Experimental and Simulation Approaches for Optimizing the Thermal Performance of Building Enclosures Containing Phase Change Materials.

摘要

It has been proven that the integration of phase change materials (PCM) into building enclosures helps with wall thermal management as well as in reducing building energy consumption. Most older and some current PCM integration methods for building enclosures are impractical and create problems such as PCM leakage and evaporation, PCM water absorption, moisture transfer problems leading to building materials degradation, and problems related to the improper mixing of PCMs with insulation products (e.g., cellulose insulation). The use of thin PCM layers assembled and contained in blanket-like or board products would be practical to install and would eliminate or ameliorate these problems.;The integration of thin PCM layers into building enclosure components, such as walls and ceilings, was accomplished via the use of thin PCM thermal shields (PCM shields) and via thin PCM boards. The thermal performance of building enclosures integrated with PCM shields and PCM boards was studied using experimental and simulation methods. For the experiments, the PCM shields were tested in the test houses of typical residential construction and the PCM boards were tested in the institutional building of commercial construction. For the modeling and simulations, a public-domain building energy simulation software, known as EnergyPlus, that included a new open-source algorithm, known as CondFD, was used. For model calibration purposes, the model predictions were compared against experimental data.;From the experimental evaluation of the PCM shields, it was observed that their thermal performance depended on their installation location within the cavities of the walls and ceilings. Therefore, a critical part of this research was to discover which installation location would produce the optimal performance of an enclosure outfitted with PCM shields.For this, several locations, measured from the interior surface of the wallboard which was in contact with the conditioned space, were specified as locations 1, 2, 3, 4, and 5. The location number increased with distance from the surface indicated in the preceding sentence. It was discovered that in terms of peak heat fluxes, the integration of PCM shields in enclosure components produced the maximum percent reductions of 57.4% when installed at location 3 (i.e., in the middle of the wall cavity) in a south-facing wall, 37.3% when installed at location 2 in a west-facing wall, and 41.1% when installed at location 4 in a ceiling. In terms of daytime total heat transfer, the integration of PCM shields produced the maximum percent reductions of 47.9% for location 3 for a south wall, 34.1% for location 3 for a west wall, and 27.5% for location 4 for a ceiling.;The PCM boards were installed in a single location over the internal surface of the indoor surface that bound the walls of the institutional building. The results indicated that the addition of the PCM boards to a standard wall panel would produce reductions in peak heat flux of 67.0% for a south wall panel and 80.2% for a west wall panel. In terms of total heat transfer, the integration of the PCM boards produced average daily reductions of 27.4% in the south wall and 10.5% in the west wall.;For evaluating overall energy savings produced by the integration of PCM shields into building walls and ceilings, simulations of a typical residential building with and without PCM shields were carried out for a building located in four cities, which were selected according to the DOE Climate Zone Map and included climate zones 1 - 4. The simulations predicted that the optimal installation location of the PCM shield would be location 2 for both the walls and ceilings of the residential building regardless of city location. Furthermore, it was discovered that PCM installation at location 1 in any enclosure component should be avoided because the heat transfer, and thus the energy consumption, in the cooling and heating seasons would both increase.