Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
1
GENERAL................................................................................................................................................................ 2
2
PURPOSE ............................................................................................................................................................... 2
3
APPLICATION ....................................................................................................................................................... 2
4
REFERENCED DOCUMENTS ....................................................................................................................... 2
5
ENQUIRIES REGARDING THIS DOCUMENT........................................................................................ 2
6
INTRODUCTION................................................................................................................................................... 3
7
CONVERSION - SINGLE FACTOR METERS.......................................................................................... 3
7.1
8
THE FORMULA TO ARRIVE AT A ‘CORRECTION FACTOR’ .................................................................... 3
INTERVAL METERED CONNECTIONS..................................................................................................... 4
8.1
8.2
8.3
CORRECTION FACTOR ................................................................................................................................. 4
CALORIFIC VALUE ......................................................................................................................................... 4
ENERGY CONVERSION. ............................................................................................................................... 4
APPENDIX A
FACTORS EXPLAINED........................................................................................................... 5
PRESSURE CORRECTION FACTOR........................................................................................................................... 5
TEMPERATURE CORRECTION FACTOR................................................................................................................... 5
ALTITUDE FACTOR. ...................................................................................................................................................... 6
COMPRESSIBILITY FACTOR. ...................................................................................................................................... 7
CALORIFIC VALUE ......................................................................................................................................................... 7
APPENDIX B
CORRECTION FACTOR, VOLUME TO ENERGY CONVERSION...................... 8
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
Page 1 of 8
Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
1
GENERAL
Powerco Tasmania Pty Ltd (Powerco) holds a Gas Distribution licence (Licensed to Construct
and Operate gas networks) under Part 3 of the Tasmanian Gas Act 2000.
Powerco’s distribution network includes the Gas Measurement System (GMS) installed at a
consumer’s installation, which establishes the individual consumers supply point.
2
PURPOSE
Powerco is obligated under the terms of its Distribution Licence, to submit to the Director of
Gas, for approval, the methodology it employs to convert the volumetric measure of gas usage
recorded at the GMS (adjacent to the consumers individual supply point) to an energy value, for
which the consumer is charged.
This document outlines the two methodologies currently applied to the metering installations
being installed by Powerco.
3
APPLICATION
This standard is applicable to those metering installations being installed within the Tasmanian
State Jurisdiction under Powerco’s approved Safety and Operating Plan, document 350S004T.
4
REFERENCED DOCUMENTS
Powerco has nominated NZS 5259:2004 within its Safety and Operating Plan as the standard
for Gas Measurement.
This document was nominated by Powerco in the absence of any Australian Industry Standard
document and will remain in place in its current, modified or amended form or as replaced by an
appropriate Australian Standard, once developed and reviewed.
5
ENQUIRIES REGARDING THIS DOCUMENT
Any enquiries pertaining to this document should be directed to that person designated as the
Chief Operating Officer for Powerco Tasmania Pty Ltd.
Currently, Mr. Richie Sheather fills this position.
Mr Sheather is based in Powerco’s Albert Road Offices, PO Box 435, Moonah, Tasmania 7009.
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
Page 2 of 8
Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
6
INTRODUCTION
Powerco, as part of carrying out its role as the ‘Distribution entity’ within Tasmania, has
established several commercial and contractual mechanisms to allow retailers to distribute gas
they have purchased, to end users.
For the purposes of this document only two are relevant.
The Gas Distribution Services Agreement and Long Form Use Of System Agreement require
Powerco to calculate the energy consumed at a consumer connection (as measured by the
metering equipment) to comply with NZS 5259: 2004.
Powerco Tasmania will measure consumer gas usage in two distinct ways, firstly single factor
sites and secondly interval meter sites.
The following describes how gas measured under each of these metering situations will be
converted from cubic metres (volumetric measurement) to Joules (energy).
7
CONVERSION - SINGLE FACTOR METERS
This applies where a standard1 regulator and meter set is provided at a consumer’s premise that
does not adjust or record the variables that can effect energy value.
Typically this sort of metering is installed in domestic and smaller commercial / industrial
installations.
7.1 The formula to arrive at a ‘Correction factor’
The referenced standard includes the following formula to allow for the calculation required to
convert measured volume to a standard value of energy.
E = V × FT × FP × F A × FZ × H = V × F
where
F = FT × FP × FA × FZ × H
E
V
T
P
A
Z
H
1
is the energy to be billed.
is the volume registered by the meter.
temperature
pressure
altitude
compressibility.
is the heating value.
Regulator with preset output pressure up to a defined volume rate.
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
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Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
Each of the factors is summarised in Appendix A of this document and where appropriate,
outlines the considerations and data used by Powerco to substitute into the given formula.
Appendix B of this document outlines the derived ‘correction factors’ that result from the
application of the formula across the regulated pressures Powerco will operate it’s metering sets
at.
8 INTERVAL METERED CONNECTIONS
Where a consumer connection requires a supply of greater than 10 TJ’s pa, Powerco Tasmania
will be installing correction units (commonly referred to simply as ‘Correctors’) as part of the
consumer metering installation.
8.1 Correction Factor
These units are designed to monitor various components of the energy conversion formula
specific to that individual consumers metering site. Therefore estimation is not required.
Absolute Pressure, Temperature and Compressibility are all automatically calculated or preprogrammed for each cubic metre of gas that flows through the meter and logged.
8.2 Calorific Value
For interval metered customers (given the volumes involved and the potential for daily
fluctuations in load) the average daily heating value of the gas supplied into Tasmania as
recorded by the transmission company’s gas measurement system connected to Powerco
Tasmania’s network monitoring system (Scada) will be used.
