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Dual Valve Converter, Demand Limiting, Setpoint Shift
Functional Description
OUTSIDE
AIR
OUTSIDE AIR
TEMPERATURE
8
16
-26
-20
PUMP
START POINT
14
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.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
H.W. SETPOINT
WARM-UP
OCCUPIED
PERIODS
PERIODS
54
68
90.5
77
RESET SCHEDULE
7
5
AUTO
1
HOT WATER
PUMP
SETPOINT
77
6
77
9
10
70
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 14.5 C, 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 68 C to
90.5 C as the OA varies from 16 C to –20 C. During occupied
periods (any AHU in occupancy mode) the HW temperature
setpoint shall vary from 54 C to 77 C as the OA varies from
16 C to –20 C. 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 Kvs 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.
363
SEQUENCE
11
OF
OPERATION
PERCENT
OPEN
65
1/3 CAPACITY
3
PERCENT
65
OPEN
2
2/3 CAPACITY
CONVERTOR C-1
M15293
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