A key review on performance improvement aspects of geothermal district heating systems and applications

This paper deals with a comprehensive analysis and discussion of geothermal district heating systems and applications. In this regard, case studies are presented to study the thermodynamic aspects in terms of energy and exergy and performance improvement opportunities of three geothermal district heating systems, namely (i) Balcova geothermal district heating system (BGDHS), (ii) Salihli geothermal district heating system (SGDHS), and (iii) Gonen geothermal district heating system (GGDHS) installed in Turkey. Energy and exergy modeling of geothermal district heating systems for system analysis and performance evaluation are given, while their performances are evaluated using energy and exergy analysis method. Energy and exergy specifications are presented in tables. In the analysis, the actual system operational data are utilized. In comparison of the local three district heating systems with each other, it is found that the SGDHS has highest energy efficiency, while the GGDHS has highest exergy efficiency.     

Barriers and enablers to geothermal district heating system development in the United States

According to the US Energy Information Administration, space and hot water heating represented about 20% of total US energy demand in 2006. Given that most of this demand is met by burning natural gas, propane, and fuel oil, an enormous opportunity exists for directly utilizing indigenous geothermal energy as a cleaner, nearly emissions-free renewable alternative. Although the US is rich in geothermal energy resources, they have been frequently undervalued in America's portfolio of options as a means of offsetting fossil fuel emissions while providing a local, reliable energy source for communities. Currently, there are only 21 operating GDHS in the US with a capacity of about 100 MW thermal. Interviews with current US district heating operators were used to collect data on and analyze the development of these systems. This article presents the current structure of the US regulatory and market environment for GDHS along with a comparative study of district heating in Iceland where geothermal energy is extensively utilized. It goes on to review the barriers and enablers to utilizing geothermal district heating systems (GDHS) in the US for space and hot water heating and provides policy recommendations on how to advance this energy sector in the US.     

Monitoring of energy exergy efficiencies and exergoeconomic parameters of geothermal district heating systems (GDHSs)

In this work, the monitoring energy and exergy efficiency results of the last heating seasons of operation of the geothermal district heating systems (GDHSs) and their technical availability analysis and monitoring exergoeconomic parameters are presented. The case studies cover the actual system data taken from the systems in Afyon and Salihli GDHSs, Turkey. General energy, exergy, technical availability, and exergoeconomic analysis of the GDHSs are introduced. Furthermore, the average technical availability, real availability, capacity factor and energy and exergy efficiencies value of GDHSs have been analyzed.     

Geothermal energy in Turkey: the sustainable future

Turkey is an energy importing nation with more than half of our energy requirements met by imported fuels. Air pollution is becoming a significant environmental concern in the country. In this regard, geothermal energy and other renewable energy sources are becoming attractive solution for clean and sustainable energy future for Turkey. Turkey is the seventh richest country in the world in geothermal energy potential. The main uses of geothermal energy are space heating and domestic hot water supply, greenhouse heating, industrial processes, heat pumps and electricity generation. The district heating system applications started with large-scale, city-based geothermal district heating systems in Turkey, whereas the geothermal district heating centre and distribution networks have been designed according to the geothermal district heating system (GDHS) parameters. This constitutes an important advantage of GDHS investments in the country in terms of the technical and economical aspects. In Turkey, approximately 61,000 residences are currently heated by geothermal fluids. A total of 665 MW_t is utilized for space heating of residential, public and private property, and 565,000 m² of greenhouses. The proven geothermal heat capacity, according to data from existing geothermal wells and natural discharges, is 3132 MWt. Present applications have shown that geothermal energy is clean and much cheaper compared to the other fossil and renewable energy sources for Turkey.     

Energetic and economic evaluations of geothermal district heating systems by using ANN

This paper proposes an artificial neural network (ANN) technique as a new approach to evaluate the energy input, losses, output, efficiency, and economic optimization of a geothermal district heating system (GDHS). By using ANN, an energetic analysis is evaluated on the Afyon geothermal district heating system (AGDHS) located in the city of Afyonkarahisar, Turkey. Promising results are obtained about the economic evaluation of that system. This has been used to determine if the existing system is operating at its optimal level, and will provide information about the optimal design and profitable operation of the system. The results of the study show that the ANN model used for the prediction of the energy performance of the AGDHS has good statistical performance values: a correlation coefficient of 0.9983 with minimum RMS and MAPE values. The total cost for the AGDHS is profitable when the PWF is higher than 7.9. However, the PWF of the AGDHS was found to be 1.43 for the given values. As a result, while installing a GDHS, one should take into account the influences of the PWF, ambient temperature and flow rate on the total costs of the system in any location where it is to be established.     

