Steam Boiler Sequence Of Operation
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The document describes the sequence of operation for six boiler rooms. It discusses the boiler safeties, EZAutomation control panel, field devices, summer and winter control programs, and relay logic/device actuation. In the summer, the steam boiler shuts down and dampers close, while the DHW boiler and tank cycle continuously. In the winter, the steam boiler is enabled and burner run time is calculated based on outdoor air temperature to maintain indoor air temperature. Relay logic opens the damper when the burner is called to run, and closes it upon burner shutdown.
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Steam Boiler Sequence Of Operation
- 1. Sequence of Operation Typical for (6) Boiler Rooms Boiler Safeties All Boiler flame safeguard controls, low water / make-up feed controls and burner shutdown controls are integral to the original boiler installation. These circuits are factory installed and have not been interrupted by the EMS control system. EZAutomation Control Panel The EZAutomation Control Panel consists of the following: 1. 32-point capable PLC 2. (2) Two Analog Input Modules (16-point capable) 3. (1) One DC Voltage Digital Output Module (8-point capable) 4. (1) One DC Voltage Digital Input Module (8-point capable) 5. 3-pole 10-amp circuit breaker 6. 24vdc power supply 7. 5vdc power supply 8. 24vac power supply 9. Boiler Enable Relay EZAutomation Control Field Devices The EZAutomation Control Field Devices consist of the following: 1. Steam Pressure Transmitter 2. Outside Air Temperature Sensor 3. Boiler Burner Proof Relay 4. Boiler Burner Flame Fail Relay 5. Combustion Damper & Motor Actuator 6. Combustion Damper Boiler Start Relay Summer Control PLC Program Sequence From 12:00 Midnight on April 30th through 12:00 Midnight October 1st, all control devices will be indexed to their standby positions and the steam boiler will shut down. 1. Steam Boiler Combustion Damper – Closed 2. Boiler Enable Relay – Normally Open 3. Domestic Hot Water Combustion Louver will always be open 4. The Domestic Hot Water Boiler and Indirect Hot Water Tank will cycle continuously
- 2. Winter Control PLC Program Sequence From 12:00 Midnight on October 1st through 12:00 Midnight April 30th, the steam boiler system will be enabled. The outside air temperature sensor will initialize a calculation comparing the outside air temperature with a fixed indoor temperature set point of 70 deg F. As the outside air temperature decreases, the algorithm calculates the heat loss of the building structure and creates two time schedules, one for burner run time and one for burner off time. The algorithm will calculate how long the burner should run to produce and maintain 3 PSIG steam pressure to input enough heat into the building to maintain the 70 deg F set point at any given outside air temperature. The second timer will calculate how long to disable the burner and allow the heat absorbed by the piping, radiators and structure to continue to heat the living space. These calculations are dynamic and are re-calculated every second. Simply, as the OAT decreases, the burner on time increases and the burner off time decreases. As the OAT increases, the burner on time decreases and the burner off time increases. These calculations depend on the boiler system and building structure to function as designed. This requires that all condensate is returned to the condensate system tanks and pumped back to the boiler and all sources of outside air infiltration are reduced as much as possible. Relay Logic & Device Actuation Upon a call for burner RUN, the boiler enable relay (R-1) is energized and CLOSES the normally open contact. This passes control power to the combustion damper actuator (D-1). When the damper drives open over 70%, the damper end switch CLOSES and energizes the burner start relay (R-2). The (R-2) normally open contact CLOSES and completes the boiler control circuit which begins the burner firing sequence. When the burner ON Timer expires, the boiler enable relay (R-1) is de-energized, closing the Combustion Damper and initiating a burner shut down. The burner OFF timer will now disable the boiler until the OFF timer expires. This sequence will repeat until the OAT rises above 60 deg F or the Summer Control program is indexed on. The Domestic Hot Water Boiler and Indirect Hot Water Tank will cycle continuously.