The August issue of Engineered Systems focused on some of the unique challenges engineers face in data centers. One of the articles titled, “Commercial vs Industrial Automation in Data Centers,” raised some interesting points about the pros and cons of using industrial programmable logic controls (PLC) over commercial BAS. In a critical environment, such as a data center, this becomes an interesting discussion. After all, uptime is key, and the added investment in a PLC solution should be readily justified.  
Building Automation Chart

So if industrial systems make more sense in this type of critical HVAC application, does the same logic follow into other critical areas? For example would you use it in a critical manufacturing environment? How about a lab or research center? Or what about a hospital or a large chiller plant? All of these projects have been done successfully (and arguably unsuccessfully) with both PLC- and BAS-based systems. So how do you go about deciding what kind of system will work best? Key issues to help you decide are found in Table 1.

Based on this scorecard, it would appear that other than cost and building protocol support, PLCs are the better solution. But this really doesn’t tell the whole story. For most HVAC solutions, the control system doesn’t need to be any faster or more reliable then the underlying system you are controlling. This generally means that BAS are more than adequate, better supported, and less expensive than the comparable industrial solution.

The same cannot be said for critical electrical control. Management of switching, power quality, and distributions need to be done at control rates much higher than for HVAC. This makes the use of a PLC-based solution the only viable solution. ES