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CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
ANYTIME ANY AHU VALVE IS OPEN GREATER THAN
MINUTES AND THE TIME IS BEFORE
ANYTIME THE LEAD CHILLER HAS RUN LONGER THAN
WATER TEMPERATURE IS GREATER THAN
THAN
MINUTES, THE BYPASS VALVE IS CLOSED, AND THE TIME IS BEFORE
4
THE OFF CHILLED WATER PUMP STARTS.
ANYTIME BOTH CHILLERS ARE RUNNING AND THE WATER DIFFERENTIAL TEMPERATURE IS
LESS THAN
KELVINS FOR MORE THAN
2.4
RUN LONGEST STOPS AND REMAINS OFF AT LEAST
ANYTIME ALL AHU CHILLED WATER VALVES ARE LESS THAN
THE CHW TEMP. SETPOINT INCREMENTS UP AT THE RATE OF
MINUTES TO A MAXIMUM OF
5
ANYTIME ANY AHU CHILLED WATER VALVE IS FULL OPEN, THE CHW TEMPERATURE SETPOINT
DECREMENTS DOWN AT THE SAME RATE TO A MINIMUM OF
ANYTIME ANY CHILLER IS RUNNING AND ALL AHU VALVES ARE OPEN LESS THAN
FOR MORE THAN
3
MINUTES, THE CHILLED WATER PUMP STOPS.
Features
1. Automatic start-stop, staging, and setpoint optimization
of chillers.
2. User friendly monitoring and adjustment.
3. Optimized unoccupied operation.
4. Chiller that has run longest since last start is first to stop.
5. Chillers cannot start late (shortly before the unoccupied
period begins).
Conditions For Successful Operation
1. Control network, software, and programming advises
chiller controller of AHU chilled water demands.
2. Interlock and control wiring coordinated with the chiller
manufacturer.
CHILLED WATER SYSTEM
CHILLED WATER SETPOINT
5.5
8
MINIMUM
CURRENT
, THE LEAD CHILLED WATER PUMP STARTS.
1545
0.5
4.0
DEGREES.
11
MINUTES, AND THE CHILLER HAS RUN GREATER THAN
Fig. 15. Dynamic Chiller Control Display.
308
10
MAXIMUM
20
% FOR MORE THAN
MINUTES, THE CHILLED
90
DEGREES ABOVE SETPOINT FOR MORE
MINUTES, THE CHILLER WHICH HAS
MINUTES.
30
% OPEN
80
KELVINS EVERY
0.15
7
DEGREES.
3. Appropriate cooling tower and control is required. See
COOLING TOWER AND CONDENSER WATER
CONTROL.
4. Two-way AHU control valves. This allows good single-
chiller, single pump operation.
5. Appropriate chilled water flow and differential pressure
controlled bypass valve to keep the minimum required
flow through the chillers (varies with chiller
manufacturers).
6. The unoccupied period 80 percent load limiting
parameters are based on the assumption that VAV AHUs
are operating under a reduced maximum airflow setpoint
during all unoccupied cooling modes (see the Air
Handling System Control Applications section) to save
fan energy while simultaneously placing the chiller
operation in its maximum efficiency range.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
3
,
1545
%
20
30
M15256
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