Hitachi RAS-8FSXN - Heat Exchanger Mode Control

5.1.3 Heat exchanger mode control
• Heat recovery
system: in accordance with the connected load of indoor units, the outdoor unit heat exchanger can
switch as indicated in the following table.
• Heat pump system: in accordance with the operation mode of the indoor units, the outdoor unit heat exchanger can
switch as indicated in the following table.
N O T E
Outdoor unit heat exchanger mode at cooling: condenser (COND).
Outdoor unit heat exchanger mode at heating: evaporator (EVAP).
1 Heat exchanger mode:
• COND: operating as condenser.
• cond: avoid using the heat exchanger (under high pressure conditions).
• EVAP: operating as evaporator.
• evap: avoid using the heat exchanger (under low pressure conditions).
2 Expansion valve control method:
• Pd:
normally, completely open (the opening depends on the refrigerant cycle conditions). PI control is
carried out to reach the discharge pressure objective value when it decreases.
• TdSH: PI control is carried out to reach the compressor TdSH objective value.
• Heat exchanger SH: PI control is carried out to reach the heat exchanger SH objective value.
The number of outdoor unit: 1
Heat exchanger mode
Cooling mode Mainly cooling mode Mainly heating mode Heating mode Defrost mode
COND D1 D1-1 D4 EVAP DEF1
Heat exchanger condition COND COND cond EVAP EVAP COND
Reversing valve
RVR2 OFF OFF OFF ON ON OFF
RVR1 ON OFF OFF OFF OFF ON
Expansion valve
MV1 Pd Pd Heat exchanger SH Completely open
MVB TdSH TdSH Ps protection TdSH
The number of outdoor unit: 2
Heat exchanger mode
Cooling mode Mainly cooling mode Mainly heating mode Heating mode Defrost mode
COND D1 D2 D3 D4 EVAP
DEF2 DEF1
With CH unit Without CH unit
Main outdoor
unit
Heat exchanger condition COND COND COND cond EVAP EVAP COND/EVAP COND
Reversing valve
RVR2 OFF OFF OFF OFF ON ON ON/OFF OFF
RVR1 ON OFF OFF OFF OFF OFF OFF ON
Expansion valve
MV1 Pd Pd Heat exchanger SH
Completely
open/Heat
exchanger SH
Completely
closed
MVB TdSH TdSH
Secondary
outdoor unit
Heat exchanger condition COND COND evap EVAP EVAP EVAP COND/EVAP COND
Reversing valve
RVR2 OFF OFF ON ON ON ON ON/OFF OFF
RVR1 ON OFF OFF OFF OFF OFF OFF ON
Expansion valve
MV1 Pd Pd Completely closed
Completely
open/Heat
exchanger SH
Completely
closed
MVB TdSH TdSH
5 Control system
94
SMGB0065 rev. 1 - 12/2010