Information Sheet



Industry Information Sheet 0nn

October 2009

CONVERSION FACTORS FOR METERED ESTATE USE

The Competition Commission Order DOMESTIC BULK LIQUEFIED PETROLEUM GAS MARKET INVESTIGATION (METERED ESTATES) Paragraph 11.0 (b) requires a conversion rate to be provided by UKLPG.

The conversion rate(s) are:

For metric meters (measurement in m3)

1m3 vapour = 3.85 litres liquid

For imperial meters (measurement in ft3)

1 cu ft vapour = 0.109 litres of liquid

The Metric Meter Calculation:

The “conversion rate” can then be calculated as:

(1000/270) * ((1042.14 * 288.15) / (1013.25 * 285.35))

Which means 1 m3 of vapour = 3.85 litres of liquid.

The Imperial Meter Calculation:

35.135 cu ft =1000 litres (1000/28.33)

so 35.315 cu ft vapour = 3.85 litres of liquid

so 1 cu ft vapour = (3.85/35.315) = 0.109 litres of liquid.

UKLPG has, for many years, published physical data on LPG in its Codes of Practice. These imply that at normal temperature and pressure (NTP: 15 °C (288.15 K), 1013.25 mbar) that 1 volume of liquid propane will expand to between 268 and 277 volumes of vapour depending on the composition. A recent revision of the data table (Code of Practice 1 part 1: January 2009) gives a figure of 270 but stresses that this is an approximate figure.

Vapour meters inevitably operate at a temperature other than 15 °C (288.15 K). Ofgem publishes an average meter temperature in the UK of 12.2 °C (285.35 K). Equally on LPG they operate at a pressure of 37 mbar above the “normal” pressure of 1013.25 mbar but this is reduced by a factor dependent on the altitude of the meter. Ofgem publishes an average height of meters in the UK of 66 m, this corresponds to a reduction of 8.11mbar.

The TSMT considered that bearing in mind all the variables the Ofgem and COP 1 part 1 values should be used in developing a single “conversion rate” but that the final figure should be quoted to no more than three significant figures.

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