Center for the Built Environment

High thermal mass radiant systems have strong potential for energy flexibility, but key parameter relationships remain unclear. This study conducts a comprehensive parameter sensitivity analysis of Thermally Activated Building Systems (TABS) and Embedded Surface Systems (ESS) using hundreds of thousands of simulations. Two representative cases, Hangzhou, China (humid subtropical) and San Francisco, USA (marine), are analyzed in depth, followed by cross-climate testing in eight additional cities spanning hot to mild climates. Results show that start/stop is the primary driver of load shifting potential, while start time has little effect on cooling energy supply. For Floor ESS, however, operation duration is critical: extending operation from 8 to 24 hours increases daily cooling supply by 25.9% in Hangzhou and 35.4% in San Francisco, compared to only 5-9% in other terminal types. Using San Francisco as an example, a comparison of fixed nighttime pre-cooling and flexible scheduling reveals key design levers, such as window-to-wall ratios and optimal orientations, that strengthen energy flexibility. Overall, the findings support a two-stage optimization: first, tuning operation timing and durations to maximize load shifting without excess cooling, and second, refining design parameters to enhance flexibility. These insights provide guidance for designing grid-interactive radiant cooling systems.