Geothermal District Heating System Research Articles

Optimization of a district heating system coupled with a deep open-loop geothermal well and heat pumps

The technical and economic aspects of a district heating system coupled with a deep open-loop geothermal well (DOLGW) and heat pumps were studied in the paper. A typical configuration of such a geothermal district heating system was proposed, and the corresponding thermal analysis was carried out. Based on the data from the DOLGW heat extraction test conducted in Hebei, China, the optimal size selections of heat pumps, plate heat exchangers, and terminal heat radiators for such a system was analyzed theoretically. In addition, an optimal control scheme for such a system with the change of environmental temperature or heating load were given.

Hybrid modeling for the multi-criteria decision making of energy systems: An application for geothermal district heating system

The efficiency analysis technique with output satisficing (EATWOS) is a successful tool for determining the most efficient design for energy systems. Since EATWOS is rationally based on the maximal output throughout the minimal inputs, the weights of input and output values considerably affect the analysis results. Therefore, the impact ratio of each input and output term should be sensitively determined. In this study, the artificial neural network (ANN) modeling was used to determine the weights of the input values due to the quantitative effects of these values, whereas the analytical hierarchic process (AHP) was used for the output values due to qualitative effects. A new hybrid method was formed, embedding the ANN and AHP results into EATWOS. The new hybrid model was then applied to a sample geothermal district heating system for optimization. In this aim, 148 designs were formed throughout the different inlet parameters and evaluated by exergoeconomic and exergoenvironmental analysis to conduct the outputs. For the optimum case, the exergy efficiency was calculated as 20.25 %, whereas the SI was determined as 1.25, with the highest score. 1/r and 1/rb were determined as 0.002337 and 0.001677, respectively. The NPV value was determined as 4.44 million $.

Exergoeconomic and exergoenvironmental based multi-criteria optimization of a new geothermal district heating system integrated with thermal energy storage driven heat pump

In this study, a new geothermal district heating system, which includes a heat pump (HP) system driven by thermal energy storage (TES) unit, was optimized throughout the multi-criteria decision making analysis named efficiency analysis technique with output satisficing (EATWOS). In this regard, the objective functions were chosen as exergoeconomic and exergoenvironmental indicators varying with the handled designs. 111 different designs formed considering different working parameters and fluids in this aim. Three environment-friendly refrigerants according to their thermal behaviour (wet, dry, and isentropic types) and suitable phase change materials (PCM) according to the design conditions were evaluated. The designed system was evaluated by energy, exergy, exergoeconomic, and exergoenvironmental tools to determine the objective functions. As conclusion, Case 108 with the refrigerant of R1234ze and PCM of RT70HC was determined as the best design. The sustainability index, exergoeconomic factor, exergoenvironmental factor, relative cost, and relative exergoenvironmental impact of this optimal case were determined as 1.24, 0.002583%, 0.0540%, 460.85%, and 649.50%, respectively. For this case, the energy and exergy efficiencies of the system were determined as 74.56% and 19.17%, respectively. In comparison to conventional system, a decrease of 38.86% in relative exergoeconomic cost (r) and a decrease of 19.21% in the relative exergoenvironmental impact (rb) were achieved.

Modelling and optimization of domestic thermal energy storage based heat pump system for geothermal district heating

In this study, a new residential heat pump system was designed for domestic use in the geothermal district heating system (GDHS). A heat pump system was integrated into the substations of the residences with this aim. The heat pump system was formed by replacing the conventional evaporator with thermal energy storage (TES) unit. In this regard, a shell and tube latent heat TES system was used and designed for the peak loads. 66 different systems were parametrically formed and analyzed thermodynamically. The observed cases were later evaluated from economical and environmental points of view. Finally, the most appropriate system was determined by a multi-criteria decision-making analysis named efficiency analysis technique with output satisficing (EATWOS). It was concluded that it is available to obtain an investable design with an NPV value of 6.35 million $, exergy efficiency of 15.24% and CO2 reduction of 1435.32 ktons per year.

