CSZ EZT-570i, Техническое руководство

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EZT-570i Technical Manual
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This process will continue until the defrost temperature switch input (I41) is made indicating that the
suction temperature of the coil has warmed up to the defrost temperature setting. This will initiate a
15 minute timer in the EZT. Defrost will continue for another 15 minutes to insure that the coil is
completely defrosted. Once the 15 minute defrost time has elapsed, prechill is started.
In prechill, the defrost solenoid will be turned off and the minimum heating/cooling output (Q41) will
be turned on. This will allow the refrigeration system to pre cool the coil prior to starting the air
circulators. Once the defrost temperature switch turns off, indicating that the suction line has dropped
below the defrost temperature, a one minute timer begins. Once this timer is complete, prechill will
terminate, the air circulators will turn back on, and the system will resume normal operation.
4.1.4 Dual Refrigeration
Dual refrigeration refers to two refrigeration systems working together or alternately to condition the
chamber. When the refrigeration systems are set to tandem operation, they work together. When
cooling or dehumidification is required, both systems will start and stop in unison as required based
on the cooling and/or dehumidification demand. When redundant operation is specified, only one
refrigeration system runs at a time, and the systems alternate back and forth on a duty cycle to
equalize runtime.
The first system, system ‘A’, uses the standard control outputs for system 1 and 2 compressor (Q3
and Q4). System ‘B’ compressors are assigned to outputs Q46 and Q47 for system 1 and system 2.
The EZT also uses input I31 for the system 1B pumpdown switch and Q45 for the system 1B
solenoids, which allows independent control and pumpdown of system 1B. When each system is
assigned to its own conditioning plenum, additional inputs and outputs are used to start and stop the
air circulators on plenum ‘B’ (Q44) as well as monitor for heater over temperature (I4), motor overload
(I5) and a second boiler system on the additional plenum (I30 and I46).
When independent system failure is configured, a safety trip on one system will not shut down the
other system. This allows the chamber to continue to “limp” along with only one system under
tandem operation, or to switch to the “back-up” system when operating in redundant mode. If
independent plenums are not used, the chamber would still operate if it was a refrigeration safety trip;
however, if the fault was associated with a motor overload or over temperature condition with the
chamber heaters, the chamber would shut down because both refrigeration systems share the same
plenum.
When independent control loops are specified, requiring independent conditioning plenums, the EZT
will send the same temperature and humidity setpoints to the 9300 controllers for each plenum. The
EZT will then average the readings together when running in tandem mode, or only utilize the values
from the operating plenum when in redundant mode.
4.1.4.1 Alternating Defrost
When alternating defrost is selected for redundant refrigeration systems, and defrost has been
initiated on the currently running system, system ‘A’ for example, the EZT will start system ‘B’ prior to
starting the defrost cycle. This minimizes the change in chamber temperature by allowing system ‘B’
to begin operation first. Once the defrost cycle has completed on system ‘A’; however, the prechill
step will not take place. Since system ‘B’ is currently cooling the chamber, there is no need to prechill
the coil because system ‘A’ not required. If for some reason system ‘B’ was faulted out and
unavailable, the prechill step would take place prior to restarting system ‘A’ because it is then
required to cool the chamber.
Note that when defrost is in automatic mode, the EZT will not begin counting down the next defrost
cycle for system ‘B’ until defrost is complete on system ‘A’ and vice versa.