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TABLE F44 Pressure Drop of 20. 0 kPa LP GAS flow through STEELPIPE

TABLE F44 Pressure Drop of 20. 0 kPa LP GAS flow through STEELPIPE

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209

AS 5601 – 2000
AG 601 – 2000

APPENDIX G
DETERMINATION OF
MAXIMUM BREATHER VENT ORIFICE SIZE
FOR DEVICES NOT VENTED TO OUTSIDE ATMOSPHERE
(Normative)

G1 INTRODUCTION

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The following nomograms are designed for use with Natural Gas, LP Gas and TLP
for room or enclosure volume from 1 to 1000 m3. The gas pressure range is from 1
to 200 kPa. The nomograms assume uniform airflow through a room or enclosure
and, in the case of an escape, uniform dispersal of gas throughout the enclosure . In
reality however, even if the overall air-change rate is acceptable (equal to or greater
than 1 air-change per hour), conditions in the vicinity of the device may be less than
ideal and some care needs to be exercised in the application of the nomograms for
any or all of the following reasons:
(a)

The RD (relative density) of a gas influences its ability to disperse in air. The
lower the RD, the greater the ease with which the gas is able to disperse.

(b)

Air flow patterns through a room or enclosure , in particular in the vicinity of a
gas escape, greatly affect the ability of the air to dilute the gas to safe levels.
The greater the local air movement, the greater the ease with which the gas is
able to disperse.

(c)

The selection of a comparatively large breather vent orifice size, using the
appropriate nomogram, may in the event of a gas escape, result in
accelerating the formation of a localised unacceptable air-gas concentration
for the above reasons.

In such instances, consideration should be given to venting the device to
atmosphere.

G2 USING THE NOMOGRAMS
To use the nomograms:
(a)

Select the applicable nomogram for gas type, gas pressure and room or
enclosure size or vent diameter

(b)

From values of V, d or P, if any two are known, the remaining unknown value
can be determined by placing a straight-edge between the known values.

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AS 5601 – 2000
AG 601 – 2000

210

G3 EXAMPLE USING A NOMOGRAM
Using Natural Gas, an inlet pressure of 1.1 kPa and a known enclosure volume of
8 m3, the following procedure should be adopted to find the breather vent orifice
size:
(a)

Select Nomogram 1 (see example)

(b)

Find value 1.1 on the ‘P’ scale and 8 on the ‘V’ scale

(c)

Place a straight-edge between the values of ‘P’ and ‘V’.

(d)

Find value ‘d’ of 1 mm. (Note that this is a maximum value).
EXAMPLE OF USING A NOMOGRAM

V
1000
900
800
700
600

d

P

20

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500
400
300

10
9
8
7

200

6
5

100
90
80
70
60

4

3

1
1.1

2

2

50
40
30

3
4

20
1
0.9
0.8
10
9
8
7
6
5

0.7
0.6
0.5
0.4

4
0.3
3

2

0.2

1

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5
6
7

211

AS 5601 – 2000
AG 601 – 2000

NOMOGRAM 1A - NATURAL GAS
DETERMINATION OF MAXIMUM BREATHER VENT ORIFICE DIAMETER (d)
FOR PRESSURES (P) BETWEEN 1 kPa AND 7 kPa
AND ROOM VOLUME (V) UP TO 1000 m³
Nomogram is based on: d =

V
1000
900
800
700
600

d

0.360 V
4

P

P

20

500
400

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300

10
9
8
7

200

6
5

100
90
80
70
60

4

3

1
1.1

2

2

50
40
30

3
4

20
1
0.9
0.8
10
9
8
7
6
5

0.7
0.6
0.5
0.4

4
0.3
3

2

0.2

1

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5
6
7

AS 5601 – 2000
AG 601 – 2000

212

NOMOGRAM 1B- NATURAL GAS
DETERMINATION OF MAXIMUM BREATHER VENT ORIFICE DIAMETER (d)
FOR PRESSURES (P) BETWEEN 7 kPa AND 200 kPa
AND ROOM VOLUME (V) UP TO 1000 m³
Nomogram is based on: d =

V
1000
900
800
700
600
500

d

0.360 V
4

P

P

8
7
6

400
5
300

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4
200
3

100
90
80
70
60

2

7
8
9
10

15
20

50
40
30

1
0.9
0.8
0.7

20

0.6
0.5
0.4

10
9
8
7
6
5

0.3

40
50
60
70
80
90
100

150
200

0.2

4
0.15
3

2

30

0.1

1

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213

AS 5601 – 2000
AG 601 – 2000

NOMOGRAM 2A - LP GAS
DETERMINATION OF MAXIMUM BREATHER VENT ORIFICE DIAMETER (d)
FOR PRESSURES (P) BETWEEN 1 kPa AND 7 kPa
AND ROOM VOLUME (V) UP TO 1000 m³
Nomogram is based on:

