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CONTROL GRAPHICS
Many digital control strategies require fine tuning to assure
systems are staged and loaded without excessive surging and
cycling. Such strategies are often more comprehensive if
presented as a "Dynamic Sequence" where the specified
sequence is repeated with dynamic commandable values
embedded (Fig. 9).
DATA PENETRATION
Figures 7, 8, and 9 present data penetration concepts from
the macro to the micro levels. Graphics should be designed for
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
4
MINUTES, THE BYPASS VALVE IS CLOSED, AND THE TIME IS BEFORE
THE LAG CHILLER STARTS.
ANYTIME BOTH CHILLERS ARE RUNNING AND THE CHILLED WATER DIFFERENTIAL
TEMPERATURE IS LESS THAN
LAG CHILLER PUMP STOPS AND REMAINS OFF AT LEAST
ANYTIME ONLY ONE CHILLER IS RUNNING AND ALL AHU CHILLED WATER VALVES ARE
LESS THAN
90
IS LESS THAN
THE RATE OF
0.2
ANYTIME ANY AHU CHILLED WATER VALVE IS FULL OPEN, THE CHW TEMPERATURE
SETPOINT DECREMENTS DOWN AT THE SAME RATE
ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLED WATER SYSTEM
CHILLED WATER SETPOINT
7
MINIMUM
1545
KELVINS FOR MORE THAN
2.4
% OPEN AND THE CHILLER PLANT DIFFERENTIAL TEMPERATURE
KELVINS, THE CHW TEMPERATURE SETPOINT INCREMENTS UP AT
3.0
KELVINS EVERY
Fig. 9. Typical Graphic to Aid System Fine Tuning in the Field.
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS
each specific operator type. For example, a security guard is
required to monitor certain critical alarm points after hours,
design special graphics of only those points, with simplified
explanations, and specific operator response messages. Use
simplified floor plan graphics with appropriately positioned
dynamic space temperatures for zone controllers. Selection of
the VAV icon (controller) presents the specified points (setpoint,
min-max airflow, damper position, etc.) on a terminal unit
graphic.
All system points should be positioned on graphics and certain
points should be specified on multiple graphics.
8
11
CURRENT
MAXIMUM
%FOR MORE THAN
20
, THE LEAD CHILLED WATER PUMP STARTS.
90
DEGREES ABOVE SETPOINT FOR
0.5
30
MINUTES
5
195
3
MINUTES, THE CHILLED
,
1545
4.0
MINUTES, THE
MINUTES.
M15135
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