Heating Value
The volume of gas flow provide by a gas meter is just that, a reading of volume. Gas volume does not take into account the quality of the gas, the amount of heat available when burned. Utility customers are billed according to the heat available in the gas. The quality of the gas is measured and adjust for in each billing cycle. This is known by several names as the calorific value, heating value, or therm value.
The calorific value of natural gas can be obtained using a process gas chromatograph, which measures the amount of each constituent of the gas, namely:
- methane
- ethane
- carbon dioxide
- water
Additionally, to convert from volume to thermal energy, the pressure and temperature of the gas must be taken into consideration. Pressure is generally not a problem; the meter is simply installed immediately downstream of a pressure regulator and is calibrated to read accurately at that pressure. Pressure compensation then occurs in the utility's billing system. Varying temperature cannot be handled as easily, but some meters are designed with built-in temperature compensation to keep them reasonably accurate over their designed temperature range. Others are corrected for temperature electronically.
Read more about this topic: Gas Meter
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