McQuay MDS030AR Applications Manual page 79

Equivalent length
Equivalent length = actual pipe length + number of elbows X equivalent length of each
elbow + number of oil traps X equivalent length of each oil trap.
Diameter
9.52
12.70
15.88
19.02
22.02
25.40
28.58
31.80-41.30
For example: when 10HP outdoor unit's actual length is 80m, the piping diameter is 25.4mm,
ten elbows and three oil traps are used, then the equivalent length is calculated as follows:
Application of equivalent length
When the equivalent length is more than 90% of the actually allowable maximum piping length
(more than 63m in 6HP, 90m in 8/10HP), the gas pipe diameter of the main piping (piping from
the outdoor unit to the first branch) should be expanded to a higher level. For instance, when
the equivalent length of 10HP outdoor unit is more than 100m, the gas pipe diameter is
changed from 28.6mm to 31.8mm.
When the diameter of gas pipes is expanded to a higher level, the equivalent length should
be recalculated as follows:
Expanded equivalent length = equivalent length of main piping X 0.5 + equivalent length of the branch pipe
For example: when the actual length of 10HP outdoor unit is 80m, branch pipe length is 20m, the
diameter of the main gas pipe is 25.4mm, ten elbows and three oil traps are used (elbows and traps
are used only in main piping).
Equivalent length = 80+0.45X10+3.4X3=94.7(m)
As the equivalent length is more than 90m, the diameter of gas pipe in the main piping is
expanded to a higher level.
Expanded equivalent length =(60+0.45X10+3.4X3) X0.5+20=59.1(m).
Item
elbow(m)
Equivalent length = 80+0.45x10+3.4x3=94.7(m).
Design & installation Guide For McQuay MDS Multi System
0.18
0.20
0.25
0.35
0.40
0.45
0.50
0.55
oil trap(m)
1.3
1.5
2.0
2.4
3.0
3.4
3.7
4.0
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