A comprehensive study of phase change materials (PCMs) for building walls applications

Air conditioning energy consumption in summer represents a challenge in many areas with hot and humid climates. When incorporated into the walls of light-weight residential and commercial buildings, phase change materials (PCMs) can increase the effective thermal mass of the walls, shift part of the space cooling loads to off-peak hours when less cooling is needed, and lower the peak space cooling load of the buildings.;In this dissertation, the working environment of the PCMs (i.e., the temperatures within the wall) was studied from summer field experimental temperature data. Results of Differential Scanning Calorimeter (DSC) tests, performed on pure PCMs, PCM/cellulose mixtures, and "aged" PCM samples, used to better understand PCMs' thermal behavior, the effects of mixing them with cellulose insulation, and the impact that ambient air had on samples when these were exposed, are presented. The results of the mass change experiments, carried out to investigate PCMs' mass changes when these were exposed to ambient air, under room temperature and under high temperature conditions, are summarized.;The performance of PCM-enhanced walls was evaluated under full weather conditions and in a laboratory setting. The PCM was integrated into test walls using two methods, namely, direct mixing of the PCMs with cellulose insulation and macro-encapsulation. Information on the test setups, experimental approach, and results are presented. The heat transfer process in PCM-enhanced walls was analyzed for different situations. A detailed explanation of how PCMs reduce the peak heat flux through PCM-enhanced wall is presented. A new method for integrating the PCM into building walls, referred to as "layer method," was proposed to overcome some of shortcomings of previous PCM integrating methods. A detailed analysis of this method is also presented.;A DSC test method and its detailed steps, used to study the performance of PCMs when these would cycle from partially-melted states, are introduced. Based on these DSC data, a modified phase change heat transfer model, for a paraffin-based PCM, was developed. The model was implemented via a FORTRN program.;Based on the developed model, numerical simulations were run. The simulation results were compared with experimental data to validate the model. To investigate the influence of various variables on the performance of the PCM-enhanced building walls, a parametric study was conducted using the validated heat transfer model.;The performance of the PCM-enhanced wall in several U.S. climate zones was studied. The simulation results for the representative cities showed that a 7 mm (0.28 in) thick PCM layer placed at (3/16)L from the wallboard would produce large peak reductions for most climate zones. For the cities located in places with hot climates, such as Phoenix, AZ, the PCM layer would need to be moved towards the colder side of the wall. For all the climate zones, the PCM-enhanced wall retrofitted with the proposed layer method could lower the peak space cooling load through the walls by about 50%.