Laars NeoTherm NTH Installation And Operation Instructions Manual

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Laars NeoTherm NTH Installation And Operation Instructions Manual Manual pdf 38 page image

LAARS Heating SystemsPage 384. Prepurge timer is started once the prepurge RPM isachieved.5. Pre ignition time of 2 seconds to check the flamesensor operation and status. During this period anintermittent spark can be seen.6. Trial for ignition period, 4 seconds. The directspark ignition switches to constant spark for threeseconds, during which time the gas valve is open.For the last second of the ignition period directspark is de-energized and the flame sensor checksfor established flame. If flame is sensed the controlenters "Run" to satisfy the demand. If flame is notestablished the control enters a retrystarting fromstep 2. If flame has not been established in theappropriate number of retries the control willlockout with a 109 error code.7. Call for heat complete8. Gas valve off9. Fan and pump over run times active to purge thesystemThis sequence is the basic operating sequence ofthe appliance whether there is a DHW, or hydronic callfor heat.8.3 Modulation ControlThe control uses a PID algorithm to adjust thefiring rate of the boiler as the control point isapproached. The goal of the control is to operate at aminimum firing rate to match the load on the appliance.This is done by using a setpoint, and on / offdifferentials. The control modulates to achieve thesetpoint temperature, which could be several degreesaway from the actual off point. The off point iscalculated by adding the setpoint + off differential. Thesetpoint and differentials used in operation is dependentupon the call for heat being applied. If there is a DHWcall the DHW setpoint and off differentials are used. Ifthere is a hydronic call the CH setpoint and offdifferential is used. When the setpoint + off differentialis achieved the control interrupts appliance firing untilthe water temperatures reaches the setpoint - ondifferential. Both the hydronic and DHW setpoints areadjustable through the USER mode menu structure.8.4 Pump ControlThe control can operate three pumps. The boilerpump is active anytime there is a call for heat applied tothe control. The DHW and system pumps are activebased upon the call and priority of the heat demandbeing supplied. When there is a hydronic call suppliedthe system pump is active. If there is a DHW callsupplied while the hydronic call is active the systempump turns off and the DHW turns on. This happensbecause of domestic hot water priority, which forces thecontrol to attempt to satisfy the domestic water demandprior to the hydronic demand. When the last heatdemand is satisfied the boiler pump enters an overruntime.8.5 Anti-Short Cycle (ASC)The anti short cycle period is started whenever thegas valve turns off. This period is to help prevent shortcycling. Depending upon the time selected the controlwill wait up to 10 minutes before attempting to start thetrial for ignition sequence. The ASC time can beadjusted by entering setup mode.8.5 High LimitThe control uses a dual thermistor sensor tomonitor the Neotherm's maximum temperature. Thehigh limit sensor is installed in the outlet water. A dualthermistor sensor is used, so that the two temperaturescan be monitored and compared to confirm accuracy.The control will automatically reduce the firing of theNeoTherm to prevent the high limit from tripping. Thehigh limit setpoint is not adjustable.8.7 Outlet Water TemperatureThe outlet water temperature is a dual thermistorsensor and is limit rated. The control compares each ofthe temperature readings to determine accuracy. Theoutlet sensor is used as the primary control point forhigh limit, temperature operation, and modulation. Theoperating setpoint can be adjusted through the USERmenu structure.8.8 Inlet Water TemperatureThe inlet water temperature uses a singlethermistor sensor and is used to calculate the delta T ofthe system.8.9 Heat Exchanger Temperature RiseThe heat exchanger temperature rise is calculatedfrom the outlet and inlet sensor temperatures. The resultis displayed in the USER menu structure.8.10 Stack TemperatureThe stack temperature is a dual thermistor sensorand is limit rated. The control compares each of thetemperature readings to determine accuracy. The stacksensor is used as a limiting feature to avoid excessivetemperatures in the venting.8.11 Domestic Hot Water TemperatureThe domestic hot water temperature sensor is usedto monitor the DHW demand. The control uses theDHW sensor to control the operation and modulationrate of the appliance when there is a DHW demand. TheDHW setpoint can be adjusted through the USER menustructure.8.12 Lead Lag / CascadingLead Lag/Cascading allows multiple boilers to beconnected together and controlled from one commonsensor input. Up to 8 boilers can be connected togetherin a single system. To setup Lead/Lag or cascading