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# How do OVO convert gas units to Kwh on a smart meter?

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The calorific value is needed by the Smart Meter to convert the volume of the gas to the energy produced by the gas Kwh. As this varies on a daily basis what value does the meter use?

Is this the same value as used by the bill?
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Best answer by Beth_OVO 14 December 2018, 12:04

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Userlevel 1
The amount of energy in a given volume of gas is dependent on the temperature of the gas. Does the smart meter take into account the temperature of the gas when converting from the volume measured to the energy kwh?

If so then does the bill receive the kwh measurement from the meter rather then the volume measurement?
Userlevel 2

Updated on 19/07/23Â by Abby_OVO

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Great question to ask. You may have noticed your smart meter will show your gas readings in both volume (metres cubed or m3) and in the kWh units that are charged on your monthly summary.

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In order to covert a m3 unit to kWh, we need to carry out a complex equation which involves taking into account the calorific value of gas. As this can change month to month, the calorific value we use to calculate your charges may differ slightly to the one used by your meter, which uses a set value of 39.2. As the calorific value changes so often, it's not practical for the meter to be constantly updated with it. However your monthly summary willÂ use the up-to date calorific value that you can find onlineÂ here.

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When submitting your meter readings manually on your online account or OVO app (download for Android or iOS), youâ€™ll only need to send us the m3 figure and weâ€™ll do the rest. Find out how to read your meter reading manually here.

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Hope this helpsÂ

Userlevel 1
Hi Beth,
Thanks for the information. What is the value that is used in my Smart Meter? If it is based on last month's bill then the Kwh readings will not match the values in my next bill as it is not known yet!

Russell
Userlevel 5
Hi @Russell - your smart meter will measure your gas in meters cubed. It clocks the volume of gas that has travelled through your meter.

Hope this helps!
Userlevel 1
Hi Nancy,
OK thanks
The volume of gas that is read by the meter is converted to Kwh that is also displayed by the meter using the Calorific Value held in the meter. The Calorific Value used on my last bill was 39.1

I have calculated the Calorific Value my meter uses by taking readings as follows
https://
It appears my meter is using 39.5 which does not match the value on my last bill.

How do I find out the Calorific Value that you have programmed into my meter?

How often is this changed and when?

Please can you confirm the Calorific Value held in the meter will never match the Calorific Value used in my next bill as it is not known until my next bill is produced. Hence can you confirm that the Kwh shown by the meter for the billing period will never match the Kwh shown on the bill for the billing period as both use different Calorific Values.

Russell
Userlevel 1
Hi Nancy,
It looks like my calculation of CV used by my meter did not render above. Hope you can see this

Russell
Userlevel 5
Hi @Russell,

I've got some more information on this. Because the calorific value changes so often, it's not practical for the meter to be constantly updated with it. The meter operates on an average calorific value of 39.2. As Beth mentioned, if you need to know the calorific value used in your bill that month, you can find it on page 5.

Hope this helps.
Userlevel 1
Hi Nancy,
Thanks for this.
I have taken readings again on 09/01 and I calculate the CV as 39.5. Is it possible to confirm the CV the meter operates on as mine does not appear to use 39.2?

For the December period my bill used 39.0 for the CV.

