Cannon Design Blog

Long gone are the days when building control systems were exclusive to large projects – control systems are everywhere now. These systems have been have been installed in projects for years and it would be easy to assume that it is always a smooth process, but this is not always the case. The control industry is suffering of chronic installation and programming issues on almost every project. It is not the product itself that is the issue, nor is it the people who work in this trade. In fact, the industry has an incredibly large number of dedicated people who are dedicated to their work. The real reasons these issues occur are the many challenges these systems face. I believe it is important to take a quick look at why this is so and why commissioning control systems more thoroughly is so vital.

Complexity
Control systems are complex. There is more interaction between different systems than most people realize. A lighting motion detection sensor can now turn on the VAV box. So often, people perceive buildings as a whole instead of separate smaller parts. This leads to the “integration process” which becomes an additional challenge as many manufacturers try to keep certain control of their share of the market. Open protocol is not quite as fully “open” or easy as some people make it seem. The demand for energy efficiency is another factor that adds to the complexity of the programming.

Go To “Guys”
The Go To “Guys” are always the first to be called upon when issues arise. When this happens, significant time is lost diagnosing other trades issues which results in time taken away from their other obligations.

Perception
The control system is prominent. Its biggest advantage is also its biggest downfall. It is front and center and you can almost see it all from the user interface.

The Profession
Competition is ferocious and control system companies find themselves having difficulty balancing profitability and service quality. Long hours are part of the day-to-day of control technicians and by the time they become experienced, they have no problem finding better positions with a healthier quality of life. Finding replacements proves to be difficult. The few remaining experts are spread thin between numerous projects and then they must go into “fire extinguishing mode.”

Last To The Finish Line
The projects come to an end and they are expected to finish on schedule with the added burden of all the delays that can be encountered during the project. This leave installers with the challenge of making up that time.

Enough said. With all these elements and pressure to finish the job, things inevitably fall between cracks. Control technicians “make it work” with the assumption of coming back later to fix it. The follow-up can take months, sometimes years, if it happens at all.

This is why it is important to commission these systems. They are important to the well being of the occupant, the energy efficiency and the life of the equipment. They are an important economic and health liability.

The commissioning of control systems usually consists of a point-to-point check and functional testing. These steps are important and should satisfy some project, but may prove insufficient with bigger and more complex projects. Campuses often are victims of this shortfall.

It is not the intent to imply that all issues will be uncovered during commissioning but that is the goal. And to do this, I believe a few more steps should be considered. It is a great differentiator for professional commissioning companies and a service that key customers might appreciate.

Trending
Trending should be implemented as soon as possible as it can help verify sequence of operations for longer periods and observe hunting issues (on valve and fan speed). The Cx should determine a list of points to be trended. The trends should be made available to him before any functional testing occurs. Any anomalies observed should be resolved before functional testing.

The Right Equipment
A check (sampling) of sensors, valves and actuators ratings and accuracy should be done. Numerous projects have suffered from improper equipment installation. Efficiency and reliability are at stake. For instance, a valve working at above-rated pressure might work for a while but will fail prematurely. Too high pressure drop for control valves is often ignored as long as the flow is reached. The problem is that cavitation becomes an issue with upper limit pressure drops across the valves.

Addressing (Binding)
I have seen this issue on small and big projects. Usually the error happens on the graphical display and is obvious, but it can also be found in the control programming. For example, room temperature impacts the discharge air temperature reset of the wrong AHU. These issues will not always show on the User Interface as they could be included in an averaging calculation of numerous sensors, but will have an impact on energy consumption that could be significant. The Cx agent should determine a list of points that might be susceptible to such errors and verify that proper addressing is done. Sampling may be adequate.

Wiring
The Cx agent should be familiar with the control system limitation to foresee wiring issues that may cause problems, such as, separating power and control wiring as much as possible. Can a network cable and a power line be in the same conduit? Making sure the proper gauge is used for communication and control A little note here, sometimes a bigger wire is not acceptable. Other important things that the Cx agent should know is what the maximum wiring length between an actuator and a controller can be. Or what is the acceptable maximum length of a communication wire. Should the wiring be insulated, grounded, twisted are things that should also be looked upon. The location of all and terminations resistance of network should be clearly indicated. Again, a targeted (where expected issues might arise) sampling of all these elements should be accomplished.

Calibration
Commissioning personnel should perform a sensor-to-controller-readout calibration accuracy check sampling to confirm that the correct temperature is displayed. Actual measurements should be done. A commonly observed issue is the interpretation of an analog signal to a graphical value. For instance, a Variable Frequency Drive is showing a speed of 50 percent on the graphics but the acutal speed at the drive panel is 36Hz (60%).

Control Network
An important factor of an extensive control network that is often overlooked is the quality of the network communication. Network bandwith analysis and traffic variable configurations are ignored. Error, collision of rates and lost data are rampant in the control network and it all happens more frequently on a network with a broadband that is used at a higher percentage. The question becomes: What is an acceptable percentage? It gets worse if integrated with facility IT network, with IP address and integration from BACNET or Lontalk to TCP/IP, security, VPN, etc…

A common solutions implemented is to increase the speed of the network and sometimes install fiber optics. But why not do a better job at controlling the traffic and reducing or eliminating interference.

It is unreasonable to ask every Commissioning agent to be an expert in all control systems but there are tools that exist that make it possible for an agent to have a better idea of the overall network health – to see what is going on inside the wires. A protocol analyzer will show how well the network is performing and give you useful information such as which variables are being transmitted, how often, and what is the collision rate. I’ve used this tool on one project and it helped determine that a router between a Siemens and Johnson Control network sued for integration located on a campus was the root of recurrent issues in a Central Plant. It was inundating the network.

With this tool, it becomes possible to determine if only a segment is causing an issue or the entire network is impacted. One the information is available, it becomes possible to make intelligent improvements. Agents can then answer important questions including: Do we need to transmit repeatedly the same variable that is only used five times a day? Is it really important to see a 2 degree change in temperature when the precision of a sensor is 2%? Not only might it resolve existing issues, but it might be crucial for the future expansion of the network. You cannot manage something you don’t understand.

Next Step
These additional steps are time consuming and not all relevant to every project. Commissioning companies will not add these tests and procedures as standard methods because it will increase their prices and prevent them from winning work. They can be mentioned as additional services but more often than not, they will be ignored unless the owner had a previous bad experience. To make sure these possibly vital verifications are done and done properly, the owner with more critical or extensive control systems needs to take ownership of the RFP and specification. It is the only way for them to level the playing field and make sure they compare apple to apple. It is easy to prevent significant issues with control systems with little additional cost. To be proactive is the best approach to encourage a problem free future with a key element of the building.

Marco DeZan - 29 Jun 2012

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