Carel pCO2 Manual

Standard Chiller/HP modulare per compressore a vite con driver CAREL
Cod.: +030221241 Rel. 1.0 dated 25 September 03
37
The purpose of this time is to delay the activation of the compressors in order to give Free Cooling sufficient time to reach the steady state
conditions and take the machine's yield to nominal value. Only after this time has elapsed, and with the main thermostat dissatisfied, the
compressors are commanded to operate. If time is set to 0, the function will be disabled.
While the unit is operating, the same parameter is used by Free Cooling control to reassess the machine's working conditions according to the
value measured by the external temperature probe.
A further temperature delta should be set. This identifies a second threshold below which the yield of the Free Cooling battery is so high that it
can fully satisfy the system's thermal load solely through combined operation of valve and fans.
If the compressors are ON, the external temperature falls below "maximum delta" set according to the following relation:
External T. < Free Cooling Input T. – Free Cooling "Maximum Delta"
and this condition continues for a continuous time period equal to the set by-pass time for the compressors. When this time has elapsed, the
compressors will be commanded to OFF followed by a changeover to pure Free Cooling operation to satisfy load requirements with minimum
use of energy.
When the by-pass time for thermostatic control of the compressors has again elapsed, the requests will be re-assessed.
An antifreeze threshold is specified . It is based on the temperature value of external air to protect the heat exchanger when operating in a cold
environment.
If the temperature of external air is lower than the set threshold, the valve controlling water flow inside the Free Cooling exchanger will be
commanded to open, and the main circulation pump will be enabled (if OFF). This pump moves the fluid and prevents the interior of the
exchanger from freezing.
If the valve is a 0-10V type, the degree of opening will depend on the unit's operating status.
• with the machine OFF, opening to 100% of capacity will be commanded
• with the machine ON, opening to 10% of capacity will be commanded
If the valve is of the ON/OFF type, it will always open to maximum value irrespective of the unit's operating mode.
The entire procedure will finish as soon as the external air temperature reaches a fixed hysteresis of 1.0°C with respect to the set threshold.
19.4 Free Cooling disabling conditions
There are two main causes of the closure of the Free Cooling valve: the first depends on the external temperature conditions, and the second on
thermostatic demand.
The Free Cooling valve will close if the Free Cooling conditions stop.
External T. <
Free Cooling Input T. – (Free Cooling Delta) + 1.5°C
The Free Cooling valve will close if the Free Cooling thermostat is satisfied.
For system safety, the reading of the water temperature probe a the evaporator outlet is checked.
According to the set thresholds, the following will be processed: an antifreeze pre-alarm, which will enable any post-heating heaters and totally
disable the Free Cooling devices; and an antifreeze alarm which will totally disable the unit.
Other system safety devices : serious alarm from digital input, circulation pump thermal cutout, failed control probe, failed antifreeze control
probe, evaporator flow-switch alarm, phase monitor alarm. These safety device will totally disabled the unit, and, therefore, stop the Free
Cooling control.
19.5 Free Cooling ON/OFF valve
19.5.1 Proportional control
Evaporator Outlet
Temperature
Free Cooling set point
Free Cooling Differential
Free Cooling
ON/OFF valve
5,0 %
If temperature conditions favour Free Cooling control, the Free Cooling ON/OFF valve will be activated as soon as temperature exceeds the
activation threshold of the individual step, identified by a temperature value of:
Control Set point - Free Cooling Differential +5.0% Free Cooling Differential
The step amplitude is fixed at 5.0% of the set Free Cooling control differential.

Carel pCO2 Specifications

General

Brand	Carel
Model	pCO2
Category	Controller
Language	English