Engineering Manual o.. - HVAC.Amickracing

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONSFeatures1. 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 staging5. User friendly monitoring and adjustment.Conditions For Successful Operation1. Control network, software, and programming to adviseheating plant controller of secondary fan and water flowdemands.2. Interlock and control wiring coordinated with the boilermanufacturer.3. Control in accord with boiler manufacturersrecommendations.4. Proper setpoint and parameter project specific settings.SpecificationThe heating plant shall operate under automatic control anytimethe 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 selectionfunction, shall be enabled anytime the date is between Octoberfirst and May first, the OA temperature drops below 60F for greaterthan 30 minutes, and an AHU is calling for heat. Each boilerprimary pump shall have a software ON-OFF-AUTO function,and each boiler shall have a software AUTO-OFF function. Theheating plant shall be disabled anytime the OA temperature risesto 65F for greater than 1 minute and after May 1.Anytime the boiler plant is enabled, the lead boiler primarypump shall start and as flow is proven, the boiler shall fire underits factory controls to maintain 180F. If the lead boiler statusdoes not change to “on”, or if flow is not proven within 5minutes, the lag boiler shall be enabled.BOILER SYSTEM CONTROLA BLENDING VALVE ON EACH BOILER MODULATES IN THE RECIRCULATING POSITION TOPREVENT THE BOILER ENTERING WATER TEMPERATURE FROM DROPPINGBELOW 145 DEGREES.LEAD BOILER ( 1 ) AND ITS ASSOCIATED PUMP START ANYTIME THE OUTSIDE AIRTEMPERATURE DROPS TO 60 AND SHUTS DOWN ANYTIME THE OUTSIDE AIRTEMPERATURE RISES TO 65 DEGREES. ANYTIME THE LEAD BOILER STARTS FROM THISOUTSIDE AIR TEMPERATURE SETTING, THE OTHER BOILER IS LOCKED OUT FOR60 MINUTES.ANYTIME THE LEAD BOILER CONTROL VALVE IS COMMANDED FULL OPEN BY THE SECONDARYWATER TEMPERATURE CONTROL LOOP FOR 5 MINUTES AND THE SECONDARY HOTWATER SUPPLY TEMPERATURE IS MORE THAN 5 DEGREES BELOWIT'S SETPOINT, THE LAG BOILER AND ITS ASSOCIATED PUMP START. ANYTIME BOTH BOILERS AREOPERATING AND THEIR CONTROL VALVES ARE LESS THAN 40 PERCENT OPEN TO THESECONDARY RETURN, THE BOILER SYSTEM OPERATING LONGEST SHUTS DOWN.THE BOILER BLENDING VALVES MODULATE (SUBJECT TO THEIR LOW LIMITCONTROL) TO PRODUCE SECONDARY WATER TEMPERATURES FROM 110 TO 180DEGREES AS THE OUTSIDE AIR TEMPERATURE DROPS FROM 55 TO 5 DEGREES.Fig. 49. Boiler System Control Dynamic Display.M15052ENGINEERING MANUAL OF AUTOMATIC CONTROL311