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ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
Variable Speed Pump Control ......................................................... 353
Decoupled Variable Speed Pump Control, Direct Return ........... 353
Pump Speed Valve Position Load Reset .................................... 355
Balancing Valve Considerations ................................................. 357
Balancing Valve Effects .......................................................... 357
Balancing Valve Elimination.................................................... 357
Differential Pressure Sensor Location Summary ........................ 357
Pump Minimum Flow Control ...................................................... 357
Hot Water Distribution Systems ........................................................... 358
General ........................................................................................... 358
Hot Water Converters ...................................................................... 358
Hot Water Piping Arrangements ...................................................... 359
General ....................................................................................... 359
Primary-Secondary Pumping ..................................................... 360
Control of Hot Water Systems ......................................................... 360
General ....................................................................................... 360
Modulating Flow Control ............................................................. 360
Supply Hot Water Temperature Control ...................................... 361
Supply Hot Water Temperature Control with Flow Control .......... 361
Hot Water Reset ......................................................................... 361
Hot Water Converter ............................................................... 361
Three-Way Valve .................................................................... 364
Coordinating Valve Selection and System Design ...................... 364
Hot Water Control Method Selection .......................................... 364
Chilled Water Distribution Systems ..................................................... 364
General ........................................................................................... 364
System Objectives ...................................................................... 365
Control of Terminal Units ............................................................ 365
Dual Temperature Systems ............................................................. 365
Changeover Precautions ............................................................ 365
Multiple-Zone Dual-Temperature Systems ...................................... 365
Steam Distribution Systems and Control ............................................. 366
Introduction ..................................................................................... 366
Advantages of Steam Systems Vs Hot Water Systems .................. 366
Steam System Objectives ............................................................... 366
Properties of Steam ............................................................................ 366
Steam System Heat Characteristics ............................................... 367
Steam Pressure, Temperature, and Density ................................... 367
Steam Quality ................................................................................. 367
Steam Distribution Systems ................................................................ 368
Steam Piping Mains ........................................................................ 368
Steam Traps .................................................................................... 368
Pressure Reducing Valve Station .................................................... 369
Types of Low Pressure Steam Distribution Systems ....................... 370
One-Pipe Steam Systems .......................................................... 370
Two-Pipe Steam Systems ........................................................... 370
Types of Condensate Return Systems ............................................ 370
Variable Vacuum Return Systems ................................................... 371
Control Principles for Steam Heating Devices ..................................... 371
General ........................................................................................... 371
Modulating Steam Coil Performance .............................................. 371
Oversized Valve .......................................................................... 372
Correctly Sized Valve .................................................................. 372
Supply and Return Main Pressures ................................................ 373
System Design Considerations for Steam Coils ............................. 373
Low Temperature Protection for Steam Coils .................................. 373
293
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