Science and Technology for the Built Environment (2015) 21, 403–412 Copyright C  2015 ASHRAE. ISSN: 2374-4731 print / 2374-474X online DOI: 10.1080/23744731.2014.1000781 Effect of clouds and dust storms on the sky radiation exchange for buildings located in hot–dry climates SALEM A. ALGARNI and DARIN W. NUTTER ∗ Department of Mechanical Engineering, University of Arkansas–Fayetteville, 863 W. Dickson Street, Fayetteville, AR 72701, USA This article evaluates the impact of effective sky temperatures on building radiation exchange under clear, cloudy, and dusty conditions for extremely hot and dry climates. In part, a dusty sky temperature model has been introduced as a function of atmospheric aerosol optical depth. The sky radiative exchange was evaluated using a one-dimensional transient heat transfer model with numerical calculations performed using the fully implicit finite-difference method. The newly available ASHRAE 2013 clear sky model was evaluated and implemented to calculate the hourly incident solar radiation for a horizontal roof under the extremely hot–dry climate conditions of Riyadh, Saudi Arabia. Results showed that in clear sky conditions, sky longwave radiation contributes to a reduction of the total heat gain. A daily mean clear sky cooling around 2645 and 2385 W-hr/m 2 was estimated for July and January, respectively. In contrast, cloud and dust covers increase effective sky temperature and diminish the role of sky radiative cooling. Depending on severity, the mean contributed sky cooling heat exchange was found to range between 436 and 1636 W-hr/m 2 for dust storm and scattered cloudy sky conditions, respectively. Similarly, the ASHRAE 2013 clear sky model and the sky temperature models were shown for four other extremely hot–dry global sites. Introduction In extremely hot and dry climates, excessive heat causes an occupant thermal discomfort. Therefore, buildings consume a substantial portion of energy due to the high demand on cool- ing (Ben Cheikh and Bouchair 2004). For example, in Saudi Arabia, about 76% of generated electric energy is used for op- erating residential, governmental, and commercial buildings. About half of the total consumption is used for the residential sector (Saudi Electric Company 2012). The residential sector high consumption is due to the inefficient buildings and harsh climate of Saudi Arabia. Moreover, the energy required to cool buildings accounts for a big portion, up to 73% of the total electric energy (Elhadidy et al. 2001; Algarni and Nutter 2013). Therefore, the optimum design of building elements is essential. Several studies have evaluated the thermal performance of building elements, analytically, experimentally, and with numerical modeling. Various methods of solving heat con- duction in building composite roofs, such as Green functions and Laplace transforms, were described by Ozisik (1993). A comprehensive review on experimental studies and several building design tools was prepared by Balaras (1996). The study presented the concept of thermal mass and summa- rized parameters that affect the performance of thermal mass Received May 15, 2014; accepted December 11, 2014 Salem A. Algarni, Student Member ASHRAE, is a PhD Candi- date. Darin W. Nutter, PhD, PE, Fellow ASHRAE, is a Professor. ∗ Corresponding author e-mail: duntter@uark.edu Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uhvc. on building cooling load. A one-dimensional transient model to evaluate the thermal behavior of building walls was de- scribed by Al-Sanea (2000); the model was solved by using the finite-difference method. The interface resistances between wall layers were ignored and constant thermal properties as- sumed. McQuiston et al. (2005) described several methods of calculating transient conduction heat through building walls and roofs; the methods included lumped parameter, numerical (finite difference and finite element), frequency response, and Z-transform methods. Specific studies, such as the optimum location of the in- sulation layer and its optimum thickness, were investigated. Al-Sanea and Zedan (2001) investigated the effect of insu- lation layer location in the building wall on the daily mean heat transfer and peak loads on the local hot–dry climate of Riyadh, Saudi Arabia. They recommended locating the insu- lation single layer near the outer wall surface. A similar study was done by Ozel and Pihtili (2007a). They investigated the most suitable location of multiple insulation layers on build- ing roofs. Using three layers of insulation on the outer, middle, and inner surfaces of the roof was recommended, while the to- tal wall thickness was kept constant. In addition, it has been shown that a similar configuration can be applied on the wall elements (Ozel and Pihtili 2007b). Al-Sanea et al. (2012) in- troduced and numerically developed the concept of optimum thermal mass thickness and location on dynamic heat trans- fer behavior of insulated walls. Adjustments were made to the wall insulation layer and varying thermal mass thickness to keep the total composite wall thermal resistance constant. In addition, the importance of a light roof color on building heat gain in hot climates has been discussed (Suehrcke et al. 2008).