Engineering notes
DDC or PLC: a shop-floor PLC is not an office AHU controller
A building DDC speaks BACnet and takes NTC heads. A shop PLC speaks Modbus and hard I/O. Mix them on one AHU and you programme twice.
The file says “controller”. The electrician thinks PLC; the air-con side thinks DDC. Both are boxes with I/O — not the same software, not the same programmer, not the same spare next year. Buying a PLC for office AHUs because it is cheaper than a named DDC often becomes two contracts: one purchase, two programmes.
Building DDCs: BACnet objects, NTC on the terminal, AHU/FCU libraries. PLCs: you write the logic; common on a shop floor, fire pumps, a line. Some jobs use both — PLC on the machine, DDC on the building — talking through a gateway. That is a schedule line, not “either will do”.
Send the communications page from the file, not just “16 I/O controller”. Choose a DDC