ET22SWE0042 - Field Study of HVAC Cost Optimized Supply Air Temperature Reset (CORE)
Variable air volume (VAV) HVAC systems dominate the commercial building market but have widely varying performance, with a well-documented performance gap between best-practice and typical operation. Two recent studies by Lawrence Berkeley National Lab and the California Energy Commission (CEC) reported a wide variation in energy performance for various typical supply air temperature (SAT) reset strategies (4-15% variation in HVAC energy). Existing SAT reset strategies have three inherent deficiencies that explain the lack of market uptake and sub-optimal real world energy performance: (1) they include simplifications and assumptions about SAT and total HVAC energy cost, (2) they require tuning of key parameters whose optimal values differ for every building and vary over the life of the building, and (3) there is no easy way to determine what those optimal settings are and whether tuning is improving savings or not. CORE (Cost Optimized Reset), a new cost-responsive supply air temperature reset open-source solution for multi-zone variable air volume systems, addresses these problems. This solution applies to the majority of the time that a building is occupied. In a VAV reheat system (the focus of this study), the air handler provides cooling most of the time, with zones providing heating where-needed. The open-source SAT reset solution developed by this research team could be deployed through two different paths: 1) the traditional path of a native building automation system (BAS) and 2) a third-party solution such as a microcontroller or a cloud based solution that integrates with an existing BAS. CORE dynamically estimates the energy cost of operating an air handling unit at its current supply air temperature setpoint, as well as slightly higher and lower setpoints. It does this using existing instrumentation commonplace in these systems. Using this information, along with the current approximate cost of electricity, chilled water, and hot water, we can dynamically estimate the cost of fan, cooling, and reheat energy at each setpoint. The algorithm then chooses the lowest cost operating point every 5 minutes, continually moving in the direction of least cost while adjusting to the changes occurring dynamically within the building, while ensuring that comfort conditions are maintained. CORE offers greater value over existing solutions because: (a) it uses existing sensors and hardware typically installed in modern VAV systems, (b) in contrast to far more complex model predictive control solutions, it is simple enough to be implemented either within the existing building automation system’s logic, or in an independent controller, and (c) it adjusts automatically to operational or weather-related changes in the building over time to directly minimize energy cost. CORE offers benefit to building owners, building operators (who will see improved occupant comfort and will spend less time and money troubleshooting), BAS manufacturers, third-party vendors, and other stakeholders. In this project, the research team will implement CORE at multiple test sites and determine energy savings.