By now, the case for considering wireless field networks has been well made—at least when you’re faced with adding a few new measurement points to an existing facility. If you can avoid the need to run new conduit or armored cable to the field; if you can avoid the need to add new cabinet space; if you can avoid the need to expand I/O capacity—you can slash installed cost per incremental measurement point by as much as an order of magnitude.
But for a capital project—a new greenfield unit or a significant brownfield expansion—the answer may not be quite so clear. No one today would argue that all measurement points in a new plant could or should be wireless. So, some traditional wire still needs to be run. That being a given, does it make economic sense to do wireless, too, on a new project?
The answer emerging from two recent engineering studies is an unqualified “yes” – but perhaps not for the reasons you might think.
Wireless + Fieldbus = new best practice
Emerson Process Management recently unveiled the results of two independent analyses of the use of wireless field networks in real-world, greenfield projects. In one case, JDI Contracts applied Emerson Smart Wireless technology to applications in a new process plant design for a major U.S. chemical manufacturer (see "The Case for Wireless: A Greenfield Chemical Plant"). In the other, Emerson modeled the application of wireless to an aromatics plant capital project (see "The Case for Wireless: A Greenfield Aromatics Plant").
Each of the studies considered the use of wireless against a baseline case of 100% hard-wired, 4-20mA HART instrumentation, as well as wireless in combination with Foundation fieldbus and other device-level bus network protocols.
Because of its persistent flexibility and ongoing productivity gains, expect a wireless field- and plant-level network infrastructure to be included in a growing number of grassroots projects right from the start.
Key installed cost savings for wireless accrued to labor savings associated with not running conduit or making wiring terminations for the points deemed suitable for wireless (25% of total measurements in the JDI study; 44% in the Emerson analysis). The Emerson study only considered monitoring points eligible for wireless; the JDI study included slow response control points as well. “The largest differential costs were conduit and associated labor between the field junction boxes and each field device, followed by labor for all terminations,” says Dan Daugherty, field architecture consultant, Emerson Process Management.
At the bottom line, today’s wireless technology presented a significant installed cost savings over traditional 4-20mA instrumentation. The studies also showed that installed cost savings with wireless technology approach those seen with Foundation fieldbus technology. Further, wireless was less expensive to implement than hardwired regardless of the wiring distances involved.
In the final analysis, however, it wasn’t installed costs that carried the day for wireless in each of the study’s conclusions. Rather, it was the forward-looking flexibility of wireless that earned it a place in the capital projects toolkit. Indeed, wireless is only the latest enabler of smarter and simpler engineering and construction, more flexible start-up, faster deployment and project completion, and the ability to better accommodate changing automation needs, both studies concluded.
“It’s part of a new best practice,” says Roger Hoyum, JCI Contracts principal engineer and author of one of the studies. “Our PePC/MAC design approach includes HART and Foundation fieldbus in the communications toolkit–and now wireless is an important new tool. It delivers savings, flexibility and speed of implementation.”
Wireless ‘delivers a better plant’
“Our recommendations regarding best practices are firmly centered around procedures and technology required to meet owner objectives and deliver expected project outcomes to our clients, including scope, schedule, budget and less tangible outcomes such as maintainability and ease of use,” continues Hoyum. “With wireless technology, we can deliver a better plant.”
“It’s also important to remember that once detailed engineering is done, every greenfield project becomes a brownfield plant,” adds Peter Zornio, Emerson Process Management chief strategic officer. “Our takeaway from these studies is that all three technologies—HART, fieldbus and wireless—should be in the design toolbox for capital projects.”
“The studies confirm that fieldbus continues to offer the lowest cost installation for process control points. For monitoring points, both fieldbus and wireless offer good alternatives and similar installation savings,” Zornio adds. “However, over the plant lifecycle, wireless adds significant benefits with simplified training, greater flexibility and allows very easy and lowest cost incremental expansion.”
So in the end, if installation savings are comparable with fieldbus (and very significant when compared to hardwired HART), the decision regarding whether to include wireless in your next capital project may not be why, but why not?