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CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
DISTRIBUTION
OUTSIDE AIR
T1
11
PSF
PRF
Fig. 144. Control of Heat Exchanger for DHW and Jet Pump for SSF.
Control Strategies
1. The SSF temperature depends on the mixing ratio of the
jet pump. Jet pumps do generally not require secondary
circulation pumps. Valve Y 33 on the return pipe provides
a limited amount of flow control. As the valve varies from
full open to 30%, flow through the jet pump varies from
full flow. When the valve is less than 30% open, SSF
flow cannot be guaranteed. TI 32 controls Y33 to maintain
the SRF temperature as reset from outdoor air.
TI
01
QIR
12
T1
13
Y
M
14
HEX1
TI
TI
19
15
SUBSTATION
CENTRAL
SYSTEM
DDC
TIC
21
T1
QIR
16
17
33
TI
18
2. Heat exchanger HEX 1 Transfers heat to the isolated
domestic hot water system (DHW). Control valve Y 14
in conjunction with temperature sensor TIC 21 control
the DHW temperature. Because the amount of DHW in
the heat exchanger is small, a fast control system response
time is required. The response times should be:
Controller
Actuator
Sensor
ENGINEERING MANUAL OF AUTOMATIC CONTROL
394
CONSUMER
TIC
31
JET
PUMP
SSF
Y
TI
32
M
SRF
cycle time
< 1 sec.
on/off time < 1 sec.
rise time
< 2 sec.
DHW
COLD
WATER
M11430
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