Carrier 30RBM 160 Installation, Operation And Maintenance Instructions page 60

12.2.8.2 - Operation
Switching between Free Cooling and Cooling modes is
controlled automatically (it is possible to disable switching in
Free Cooling by configuring - see the control manual).
The parameters (configurable) for switching are as follows:
• the ambient air temperature (OAT)
• the leaving water setpoint (LWTstp)
Once the LWTstp – OAT difference is greater than 5K, a
current capacity calculation in Cooling mode is performed
(cooling requirement) and compared to the theoretical Free
Cooling power (cooling possibility). This comparison
authorises or disables switching in Free Cooling mode.
When switching from a circuit in Free Cooling mode, all of its
compressors and fans are shut down and the three-way valve
changes position, establishing the evaporator/condenser
connection (the compressor function is bypassed).
Once the valve has switched, a vacuum is produced on the
compressors to transfer the refrigerant charge remaining in
the compressors to the Free Cooling system, then the circuit
ventilation is restarted and the Free Cooling pump starts up.
This logic takes around 10 minutes to switch the two circuits
in Free Cooling mode.
Given this timing, only one Cooling/Free Cooling switch per
hour is permitted.
If the power in Free Cooling mode is not sufficient (setpoint
not reached), the circuit automatically returns to Cooling
mode.
Therefore, depending on the operating conditions and the
cooling requirements, the unit may operate either in full
Cooling or Free Cooling mode, or in Mix Mode (one circuit
operates in Cooling mode and one in Free Cooling mode).
To optimise operation in Free Cooling mode, it is strongly
recommended to use the setpoint reset function (increases the
capacity in Free Cooling mode and encourages switching to
this mode).
IMPORTANT:
The volume of air supplied to the condensation coils is an
essential parameter for the correct operation of the Free
Cooling system and the function's stability.
It is vital not to degrade the unit configuration as defined.
Hence, be sure not to install devices and/or accessories on
the unit that may alter the volume of air generated by the
fans and/or modify its distribution to the various heat
exchangers.
IMPORTANT:
During operation in Free Cooling mode, the compressors are
not used. However, depending on the operating conditions
and the monitored pressure limits, the system may be required
to start them to create a vacuum on the compressor function
(recovery of refrigerant charge in the compressors and transfer
for use in the Free Cooling circuit). This may occur regularly
and is a normal operating condition.
60
12.2.8.3 - Operating limits
Cooling mode
Evaporator (water)
Entering water temperature at start-up
Leaving water temperature during operation
Condenser (air)
30RBM outside ambient temperature
30RBP outside ambient temperature
Available static pressure
Free Cooling mode
Evaporator (water)
Entering water temperature at start-up
Leaving water temperature during operation
Condenser (air)
30RBM outside ambient temperature
30RBP outside ambient temperature
Available static pressure
(1) The unit must be equipped with option 28B.
Minimum Maximum
°C 8
°C 5
Minimum Maximum
°C -10
(1)
°C -20
Pa 0
Minimum Maximum
°C 8
°C 5
Minimum Maximum
°C -10
(1)
°C -20
Pa 0
40
20
45
45
0
40
26
20
20
0