Evaluation of the Energy Demand Flexibility of a Radiant Cooling System With Thermal Energy Storage

The accelerated growth of renewable energies in recent years has made it necessary to implement Demand-Side Management (DSM) strategies that can help to adjust the energy demand according to energy production. In the context of DSM, buildings can play a significant role as they consume almost 40% of the energy use worldwide and show a significant potential for implementing energy demand flexibility measures. DSM strategies in buildings generally rely on short-term heat storage in structural thermal mass. However, the Thermal Energy Storage (TES) capacity is limited by the available thermal mass in dense building elements. In addition, the structural thermal mass generally has low heat storage and release rate (passive system), limiting the ability to manage building thermal loads. To overcome these limitations, a flexible heating and cooling system that can be installed in office buildings to replace the conventional all-air system was proposed and evaluated in this study. The system utilizes the high TES capacity of macro-encapsulated Phase Change Materials (PCM) discreetly incorporated below the serpentine copper coil of a standard Radiant Ceiling Panel (RCP), which allows shifting the energy demand for conditioning buildings. At first, the thermal storage properties of the TES units were determined using the standard ASTM C1784-20. Then, a walk-in dual climate chamber was used to experimentally evaluate the ability of the Radiant Ceiling Panel incorporating macro-encapsulated PCM (RCP-PCM) to shift heating/cooling loads to off-peak hours, measure its heat removal capacity, and the resulting indoor thermal environment. The obtained properties and the measurements from the experimental and field studies were used to validate a whole-building simulation model. The validated model was used to develop a simplified method for designing and controlling a RCP-PCM system. The validated model was also used to evaluate the energy demand flexibility potential of office buildings conditioned by the proposed system. Three different performance indicators were used to quantify energy demand flexibility: available TES capacity, storage efficiency, and power shifting capacity. The results of this study indicate that the RCP-PCM system can effectively shift the heating/cooling loads to off-peak hours while maintaining acceptable thermal comfort conditions during typical office occupancy hours (8:00 to 18:00). This load-shifting capability of the RCP-PCM system can be of great help in planning DSM strategies for increased penetration of renewable electricity in building heating and cooling applications.