hvac - PLC Programming & Automation

PLC HVAC Control: An Air Handler Sequence That Holds

Timing chart of an air handler start: occupied signal, outside air damper to minimum, supply fan running, and the cooling loop enabled after the delay

Write an AHU sequence on a CompactLogix: damper minimum position, supply fan VFD, chilled water PID, economizer changeover, compressor staging and BACnet.

HVAC Point Names, BACnet Objects and Overrides That Expire

by PLC

Ladder rung for stage 2 cooling: cooling demand in series with stage 1 running, the interstage delay timer done bit, and a normally closed contact on the minimum off timer, driving the stage 2 command

PLC building automation that a stranger can maintain: naming, sequences of operation in the code, staging, BACnet mapping, trends, alarms and overrides.

Predicting the Demand Peak and Shedding Load from the PLC

by PLC

Ladder rung for load shedding: predicted demand high in parallel with the shed seal-in bit, in series with the shed permit and the chiller alarm contact, driving the shed output for chiller 2

Wire a power meter into Logix or S7, totalize kWh in Structured Text, hold the demand peak with priority load shedding, and check if a VFD retrofit pays.