气候条件对地源热泵系统性能的影响-外文翻译

1、气候条件对地源热泵系统性能的影响摘要： 在中国的建筑物中，初级能源的30用于加热和冷却。在这方面应用最广泛的设备是锅炉和空调。在许多应用中，热泵是唯一能满足加热和冷却要求的运行方式，因为他们可以利用建筑物周围的可再生能源。在本文中，对气候对应用地源热泵系统技术的影响进行了对比讨论。对结果进行分析能得出以下结论：如果只从土壤中吸取热量，在两个月后，地源热泵附近的土壤温度将减少到20 摄氏度以下。如果向土壤排入相同的热量三个月，土壤温度将会超过37 摄氏度，那将不再适合于空调系统。 为了使作为热源/ 冷源的土地资源实现可持续利用，就应该使向土地排入的热量与从土地吸取的热量保持平衡。在一些热不平衡的

2、工程实例设计中，一些措施是可以考虑的。关键词： 气候条件；地源热泵；热不平衡1. 导言用于家庭取暖和降温的能源消费量在世界能源消费量中所占的比例是一样的。 在中国大约一半的初级能源是以煤的形式供给的，而煤是不可再生能源。在很多应用中，地源热泵 (GSHPs)是供暖和降温的最有效方式， 因为它们依赖于建筑物周围的可再生热源。 Lund JW(2000)指出地源热泵系统可以看成一个能高效利用能量的机械系统， 而且比空气源热泵多了几个明显的优点。主要有： (a) 他们消耗较少的能量来维持运转， (b) 在极低的外界温度下，他们不需要补充热量， (c) 他们使用较少的制冷剂， (d) 他们的设计比较简

3、单，并且后期的维修保养费用较少， (e) 他们并不需要专门的设备去查找那些因暴露而风化的部位。不过，主要的缺点是初期投资比较高，大约比空气源设备高出 3050。这是由于要花费额外的人力物力来埋设热交换器或者为能源提供一口储蓄井。但是，一旦安1,2装完毕后，就整个系统的使用寿命而言每年的费用是比较低的，从而导致了净储蓄在地源热泵应用中，对土壤热能的储存或提取是通过地热换热器(GHE)实现的。地热换。热器和贴邻的土壤之间的传热主要是热传导并在以一定程度上是以水分迁移的方式实现的 3 。因此，它主要依赖于土壤类型，温度和湿度梯度。热提取/ 储存的整个过程是暂时性的。从与地面水平或垂直铺设的管道提取/

4、 储存热量。热容量随潮湿程度和气候条件的变化而变化。因为热量的提取/ 储存会提高 / 降低土壤温度，温度完全复原是有可能4的。纵向回路系统被认为运营操作较好，特别是在制冷模式中。但是，人们发现在高出土壤饱和度 50的水分含量影响下，相对来说，热泵就没有实际价值了 5 。垂直式地热换热器通常是在垂直钻孔中插入一个或两个高密度聚乙烯 U 型管来充当接地环路的，分别称之为单 U 型管，双 U型管或套管地热换热器。本篇研究报告分别在制冷和制热模式下，对这三种类型的地热换热器进行了性能分析。下一部分的描述中，一套试验设备在一所大学研究的基础上第一次进行建造和测试，并在广州市成功实施。沈阳农业大学学士学位

5、论文外文翻译2. 系统说明构成试验系统的示意图如图1 所示。该系统主要由两个独立的环路构成：(a) 水环路， (b) 冷媒环路。在水环路中配置一个水塔，以补给足够的水。冷媒环路是由两个闭环铜管组成的。热泵的工作流体是R-22。图 3 中给出了这三个地热换热器的主要特点，图 3 中标有 (a) 单 U 型管， (b) 双 U 型管，和 (c) 套管。这些地热换热器在并联接法方式下运行。图 2 中描绘了地热换热器的配置线路。图 1. 地源热泵系统图 2. 地热换热器周围热电偶的分布地热换热器有30 米的深度，换热器间的间距是5 米。沿地热换热器垂直布置六个热电偶，用来获取土壤的温度。从上往下，这六

6、个热电偶之间的距离是10 米、8 米、 6米、 3 米和 3 米( 图 2) 。图 2 中的黑色圆点表示了热电偶的位置。热电偶的输出温度被传输到数据记录器中并记录在计算机中。热电偶也被用来测量水和冷媒的进出口温度。为了获得地热换热器的进出口水温或者冷凝器和蒸发器的冷媒温度， 热电偶被安置在管内的各个测试位置。正如图 1 描绘的那样，转子流量计被用来获取每一个地热换热器的流速。制热循环转换到制冷循环是通过一个四通阀实现的。从夏季到冬季该实验室都能够适应。1气候条件对地源热泵系统性能的影响图 3. 垂直式地热换热器的钻孔示意图(a) 双 U型管 (b) 单 U 型管 (c) 套管3. 结果与讨论对

