Energy and exergy analysis of geothermal district heating systems: an application

In this study we present an energy and exergy assessment and modeling of geothermal district heating systems for their system analysis, performance evaluation and optimization. A comprehensive case study is conducted in Balcova geothermal district heating system (BGDHS) in Izmir, Turkey and actual thermal data are collected and employed for analysis. Using actual system data, an assessment of the district heating system performance, energy and exergy efficiencies, and exergy destructions in the system is conducted in this regard. The exergy destructions in the overall BGDHS are quantified and illustrated using exergy flow diagram. Furthermore, both energy and exergy flow diagrams are exhibited for comparison purposes. It is observed through analysis that the exergy destructions in the system particularly take place as the exergy of the fluid lost in the pumps, the heat exchanger losses, the exergy of the thermal water (geothermal fluid) reinjected and the natural direct discharge (hot water distribution losses) of the system, accounting for 1.64%, 8.57%, 14.84% and 28.96%, respectively, of the total exergy input to the BGDHS. For system performance analysis and improvement, both energy and exergy efficiencies of the overall BGDHS are investigated and are determined to be 41.9% and 46%, respectively.     

欣苑小区地热供暖站房设计

针对当地地热资源丰富的具体情况 ,经综合分析比较 ,住宅小区采用以地热热源为主、燃油热水锅炉为辅的间接连续供暖方式 ;介绍了供热站房的设计及采取的质调与量调等节能措施。运行情况表明该系统节能效果显著。     

地热供热系统调峰负荷的确定方法

介绍了直接式和间接式地热供热系统调峰负荷的理论计算方法。重点分析了间接式地热供热系统调峰负荷随环境温度的变化,以及所受末端散热器设计、地热水与循环水换热器设计运行参数的影响。     

Exergoeconomic analysis of the Gonen geothermal district heating system for buildings

This paper presents an application of an exergoeconomic model, through exergy and cost accounting analyses, to the Gonen geothermal district heating system (GDHS) in Balikesir, Turkey for the entire system and its components. This exergoeconomic model is used to reveal the cost formation process and the productive interaction between components. The exergy destructions in the overall Gonen GDHS are quantified and illustrated for a reference temperature of 4 °C. The results indicate that the exergy destructions in the system occur primarily as a result of losses in the cooled geothermal water injected back into the reservoir, pumps, heat exchangers, and pipelines. Total exergy destruction and reinjection exergy of the cooled geothermal water result in 1010 kW (accounting for 32.49%), 320.3 kW (accounting for 10%) of the total exergy input to the Gonen GDHS, respectively. Both energy and exergy efficiencies of the overall Gonen GDHS are also investigated to analyze the system performance, as these efficiencies are determined to be 42% and 50%, respectively. It is found that an increase of the load condition leads to a decrease in the overall thermal costs, which will result in more cost-effective energy systems for buildings.     

区域供冷系统能耗分析

针对区域供冷系统存在的能耗问题,通过对日本两个典型区域供冷项目具体案例的深入分析,指出其能耗水平,结合国内典型公共建筑分散供冷供暖系统的能耗数据,指出区域供冷高能耗的根源所在.在分析了国外一些成功区域供冷案例的成功之处后,进一步指出区域供冷遇到的各种问题,认为区域供冷系统节能的前提条件是具备高密度的冷负荷用户和足够量的廉价天然冷源.     

Economic assessment of geothermal district heating systems: A case study of Balcova–Narlidere,Turkey

Geothermal energy is an important renewable energy resource in Turkey. The aim of this research is to evaluate the Balcova–Narlidere geothermal district heating system from an economic perspective. The system is the largest one in Turkey in terms of heating capacity and located in Izmir. Although there are some assessments regarding energy and exergy analysis for the Balcova–Narlidere geothermal district heating system, an economic assessment was not performed, previously. The profitability of the investment is investigated by using internal rate of return method. Seven hundred and eighty different scenarios are developed in this assessment. In order to estimate the potential cash flows in the remaining project life, operating cost in 2002 is decreased and increased, alternatively, between 5% and 30% by 5% in each step, while monthly energy utilization price is changed between US$ 17 and 72 in those scenarios. The energy utilization prices are suggested according to zero IRR value for all scenarios due to the consideration of social and environmental concerns in this investment. It is found that, the proper monthly energy utilization price for a 100 m² household would be US$ 55.5 when the operating cost and heating capacity in 2002 were remained constant.     

