Honeywell AUTOMATIC CONTROL Engineering Manual page 375

Dual Valve Converter, Demand Limiting, Setpoint Shift
Functional Description
OUTSIDE
OUTSIDE AIR
TEMPERATURE
8
60
-5
-5
PUMP
START POINT
58
4
Fig. 95. Dual Valve Converter, Demand Limiting, Setpoint Shift Graphic.
Item No. Function
1 Dynamic pump symbol. Pump starts on drop
in OA temperature.
2,3 Steam valves staged for hot water temperature
control.
4,5 Pump runs below OA temperature setpoint,
subject to ON-OFF-AUTO selector.
6-8 Hot water temperature setpoint varied by dual
reset schedule as OA temperature varies.
9 Controlled leaving water temperature.
10 Entering water temperature, operator
information.
11 Icon, selects the sequence of operation text
display.
Features
1. Staged 1/3 - 2/3 capacity control valves.
2. Dual reset schedule to accommodate the warm-up mode
and occupied periods.
3. Demand limiting to prevent the converter from exceeding
its required capacity when controls demand full load.
Conditions For Successful Operation
1. Technicians and users capable of understanding and
tuning the control strategy.
2. Proper settings and timings of all control parameters.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
H.W. SETPOINT
WARM-UP OCCUPIED
AIR
PERIODS PERIODS
130
155
195 170
RESET SCHEDULE
7
5
AUTO
1
HOT WATER
PUMP
SETPOINT
170
6
170
9
10
158
Specification
Converter Control:
Anytime the pump does not prove operation, the converter
valves shall close.
Control:
The control system shall be enabled anytime steam pressure
is available. The hot water pump shall start anytime the OA is
below 58F, subject to a software on-off-auto command.
Control:
During early morning periods (AHUs in warm-up mode) the
hot water (HW) temperature setpoint shall vary from 155 to
195F as the OA varies from 60 to –5F. During occupied periods
(any AHU in occupancy mode) the HW temperature setpoint
shall vary from 130 to 170F as the OA varies from 60 to –5F.
Setpoint warm-up to occupied period switching shall be ramped
such that the change occurs over a 15-minute time duration. A
PID function shall modulate the hot water valves as required to
maintain the setpoint.
Staging:
Two normally closed valves shall be provided with Cvs of
25 and 63. On a demand for heating, the small valve shall
modulate open. Upon demand for steam beyond the capacity
of the small valve for a period of five minutes, the small valve
shall close and the large valve shall assume the load. Upon a
demand for steam beyond the capacity of the large valve for a
period of five minutes, the small valve shall be re-enabled and
both valves shall operate in unison, but with a combined capacity
not to exceed the capacity noted in Demand Limiting.
365 ENGINEERING MANUAL OF AUTOMATIC CONTROL
SEQUENCE
11
OF
OPERATION
PERCENT
OPEN
65
1/3 CAPACITY
3
PERCENT
65
OPEN
2
2/3 CAPACITY
CONVERTOR C-1
M15069