7、地源热泵进行的各项测试是在稳态条件下进行的，以确定整体系统的性能特点。对于每个钻孔， 钻孔壁所反映的温度 ( 土壤温度 ) 是由构成地热换热器的两个部分加热达到的：一部分温度增加 / 减少是由于运行过程中钻孔本身的线源 (U 型管 ) 所导致的，另一部分是由土壤的湿度所导致的。(a) 夏季(b)冬季图 4. 不同季节周围空气的温度和湿度的分布土壤湿度主要受空气湿度的影响。 图 4 中分别显示了夏季和冬季周围空气的平均温度和湿度的分布情况。该图显示夏季平均温度是 29 摄氏度，冬季平均温度是 16 摄氏度。空气湿度随季节变化而有很大波动并且在夏季最高。 空气的平均湿度在夏季是 70，在2沈阳农业

8、大学学士学位论文外文翻译冬季是 50。因为在广州夏季持续的时间要比冬季长，所以该项测试在夏季持续了 100 天，而在冬季只持续了 49 天。(a) 夏季(b) 冬季图 5. 不同季节换热器周围的土壤温度图 5.(a) 和(b) 显示了不同季节20 米深度处的土壤日平均温度。热泵开启40 小时后作为记录起始点。在试验的开始阶段，夏季的土壤温度是28 摄氏度。由试验得知，土壤温度迅速上升。逐渐地，从第40 天至第 90 天，由于正处于热平衡状态，温度的升高很轻微，最后不同钻孔的温度停留在一个稳定的点，此时平均温度超过37 摄氏度。冬季的土壤温度呈现相反趋势，从开始的 22 摄氏度左右降到稳态下的

9、17 摄氏度以下。在这里必须指出，当夏季土壤温度高于 37 摄氏度和冬季低于 17 摄氏度之后，热泵开始间歇运行。这就是说，土壤温度已达到其传热的极限容量，已不再满足空调系统运行的条件。3气候条件对地源热泵系统性能的影响(a) 夏季(b)冬季图 6. 不同季节不同地热换热器的传热能力(a) 土壤温度分布(b)传热能力分布图 7. 制冷模式下运行一年后的土壤温度和不同地热换热器的传热能力在不同季节受空气温度、湿度和土壤温度的影响，不同地热换热器的传热能力有很大的变化。正如图 6.(a) 和(b) 分夏季和冬季所显示的那样，随着运行时间的延长， 不同地热换热器的每米传热能力逐渐下降。在夏季，单U型

10、管和双 U型管每米传热能力的变化幅度大致是一样的， 从开始约 40 瓦特 / 米下降到 30 瓦特 / 米以下，特别地，在运行 40 天后，其降幅最大。在运行 40 天后，套管的传热能力下降到 20 瓦特 / 米以下。原因就是上文所述的土壤传热特性日益恶化。这于图 6.(b) 所呈现的相类似。热泵停止运行一段时间后，单 U型管和双 U型管的传热能力将从起始的 60 瓦特 / 米下降到能从土壤吸取热量的 45 瓦特 / 米以下。套管的传热能力将从 45 瓦特 / 米下降到 25 瓦特 / 米以下。正如上文所述，热泵系统不能连续运行。运行一年后，土壤温度要恢复到热泵能够再次运行的水平。图 7.(a

11、) 显示了制冷模式下运行一年后的土壤温度。 土壤温度从开始的 25 摄氏度上升。图 7.(b) 显示了制冷模式下运行一年后地热换热器的传热能力分布情况。能够4沈阳农业大学学士学位论文外文翻译看出，在相同的运行阶段，这三种地热换热器的传热能力与图 6.(a) 所示的相比是比较高的。对结果进行分析可以得出，在混合运行一定时间后地热换热器和土壤的传热性能都有所提高。向土壤排放的热量应该与从土壤吸取的热量保持平衡。4. 结论本文进行了一系列试验，来说明气候对应用地源热泵系统技术的影响。从结果可以看出，气候条件对地源热泵系统性能的影响非常显著。如果仅是吸取热量，两个月后，换热器附近的土壤温度将会下降到

12、20 摄氏度以下。如果仅是排入热量，三个月后，土壤温度将会超过 37 摄氏度，这已不再满足空调系统的运行条件。为了使作为热源 / 冷源的土地资源实现可持续利用， 就应该使向土地排入的热量与从土地吸取的热量保持平衡。作为最后的结论， 应该使地源热泵的地热换热器能够适应具有更多优势的中国南方气候。在一些热不平衡的工程实例设计中，一些措施是应该考虑的。由广州科学工程项目主办2005Z3-D0491。原文出处： Xiangyun LIU,Min YANG,Ying CHEN,etc.EFFECT OF CLIMATIC CONDITIONS ON THEPERFORMANCEOFGROUNDSOURC

