81
8. Release
valve control
1. SV2 gas balance control
This control function is aimed at achieving gas balance by opening SV2 while
compressors are turned off so as to reduce their startup load the next time they are
turned on. It is individually performed by the header outdoor unit and each follower
outdoor unit.
1) Control conditions
• In cooling, compressors have been turned off.
• In heating, the header unit has been shut down.
2) Control details
• The control point is changed according to
#
P (Pd pressure - Ps pressure) registered
just before the compressors were turned off.
• When
#
P P1, SV2 is opened. When this results in
#
P < P2, SV2 is closed.
• When
#
P < P1, SV2 is closed.
2. SV2 high pressure release control
This control function is aimed at mitigating pressure rise while a compressor is in
operation at low speeds.
1) Control conditions
• Heating operation is in progress (except periods of defrosting control).
• A lone compressor from the header unit is in operation at low speeds of up to 36 rps.
2) Control details
• When Pd pressure becomes 3.4 MPa, SV2 is opened.
• When Pd pressure becomes 2.8 MPa, SV2 is closed.
3) Termination conditions
• Shutdown, thermo OFF, defrosting operation, or cooling operation.
• The number of header unit compressors in operation increases to two or more.
• At least one follower unit compressor is turned on.
• The speed of the compressor rises to 40 rps or more.
3. SV2 low pressure release control
This control function is aimed at preventing a rapid fall in pressure during transient
operation. It is individually performed by the header outdoor unit and each follower
outdoor unit.
The control is always provided except during periods of stoppage or thermo OFF.
1) Control details
• When Ps pressure becomes 0.16 MPa, SV2 is opened.
• When Ps pressure becomes > 0.20 MPa, SV2 is closed.
Item
Description of operation, numerical data, and other information
Remarks
(Unit: MPa)
Control points
for Pd
pressure
P1, P2
Heating
Cooling
Header unit compressors
Header unit compressors
Header unit compressors
OFF
OFF
ON
P1
P2
P1
P2
P1
P2
Header unit
1.3
1.1
1.3
1.1
—
—
Follower unit
1.3
1.1
1.3
1.1
0.5
0.4
