4.3 Permitted Piping Lengths and Level Differences
4.3.1 Connection with only VRF indoor units
The piping length and level difference requirements that apply are summarized in Table 3-4.3 and are fully described as
follows (refer to Figure 3-4.2):
1. Requirement 1: The total length of piping in each refrigerant system should not exceed 1000m. When calculating the
total length of piping, the actual length of the indoor main pipes (the piping between the first indoor branch joint and
the MS box, L2 to L9) should be doubled.
2. Requirement 2: The piping between the farthest indoor unit and the first outdoor branch joint should not exceed 175m
(actual length) and 200m (equivalent length). (The equivalent length of each branch joint is 0.5m and the equivalent
length of each MS box is 1m.) When the equivalent piping length from outdoor units to the farthest indoor unit is larger
than 90 m, the liquid pipe of the main pipe (L1) should be increased as Table 3-4.2
3. Requirement 3: The piping between the farthest indoor unit (N8) and first indoor branch joint (A) should not exceed
40m in length (L2 + L4 + f + i ≤ 40m) unless the following conditions are met and the following measures are taken, in
which case the permitted length is up to 90m:
Conditions:
a) The piping from each indoor unit to its nearest branch joint or MS box does not exceed 40m in length (a to m each
≤ 40m).
b) The difference in length between {the piping from the first indoor branch joint (A) to the farthest indoor unit (N8)}
and {the piping from the first indoor branch joint (A) to the nearest indoor unit (N3)} does not exceed 40m. That
is: (L1 + L2 + L4 + f + i) - (L1 + L2 + L3 + c) ≤ 40m.
Measures:
a) Increase the diameter of the indoor main pipes (the piping between
the first indoor branch joint and the MS box, L
2
to L
9
) as per Table 3-
4.2, except for indoor main pipes which are already the same size as
the main pipe (L
1
), for which no diameter increases are required.
4. Requirement 4: The largest level difference between indoor unit and
outdoor unit should not exceed 110m.
If the outdoor unit is above and the level difference is greater than 50 m, the liquid pipe of the main pipe (L1) should
be increased as Table 3-4.2. And it is recommended that an oil return bend with
dimensions as specified in Figure 3-4.1 is set every 10m in the gas pipe of the
main pipe.
If the outdoor unit is below and the level difference is more than 40 m, the
liquid pipe of the main pipe (L1) should be increased as Table 3-4.2.
5. Requirement 5: The largest level difference between indoor units should not
exceed 30m.
6. Requirement 6: Piping between outdoor unit and outdoor branch joint should
not exceed 30m. g1 ≤ 10 m; g2+G1 ≤ 10 m; g3 + G1 ≤ 10 m
Notes:
1. The size of main liquid pipe (L1) and indoor main liquid pipes (L2 to L9) can only be increased once if one or more of requirements are met in the requirement
2 to requirement 4.
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