PhD Oral Exam – Arash Bastani

Abstract

While space conditioning load contributes largely to the grid critical peak, shifting it partially or entirely to the off-peak period could have significant economical impact on both energy supply and demand sides. This shifting technique is accomplished by storing energy during off-peak periods in order to be utilized during peak periods. The building envelope integrated with phase change material (PCM) can provide latent heat thermal energy storage (TES) distributed in its entire surface area and inhibit the enhanced thermal mass in lightweight buildings. Selecting the most appropriate PCM wallboard based on its thickness and thermo-physical properties, is the main target; yet, there is a lack of an appropriate design tool. Accordingly, this dissertation focuses on the development of a design framework to quantify and qualify the application of PCM wallboards in a building envelope in order to efficiently shave and shift the demand peak.

In this study, the non-dimensionalized analysis was conducted, and the dimensionless numbers influencing the thermal behavior of a PCM wallboard were identified. Moreover, the correlations between the dimensionless parameters and the performance of the PCM wallboard were determined through a comprehensive parametric study. Consequently, these correlations were presented as the design framework to select and size a PCM wallboard. The tool consists of a number of charts identified as the extention of the well-known Heisler chart of transient temperature and heat transfer for materials that undergo the phase transition.

Finally, the developed design framework was applied to select and size three PCM wallboards for an existing residential house, and TRNSYS simulation software was used to study the thermal performance of the house furnished with the PCM wallboard. The application of PCM wallboards was evaluated for both charging and discharging periods at three different outdoor climates: cold, very cold, extremely cold. It was observed that the tool can appropriately size the wallboards to efficiently store energy and postpone the peak. In addition, the wallboard with the thickness identified by the framework provides the longest shift of load compared to other simulated sizes of the same material. Moreover, the building refurbished with either one of those PCM wallboards was able to have longer shift of load and lower daily energy consumption than the conventional gypsum board.