Contents lists available at ScienceDirect Geothermics journal homepage: www.elsevier.com/locate/geothermics Thermodynamic and economic investigation of geothermal powered absorption cooling system for buildings Ceyhun Yilmaz Department of Mechanical Engineering, Afyon Kocatepe University, 03200 Afyonkarahisar, Turkey ARTICLE INFO Keywords: Geothermal energy Absorption cooling system Thermodynamic analysis DD (degree - Days) method Economic analysis Life cycle cost analysis ABSTRACT A geothermal powered absorption cooling system is considered for cooling of buildings. The system is analyzed by thermodynamic performance parameters such as cooling load and coefficient of performance (COP). An economic analysis of the system is performed to assess cost structure, potential revenues, payback periods and life cycle cost analysis. Effect of geothermal water temperature on the annual cooling cost and payback periods are investigated. A liquid geothermal source at a temperature of 100 °C with a mass flow rate of 100 kg/s is considered for İzmir city of Turkey. The COP of the ammonia-water absorption cycle is determined to be 0.441. The number of degree-days for the cooling season is calculated to be 1791 °C and cooling load is calculated to be 12,870,000 kWh by the DD (degree - days) method. The annual potential revenue of geothermal cooling is estimated to be 653,818 $/yr with simple and discounted payback periods of 5.684 and 8.816 years. The geothermal cooling is provided an annual monetary benefit of 166,610 $/yr on the entire lifetime of the system by the life cycle cost analysis. So, the unit product cooling cost is calculated to be 0.01295 $/kWh, respectively. 1. Introduction Geothermal energy has been used for power generation, space and process heating and space cooling. Some part of this energy is rarely used for cogeneration. Geothermal energy is a promising source for any heat driven applications whether involving direct or indirect thermal processes. A separation process of a geothermal fluid mixture is needed for indirect geothermal utilization, especially in power generation cy- cles. The separation process disposes of the liquid form of low grade thermal energy which could be utilized further for other direct and indirect utilizations such as a power plant bottoming unit, heating and cooling purposes or other heat driven processes, depending on how much of the available energy remains (Febrianto et al., 2016). Geothermal resources vary widely from one location to another, depending on the temperature and depth of the reservoir, the type of rock and the chemistry and abundance of ground water. Geothermal resources are usually classified into three categories: i) high enthalpy resources (liquid and vapor reservoirs at temperature above 180–200 °C), ii) medium enthalpy resources (at temperatures around 100–180 °C), iii) low enthalpy resources (at temperatures below 100 °C). The wide spectrum of geothermal energy applications is given on the diagram of Fig. 1 (Tesha, 2009). In developed countries, around 35% of total primary energy con- sumption is used in buildings. The European Union’s commitment to reduce green house gas emissions by 20% by the year 2020 opens a huge potential for geothermal applications. In direct use, the potential of geothermal energy is large for space cooling and heating, and water heating. Geothermal resources are already widely used in the world for space heating and cooling (Li et al., 2014). The utilization of geo- thermal steam for electricity generation is not the only one way ap- plication of geothermal energy. Hot geothermal water that appears to be present in big parts of all the continents can also be exploited and offer interesting prospects for the future. Especially in Turkey geo- thermal sources are to be proper to the space heating and cooling processes. Geothermal energy is used to generate electricity and for direct uses such as space heating and cooling, industrial processes, and greenhouse heating. The geothermal electrical capacity and the direct use capacity in the world are about 7000 MW and 8500 MW, respectively. High temperature geothermal resources above 150 °C are generally used for power generation. Moderate temperature (between 90 °C and 150 °C) and low-temperature (below 90 °C) geothermal resources are best suited for direct uses (Kanoglu, 2002). A geothermal well can produce hot water, wet steam (liquid–vapor mixture), dry steam (saturated steam), or superheated steam. Liquid- dominated systems are much more common than vapor-dominated systems and can be produced either as brine or as a brine–steam mix- ture, depending on the pressure maintained on the production system (Kanoğlu and Çengel, 1999). Geothermal energy is more effective when used directly than when converted to electricity, since the direct use of http://dx.doi.org/10.1016/j.geothermics.2017.06.009 Received 7 April 2017; Received in revised form 26 May 2017; Accepted 19 June 2017 E-mail address: ceyhunyilmaz@aku.edu.tr. Geothermics 70 (2017) 239–248 0375-6505/ © 2017 Elsevier Ltd. All rights reserved. MARK