Bulletin 100-50-9.1 –
Page 115
16. SYSTEM OPERATION
16.1 EEV
EEVs Maintain Control Temperature or Superheat dependent
upon set points and refrigeration system conditions. In order
for the EEV to switch from controlling superheat to control
temperature, the superheat must be above the superheat
set point and the calculated required saturated suction
temperature at the evaporator must be satisfied. The S3C Case
Control reverts to superheat control when:
1. The above conditions are not met.
2. During pull down after defrost.
3. Superheat falls below the set point (for flood back
prevention).
16.2 TEV WITH EEPR
EEPRs can be controlled to maintain case air temperature
or suction pressure as according to user selected control
parameter values. The EEPR will close during defrost and
return to controlling the selected parameter when defrost
terminates.
16.3 EEV WITH EEPR
The S3C Case Control operates attached EEVs and the EEPR
according to user selected control parameter values and the
valve arrangement. The EEV controls superheat only to a
superheat set point. The EEPR can be controlled to maintain
case air temperature or suction pressure in accordance with
user selected control parameter values. The EEV closes during
defrost for electric defrost systems and open to 100% when hot
gas is used. The EEPR will close during defrost and return to
controlling the selected parameter when defrost terminates.
16.4 EEV WITH EPR
If an EPR is detected on the line-up (by menu configuration or
valve module DIP switch position) the EEV defaults to superheat
control only. The EEV closes during defrost for electric defrost
systems and opens to 100% when hot gas is used.
16.5 MULTIPLE EEVS WITH EEPR
The S3C Case Control operates attached EEVs and the EEPR
according to user selected control parameter values and the
valve arrangement. EEVs control superheat only to a superheat
set point. The EEPR can be controlled to maintain case air
temperature or evaporator pressure in accordance with user
selected control parameter values. The EEV closes during
defrost for electric defrost systems and open to 100% when
hot gas is used. The EEVs resume controlling superheat during
pulldown. The EEPR will close during defrost and return to
controlling the selected parameter when defrost terminates.
16.6 MULTIPLE EEV WITH EPR
If an EPR is detected on the line-up (by menu configuration
or valve module DIP switch position) the EEVs default to
superheat control only. The EEVs close during defrost for
electric defrost systems and open to 100% when hot gas is used
and will resume controlling superheat when all evaporators in
the case have reached termination temperature or the defrost
fail-safe time has elapsed.
17. OPERATING MODES
17.1 REFRIGERATION
17.1.1 DELAY ON START UP
For systems that use cut-in/cut-out case temperature
control, there will be a delay on start up prior to opening
the liquid line solenoid valve or powering the compressor
contactor. This delay is set by the minimum off time,
off
.
17.2 DEFROST
The S3C Case Control supports multiple defrost schemes
and controls attached valves, fans and heaters as dictated
by the defrost scheme and user selected defrost parameters.
Termination can be determined by temperature or time.
Temperature termination can be selected to be from a
Defrost Termination Sensor or Discharge Air Sensor if Air
(Off-Time) defrost is selected. For line-up control, all cases
will enter defrost together. Each case on the line-up will
terminate separately and will resume refrigeration once all
the cases have terminated defrost.
If a case is in defrost during power loss, it will resume defrost
once power is restored only if it has been less than one hour
before the start of defrost.
The following chart shows what each electronic valve will
do during the specified defrost type:
17.2.1 PUMP DOWN
When defrost is initiated, the system will first go into
pumpdown mode to remove any refrigerant from the
evaporator.
If a liquid line solenoid valve is present
(
set to
under Valve Configuration), the S3C will
first close the liquid line solenoid valve and then wait until
the pumpdown delay time,
d
, has elapsed. Once it has
elapsed, the EEV and EEPR (if used) will close to 0%.
If a
liquid line solenoid valve is not present
, the EEV will
close to 0% then wait until the pumpdown delay time has
elapsed before closing the EEPR (if used) and going into
active defrost.
By setting pumpdown delay time,
d
, to 0 seconds, the
system will skip pumpdown mode and go immediately into
active defrost upon defrost initiation.
17.2.2 ACTIVE DEFROST
After pumpdown mode, the S3C will go into active defrost
mode and will operate the defrost mechanism such as
heaters or hot gas solenoid valve. For applications that use
off time defrost, the refrigeration will turn off and the fans
will remain on. Active defrost mode is terminated when
the defrost termination sensor has reached its temperature
setpoint defined by
d
or the termination time, set by
d
, has been met.
Electric Defrost
Hot Gas Defrost
EEV (Stepper or Pulse)
Close
Open
EEPR
Close
Close
Liquid Line
Solenoid Valve
Close
Open
