University of California Los Angeles Microencapsulated Phase Change Composite Materials for Energy Efficient Buildings A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Mechanical Engineering by Alexander Thiele 2016 © Copyright by Alexander Thiele 2016 Abstract of the Dissertation Microencapsulated Phase Change Composite Materials for Energy Efficient Buildings by Alexander Thiele Doctor of Philosophy in Mechanical Engineering University of California, Los Angeles, 2016 Professor Laurent G. Pilon, Co-Chair Professor Gaurav Sant, Co-Chair This study aims to elucidate how phase change material (PCM)-composite materials can be leveraged to reduce the energy consumption of buildings and to provide cost savings to ratepayers. Phase change materials (PCMs) can store thermal energy in the form of latent heat when subjected to temperatures exceeding their melting point by undergoing a phase transition from solid to liquid state. Reversibly, PCMs can release this thermal energy when the system temperature falls below their solidification point. The goal in implementing composite PCM walls is to significantly reduce and time-shift the maximum thermal load on the building in order to reduce and smooth out the electricity demand for heating and cooling. This Ph.D. thesis aims to develop a set of thermal design methods and tools for exploring the use of PCM-composite building envelopes and for providing design rules for their practical implementation. First, detailed numerical simulations were used to show that the effective thermal con- ductivity of core-shell-matrix composites depended only on the volume fraction and thermal conductivity of the constituent materials. The effective medium approximation reported by Felske (2004) was in very good agreement with numerical predictions of the effective thermal conductivity. Second, a carefully validated transient thermal model was used to simulate microencapsulated PCM-composite walls subjected to diurnal or annual outdoor tempera- ii ture and solar radiation flux. It was established that adding microencapsulated PCM to concrete walls both substantially reduced and delayed the thermal load on the building. Several design rules were established, most notably, (i) increasing the volume fraction of microencapsulated PCM within the wall increases the energy savings but at the potential expense of mechanical properties [1], (ii) the phase change temperature leading to the max- imum energy and cost savings should equal the desired indoor temperature regardless of the climate conditions, (iii) microencapsulated PCM-concrete walls have the best energetic performance in climates where the outdoor temperature oscillates around the desired indoor temperature, (iv) microencapsulated PCM offers the largest energy and cost savings when embedded in South- and West-facing walls and during the summer months in San Francisco and Los Angeles, CA. Third, a novel experimental method was developed to rapidly quantitatively character- ize the thermal performance and potential energy savings of composite materials containing phase change materials (PCM) based on a figure of merit termed the energy indicator (EI). The method featured (i) commonly used specimen geometry, (ii) straightforward experimen- tal implementation, and (iii) sensitivity to relevant design parameters including PCM volume fraction, enthalpy of phase change, composite effective thermal conductivity, and specimen dimensions. Finally, the widely-used admittance method was extended to account for the effects of phase change on the thermal load passing through PCM-composite building walls subjected to realistic outdoor temperature and solar radiation flux. The speed and simplicity of the admittance method could facilitate the design and evaluation of the energy benefits of PCM- composite walls through user-friendly design software for a wide range of users. iii The dissertation of Alexander Thiele is approved. Adrienne Lavine Richard Wirz Gaurav Sant, Committee Co-Chair Laurent G. Pilon, Committee Co-Chair University of California, Los Angeles 2016 iv Table of Contents 1 Introduction :::::::::::::::::::::::::::::::::::::: 1 1.1 Building energy consumption..........................1 1.2 California climates and energy landscape....................2 1.2.1 California climate zones.........................2 1.2.2 Peak electricity demand and time of use pricing............3 1.3 Zero net energy..................................5 1.4 Energy efficient building envelopes.......................7 1.5 Objectives and scope...............................8 2 Background :::::::::::::::::::::::::::::::::::::: 11 2.1 Phase change materials.............................. 11 2.1.1 Classification............................... 