Economic and Environmental Analysis of Incorporating Geothermal District Heating System Combined with Radiant Floor Heating for Building Heat Supply in Sarein, Iran Using Building Information Modeling (BIM)

Despite the considerable breakthrough in district heating systems (DHS) globally, there is not yet any policy on developing this technology in Iran. This country has a high range of energy demand, while renewable energies play a minor role in its energy supply chain. Furthermore, the world is going through a transition towards renewable resources, which currently consist of only 10% of the total energy mix. As the first contribution in this area, this paper aims to design a 100% renewable DHS integrated with radiant floor heating for a group of residential buildings in Sarein, Iran. Moreover, the literature proposes a novel approach for combining geothermal energy and Municipal Solid Waste (MSW) to achieve a 100% renewable energy system. Building Information Modeling (BIM) is used for thermal analysis by 3D designing the buildings in SketchUp and OpenStudio and simulating the heat load in EnergyPlus. Three scenarios are presented to better compare the DHS with the decentralized heating system regarding fuel consumption, as well as environmental and economic aspects. The town’s existing heating system that consumes natural gas for both space heating and hot water demand is referred to as the IHS-G scenario. The DHS-G scenario represents an 87% renewable DHS system, working with natural gas and geothermal energy, while the DHS-MSW scenario is a 100% renewable system, consuming both geothermal energy and Municipal Solid Waste (MSW). Finally, findings suggest that DHS-MSW and DHS-G scenarios reduce the annual energy consumption of buildings by about 595 and 33 toes, respectively. Hence, the greenhouse gas effect will alleviate by mitigating the emission of 1403 and 1339 tons of CO2-eq./year, respectively. Moreover, exporting the extra natural gas through both LNG and pipeline provides about 26 million and 28 million USD/year revenue in DHS-G and DHS-MSW scenarios.

Performance evaluation and multi-criteria decision analysis of thermal energy storage integrated geothermal district heating system

Geothermal energy use in district heating systems has been prevalent and familiar in areas with rich sources for many years. In conventional geothermal district heating systems (GDHS), the geothermal fluid is transported to a heat center to give its heat energy to the secondary fluid. Then, this secondary fluid is circulated in the city network to give its heat energy to the heating circuit by the heat exchangers in the substations. Finally, the geothermal fluid is re-injected to handle the continuity of the resources. This current system works under the designed conditions of a heating system with significant electricity consumption and enormous heat waste. In this study, a thermal energy storage (TES) system was integrated into substations instead of heat exchangers to prevent the waste of heat and overconsumption of electricity by obtaining just-in-time working conditions. In this regard, a shell and tube latent heat TES system was designed for residential use for peak loads and integrated into the heating circuit of GDHS, preserving the current main structure. A number of 37 available cases were formed parametrically to evaluate the system's performance. These cases were analyzed thermodynamically by energy and exergy methods. The net present value (NPV) method was used to evaluate the cases' economics. Finally, an efficiency analysis technique with output satisficing (EATWOS) was conducted to determine the most efficient design from the viewpoints of exergy efficiency, NPV, and CO2 emissions.

Pareto principle-based advanced exergetic evaluation of geothermal district heating system: Simav case study

Geothermal energy has been used in district heating systems for many years. In these old-fashion systems, the heat of geothermal fluid is transferred to secondary fluid (water) by pipes, pumps, and heat exchanger systems. Although these systems have an easy engineering structure, the efficient use of the geothermal source is deficient depending on the thoughtless installations. In this regard, the operating parameters such as temperature and operations provided against the losses such as insulation are much more important; however, the limits of these treatments are not definite. In this regard, advanced exergy analysis is a useful tool since it takes the systems' real, unavoidable, and ideal cases into consideration through conventional exergy analysis. So, the advanced exergy method enables the determination of the improvement potential of the systems. In the advanced exergy method, the unavoidable conditions are decisive factors that should be determined, taking the economic, technological, and available thermodynamic factors into account. Pareto principle can be an alternative solution to determine the unavoidable conditions. Pareto principle indicates that 80% of the impact is sourced from the 20% potential cause. Therefore, according to Pareto principle, it is available to increase benefits by 80% through a change of 20% in the technical parameters. In this study, the advanced exergy method was conducted for the whole Simav geothermal district heating system. The unavoidable conditions were determined based on Pareto principle. According to the analysis, the highest avoidable exergy destruction ratio was determined as 8.14% for the production (well) field, where the total was 19.96%. In conclusion, an improvement potential of 10.33% was determined for the overall system.

