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 41 page image

NeoTherm Boilers and Water Heaters Page 41setpoint is used to limit the maximum water temperatureleaving the boiler only. The modulation rate iscontrolled by a 4-20mA (0-10Vdc using converter)signal supplied by an external control. When setting upa system using an external control care must be taken toset the external control algorithms to prevent the boilerfrom short cycling or "hunting " to prevent prematurecomponent failure.9.5 Hydronic Heating Using Local Lead-Lag/Cascading FeatureWhen using single or multiple NeoTherms in leadlag configuration, the system sensor and TT terminals ofthe Master boiler create heat demand. The TT terminalson the slave boilers are ignored as the demand for thoseheaters is given from the master control. The systemsensor is also used to control the modulation rate of thelead lag system. (see Section 7 for wiring instructions).Let’s consider the following example:Three NeoTherm boilers (let’s call them “Lead”,“Slave1” and “Slave2”) tied together via Modbus 1connection, with appropriate RMT Address (1, 2, 3).System sensor input is used to indicate commonsecondary loop temperature.System setpoint = 150°FHS (hysteresis) = 10°F (default)BL (base load) = 50% (default)Anti-short-cycle = 5 minutesRun sequence is initiated when system temperaturefalls to 140°F (setpoint less hysteresis value). Leadboiler will start. All firing rates will depend on severalapplication characteristics, including flow rate, systemload, water volume, etc. Boilers will start at a rate of35%. If the load is such that Lead’s rate increases to50%, “Slave1” will go through its startup sequence andbegin firing at 35%. At this point, both boilers (Leadand Slave1) will continue to respond simultaneously tothe load/system characteristics, by modulating up ordown together, in relation to the relative system setpointand load characteristics.Scenario 1: If the system loop temperature risesquickly, and moves above setpoint, then theboilers will simultaneously drop their firing rate. Ifwhen reaching the point where both boilers droptoward their minimum firing rate (20%), then thefirst slave will drop out. Slave1 will remainunavailable until its ASC timer has expired (5minutes). If the load were to increase such to driveall active boilers to 50% firing rate or more, duringthe ASC time, Slave2 will begin its startup se-quence and begin to fire at 35%, etc.Scenario 2: If the system loop temperature continues todrop (load increases), then the two boilers willincrease firing rate together. At 50%, Slave2 willbegin its firing sequence and be added to the group.All three boilers will continue to fire simultaneously atequal input rates or…1. Modulation rate approaches minimum firing rate(20%), in which case Slave2 will first drop out,and then Slave1, accordingly.2. System temperature reaches 10F (HS- hysteresisvalue) above setpoint (e.g. 160F), in which caseremaining boiler will shut off3. Any of the boilers approach its high limit tempera-ture the individual boiler will modulate back.9.6 Hydronic Heating Using Local Lead-Lag/Cascading Feature with IndirectHot WaterWhen using the lead lag boiler system to provideindirect domestic hot water heating, the DHW demandshould be supplied to the master boiler through the existingDHW terminals. The lead lag system will change theoperating mode of the Master boiler only to supply water atthe DHW setpoint. The remaining boilers on the systemwill continue to supply hydronic heating.When the system is supplying both hydronic heat anddomestic hot water at the same time both the system pumpand DHW pump contacts are closed, so special attentionmust be paid to allow for proper operation. During a DHWcall, the master boiler pump may need to be turned off inapplications serving both hydronic and domestic heating.This will cause the DHW pump to provide flow throughthe boiler and indirect tank (pump must be sized properly)when there is a DHW call. To turn off the boiler pump inthis application the "boiler pump interrupt" jumper shouldbe installed. The terminal block location is terminal block 5(TB5) contacts labeled "boiler pump interrupt" in thecontrol panel.9.7 Warm Weather ShutdownWarm weather shutdown overrides a hydronic callfor heat when the outdoor air temperature is greater thanthe warm weather shutdown setpoint. Warm weathershutdown is always active whenever there is an outdoorsensor attached to the control. To avoid warm weathershutdown the warm weather shutdown temperatureshould be increased as necessary. The warm weathershutdown setpoint can be adjusted in SETUP mode,using the SD menu.9.8 Domestic Hot Water Demand (NTV only)When using the NeoTherm for DHW heating a callfor heat must be supplied to the "DHW stat" terminallocated on terminal block 6 (TB6). The DHW heatingcall can be from the supplied DHW sensor or from anaquastat. If the DHW sensor is used the heater operatesto maintain the temperature at the DHW sensor. Thismay allow the actual heater outlet water temperature toexceed the DHW sensor setpoint. If an aquastat is usedto supply the DHW demand the heaters firing rate iscontrolled by the DHW setpoint temperature and the