Emerson iCOM user manual SCR Reheat, Tight Mode

Page 31

Operation

3.5.2SCR Reheat

SCR reheat is a type of electric reheat that provides tighter temperature control than staged electric reheat. SCR reheat capacity modulation is achieved by pulsing the reheat On and Off. Full capacity is achieved by constantly energizing the reheat. Units equipped with SCR reheat can operate in Tight or Standard mode. By default, cooling units with SCR reheat are factory-set to operate in Tight mode.

The mode of operation can be set by adjusting the SCR Control Type parameter (Service Menu, Set- points).

Tight Mode

In Tight mode, the compressors and reheats are operated at the same time to provide maximum tem- perature control. The temperature deadband is set to zero at the factory. In a cooling unit with SCR reheat and two single-step compressors, the first single-step compressor is started and full reheat capacity is provided at 0% calculated output from the Temperature Proportional Band. As the call for cooling increases from 0% to 100%, the reheat capacity is slowly reduced by pulsing the reheat. At 100% call for cooling, the reheat is deactivated and the second single-step compressor is started. As the call for cooling is reduced, the reheat capacity is slowly increased. When the call for cooling returns to 0%, the second single-step compressor is deactivated.

If the Temperature Proportional Band calculates a call for heating from 0% to -200%, the first sin- gle-step compressor remains activated and full reheat capacity is provided. Based on the factory default settings, the first single-step compressor is deactivated when the control reaches -200% call for heating. The compressor remains deactivated until the control calls for 0% heating. The compres- sor activation and deactivation points can be adjusted in the Service menu under Setpoints.

Figure 20 illustrates how a cooling unit with two single-step compressors and SCR reheat operates when the SCR Control Type is set to Tight mode.

NOTE

Some cooling units are not suited for a strict NO LOAD application. These cooling units require a minimal load in the space. Consult factory for verification.

Figure 20 Two single-step compressors with SCR reheat set to Tight mode

Temp Setpoint: 70°F

 

 

 

 

 

 

 

 

 

Cool 2

Proportional Band: 8°F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On

Deadband: 0°F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SCR On

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cool 1 On

 

 

 

 

62

63

64

65

66

67

68

69

70

71

72

73

74

-200%

 

 

-100%

 

 

 

0%

 

 

 

 

100%

Heating Cool 1

 

 

Heating

 

 

 

 

 

 

 

 

Cooling

 

 

 

 

 

 

Cool 2

 

 

 

SCR

Off

 

 

 

 

 

 

 

Off

 

 

 

Off

½ Proportional Band

½ Proportional Band

½ Proportional Band

 

SCR Reheat On

 

 

Cooling 1 On

 

Cooling 2 On

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Contents Liebert iCOM Page Table of Contents Teamwork Installing a Liebert Icom UNIT-TO-UNITNETWORKMounting a Large Display on a Wall Figures Tables Large and Small Displays FeaturesESC Icon Key Name Function Keyboard icons and functionsStatus menu, large display, graphical view Navigating Through the Liebert iCOM Menus Accessing SubmenusAccessing Submenus on Small Displays Accessing Submenus on Large DisplaysMenu tree-Small display, stand-alone or networked Entering a PasswordStatus Menu System View Status Menu Unit 1 View User Menu Service Menu UnitAdvanced Menu Unit Viewing Multiple Units with a Networked Large Display Service Menu Unit #Advanced Menu Unit # SET User menu icons Service menu icons Unit/Fan Control Start Stop Single Unit FunctionsAutorestart Loss of Power AlarmFan Alarm / Fan Protection Settings VSD Setpoint VSD Fan Speed SettingPump Down High Pressure AlarmCompressor Timing-Units With Two Compressors Digital Scroll High TemperatureCompressor Sequencing Motorized Ball Valve in Digital Scroll Units Service Offset-Changing System Pressure SettingsMBV Operation After Compressor is Turned Off Temperature proportional band Temperature Proportional BandTwo Single-Step Compressors Without Unloaders-Two-Step Compressor ControlCompressor Proportional Bands One Single-Step Compressor Without Unloaders-One-StepTwo compressors with unloaders four-step Two Compressors With Unloaders-Four-StepDigital scroll capacity modulation, 10-100% variable Digital Scroll CompressorsChilled Water Control Temperature Control-Second Cooling SourceDifferential Temperatures / Controls Comparator Circuit Delta T Temperature Difference Between Room and GlycolSecond cooling source and compressorized cooling Dual Cooling Source Temperature Control-ReheatReheat configuration types Glycool Cooling-Free-CoolingHeat On ½ Dead Band 100% Off ½ Proportional Band Decreasing TemperatureSCR Reheat Tight ModeStandard Mode Humidification Dehumidification Humidity ControlHumidification Parameters for infrared humidifier control Humidification Infrared HumidifierExternal Humidifier Control-Optional Dehumidification Compressor Quantity Dehumidification With Comp settingsDehumidification Dehumidification Low LimitControl Types Temperature and Humidity Control TypesReheat During Dehumidification Humidity Sensor Reading Control Types Supply Limit-Optional High and Low, Temperature and Humidity EventsCustomer inputs User Inputs / Customer InputsEvent Types Time DelayEnable or Disable Event Types and PropertiesMain FAN Overload Event notifications-large or small display Possible Event NotificationsCalculation of Next Maintenance and Diagnostics Next Maintenance CalculationCalculating Unit Wellness Compressor 1 / 2 Settings and Diagnostics Parameters for Next Maintenance CalculationGeneral Maintenance Settings Fans / Heaters / Humidifier Settings and DiagnosticsNo Teamwork Teamwork ModeTeamwork Modes Application of Teamwork ModesTeamwork Mode 1 with two cooling units Standby and Cascade Standby Rotation Typical Standby Lead/Lag FunctionU2U Hardware Cables and Network Switch Placement of Cooling UnitsMinimum Network Switch Requirements Sample Liebert iCOM network configurations Wiring for Unit-to-Unit Communications-U2ULiebert iCOM U2U Ethernet Network Combining Large and Small Displays on a U2U Network Wiring a Liebert iCOM U2U Network Small DisplaysLarge Displays Wall-Mount Large DisplayWiring a small display for stand-alone operation Wiring a large display for stand-alone operation Liebert vNSA Ports available for connecting Liebert iCOM control devices298 84mm 305mm 14.25 362mm DPN001136 Rev Necessary Mounting Items Location ConsiderationsMounting Instructions Liebert iCOM display dimensions Event log parameters Spare Part List-Large Display OnlySetpoints parameters Spare part list parameters-large display onlySensor data Set alarms parametersActive alarms parameters Active AlarmsDisplay setup parameters Total run hours parameters Timer parameters-Sleep ModeService contacts parameters Service Menu Parameters Unit diary parameters Unit Diary-Large Display OnlyMaintenance / wellness settings parameters Standby settings / lead-lag parametersWellness COMP2 Wellness HEAT2 Diagnostics / service mode parameters ALM REL 7of Delay Enable Disab Enable Disab Comp 1 Overload Unit X Disconnected WRN Loss of Power LOP MSG, WRN, ALM Call Service MSG, WRN, ALM High Temperature Sensor calibration / setup parameters System / network setup parameters-large display only GBP Network setup parametersStatic RAM Not Available, Invalid, OK HUM Steam Options setup parametersService contact info parameters Service Menu Parameters Service Menu Parameters Page That Ne tIti Ti n
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