Techno-economic optimization of large-scale deep geothermal district heating systems with long-distance heat transport

Geothermal energy can play an important role in decarbonizing the heating sector, however, a limiting factor is that heat demand in urban areas does not usually coincide spatially with geological settings favorable to the extraction of geothermal energy. Long-distance heat transport could enable the direct use of geothermal resources even in areas with low or no geothermal potential. This paper proposes the cost-optimal coordinated deployment of geothermal heating plants together with heat transport and distribution networks to simultaneously supply geothermal heat to multiple urban areas. To this end, a holistic approach comprising the mapping of geothermal potential for direct-use, the estimation of district heating potential, and a two-step optimization model to calculate cost-optimal large-scale geothermal district heating systems, is presented and applied to the Free State of Bavaria in Germany. As a result, heat supply costs can be reduced by 15% if fewer geothermal wells are drilled in more geologically favorable areas at greater distances from heat sinks. Calculated levelized costs of heat without local distribution networks of 33–39 €/MWh show that geothermal energy could transition from a local to a regional use if utilized in in scenarios with high full-load hours. The proposed methodology can be adapted to develop expansion strategies for deep geothermal energy in other similar regions worldwide.

Hydrogeology and hydrogeochemistry of the geothermal systems and its direct use application: Balçova-Narlıdere geothermal system, İzmir, Turkey

The Balçova-Narlıdere geothermal system, located in western Turkey, is an extensional domain type geothermal play. Geological, hydrogeological, and geothermal studies have been done in the Balçova-Narlıdere geothermal field since 1960. As a result of these studies, production and research wells were drilled in the area by both the public and private sectors. Of the 37 wells drilled in the Balçova-Narlıdere geothermal field, 26 were drilled by İzmir Geothermal Energy Company Inc. (16 productions, 4 re-injection, 4 gradientst, 2 unused) and 11 by the İzmir Governorship Investment Monitoring and Coordination Department and companies in the private sectors. There are two reservoirs, one shallow and one deep, in the geothermal field. Well depths are less than 200 m in the shallow reservoir. The deep production wells have depths ranging from 400 to 1,100 m and reservoir temperatures reaching 140 °C. The electrical conductivity (EC) values in the shallow production wells range from 1,200 to 1,500 µS/cm. EC values in the deep production wells vary from 1,871 to 2,025 µS/cm, and all geothermal fluids in the field are mineral-rich waters. In the İzmir geothermal district heating system, the newest technologies are used, and operational costs are very low. İzmir Geothermal Energy Company Inc. has been operating since 1996 and has reached 38,460 residences. The current capacity of the system is approximately 160 MWt. Cooling systems continue to spread in Turkey, focusing on electric air conditioning systems and geothermal heating systems, but both economic and applicability problems have slowed the expansion of cooling systems. However, İzmir Geothermal Energy Company Inc. began operating its first geothermal cooling application in Balçova in 2018, cooling 1,900 m2 of the indoor area by lithium bromide absorption and 90/85 °C geothermal temperature regime by supplying 6/9 °C clean cold water to the coolers in the buildings. These results show that the extensional domain type geothermal system in the Balçova-Narlıdere region is suitable for both heating and cooling applications.

Pareto Principle-Based Advanced Exergetic Evaluation of Geothermal District Heating System: Simav Case Study

Pareto Principle-Based Advanced Exergetic Evaluation of Geothermal District Heating System: Simav Case Study

Evaluating the feasibility of geothermal deep direct-use in the United States

This paper investigates the techno-economic feasibility of geothermal deep direct-use for heating, cooling, and thermal energy storage in the United States. The six 2017–2019 deep direct-use projects funded by the U.S. Department of Energy are reviewed and evaluated using the simulation tool GEOPHIRES, and results are compared with prior studies, existing geothermal district heating systems in Europe and the United States, as well as non-geothermal centralized and non-centralized heating, cooling, and thermal energy storage systems. Analysis indicates that deep direct-use feasibility varies widely, depending on subsurface characteristics, system design, and financial conditions. Project base case levelized cost of heat values ranged between $13 and $350/MWh; key drivers lowering the levelized cost of heat include higher reservoir temperatures, shallower reservoir depths, higher well flow rates, higher utilization rates, lower drilling costs, and lower discount rates. Incentives such as grants and an investment tax credit resulted in small improvements in project economics. Base case levelized cost of heat values for four projects fell within the range of levelized cost values for existing systems in Europe and the United States, and were comparable to values found in previous studies, including the 2019 GeoVision study. The lowest-cost projects for district heating had comparable levelized cost of heat values to existing fossil-fuel-driven district heating systems, and lower values than decentralized heating with natural gas boilers or heat pumps. Chilled water production with absorption chillers driven by a high-quality geothermal resource obtained attractive levelized cost of cooling values, in line with values from typical centralized cooling production facilities and lower than domestic decentralized cooling with air-conditioning units. Also, thermal energy storage is a potential deep direct-use application, where levelized cost of storage values can be obtained that are comparable to those of other thermal storage techniques such as borehole thermal energy storage and hot water storage tanks. Other aspects of deep direct-use, which are not captured in a standard levelized cost of energy metric, include the ability to decarbonize the heating and cooling supply, and provide reliability and resiliency to the energy infrastructure. These attributes are gaining increased attention and improve overall project feasibility. Finally, this paper identifies technical, market, policy, and social barriers for deep direct-use development in the United States, and provides potential approaches for reducing these barriers.

