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Control points
for Pd
pressure
P1, P2
Heating Cooling
(Unit: psi (MPa))
Header unit compressors Header unit compressors Header unit compressors
OFF OFF ON
P1 P2 P1 P2 P1 P2
189 (1.3) 160 (1.1)Header unit 189 (1.3) 160 (1.1) — —
189 (1.3) 160 (1.1)Follower unit 189 (1.3) 160 (1.1) 73 (0.5) 58 (0.4)
NO. Item Specification outline Remarks
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 ΔP (Pd pressure - Ps pressure)
registered just before the compressors were turned off.
• When ΔP ≥ P1, SV2 is opened. When this results in ΔP < P2, SV2 is closed.
• When ΔP < 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
•
In case of all heating, all cooling, mainly heating or mainly cooling is operating
•
In case that a header unit singly operates a compressor
2) Control details
• When Pd pressure becomes 493 psi (3.4 MPa), SV2 is opened.
• When Pd pressure becomes 406 psi (2.8 MPa), SV2 is closed.
3) Termination conditions
• Shutdown, thermo OFF, defrosting operation.
• The number of header unit compressors in operation increases to two or more.
• At least one follower unit compressor is turned on.
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 ≤ 23 psi (0.16) MPa, SV2 is opened.
• When Ps pressure becomes > 29 psi (0.20) MPa, SV2 is closed.
4. SV41, 42, 43 low pressure release control
This control function is aimed at providing low pressure protection, and is
individually performed by the header unit and each follower unit.
The control takes place during defrost operation, heating operation, mainly heating,
mainly cooling and all cooling operation.
1) Control details (heating)
When Ps pressure becomes 15 psi (0.1 MPa), SV41, 42 and 43 are opened;
when Ps pressure becomes 22 psi (0.15 MPa), SV41, 42 and 43 are closed.
2) Control details (cooling)
When Ps pressure and Pd pressure become 20 psi (0.14 MPa) and 247 psi
(1.7 MPa), respectively, SV41 and 42 are opened; when Ps pressure and Pd
pressure become 28 psi (0.19 MPa) and 319 psi (2.2 MPa), respectively, SV41
and 42 are closed.
5. SV6 valve clean bypass control
This control is provided for controlling liquid refrigerant bypass to control discharge
temperature-up or temperature inside of the compressor. It works during all
cooling, all heating, mainly cooling, mainly heating, mainly heating and defrost
operation.
1) Control contents (All cooling)
When TD temperature ≥ 203°F (95°C) and compression ratio ≥ 3.0, turn SV6 to
ON, and when TD temperature ≤ 181.4°F (83°C) or compression ratio ≥ 2.0, turn
SV6 to OFF.
2) Control contents (Other operation)
When TD temperature ≥ 203°F (95°C) and compression ratio ≥ 4.2, turn SV6 to
ON, and when TD temperature ≤ 181.4°F (83°C) or compression ratio≥ 3.2, turn
SV6 to OFF.
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