Laars NeoTherm NTH Installation And Operation Instructions Manual

Also see for Neotherm NTH: Service manual Installation and operation instructions User information Installation and operation instructions Installation and operation instructions

Laars NeoTherm NTH Installation And Operation Instructions Manual Manual pdf 42 page image

LAARS Heating SystemsPage 42water temperature at the heat exchanger outlet. Once theDHW call is supplied the control starts the boiler andDHW pumps and begins the ignition process. Theignition process consists of a prepurge, trial for ignition,and run period. The prepurge period starts on a call forheat once the fan RPM reaches a preset level. The trialfor ignition period follows once the start-up RPM of thefan is reached. The trial for ignition period lasts 4seconds during which the direct spark ignition systemand gas valve are energized. At the end of the trial forignition period the flame signal is compared with thepreset flame threshold value. If the flame signal ishigher than the flame threshold the NeoTherm enters"run". If the flame signal is below the threshold theNeoTherm returns to prepurge and starts the ignitionprocess over. In "run" the NeoTherm monitors the flamesignal, call for heat, safeties, and water temperaturesmodulating as needed between 100% and 20% of rate tosatisfy the call for heat.9.9 Domestic Hot Water Heating UsingExternal Modulation ControlWhen using the NeoTherm for DHW heating withexternal modulation control a call for heat must be suppliedto the "T-T or Interlock" terminal. By supplying a call tothe "T-T or interlock" terminal the operating temperaturesetpoint defaults to the hydronic heating setpoint, so all ofthe temperature adjustments must be made to the hydronicsetpoint. Once the call is supplied, the control starts theboiler and system pumps and begins the ignition process.The ignition process consists of a prepurge, trial forignition, and run period. The prepurge period starts on acall for heat once the fan RPM reaches a preset level. Thetrial for ignition period follows once the start-up RPM ofthe fan is reached. The trial for ignition period lasts 4seconds during which the direct spark ignition system andgas valve are energized. At the end of the trial for ignitionperiod the flame signal is compared with the preset flamethreshold value. If the flame signal is higher than the flamethreshold the NeoTherm enters "run". If the flame signal isbelow the threshold the NeoTherm returns to prepurge andstarts the ignition process over. In "run" the NeoThermmonitors the flame signal, call for heat, safeties, and watertemperatures. The heater setpoint is used to limit themaximum water temperature leaving the boiler only. Themodulation rate is controlled by a 4-20mA (0-10Vdc usingconverter) signal supplied by an external control. Whensetting up a system using an external control care must betaken to set the external control algorithms to prevent theboiler from short cycling or "hunting " to prevent prema-ture component failure.9.10 Domestic Hot Water Heating UsingLocal Lead-Lag/Cascading FeatureWhen using multiple Neotherms to supplyDomestic hot water only the heaters should be setup asstated in Section 8.12 “Lead/Lag Cascading,” andSection 9.5 “Hydronic Heating Using Local Lead/LagCascading Feature.” When the heaters are installed inthis fashion, all of the setpoints and adjustments aredone through the Lead Lag menus.