Performance analysis of U-vertical direct-expansion ground-source heat pump

The performance of a direct-expansion ground-source heat pump（DX GSHP）system is theoretically analyzed.Compared with the conventional ground-source heat pump（GSHP）,the DX GSHP has a lower condensing temperature in the cooling mode and a higher evaporating temperature in the heating mode,and the ground heat exchanger（GHE）in the DX GSHP has a low thermal resistance.Therefore,the coefficient of performance（COP）of the DX GSHP is higher than that of the GSHP.In addition,the system performance of the DX GSHP system is higher than that of the conventional GSHP system because there are no secondary solution loops and water circulating pumps in the DX GSHP system.The experimental energy performance of the DX GSHP system is also investigated based on the actual operational data.The tested DX GSHP system is installed in Xiangtan,China.The U-vertical GHE of the DX GSHP is buried in a water well.The length and the outside nominal diameter of the GHE are 42 m and 12.7 mm,respectively.The experimental results show that the maximum（COP）and the average COP of the DX GSHP system in the heating mode are 5.95 and 4.72,respectively.

Thermal comfort assessment and energy consumption analysis of ground-source heat pump system combined with radiant heating/cooling

A new ground source heat pump system combined with radiant heating/cooling is proposed, and the principles and the advantages of the system are analyzed. A demonstration of the system is applied to a rebuilt building： Xijindu exhibition hall, which is located in Zhenjiang city in China. Numerical studies on the thermal comfort and energy consumption of the system are carded out by using TRNSYS software. The results indicate that the system with the radiant floor method or the radiant ceiling method shows good thermal comfort without mechanical ventilation in winter. However, the system with either of the methods should add mechanical ventilation to ensure good comfort in summer. At the same level of thermal comfort, it can also be found that the annual energy consumption of the radiant ceiling system is less than that of the radiant floor system.

Experimental Investigation on System with Combination of Ground-Source Heat Pump and Solar Collector

This paper presents the heating performance and energy distribution of a system with the combination of ground-source heat pump and solar collector or a solar-assisted ground-source heat pump system (SAGSHPS) by calculation and experiment.The results show that the average absolute error is less than 0.6 ℃ and the relative error is less than 5% under the pulse load when the analytical solution to the 2-D solid cylindrical source model is used for the SAGSHPS.The coefficient of performance (COP) of the SAGSHPS is 2.95-4.70.The average fluid temperature in the borehole heat exchanger can increase by 3 ℃ with the assistance of solar collector,which will improve the COP of the heat pump by approximately 10% from the experimental data.The energy contributions to the total heating load of soil,electricity and solar are 56.30%,36.87% and 6.83%,respectively.

Research on Performance of Ground-Source Heat Pump Double U Underground Pipe Heat Exchange

This paper uses FLUENT software building the three-dimensional unsteady state model of ground source heat pump single U and double U underground pipe to study on heat exchange of underground pipe system in the condition of unsteady state long-term continuous running, analyzes the change of soil temperature filed around underground pipe and performance of underground pipe heat exchange between single U and double U pipe system. The results show that double U pipe system is better than single U system, which can improve unit depth heat exchange efficiency, reduce the number of wells and reduce the initial investment.

Heat flow balance and control strategies for a large GSHP

The possibility of underground imbalance between heat emission and absorption has a negative impact on the performance of ground-source heat pump systems （GSHPs）. Numerical and experimental researches were made in a residential building, which is supplied with a GSHP system and a ceiling radiation system combined with a replacement fresh air system. EnergyPlus simulations were used to estimate heating and cooling loads, and to assess the heat generated from the water pump, the fan and the heat pump unit. Then, Fluent simulations were used to compare three different control strategies of handling the underground heat exchange. These simulations were strongly based on an experimentally verified model. It is obtained that a ratio between cooling and heating loads is 5.08 ： 1 in a case study in Nanjing. Moreover, the control strategy based on the starting time is more efficient and reliable than the temperature and temperature difference strategies to control the underground heat exchange.