Exergetic modeling and performance evaluation of solar water heating systems for building applications

Solar water heating (SWH) is a well-proven renewable energy technology and has been used in many countries of the world. The basic technology is straightforward, although there are a variety of various types of SWH systems. In the performance assessment of SWH systems, energy analysis (first law) method has been widely used, while the number of the studies on exergetic assessment is relatively low. The SWH system investigated consists of mainly three parts, namely a flat plate solar collector, a heat exchanger (storage tank) and a circulating pump. The main objectives of the present study are as follows, differing from the previously conducted ones: (i) to model and assess SWH systems using exergy analysis (second law) method as a whole, (ii) to investigate the effect of varying water inlet temperature to the collector on the exergy efficiencies of the SWH system components, (iii) to study some thermodynamic parameters (fuel depletion ratio, relative irreversibility, productivity lack and exergetic factor) and exergetic improvement potential, and (iv) to propose and present an exergy efficiency curve similar to the thermal efficiency curve for solar collectors. The system performance is evaluated based on the experimental data of the Izmir province, Turkey, which is given as an illustrative example. Exergy destructions (or irreversibilities) as well as exergy efficiency relations are determined for each of the SWH system components and the whole system. Exergy efficiency values on a product/fuel basis are found to range between from 2.02 to 3.37%, and 3.27 to 4.39% at a dead (reference) state temperature of 32.77 °C, which is an average of ambient temperatures at eight test runs from 1.10 to 3.35 p.m., for the solar collector and entire SWH system, respectively. An exergy efficiency correlation for the solar collector studied was also presented to determine its exergetic performance. It is expected that the model presented here would be beneficial to the researchers, government administration, and engineers working in the area of SWH systems for residential applications.     

典型集中供热系统能源利用分析

为分析集中供热系统及各环节的能源利用状况,采用能分析和分析方法建立了供热系统能分析及分析模型,对集中供热系统进行了热力学分析,并以天津某供热系统热源厂为例采用能分析和分析方法进行了计算。结果表明:第一、第二热源厂的热效率分别为32.56%,57.03%,效率分别为7.77%,13.88%,该集中供热系统对能的数量利用效果一般,能质利用效果较差,具有较大节能潜力。     

地热供暖系统经济性模型设计

通过比较地热供暖系统与传统供暖系统的特点,提出了地热供暖系统经济性的主要影响因素调峰比和地热尾水排放温度,并分析了其对地热供暖系统的影响.利用MATLAB多项式拟合工具对供暖度日数数据进行处理,得到了供暖度日数的数学模型,为进一步计算供暖期燃料消耗量并最终得到地热供暖系统的年运行费用提供数据.以费用年值作为地热供暖系统的优化指标对系统进行了优化计算.     

Exergoeconomic evaluation on the optimum heating circuit system of Simav geothermal district heating system

Simav is one of the most important 15 geothermal areas in Turkey. It has several geothermal resources with the mass flow rate ranging from 35 to 72 kg/s and temperature from 88 to 148 °C. Hence, these geothermal resources are available to use for several purposes, such as electricity generation, district heating, greenhouse heating, and balneological purposes. In Simav, the 5000 residences are heated by a district heating system in which these geothermal resources are used. Beside this, a greenhouse area of 225,000 m² is also heated by geothermal. In this study, the working conditions of the Simav geothermal district heating system have been optimized. In this paper, the main characteristics of the system have been presented and the impact of the parameters of heating circuit on the system are investigated by the means of energy, exergy, and life cycle cost (LCC) concepts. As a result, the optimum heating circuit has been determined as 60/49 °C.     

Optimized control strategies for solar district heating systems

Solar district heating (SDH) systems are a proven concept for the supply of space heating and/or domestic hot water using solar energy as the main heat source. SDH systems with a high solar fraction include seasonal thermal storage and various subsystems with different time scales that must be managed by the supervisory control system. This paper presents the development of optimized control strategies for the Drake Landing Solar Community in Okotoks (Alberta, Canada). The proposed strategies, based on the application of model predictive control concepts, aim to further reduce the use of auxiliary energy for heating (gas) while also reducing the pumping energy (electricity). Perfect forecasts for the weather and the SDH loads are assumed in the study and a detailed TRNSYS model is used. Results show that the primary energy consumption can be reduced by 5% by updating the supervisory control strategies.     

供热系统分阶段质-量调节的节能分析

该调节方法在传统方法的基础上,依据供热负荷大小分为最小流量质调节和定供水温度量调节两个阶段。介绍了调节曲线,分析了系统最小流量的影响因素,并给出了供热参数的计算方法。实例计算分析表明该方法具有较好的节能效果。     

多种供热供暖方式的能耗分析

根据北京地区调研和测试数据,对多种供暖方式的能耗进行了分析和比较,指出不同的供热供暖方式有不同的供热环节,不同的供热环节涉及不同的能耗。强调在目前管网调控水平下,不均匀热损失不容忽视,并应重视供热系统各个环节的节能。     

Effect of reference state on the performance of energy and exergy evaluation of geothermal district heating systems: Balcova example

In this paper, we undertake a parametric study to investigate how varying reference temperature from 0 to 25 °C will affect the energy and exergy efficiencies of the Balcova geothermal district heating system (BGDHS) and develop two significant correlations (with a correlation coefficient of 0.99) that can be used for predicting the efficiencies. The exergy losses in the overall BGDHS are quantified and illustrated using exergy flow diagram particularly for a reference temperature of 11.4 °C for comparison purposes. This reference temperature is taken as an average value of the ambient temperatures measured during the past 5 years for the day of 2nd January to reflect the actual situation. The results show that the exergy losses within the system occur mainly due to the losses in pumps, heat exchangers, reinjection sections of the geothermal water back into reservoir and pipeline, and account for 1.75%, 8.84%, 14.20%, and 28.69%, respectively. In addition, we study energy and exergy efficiencies to determine the possibilities to improve the system, and energy and exergy efficiencies of the system are found to be 42.36% and 46.55%, respectively, for 2nd January 2004.     

