## Monday, 14 May 2018

### WHY YOUR GAS BILL IS WRONG

#### Domestic gas users are being overcharged by an average of £46 a year. That is the claim by an energy firm Canetis Technologies.

More than 20 million households use mains piped gas to provide hot water and central heating and often to cook their dinner too.

The way gas is charged for is an approximation. Canetis has calculated that three errors in these approximations leads to us being overcharged by an average of £46 a year.

Origin
Gas comes into the country from the North Sea, from Europe, and by tanker mainly from the middle east. It then passes through 190,000 miles of pipes and ends up flowing into what is usually a rather primitive meter in our home.

That meter measures the volume of gas passing through it. Traditional meters use a pair of bellows to measure the gas flow. The bellows then push a plastic clockwork mechanism to convert that flow into a numerical display which records either cubic metres (cu.m) or, in older and often greyer meters, cubic feet.

Formula
That volume then has to be converted into the kilowatt-hours units which energy firms charge us for. The formula used to make that conversion will be somewhere on your gas bill and should look like this:

Units used x the calorific value of the gas x a volume correction of 1.02264 divided by 3.6.

Definitions
1. Units used is the volume of gas recorded by the gas meter in cubic metres or cubic feet.

2. The calorific value of the gas is the amount of energy stored in the molecules of the gas.

3. The volume correction takes account of the average pressure and temperature of Great Britain which is different from the standard used to work out the calorific value of a cubic metre of gas.

The same amount of gas – the same number of molecules which store the energy which is released when it burns – will not fill a constant volume. As the pressure rises the molecules are squeezed together and the volume falls. As the temperature rises the molecules get more excited and the volume increases. That means the same volume of gas at different temperatures and pressures will give different amounts of energy when burned.

When the energy stored in a volume of gas is calculated the international standard is to use a temperature of 15C and atmospheric pressure at sea level of 1013.25 millibars (mb).

This correction adjusts that calorific value to take account of the temperature and pressure of Great Britain.

Each of these three parts of the formula is subject to error. The final part is not.

4. Divided by 3.6. Calorific value is measured in MegaJoules per cubic metre. A MegaJoule (MJ) is a million Watts per second. So to convert a MegaJoule (MJ) to a kiloWatt-hour (kWh) you multiply by 1000 and then divide by the number of seconds in an hour. So 1000/3600 = divide by 3.6. That is the one accurate number in the formula!

Errors
1. Units used
The energy technology firm Canetis claims that old style meters systematically overstate the volume of the gas passing through them. They are tested over a wide rage of gas flows. Low flows overstate the volume; higher flows underestimate it. But the meters are limited in the flow they are allowed to use and modern gas appliances tend to use lower flows anyway. The result is that the actual flows are always in the lower part of the range where the volume is systematically overstated.

2. Calorific value
The calorific value of natural gas varies depending on its exact composition - different sources have different mixtures of gases. It will be between 37.5 and 43.0 MJ per cubic metre.

Great Britain is divided into seven regions reflecting where the gas arrives. The calorific value of the gas in those regions is measured every day. The value on your bill is the average of those daily amounts in your area over the days the bill covers . It will therefore be approximate but the hope is that the over- and under-estimates will average out to zero.

3. Volume correction
In 1996 the Government decided that the international standard temperature of 15C and pressure of 1013.25mb for measuring the energy in a volume of gas were not correct for Great Britain. The average temperature in GB was lower at 12.2C. So the measured volume at that temperature was lower than it should be. And despite the UK being at an average height of 66m above sea level, when the pressure inside the meter was added it came to 1026mb, which is higher than the standard. So again the measured volume is lower than it should be.

As both errors lower the volume, the measured volume was multiplied by 1.02264 to correct it. This amount is set down in law.

Canetis and other engineers claim the assumptions behind the volume correction are wrong.

Pressure: recently analysed postcode data from the Office for National Statistics shows that GB homes are on average slightly higher than 66m above sea level, and the meters are normally above floor level. So the pressure is lower at the meter and the volume of gas greater than the regulations assume.

Temperature: the actual ambient temperature over the year is around 12C but most meters are located indoors in heated rooms so gas enters the meter at a warmer temperature than outside, again raising the volume.

So the volume correction is simply wrong.

Overcharge
The result is that these three errors
• meters which overstate the volume flowing through
• higher temperature at the meter than allowed for
• lower atmospheric pressure at the meter than allowed for
all create an over estimate of the volume of the gas passing through the meter for the standard energy contained in it. So charging by volume overcharges us for the energy stored. Canetis claims the average overcharge in England is £46 a year.

Action
Under the rules governing gas nothing can be done about any of these factors. They are all set in various laws and standards.

All customers can do is try to ensure that their gas meter is as low and cool as possible rather than high up in a heated room.

vs. 1.01
16 May 2018