8.3 Energy Conversion.
The consumers corrected volume usage as recorded by the consumer’s corrector is, on a daily
basis, multiplied by the corresponding days heating value to give a daily energy usage (Joules).
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
Page 4 of 8
Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
APPENDIX A
FACTORS EXPLAINED
Pressure correction factor.
When a meter is commissioned, the set pressure from its individual records is to be used. If
meters are set consistently, then the following pressure factors will apply.
Fp =
Pg + 101 .325
101 .325
Powerco Tasmania intends delivering pressure to residential, commercials and light industry
consumers at the regulated gauge pressures listed below (with the corresponding calculated
factor) unless specifically requested or the consumer demand is large enough to warrant
specific site pressure.
Regulated Pressure
(gauge 2)
3 kPa
7 kPa
35 kPa
70 kPa
100 kPa
Factor
(unitless)
1.0296
1.0691
1.3454
1.6908
1.9869
Temperature correction factor.
The average temperature of gas flowing through an individual meter may vary with flow rate,
season and other influencing factors. In general, the gas will be close to ground temperature
where the meter is remote from the offtake heating facility and the service line is not significantly
exposed to sunlight or ambient air.
Reviewing eight weather station sites from the Australian Government Bureau of Meteorology in
Hobart, Devonport, Launceston and Burnie (areas of reticulation during the second stage of the
natural gas rollout). Using the available data regarding soil temperature at 20cm depth recorded
at 0900 hours the following is noted:
Weather Station:
Burnie (Round Hill)
Hobart (Ellerslie Rd)
Hobart (Botanical Gardens)
Devonport East
Devonport
Launceston (Ti Tree Bend)
2
Mean average annual temp.
12.9 °C
12.1 °C
11.9 °C
12.0 °C
12.1 °C
11.3 °C
Note that absolute pressure is considered gauge pressure +101.325kPa.
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
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Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
11.8 °C
11.6 °C
Launceston (Pumping Station)
Launceston (Mount Pleasant)
An average ground temperature across these stations reports a figure of 12°C.
With the monthly site minimum figure being 5.1°C during July and a maximum monthly site
average of 17.6°C for January. Allowing for seasonal usage fluctuations i.e. more usage during
winter months than summer periods, a seasonal weighted average temperature of 11°C results.
Applying a Joule-Thomson factor of 0.5C for every 100kPa drop in regulated pressure this will
also affect the temperature correction factor.
Consequently using the above estimation for ground temperature the following temperature
correction factor can be determined.
FT =
288.15
273 .15 + 11 − (0.005 × ∆P)
Regulated Pressure
3
kPa
7
kPa
35
kPa
70
kPa
100
kPa
Factor
1.0230
1.0230
1.0224
1.0218
1.0213
Altitude factor.
Given the geography of zones in which the second stage of the natural gas network reticulation
will occur, an average altitude of 85m elevation above sea level can reasonably be adopted.
h
FA = 1 −
k2
FP
where
h = altitude = 85m
k 2 = 8500 m
This yields the following altitude correction factors for the relevant regulated delivery pressure.
Regulated Pressure
3 kPa
7 kPa
35 kPa
70 kPa
100 kPa
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
Factor
0.9903
0.9906
0.9926
0.9941
0.9950
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Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
Compressibility factor.
Compressibility is a physical characteristic of Natural Gas determined by its composition. Using
the composition anticipated in Alinta’s Master Gas Trading Terms and Conditions, we have the
following:
Compressibility at delivery pressure (regulated) and temperature (11°C- Joule-Thomson effect)
= Z.
Compressibility at standard temperature and pressure3 = Zb:
FZ = Z
Zb
For all cases anticipated this factor is 0.998.
Calorific value.
Calorific value for natural gas is a physical characteristic determined by it’s composition. Upon
reviewing the last 12 months average daily data as recorded by the transmission company for
gas delivered to Tasmania, the average higher heating value figure sits at 38.6405. Reviewing
this against a three month rolling average (the anticipated long term reading cycle to this
customer class), the maximum resulting variation during the 12-month period was +/- 0.4%.
Given these minor variations it is reasonable to apply the average result.
H = 38.6405
3
STP is 101.325kPa and 288.15K.
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
Page 7 of 8
Status - Issued
Standard - 170S003T
Version 2 - February 2006
GAS CONNECT IONS – MET ER ING CORRECT ION MET HODOLOGY
APPENDIX B
CORRECTION FACTOR, VOLUME TO ENERGY CONVERSION.
Given the factors and values provided in Appendix A and substituting these as appropriate in
the formula below (outlined in the main body of this standard) we can arrive at a series of
standard ‘correction factors’ that allow for the direct conversion from volume to energy for
each of the different meter operating pressures.
E = V × FT × FP × F A × FZ × H = V × F
The factor F is the product of all the individual correction factors and the calorific value of the
gas.
In short this is strongly influenced by an estimation of average gas temperature in the network
being similar to the average soil temperature of 11°C reduced at regulation by the JouleThomson effect.
The table of factors for the relevant regulated pressures based on the above is:
Regulated Pressure
3 kPa
7 kPa
35 kPa
70 kPa
100 kPa
Correction Factor (MJ)
40.2248
41.7781
52.6554
66.2337
77.8567
As part of Powerco Tasmania’s ongoing operations each of the components that make up the
energy correction factor will be monitored on an annual basis to identify any material changes or
trends that would affect the accuracy of the above factors.
Authorised by: Chief Operating Officer
© Powerco Tasmania Pty Ltd 2006
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