Gas vs. Electricity Smart Meter - What's So Hard?

If you are an energy manager, you may have been getting high time resolution monitoring of electricity meter usage for a long time.  Not so much with gas!

Why Is Gas Smart-Metering so far behind Electricity ?

There are four fundamental differences on the measuring side of the coin and far more on the management side. Lets look at measurement purely in terms of practical complexity. For convenience we assume that an existing gas meter or electricity meter pops out a little pulse to measure an amount of something delivered. Usually this is done simply by making and breaking a connection - its a switch or relay.

So what do electricity meters measure ?

Answer -
Generally Watt-hours or some multiple (kWh) of the benefit delivered. (Technically we assume power factor correction on site but most readers can ignore this)

So what do gas meters measure ?

Answer - 
The volume of gas that has been delivered - NOT the benefit of that gas.

The differences are compounded:

  1. A volume of gas is not the same as an amount of gas. When gas pressure changes in the supply line (and it does) more or less gas is "squeezed" into the same space. This means that the gas pressure (and how it changes with time) must be known to allow a utility company to figure out how much gas you have had. This first calculation gives you a weight or number of molecules of gas delivered (roughly) at a particular temperature.
  2. The temperature of the gas delivered can also change over time - The first calculation must then be modified for the varying amount of gas because of temperature fluctuations.
  3. An amount of a particular gas carries a certain amount of energy that can be released by combustion, but the same amount of different gases carry different amounts of energy. Since the mix of gas delivered changes slightly every day, the amount of energy delivered in a weight of gas is not constant. Some very, very expensive gas meters can calculate and display these values.  Gas bills cannot therefore be accurately reconciled to the energy delivered.
Congratulations ! - You know have a big picture understanding of the following four laws of thermodynamics :
  • Boyle's Law,
  • Charles's law,
  • Gay-Lussac's law &
  • Avogadro's law

Isotherms of an ideal gas. The curved lines represent the relationship between pressure (on the vertical, y-axis) and volume (on the horizontal, x-axis) for an ideal gas at different temperatures: lines which are further away from the origin (that is, lines that are nearer to the top right-hand corner of the diagram) represent higher temperatures.

These are combined to form the Combined and ideal gas laws - for an intro try but you don't need to know that.

The fourth issue is very practical ...

 What you as an energy manager need to know is that Gas is EXPLOSIVE !  This means that getting power to a meter reader, GPRS signals and other things all lead to risk! So even after the brilliant boffin's know what to do with your data, remember that getting hold of it can be much tougher in the first place.

The practical impact is that not only is understanding gas data more complex, (where we can help ) but you should expect to pay your gas utility or metering provider more for a similar quality of service (where we cannot).  Natural Gas is usually cheaper than electricity per unit energy and cleaner than conventional power-station sourced electricity .

Disclaimer: We benefit from partnerships with various suppliers of energy data.
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