Parametric Study of the Effect of Reference State on Energy and Exergy Efficiencies of Geothermal District Heating Systems (GDHSs): An Application of the Salihli GDHS in Turkey

A parametric study of the effect of reference state on the energy and exergy efficiencies of geothermal district heating systems is presented. In this regard, the work consists of two parts: a modeling study covering energy and exergy analysis and a case study covering the actual system data taken from the Salihli Geothermal District Heating System (SGDHS) in Manisa, Turkey. General energy and exergy analysis of the geothermal district heating systems is introduced along with some thermodynamic performance evaluation parameters. This analysis is then applied to the SGDHS using actual thermodynamic data for its performance evaluation in terms of energy and exergy efficiencies. In addition, a parametric study on the effect of varying dead state properties on the energy and exergy efficiencies of the system that has been conducted to find optimum performance and operating conditions is explained. Two parametric expressions of energy and exergy efficiencies were developed as a function of the reference temperature. Both energy and exergy flow diagrams illustrate and compare results under different conditions. It has been observed that the exergy destructions in the system particularly take place as the exergy of the fluid lost in the heat exchanger, the natural direct discharge of the system (pipeline losses), and the pumps, which account for 31.17%, 8.98%, and 4.27% of the total exergy input to the SGDHS, respectively. For the actual system that is presented, the system energy and exergy efficiencies vary between 0.53 and 0.73 and 0.58 and 0.59, respectively.     

Exergoeconomic analysis of geothermal district heating systems: A case study

An exergoeconomic study of geothermal district heating systems through mass, energy, exergy and cost accounting analyses is reported and a case study is presented for the Salihli geothermal district heating system (SGDHS) in Turkey to illustrate the present method. The relations between capital costs and thermodynamic losses for the system components are also investigated. Thermodynamic loss rate-to-capital cost ratios are used to show that, for the devices and the overall system, a systematic correlation appears to exist between capital cost and exergy loss (total or internal), but not between capital cost and energy loss or external exergy loss. Furthermore, a parametric study is conducted to determine how the ratio of thermodynamic loss rate to capital cost changes with reference temperature and to develop a correlation that can be used for practical analyses. The correlations may imply that devices in successful district heating systems such as the SGDHS are configured so as to achieve an overall optimal design, by appropriately balancing the thermodynamic (exergy-based) and economic (cost) characteristics of the overall systems and their devices.     

Correlations for cost of ground‐source heat pumps and for the effect of temperature on their performance

Ground source heat pump systems are becoming more and more popular, even though their high initial cost is an obstacle to their wider penetration of the heating and cooling market. The purchase of the heat pump itself is one of the dominant costs, and the heat pump selection also influences the operation costs through its coefficient of performance (COP) value. However, few studies are available on this topic. Based on 23 water–water heat pump models available on the market, a correlation was developed to estimate their purchase cost as a function of the nominal cooling load of the heat pump. These heat pumps can be used in geothermal applications as well as in other heating, ventilating, air conditioning and refrigeration (HVAC&R) systems. The correlation is valid for a nominal cooling load between 20 and 841 kW. The nominal COP of the heat pumps was found to have virtually no effect on their purchase costs. Also, two correlations were developed to relate variations of cooling power and COP to the temperature levels on both sides of the heat pump. The heating mode is also considered. The correlations are useful to estimate the required nominal size of a heat pump given design operating conditions and to optimize ground source heat pump systems from a techno‐economical standpoint. Copyright © 2014 John Wiley & Sons, Ltd.     

The thermal effects of some control logics used in GDHS

The temperature of the water returning from the network affects greatly the efficiency of a geothermal district-heating system (GDHS). The temperature of the returning water depends on whether there is a heat exchanger between network flow and indoor circulation. The return temperature also depends on outdoor temperature and logic of the indoor temperature control system. In this paper, four control logics are defined depending on whether indoor circulation is separated from network circulation or not. Return temperature and circulation rate of network flow are calculated for these control logics. The results show that the flow rate of the network flow and annual consumption of the geothermal fluid could be decreased about 10% or over by using optimum control logic in district heating systems.     