New medium-low temperature hydrothermal geothermal district heating system based on distributed electric compression heat pumps and a centralized absorption heat transformer

Development of geothermal heat for district heating has attracted considerable attention in China. However, transporting geothermal heat for long distance has become the bottleneck for developing large-scale medium-low temperature hydrothermal geothermal fields that located far away from heat load areas. To solve this problem, a new medium-low temperature hydrothermal geothermal district heating system based on distributed electric compression heat pumps and a centralized absorption heat transformer is proposed and evaluated both from the aspects of thermodynamic performance and economic benefit. Analysis of the results may lead to following main conclusions: (i) for the proposed system, its cost-effective main line length of the primary heating network is about 10 km. (ii) The annual coefficient of performance, annual product exergy efficiency, and heating cost of the proposed system are found to be 24.5, 61.4% and 55.62 ¥/GJ, respectively. The centralized absorption heat transformer can reduce irreversible loss of the heating station and improve performance of distributed electric compression heat pumps. (ⅲ) Unlike the conventional medium-low temperature hydrothermal geothermal district heating system with longer distance of transporting geothermal heat, the annual coefficient of performance and annual product exergy efficiency of the proposed one can be improved by about 4.34 and 7.4%, respectively.

Performance analysis of a cascade PCM heat exchanger and two-phase closed thermosiphon: A case study of geothermal district heating system

In this paper, a geothermal energy extraction system has been designed based on a two-phase closed thermosiphon, cascade phase change material heat exchanger, and an organic Rankin cycle. The proposed system is thermodynamically analyzed for supplying power and heat to a selected hotel in Sarein city in Iran. In the first step, the optimum diameter of the two-phase closed thermosiphon, according to the average yearly energy consumption rate (3100kW), is obtained. A two-level cascade heat exchanger with a storage medium of phase change materials is used to supply the building's energy consumptions. For the summertime, only the first level of the heat exchanger is operating to drive the ORC unit with two turbines for power generation. The second turbine output power is transmitted to the upper grid. On the other hand, in the wintertime, since the heating demands dominated, besides the first level of the heat exchanger, the second level of the heat exchanger is operated to supply the heating demand. Based on the thermodynamic analysis, employing phase change materials in the heat exchanger is an effective method for reducing overall exergy destruction, and consequently, increasing system efficiency. The energy and exergy efficiency is more favorable in terms of the application of PCM in the heat exchanger.

Numerical Investigation of Techno-Economic Multiobjective Optimization of Geothermal Water Reservoir Development: A Case Study of China

Renewable geothermal utilization is a significant approach for residential heating with two principal modes, direct geothermal district heating systems (DGDHSs) and indirect geothermal district heating systems (IGDHSs). The key principle of geothermal development design is to prevent premature thermal breakthrough, which could result in low efficiency of geothermal heating systems. In this paper, a new approach considering building heating demand, geothermal water resource protection, and optimal economic benefits is presented systematically. The results simulated by OGS software show that well spacing, reinjection temperature, and production rate are the most significant parameters affecting thermal breakthrough in geothermal reservoirs. In addition, production rate and reinjection temperature have a huge effect on the payback period of investment. Comparing IGDHS to DGDHS, the investment in construction of geothermal wells and the annual water consumption decrease by up to 10% and 50%, respectively. Additionally, electricity costs increase by 5% to 30%. The indirect geothermal district heating system with a well spacing of 300 m, a production rate of 100 m3/h, and a reinjection temperature of 301.15 K is much better for this case, both technically and economically. The systematic calculation approach can be reasonably applied to other regions with geothermal energy utilization.

