My steam boiler sequence of operation for a specialized control systems project in 2009.

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.