الفهرس 
الغلافOnly 14 pages are availabe for public view
 |  | from | 215 |  |  |
| | | from | 215 | | |
Abstract
ABSTRACT
Nowadays, the continuous growth in energy consumption, shrinking resources, and rising energy costs are real challenges facing the world. Air conditioners represent the largest consumer in the domestic sector, which reaches 40% of the world’s energy consumption. The building envelope plays a main role in controlling building energy by adjusting the cooling and heating loads between the indoor and outdoor environments to satisfy the building’s thermal requirements. In recent years, the application of phase change materials (PCMs) in building envelopes provides an encouraging way to regulate indoor air temperature by passive cooling with thermal energy storage. In the present work, experimental and theoretical investigations are carried out to predict the performance characteristics of a building integrated with PCMs.
In the first part of the present work, experiments are conducted on the test room with and without PCM in the charging and discharging modes. The experimental study aimed to explore the benefits of the PCM on indoor thermal comfort. Influences of charging air temperatures (36°C, 41oC and 46oC), two PCMs with different melting temperatures (25°C and 30°C), PCM thickness and the PCM layer location in the test room on indoor thermal comfort are investigated. Experimental results confirm that the PCM improves the time delay of air temperature to 3.5h at an indoor air temperature of 27.5°C, while the air temperature DROP (ATD) is about 3.8°C at 4.5h of operation. The charging air temperature has a significant effect on the PCM efficacy and room temperature. Increasing the charging air temperature from 36 to 46°C resulted in a decrease in phase shift from about 3.52 to 1.72h. The indoor air temperature, using the PCM-25, reduces by approximately 1.54, 2.0, and 3.3°C, at charging air temperatures of 36, 41, and 46°C, respectively, over the base case. PCM-25 produces better indoor air temperature than PCM-30 as it has a higher ATD of 1.09°C at 4.8 hours of operation compared to PCM-30. Also, the phase shift of the PCM-25 increases by 2.15h and PCM-30 by 1.4h, compared to the base case. As the PCM thickness is doubled, the indoor air temperature decreases by 1.7°C, and the time required to reach 25.5°C increases from 3.2 to 6.0h. As the PCM-25 location changes from the wall inside to the wall outside, the phase shift decreases by 1.5 h, and the indoor air temperature increases by 0.9°C at 5.5h of operation. Thus, the PCM integrated into the wall inside yields better performance of the building envelope in summer.
The second part of the current research deals with the dynamic simulation of thermal comfort in heavy structural buildings in both free-floating and air conditioning modes under hot-dry conditions. The simulation model is developed using dedicated building simulation software and validated against the present indoor experiment, and the published outdoor experiment. The simulation work focuses on the following two objectives.
The first objective is to examine the essential properties governing the appropriate selection of phase change materials integrated into heavy structure buildings during different seasons. Nine PCMs with various thermophysical properties were evaluated, in the free-floating mode, under hot and dry climate conditions. The examined range of each property is extracted from the actual data of the nine considered PCMs. The results confirm that the large latent heat of fusion and low thermal conductivity of PCMs enhance indoor thermal comfort at the same melting temperature. The Intensity of Thermal Discomfort (ITD) decreases from 51 to 36.4% as the energy density (product of latent heat and density) increases from 138.6 to 180.6MJ/m3, for two PCMs with the same melting temperature of 21°C. As the PCM melting temperature increases from 21 to 29°C, the ITD index decreases from 27 to 10°C.day, respectively. The occupants’ thermal comfort enhances as the PCM melting temperature approaches the upper limit of the adaptive thermal comfort. In brief, the mean ITD sensitivity index is highly affected by the PCM melting temperature (5.85), followed by latent heat (1.37), density (0.71), thermal conductivity (0.41), and the phase transition region (0.096) that has a negligible effect on the indoor thermal comfort. The stated dimensionless numbers indicate the importance of the different properties on thermal comfort.
The second objective is to evaluate the efficacy and economic viability of phase change materials in improving the thermal comfort of inhabitants in heavy-structure buildings, with different wall characteristics, under hot-dry (e.g., Cairo city) and extremely hot-dry (e.g., Aswan city) conditions. The PCM efficacy is assessed in free-floating mode (in terms of exceedance hours) and air-conditioning mode (in terms of cooling demand reductions) for six-phase change materials with melting temperatures of 21-31°C. The results indicate that the best material in the free-floating and air conditioning modes is the materials with melting temperatures of 29 and 25°C, respectively. The phase change material achieves 373 reductions in the exceedance hours more than the thermal insulation when integrated into a wall with a thermal resistance of 0.5m2K/W. As the thermal resistance of the building envelope increases from 0.3 to 1.02m2K/W, the PCM efficacy continually decreases. Also, the reduction in exceedance hours declines from 52.8 to 9.24% as the climate changes from hot-dry to extremely hot-dry. Remarkably, combining a thin 1cm layer of phase change material and a 3cm thermal insulation layer reduces the exceedance hours by 65.5%, the air conditioning energy consumption by 27.2%, and the payback period by 54%.