30 KOMAC00607-09EN
Circuit Functions
Calculations
Refrigerant Saturated Temperature
Refrigerant saturated temperature is calculated from the pressure sensor readings for
each circuit. A function provides the converted value of temperature to match values
published data for R134a
-within 0.1 C for pressure inputs from 0 kPa to 2070kPa,
-within 0.2 C for pressure inputs from -80 kPa to 0 kPa.
Evaporator Approach
The evaporator approach is calculated for each circuit. The equation is as follows:
Evaporator Approach = LWT – Evaporator Saturated Temperature
Suction Superheat
Suction superheat is calculated for each circuit using the following equation:
Suction superheat = Suction Temperature – Evaporator Saturated Temperature
Discharge Superheat
Discharge superheat is calculated for each circuit using the following equation:
Discharge superheat = Discharge Temperature – Condenser Saturated
Temperature
Oil Differential Pressure
Oil Differential Pressure is calculated for each circuit with this equation:
Oil Differential Pressure = Condenser Pressure - Oil Pressure
Maximum Saturated Condenser Temperature
The maximum saturated condenser temperature calculation is modeled after the
compressor operational envelope.
If Sat Evap Temp < 0°C then
Max Sat Cond Temp = 1.596(Sat Evap Temp) + 68.3°C
Otherwise, Max Sat Cond Temp = 68.3°C
High Saturated Condenser – Hold Value
High Cond Hold Value = Max Saturated Condenser Value – 2.78°C
High Saturated Condenser – Unload Value
High Cond Unload Value = Max Saturated Condenser Value – 1.67°C
Condenser Saturated Temperature Target
The saturated condenser temperature target is calculated by first using the following
equation:
Sat condenser temp target raw = 0.8332(evaporator sat temp) + 35.0
°C
This value is then limited to a range defined by the Condenser Saturated Temperature
Target min and max set points. These set points simply cut off the value to a working
range, and this range can be limited to a single value if the two set points are set to the
same value.
Circuit Control Logic
Circuit Availability
A circuit is available to start if the following conditions are true:
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