The quantitative evaluation of design parameter's effects on a ground source heat pump system

The main solution for the reduction of energy consumption in the field of HVAC is the development of new and renewable energy technologies. Among the various renewable energy systems, ground source heat pump (GSHP) systems have been spotlighted as efficient building energy systems because of their great potentials for energy reduction in building air conditioning and reducing CO₂ emissions. However, higher initial cost works as a barrier to the promotion of their use. Therefore, it is critical to reduce the initial costs by optimizing the design of the system. In this paper, parameters that affect the performance of the GSHP system and the size of ground loop heat exchanger (GLHX) have been investigated. Ratio of GLHX length to unit capacity (L/Q) decreased according to increasing value of thermal conductivity, but L/Q increased according to increasing value of borehole heat transfer resistance. In cooling mode, L/Q decreased according to increasing EWT of underground circulating water and borehole distance but increased in heating mode. The value of L/Q tended to increase according to increasing underground initial temperature in cooling mode, but decreased in heating mode. L/Q decreased according to increasing U-tube separation distance and decreasing underground circulating water flow rate, because the thermal interference effect of underground circulating water and heat absorption and emission rate from the ground decreased. The reduction of the size of GLHX is very important in the aspect of saving total installation cost of a GSHP system. Therefore, the size of GLHX and the performance of GSHP system should be considered together for optimum design of the GSHP system.     

水源热泵热水器实验研究

水源热泵技术利用少量电能将地表水或地下水的低品位能量转移至高品位,目前正成为节能领域的研究热点.针对水源热泵变冷凝参数的相关研究缺乏的现状,通过搭建水源热泵热水器实验台进行了相应实验研究.在水流量Q为0.7~1.3 m~3·h~(-1),进水温度t为15~30℃范围内,对系统功耗、制热量、制冷量、热泵性能系数COP等参数进行了测量.实验结果表明,在水流量为1.1 m~3·h~(-1),进水温度为20℃时,COP达到最大值,系统平均热泵性能系数COP_(ave)为3.23,此时系统处于最佳运行工况.由此可知,寻找系统的最佳运行工况对热泵系统设计和实际工程应用具有重要的意义.     

复合地源热泵系统冬季供暖运行实验研究

介绍了地源热泵在冬季运行供暖的实验研究,具体分析了长期连续运行时土壤温度的变化规律,热泵机组系统的COP变化情况,以及太阳能辅助系统与地源热泵系统联合运行时土壤温度的变化规律,热泵机组系统的COP变化情况.试验数据表明了增加太阳能辅助地源热泵系统后,显著地提高了冷凝器出口温度和室内温度,有效地提高了热负荷,增加了供热面积.总结出了本地区地源热泵系统的一般运行规律.     

太阳能-地源热泵耦合方式的工程应用分析

利用太阳能辅助地源热泵既节能环保又能进一步提高能源的利用率且对环境无污染。从天津地区的太阳光照强度的角度考虑,以利用太阳能提高机组的效率和承担部分建筑物负荷这两种方式辅助地源热泵。从节能和经济性两个角度进行分析并得出结论:在天津地区利用太阳能分担建筑的部分负荷更节能、经济。     

Experimental study of heat transfer of buried finned pipe for ground source heat pump applications

Ground heat exchangers have vital importance for ground source heat pump applications. Various configurations tried to improve heat transfer in the soil. A new kind of aluminium finned pipe buried in the soil for this aim. In order to compare effectiveness of the Al finned pipe over the traditional PPRC pipe an experimental study carried out. The experimental GSHP system was installed at Y?ld?z Technical University Davupasa Campus on 800 m² surface area with no special surface cover. Temperature data were collected using thermocouples buried in soil horizontally and vertically at various distances from the pipe center and at the inlet and the outlet of the ground heat exchanger. Experimental results were compared with results from analytical study. To compare effectiveness of the Al finned pipe and PPRC pipe a new parameter defined as transferred amount of heat per unit mass of working fluid per unit time for this aim. It is found that Al finned pipe has higher heat transfer values than the traditional PPRC pipe.     

An investigation of the heat pump performance and ground temperature of a piled foundation heat exchanger system for a residential building

Novel methods are sought to provide greater efficiency of the installation of ground heat exchangers for GSHPs (ground source heat pumps) in domestic buildings. An economically viable option is to utilise concrete foundation piles as ground heat exchangers. The objective of this study is to investigate the operation of utilising a piled foundation structure as a ground heat exchanger. A test plot of 72 m² (ground floor area) was produced with 21 × 10 m deep concrete piles, with a single U tube pipe in each. Ground heat was extracted by a heat pump with the heat loading being varied in line with the date and the average air temperature. Over the 2007/2008 heating season this study had investigated the temperature changes in the foundation piles and the surrounding ground in addition to the heat pump operational performance. The temperature changes observed in the region of the test plot were compared with variations naturally experienced in the ground due to the seasonal climatic influence. The SPF (seasonal performance factor) of the heat pump was 3.62 and the ground temperature at a distance of 5 m from the test plot was seen to be undisturbed by the heat extraction and followed the predicted seasonal variation.     

