Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual page 157

If the DDC system is provided with a BMS having a color
monitor, a graphic may be required to be displayed with live,
displayable and commandable points (12 total). If a BMS is
not provided, the points may be required to be displayed on a
text terminal (fixed or portable) at the system level controller.
Step 3—Write a detailed sequence of operation for the process.
The hot water pump starts anytime the outside air temperature
drops to 11 C, subject to a software on-off-auto function.
When hot water pumping is proven by a current sensing relay,
converter controls are energized. Hot water temperature setpoint
varies linearly from 50 C to 77 C as the outside air temperature
varies from 16 C to -20 C. The converter steam valve is
modulated to maintain a converter leaving water temperature
according to a varying reset schedule.
The steam valve closes anytime hot water pumping is not
proven and anytime the valve actuator loses motive power.
Step 4—Develop the detailed flowchart.
Step 5— Write the program.
See the Air Handling System Control Applications section
and the Chiller, Boiler, and Distribution System Control
Applications section for other examples of Microprocessor-
Based/DDC systems.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
MICROPROCESSOR-BASED/DDC FUNDAMENTALS
START
O.A.
TEMP
NO
EQUAL TO OR
BELOW
11 C
YES
PUMP
ON?
NO TURN
PUMP
OFF
CLOSE
STEAM
VALVE
END
Fig. 18. Flowchart Example.
147
YES
YES
NO
PUMP
ON?
START
CONTROL
PUMP
SYSTEM
ENERGIZED
NO
ENERGIZE
CONTROL
SYSTEM
CONTROL
SYSTEM
MAINTAINS
RESET
SCHEDULE
M13120
YES