两个系统参数对地热热泵循环的影响

为了解决地热热泵系统输出能量和用户需求能量之间的动态平衡问题，该文对系统的两个主要参数(冷凝器侧水流量和压缩机输入频率)对地热热泵循环特性的影响进行了相应的实验研究。在小型地热热泵系统上进行了变频及变水流量实验研究，频率变化范围为30Hz～55Hz，冷凝器水流量变化范围为0．054kg／s～0．174kg／s；然后，通过对实验数据的分析，发现了系统各参数，如COP值、制热量、压缩机能耗等随频率及水流量的变化规律。该文的结论可以在制定地热热泵系统能量输出的调节策略中起到一定的指导作用。     

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.     

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.     

Efficiency of Vertical Geothermal Heat Exchangers in the Ground Source Heat Pump System

Taking the fluid temperature distribution along the borehole depth into account, a new quasi-three-dimensional model for vertical ground heat exchangers has been established, which provides a better understanding of the heat transfer processes in the geothermal heat exchangers. On this basis the efficiency of the borehole has been defined and its analytical expression derived. Comparison with the previous two-dimensional model shows that the quasi-three-dimensional model is more rational and more accurate to depict the practical feature of the conduction of geothermal heat exchanger, and the efficiency notion can be easily used to determine the inlet and outlet temperature of the circulating fluid inside the heat exchanger.     

Sustainability aspects of geothermal heat pump operation, with experience from Switzerland

Geothermal heat pumps are the key to the utilization of the ubiquitous shallow geothermal resources. Theoretical and experimental studies, performed in Switzerland over several years, have established a solid scientific base of reliable long-term operation of borehole heat exchanger-coupled heat pump systems. Proper design, taking into account local conditions like ground properties and building needs, ensures the sustainability of production from systems with single and multiple borehole heat exchangers. Long-term experience acquired at operational objects confirms the predictions.     

Field-scale evaluation of the design of borehole heat exchangers for the use of shallow geothermal energy

A numerical model for the simulation of temperature changes in a borehole heat exchanger (BHE) with fluid circulating through U-tubes is developed. The model can calculate the thermal power transferred from heat pumps to BHEs while considering the nonlinear relationship between temperature of the circulating fluid and the thermal power. The use of the developed model enables the design of a geothermal heat pump (GHP) system with the view of pursuing efficiency and financial benefit. The developed model is validated by comparing two measurement datasets with their respective simulation results. The numerical evaluation of a real GHP system with 28 BHEs and 79 heat pumps involved consideration of a base case and modified cases. In all cases, the temperatures of the circulating fluid at the BHE inlet and outlet, heat pump efficiency, and the heating power and electric power of heat pumps were obtained. The estimated cost of electricity in the year 2030 is 0.146 US$/kW. The most cost-effective system in this case is for there to be 4, 6, and 6 BHEs on the first, second, and third floors, respectively.     

变频系统在单、双级组合式热泵空调系统中的应用

本文根据我国北方的地域特点,提出了一种单、双级定频-变频组合式混合热泵系统。这种热泵 在单、双级混合热泵系统的基础上,引入了变频系统,使之既能在夏季满足制冷要求,又能在冬季热泵采 暖中,在外界环境温度变化范围大的情况下高效节能地运行,同时还可提高系统的部分负荷性能,从而 提高了整个系统的能效比EER,增大了热泵的季节性能系数HSPF,是一种既节能又满足舒适性要求的 热泵系统。     

桩埋管地源热泵系统及其应用

桩埋管是地源热泵系统新的埋管方式.它与建筑结构相结合,充分地利用了建筑物面积,通过桩基与周围大地形成换热,从而减少了钻孔和埋管费用.文章阐述了桩埋管地源热泵地下换热器的设计和施工中应注意的问题,并结合温州市会所的实际工程作了说明.     

Experimental research and operation optimization of an air-source heat pump water heater

In order to optimize design and operation strategy of air-source heat pump water heater, an experimental set-up and simulation model were constructed. Also, a methodology of optimizing operation, which takes into account thermostatic and timing control patterns, was presented and applied. Experimental results indicated that the average COP ranged from 2.82 to 5.51 under typical conditions. The recommended outside area ratio of condenser coil to evaporator is 0.14−0.31 when the evaporator outside area is between 6.0 and 6.5 m² for this set-up. The optimal start-up time was between 12:00 and 14:00 if there was no electricity price difference between day and night, or it was near 22:00. The optimal setting water temperature should be adjusted according to the variation of seasonal ambient temperature. It was suggested that, based on this set-up, setting water temperature should be set higher than 46 °C in summer and 50 °C in other seasons.     

A study on the performance of a geothermal heat exchanger under coupled heat conduction and groundwater advection

Being environmental friendly and with the potential of energy-efficiency, more and more ground-source heat pump (GSHP) systems are being widely used. However, the influence of groundwater advection on the performance of the geothermal heat exchanger (GHE) in a GSHP is not still clearly known. In this paper, the configuration of a vertical dual-function GHE used in an integrated soil cold storage and ground-source heat pump (ISCS&GSHP) system, which charged cold energy to soil at night and produced chilled water in daytime in summer, and hot water for heating in winter, is firstly presented. This is then followed by a report on a mathematical model for the GHE considering the impact of the coupled heat conduction and groundwater advection on the heat transfer between the GHE and its surrounding soil. The GHE model developed was then integrated into a previously developed simulation program for an ISCS&GSHP system, and the operating performances of the GHE in an ISCS&GSHP system having a vertical dual-function GHE have been studied by simulation and reported. These simulation results, firstly seen in open literature, are much helpful to the design of a GHE buried in soil and widely used in GSHP systems or ISCS&GSHP systems.     

