Brute Elite | Page 41 |
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setpoint is used to limit the maximum water temperature leaving the boiler only. The modulation rate is controlled by a
9.5Hydronic Heating Using Local Lead- Lag/Cascading Feature
When using single or multiple Brute Elites in lead lag configuration, the system sensor and TT terminals of the Master boiler create heat demand. The TT terminals on the slave boilers are ignored as the demand for those heaters is given from the master control. The system sensor is also used to control the modulation rate of the lead lag system. (see Section 7 for wiring instructions).
Let’s consider the following example:
Three Brute Elite boilers (let’s call them “Lead”, “Slave1” and “Slave2”) tied together via Modbus 1 connection, with appropriate RMT Address (1, 2, 3). System sensor input is used to indicate common secondary loop temperature.
System setpoint = 150°F
HS (hysteresis) = 10°F (default) BL (base load) = 50% (default)
Run sequence is initiated when system temperature falls to 140°F (setpoint less hysteresis value). Lead boiler will start. All firing rates will depend on several application characteristics, including flow rate, system load, water volume, etc. Boilers will start at a rate of 35%. If the load is such that Lead’s rate increases to 50%, “Slave1” will go through its startup sequence and begin firing at 35%. At this point, both boilers (Lead and Slave1) will continue to respond simultaneously to the load/system characteristics, by modulating up or down together, in relation to the relative system setpoint and load characteristics.
Scenario 1: If the system loop temperature rises quickly, and moves above setpoint, then the boilers will simultaneously drop their firing rate. If when reaching the point where both boilers drop toward their minimum firing rate (20%), then the first slave will drop out. Slave1 will remain unavailable until its ASC timer has expired (5 minutes). If the load were to increase such to drive all active boilers to 50% firing rate or more, during the ASC time, Slave2 will begin its startup se- quence and begin to fire at 35%, etc.
Scenario 2: If the system loop temperature continues to drop (load increases), then the two boilers will increase firing rate together. At 50%, Slave2 will begin its firing sequence and be added to the group.
All three boilers will continue to fire simultaneously at equal 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- hysteresis value) above setpoint (e.g. 160F), in which case remaining boiler will shut off
3.Any of the boilers approach its high limit tempera- ture the individual boiler will modulate back.
9.6Hydronic Heating Using Local Lead- Lag/Cascading Feature with Indirect Hot Water
When using the lead lag boiler system to provide indirect domestic hot water heating, the DHW demand should be supplied to the master boiler through the existing DHW terminals. The lead lag system will change the operating mode of the Master boiler only to supply water at the DHW setpoint. The remaining boilers on the system will continue to supply hydronic heating.
When the system is supplying both hydronic heat and domestic hot water at the same time both the system pump and DHW pump contacts are closed, so special attention must be paid to allow for proper operation. During a DHW call, the master boiler pump may need to be turned off in applications serving both hydronic and domestic heating. This will cause the DHW pump to provide flow through the boiler and indirect tank (pump must be sized properly) when there is a DHW call. To turn off the boiler pump in this application the "boiler pump interrupt" jumper should be installed. The terminal block location is terminal block 5 (TB5) contacts labeled "boiler pump interrupt" in the control panel.
9.7 Warm Weather Shutdown
Warm weather shutdown overrides a hydronic call for heat when the outdoor air temperature is greater than the warm weather shutdown setpoint. Warm weather shutdown is always active whenever there is an outdoor sensor attached to the control. To avoid warm weather shutdown the warm weather shutdown temperature should be increased as necessary. The warm weather shutdown setpoint can be adjusted in SETUP mode, using the SD menu.
9.8Domestic Hot Water Demand (BNTV only)
When using the Brute Elite for DHW heating a call for heat must be supplied to the "DHW stat" terminal located on terminal block 6 (TB6). The DHW heating call can be from the supplied DHW sensor or from an aquastat. If the DHW sensor is used the heater operates to maintain the temperature at the DHW sensor. This may allow the actual heater outlet water temperature to exceed the DHW sensor setpoint. If an aquastat is used to supply the DHW demand the heaters
