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CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
Control Strategies
1. Secondary Supply Flow Temperature Control: The SSF
temperature is reset from outdoor air temperature. TIC 32
provides the SSF temperature to the DDC controller. Valve
Y 13 regulates flow through HEX3 primary.
2. Secondary Flow Loop Differential Pressure Control:
Circulating pumps Y 37 and Y 36 are switched off or on
and the speed varied to maintain the differential pressure
setpoint. The pump speed is controlled by a frequency
converter (fc).
3. Secondary Supply Flow Temperature Control: The SSF
temperature is reset from outdoor air temperature (Fig. 141).
The actual SSF temperature is measured by sensor TIC 32.
The regulation of the heat flow through the HEX is provided
by the actuator control valves Y 13 in the primary supply
flow line of HEX3.
4. Secondary Loop Make-up Water: Pumps Y 38 and Y39
through Valve Y 310 provide make-up water from the PRF.
5. DHW Pressure Control: Booster Pumps Y29, Y210,
Y211, and Y212 boost the cold water pressure to the
pressure at PI 213.
DDC Control of Combination Heat Exchanger and Domestic Hot Water Storage Tank
DISTRIBUTION
QIR
02
COLD WATER
TI
11
PSF
PRF
QIR
15
Fig. 142. DDC Control of Dual Heat Exchangers for SSF and DHW Storage.
TI
01
OUTSIDE AIR
TZA+
TIC
Y
21
22
12
SSF
M
SRF
HEX1
TI
TIC
14
13
6. DHW Circulating Pumps Control: Circulating Pumps Y
25, Y26, and Y27 circulate DHW through the pipes to
maintain hot water temperature at the end of the DHW
system.
7. DHW Supply Temperature: Valve Y 14 modulates the
PSF water to HEX 1 and HEX 2 to maintain the DHW
supply temperature at Y 27.
Functional Diagram
180
160
140
120
100
80
60
-25
-21
-17
Fig. 141. Secondary Supply Flow
Temperature Reset schedule.
SUBSTATION
C-BUS/S-BUS
DDC
Y
49
Y
24
TIC
31
TIC
32
HEX2
Y
34
ENGINEERING MANUAL OF AUTOMATIC CONTROL
392
-13
-5
-1
3
7
11
-9
OUTSIDE AIR TEMPERATURE (˚C)
CONSUMER
CENTRAL
SYSTEM
DHW SUPPLY
HW
DHW
STORAGE
RECIRCULATED
TANK
Y
33
COLD WATER
15
19
M15296
SSF
SRF
M11432
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