Optimizing Control for Efficient Load Shifting with Thermal Energy Storage in Existing HVAC Systems

Technical Report · Mon Sep 01 00:00:00 EDT 2025

DOI:https://doi.org/10.2172/3002176· OSTI ID:3002176

Qiao, Yiyuan ^[1]; Li, Zhenning ^[1]; Ishmael, Mitchell ^[2]; Liu, Xiaobing ^[1]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
2. Active Energy Systems, Inc., Knoxville, TN (United States)

This project developed the integration of a direct-contact heat exchanger (DCHX) based thermal energy storage (TES) system with a chiller–air handling unit (AHU) plant to evaluate its potential for reducing building energy costs. Detailed physical models of the TES unit, building envelope, and HVAC components were developed alongside simplified control-oriented models to support both high-fidelity simulation and real-time optimization. Two control strategies were implemented and compared: a rule-based control (RBC) aligned with utility time-of-use (ToU) rates, and a model predictive control (MPC) framework leveraging forecasts of building load, weather, and internal gains. Simulation results show that the RBC strategy reduced daily electricity costs by around 30% by shifting cooling production from on-peak to off-peak hours. In contrast, the MPC strategy achieved significantly greater performance, reducing daily operating costs by up to 44% and peak-hour costs by more than 60%. Both strategies maintained indoor thermal comfort within acceptable limits, with MPC further improving load distribution and reducing equipment cycling. The outcomes confirm that TES integration, particularly when coordinated with advanced predictive control, can provide substantial cost savings and on-peak demand reduction. . These findings directly support the U.S. Department of Energy’s goals for grid-interactive efficient buildings and demonstrate the potential of TES-enabled HVAC systems for scalable deployment across the commercial building.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Active Energy Systems, Inc., Knoxville, TN (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Building Technologies Office
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 3002176
• Report Number(s): ORNL/TM--2025/4135; NFE-24-10403
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION