I inherited a building full of networked TI505 and 545's to run all the HVAC, a separate one for each airhandler. 21 PLCs in all, built in the early 80's. Complete overkill, and a nightmare since we got no documentation. One 545 does nothing but play traffic cop for data interchange . The HMI is two computers running FIX32 on NT. One by one we are replacing them with a building automation system that is designed to control HVAC.