Circuit Functions; Definitions; Circuit Control Logic; Circuit Control Functions - Daikin AGZ 025D Operating & Maintenance Manual

Circuit Functions

Definitions

Refrigerant Saturated Temperature

Refrigerant saturated temperature shall be calculated from the pressure sensor readings for each circuit.
Evaporator Approach
The evaporator approach shall be calculated for each circuit. The equation is as follows:
Evaporator Approach = LWT – Evaporator Saturated Temperature
Condenser Approach
The condenser approach shall be calculated for each circuit. The equation is as follows:
Condenser Approach = Condenser Saturated Temperature - OAT
Suction Superheat
Suction superheat shall be calculated for each circuit using the following equation:
Suction superheat = Suction Temperature – Evaporator Saturated Temperature
Pumpdown Pressure
The pressure to which a circuit will pumpdown is based on the Low Evaporator Pressure Unload set point.
The equation is as follows:
Pumpdown pressure = Low Evap Pressure Unload set point – 103KPA (15 PSI)

Circuit Control Logic

Circuit Enabling
A circuit should be enabled to start if the following conditions are true:

Circuit switch is closed

No circuit alarms are active

Circuit Mode set point is set to Enable

At least one compressor is enabled to start (according to enable setpoints)
Compressor Availability
A compressor is considered available to start if all the following are true:

The corresponding circuit is enabled

The corresponding circuit is not in pumpdown

No cycle timers are active for the compressor

No limit events are active for the corresponding circuit

The compressor is enabled via the enable setpoints

The compressor is not already running
Circuit States
The circuit will always be in one of four states:
Off – Circuit is not running
Preopen – Circuit is preparing to start
Run – Circuit is running
Pumpdown – Circuit is doing a normal shutdown
OMM 1166-1 AGZ 025D through 190D 29