Determination of optimum pipe diameter along with energetic and exergetic evaluation of geothermal district heating systems: Modeling and application

This study deals with determination of optimum pipe diameters based on economic analysis and the performance analysis of geothermal district heating systems along with pipelines using energy and exergy analysis methods. In this regard, the Dikili geothermal district heating system (DGDHS) in Izmir, Turkey is taken as an application place, to which the methods presented here are applied with some assumptions. The system mainly consists of three cycles, namely (i) the transportation network, (ii) the Danistay region, and (iii) the Bariskent region. The thermal capacities of these regions are 21,025 and 7975 kW, respectively, while the supply (flow) and return temperature values of those are 80 and 50 °C, respectively.     

Criteria for use of groundwater as renewable energy source in geothermal heat pump systems for building heating/cooling purposes

Environmental protection measures are conducted directly by the use of renewable energy sources. The energy development of cities in Europe is aimed at the sustainable use of renewable energy sources in order to achieve the substitution of fossil fuels and the reduction of the hazardous gas emission into the atmosphere. Geothermal resources of medium and low enthalpy in Europe being used for obtaining heat energy are providing about 6600 MW_t, currently having the growth trend of 50 MW_t annually. The use of geothermal low enthalpy, namely of subgeothermal groundwater resources, has even higher annual growth rate, and if such a trend is kept till the year 2010, the produced energy will amount about 8000 MW_t. Criteria of the groundwater use as a hydrogeothermal energy resource in heat pumps are complex, and they deal with aspects of incoming temperatures and groundwater quantities. The precise limit temperature of groundwater that would separate the direct use of geothermal energy (only by the use of heat exchangers), and indirectly by the use of a heat pump has not been determined in the professional and scientific practice of Serbia so far. Taking into account that relatively small number of new flat is being built in Serbia nowadays, if we want to save energy it is necessary to carry out the energy reconstruction of the existing flats whose number is estimated to be more than 2.8 million. By the application of subgeothermal energy and the use of heat pumps, energy consumption would be significantly reduced.     

区域集中供热系统水力平衡探讨

从理论上分析了水力失调现象,提出了有效的水力平衡调节方法。详细探讨了区域集中供热系统的两种集中控制策略:流量控制和温度控制。     

Simulation and analysis on control effectiveness of TRVs in district heating systems

Based upon an existing building and heating system with thermostatic radiator valves (TRVs), an integrated model is developed for simulating the thermal and hydraulic behavior of the heating system under various operation cases. According to the simulation results, the effectiveness of TRVs in reducing overheating has been studied. The results indicate that when the set value of the TRV is kept at 2-3, its effectiveness in reducing the overheating phenomena caused by an excessive water flow rate is less than 60%. If the overheating phenomena is caused by an excessive supply water temperature and radiator area, the effectiveness of the TRV can reach about 80%; the TRV's effect becomes more obvious with increasing overheating degree; however, about 20%-40% of overheating loss still needs to be resolved by improving improper operation adjustment and design. Considering these results, a control strategy is proposed, in which the supply water temperature is adjusted daily according to the flow performance of the system, and the pump is operated with frequency conversion and constant pressure difference. Further simulation indicates that, under the new control strategy, the variation of the heat supply quantity of the system can match the heat load change, and the flow rate of the system can be controlled at an appropriate range.     

室内热系统温度调节与节能分析

分析了温控阀的调节特性及变流量工况下散热器的热力特性,分别对住宅和公共建筑按照住宅供暖模式和公共建筑供暖模式进行了实验,记录房间的温度变化和室外温度变化,作为节能率估算参考,考察温控阀作用下供热系统的节能效果.     

过热蒸汽型热网换热设备的开发和研究

针对过热蒸汽放热器过程中不同阶段的特点,研制了一种以过热蒸汽为加热介质的城市热网换热器。采用冷轧高肋片管作为传热元件,并对肋片管表面几何尺寸进行了优化分析,采用自由旋转化传热技术,在提高换热系数的同时,降低了污垢的生成速度,换热器由主、副换热器两部分组成,采用复合流程结构,使凝结水过冷,消除了二次蒸汽损失,凝结水出口不必再装疏水器。