Laars NeoTherm NTH Installation And Operation Instructions Manual

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Laars NeoTherm NTH Installation And Operation Instructions Manual Manual pdf 40 page image

LAARS Heating SystemsPage 40SECTION 9.Modes of OperationThe NeoTherm control allows the boiler to operatein many different modes of operation. The mode mustbe selected based upon the requirements of theinstallation. The following sections describe the basicoperation of the NeoTherm in each of the differentmodes. Familiarize yourself with each mode and howthe operation of the boiler varies, depending upon theinstallation and inputs the control is monitoring.9.1 Hydronic Heating DemandWhen using the NeoTherm for hydronic heating acall for heat must be supplied to the "T-T or Interlock"terminal. Once the call is supplied the control starts theboiler and system pumps and begins the ignitionprocess. The ignition process consists of a prepurge,trial for ignition, and run period. The prepurge periodstarts on a call for heat once the fan RPM reaches apreset level. The trial for ignition period follows oncethe start-up RPM of the fan is reached. The trial forignition period lasts 4 seconds during which the directspark ignition system and gas valve are energized. Atthe end of the trial for ignition period the flame signal iscompared with the preset flame threshold value. If theflame signal is higher than the flame threshold theNeoTherm enters "run". If the flame signal is below thethreshold the NeoTherm returns to prepurge and startsthe ignition process over. In "run" the NeoThermmonitors the flame signal, call for heat, safeties, andwater temperatures and modulates as needed between100% and 20% of rate to satisfy the call for heat.9.2 Hydronic Heating with Outdoor ResetOutdoor reset varies the control point setpointbased on the actual outdoor temperature. The resetfunction works as shown in Figure 32. When theoutdoor air temperature reaches the "high outdoortemperature setpoint (HOD), the control point setting isadjusted to the low boiler temperature setpoint (LBT).When the outdoor air temperature reaches the lowoutdoor temperature setpoint (LOD), the controlsetpoint is adjusted to the CH/Outlet water setpointtemperature. HOD, LOD and LBT can be adjusted byaccessing SETUP mode. CH setpoint is adjustable fromthe USER menu structure.9.3 Hydronic Heating with Domestic HotWater (DHW) PriorityWhen using the NeoTherm for hydronic heatingwith domestic hot water priority a call for heat must besupplied to the "T-T or Interlock" terminal. Once thecall is supplied the control starts the boiler and systempumps and begins the ignition process. The ignitionprocess consists of a prepurge, trial for ignition, and runperiod. The pre-purge period starts on a call for heatonce the fan RPM reaches a preset level. The trial forignition period follows once the start-up RPM of the fanis reached. The trial for ignition period lasts 4 secondsduring which, the direct spark ignition system and gasvalve are energized. At the end of the trial for ignitionperiod the flame signal is compared with the presetflame threshold value. If the flame signal is higher thanthe flame threshold the NeoTherm enters "run". If theflame signal is below the threshold the NeoThermreturns to pre-purge and starts the ignition process over.In "run" the NeoTherm monitors the flame signal, callfor heat, safeties, and water temperatures modulating asneeded between 100% and 20% of rate to satisfy the callfor heat. When a DHW demand is applied during ahydronic call for heat the priority feature forces theboiler to switch to the DHW demand for the prioritytime. The DHW priority demand forces the control tooperate to the DHW setpoint, de-energizes the systempump and energizes the DHW pump.9.4 Hydronic Heating Using ExternalModulation ControlWhen using the NeoTherm for hydronic heatingwith external modulation control a call for heat must besupplied to the "T-T or Interlock" terminal. Once thecall is supplied the control starts the boiler and systempumps and begins the ignition process. The ignitionprocess consists of a prepurge, trial for ignition, and runperiod. The prepurge period starts on a call for heatonce the fan RPM reaches a preset level. The trial forignition period follows once the start-up RPM of the fanis reached. The trial for ignition period lasts 4 secondsduring which the direct spark ignition system and gasvalve are energized. At the end of the trial for ignitionperiod the flame signal is compared with the presetflame threshold value. If the flame signal is higher thanthe flame threshold the NeoTherm enters "run". If theflame signal is below the threshold the NeoThermreturns to prepurge and starts the ignition process over.In "run" the NeoTherm monitors the flame signal, callfor heat, safeties, and water temperatures. The boilerFigure 32. Outdoor Reset Setpoint Temperatures.