CRR-20 & CRR-40, October 1999
µ
P-D Controller
Sequence of Operation
4-13
Continuous Temperature Control Operation
Chill Loads — Controller Setpoint at -9.9 C (14.1 F)
and Above
After the unit reaches setpoint on initial start-up operation, the
controller regulates the compressor, KVQ valve and electric
heaters based on a CALCULATED TEMPERATURE DIF-
FERENTIAL (see “General Theory of Operation” in this chap-
ter for more detail). This means the unit operating mode can
NOT be predicted based ONLY on the setpoint and supply air
sensor temperatures. The controller operates the unit on:
• Cool mode
• Modulation Cool mode
• Null mode
• Heat mode
• Defrost mode
• Evaporator fans operate on high speed (except when
Economy mode is ON and temperature is In-range) and
continuously circulate air inside the container (except
during defrost).
• Controller display shows the setpoint and supply air sen-
sor temperatures.
• Controller uses the condenser fan pressure switch input
to cycle a single-speed condenser fan between ON
(switch open) and OFF (switch closed). The controller
uses the compressor discharge and condenser coil tem-
peratures to cycle the condenser fan ON and OFF on unit
with customer configurations 5015 or 5016 loaded
(CRR-40-52 units).
Cool
• Controller calls for the Cool mode whenever the
Calculated Temperature Differential is more than 10.0 C
(17.9 F) above setpoint.
• KVQ valve is fully open so the unit provides maximum
cooling capacity.
• Power limit is active when the unit is operating in the
Cool mode.
Chill Loads
Frozen Loads
Setpoints at -9.9 C
Setpoints at -10.0 C
(14.4 F) and Above
(14.0 F) and Below
Cool Mod
Null
Heat Defr
Cool
Null
Defr
Unit Function
Economy Mode ON: Evaporator Fans HIGH SPEED1
•
•
•
•
•
Economy Mode ON: Evaporator Fans LOW SPEED1
•
•
•
Economy Mode ON: Evaporator Fans OFF1
•
Dehumidify ON: Dehumidify Valve CLOSED (energized)2
•
Dehumidify ON: Electric Heaters ON (energized)2
•
•
•
•
Humidify ON: Air Compressor ON (energized)3
1Economy Mode ON: • On Chill Loads, the evaporator fans operate on low speed when the supply air temperature is In-range.
• On Frozen Loads, the evaporator fans stop during the Null mode when the return air temperature is In-
range. A timer re-starts the evaporator fans on low speed for 5 minutes every 45 minutes. If cooling is
required, the evaporator fans operate until the unit returns to Null mode.
2Dehumidification Option: When the Dehumidify Mode is set to ON, the supply air temperature must be in-range to CLOSE
(energize) the dehumidify valve:
• When the humidity is 1 to 5% above setpoint, the controller CLOSES (energizes) the dehumidify valve.
• When the humidity is more than 5% above setpoint, the controller CLOSES (energizes) the dehumidify valve AND pulses
the electric heaters ON and OFF.
3Humidification Option: When the container humidity is more than 2% below the humidity setpoint, the controller operates (ener-
gizes) the air compressor to inject atomized water directly into the evaporator supply air stream.
Operating Mode Function Chart — Optional Feature Operation
Содержание CRR-20
Страница 4: ......
