Ground source heat pump can increase the low-level heat energy in the earth in winter, heat buildings, and reduce the temperature in the earth at the same time, that is, store cold energy for summer use. In summer, the heat in the building is transferred to the ground through the heat pump to cool the building, and at the same time, the heat is stored underground for use in winter. Ground source heat pump system mainly uses groundwater or surface water and rock and soil as low-temperature heat sources, and it is composed of water source heat pump unit, geothermal energy exchange system and building system respectively. Ground source heat pump system mainly uses shallow surface energy storage, which is not limited by geographical location and can be used indefinitely. This kind of energy is called renewable energy. The ground source heat pump technology using this renewable energy has the advantages of energy saving, high efficiency and low operating cost.
1 heat balance of ground source heat pump
1. 1 The cooling and heating load of the shallow surface is unbalanced.
Ground source heat pump is a kind of geothermal heat exchanger which extracts the temperature difference energy of shallow surface and then diffuses the heat source and heat sink to the surrounding surface through heat pump unit. Therefore, it is necessary to consider the balance between extracting heat energy from shallow surface and releasing heat energy all the year round when operating the ground source heat pump system using shallow surface heat energy. This is what we often call the heat balance of ground source heat pump. Because the climate difference in China is obvious, especially in the northwest. This leads to the imbalance of cold and heat load on the surface of buildings in most parts of China, which makes the surface of buildings in a state of heavy cold and heat load all the year round, and even leads to what we call "heat accumulation" in underground soil because of the inconsistency in extracting and releasing heat from the surface all the year round, which is actually the imbalance of soil heat. If this problem occurs, it will be difficult for the earth's soil to repair itself, and even the energy in the earth's soil cannot be recycled. This is the main reason for the imbalance of soil heat, and this objective factor is difficult to change. If the soil runs under "heat accumulation" for a long time, it will often exceed the heat dissipation capacity of the soil, which will eventually lead to the gradual deviation of the temperature in the soil from the original temperature, which may lead to the continuous increase or decrease of the shallow surface temperature, thus seriously reducing the cooling effect and efficiency of the heat pump unit in summer, and ultimately affecting the operating efficiency of the heat pump unit.
1.2 design problems of ground source heat pump
Ground source heat pump operates according to the law of extracting and releasing heat energy from the shallow surface, which can cool the surface buildings in summer and keep them warm in winter. When the ground source heat pump runs alternately in summer and winter, the surface soil becomes the carrier and transmission medium of energy, and it spreads radially outward from the vicinity of the buried pipe. The decrease or increase of soil temperature within the thermal diffusion radius and the diffusion of each borehole itself are very important. This is because the soil itself is a huge energy storage body. When storing energy, the energy storage volume will continue to increase, thus reducing the variation range of the average soil temperature. Therefore, if the holes are arranged reasonably within a certain distance, thermal interference between buried pipes will not occur, which can avoid the continuous superposition of temperatures and alleviate the state of soil temperature decreasing or rising rapidly. Ground-source heat pump runs under heavy cold and heat load all the year round, which is easy to cause heat balance problems and lead to "heat accumulation", thus increasing the temperature difference between cold and heat of the earth's soil and having a great impact on the ecological environment. This problem has always been everyone's concern. According to relevant data, the quality of each ecological environment is closely related to the heat flow around it. In areas with high heat flow, the ecological environment is better, and the more perfect the ecosystem, the better the ecological environment. However, the ecological environment in low geothermal flow area is relatively poor, and geothermal flow directly affects the surface ecosystem of a region. The decrease of ecosystem energy will affect the diversity of ecosystem in a region, thus affecting the stability of ecosystem in this region. Ground source heat pump system will pulsate ground heat flow, and the fluctuation of ground heat flow will affect the precipitation distribution and the degree of dryness and wetness in an area. Therefore, the temperature difference in this area is gradually increasing, which has a great impact on the ecosystem of the surface.
2 Countermeasures for Heat Balance of Ground Source Heat Pump
2. 1 Correct understanding of ground source heat pump
First of all, we should understand and correctly understand the essence of ground source heat pump. Some people tend to think that ground source heat pump is actually a technology that facilitates shallow heat exchange to achieve the purpose of heating and air conditioning, and it is an inexhaustible constant temperature heat energy. In fact, we should take the heat energy in the "constant temperature zone" as the "energy storage body", that is, release as much heat energy as possible from the ground to ensure the balance of heat sources. This has become the only solution to correctly design and use the system at present. The key to solve the problem of land heat imbalance. In addition, in areas where the load gap between winter and summer is large, whether to install auxiliary cold and heat source equipment should be considered first to eliminate or reduce the heat energy released by underground buried pipes, especially in areas where the heat load is greater than the cold load in northern China, the depth and length of buried pipes can be designed according to the summer cold load. Auxiliary heat energy is used as a supplement to solar energy or boiler or solar energy. In the south of China, where the cooling load is greater than the heat load, it is necessary to calculate the depth and length of buried pipes according to the winter load to assist the heat recovery technology or cooling tower and reduce the influence of ground source heat system on the thermal energy of underground soil.
2.2 Reduce underground heat exchangers
In order to reduce the influence of ground source heat pump on shallow surface, we must first reduce the density of ground heat exchanger and increase the layout area of ground heat exchanger, which is easily limited by the actual situation. In recent years, the buried pipe technology of pile foundation can solve the problem of insufficient buried pipe area to a certain extent, that is, burying underground U-tube heat exchanger in the concrete pile foundation of buildings expands the buried pipe area, and also forms the heat exchange between pile foundation and surrounding land, thus reducing the construction cost of drilling and buried pipe. Finally, by matching the buried heat exchanger in the pile foundation, the occupied area is reduced. Building pile foundation has different structures, which can make the pile foundation and U-shaped pipe fit closely, thus reducing the resistance between them and finally strengthening the heat transfer function of soil.
Thermal application of ground source heat pump
In this paper, the thermal engineering of ground source heat pump in an office building in a certain area is selected as a research example. First of all, we should build a model of an office building on the computer, divide the area according to the function, and then divide the buildings according to the types of buildings. Then, according to the architectural drawing of the office building as a reference, the architectural model is established with DeST software. Then according to various data parameters, such as thermal parameters of envelope structure, outdoor design parameters, indoor design parameters and so on, reference and comparison are made. Then, Tsinghua University DeST load simulation software is used for simulation. According to the architectural drawings and air conditioning design parameters of the office building, the building load model can be established in DeST load simulation software, and then the hourly dynamic load simulation of air conditioning in the office building can be started, and finally the hourly load of the office building can be obtained. From the data, it is found that the general comfort air conditioning system will not cool in the heating season in the actual operation process, and sometimes the unit will be turned on to adjust the cooling and heating load in the transition season. From the simulation results of hourly load throughout the year, reasonable correction can make the simulation results more realistic. Finally, the revised load hour chart should be analyzed according to the local principle. It is found that the air conditioning load is the largest in July and August, and the maximum load in the heating period of air conditioning appears from February to February. According to the hourly load calculation, the design heat load of the building is less than the design cooling load, which will cause the air conditioning design load to be unable to bear the maximum load and lead to continuous operation. Therefore, it is very necessary to understand the operating characteristics of the system under partial load to improve the system operation.
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