TA-23-C063 – Considerations in Intelligently Sizing and Controlling TES-Integrated HVAC Systems

Greenhouse gas emissions related to operating buildings make up about 30% of the US annual emission total, which is why decarbonization of buildings has become a major priority for many local and national regulators, including of the Department of Energy. One avenue for decarbonization is electrification of space heating with heat pumps (HP). To supplement this, the addition of thermal energy storage (TES) allows HVAC loads to be more flexible and achieve deeper carbon reductions, by shifting thermal loads to periods of the day where emissions from electricity generation are lower and/or equipment performance is higher. While the combination of HP and TES technologies presents an opportunity for increased flexibility and decarbonization, it requires a more complex control strategy and thoughtful equipment sizing to effectively use the integrated HVAC system. In fact, storage allows for downsizing of the equipment, if controlled adequately, but the tradeoff between cost and risk to violate comfort, with different equipment/storage sizes, is not trivial to determine. This study analyzes the interaction between sizing of these components and appropriate control schemes to ensure maximum flexibility and lower costs while providing the same quality of service to the building system. We build upon previous work to develop and present a repeatable sizing process and describe implications of heuristic and optimized predictive control sequences for four combinations of HP and TES sizes. In our case study scenario, we show the inclusion of TES can reduce the HP sizing by 36%. Additionally, we discuss the first and operating cost savings and flexibility potential made possible by each configuration in response to a representative dynamic price signal. Armando