Commissioning - often abbreviated as “Cx” - is the process of thoroughly testing mechanical and electrical systems in a building to ensure they operate as intended, and that systems are not conflicting with each other. While commissioning is typically associated with the mechanical systems of a building, it can also incorporate lighting controls, automatic shading devices, and automatic door controls.
Commissioning is typically always required by the construction team at the minimum, but formal commissioning involving the engineers and/or other consultants is not always a requirement. Sustainability and energy incentive programs such as LEED encourage a more formal commissioning process, including the requirement of having a separate commissioning authority to ensure compliance with the engineering design.
Some aspects of commissioning can be extremely simple, such as testing if a heater responds to a call from a thermostat. However, the main purpose for commissioning is for testing large, interconnected systems with dozens of input and output signals from a building management system (BMS). A good example is a central cooling plant in a building, which will have a combination of chillers, pumps, valves and heat exchangers, all being measured by inputs to the BMS in the form of temperature and pressure readings, pump speeds, chiller compressor status, and many others.
The ultimate goal is to ensure that the systems are operating according to the sequence of operations provided as part of the design of the building. Some systems and equipment have their own, standalone controls, not affecting other systems, but most commissioning takes place in the more complicated systems where various pieces of equipment impact each other in their operation. A good example is in the interaction between terminal units and VFD powered fans in a VAV air handling units. Room thermostats control the status of a VAV terminal unit damper, which changes the static pressure in the air system, causing the air handling unit to change its fan speed. With less airflow through the unit, less chilled water would then be required to achieve the same supply air temperature, closing the chilled water valve. This then causes the chilled water plant to respond, and the chain continues.
A building management system (BMS) is a central control system to monitor input points from the systems and provide the output signals for controlling all devices in the system. A BMS typically comes in the form of a computer with a program installed. This computer can be a fixed workstation, or the BMS software can be accessible through a portal from various computers. The BMS will typically show graphical schematic diagrams of pipe and duct flows, as well as the status of pumps, dampers, temperature sensors, and any other inputs or outputs that form the control system.
LEED stands for Leadership in Energy and Environmental Design. It is an incentive program developed to encourage sustainability in the built industry. For a building to obtain LEED certification, it must meet all prerequisites and reach a minimum number of points. For new buildings, LEED has prerequisites and additional points that can be earned for commissioning.
The prerequisite for commissioning requires basic commissioning activities to take place, covering HVAC, lighting, domestic water, and renewable energy. For smaller buildings, commissioning can be organized and performed by the design or construction team, but for larger buildings a dedicated commissioning agent must be engaged who is specifically not a part of the design or construction team. Beyond the commissioning prerequisite, points are available to contribute to the LEED rating for enhanced commissioning, building envelope commissioning, and performance monitoring. LEED emphasizes the necessity for commissioning because of the impact it can have on eliminating the potential for errors to cause malfunctioning systems or wasted energy.
