Real Air-Conditioning Performance of Ejector Refrigerator Based Air-Conditioner Powered by Low Temperature Heat Source

energies Article Real Air-Conditioning Performance of Ejector Refrigerator Based Air-Conditioner Powered by Low Temperature Heat Source Tongchana Thongtip 1 and Natthawut Ruangtrakoon 2,* 1 Thermal and Fluid Laboratory (TFL), Department of Teacher Training in Mechanical Engineering, King Mongkut’s University of Technology North Bangkok, 1518, Bang Sue, Bangkok 10800, Thailand; [email protected] 2 Department of Mechanical Engineering, School of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand * Correspondence: [email protected]; Tel.: +66-2329-8350#1 Abstract: In this present work, the air-conditioning test performance of an ejector refrigerator-based air-conditioner (ERAC) was proposed. The ERAC was operated as the water chiller to produce the cooling load up to 4.5 kW. The chilled water temperature was later supplied to the fan-coil unit for producing the thermal comfort condition. The cooling water used to cool the condenser was achieved from the cooling tower which was operated under the hot and humid ambient. This is to demonstrate the feasibility of using the ERAC in real working conditions. The cooling load supplied to the air- conditioned space was applied by the air heater. The ERAC could efficiently be operated to produce ◦ the thermal comfort condition which was driven by the hot water temperature (Thot) of 90–98 C. The system performance could vary with the heat source temperatures, cooling load, primary nozzle, and air-conditioned space temperature. The optimal performance was determined when varying the Thot, and, hence, the optimal Thot was indicated. The optimal Thot varied significantly with variations in the working condition. The test results demonstrated high potential to further using the ejector refrigeration system in the actual air conditioning application. Citation: Thongtip, T.; Ruangtrakoon, Keywords: ejector refrigeration system; air-conditioning; thermal comfort; low grade heat utilization N. Real Air-Conditioning Performance of Ejector Refrigerator Based Air-Conditioner Powered by Low Temperature Heat Source. Energies 1. Introduction 2021, 14, 711. https://doi.org/ 10.3390/en14030711 For many years, the topic of energy savings, especially for electricity consumption in buildings, industries or even households, has been widely discussed in many aspects. One Received: 8 December 2020 of the major sources of energy consumption (in the form of electricity) is air conditioning Accepted: 8 January 2021 and refrigeration systems. Additionally, such systems are widely used in many cooling Published: 30 January 2021 applications from large scale to small scale in industries. Currently, many solutions have been proposed to reduce the electricity consumption in air-conditioning applications Zhu Publisher’s Note: MDPI stays neu- and Jiang [1], Fong et al. [2], Sánchez et al. [3], Xia et al. [4]. Most of them concentrated tral with regard to jurisdictional clai- on the performance improvement of the vapour compression refrigeration system (VCR) ms in published maps and institutio- which is the most extensively used refrigeration method to produce the cooling produc- nal affiliations. tion under various applications. However, even though many advancement researches, Lin et al. [5], Jeon et al. [6], Pottker et al. [7], Jeon et al. [8], have demonstrated the feasibility to reduce the electricity consumption for VCR, an air-conditioning application or other cooling applications are still the part that highly consumes the electricity. Therefore, Copyright: © 2021 by the authors. Li- many researchers have proposes an alternative refrigeration machine which can be driven censee MDPI, Basel, Switzerland. This article is an open access article by alternative energy as proposed by Lillo et al. [9], Bai et al. [10], Hamzaoui et al. [11]. distributed under the terms and con- Their interpretations indicated that the thermally driven refrigeration machine (TDR) is ditions of the Creative Commons At- a promising machine. This is because it can produce the refrigeration effect by means of tribution (CC BY) license (https:// a low grade heat source (available from waste heat from industrial process, solar water creativecommons.org/licenses/by/ heater, flue gas of combustion, geothermal, etc.). 