V

d

d=

0.296 V
4

P

P

1000
900
800
700
600

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500
400

10
9
8

300

7
6

200

5
4

100
90
80
70
60

3
1
2

50
40

2

30
3
20

1
0.9
0.8
0.7
0.6

10
9
8
7
6

0.5
0.4

5
0.3
4
3
0.2
2
0.15

1

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4
5
6
7

AS 5601 – 2000
AG 601 – 2000

214

NOMOGRAM 2B - LP GAS
DETERMINATION OF MAXIMUM BREATHER VENT ORIFICE DIAMETER (d)
FOR PRESSURES (P) BETWEEN 7 kPa AND 200 kPa
AND ROOM VOLUME (V) UP TO 1000 m³
Nomogram is based on:

V
1000
900
800
700
600

d

d=

0.296 V
4

P

P

6

500
5
400
4

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300
3
200
7
8
9
10

2
100
90
80
70
60
50
40
30

15
1
0.9
0.8

20

30

0.7
0.6

40
50

20

0.5
0.4

10
9
8
7
6

0.3

150
0.2

5
4

60
70
80
90
100

0.15

3
0.1
2

1

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200

215

AS 5601 – 2000
AG 601 – 2000

NOMOGRAM 3A - TLP GAS
DETERMINATION OF MAXIMUM BREATHER VENT ORIFICE DIAMETER (d)
FOR PRESSURES (P) BETWEEN 0.5 kPa AND 7 kPa
AND ROOM VOLUME (V) UP TO 1000 m³
Nomogram is based on:

V

d

d=

0.546 V
4

P

P

1000
900
800
700
600
500

20

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400
300

200

10
9
8
7

100
90
80
70
60

6
5

0.5
0.6
0.7
0.8
0.9
1

4

50
40

3

2

30
3
2
4

20

5
6
7
10
9
8
7
6

1
0.9
0.8

5

0.6

4

0.7

0.5

3

0.4

2

0.3

1

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AS 5601 – 2000
AG 601 – 2000

216

NOMOGRAM 3B - TLP GAS
DETERMINATION OF MAXIMUM BREATHER VENT ORIFICE DIAMETER (d)
FOR PRESSURES (P) BETWEEN 7 kPa AND 200 kPa
AND ROOM VOLUME (V) UP TO 1000 m³
Nomogram is based on:

V

d

d=

0.546 V
4

P

P

20
1000
900
800
700
600
500

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400
300

10
9
8
7
6

200

5
4

100
90
80
70
60

7
8
9
10

3
15
2

20

50
40

30

30

20

40
1
0.9
0.8
0.7
0.6

10
9
8
7
6
5

2

1

60
70
80
90
100

0.5
0.4

150
200

0.3

4
3

50

0.2

0.15

0.1

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217

AS 5601 – 2000
AG 601 – 2000

APPENDIX H
FLUE DESIGN
(Normative)
NOTE: For appliances with atmospheric burners, see H1. For appliances with power
flues, see H2.

H1 FLUE DESIGN FOR APPLIANCES WITH ATMOSPHERIC
BURNERS
H1.1 Introduction
NOTE: Flue design requirements for appliances with forced draught burners should be
obtained from the Authority.

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The tables and procedures relating to H1 have been based on information from the
American Gas Association.
The tables have been calculated to allow for
approximately 50% burner excess air and approximately 100% draught diverter
dilution air.

Flues required to convey flue gases with greater quantities of excess air, dilution
air, or other combustion products are to be designed for the total quantity of flue
gas discharge, using sound engineering practice.
Tables H1 to H7 show the extent and limitations of natural draught flues, relative to
the thermal input, height, total length, diameter and other important factors to suit a
wide variation in flue configuration.
Table H8 shows equivalent sizes for round and rectangular flues.
Table H9 shows the relationship between percentage carbon dioxide (% CO 2),
volume of flue gases and amount of excess air.

