BLOWER ON indicator light (Fig. 2)
This indicator light denotes the status of the combustion air blower. When the indicator light is on electrical power is connected to the blower motor controller. When the light is off, no power is connected to the controller. The light has a blue lens. Power to the controller is controlled by the flame monitor.
CIRC. PUMP OFF-ON switch (Fig. 2)
This is a manually controlled switch for applying/removing power to/from the circulating pump motor. This switch must be on for the heater to operate. The switch is in series with the low media level relay and the motor controller breaker auxiliary switch, both of which must be closed for power to reach the motor.
HEATER CONTROL OFF-ON switch (Fig. 2)
This is a manually controlled switch for turning the heater on and off. It must be on for the heater to operate.
GAS-OIL switch (Fig. 2)
This is a manually controlled switch for selecting either gas or oil as a fuel source to operate the heater. Setting the switch to OIL allows the flame monitor to energize and open the two solenoid valves (main and auxiliary) in the fuel oil supply line. This setting prevents the main gas valve from energizing.
Setting the switch to GAS allows the flame monitor to energize and open the automatic gas valve. This setting prevents the two fuel oil shutoff valves from energizing.
HEATER ALARM OFF-ON switch (Fig. 2)
This switch is provided in the horn circuit so that the horn can be switched off until the problem that set off the alarm can be cleared. It should be turned back on after the problem is cleared.
AUX. PUMP OFF-ON switch (Fig. 2)
This is a manually controlled switch for applying/removing power to/from an auxiliary pump motor. This switch must be on to pump thermal fluid through the piping circuit connected to the pump. The switch is in series with the motor controller breaker auxiliary switch, which must be closed for power to reach the motor.
Note: there may be more than one of these switches on the control panel, depending upon the number of independent thermal fluid circuits used. When there is more than one, the switches are marked #1, #2, #3, etc. to identify different independent circuits. Only heaters with manifolds have auxiliary pumps to circulate thermal fluid through independent piping circuits, each with its own pump. These circuits operate independently of the thermal fluid circuit that circulates thermal fluid through the coil of the heater. (The thermal fluid of heaters without manifolds is circulated through all piping circuits by the same pump that circulates the fluid through the heater.)
MANUAL RESET switch (Fig. 2)
A switch for resetting the flame monitor is on the outside of the control panel. It duplicates the function of the switch actually on the flame monitor, which is mounted inside the control panel. The external switch eliminates the need to open the control panel to reset the monitor.
FIREYE FLAME MONITOR (Fig. 2)
The flame monitor normally used is a Fireye Flame Monitor E110 with Programmer Module EP160. It is a microprocessor based burner management control system. The unit provides the proper burner sequencing, ignition and flame monitoring protection. In conjunction with limit and operating controls it sequences the burner/blower motor, ignition and fuel valves to provide for proper and safe burner operation.
The unit will deenergize all fuel valve circuits within four seconds (maximum) following a flame failure or at the end of the pilot trial for ignition period if no flame is detected. An alarm circuit will be energized following a safety lockout.
The flame monitor must be manually reset after the abnormal condition has been cleared.
The unit incorporates a display panel that shows up to 42 different messages related to the safe operation state of the heater. A logic flow diagram of the unit is shown in a Fig. 14.
MODULATING CONTROLLER (Fig. 2)
The modulating controller normally used is a Honeywell UDC3300. It provides three functions:
- Burner modulation control
- Burner low-fire hold control
- Burner on/off control
Burner modulation control. This function of the controller controls heating of the thermal fluid to maintain a temperature setting (known as set point or SP) that has been preset by the operator. It senses fluid temperature (known as a process variable or PV) from a thermocouple. It processes the output voltage of the thermocouple and sends control signals to Honeywell modulating actuator M9174C1025 (Fig. 7), which either increases or decreases the firing rate as required to maintain fluid temperature at set point. The difference between set point and PV is known as error or deviation (DEV).
The controller maintains the temperature within one or two degrees of set point when the heating system is in a steady state or maintenance mode. However, when starting up a cold system the burner fires at its maximum rate until the temperature of the thermal fluid (PV) reaches the preset proportional band (PB) of the modulating controller. The proportional band is the modulating range of the controller. While thermal fluid temperatures are within the proportional band, the controller causes small incremental changes in the burner firing rate (in proportion to the error) allowing its temperature to reach set point.