Performance characterization of PCM impregnated gypsum board for building applications

摘要

Previous research studies conducted on building components containing a phase-change material (PCM) have shown a great potential for direct and indirect energy and cost savings in the building envelopes. In particular, PCM impregnated gypsum boards, one of the most popular application of PCMs in buildings, have been reported to reduce building cooling loads by 7-20%. However, in order to best design and optimize the PCM-enhanced building materials, it is critical to accurately characterize the dynamic thermal properties such as enthalpy curve, volumetric heat capacity, sub-cooling, hysteresis-of these PCM-enhanced components. In addition, test data on these dynamic characteristics is necessary for whole-building simulations, energy analysis, and energy code work. In the past, the only existing readily-available method of thermal evaluation of PCMs utilized the Differential Scanning Calorimeter (DSC) methodology. Unfortunately, this method required small and 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 with gypsum, concretes, fiber insulations, plastic foams etc., since these materials are often not homogeneous. In this paper, dynamic thermal properties such of a 1/2" thick PCM impregnated gypsum board are analyzed based on a novel dynamic experimental procedure: using the conventional HFMA. The gypsum board tested in this work contained 20-25% by weight of a microencapsulated PCM with latent heat of ～120 kJ/kg. First, the theoretical details of the dynamic HFMA (DHFMA) are described. In essence, top and bottom plates of the HFMA are set to the same temperature and heat flow signals from the corresponding heat flux meters are integrated over time to compute the enthalpy changes during a temperature step change. Volumetric heat capacity profile is determined by taking the slope of the enthalpy curve. A negligible sub-cooling and hysteresis is observed for the PCM impregnated gypsum board, In addition, thermal properties such as onset of melting and solidification, and sensible heat of the specimen when PCM was in solid and liquid state were also determined. Dynamic properties such as heat capacity profiles and peaks of melting and solidification cycles, and amount of sub -cooling as measured by DHFMA were found to be relatively close to the DSC results on the same microencapsulated PCM.