H1.2 Factors influencing flue design
H1.2.1 Heat loss
In determining the correct size and configuration for a flue , the heat losses that will
occur due to the materials used and the environment in which the flue will be
located must always be considered. Since the motive force in a flue is due to the
heat of the flue gases, the ideal conditions are those in which heat losses from the
flue are very low.
Materials which are insulated against heat loss (eg. approved twin-wall flue ) or
materials of low thermal conductivity are particularly suitable when the flue is
located outdoors or is very long.
Non-insulated flue materials when located ‘indoors’ and not exposed to draught can
be classified as ‘low heat loss’ in applying the flue tables contained in this Standard.
The same materials when located ‘outdoors’ are classified as ‘high heat loss’.

H1.2.2 Resistance to flow of flue gases
Resistance to the flow of flue gases needs to be considered in the design of the
flue. The capacities shown in the tables for flues with laterals make an allowance
for two 90° changes of direction.
Where more than two 90° changes of direction are required, the flue is to be sized
using one of the following methods:

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AS 5601 – 2000
AG 601 – 2000

218

(a)

A 10% capacity reduction is made to the table for each additional bend or
change of direction (eg. one additional change, 90% of table capacity or two
additional changes, 80% of table capacity); or

(b)

Increase the flue diameter from the draught diverter outlet size to one size
larger.
NOTE: For calculation purposes, the flue capacity will be increased by
approximately 60% of the difference in capacity of the actual appliance or
draught diverter flue size, and the capacity of a similar flue one size larger.
Any further increase in size is not recommended because it will not have a
similar corresponding effect.

When using the tables to determine the flue size of wall furnaces and room heaters
(but not forced air central heaters), appliance gas consumption is to be regarded as
40% greater than the nominal figure on the data plate, eg. a wall furnace having a
gas consumption of 40 MJ/h would need to be sized for 40 x 1.4, that is, 56 MJ/h.

H1.3 Designing individual appliance flues

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The procedures for using the tables for individual flues, whether for low heat loss or
high heat loss, are identical.
Use Table H2 or H3, as appropriate, based on the type of material selected and the
location of the flue in regard to heat loss.
STEP 1 Determine the total flue height (H) of the system and the length of any
lateral. (See Figure H1).
STEP 2 Refer to Table H2 for low heat loss situations or Table H3 for high heat
loss situations.
Read down the ‘Total height of flue’ column at the left of the appropriate
table until a height equal to the height of the flue or the next lower flue
height figure is listed.
STEP 3 Select the horizontal row for the appropriate ‘Length of lateral’ (L). (Zero
for straight vertical systems).
STEP 4 Read across to the first column which shows a capacity equal to or
greater than the appliance gas consumption (after any factor indicated by
H1.2.2 has been applied).
STEP 5 If the flue diameter shown at the top of the column listing the appliance
gas consumption (or corrected gas consumption) is equal to or larger than
the appliance flue outlet, use the diameter indicated in the table.
If the diameter indicated is less than the appliance flue outlet size, the
smaller diameter may be used only where –
(a)

the flue height is greater than 3 m;

(b)

flues exceeding 300 mm in diameter are not reduced by more than
two sizes (600 mm to 500 mm is a two size reduction); or

(c)

flues 300 mm in diameter or less are not reduced by more than one
size (200 mm to 175 mm is a one size reduction).

However, under no circumstances shall a 75 mm flue be connected to an
appliance having a 100 mm flue outlet.
NOTE: Contact should be made with the Authority if a greater heat input into
a flue is required. Some Authorities do allow a greater heat input.

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219

AS 5601 – 2000
AG 601 – 2000

EXAMPLE OF FLUE DESIGN
A water heater is to be installed with a flue configuration as in Figure H1.
Total height is 2.5 m.
Length of lateral is 600 mm.

Appliance gas consumption is 120 MJ/h.
Appliance flue connection (draught diverter) is 125 mm diameter.
The flue will be located in a duct within the building except for 600 mm through the
roof.
STEP 1 Because the flue will be inside the building, the appropriate table will be
Table H2.
STEP 2 Under the column headed ‘Total height of flue’ locate 2.5 m.

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STEP 3 Locate the line in the next column corresponding to a lateral of 0.6 m.
STEP 4 Reading across the line to the right, note that the figures in the first two
columns (ie. 42 and 79) are less than the appliance gas consumption
(120 MJ/h). The figure in the third column is greater than the appliance
gas consumption and so the diameter (125 mm) at the top of this column
would be suitable. Therefore a 125 mm diameter flue would be used.
If it is essential to locate the 2.5 m of vertical flue on an external wall using noninsulated materials, then Table H3 would need to be used. Adopting the former
procedure, Table H3 indicates that a 150 mm diameter flue would be required.

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