Numerical and Experimental Thermal Analysis of PCM-Enhanced Insulations

Abstract

Different types of Phase Change Materials (PCMs) have been tested as dynamic components in buildings for at least 4 decades. This paper presents experimental and numerical results from a thermal performance study focused on building envelope materials enhanced with micro-encapsulated or micro-packaged PCMs. The PCMs store energy and alter the temperature gradient through an insulated cavity, remaining at a nearly constant temperature during the melting and solidifying stages. PCM-enhanced sheathing boards and insulation-PCM blends can be utilized as lightweight thermal mass components in low-energy buildings. It is expected that these types of dynamic thermal systems will contribute to the reduction of overall energy usage peak load shifting in future buildings. A lab-scale testing procedure (one to two foot size specimens) was introduced in 2009 for the analysis of dynamic thermal characteristics of PCM-enhanced materials. Today, test data on these characteristics is necessary for whole-building simulations, energy analysis, and energy code work. The transient characteristics of PCM-enhanced products depend on the PCM content and quality of the PCM carrier. In the past, the only existing readily available method of thermal evaluation utilized the differential scanning calorimeter. Unfortunately, this method required small, relatively uniform test specimens. This requirement is unrealistic in the case of many PCM-enhanced building envelope products. Small specimens are not representative of PCM-based blends, since these materials are not homogeneous. In this paper, dynamic thermal properties of materials, in which phase change processes occur, are analyzed based on a recently-refined dynamic experimental procedure: using the conventional heat flow meter apparatus. In order to theoretically analyze performance of these materials, an integral formula for the total heat flow in finite time interval, across the surface of a slab of the phase change material, was derived. Experimental results are reported for laboratory-scale samples of PCM-enhanced thermal insulation