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CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
Primary Thermal Units: Thermal production water elements such
as chillers and boilers. Thermal production air elements
such as air handlers.
Rangeability: The ratio of maximum to minimum flow of a valve
within which the deviation from the inherent flow
characteristic does not exceed some stated limits.
Refrigerant pressure: The pressure difference between
compressor suction and discharge pressures or the
temperature difference between condensing and
evaporating temperatures.
Secondary Thermal Units: Thermal consumption water elements
such as AHU coils. Thermal consumption air elements
such as VAV boxes.
SYMBOLS
The following symbols are used in the system schematics following. These symbols denote the nature of the device, such as a
thermometer for temperature sensing.
13
13
NORMAL
AUTO
CONTROLLER, TEMPERATURE
SENSOR, TEMPERATURE
LOW LIMIT
HIGH LIMIT
MANUAL RESET NOTATION
INSERTION TEMPERATURE SENSOR
TEMPERATURE SENSOR,
AVERAGING
TEMPERATURE CONTROLLER,
MANUAL RESET, SAFETY LOW LIMIT
MANUAL MULTI-STATE
COMMAND (ON-OFF-AUTO)
STATUS POINT
ON
63
VALUE POINT (% LOAD)
COMMANDABLE VALUE
74
3-WAY VALVE WITH ACTUATOR
2-WAY VALVE WITH ACTUATOR
DAMPER WITH ACTUATOR
Superheat: The additional heat contained in a vapor at a
temperature higher than the saturation (boiling)
temperature corresponding to the pressure of the vapor.
Surge: A condition where refrigerant reverses flow approximately
every two seconds creating excessive noise, vibration,
and heat. Surge is caused by insufficient pumping
pressure to meet the rise in pressure from evaporator to
condenser.
Symmetrical loading: Diversity in multiple load systems, where
individual loads operate at the same time and same
percentage loading as the others.
Variable speed pumping (VSP): A pumping system where the
flow/pressure is varied by changing the pump speed.
Diversity factor = 1.
FAN
PRESSURE CONTROLLER,
HIGH LIMIT CUT-OUT,
MANUAL RESET
PRESSURE SENSOR
0.45
COOLING COIL
HEATING COIL
FILTER
PUMP
SOLENOID VALVE
SMOKE DETECTOR
(NFPA SYMBOL)
PROPELLER EXHAUST FAN
ENGINEERING MANUAL OF AUTOMATIC CONTROL
296
M15150
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