Evaluating the effect of design and construction deficiencies on the economic performance of wall thermal insulation systems.

Abstract

This study demonstrates a systematic approach for evaluating the effect of design and construction deficiencies on the economic performance of insulated residential wall systems within a given context. In doing so, the study draws attention to the effect of construction practice and economic climate on the cost effectiveness of insulated walls. Serving as an exemplary case study, walls commonly constructed in the hot arid region of Saudi Arabia are considered. To assess the effect of deficiencies in the form of insulation voids, a finite difference model was employed to simulate the daily dynamics of heat transfer coefficients (h) for air filled voids in the insulated cavity of a stud wall. Comparison of daily heat flux for dynamic conditions with the heat flux calculated when a constant value is assumed for the cavity h coefficient shows that dynamic conditions with respect to the cavity behavior may be ignored safely under most conditions. However, the average temperature difference between the bounding surfaces of cavities as well as their mean temperatures were significantly less than the values recommended as typical in the ASHRAE literature. To simulate the overall thermal performance of a prototype building incorporating superior and deficient cases of the insulated stud wall, the Building Loads Analysis and System Thermodynamics program (BLAST) was used. Results of this analysis agree very closely with the results of theoretical and experimental work on deficiencies in insulated stud walls reported by others. Finally, life cycle costs of the walls were calculated and compared in order to assess the cost effectiveness of insulation with and without deficiencies. Results indicate that insulation deficiencies drastically degrade the cost effectiveness of insulation. The last two Chapters of the study illustrate the systematic application of the algorithms to rank the economic performance of some walls commonly constructed in Saudi Arabia, and to evaluate the optimal insulation thickness. The specific construction deficiencies associated with the walls were determined according to the findings of a field survey of several construction sites. Results indicate that the walls' relative economic ranking and optimal insulation thickness are extremely sensitive to the assumed parameters of the application (such as building orientation, and energy costs).