ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
336
BOILER SYSTEM CONTROL
A BLENDING VALVE ON EACH BOILER MODULATES IN THE RECIRCULATING POSITION TO
PREVENT THE BOILER ENTERING WATER TEMPERATURE FROM DROPPING
BELOW DEGREES.
LEAD BOILER ( ) AND ITS ASSOCIATED PUMP START ANYTIME THE OUTSIDE AIR
TEMPERATURE DROPS TO AND SHUTS DOWN ANYTIME THE OUTSIDE AIR
TEMPERATURE RISES TO DEGREES. ANYTIME THE LEAD BOILER STARTS FROM THIS
OUTSIDE AIR TEMPERATURE SETTING, THE OTHER BOILER IS LOCKED OUT FOR
MINUTES.
ANYTIME THE LEAD BOILER CONTROL VALVE IS COMMANDED FULL OPEN BY THE SECONDARY
WATER TEMPERATURE CONTROL LOOP FOR MINUTES AND THE SECONDARY HOT
WATER SUPPLY TEMPERATURE IS MORE THAN DEGREES BELOW
IT'S SETPOINT, THE LAG BOILER AND ITS ASSOCIATED PUMP START. ANYTIME BOTH BOILERS ARE
OPERATING AND THEIR CONTROL VALVES ARE LESS THAN PERCENT OPEN TO THE
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 TO
DEGREES AS THE OUTSIDE AIR TEMPERATURE DROPS FROM TO DEGREES.
145
1
60
65
60
5
5
40
110
180
55
5
M15052
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.
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.
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