Energy and exergy analysis of Salihli geothermal district heating system in Manisa,Turkey

This study deals with an energy and exergy analysis of Salihli geothermal district heating system (SGDHS) in Manisa, Turkey. In the analysis, actual system data are used to assess the district heating system performance, energy and exergy efficiencies, specific exergy index, exergetic improvement potential and exergy losses. Energy and exergy losses throughout the SGDHS are quantified and illustrated in the flow diagram. The exergy losses in the system, particularly due to the fluid flow, take place in the pumps and the heat exchanger, as well as the exergy losses of the thermal water (e.g. geothermal fluid) and the natural direct discharge of the system. As a result, the total exergy losses account for 2.22, 17.88 and 20.44%, respectively, of the total exergy input to the entire SGDHS. The overall energy and exergy efficiencies of the SGDHS components are also studied to evaluate their individual performances and determined to be 55.5 and 59.4%, respectively. Copyright © 2005 John Wiley & Sons, Ltd.     

New energy and exergy parameters for geothermal district heating systems

This paper introduces four new parameters, namely energetic renewability ratio, exergetic renewability ratio, energetic reinjection ratio, and exergetic reinjection ratio for geothermal district energy systems. These parameters are applied to Edremit Geothermal District Heating System (GDHS) in Balikesir, Turkey for daily, monthly and yearly assessments and their variations are studied. In addition, the actual data are regressed to obtain some applied correlations for practical use. Some results follow: (i) Both energetic and exergetic renewability ratios decrease with decreasing temperature in heating season and increasing temperature in the summer. (ii) Both energetic and exergetic reinjection ratios increase with decreasing temperature for heating season and increase with increasing temperature for summer season.     

Energy conservation measures in an institutional building in sub-tropical climate in Australia

In this study, various energy conservation measures (ECMs) on heating, ventilating and air conditioning (HVAC) and lighting systems for a four-storied institutional building in sub-tropical (hot and humid climate) Queensland, Australia are evaluated using the simulation software called DesignBuilder (DB). Base case scenario of energy consumption profiles of existing systems are analysed and simulated first then, the simulated results are verified by on-site measured data. Three categories of ECMs, namely major investment ECMs (variable air volume (VAV) systems against constant air volume (CAV); and low coefficient of performance (COP) chillers against high COP chillers); minor investment ECMs (photo electric dimming control system against general lighting, and double glazed low emittance windows against single-glazed windows) and zero investment ECMs (reset heating and cooling set point temperatures) are evaluated. It is found that the building considered in this study can save up to 41.87% energy without compromising occupancies thermal comfort by implementing the above mentioned ECMs into the existing system.     

Evaluation of the performance of a centralized ground-water heat pump system in cold climate region

The aim of this study is to evaluate the performance of a centralized open-loop ground-water heat pump (GWHP) system for climate conditioning in Beijing with a cold climate in China. Thus, a long-time test was conducted on a running GWHP system for the heating season from December 2011 to March 2012. The analysis of the testing data indicates that the average heat-pump coefficient of performance (COP) and the COP of the system (COPs) are 4.27 and 2.59. The low value and large fluctuation in the range of COP are found to be caused by the heat transfixion in the aquifer and the bypass in the circulation loop. Therefore, some suggestions are proposed to improve the performance for GWHPs in the cold climate region in China.     

Experimental study of vertical ground-source heat pump performance evaluation for cold climate in Turkey

Heat pump systems are recognized to be outstanding heating, cooling and water heating systems. They provide high levels of comfort as well as offering significant reductions in electrical energy use. In addition, they have very low levels of maintenance requirements and are environmentally attractive. The purpose of this study is to evaluate the experimentally performance and energy analysis of vertical ground-source heat pump (GSHP) for winter climatic condition of Erzurum, Turkey. For this aim, an experimental analysis was performed on GSHP system made up in the Energy Laboratory in the campus of Ataturk University. The experimental apparatus consisted of a ground heat exchanger, the depth of which was 53 m, a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement and control equipments. Tests were performed under laboratory conditions for space heating, in which experimental results were obtained during January–May within the heating season of 2007. The experimentally obtained results were used to calculate the heat pump coefficient of performance (COP) and the system performance (COPs). The COP and COPs were found to be in the range of 2.43–3.55 and 2.07–3.04, respectively. This study also shows that the system proposed could be used for residential heating in the province of Erzurum which is one of the coldest climate region of Turkey.     

