An engineered approach to ongoing commissioning
Ongoing commissioning improves energy efficiency in existing buildings.
The topic of energy use is a major one in the commercial building industry. It has led to advances in improved equipment efficiency, integrated design, and the use of energy modeling to analyze different system types and control strategies. However, more attention needs to be paid to the operation of building systems if energy savings are to be more fully realized.
Once a building HVAC system is installed and operational, the building operator may be primarily concerned with addressing comfort complaints. A system fault that wastes energy may be chronically present, but may not be detected because there is no indication of a problem. For instance, an air handling unit may have heating- and cooling-coil valves modulating simultaneously or an airside economizer sequence that functions improperly. These faults may result in a supply-air temperature that meets setpoints and maintains occupant comfort, but heating and cooling energy is being used unnecessarily. The solution to identifying these sometimes hidden problems is automated fault detection and diagnostics (FDD).
FDD is a rules-based approach that can be used to analyze the operation of HVAC systems. The method is to identify a list of rules, which when met identify a "fault." The variables in the rules are information present in the building automation system (BAS), such as temperature setpoints, actual measured temperatures, outside air conditions, and operational schedules. The rule may be something simple, like: If a system is heating and cooling at the same time, a fault is identified. More complex sequences of operation, which are becoming more commonplace to meet energy efficiency goals, will have more complex rules with more inputs. To identify which faults are most chronic, the fault can be measured based on the duration that it occurs. Faults may be converted to energy based on equipment capacities, and energy may be translated into dollars to identify the cost associated with each fault over a period of time.
FDD can be used to perform ongoing commissioning. Over the past several years, the commercial building industry and its adoption of ongoing commissioning have evolved. Early ongoing commissioning efforts centered on standard software packages that had trouble being customized to each unique building. While an overwhelming amount of data is generated and issues identified with this software, the reporting that could lead to actionable adjustment has been lacking. The opportunity exists for ongoing commissioning to take on a more engineered approach that begins in the design period for new buildings. The result is a unique solution for each unique building that optimizes functionality and energy savings while giving the building operator the appropriate amount of information and direction to produce results.
FDD may be part of a formal retro-commissioning effort for HVAC systems to improve energy performance and operations. Control sequences that have not been correctly implemented or mechanical components that are not fully functional are more likely to be found in a building that has not been initially commissioned, than in a building that has had its mechanical systems fully commissioned. Retro-commissioning involves a detailed study of building system operation. Faults in building systems are identified for resolution (e.g., fans that are not operating according to schedule, inoperable or leaky valves/dampers) and control changes may be recommended that increase energy efficiency, such as changes in system setpoints or operating schedules.
In all cases, the key is to use any ongoing commissioning software as a tool, and not to rely on the tool for the full scope of reporting, analysis, and recommendation of actions that are necessary. That is, and will always be, the role of a trained engineer with the education, experience, and even basic common sense that will lead to fully optimized HVAC operation.
Michael Eardley is vice president at CannonDesign. He is an expert across new, existing, envelope, and whole-building commissioning while helping clients achieve their sustainability and cost-savings goals.
- Continuous commissioning
- U.S. Green Building Council ongoing commissioning
- Building Commissioning Association Best Practices in Commissioning Existing Buildings