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Ground source heat pump system underground heat exchanger construction technology (Figure)
Underground heat exchanger is one of the key technologies in ground source heat pump system. Based on the project construction, this paper further studies the construction technology of this system. Including engineering drilling problems, grouting process, etc., the results of the study can be applied in the design and construction of the system, the actual project has a strong guiding significance. 0 Introduction Ground source heat pump refers to the traditional air conditioner condenser or evaporator extended underground to make it with shallow soil or groundwater heat exchange or through the intermediate medium as a heat carrier and the intermediate medium in a closed environment Through the shallow soil circulation flow. So as to realize a new energy-saving and environment-friendly new energy technology that can use low-temperature shallow ground to heat or cool the building. According to "GB50176-1993 Thermal Design Code for Civil Buildings", the number of days of cooling and heating in the hot summer and cold in the Yangtze River Delta is roughly the same, that is, the same heat and cold load. The use of this technology can give full play to the role of shallow surface energy storage and storage, to environmental protection, energy saving dual effect. Therefore, this technology is hailed as "the most effective air conditioning technology in the 21st century" [1]. Figure 1 for ground source heat pump working principle diagram. Figure 1 At present, the domestic research in this area mainly focuses on direct buried underground heat exchangers. Because with the application of heat pump technology to ground source technology matures, the study of underground heat exchanger has become the key to the technology. This article is the author to participate in the ground-source heat pump in Changchun Geotechnical Design and Construction Engineering based on further research. Ground source heat pump underground heat exchanger construction process shown in Figure 2. Figure 2 1 engineering drilling problems Engineering drilling is the construction of underground heat exchanger in the most important part of [2]. As the ground source heat pump underground heat exchanger into the depth of 40m ~ 100m between the construction of low difficulty, the rig used by the general survey of drilling rig or shallow core drilling rig. Table 1 lists several common rig types and their important parameters. Table 1 drilling method is relatively simple, the general use of positive or reverse circulation rotary drilling method. Figure 3 shows the positive cycle drilling. During the construction of drilling construction should first understand the geological conditions of the site, to master the existing geological profile. And should pay attention to whether there are underground pipelines and determine its exact location, in particular, pointed out that in the drilling process should promptly find the problems in drilling. Such as drilling loss, etc., which is essential for the entire system of environmental safety. And then clean up the site, eradication of weeds on the ground, clean up debris and floating soil. Determine the exact location of the hole. At the same time, taking into account the grouting slurry overflow from the hole, so before construction can design and layout of the drainage ditch. Ordinarily potential digging, and in the groove end connected to a grouting pond. The mud generated in the drilling process can also be precipitated in the grouting pond and can be backfilled after being precipitated. Consider the impact on the environment, in particular, to consider the construction of the cause of the leakage of antifreeze and so on. Requiring casing for Quaternary loose formations during borehole drilling. Ensure the safety of the environment. Therefore, before drilling construction, it is necessary to design the hole structure of the project hole according to the formation obtained from the engineering survey. In the north, considering the depth of pipe burial, the depth of the shallowest burial pipe should be determined according to the depth of the frozen earth in winter. For example, the depth of permafrost in Changchun is between 140cm ~ 170cm. Therefore, the level of pipe often require buried depth of about 250cm. In the South, the effects of weather and seasonal changes as well as biological destructiveness should be considered. General requirements laying pipe should be less than 100cm. Figure 3 2U-tube connection method buried in the underground pipe must first ensure chemical stability, corrosion resistance, and have good thermal conductivity to ensure system performance. U-tube connection is the U-tube hot melt connection process. That is, the U-tube is first trimmed, cleaned, aligned, heated to the melting point, and then cooled down to be connected together. In order to ensure the normal operation of the system, it is necessary to ensure the U-shaped pipe connection is reliable, generally using hot melt connection, mainly for the following reasons: 1. The strength of the hot melt connection joint is greater than that of the U-shaped pipe itself. The thickness of the pipe wall at the joint part is large, so its strength also increases; 2. The joint or the connecting part is made of plastic material and there is no corrosion problem; 3. The U-shaped plastic pipe is clearly recommended by many industrial standards. In the industry, there are two kinds of hot melt technology: socket connection and docking. When the socket is connected, the ends of the two U-shaped pipes to be connected are respectively heat-welded with the two ends of a thick receiving pipe. To undertake the connection shown in Figure 4. Figure 4 docking, the two U-tube to be connected to the end of the heating plate while heating and connected together. Shown in Figure 5. Each connector only needs to be heated once. Connection, you must ensure that the two U-shaped pipe alignment, and the end of the formation of flat, welded after the two U-shaped tube must be fixed coaxial cooling 20s, to ensure the welding strength. U-tube connection during winter construction should be carried out indoors. 3 under the tube after drilling should be under the tube. Because of the large amount of sediment to be drilled, this reduces the effective depth of the borehole. Therefore, every time a hole drilled, u-tube or casing should be immediately put into. Figure 5 under the tube is a very crucial step, the success of the next tube determines whether the system can be installed successfully. The down pipe process so far has not reached the level of mechanization, automation. Artificial under the tube. More manpower required, there is a righting, under pressure, such as the division of labor. Under the tube, should try to maintain concentricity, and tube and tube do not close contact, in order to avoid heat exchanger "short circuit" phenomenon. After the down tube to be taken to prevent the floating fixed measures, and the end of the U-tube seal to prevent debris falling into the pipeline, the impact on the operation of the system. 4 Grouting grouting, the first cement, bentonite, sand and water in accordance with the design of a good ratio into the mixing machine stirring 2 ~ 3min, and then discharged into the low-speed mixing tank stirring. Grouting, the first open the valve into the slurry storage tank slurry, high pressure mud pump into the hole. Whether the density of the slurry is equal to determine whether to stop grouting, if equal, said the slurry has filled the hole, you can stop the grouting. Figure 6 shows the grouting system. Figure 6 5 Engineering Example Changchun City, Jilin Province ground source heat pump heating and cooling demonstration project is the use of direct heat exchange heat exchange, the combined effect of plumbing + fan indoor system ground source heat pump system. The construction site is located on the bank of Yitong River and is affected by river sedimentation. The upper 1m ~ 3m is miscellaneous fill, silty clay, pebbles and sand-bearing Quaternary formations. The lower part is bedrock, including shale, sandstone and limestone , Higher hardness level. Due to the influence of geological environment, the sand depth varies a lot, but the total depth does not exceed 10m. The design of 16 underground heat exchangers of 100m depth and 150-200mm diameter (obtained through the cores returning while drilling) Different aperture of the heat transfer to make the evaluation. Since the project was put into operation in January 2001, the project has been operating well and the system is operating normally. The system itself is basically maintenance-free (due to the experimental nature of the system, the test data must be read). The COP of system operation is 3.1 [3], which has good energy-saving effect. Because it does not cause pollution to the surrounding environment, the air in the room is served fresh by the fan, and the human body feels comfortable and environment-friendly.