4.0/). Energies 2021, 14, 711. https://doi.org/10.3390/en14030711 https://www.mdpi.com/journal/energies Energies 2021, 14, x FOR PEER REVIEW 2 of 22 interpretations indicated that the thermally driven refrigeration machine (TDR) is a prom- Energies 2021, 14, 711 ising machine. This is because it can produce the refrigeration effect by means of a2 low of 20 grade heat source (available from waste heat from industrial process, solar water heater, flue gas of combustion, geothermal, etc.). AA kind kind of of thermally thermally driven driven refrigeration refrigeration machine, machine, which which has has recently recently been been gaining gaining popularitypopularity in in this this research research field, field, is is the the ejector ejector refrigeration refrigeration machine. machine. This This is is because because of of its its simplicitysimplicity of of construction construction an andd operation operation compared compared to to the the other other types types of of TDR TDR (absorption (absorption oror adsorption adsorption machine). Additionally,Additionally, itit hashas almost almost no no moving moving parts, parts, low low corrosion corrosion and and no nochemical chemical reaction reaction for for producing producing refrigerating refrigeratin effects,g effects, unlike unlike the the case case of of the the absorption absorption or oradsorption adsorption machine. machine. The The major major equipment equipment used used forfor thethe ejectorejector refrigeration system and and statestate of of the the refrigerant refrigerant on on pressure-enthalpy pressure-enthalpy ch chartart (P-h (P-h diagram) diagram) are are depicted depicted in in Figure Figure 11.. FigureFigure 1. 1. TheThe ejector ejector refrigeration refrigeration cycle cycle and and its its refrigerant refrigerant flow flow state. state. FromFrom the the ejector refrigerationrefrigeration systemsystem (seen (seen in in Figure Figure1), 1), the the ejector ejector is the is keythe key equipment equip- mentto produce to produce the refrigeration the refrigeration effect. effect. It uses It us thees highthe high pressure pressure refrigerant refrigerant called called “primary “pri- maryfluid” fluid” to produce to produce a low a pressure low pressure region regi insideon inside the mixing the mixing chamber chamber which which is connected is con- nectedto the to evaporator. the evaporator. When When the primary the primary fluid fluid is accelerated is accelerated through through the the primary primary nozzle, nozzle,the the low low pressure pressure and and low low temperature temperature fluid fluid from from the the evaporator evaporator (called (called the the “secondary “second- aryfluid”) fluid”) can can entrain entrain into into the the mixing mixing chamber. chamber. This This results results in the in the production production of refrigeration of refriger- ationeffect. effect. The massThe mass entrainment entrainment ratio ratio (Rm) (Rm) which which is the is ratiothe ratio of the of secondarythe secondary mass mass flow flowrate rate to the to the primary primary mass mass flow flow rate rate is usedis used to to indicate indicate the the ejector ejector performance. performance. This This RmRm indicates indicates the the overall overall system system performance performance of of the the ejector ejector refrigeration refrigeration system system under under various working conditions. Therefore, the ejector refrigeration system has been extensively investigated and discussed based on the variation in the Rm under various operating conditions. Some researchers have investigated the ejector refrigerator in an attempt to produce the maximum Rm. The main aims were to determine the optimal operating Energies 2021, 14, 711 3 of 20 condition, Hamzaoui et al. [11], Narimani et al. [12], Fang et al. [13], Dong et al. [14], and to enhance the system performance via the careful design of the ejector geometries, Van Nguyen et al. [15], Thongtip and Aphornratana [16], Chen et al. [17]. In addition, due to the advantage of the CFD simulation technique, it has been extensively used to design and to optimize the ejector geometries. Besagni et al. [18], Zhang et al. [19], Allouche et al. [20], Zhang et al. [21] and Mahmoudian et al. [22] have implemented the CFD simulation to discuss the ejector performance influenced by the operatiing conditions. Their findings could support some phenomenon found from the experiments. This can help the researchers to explore the flow characteristics of the supersonic stream inside the ejector which is quite complicated. For a certain operating temperature of the generator, evaporator and condenser, Van Nguyen et al. [15], Thongtip and Aphornratana [16], Chen et al. [17], have found experimentally that the key parameters to dominate the entire ejector performance are the ejector area ratio and primary nozzle area ratio. These parameters are the key to produce the Rm and the critical condensation temperature. Therefore, the ejector area ratio and primary nozzle area ratio were then optimized for a certain operating condition. Another interesting point of the ejector refrigeration system is that many kinds of the working fluids (various refrigerants) or even water (steam-water) can

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