March 12, 2013

Commissioning Controls Systems: Sampling vs. 100% Point to Point Verification

The purpose of conducting verification of the controls system is to provide a third party review of the system. It is an important part of the quality control process, to ensure the Owner has a fully functional system.  Are Owners truly aware of the service that will be provided when they ask for “Sampling” in the tender documents, rather than the traditional “100% Point-to-Point Verification” of a controls system?

When a tender comes out requesting for 20% sampling, it means the commissioning consultant will verify only 20% of the system. In this process, the commissioning consultant will verify all of the major equipment, and the 20% sampling will be done on the terminal equipment. This can be heating elements, space temperature sensors, exhaust fans, etc.  In 100% Point-to-Point Verification however, each control point is reviewed.

In the ideal world, the controls contractor will verify that the system is 100% complete prior to demonstration, training and the third party performance verification.  However, due to the construction schedule, some controls contractors cannot truly verify their systems. For example, if substantial completion is in September, have the controls contractors verified the heating valves? From our experience, they may have verified that the valves stroke, but that doesn’t guarantee the valve is really functioning correctly under heating conditions. For example, when a heating control valve is being commissioned as per above, and the heating system is not active, the control valve cannot be checked to ensure it is not operating in reverse or passing water.

How does a poorly commissioned controls system affect owners? It can ultimately lead to occupancy discomfort or energy inefficiency. Once an owner inherits a building that was poorly commissioned, they depend on occupants and building operators to report controls deficiencies. Unfortunately, this may not be very effective on subjective topics, such as space temperature comfort. I remember an incident during verification: a room was reporting a space temperature of 2 degrees C above the set point, but the heating control valve in that room was closed.  Upon walking into that room, I could feel the blast of hot air and I turned to the lone occupant in the room and asked “Is your room typically this warm?” The lone occupant replied, “No, this room is usually really comfortable.” It turned out the heating valve was passing water.  Had 100% verification been done, this would have been caught in the verification process.

I recently spoke to one of my fellow colleagues, who is working on a project that required 20% sampling. He was frustrated, as out of the ten rooms he sampled, three rooms were not operating as commanded. Apparently, it was the same for several floors of that building. At the end of the project, as long as the problems with the sampled rooms are corrected, we have fulfilled our contract with the client. However, we cannot guarantee, or imagine, what the other 80% of the building is doing. Sampling just does not provide an accurate enough snapshot of the controls function for a whole building.

In cases of working with clients where there is “100% Point-to-Point Verification”,  I have had  projects on which I reported more than 50 controls items operating incorrectly, and I have also worked on projects on which I reported less than 10 controls items operating incorrectly. It can vary greatly from project to project, but the difference is: in a building with a controls system verified “100% Point-to-Point”, the Owner is guaranteed that each point has been verified by a third party; whereas with “Sampling”, the Owner is really gambling the unverified portion  of the building is operating correctly.

Why Commissioning