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APEX Installation, Operating, & Service Instructions APEX Installation, Operating, & Service Instructions
Figure 8-11: Multiple Boiler Wiring Diagram w/Tekmar 264 Control
Tekmar 264 Based Control System (or equal)
Sequence of Operation
The Tekmar 264 Control (or equal) can control up to four (4) boilers and an Indirect Water Heater by utilizing stage firing. When a call for heat is received by the Tekmar 264
Control, the control will fire either one or more boilers in sequential firing mode to establish a required reset water temperature in the system supply main based on outdoor
temperature. The boilers will modulate on their own based on each boiler’s control and will target a setpoint temperature to supply enough input to the system main to satisfy
the desired reset water temperature in the main established by the Tekmar 264 Control. When a call for Indirect Hot Water is generated to the Tekmar 264, the control will
de-energize the zone pump control (ZC terminal), energize the Indirect pump and sequentially fire the boilers to establish a setpoint temperature in the main for the Indirect
Heater using Priority. The Tekmar 264 Control will disable the stage firing and post purge the Indirect Pump to reduce the temperature in the Supply Main near the end of the
Indirect Mode to a point where it will need to be when it changes back to Space Heating Mode. The Tekmar 264 Control also has the ability to rotate the lead-lag firing of the
boilers to establish equal operating time for each boiler stage.
8 Electrical (continued)
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