Evaporator Refrigerant Temperature Limit - Trane CVHE Troubleshooting Manual

Condenser Refrigerant Pressure Limit
Prevents chiller shutdown due to High Condenser Pressure.
Explanatory Comments:
This is a multistage control that acts to prevent chiller shutdown when the condenser refrigerant
pressure approaches the cutout setpoint by reducing chiller capacity. Chiller capacity is reduced
via the following steps, providing increasingly aggressive action as the trip point is approached:
1 Limit requests for capacity increases.
2 Prohibit requests for capacity increases.
3 Initiate stepped capacity reduction.
4 Initiate maximum capacity reduction.
The intent of this control is to provide maximum capacity while preventing chiller shutdown due to
high condenser pressures.
The condenser pressure limit function is based on the Condenser Pressure sensor if the
Condenser Pressure sensor option is selected as 'Installed' on the CLD. The limit is based on the
Saturated Condenser Refrigerant Temperature if the Condenser Pressure sensor is selected as
'Not Installed' on the CLD.
Setpoint (CPLS) range: (80 - 120)% HPC (Factory set to 93% HPC)
Figure 11
provides a graphical representation of the condenser pressure limit control regions
for an arbitrary setpoint and the condenser pressure limit control output Ds2.
Where ERR2 = CPLS(% HPC) - actual pressure (% HPC)
Figure 11
Condenser Pressure Limit Control Regions for an Arbitrary Setpoint
CVHE-SB-32A
Forced
Unload
DS2
(#steps)
ERR2 = Pressure Error %
375.0*Err2
CPLS
No
Limit
Limit
Hold Loading
100.0*(Err2 - 4.0)
4 10
1250
95