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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
Liebert iCOM
Page
Table of Contents
Teamwork
Installing a Liebert Icom UNIT-TO-UNITNETWORK
Mounting a Large Display on a Wall
Figures
Tables
Large and Small Displays
Features
ESC
Icon Key Name Function
Keyboard icons and functions
Status menu, large display, graphical view
Navigating Through the Liebert iCOM Menus
Accessing Submenus
Accessing Submenus on Small Displays
Accessing Submenus on Large Displays
Menu tree-Small display, stand-alone or networked
Entering a Password
Status Menu System View Status Menu Unit 1 View User Menu
Service Menu Unit
Advanced 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 Functions
Autorestart
Loss of Power Alarm
Fan Alarm / Fan Protection Settings
VSD Setpoint VSD Fan Speed Setting
Pump Down
High Pressure Alarm
Compressor Timing-Units With Two Compressors
Digital Scroll High Temperature
Compressor Sequencing
Motorized Ball Valve in Digital Scroll Units
Service Offset-Changing System Pressure Settings
MBV Operation After Compressor is Turned Off
Temperature proportional band
Temperature Proportional Band
Two Single-Step Compressors Without Unloaders-Two-Step
Compressor Control
Compressor Proportional Bands
One Single-Step Compressor Without Unloaders-One-Step
Two compressors with unloaders four-step
Two Compressors With Unloaders-Four-Step
Digital scroll capacity modulation, 10-100% variable
Digital Scroll Compressors
Chilled Water Control
Temperature Control-Second Cooling Source
Differential Temperatures / Controls Comparator Circuit
Delta T Temperature Difference Between Room and Glycol
Second cooling source and compressorized cooling
Dual Cooling Source
Temperature Control-Reheat
Reheat configuration types
Glycool Cooling-Free-Cooling
Heat On ½ Dead Band 100%
Off ½ Proportional Band Decreasing Temperature
SCR Reheat
Tight Mode
Standard Mode
Humidification Dehumidification
Humidity Control
Humidification
Parameters for infrared humidifier control
Humidification Infrared Humidifier
External Humidifier Control-Optional
Dehumidification Compressor Quantity
Dehumidification With Comp settings
Dehumidification
Dehumidification Low Limit
Control Types
Temperature and Humidity Control Types
Reheat During Dehumidification
Humidity Sensor Reading Control Types
Supply Limit-Optional
High and Low, Temperature and Humidity Events
Customer inputs
User Inputs / Customer Inputs
Event Types
Time Delay
Enable or Disable
Event Types and Properties
Main FAN Overload
Event notifications-large or small display
Possible Event Notifications
Calculation of Next Maintenance and Diagnostics
Next Maintenance Calculation
Calculating Unit Wellness
Compressor 1 / 2 Settings and Diagnostics
Parameters for Next Maintenance Calculation
General Maintenance Settings
Fans / Heaters / Humidifier Settings and Diagnostics
No Teamwork
Teamwork Mode
Teamwork Modes
Application of Teamwork Modes
Teamwork Mode 1 with two cooling units
Standby and Cascade
Standby Rotation Typical Standby Lead/Lag Function
U2U Hardware Cables and Network Switch
Placement of Cooling Units
Minimum Network Switch Requirements
Sample Liebert iCOM network configurations
Wiring for Unit-to-Unit Communications-U2U
Liebert iCOM U2U Ethernet Network
Combining Large and Small Displays on a U2U Network
Wiring a Liebert iCOM U2U Network Small Displays
Large Displays
Wall-Mount Large Display
Wiring a small display for stand-alone operation
Wiring a large display for stand-alone operation
Liebert vNSA
Ports available for connecting Liebert iCOM control devices
298 84mm 305mm 14.25 362mm DPN001136 Rev
Necessary Mounting Items
Location Considerations
Mounting Instructions
Liebert iCOM display dimensions
Event log parameters
Spare Part List-Large Display Only
Setpoints parameters
Spare part list parameters-large display only
Sensor data
Set alarms parameters
Active alarms parameters
Active Alarms
Display setup parameters
Total run hours parameters
Timer parameters-Sleep Mode
Service contacts parameters
Service Menu Parameters
Unit diary parameters
Unit Diary-Large Display Only
Maintenance / wellness settings parameters
Standby settings / lead-lag parameters
Wellness 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 parameters
Static RAM Not Available, Invalid, OK
HUM Steam
Options setup parameters
Service contact info parameters
Service Menu Parameters
Service Menu Parameters
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