复合式土壤源热泵的研究现状及发展趋势

综述了国内外复合式土壤源热泵系统应用研究的最新进展和研究成果,分析了土壤热平衡问题的形成原因、解决方案,以及目前常用的几种复合土壤源热泵系统的工作原理,对比了不同连接方式的优缺点,并对系统存在的问题提供了相应的解决办法,以及对复合式土壤源热泵未来的发展及研究的方向提出了新的观点。     

Computer simulation of borehole ground heat exchangers for geothermal heat pump systems

Computer simulation of borehole ground heat exchangers used in geothermal heat pump systems was conducted using three-dimensional implicit finite difference method with rectangular coordinate system. Each borehole was approximated by a square column circumscribed by the borehole radius. Borehole loading profile calculated numerically based on the prescribed borehole temperature profile under quasi-steady state conditions was used to determine the ground temperature and the borehole temperature profile. The two coupled solutions were solved iteratively at each time step. The simulated ground temperature was calibrated using a cylindrical source model by adjusting the grid spacing and adopting a load factor of 1.047 in the difference equation. With constant load applied to a single borehole, neither the borehole temperature nor the borehole loading was constant along the borehole. The ground temperature profiles were not similar at different distances from the borehole. This meant that a single finite difference scheme was not sufficient to estimate the performance of a borefield by superposition. The entire borefield should be discretized simultaneously. Comparison was made between the present method and the finite line source model with superposition. The discrepancies between the results from the two methods increased with the scale of borefield. The introduction of time schedule revealed a discrepancy between the load applied to the ground heat exchanger and that transferred from the borehole to the ground, which was usually assumed to be the same when using analytical models. Hence, in designing a large borefield, the present method should give more precise results in dynamic simulation.     

Potential of ground heat source systems

This paper presents a historical background of ground source heat pump technology, followed by a review of its current shortcomings. Based on these observations the author assesses the R&D needs and recommendations for future research.     

Investigation on the feasibility and performance of ground source heat pump (GSHP) in three cities in cold climate zone,China

As a renewable energy technology, ground source heat pump (GSHP) system is high efficient for heating and cooling in office buildings. However, this technology has strong dependence on the meteorological and building envelope thermal characteristic parameters. For the purpose of quantitative investigation on the feasibility and performance GSHP, three cities located in cold climate zone, Qiqihaer, Shenyang and Beijing, were sampled. Firstly, the office building dynamic loadings in these cities were calculated on basis of the different meteorological and envelope thermal characteristic parameters. The TRNSYS, one kind of energy simulation software, were employed to simulate the operation performances of GSHP on basis of these parameters. The simulation revealed the data on the outlet/inlet temperature of buried pipes, soil temperature, energy consumption distribution and the coefficient of performance (COP) for one year operation. Furthermore, ten years operation was also simulated to show the stability of the performance based on the outlet/inlet temperature of buried pipes and soil temperature. From these results, the GSHP had shown its most suitable performance in Beijing, second in Shenyang and worst in Qiqihaer. These results could be used as a reference on suitable utilization of GSHP systems in office buildings located in cold climate zone, China.     

回热器对跨临界CO_2水源热泵的影响判别式及实验研究

分析了回热器对跨临界CO2压缩循环效率等的影响,推导出回热器对系统的制热效率影响的判别式。在带回热器和不带回热器两种情况下完成了跨临界CO2水源热泵系统的实验。实验结果表明：带回热器的跨临界CO2水源热泵系统的制热效率和制冷效率略高于不带回热器时系统的效率;带回热器时热泵系统的制热效率比不带回热器系统的制热效率高约4%-8%。     

U型波纹埋管对于增强土壤源热泵换热性能的研究

为了增强土壤源热泵系统地下埋管换热器的换热性能,通过CFD方法,探讨改用波纹管对地下换热所产生的影响,首次提出采用波纹管代替光管作为强化地下埋管换热器换热效率。     

Year round experimental study on a constant temperature and humidity air-conditioning system driven by ground source heat pump

Numerous studies about the ground source heat pump building heating and cooling systems have been constructed in office building, hotel, residential building and school et al. However, few researches about the constant temperature and humidity air-conditioning system driven by ground-coupled heat pumps were carried out. In this paper, a constant temperature and humidity air-conditioning system driven by ground source heat pump was designed and constructed in an archives building in Shanghai, China. During the operation in the cooling mode, the heat extraction from the condenser of the heat pump was divided: part was rejected to the soil while another was used to reheat the air in AHUs. According to the experimental results, the indoor temperature and relative humidity fulfilled the “Archives Design Code”. In summer, the heat rejected to the soil was reduced by 32%, which was helpful for the earth energy conservation. The soil temperature increased only 0.5 °C after the GSHP system operating for a year. The energy cost of the air-conditioning system was 56.1 kWh/m². Compared with air source heat pump system and water cooled unit with boiler system, the operating cost of ground source heat pump was reduced by 55.8% and 48.4%, respectively.     