13、EHEATPUMPSYSTEMA.InternationalCongressofRefrigeration C.Beijing:2007.1-7.5气候条件对地源热泵系统性能的影响EFFECT OF CLIMATIC CONDITIONS ONTHEPERFORMANCE OFGROUND SOURCE HEAT PUMPSYSTEMABSTRACT: Heating and cooling in buildings consume about 30% of the primary energy used in China. The most widely applied systems in

14、 this aspect are boilers and air-conditionings. Heat pumps are the only monovalent action way to satisfy the requirements of heating and cooling in many applications,becausethey can use renewable energy in the building s surroundings. In this paper, a comparative discussion is given to the effect of

15、 climatic on applying ground source heat pump system technology.Analysis of the results can lead to the following conclusions: If only extracting heat from the earth,in two months, the soil temperature near the GSHP would be reduced to lower than 20 . If only injecting mheat for three months, the so

16、il temperature would be over 37 , which is no longer suitable for air-conditioning. To preserve the ground resource for sustainable utilization as heat source/sink, it should be balanced between the heat injected to the ground and that extracted from the ground. Some measures can be considered in th

17、e design for the case of heat unbalance.Key words: climatic condition, Ground Source Heat Pump, heat unbalance.1. INTRODUCTIONDomestic heating and cooling consumption are responsible for a average percentage of world energy consumption. About half of this primary energy in China is consumed in the f

18、orm of coal,which can not be regenerated. Ground source heat pumps (GSHPs) offer the most efficient way to provide heating and cooling among many applications, as they rely on renewable heat sources of the building's surroundings. Lund JW (2000) observed that ground source heat pump system was c

19、onsidered to be a machine system which can use energies efficiently, and GSHPs have several advantages over air source heat pumps. These are: (a) they consume less energy to operate, (b) they do not require supplemental heat at extremely low outside temperature, (c) they use less refrigerant, (d) th

20、ey have a simpler design and less maintenance subsequently and (e) they do not require the unit to locate where it is exposed to weathering. However, the main disadvantage is the higher initial capital cost, being about 3050% more expensive than air source units. This is due to the extra expense and

21、 effort to bury heat exchangers in the earth or provide a well for the energy sources. However, once installed, the annual cost is less over the life of the system, resulting in net savings 1, 2. In ground heat pump applications, deposition or extraction of thermal energy from the ground is accompli

22、shed through a ground heat exchanger (GHE). Heat transfer between the GHE and adjoining soil is primarily by heat conduction and to a certain degree by moisture migration3.Therefore, it depends strongly on the soil type, temperature and moisture gradients. The entire process of heat extraction/depos

23、ition is a transient one. Heat is extracted/deposited from pipes laid horizontally or vertically in the ground. The thermal capacity of the soil varies with the moisture content and the climatic condition. Because the extraction/deposition of the heat will raise/reduce the ground temperature, comple

24、te temperature recovery may be possible. Vertical loop systems are known as operating better, especially in the cooling mode 4. It was6沈阳农业大学学士学位论文外文翻译found, however, that the effect of moisture content variation above 50% of saturation on ground heat pump performance is relatively insignificant 5.

25、The vertical ground heat exchangers are usually constructed by inserting one or two high-density polyethylene U-tubes into vertical boreholes to serve as the ground loops, which are referred to as single U-tube, double U-tube or cannula GHEs, respectively. The study reported here includes the perfor

26、mance analysis of three types of ground heat exchanger described above at cooling and heating mode. An experimental set-up, described in the next section, is constructed and tested for the first time on the basis of a university study performed in city of Guangzhou.2. System descriptionA schematic d

27、iagram of the constructed experimental system is illustrated in Figure1. This system mainly consists of two separate circuits: (a) the water circuit, (b) the refrigerant circuit. A water tower is configured in the water circuit to supply enough water. The refrigerant circuit is built by the closed l

28、oop copper tubing. The working fluid of the heatpump is R-22. The main characteristics of three ground heat exchangers (GHE) are given in Figure 3, which are marked with (a)Single U-tube, (b)Double U-tube, and (c) Cannula. These ground heat exchangers operate in parallel connection. The ground heat

29、exchangers are configured in line as depicted in Figure 2.Fig.1 Ground source heat pump system Fig.2 Distribution of thermocouples around GHEThe ground heat exchangers are 30m depth, and the space between GHEs is 5m. Six thermocouples are configured along the ground heat exchange vertically to obtai

30、n the temperature of soil. The distance between thermocouples are 10m、8m、6m、3m and 3m from down to up(Fig.2). The black dots in Figure 2 denote the position of the thermocouples. The output temperature of the thermocouples are transferred to a data logger and are recorded in a computer. Thermocouple

31、s are also used to measure the inlet and outlet temperature of water and refrigerant. To obtain the inlet and outlet water temperature of the ground heat exchanger or refrigerant temperature of condenser and evaporator, thermocouples are put inside the tube7气候条件对地源热泵系统性能的影响at every tested position.

