Honeywell AUTOMATIC CONTROL SI Edition User Manual

ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
389
Control Strategies
1. Primary Flow Loop Differential Pressure Control:
Provides a constant value pressure drop across the heat
exchangers. Actuator control valves (Y17, Y18) open or
close sequentially to maintain the pressure drop measured
by PDIC 14.
2. Secondary Loop Supply Flow Temperature Control: The
SSF temperature is reset from outdoor air temperature
(Fig. 137). The actual SSF temperature is measured by
sensors TIC 28 and TIC 38. The regulation of the heat
flow through the HEX is provided by the actuator control
valves Y 23 and Y 33 in the primary return flow line of
each heat exchanger.
3. Secondary Flow Loop Differential Pressure Control:
Circulating pumps Y 48 and Y 49 are switched off or on
and the speed varied to maintain the differential pressure
setpoint. A frequency converter (fc) controls pump speed.
4. SSF Loop Pressure Control: Maintains the pressure
sensed by transmitter PIC 57 within a defined range to
avoid too low pressure (vaporization) and too high
pressure (pump overload). Vent valve Y 54 maintains the
high limit and compressor Y 55 maintains the low limit.
5. Expansion Tank Water Level Control (WLC) Loop:
LIC 56 maintains the expansion tank water level. Normally
PRF water through Valve Y 51 provides make-up water, in
cases of a high quantity water loss, Pump Y 64 pumps make-
up water from the water supply tank. The WLC protects
the circulating pumps against running without water.
6. Water Supply Tank Water Level Control: LIC 63) controls
Valve Y 61, providing make-up water from the cold water.
7. Secondary Return Flow (SRF) and the Primary Return
Flow (PRF) temperatures are limited to provide a high
temperature drop between supply and return flow.
Fig. 137. Adjustment of Temperature Curves.
DDC CONTROL OF A SMALL HOUSE SUBSTATION
Fig. 138. DDC Control of a Small House Heat Transfer Substation.
Y
11
M
DDC
DISTRIBUTION
SUBSTATION
CONSUMER
TI
01
OUTSIDE AIR
TI
31
Y
23
TIC
22
TIC
24
TI
12
TZA+
21
ROOM
PSF
PRF
SSF
SRF
HEX 1
HEAT
TRANSFER
STATION
M11436
160
180
140
120
100
80
60
-25 -21 -17 -13
-9
-5
-1
3
7
11
15 19
SSF SETPOINT TEMPERATURE (˚C)
OUTSIDE AIR TEMPERATURE (˚C)
LIMIT SSF SETPOINT
TEMPERATURE IS
UNLIMITED
M15294

Honeywell AUTOMATIC CONTROL SI Edition Specifications

General

Brand	Honeywell
Model	AUTOMATIC CONTROL SI Edition
Category	Control Systems
Language	English