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The following is an example of manual pipe size calculations. Designers are highly encouraged to use LATS instead of manual calculations.
Water Mini System Using Y-branches and Header
Example: Five (5) indoor units connected
Water Source Units (WSU).
IDU: Indoor Units.
Y-branches.
Header.
A: Main Pipe from First Y-branch.
B: Pipe from Y-branch to Y-branch or Header.
C: Pipe from Y-branch or Header to Indoor Unit.
D: Pipe to Farthest Indoor Unit.
• Indoor units must be installed at a lower position
than the Header.
• Y-branch pipes cannot be used after Headers.
• Install the Header so that the pipe distances
between the between the connected indoor
units are minimized. Large differences in pipe
distances can cause indoor unit performances
to fluctuate.
• Always reference the LATS software report.
Table 29: Pipe Capabilities.
Length
A + ΣB + ΣC + D ≤475.7 feet
ℓ
Elevation1
Elevation2
Distance between fittings and indoor units
Distance between fittings and
Y-branches
Distance between two Y-branches
Distance between Header and indoor units
For calculation purposes, assume equivalent pipe length of Y-branch is 1.6 feet, and equivalent pipe length of header is 3.3 feet.
1
Table 30: Refrigerant Pipe Diameter (B) from Y-branch to Y-branch / Header.
Downstream Total Capacity of Indoor Units (Btu/h)
≤19,100
< 54,600
≤76,400
• Connection piping from branch to branch cannot exceed the main pipe diameter (A) used by the water source unit.
• Y-branches and other header branches cannot be installed downstream of the initial header branch.
REFRIGERANT PIPING DESIGN
First Y-branch
Total pipe length
Elevation differential (Water source unit ↔ Indoor unit)
Elevation differential (Indoor unit ↔ Indoor unit)
Liquid Pipe (Inches O.D.)
Due to our policy of continuous product innovation, some specifications may change without notification.
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Water Source Unit
To Water
Source
Unit
B
C
IDU
C
Second Y-branch
IDU
Longest actual pipe length
A + B + D ≤230 feet
Longest pipe length after first branch
B + D ≤ 131 feet
≤ 98.4 feet
≤ 49 feet
Vapor Pipe (Inches O.D.)
Ø1/4
Ø3/8
Ø3/8
Y-branch
To Indoor
Units
Header
C
IDU
IDU
Length: ≤230 feet
: ≤131 feet
D
Longest Equivalent pipe length
A + B + D ≤295.2 feet
≥20 inches
≥20 inches
≥20 inches
≥20 inches
Ø1/2
Ø5/8
Ø3/4
LIMITS / PL ACEMENT | 61
Pipe Sizing
Brazed Cap
C
IDU
1
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