32、Rotameters are used to obtain the flow rate of every ground heat exchanger as depicted in figure 1. Conversion from the heating cycle to the cooling cycle is obtained thtough a four-way valve. The laboratory will be conditioned during the summer and winter seasons.(a)(b)(c)Fig. 3. Schematic diagram

33、of boreholes in the vertical GHE:(a) double U-tube and (b) single U-tube.(c) cannula3. Results and discussionThe tests conducted on the GSHP system are under steady state conditions to determine the overall performance of the system. For each borehole, its temperature (soil temperature) response on

34、the borehole wall to heating of the GHE consists of two parts: the primary temperature increase/decrease due to the line source (U-tube) in the borehole itself during the operation and the second one caused by the humidity of the soil.(a) In summer (b) In winterFig. 4. Distributions of temperature a

35、nd humidity of ambient air in different seasonThe humidity of the soil is affected mainly by the humidity of air. The mean temperature and humidity of ambient air were distributed in Fig.4 for summer and winter individually. The figures present that the mean temperature is 29 in summer and 16 in win

36、ter. The8沈阳农业大学学士学位论文外文翻译humidity of the air varies greatly all the season and is higher in summer. The mean humidity of the air is 70% in summer and 50% in winter. Because the summer season is longer than winter season in Guangzhou, the tests have been carried out in summer for 100 days, and for 49

37、days in winter.Fig.5 The ground temperature around ground heat exchanger in different seasonsThe average day ground temperature in different seasons at 20m depth are presented in Fig.5(a) and (b).The initial points are taken 40 hours after the pump start. At the beginning of the experiment,the groun

38、d temperature is about 28 in summer. As the experiment proceeds, the temperature increases rapidly. Gradually, from the 40th day to the 90th day, because the heat balance is being established, the temperature increases very slightly and finally stays at a stable point for different boreholes, and th

39、e mean temperature rises over 37 . The ground temperature in winter shows a reverse trend, decreasing from around 22 atthe beginning to lower than 17 when stabilized. It must be mentioned here that the heat pump begin to run intermittently after the ground temperature is over 37 in summer and lower

40、than 17 in winter. It means that the ground temperature has reached its ultimate capacity for heat transfer, which is not suitable for air-conditioning any longer.9气候条件对地源热泵系统性能的影响(a) In summer (b) In winterFig.6 Heat transfer capacity of different ground heat exchanger in different seasons(a) Groun

41、d temperature distributions (b) Heat transfer capacity distributions Fig.7 Ground temperature and Heat transfer capacity of different ground heat exchanger at cooling mode after a year runningAffected by the air temperature, humidity and ground temperature in different seasons, the heat transfer cap

42、acity of different ground heat exchangers varies greatly. As shown in Fig6(a) and (b) for summer and winter individually, the per meter heat transfer capacity for different GHEs decreases with the increase of the operating time. In summer, the per meter heat transfer capacity of single U-tube and Do

43、uble U-tube change similarly, which decreasefrom about 40W/m at the beginning to lower than 30W/m, and specially decrease greatly after running for 40days. The heat transfer capacity of cannula decreasesto lower than 20W/m after running for 40 days. These are because of the deteriorating of the heat

44、 transfer characteristics of ground described above. The case is similar in winter as presented in Fig.6(b). After a period of stopping operation of heat pump, the heat transfer capacity of single U-tube and Double U-tube decrease from about 60W/m at the beginning to lower than 45W/m when extracting

45、 heat from ground. The heat transfer capacity of cannula decreases from 45W/m to lower than 25W/m. The heat pump system can not be operated continuously just described above. After running for a year, the ground temperature recovered to a level in10沈阳农业大学学士学位论文外文翻译which the heat pump can operate aga

46、in. Fig.7.(a) shows the ground temperature at cooling mode after running for a year . The ground temperature increases from 25 of the beginning . Fig.7(b) presents the heat transfer capacity distributions of GHEs at cooling mode after running for a year. It can be noticed that the heat transfer capa

47、city of three GHEs are higher compared to that presented in Fig.6 (a) during same operation times. Analyzing the results, it can be inferred that the heat transfer characteristics of GHEs and ground have been enhanced after a certain time of hybrid operation. The heat emitted to the ground and heat

48、extracted from the ground should be balanced.4. ConclusionsThis paper conducted serial experiments of the effect of climatic on applying Ground source heat pump system technology. From the results, it can be conducted that climate conditions significantly affect the performance of Ground source heat pump system. If only extracting heat, after two months, the Ground temperature near the GHEs would