Stationary operation of a unit in a multi-unit heat pump system

In the paper, a method for the determination of the parameters of the units, stationary operating in a multi-unit heat pump system, is presented. This method is used for the consideration of six schemes of hydraulic connection of the heat exchangers in groups.     

Development of suitability maps for ground-coupled heat pump systems using groundwater and heat transport models

The thermophysical properties of subsurface materials (soils, sediments and rocks) and groundwater flow strongly affect the heat exchange rates of ground heat exchangers (GHEs). These rates can be maximized and the installation costs of the ground-coupled heat pump (GCHP) systems reduced by developing suitability maps based on local geological and hydrological information. Such maps were generated for the Chikushi Plain (western Japan) using field-survey data and a numerical modeling study. First, a field-wide groundwater model was developed for the area and the results matched against measured groundwater levels and vertical temperature profiles. Single GHE models were then constructed to simulate the heat exchange performance at different locations in the plain. Finally, suitability maps for GCHP systems were prepared using the results from the single GHE models. Variations in the heat exchange rates of over 40% revealed by the map were ascribed to differences in the GHE locations, confirming how important it is to use appropriate thermophysical data when designing GCHP systems.     

地热水高温热泵及风机盘管系统的优化

针对60～85℃地热水的高温热泵及风机盘管供热空调系统,建立系统模型的目标函数;采用MATLAB软件求解出满足约束条件下的各级温度参数以及地热水第一、二级利用的最佳回水温度;从理论上分析了负荷侧供水温度对高温热泵价格和性能系数的影响。     

地源热泵在室内游泳池供暖空调中的应用研究

在分析了地源热泵系统的特点和概算了室内游泳池的冷热负荷的基础上，提出采用地源热泵系统可同时满足室内游泳池的供暖、空调及池水加热3项需求；分析了不同季节地源热泵在游泳池的运行工况。通过分析比较表明，地源热泵系统的运行费用比传统的冷水机组加燃油锅炉系统的运行费用节省约50％，比冷水机组加燃气锅炉系统的运行费用节省21％。     

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.     

Feasibility study of hybrid fuel cell and geothermal heat pump used for air conditioning in Algeria

Hybrid Energy System (HES) is mainly based on proton exchange membrane fuel cell (PEMFC) technology, which is supplied by a fuel reforming process for hydrogen production, starting from natural gas. The exhaust heat from the PEMFC is evacuated to a thermal storage tank (TST) mixed with water provided by geothermal source, The bath (Hammam) Sidi Aïssa 47 °C, TST hot water maintained to 47 °C is used in a fan coil for canteen heating in Si Ben Salah School located in Saïda (NW of Algeria). Cooling is assured by the air conditioning sub-system made of a fan coil and heat pump using cool water tank. The experimental analysis of the air conditioning device is done for canteen application for cooling and heating modes. The feasibility study shows that using the geothermal sources located in Northern Algeria and low temperature PEMFC for air conditioning is a promising solution.     

太阳能-土壤源热泵系统(SESHPS)交替运行性能的数值模拟

针对青岛地区的气象与地质条件,以土壤温度恢复率为指标,对太阳能-土壤源热泵系统（SESHPS）的交替运行性能进行了数值模拟。结果表明：SESHPS以24h为周期交替运行时,近盘管处土壤温度恢复率取30％～60％为宜,太阳能热泵投入运行的时间比例应控制在42％～58％,以此可确定出太阳能集热器的面积,为SESHPS的实际工程设计与运行提供了理论参考。     

Performance assessment of a horizontal-coil geothermal heat pump

This paper evaluates the performance of a geothermal heat pump in Iran. An air-to-air 5.275 kW heat pump has been changed and redesigned to a geothermal heat pump system for the first time in Iran. Air-to-air condenser has been replaced by a tube-in-tube heat exchanger and assembled system has been tested under ARI-325 standard at the national energy lab of Iran and the results have been compared with the original system. Then, local weather conditions and soil properties of Tabriz (located at the north-west of Iran) have been applied and geothermal coil has been designed. Coil has been connected to the heat pump and the average coefficient of performance (COP) of rather more than three has been recorded in cooling mode. Results obtained from experimental measurements show that horizontal GSHP systems can be used for Tabriz-like climates in Iran. Copyright © 2006 John Wiley & Sons, Ltd.     

The geothermal characteristics of the ground and the potential of using ground coupled heat pumps in Cyprus

The ground can be used as an energy source, an energy sink, or for energy storage and for this reason ground characteristics should be available. Therefore the purpose of this paper is to present the recorded ground temperatures at eight representative sites of Cyprus, in relation to depth, time of year, geology and altitude and discuss the efficiency of Ground Coupled Heat Pumps. The ground temperature was recorded for a period of one year, from October 2009 to October 2010. According to the results obtained, in several locations in Cyprus the surface zone reaches a depth of 0.5 m. The shallow zone penetrates to 7-8 m and there after the deep zone follows in which the temperature remains constant throughout the year with a range between 18 and 23 °C. For the eight boreholes, additional geothermal data were also recorded like the type of ground and thermal conductivities of the various geologic layers. The data collected clearly indicate that there is a potential for the efficient use of Ground Coupled Heat Pumps (GCHPs) in Cyprus leading to significant savings in heating and cooling energy consumption.