. Mine has varied from 39.1 to 40.4 since the beginning of Oct.

Now a question for the experts ...... why do Stranraer and the Scottish Independents have a consistent figure whereas all the others vary daily ?

Ken68

It all sounds very LIBOR'ish.

C_Mababejive

Most of our gas is Imported via subsea pipeline or LNG tanker from the middle east so that would also lead to variations/blending..

[Deleted User]

Ken68 wrote: »

It all sounds very LIBOR'ish.

Not really, gas is a natural product, so it's characteristics will vary. If they sold you gas by volume instead of energy content that would be a bit unsatisfactory because the amount of energy you'd get for your money would vary.

Ken68

jack_pott wrote: »

Not really, gas is a natural product, so it's characteristics will vary. If they sold you gas by volume instead of energy content that would be a bit unsatisfactory because the amount of energy you'd get for your money would vary.

I was thinking about the LIBOR traders taking the wrong average, it was small change per customer, but made millions for the bank.

macman

Isn't the CV primarily determined by the amount of water in the gas? More water content lowers the calorific value.

[Deleted User]

Ken68 wrote: »

I was thinking about the LIBOR traders taking the wrong average, it was small change per customer, but made millions for the bank.

I see what you mean, but for any given level of profit it doesn't make any difference whether it's the number of units that's inflated or the unit price, especially as most customers don't really understand their bills anyway.

If your bill is calculated on an average CV, you will gain in periods when you use gas while the actual CV is above average and lose when it's below, but in the longer run the gains will cancel out the losses.

With the VCF, I don't recall whether it's calculated using the average temperature for the whole year, or just for the winter months when people use most gas. It doesn't really matter either way, all that would matter is whether you have a substantially different usage pattern to that of most other subscribers. Someone consuming more than an average user in the summer would lose out slightly to another who used above average in winter.