The Potential of Wind Power-Supported Geothermal District Heating Systems—Model Results for a Location in Warsaw (Poland)

Geothermal heat is considered a sustainable energy source with significant global potential. Together with heat distribution networks, it can provide clean thermal energy to individual and commercial consumers. However, peaks in heat demand can require additional peaking sources at times. In this paper, we investigated how wind turbines can act as a peak energy source for a geothermal district heating system. We studied a model consisting of a geothermal heat source, a heat storage and wind power generator using historical weather data of Warsaw (Poland) and showed that wind power could increase the renewable share to supply a considerable heat demand compared to a geothermal heat source alone. The results indicate that wind power can be a suitable complement for a geothermal heat source to provide energy for heating. It is shown that a theoretical geo-wind-thermal storage based district heating network supplying 1000 m2, which requires 100 W/m2 at an outdoor temperature of −20 °C should have the following parameters: 4.8 MWh of thermal energy storage capacity, 45 kW of geothermal capacity and 5 kW of wind capacity. Such a system would ensure minimal wind curtailment, high utilization of geothermal source and high reliability of supply.

Economic and Environmental Analysis of Different District Heating Systems Aided by Geothermal Energy

As a renewable energy source, geothermal energy can provide base-load power supply both for electricity and direct uses, such as space heating. Regarding this last use, in the present study, district heating systems aided by geothermal energy, the so-called geothermal district heating systems, are studied. Thus, three different options of a geothermal district heating system are evaluated and compared in terms of environmental and economic aspects with a traditional fossil installation. Calculations were carried out from a particular study case, a set of buildings located Province of León in the north of Spain. From real data of each of the assumptions considered, an exhaustive comparison among the different scenarios studied, was thoroughly made. Results revealed the most suitable option from an economic point of view but always considering the environmental impacts of each one. In this regard, the assumption of a district heating system totally supplied by geothermal energy clearly stands out from the rest of options. Thus, the manuscript main objective is to emphasise the advantages of these systems as they constitute the ideal solution from both the economic and environmental parameters analysed.

Inhibition of calcium carbonate scaling by precipitation using secondary nucleation coupled to degassing with atmospheric air

Scaling by calcium carbonate precipitation is an important challenge during exploitation of geothermal water or geothermal district heating systems. Water decarbonation is a promising solution to mitigate calcium carbonate precipitation and reduce the scaling risks. In the current work, the decarbonation of geothermal water by coupling atmospheric air bubbling with seeding was investigated. For that, several operating conditions were studied and optimized such as air and water flows, hydrodynamics, residence time, and bubbling rate. Synthetic and real solutions were tested. To reveal the efficiency of the proposed process, the addition of chemicals was avoided. Results showed that, using continuously operating reactor and under optimized operating conditions, the decarbonation rate of a calcium carbonate solution tested (4 mmol/L of CaCO3, T = 50 °C) can exceed 30% without using chemicals. It was also shown that he residence time in the reactor is relatively short (2.5 min) and the protection of the walls from precipitate adherence was guaranteed.

Fuzzy control of calcium carbonate and silica scales in geothermal systems

Calcium carbonate scaling and silica scaling are critical challenges directly affecting the efficiency of production during operational periods for geothermal power plants or geothermal district heating systems. Although their precipitation mechanisms are different from each other, both can be observed in varied proportions in production and reinjection wells as well as surface equipment in geothermal systems. Thus, scale prevention and control systems are essential, as abatement of scaling is more efficient than removal from wells and equipment after precipitation in a geothermal system. There are a few methods for control of silica and calcium carbonate precipitation in geothermal wells and surface equipment. Most production and reinjection wells require the implementation of a silica/calcium carbonate inhibition system to prevent silica/calcite precipitation inside casings, pipes, separators and other surface equipment in geothermal power systems. Installation of inhibitor systems are the most effective and practical solution for prevention of scaling problems and production loss, if the optimum inhibitor dosages are determined and applied effectively in geothermal systems. Less than optimum ratios of inhibitors may result in product overfeed, increased costs, and in some cases, inhibitor-induced fouling. The system is nonlinear and has multiple dependent and independent variables thus, it is difficult to obtain a mathematical model that describes the relation of geothermal fluid characteristic and inhibitors and with this reason, a fuzzy controller may be good option to resolve it in geothermal systems. Fuzzy control may replace the role of the mathematical model in conservative controllers, substituting it with a different model that is built from a number of smaller rules that only describe a sub-section of the complete system. In this study, two fuzzy logic controllers have been designed to control precipitation of silica and calcium carbonate by using scale inhibitors.

Energy Analysis of a Small Geothermal District Heating System in Southern Italy

Energy Analysis of a Small Geothermal District Heating System in Southern Italy

Energy Analysis of a Small Geothermal District Heating System in Southern Italy

Energy Analysis of a Small Geothermal District Heating System in Southern Italy