So based on the volume used of 212 m2 with a difference of 0.5 between the meter CV
and the Gas Bill CV the meter displays another 30 kwh used.
This means the meter overestimates the charge by 0.0333 * 30 = Â£1.00 plus VAT
Is this correct?
Thanks,
Russell
Userlevel 1
https:///members/russell-21378 raises an interesting question about how you determine the calorific value you need to apply when you're trying to check your gas charges. As already explained in this thread, the complication here is that the actual calorific value of the gas coming out of the pipe varies from day to day. But without knowing the relevant calorific value used by OVO, you can't accurately convert the smart meter's gas volume measurement (in cubic meters) to the kWh figure that is used to work out what you're actually charged for your gas.
In answering this query @Nancy_OVO and @Beth_OVO point out that you can check the relevant calorific value on page 5 of your last gas bill.
This used to be true, but I don't think this information is available any more to those of us who have been moved over to the new "OVO online account". That's because you can't download an old-style monthly bill any more. I don't think the relevant calorific value used by OVO appears anywhere on the new 'online account" web pages. My apologies if I'm wrong about this - if I've missed it, please could someone let me know where the value is?
By the way, the old-style pdf bills stated the gas meter readings at the beginning and end of the monthly billing period - so you could check that the correct number of units (ie., cubic meters of gas) had been used to work out your bill.
You can still see this info on the new online screens - but not in a form that can be downloaded. What you have to do is go to the 'usage' screen and then mouse over the bar showing usage for the first day of the month on the usage graph. This reveals a pop-up that shows the meter reading at the beginning of that day. If you then do the same thing for the last day of the month you can see the reading at the end of that day. Then you've got the readings used for the beginning and end of the monthly period. If you also happen to know the calorific value to apply, bingo, you can still check your gas charges!
Finally, should you want to store a record of the above meter readings, the pop-up won't print, but you can, of course, screenshot the graph while the pop-up is displayed. That's all a bit of a hassle - it would be nice if the new system could be enhanced so that a pdf containing comprehensive info for the month could be downloaded by customers who want it.
Userlevel 7

@Russell

this is a tough one for a simple old moderator for me to answer. If there's anyone I know in this community that could advise, it's our NinjaÂ @Transparent - they might not be inclined with this not being the most fun of challenges. If so, send us a message on webchat via the Help CentreÂ to ask for our billing team, as they get paid to work this out.

RobC make sure to post this in this subforum to make sure your feedback is noted!

Tim

Userlevel 7
+2
Well, as a starter: can I direct other Forum Members to have a look at this Topic where I actually ran through the calculations used to generate a gas bill in kWh.

My next observation about @Russell's precise question is that no meter is going to be 100% accurate. I would expect to see a margin of error being stipulated by the manufacturer when they perform the final test on each unit. So it wouldn't surprise me if the "error" of Â£1 you've calculated is still within the acceptable range.

I wonder if @Nancy_OVO or @Tim_OVO can find someone in OVO who actually holds a copy of a Final Test Certificate for a Secure meter. It could be printed on there.

Finally, I believe that the CV also differs according to where you are in the UK. I don't know how much granularity there is in defining this, but I expect there's a website somewhere with a table that displays the CV against a number of sampling points at various places in the network. Perhaps I need to have a nose around to see what I can find.
Userlevel 7
+2
Further to what I've just posted, the National Grid for Gas website gives some background to how they assess the CV and supply that information.

There are 110 sampling points in England and Wales, with a further 13 in Scotland.
Userlevel 1
Energy regulator Ofgem has provided a useful explanation of calorific value and guidance on how it is used to calculate charges by gas supply companies such as OVO.

Basically National Grid (the high pressure gas pipeline network operator) works out the average 'gas day' calorific value for each local area in the UK - these are known as LDZs or local distribution zones. These daily figures are then sent to the gas supply companies. In fact you can download these figures yourself via a 'Data Item Explorer' link from the National Grid web page identified above by @Transparent .

In order to work out a customer's average calorific value for a particular charging period, the gas supply company then totals up the daily figures for the relevant LDZ - and then divides the total by the number of days in the period to give the average figure.

This is my understanding of how it works - but, as always, I'm open to correction!
Userlevel 1

Anyone want to take a stab at this? Bear in mind I don't have a smart meter so the readings are actual.Â

As an example of one statement. On checking my last statement re my meter readingsÂ my recorded gas usage was 67 ft3.