土壤源热泵埋地换热器的简便计算

土壤源热泵是利用土壤作为吸热和排热源的一种高效、节能、环保的热泵技术,近年来得到了快速的发展。本文介绍了一种简化的土壤与埋地换热器的传热数学模型,并利用Foxpro编制了简便、快速的计算程序。     

Performance evaluation and modeling of a hybrid cooling system combining a screw water chiller with a ground source heat pump in a building

The performance of a hybrid cooling system that combines a screw water chiller with a ground source heat pump (GSHP) was measured and analyzed at various cooling loads. In addition, the hybrid cooling system in a building was modelled sophisticatedly using EnergyPlus and then validated with the measured data. The coefficient of performance of the GSHP was lower than that of a conventional chiller in the monitored building, but the hybrid cooling system helped to stably provide the required cooling capacity at high-load conditions. The mean bias error and the normalized root-mean squared error of the predicted cooling load of the building were −8% and 12.4%, respectively. The hybrid cooling system was simulated by varying four operating parameters: the operating schedule, chilled water temperature (T_CW), dry-bulb temperature (T_DB), and entering water temperature (T_EW). The T_CW is ascertained as being the most effective control parameter in the hybrid cooling system.     

复合式土壤源热泵系统设计

设计了一套复合式土壤源热泵性能实验台,采用冷却塔作辅助冷源、太阳能热水器作辅助热源,能够实现冬季供暖、夏季供冷、一年四季提供60~80℃生活热水的功能。给出了系统中热泵机组、空调末端设备、冷却塔、水泵、太阳能热水器等主要部件的选型计算方法,经搭建好的土壤源热泵性能实验台运行测试,制冷和制热效果良好,同时也解决了土壤热平衡问题。     

我国地源热泵相关技术专利综合分析

地源热泵是一种利用浅层土壤或含水层实现供热和空调制冷的高效节能设备。随着我国政府和社会对节能环保越发重视,地源热泵技术的优势将更加突出。最近几年我国地源热泵发展较迅速,在设计、制造、运行、管理等方面都取得了一些研究成果。对国内最近地源热泵的相关专利进行了检索,并进行了定性与定量分析,为该领域的研究者和企业提供专利信息参考,并归纳总结了一些研究热点,以期为我国地源热泵行业的研究开发与市场发展提供决策参考和技术依据。     

水源热泵空调系统运行优化

以采用水源热泵机组的某住宅小区为例,分析其建筑的冷热负荷特性,探讨其变化规律;对水源热泵机组、水泵系统、热源井的运行控制策略提出优化方案,为同类工程的节能运行提供参考。     

Evaluation of heat exchange rate of GHE in geothermal heat pump systems

Total thermal resistance of ground heat exchanger (GHE) is comprised of that of the soil and inside the borehole. The thermal resistance of soil can be calculated using the linear source theory and cylindrical source theory, while that inside the borehole is more complicated due to the integrated resistance of fluid convection, and the conduction through pipe and grout. Present study evaluates heat exchange rate per depth of GHE by calculating the total thermal resistance, and compares different methods to analyze their similarities and differences for engineering applications. The effects of seven separate factors, running time, shank spacing, depth of borehole, velocity in the pipe, thermal conductivity of grout, inlet temperature and soil type, on the thermal resistance and heat exchange rate are analyzed. Experimental data from several real geothermal heat pump (GHP) applications in Shanghai are used to validate the present calculations. The observations from this study are to provide some guidelines for the design of GHE in GHP systems.     

基于预测的复合地源热泵系统控制方法实现

在冬冷夏热且夏季冷负荷远大于冬季热负荷的地区常采用带有冷却塔的复合式地源热泵系统,其控制策略存在极大的优化空间。文章提出了直接比较冷却塔和与土壤换热器相连的板式换热器的出口温度的控制方法,并通过人工神经网络预测板式换热器机组侧的出口水温来实现此控制方法。通过FLUENT软件建立复合式地源热泵系统动态数值模型,获取建立神经网络的数据,采用3层BP网络,建立了多个预测板式换热器机组侧出口温度的模型。研究结果表明,采用神经网络可以准确实现此预测,绝对误差不超过0.4℃。