Insulation in the opaque envelope : effects on thermal performance of residential buildings in hot-arid climates

Abstract

The purpose of the study was to evaluate the thermal performance of insulated opaque building envelopes when the order of envelope insulating layers was altered. The study emphasized the effect on cooling load. Three room-sized buildings were used in the field experiment. All buildings were identical in size, color, orientation, and openings. One building was externally insulated, one was internally insulated, and one was uninsulated. The experiment was conducted in the hot-arid climate of Saudi Arabia. Descriptive, inferential, and implication analyses were compared. The descriptive analyses included the black globe temperature (BGT) daily profile plot. The inferential analyses included general linear model (GLM) procedures and Fisher's least significant difference (LSD) pairwise comparisons of the BGT means, maximums, minimums, and ranges. The results of BGT analyses were used in an energy simulation program to assess the implications of the results on annual energy consumption and on the sizing of HVAC systems. Results from these analyses indicated significant differences in the average of maximums, ranges, and overall means of the BGT among the three buildings. There were no significant differences at the 95% confidence level in the average of minimums among the three buildings. Findings strongly support the first three hypotheses which were about the BGT means, maximums, and ranges. The implications of the BGT results were found to be within expectations. The annual energy consumption and the size of HVAC equipment were the lowest in the externally insulated house. The cost benefit analysis indicated substantial savings for households; the simple payback period was less than three years. Some of the design recommendations for building in hot-arid climates emphasized the protection of external insulation from impact forces and other environmental effects such as ultraviolet rays. External insulation should be used in buildings with continuous use and continuous air conditioning. More thermal benefits may be attained when external insulation is utilized with night ventilation, although the ventilation aspects had not been studied conclusively here.