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Converted to cubic metres is 189.7229

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Converted to kWh is 2122.3869

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Ovo charged me for 2138 kwh

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Userlevel 5

Hey @NoiseMaker,

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Youâ€™ll need to convert the volume you used to the energy value, youâ€™ll need your calorific value to do this. Check the best answer for info on where to find this.Â

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Hereâ€™s the calculation for Imperial meters:

(Number of gas units used) x 1.02264 (Volume correction, which takes into account changes such as temperature and pressure) x 39.42 (an average Calorific value) / 3.6 (conversion to Kwh) x 2.83 (adjustment for imperial units) = Usage in Kwh
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Hereâ€™s the calculation for Metric meters:Â

(Number of gas units used) x 1.02264 (Volume correction, which takes into account changes such as temperature and pressure) x 39.42 (an average Calorific value) / 3.6 (conversion to Kwh) = Usage in Kwh

Â

Userlevel 1

HeyÂ @NoiseMaker,

Â

Youâ€™ll need to convert the volume you used to the energy value, youâ€™ll need your calorific value to do this. Check the best answer for info on where to find this.Â

Â

Hereâ€™s the calculation for Imperial meters:

(Number of gas units used) x 1.02264 (Volume correction, which takes into account changes such as temperature and pressure) x 39.42 (an average Calorific value) / 3.6 (conversion to Kwh) x 2.83 (adjustment for imperial units) = Usage in Kwh
Â

Hereâ€™s the calculation for Metric meters:Â

(Number of gas units used) x 1.02264 (Volume correction, which takes into account changes such as temperature and pressure) x 39.42 (an average Calorific value) / 3.6 (conversion to Kwh) = Usage in Kwh

Â

Yes. I've seen this. So please go ahead and apply that to my meter reading above and tell me your answer at each stage. Don't forget,Â  you're using the 67 ft3 to start.

Userlevel 6

We really need to see the calorific value used on your statement,Â @NoiseMaker, if you need this lookingÂ  into as it is account specific, please reach out to the team.Â

You can send us a message on Facebook, Twitter, webchat via the Help Centre. You can reach our team on: 0330 303 5063. Our opening hours are 8am-6pm Monday to Friday.

Thanks!

Userlevel 7
+2

Hi @NoiseMaker. I gave quite a full answer to this very issue over here on another Topic last year.

Userlevel 1

Hi Everybody

Â

Iâ€™m trying to figure out roughly how much per hour it costs me to have my heating on.

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I swithched my heating on for 1 hourÂ and did readings just before and just after. Â I used 0.765 m3. Â How on earth do I tell how much that is in kWh so I can tell roughly how much per hour my heating costs? Â I know it can vary due to temp of gas â€¦etc etc , but I just want a ball park figure?

Â

Userlevel 7
+2

I make it 88p but prepared to be corrected !!

(assuming calorific value average figure of 39.2)

(vol x calval x 1.02264) / 3.6

assuming 10.3 p/kWh

Userlevel 1

Thanks! Â The calculation is very complicated for me! Â

I check my app nearly every day, checking my KWH (as opposed to cost). I figured the kwh don't change, I use what I use each day (I am on a smart meter).

I checked all through Dec and every say was between 11 and 13 kwh. HOWEVER, I go in on the day I am billed and every single day in Dec shows TWICE as many kwh used as when I was checking.

Question - why did my kwh change? I didn't suddenly use more kwh once I got my bill! Has this happened to anyone else? I am writing everything down this month and taking screwn shots as proof should OVO do that again!!!!

Userlevel 7
+5

HiÂ @KayCommisÂ have you checked your meter readings? If so are these actual or estimated? (They might still be estimated at some times even with a smart meter). This might be the reason. Otherwise, depending on your heating, it was much colder during that time so your heating probably use more

HiÂ @KayCommisÂ have you checked your meter readings? If so are these actual or estimated? (They might still be estimated at some times even with a smart meter). This might be the reason. Otherwise, depending on your heating, it was much colder during that time so your heating probably use more

But the app tells me about 2 days later what I used on the day.... so for example, on the 13th of the month the app will tell me my exact daily use of 11th of the month.Â

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I thought smart readers meant that I don't need to send meter readings anymore?

Userlevel 7
+5

HiÂ @KayCommisÂ have you checked your meter readings? If so are these actual or estimated?Â

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I thought smart readers meant that I don't need to send meter readings anymore?

Generally yes but they can occasionally lose signal so itâ€™s worth just checking what it says against your meter readings