Modelling and Experimental Evaluation of an Active Thermal Energy Storage System with Phase-Change Materials for Model-Based Control

This thesis presents an experimental and numerical investigation of an active thermal energy storage (TES) system utilizing phase change material (PCM). The PCM-TES intended for building integration consists of PCM panels with active air circulation between the panels. Air is drawn through a channel to charge and discharge the PCM enabling the system to be used for both heating and cooling purposes – conditioned air, room air or outdoor air for night cooling can be utilized. This creates the possibility of a low thermal mass building to operate more like a high mass building and thereby gaining advantages commonly associated with traditional TES systems such as an ability to incorporate peak load reducing and shifting strategies without the significant weight of a traditional high mass building. A prototype PCM-TES is built and tested in an environmental chamber. The experimental data collected is used for model validation. A 30th order non linear model with varying thermal capacitance {C(T)} is developed and compared for fitness to experimental data. A simplified 2nd order model is shown to adequately predict the dynamic response of the system for thermal charging/discharging and can be incorporated into model-based control systems, which are effective in peak load reducing and shifting strategies. Simplified models are easier to implement and calibrate since they contain fewer parameters to adjust which could be learned in real time (online calibration) by using measurements from the building automation system to compensate for installation and construction tolerances. The model was extended to investigate the effect of increasing the exposed surface area to the air stream by having more air circulation channels while keeping the total air mass flow rate and convective heat transfer coefficients constant. Increasing the exposed area resulted in faster responding systems. A case study was simulated to demonstrate the use of the simplified 2nd order non-linear PCM-TES model for heating peak load reduction. The PCM-TES was shown to reduce the peak by at least 50% for the simulated conditions.