PLC or DDC Wi-fi Communication

This is dependent on whether your net work is running in real time and looking after a critical process. If if is just data logging and some gaps can be allowed for then ok not so much of a problem. Try to make you local control systems as autonomous as is possible, have alarms for any condition where the situation requires it. Don't get to rely on only one system for any safety related issues. Think what can go wrong then use a flow chart to see where to put your money into the most important things. Think safe be safe.

The PLC or DDC will continue to operate normally, but without network communication.