Page 38 | BRADFORD WHITE CORP. |
|
|
|
|
4.Prepurge timer is started once the prepurge RPM is achieved.
5.Pre ignition time of 2 seconds to check the flame sensor operation and status. During this period an intermittent spark can be seen.
6.Trial for ignition period, 4 seconds. The direct spark ignition switches to constant spark for three seconds, during which time the gas valve is open. For the last second of the ignition period direct spark is
7.Call for heat complete
8.Gas valve off
9.Fan and pump over run times active to purge the system
This sequence is the basic operating sequence of the appliance whether there is a DHW, or hydronic call for heat.
8.3 Modulation Control
The control uses a PID algorithm to adjust the firing rate of the boiler as the control point is approached. The goal of the control is to operate at a minimum firing rate to match the load on the appliance. This is done by using a setpoint, and on / off differentials. The control modulates to achieve the setpoint temperature, which could be several degrees away from the actual off point. The off point is calculated by adding the setpoint + off differential. The setpoint and differentials used in operation is dependent upon the call for heat being applied. If there is a DHW call the DHW setpoint and off differentials are used. If there is a hydronic call the CH setpoint and off differential is used. When the setpoint + off differential is achieved the control interrupts appliance firing until the water temperatures reaches the setpoint - on differential. Both the hydronic and DHW setpoints are adjustable through the USER mode menu structure.
8.5 Anti-Short Cycle (ASC)
The anti short cycle period is started whenever the gas valve turns off. This period is to help prevent short cycling. Depending upon the time selected the control will wait up to 10 minutes before attempting to start the trial for ignition sequence. The ASC time can be adjusted by entering setup mode.
8.5 High Limit
The control uses a dual thermistor sensor to monitor the Brute Elite's maximum temperature. The high limit sensor is installed in the outlet water. A dual thermistor sensor is used, so that the two temperatures can be monitored and compared to confirm accuracy. The control will automatically reduce the firing of the Brute Elite to prevent the high limit from tripping. The high limit setpoint is not adjustable.
8.7 Outlet Water Temperature
The outlet water temperature is a dual thermistor sensor and is limit rated. The control compares each of the temperature readings to determine accuracy. The outlet sensor is used as the primary control point for high limit, temperature operation, and modulation. The operating setpoint can be adjusted through the USER menu structure.
8.8 Inlet Water Temperature
The inlet water temperature uses a single thermistor sensor and is used to calculate the delta T of the system.
8.9 Heat Exchanger Temperature Rise
The heat exchanger temperature rise is calculated from the outlet and inlet sensor temperatures. The result is displayed in the USER menu structure.
8.10 Stack Temperature
The stack temperature is a dual thermistor sensor and is limit rated. The control compares each of the temperature readings to determine accuracy. The stack sensor is used as a limiting feature to avoid excessive temperatures in the venting.
8.4 Pump Control
The control can operate three pumps. The boiler pump is active anytime there is a call for heat applied to the control. The DHW and system pumps are active based upon the call and priority of the heat demand being supplied. When there is a hydronic call supplied the system pump is active. If there is a DHW call supplied while the hydronic call is active the system pump turns off and the DHW turns on. This happens because of domestic hot water priority, which forces the control to attempt to satisfy the domestic water demand prior to the hydronic demand. When the last heat demand is satisfied the boiler pump enters an overrun time.
8.11 Domestic Hot Water Temperature
The domestic hot water temperature sensor is used to monitor the DHW demand. The control uses the DHW sensor to control the operation and modulation rate of the appliance when there is a DHW demand. The DHW setpoint can be adjusted through the USER menu structure.
8.12 Lead Lag / Cascading
Lead Lag/Cascading allows multiple boilers to be connected together and controlled from one common sensor input. Up to 8 boilers can be connected together in a single system. To setup Lead/Lag or cascading
