I am in debate with Bulb energy over the calorific values they charge, it only amounts to a few pence (7p) but as it stands I cannot argue my case. Is there a website that gives the calorific values for gas on daily/weekly or monthly basis by area?
Why?
According to [the] National Grid,
"Gas passing through the National Grid pipeline system has a CV of 37.5 MJ/m3 to 43.0 MJ/m3."
Along with
"At present the CV of gas is measured at over 110 different locations in the UK mainland."
This accords with something I read before, about its being variable, But not quite that variable. According to my calculations a range of 5.5 is equivalent to 12.8%.
That also accords with my own somewhat less scientific observations when cooking by gas, that on some days the gas seems a lot hotter than on others. 12.8% hotter as it turns out.
I very much doubt [the] National Grid would ever publish figures indicating any difference in the CV values as measured at the 110 different locations. As these probably vary on a daily basis and would open them up to all sorts of claims and complaints.
michael adams
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Thanks Michael. The reason being the CV of gas bulb quote on my statement does not equate to what they charge on my statement. When questioned they say it was what the rate was on the day my statement was issued which means I cannot check (accurately) my bill for that month.
Example: They quote a CV of 39.3 on my statement but then charge me at
39.57.Previous suppliers had the 2 figures matching. So now I am attempting to track down a source for the CV figures to compare to what they state/charge.
As both figures fall within the range given by National Grid of 37.5 MJ/m3 to 43.0 MJ/m3, you simply have no case I'm afraid.
Basically National Grid are saying that they can only guarantee to supply gas to the various Gas Co's within that range. But they can't guarantee to supply a specific value at any one time. As National Grid they'll take regular readings to ensure the supply falls within that range but won't supply that information to the Gas CO's.
Both your previous supplier and this one are simply quoting nominal figures which are slightly less than the mid point of the National Grid range which would be 40.25. Other than that, neither they nor National Grid have any way of measuring the CV value of the supply to your house with any accuracy.
michael adams
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I understand your comments and I couldnt care less about the few pence, but if they are going to charge 39.57 on the statement which then on that same statement I argue that they should quote 39.57 and not 39.3.
I am probably having a personal tantrum over this but I have my own spreadsheet and each month I enter the gas and elec readings and it gives me the exact amount the utility company charges (or did previously) so it gives me a check on their charges plus a bit of personal satisfaction that my spreadsheet actually works. I now have to do other manual changes to cope with their inaccurate statements/figures.
Ah the joys of retirement when you have the time to get uptight over the small things in life.
Reading further down the link it states the following
quote The amount of energy consumed by a customer is calculated using the following formula: The United Kingdom mainland has been subdivided into thirteen charging areas. A daily CV average for each charging area is provided by National Grid to the gas shippers and suppliers, and is calculated as follows:-
[...]The daily CV average for the charging area is then calculated by summing the product of the CV and volume for all the inputs and dividing by the total volume of gas entering the charging area.
/quote
Basically the CV for your charging area changes daily. Your bill for say 90 days will be the average of those CV's.
Possibly that's where the two figures come in. One figure was the CV on a particular day while the other is the average CV over the whole charging period.
And its on this (higher in this case) average that your charge will be based.
Given that the CV changes daily -
Say you go on holiday for 2 weeks, then your bill won't be correct because it includes 14 readings for days when you didn't use any gas. Similarly if you use a different amount of gas on different days with a different CV then again the bill won't accurately reflect your use.
Possibly the reason the figures don't reconcile is simply because you're not using the higher (in this case) average CV which covers the whole month ?
If you had a sufficiently long supply pipe from the main, and used very little gas as compared with your neighbours, then quite possibly the CV of your gas might differ markedly from that of your neighbours. They'd be getting fresh supplies while yours might have been sitting in your supply pipe since yesterday.
michael adams
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as measured by a very accurate instrument fitted to your own and your neighbours meters could differ markedly.
From what I gather the companies use set points to monitor the CV, I have now got that on a website so can check against their readings for accuaracy.
OOI, why does the CV vary? I assume it's down to the mix of gases within the supply (methane, propane, butane etc.), but is this actually the case do you know, or does it also contain non-combustibles such as nitrogen or CO2 in varying amounts depending on source, processing etc. ?
A good working approximation is mostly methane 96% with some ethane 3% and traces of propane and butane. Some CO2 and N2 as inerts 1%.
Can't find a UK analysis certificate but natural gas is similar the world over and Canada gas are a bit more open:
Since it is a by volume supply measure you get more calorific value in an ethane rich mix and less if there is more N2 and CO2 than normal.
Thanks. Following your reply, I did a little searching and came across this calculator, which allows you to calculate the CV in various units, for different natural gas compositions.
I also found references to High CV and Low CV* depending on whether the latent heat is recovered from the water vapour, e.g. in a condensing boiler. I assume the NG figures refer to the former, although they don't specifically say so.
*described as Superior and Inferior in the calculator above.
There is legislation which governs how suppliers use CVs to bill you plus OFGEM guidance on its interpretation. I suggest you look at:
Note especially:
"National Grid is responsible for determining the daily average CV for each charging area. National Grid publishes this daily average CV for each charging area rounded to one decimal place in accordance with Regulation 4 (4) (set out in Appendix 1). National Grid then transmits this daily calorific value electronically to gas transporters and gas suppliers for their respective uses."
You can get the data at:
So your previous suppliers designed their billing software better. Presumably your current bill was designed a) by someone who didn't think about the presentation and b) who didn't understand the natural variations in the supply anyway.
It was a long time ago, but when I worked for BG in the Central Control department, there was one guy whose job was to collate all the data from the terminals where gas was bought onshore including the various factors needed to calculate the cv. (Temperature, humidity and so on). These were processed and submitted to the regulator to demonstrate that BG was supplying gas properly.
So there will be records somewhere.
(That was one of the first sections I affected with IT. An IBM PC, copy of Lotus and 7475 plotter, and what used to take 3 weeks was done in 3 hours.)
Certainly with North Sea Gas (if there's any left) there's a certain amount of moisture in the mix.
The CV used for the charging period will be an average of all the daily CV readings for the OP's charging area, during that period . Its almost certain that one of the CV values on the OP's bill will match that average.
If the site includes historical data this will allow the OP to calculate this for himself for past bills. Otherwise preumably it will need to be updated on a daily basis.
The OP's problem however is why there are two figures given on his Bill.
" They quote a CV of 39.3 on my statement but then charge me at
39.57 ".Now if the company's customers were confined to statisticians*; then quite possibly one of those the figures might represent something quite exotic. But as the bills are aimed at the public that doesn't really wash.
michael adams
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Indeed it ought to. As stated in the regs and in the OFGEM guidance.
But the OP seemed to want to _check_ their calculation.
Anyhow, his opening question was "Is there a website that gives the calorific values for gas on daily/weekly or monthly basis by area?" so I thought I'd answer that. I didn't seem any harm in doing so.
It allows one to download the daily figures for whatever period you want for at least the past 6 years. That's why I pointed him to it.
I'd prefer to see exactly what the bill shows before commenting on that.
Indeed. It should allow him to find out whch of the two CV figures on the bill is the actual average. Possibly the actual start and finish dates might be crucial depending on the the daily rate of change, so he might need to adjust the dates to get a match.
Unfortunately the company in question Bulb Energy don't seem to provide much information about their bills online along the lines of "What do the figures mean" or maybe I simply can't find it.
michael adams
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How is gas pressure taken into account in these calcs?
That's the point where I bow out, and the experts enter :)
All I can tell the OP is that cv calculations were taken very seriously in the 1980s in the clear understanding that it was a legal requirement.
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