Mitsubishi Electric BDT CITY MULTI Installation And Pre-Commissioning Booklet page 13

Twinning on the outdoor unit side
The tilt angle of the twinning pipe
The tilt angle of the twinning pipe must be within ±15° with the horizontal plane.
Tilting the twinning pipe more than specified will cause damage to the unit.
The length of the straight part of the pipe before the branching
For the twinning kit, always use the accessory piping parts.
The length of the straight part of pipe connected in front of the
twinning pipe must be 500 mm [19-11/16 in.] or longer.
(Connect the field piping so that the length of the straight part
of pipe connected in front of the twinning pipe can be 500 mm
[19-11/16 in.] or longer.)
If the length is less than 500 mm [19-11/16 in.], it will cause damage
to the unit.
Precautions for outdoor unit combinations
<A> Install the piping so that oil will not accumulate in the stopped outdoor unit.
unit 1 unit 2
1.
To Indoor unit
Twinning pipe Twinning pipe
The NG example shows that oil accumulates because the units are installed on a reverse gradient while unit 1 is in operation, and unit 3 is stopped.
unit 1 unit 2
2.
unit 1 unit 2
h1
h1 = 0.2 m (7-7/8 in) max
The NG example shows that oil accumulates into units 1 and 2 while unit 3 is in operation, and units 1 and 2 are stopped.
Vertical pipe height (h) should be 0.2 m (7-7/8 in) or below.
unit 2
3.
unit 1
h2
h2 = 0.1 m (3-15/16 in) max
The NG example shows that oil accumulates into unit 1 while unit 3 is in operation, and unit 1 is stopped. Vertical pipe height (h) should be 0.2 m (7-7/8 in) or below.
unit 1 unit 2
4.
h2 = 0.1 m (3-15/16 in) max
The NG example shows that oil accumulates into unit 3 while unit 1 is in operation, and unit 3 is stopped. Vertical pipe height (h) should be 0.2 m (7-7/8 in) or below.
<B> When the piping on the outdoor unit side (from the twinning pipe) exceeds 2 m [6 ft], ensure a trap (gas pipe only) within 2 m [6 ft].
Make sure the height of the trap is 200 mm [7-7/8 in] or more.
If there is no trap, oil can accumulate inside the pipe, causing a shortage of oil and possible damage to the compressor.
<2 m [6 ft.] or less>
2m [6 ft.]
Caution:
• Do not install traps other than the ones between outdoor units described on a separate sheet to prevent oil backflow and compressor start-up failure.
• Do not install solenoid valves to prevent oil backflow and compressor start-up failure.
• Do not install a sight glass because it may show improper refrigerant flow.
If a sight glass is installed, inexperienced technicians that use the glass may overcharge the refrigerant.
unit 3
Downward slope
unit 3
unit 3
unit 3
unit 3
h2
<More than 2 m [6 ft.]>
200 mm [7-7/8 in.]
To Indoor unit or over
Note: See the following drawing for the fitting
position of the twinning pipe.
The tilt angle of the twinning pipe should
±
be within 15
unit 1 unit 2
To Indoor unit
Twinning pipe
Twinning pipe
unit 1 unit 2
h1
h1 > 0.2 m (7-7/8 in)
unit 2
unit 1
h2
h2 > 0.1 m (3-15/16 in)
unit 1 unit 2
h2
h2 > 0.1 m (3-15/16 in)
Trap
(gas pipe only)
To Indoor unit
Less than 2 m [6 ft.]
Twinning pipe
°
with the horizontal plane.
unit 3
Upward slope
unit 3
unit 3
unit 3
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