11 2.1.2 Thermophysical properties........................ 12 2.1.3 PCM-composite building materials................... 13 2.2 Simulating phase change in single phase systems................ 17 2.3 Simulation tools for energy efficiency of buildings............... 18 3 Effective Thermal Conductivity of Three-Component Composites Contain- ing Spherical Capsules ::::::::::::::::::::::::::::::::: 21 3.1 Background.................................... 21 3.2 Analysis...................................... 25 3.2.1 Schematics................................. 25 3.2.2 Assumptions................................ 27 3.2.3 Governing equations and boundary conditions............. 29 v 3.2.4 Data processing.............................. 29 3.2.5 Method of solution............................ 30 3.3 Results and discussion.............................. 31 3.3.1 Effect of capsule dimensions and packing arrangement......... 31 3.3.2 Effect of core and shell volume fractions................ 32 3.3.3 Effect of constituent thermal conductivities............... 34 3.3.4 Effect of capsule spatial and size distributions............. 37 3.3.5 Critical condition for effective thermal conductivity.......... 40 3.3.6 Comparison with experimental data................... 40 3.4 Conclusion..................................... 41 4 Diurnal Thermal Analysis of Microencapsulated PCM-Concrete Compos- ite Walls :::::::::::::::::::::::::::::::::::::::::: 43 4.1 Background.................................... 43 4.2 Analysis...................................... 45 4.2.1 Schematic................................. 45 4.2.2 Assumptions................................ 47 4.2.3 Heterogeneous wall simulations..................... 47 4.2.4 Homogeneous wall simulations...................... 50 4.2.5 Performance metrics........................... 53 4.2.6 Method of solution............................ 54 4.2.7 Validation................................. 55 4.3 Results and discussion.............................. 55 4.3.1 Heterogeneous vs. homogeneous wall.................. 55 4.3.2 Diurnal thermal behavior......................... 59 vi 4.3.3 Equivalent wall thickness......................... 69 4.4 Conclusion..................................... 71 5 Annual energy analysis of concrete containing phase change materials for building envelopes :::::::::::::::::::::::::::::::::::: 72 5.1 Background.................................... 72 5.2 Analysis...................................... 76 5.2.1 Schematic and assumptions....................... 76 5.2.2 Governing equations........................... 78 5.2.3 Initial and boundary conditions..................... 79 5.2.4 Constitutive relationships........................ 79 5.2.5 Data processing.............................. 82 5.2.6 Method of solution............................ 85 5.3 Results and discussion.............................. 86 5.3.1 Inner surface heat flux.......................... 86 5.3.2 Effect of wall orientation......................... 89 5.3.3 Effect of phase change temperature................... 91 5.3.4 Effect of season.............................. 93 5.3.5 Annual energy and cost savings..................... 95 5.3.6 Payback period.............................. 97 5.4 Conclusion..................................... 98 6 Figure of Merit for the Thermal Performance of Cementitious Composites Containing Phase Change Materials ::::::::::::::::::::::::: 100 6.1 Background.................................... 100 6.1.1 Performance metrics of PCM-composite materials........... 100 vii 6.1.2 Numerical modeling of phase change in three-component composites. 102 6.2 Materials and Methods.............................. 104 6.2.1 Material synthesis............................. 104 6.2.2 Specimens................................. 104 6.2.3 Material characterization......................... 106 6.2.4 Experimental apparatus......................... 107 6.2.5 Experimental procedure......................... 107 6.2.6 Experimental uncertainty........................ 108 6.3 Analysis...................................... 108 6.3.1 Schematic and assumptions....................... 108 6.3.2 Governing equations........................... 109 6.3.3 Initial and boundary conditions..................... 110 6.3.4 Constitutive relationships........................ 111 6.3.5 Method of solution............................ 112 6.3.6 Data processing.............................. 112 6.3.7 Validation................................. 113 6.4 Results and discussion.............................. 114 6.4.1 Material characterization......................... 114 6.4.2 Experimental/numerical comparison.................. 116 6.4.3 Parametric study............................. 123 6.4.4 Correlation to performance metrics..................