PNNL

Abstract

Improvements to building control systems can lead to energy savings and increased occupant comfort. In an optimized system, process variables such as air temperature will closely follow their desired setpoints and avoid excess energy use. Typically, experts must manually inspect individual control loops to identify poor performance and opportunities for improvement. However, this approach is difficult in modern buildings that have a prohibitively large number of controllers. To address this issue, Pacific Northwest National Laboratory (PNNL) created the ControlScore tool which captures operating data from the many controllers within a building and generates standardized scores for each loop on a scale of 0 to 10 (a score of 0 indicates poor control, a score of 10 indicates good control). In order to test real world performance of the ControlScore and gain feedback from building operators, PNNL applied the Building ControlScore tool to all available real operational data from a laboratory building within the period of May 1, 2020, to January 1, 2023. The building scored a 5.36 overall, with all four of the building’s sections scoring between 4.5 and 6.5. The scoring methods are calibrated so that the 0-10 score range roughly represents a normal distribution of building control in the real world. As such, most buildings fall near the middle of the range. Thus, these results indicate that the analyzed systems have a fair performance with moderate room for improvement. No specific type of loop was problematic, but the lowest and highest performing loops in each building section were identified. While the ControlScore identifies loops and systems that aren’t meeting their designated setpoints, it does not indicate the cause of those issues. For example, consider a supply air terminal unit’s airflow loop that received a low score due to it delivering less air than specified by the setpoint. The lower-than-desired airflow could be due to equipment limitation (e.g., the terminal unit or duct serving is too small to accommodate that airflow), malfunctioning equipment (e.g., a stuck damper or bad sensor), or something else entirely. The ControlScore does not diagnose problems, it simply identifies the symptoms that can be explored and addressed by building operators. For this study, building operators were provided with the ControlScore findings so they could investigate performance issues. The building operators also provided feedback on how the tool could be enhanced.