Event Condition to Trigger Action Action
At E and H
upward
Pump 1 at maximum speed; and Pump 2 at minimum
speed
and
Delta T >1°F (-0.6°C)
Pump 1 runs at maximum speed, while Pump 2 runs on PID.
At E and H
downward
Pump 1 at maximum speed; and Pump 2 at minimum
speed; and
Delta T <-1°F (-0.6°C)
Pump 1 runs on PID, while Pump 2 runs at minimum speed.
J to K
Both Pump 1 and Pump 2 at minimum speed for 60 sec.
and
Delta T <-1°F (-0.6°C)
Pump 2 turns Off, while Pump 1 runs at minimum speed.
Pump 2 Early
Start-up
Pump 2 Off
and
Delta T >2°F (1.1°C)
No action to Pump 1; turn On Pump 2 at 80% speed.
Once the start-up procedure is finished, step change to minimum speed
immediately.
Table 10.1 Events and Actions of 2 Circuit Pump Control (continued)
In the case of a transition from Compressor Mode to Pump Mode, the pumps will be given initial speeds based on the call for
cooling at the time of transition. The pumps will go to this initial speed after the start-up routine is completed. This will mean
that, depending on the load, both pumps will start immediately at the transition to Pump Mode from Compressor Mode.
When the system is in Mixed Mode, the room temperature is controlled either by modulating the digital compressor(s) on
Circuit 2 with the pump on Circuit 1 at 100%, or by modulating the pump speed on Circuit 1 with the compressor(s) operating
at the minimum digital percent.
Refrigerant Temperature
When a circuit is running in Pump Mode, the refrigerant temperature is controlled by the condenser fan speed. When a circuit
switches from Compressor Mode to Pump Mode, the condenser fan speed control changes from pressure control to
temperature control, with the controlled parameter being condenser outlet refrigerant temperature.
The default setpoint on Circuit 1 is 45°F, while on Circuit 2 it is 37°F. The condenser fan speed will modulate to provide the
respective temperature. But if the outdoor temperature is warm enough, or if the load is high enough, the fans might be at
100% and the actual refrigerant temperature might be above the setpoint. In that case, the temperature will depend on the
heat rejection capability of the condenser at the given conditions.
Actual fan speed will depend on the load and the outdoor temperature. The fan speed will be lower for a given heat load with
lower outdoor temperature in order to maintain the setpoint.
Because the refrigerant temperature could be below the dew point inside, the indoor piping must be insulated to prevent
condensation. In addition, the outdoor piping must be insulated so that heat is not lost to the outdoor air at very low ambient
temperatures, causing the refrigerant temperature to fall and increasing the possibility of frost at the evaporator.
38 Proprietary and Confidential ©2024 Vertiv Group Corp. 10 Control Operation
Vertiv™ Liebert® MCV Installer/User Guide
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