Honeywell AUTOMATIC CONTROL Engineering Manual page 346

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
Features
1. Full flow through operating boilers.
2. Minimum temperature limit on boiler entering water.
3. Variable flow secondary system with full boiler flow.
4. Automatic boiler staging
5. User friendly monitoring and adjustment.
Conditions For Successful Operation
1. Control network, software, and programming to advise
heating plant controller of secondary fan and water flow
demands.
2. Interlock and control wiring coordinated with the boiler
manufacturer.
3. Control in accord with boiler manufacturers
recommendations.
4. Proper setpoint and parameter project specific settings.
A BLENDING VALVE ON EACH BOILER MODULATES IN THE RECIRCULATING POSITION TO
PREVENT THE BOILER ENTERING WATER TEMPERATURE FROM DROPPING
LEAD BOILER (
TEMPERATURE DROPS TO
TEMPERATURE RISES TO
OUTSIDE AIR TEMPERATURE SETTING, THE OTHER BOILER IS LOCKED OUT FOR
ANYTIME THE LEAD BOILER CONTROL VALVE IS COMMANDED FULL OPEN BY THE SECONDARY
WATER TEMPERATURE CONTROL LOOP FOR
WATER SUPPLY TEMPERATURE IS MORE THAN
IT'S SETPOINT, THE LAG BOILER AND ITS ASSOCIATED PUMP START. ANYTIME BOTH BOILERS ARE
OPERATING AND THEIR CONTROL VALVES ARE LESS THAN
SECONDARY RETURN, THE BOILER SYSTEM OPERATING LONGEST SHUTS DOWN.
THE BOILER BLENDING VALVES MODULATE (SUBJECT TO THEIR LOW LIMIT
CONTROL) TO PRODUCE SECONDARY WATER TEMPERATURES FROM
DEGREES AS THE OUTSIDE AIR TEMPERATURE DROPS FROM
ENGINEERING MANUAL OF AUTOMATIC CONTROL
BOILER SYSTEM CONTROL
BELOW
145
) AND ITS ASSOCIATED PUMP START ANYTIME THE OUTSIDE AIR
1
60
AND SHUTS DOWN ANYTIME THE OUTSIDE AIR
DEGREES. ANYTIME THE LEAD BOILER STARTS FROM THIS
65
MINUTES.
60
Fig. 49. Boiler System Control Dynamic Display.
Specification
The heating plant shall operate under automatic control anytime
the secondary pump ON-OFF-AUTO function is not "OFF",
subject to a heating system ON-OFF-AUTO software function.
The lead boiler, as determined by a software lead boiler selection
function, shall be enabled anytime the date is between October
first and May first, the OA temperature drops below 60F for greater
than 30 minutes, and an AHU is calling for heat. Each boiler
primary pump shall have a software ON-OFF-AUTO function,
and each boiler shall have a software AUTO-OFF function. The
heating plant shall be disabled anytime the OA temperature rises
to 65F for greater than 1 minute and after May 1.
Anytime the boiler plant is enabled, the lead boiler primary
pump shall start and as flow is proven, the boiler shall fire under
its factory controls to maintain 180F. If the lead boiler status
does not change to "on", or if flow is not proven within 5
minutes, the lag boiler shall be enabled.
DEGREES.
MINUTES AND THE SECONDARY HOT
5
5 DEGREES BELOW
40
55
336
PERCENT OPEN TO THE
TO 180
110
TO DEGREES.
5
M15052