© 2018 Copyright held by the author(s). Published by AIJR Publisher in Proceedings of First Conference for Engineering Sciences and Technology (CEST-2018), September 25-27, 2018, vol. 2. This is an open access article under Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license, which permits any non-commercial use, distribution, adaptation, and reproduction in any medium, as long as the original work is properly cited. ISBN: 978-81-936820-6-7 Theoretical Investigation of an Indirect Evaporative Air Cooling System Mohamed I. Alowa, Gassem A. Azzain Department of Renewable Energies, Faculty of Energy and Mining Engineering, Sebha University, Libya DOI: https://doi.org/10.21467/proceedings.4.17 * Corresponding author email: moh.alowa@sebhau.edu.ly ABSTRACT In this paper an indirect evaporative cooler theoretically investigated. Because of its low cost and low environment pollution, the indirect evaporative coolers have great potential as an alternative to conventional air conditioning in an arid hot climates such as southern of Libya where the temperature and relative humidity reach 45 º C and 20 % respectively. The present investigated system consists of cooling tower, cross unmixed heat exchanger, air blower, circulating pump, air filter, humidifier , and air duct. The main factors that affect on the temperature output of the system are presented. The affect of air conditions input to the cooling tower and air duct were clarified by solving the control equations using Matlab program. The results show that the air dry bulb temperature directly proportion to the outlet dry bulb temperature, and air input relative humidity notable proportion to the outlet dry bulb temperature. The water flow rate in the cooling tower affect on the outlet air temperature, were as it increases the outlet air temperature decreases. Also the air flow rate through the cooling tower contributes in the outlet air temperature, while the increasing in the air flow rate leads to decreasing in the outlet air temperature. Furthermore as the flow rate of the air inside the air duct increases, the outlet temperature decreases. Moreover investigation proves that the indirect evaporative cooling successfully can be used in the southern of Libya. KEYWORDS: Indirect evaporative cooling, Cooling tower, Arid hot climates 1 Introduction An indirect evaporative air cooler (IEC) is one of the promising solution for air conditioning specially in the arid hot climates, which encouraging the researchers to taken up different studies concerning of this subject. The analysis for theoretical and experimental works takes place over a wide world locations even in the cold weather State, such as European countries where the experimental analysis of (IEC) system studied [1]. The components of the (IEC) have factors effecting on the system performance, [2] investigated the conductivity of metal, fibers, ceramics and how they impact on the (IEC) system. The (IEC) acts as an energy recovery device in air conditioning systems which called a semi-indirect evaporative cooler [3]. The outdoor conditions have a most effect on the (IEC) availability applications that provide