Experimental and theoretical investigation of a solar heating system with heat pump

In this study, the performance of a solar heating system with a heat pump was investigated both experimentally and theoretically. The experimental results were obtained from November to April during the heating season. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load met by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. The average seasonal heating performance values are 4.0 and 3.0 for series and parallel heat pump systems, respectively. A mathematical model was also developed for the analysis of the solar heating system. The model consists of dynamic and heat transfer relations concerning the fundamental components in the system such as solar collector, latent heat thermal energy storage tank, compressor, condenser, evaporator and meteorological data. Some model parameters of the system such as COP, theoretical collector numbers (N_c), collector efficiency, heating capacity, compressor power, and temperatures (T₁, T₂, T₃, T_T) in the storage tank were calculated by using the experimental results. It is concluded that the theoretical model agreed well with the experimental results.     

Thermodynamic analysis of a hybrid geothermal heat pump system

A thermodynamic analysis of a hybrid geothermal heat pump system is carried out. Mass, energy, and exergy balances are applied to the system, which has a cooling tower as a heat rejection unit, and system performance is evaluated in terms of coefficient of performance and exergy efficiency. The heating coefficient of performance for the overall system is found to be 5.34, while the corresponding exergy efficiency is 63.4%. The effect of ambient temperature on the exergy destruction and exergy efficiency is investigated for the system components. The results indicate that the performance of hybrid geothermal heat pump systems is superior to air-source heat pumps.     

Exergy analysis and experimental study of heat pump systems

Exergy analysis of heat pump—air conditioner systems has been carried out. The irreversibilities due to heat transfer and friction have been considered. The coefficient of performance based on the first law of thermodynamics as a function of various parameters, their optimum values, and the efficiency and coefficient of performance based on exergy analysis have been derived. Based on the exergy analysis, a simulation program has been developed to simulate and evaluate experimental systems. The simulation of a domestic heat pump—air conditioner of 959 W nominal power (Matsushita room air conditioner model CS-XG28M) is then carried out using experimental data. It is found that COP based on the first law varies from 7.40 to 3.85 and the exergy efficiency from 0.37 to 0.25 both a decreasing function of heating or cooling load. The exergy destructions in various components are determined for further study and improvement of its performance.     

Investigation of a combined solar–heat pump system for residential heating. Part 1: experimental results

In order to investigate the performance of the combined solar–heat pump system with energy storage in encapsulated phase change material (PCM) packings for residential heating in Trabzon, Turkey, an experimental set‐up was constructed. The experimental results were obtained from November to May during the heating season for two heating systems. These systems are a series of heat pump system, and a parallel heat pump system. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load meet by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. Copyright © 1999 John Wiley & Sons, Ltd.     

Second law-based thermodynamic analysis of ammonia/sodium thiocyanate absorption system

In this study, the first and second law of thermodynamics are used to analyze the performance of a novel absorption system for cooling and heating applications. The active component of the sorbent used in this study is sodium thiocyanate (NaSCN). Ammonia (NH₃) is chosen as sorptive. A mathematic model based on exergy analysis is introduced to analyze the system performance. Enthalpy, entropy, temperature, mass flow rate and exergy loss of each component and the total exergy loss of the system are evaluated. Furthermore, the coefficient of performance (COP) and exergetic efficiency of the absorption system for cooling and heating processes are calculated from the thermodynamic properties of the working fluids under different operating conditions. The results show that the COP of cooling and heating increases with the heat source temperature and decreases with the cooling water inlet temperature, but the system exergetic efficiency does not show the same trends for both cooling and heating applications. The simulation results can be used for the thermodynamic optimization of the current system.     

Optimum allocation of heat exchanger inventory of irreversible air heat pump cycles

This study has determined the optimal ratios of heat conductance of a cold-side heat exchanger to that of a hot-side heat exchanger when the heating load and the coefficient of performance (COP) of the irreversible air heat pump cycles are taken as the optimization objectives. Both the optimum distributions of heat conductance corresponding to the maximum heating load and the maximum COP are less than 0.5 for the fixed total heat exchanger inventory. The influences of the heat reservoir temperature ratio, the total heat exchanger inventory, and the efficiencies of the compressor and expander on the optimum distribution of heat conductance and the maximum heating load and the maximum COP are analysed and shown by numerical examples.