What is the calorific value for billing purposes?

Natural gas is a natural product

Natural gas is a natural product. This means that its composition can vary. Put simply: not every cubic metre of gas contains exactly the same amount of energy (heat).

The billing calorific value is therefore the key factor in ensuring a fair bill.

• What it measures: It indicates how much pure energy is actually contained in the gas that reaches you.
• How we measure it: As the quality can vary, the calorific value is constantly measured within the network.
• Your bill: For your bill, we do not use individual snapshots, but calculate a weighted average over the entire billing period. This ensures that you pay exactly for the amount of energy you have actually received.

Our commitment to transparency In accordance with Section 40(1), first sentence, No. 7 of the GasNZV, we, as the network operator, publish the previous month’s billing calorific value at all entry and exit points on the 10th working day of the month. This is done in a standard format so that you can view the data at any time.

Gas billing in accordance with G 685

Your gas meter measures the volume of gas passing through it in cubic metres (m³). But cubic metres are not always the same! The volume of gas changes depending on how cold or warm it is and the pressure it is under.

The condition factor is a factor that compensates for this change in volume. It ensures that the amount of gas billed is always based on a standardised condition, regardless of whether it is winter or summer.

The state factor is ‘calculated’ from three main components:

Temperature of the gas:

• Think of a balloon in the sun: when it’s warm, the air (and gas too) expands and takes up more space. When it’s cold, it contracts and takes up less space.
• It’s exactly the same with gas: warm gas occupies more volume than cold gas – even if the same amount of gas is present.
• The state number takes this into account: if the gas is warmer than ‘normal’, the state number becomes slightly smaller. If it is colder, it becomes slightly larger. This balances out the effect of temperature on volume.

Gas pressure:

• Imagine a syringe: when you push the plunger in, you reduce the space and increase the pressure. The same amount of air (or gas) is ‘compressed’ into a smaller space.
• It’s similar with the gas network: the pressure in the gas network can fluctuate slightly. Higher pressure means that the gas is slightly ‘compressed’ and occupies less volume. Lower pressure means that it can expand slightly and occupy more volume.
• Here, too, the state number corrects for this: at higher pressure, the state number becomes slightly smaller; at lower pressure, it becomes slightly larger, to compensate for the difference in pressure.

Geodetic height (height above sea level):

• Think about air pressure: on a mountain, the air pressure is lower than in the valley. This is because there is less ‘column of air’ weighing down on you.
• Gas pressure is also slightly affected: at higher altitudes, the ambient pressure is lower. This means that gas can expand slightly more than at lower altitudes, where the higher air pressure ‘holds it together’ to some extent.
• The condition factor takes your altitude into account: if your house is at a higher altitude, the condition factor is adjusted slightly to compensate for this effect of lower air pressure.

How is it calculated?

Network operators measure temperature and pressure and know the geodetic altitude of your location. From this, they calculate the condition factor. This condition factor is then used to correctly convert your gas consumption into thermal energy (kWh).

Thermal energy – this is the energy you actually use

Thermal energy is what you’re actually interested in: the amount of heat you’ve actually used and which you’re billed for. It’s measured in kilowatt-hours (kWh), just like electricity.

• Put simply: thermal energy is the ‘final’ energy value that determines your heating costs.
• Why is this important? Because your heating, hot water and cooker generate heat. This heat is measured in kWh and billed accordingly.
  

How it all fits together: How your gas bill is calculated

Now let’s put it all together to understand how your gas bill is calculated:

1. Your gas meter measures gas consumption in cubic metres (m³). This is the meter reading.
2. This meter reading is multiplied by the condition factor. This converts the measured volume into a standard volume that is independent of temperature and pressure. This is referred to as standard cubic metres (Nm³).
3. The standard volume (Nm³) is multiplied by the billing calorific value. This converts the standard volume into thermal energy (kWh). After all, the calorific value tells us how much heat is contained in one cubic metre of gas.

Formula:

Thermal energy (kWh) = Meter reading (m³) × condition factor × billing calorific value

Calculation example:

Let’s assume you have consumed 100 cubic metres of gas during the billing period. Your bill shows the following figures:

• Meter reading: 100 m³
• Condition factor: 0.95 (less than 1 indicates, for example, a slightly higher temperature or lower pressure than standard)
• Billing calorific value: 11.0 kWh/Nm³

Calculation:

• Standard volume: 100 m³ x 0.95 = 95 Nm³
• Thermal energy: 95 Nm³ x 11.0 kWh/Nm³ = 1,045 kWh

Result: You will be billed for 1,045 kWh of thermal energy. This figure is then multiplied by the agreed gas price per kWh to determine the final amount of your bill.

In summary:

• Calorific value for billing: The ‘quality’ of the gas, i.e. how much heat it provides.
• Condition number: A correction factor for volume changes due to temperature and pressure.
• Thermal energy: The actual amount of energy billed in kWh.

These three factors ensure that your gas bill is accurate and reflects your actual energy consumption.

Good to know: This method of calculation and the use of the billing calorific value and condition number are regulated in Germany by DVGW worksheet G 685. This set of regulations ensures uniform and transparent billing standards in the gas supply sector.

We hope this explanation helps you to better understand your gas bill.

If you have any further questions, please do not hesitate to contact us!