Honeywell AUTOMATIC CONTROL User Manual

ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
392
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.
356
320
284
248
140
212
176
-13 -6 1 9
16
23
30
37
45
52
59 66
SSF SETPOINT TEMPERATURE (F)
OUTSIDE AIR TEMPERATURE (F)
LIMIT SSF SETPOINT
TEMPERATURE IS
UNLIMITED
M11439
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

Honeywell AUTOMATIC CONTROL Specifications

General

Brand	Honeywell
Model	AUTOMATIC CONTROL
Category	Controller
Language	English