Journal of Mechanical Engineering Research and Developments (JMERD) 42(5) (2019) 148-152 Cite The Article: Ahmed Qasim Ahmed, Adel A. Eidan, Assaad AlSahlani, Entihaa R. Aga, Mohamed Al-Fahham (2019). Effect of Thermosyphon Heat Exchanger on the Performance of HVAC Systems in Subtropical Climatic – Numerical Investigation. Journal of Mechanical Engineering Research and Developments, 42(5) : 148-152. ARTICLE DETAILS Article History: Received 15 July 2019 Accepted 26 August 2019 Available online 29 August 2019 ABSTRACT This work presents a theoretical study about the advantages of using thermosyphon heat exchanger (THEs) in the subtropical region (Iraq- Basrah) HVAC systems, where the weather is extremely hot with a normal DBT at (35-50) ºC and RH of (35-90) %. The theoretical study compares three cases as follows: case (1) HVAC system that uses the precooling a refrigeration system and for the reheating process an electric heater, case (2) a HVAC system that uses for the precooling a refrigeration system and for reheating the condenser of the same refrigeration system used for precooling and case (3) for the precooling and preheating a thermosyphone system is used. The three cases are mathematically modeled, and corresponding programs are developed in Engineering Equation software. The input data in the programs is obtained experimentally form a facility corresponding to case 3) which is established in the Technical Institute of Najaf, Iraq. Preliminary results point out that the power consumption for case (3) is lower than the one for case (2). The power consumption for case (2) is lower than the one for case (1). KEYWORDS Severe hot weather, cooling, air conditioning enhancement, HVAC Thermosyphon heat exchangers, THEs. 1. INTRODUCTION It was announced by EIA (Energy Information Administration) that in 2011 the entire consumed energy was 1.8*l0 8 GWh and about 32 * 10 3 million of metric tons of carbon were released to the atmosphere [1]. Whereas, in 2015 the world consumed energy and about 6% of these resources released 34 * 10 3 million of metric tons of carbon. The world need of energy is increasing and it is expected to reach 2.7*l0 8 GWh by 2020 where 48 *10 3 million metric tons of carbon to be released [2,3]. Based on that, the world demand for energy is increasing and more energy resources should be obtained. One of the most consuming utilities in the domestic building is the air conditioning and mechanical ventilation where the cost bills represent about 65% of total energy consumption in domestic buildings as shown in Fig. 1. [1]. Figure 1: The consumption in Electricity Based on consumers categories in GWh [1]. The concept of energy rationalization and optimum use of the energy necessary to operate industrial units or the provision of public services or home uses, without prejudice to the comfort of its users or their productivity or to affect the efficiency of the devices and equipment used or the production rates. With comparison with other heat transfer devices, the thermosyphon is the most efficient heat transferring device where the latent heat required for the vaporization is implemented to convey the heat with small temperature difference and thermal resistance. Where the evaporation and condensation occur in two different and separated sections [4]. As it is shown in figures 2 and 3 for the conventional THEs HVAC system where the entire process occurs as follows: precooling process starts from state 1 to state 2 and the air passes through chilled water coil where the temperature and moisture content are both reduced up to state 3 [5]. The cool air leaves the chilled water coil at state 3 and then being reheated by the heat which is recovered at the THEs condensation section. At state 5 the air arrives the conditioned room which has sensible and latent loads [5-7]. Figure 2: Simple schematic diagram for a typical HVAC model running with a THE [6,7]. Figure 3: The psychometric process of HVAC system integrated with THE for a subtropical climate [1,6,7]. Journal of Mechanical Engineering Research and Developments (JMERD) DOI : http://doi.org/10.26480/jmerd.05.2019.148.152 EFFECT OF THERMOSYPHON HEAT EXCHANGER ON THE PERFORMANCE OF HVAC SYSTEMS IN SUBTROPICAL CLIMATIC – NUMERICAL INVESTIGATION Ahmed Qasim Ahmed 1 , Adel A. Eidan 1 , Assaad AlSahlani 2 , Entihaa R. Aga 1 , and Mohamed Al-Fahham 2 1 Najaf technical institute, Al-Furat Al-Awsat Technical University, Najaf, 31001, Iraq. 2 Engineering Technical College of Al-Najaf, Al-Furat Al-Awsat Technical University, Najaf, 31001, Iraq Corresponding Author Email: aq.ahmad@atu.edu.iq; inj.adel@atu.edu.iq; coj.asd@atu.edu.iq; inj.ent@atu.edu.iq; coj.moh@atu.edu.iq This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ISSN: 1024-1752 CODEN : JERDFO RESEARCH ARTICLE