The term “running” is ubiquitous to building controls and the commissioning world. It is used repeatedly in sequence after sequence and in everyday discussion about equipment. But what does “running” really mean? How is it sensed or determined? And, why does it matter? This article examines what “running” means in the real world of building MEP systems.
In nearly all cases related to building MEP systems, the intent of the term “running” is to determine whether a piece of equipment is performing the “work” it was intended to do. This may sound simple, but let’s contrast this to your automobile. How often have you heard someone say, “hurry up, the car is running.” Typically this means that the car’s engine is running, but the car itself isn’t moving. The engine may be running, but it’s not producing work, as no power is getting to the wheels to make is move.
Now let’s compare this to a fan in a building. The fan motor can be running, but if the belt connecting the motor to the fan is broken, it’s not producing work, and therefore not actually running. This is a simple example and the appropriate status can be easily achieved by several methods, but the point is that the term “running” can mean different things.
Variable Frequency Drives (VFD) are now commonplace throughout buildings and are used to control the speed of electric motors that power fans, pumps, etc. Often the VFD has an output called “VFD running,” but what does that mean? Does it mean the VFD itself is powered and therefore “running” or does it mean the motor it’s connected to is running? Does it mean the pump or fan powered by the motor is actually “running”?
Building controls systems monitor many statuses including run status and process the information to determine what actions are necessary to keep a building and its occupants comfortable and safe. An example of such a system is a refrigerant leak evacuation fan. Code requires the run status of this type fan to be derived by either a current switch tuned to activate only when the fan motor is drawing a predefined minimum current, or by a differential pressure switch across the fan inlet and outlet. Stair pressurization fans have very similar requirements. VFD “running” signal is not an acceptable status in these cases.
Part of a commissioning agent’s job is to determine that contact documents, shop drawings, installation, and control programming support the selection and monitoring appropriate equipment “running” status.
- The commissioning agent reviews the engineer of record’s design and specifications to ensure the documents support proper monitoring
- The commissioning agent reviews the control’s contractors shop drawings and detailed sequence of operation narratives to ensure the proposed installation uses the means and methods necessary to conform to the EOR’s intent
- The commissioning agent observes selected equipment and systems during startup and functional performance testing to determine that the intended equipment “running” statuses are used and are providing the information required for proper execution of the sequences of operation.
– Al MacIver, Project Manager, Commissioning, HTS, Inc., AMacIver@consultHTS.com