主动式热平衡NG-CHP与GSHP耦合分布式系统集成研究

针对浅层地热能应用过程中尚未解决的热平衡控制、天然气基分布式能源系统含硫低温烟气余热无法回收利用两个关键问题,基于能的综合梯级利用以及主动式热平衡思想,提出基于主动式热平衡集成机理的燃气轮机与热泵耦合一体化应用分布式热电联产系统,借助新型集成方式将含硫低温烟气余热回收与土壤源热泵一体化应用,不仅同时解决含硫低温烟气余热回收以及热失衡问题,并大幅提高系统热力性能与系统运行稳定性。采用流程模拟软件Aspen-plus完成新型系统以及参比系统性能对比计算,计算结果表明,较之参比系统,该新型系统总能系统效率达到82.7%,较参比系统73.8%,提高8.9个百分点;?效率为28.8%,较参比系统25.8%,提高3个百分点。该新型统的集成方法与思路为中低温烟气余热的高效应用提供一种新解决途径。

Numerical simulation on heat transfer performance of vertical U-tube with different borehole fill materials

Heat exchange performance of vertical U-tube heat exchanger was studied with two different borehole fill materials and CFD software. Borehole surface temperature and water temperature distribution were simulated on the condition of continuous operation for 8 h in winter with inlet water temperature being 10℃. The results show that there is no obvious difference on heat exchanger performance between the two different borehole fill materials.

Techno-economic analysis of single U-tube and double U-tube heat exchangers in Chongqing area

On the basis of practical projects in Chongqing,the thermal performance of heat exchangers (single U-tube type and double U-tube type) of the ground-source heat pump (GSHP) system in the hot summer was obtained and analyzed. The data obtained from test could match with the result deduced from theoretical calculation. From the test results,the cooling capacity of double U-tube is 1.6 times that of single U-tube. Taking cost per depth per watt Clq as the evaluation standard,Clq of single U-tube is 4.69 RMB$/W,and Clq of double U-tube is 3.14 RMB$/W. The double U-tube heat exchangers usage should be prioritized.

湿土壤含湿特性对传热影响研究

针对于地源热泵地能换热系统在具有热源条件下土壤热湿迁移现象,进行了初步分析和实验,并对模拟计算应用可行性进行了认证。土壤含水静态传热实验,目的在于探讨土壤含湿程度对传热能力的影响,以及地下含水程度对换热区域换热性能的影响。研究土壤不同含水率情况下的传热性能,从而推断含水率在工程中的影响程度。

U型管埋地换热器三维传热模型及实验对比分析

针对U型管埋地换热器的传热特点,考虑了两管脚之间的相互影响,建立起非稳态传热模型。采用数值解法对该理论模型进行了求解,并将结果与实验值进行了对比分析,发现两者变化趋势一致,但理论计算结果比实验测试值低,其中的一个重要原因是因为换热器与土壤间的热交换不是纯导热过程,还应该进一步考虑土壤中热湿迁移等因素的影响。

地温规律及其可恢复特性增强传热研究

利用间歇过程 ,恢复地下温度 ,弥补土壤传热慢特点。在地源热泵地能应用中 ,提高地下换热能力 ,减少井数 ,最大地发挥每一换热单元的换热能力。实验是在建造的两口分别为 10 0m和 2 0 0m竖直换热井的地源热泵系统上完成 ,并分别进行了自然状况地下温度分布、连续运行地温变化规律和间歇性地温变化规律的试验研究工作。着重对间歇性恢复过程地温变化趋势进行了研究。间歇时间可以改变温度变化规律和趋势 ,实现更佳的热泵运行工况。因此 ,文中提出的可控间歇技术对未来发展利用地能供热供冷系统具有重要意义和应用价值。

基于TRNSYS的土壤源热泵热平衡问题的影响因素分析

夏热冬冷这种冷负荷占优地区,若由土壤源热泵系统承担所有的空调负荷,则会造成全年土壤取放热量的不平衡,从而出现常年运行后土壤温度的逐渐上升,降低系统夏季的运行效率,不利于系统持续稳定高效的运行。为此首先利用模拟软件TRNSYS搭建土壤源热泵系统模型,对土壤源热泵系统长期运行性能进行模拟分析,从冬夏累计负荷比、埋管间距、埋管深度、土壤导热系数、回填料导热系数这几个影响因素出发,研究土壤源热泵长期运行的热平衡问题,以期对土壤源热泵系统的合理应用和发展提供支持。

间歇过程地温恢复特性及其规律模拟计算分析

通过试验和模拟分析 ,研究了地源热泵 ( GSHP)地能利用中 ,间歇控制过程对系统输出性能的影响、对井壁附近温度恢复的影响以及井的结构参数对系统输出性能的影响。试验和模拟计算结果表明 ,间歇控制技术能使井壁附近温度得到有效恢复 ,对发展利用地能供热供冷系统具有非常重要的实用价值。

