Development of condensation-free operation strategy for thermally activated building systems using model predictive control

Abstract

Integrating ceiling thermally activated building systems (TABSs) with ventilation systems in buildings is expected to enable more efficient spatial cooling to cope with Japan’s hot, humid summer. However, the inherently large thermal mass of TABSs, which results in slow thermal responses, may pose a risk of surface condensation under these conditions. In this study, to ensure TABS operation while preventing surface condensation, a computational fluid dynamics (CFD) model was developed that reproduces an entire floor of a building and the TABS. Through unsteady CFD analysis, the moisture generation sources in the indoor environment were evaluated, and a dew point temperature prediction formula was constructed based on the indoor moisture balance. Next, the surface temperature fluctuations caused by the moisture absorption and desorption of concrete were addressed, as well as the problem of uneven surface temperatures arising from the architectural structure. A safety rate was added to the predicted dew point temperature to mitigate the risk of condensation further. For the control method that keeps the entire TABS surface condensation-free, a model predictive control (MPC)-based control method was used to minimize energy consumption. The effectiveness of the proposed control method was validated through coupled analysis using MATLAB and CFD. The results demonstrated that the proposed MPC-based condensation-free TABS operation method could reduce energy consumption by 12.4 % compared with on/off control and by 9.3 % compared with standard MPC while keeping the entire surface condensation-free. Additionally, the indoor temperature was maintained at approximately 24 °C, providing a comfortable indoor thermal environment.