地源热泵竖直埋管数值线源综合模型

为了在保证计算精度的基础上提高地源热泵换热器传热模型的计算速度,基于对地源热泵换热器地下竖直埋管非稳态传热分析,探讨了数值模拟和有限长线热源模型求解的特点,提出了数值计算与有限长线热源综合模型(数值线源综合模型).模拟结果表明:该模型与其他同类模型相比,避免了在替代半径以外区域用数值方法的反复迭代求解,从而在保证精度的条件下,可以快速模拟地下温度响应,尤其对于春秋季长期停机后土壤温度变化的模拟,能够迅速求出土壤温度恢复情况.文中还给出了一般情况下综合模型中替代半径的取值.

地下群井换热强化与运行模式影响规律

利用传热模拟分析,研究了地源热泵(GSHP)地能利用中地下群井多源换热及其运行模式影响规律。探讨间歇运行模式和连续运行模式对群井区域内温变特性的影响规律及各井热源的交互影响。分别对间隔周期、传热能力和温度场变化等进行了综合分析,指出运行模式调控有利于强化地能利用以及多井源间的协调排列。为地能在地源热泵供热供冷中大规模利用奠定理论基础。

超强吸水树脂与源土混合作为地源热泵供热系统回填材料的实验研究

在热泵制热工况下,超强吸水树脂与源土混合作为回填材料,分别对螺旋盘管、U型管以及整个系统进行了实验研究,得出系统性能变化曲线。实验结果表明,超强吸水树脂与源土混合作为回填材料,特别是螺旋盘管换热器,可明显增大地下换热器换热量,提高地源热泵系统的效率和稳定性,适用于干旱、土壤非饱和以及地下水位比较低的地区。

地源热泵非连续过程地下传热特性及其控制

通过试验和模拟计算,研究了地源热泵在地能利用中实施非连续运行操作过程的地下温度变化规律,并对可变负荷间歇过程进行了研究,指出负荷周期调节可以实现地温变化趋势的控制。通过控制地温变化可使热泵机组运行在有利的温度工况下,提高地源热泵系统的运行性能系数。利用空调系统的经常性非连续运行特点,实现有效的非连续性控制对未来利用地能具有重要的应用价值。

群井地下换热系统初温和构造因素影响传热的研究

利用传热模拟计算 ,研究了地源热泵 (GSH P)地能利用中群井系统初态因素对温变特性的影响规律。探讨地下初始温度、井群基本构造尺寸等对地下土壤温度场分布的影响。指出土壤初始温度是决定土壤源热泵运行的重要因素 ,初始温度提高 1倍 ,系统运行时间和输出总热量增加约 2 4倍。小井径对负荷因素影响更加敏感 ,相同的热负荷下 ,热流密度高 ,温度场变化剧烈。对于大井径而言 ,温度场变化相对平缓 ,但更易于发生井间传热交互影响。初态因素是强化地能利用中的重要因素之一 ,据此合理布置大区域群井意义重大。

一种新型的地源热泵与冰蓄冷空调联合运行系统

分析了目前国内外地源热泵与冰蓄冷空调系统的研究现状、技术优点及存在的问题。进而论述了两者联合运行的必要性,在此基础上构思出了一套以生态理念构建的复合式新型能源系统。最后结合目前国内在建的首个地源热泵及冰蓄冷中央空调系统工程,阐述了该工程冬季供暖,夏季制冷的控制策略,并对该新系统的经济性做了初步的分析。研究表明,该新型的复合式能源系统具有广阔的发展前景。

运行模式对地埋管换热器热交换性能的影响试验

运行模式对地埋管换热器的热交换性能具有显著影响。文章借助桂林理工大学建立的地源热泵实验平台,对桂林地区地源热泵制冷工况下3种运行模式进行试验,研究地源热泵的运行状况及管壁温度变化特性,分析运行模式对地埋管热交换性能的影响规律。研究结果表明：3种运行工况下,地源热泵机组的性能系数COP分别为4.30,4.03,3.48,竖埋管单位管长换热量为14.4~32.8 W/m,水平埋管单位管长换热量为14.8~17.9W/m;地埋管的管壁温度随着地源热泵的运行发生变化,其恢复程度与停机时间的长短有关;间歇运行模式有利于土壤温度场的恢复,提高地埋管换热器的热交换性能;停运比Ps-o由0变化到1时,热泵机组性能系数COP增加了15.8%。