Current situation and application of the hottest g

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The current situation and application of ground water source heat pump

Abstract: This paper introduces the basic working principle of ground water source heat pump and its engineering application examples in China, analyzes the main problems existing in the technology of ground water source heat pump, and expounds its own views and thoughts

Keywords: low-level heat source ground source heat pump groundwater 0. Introduction

ground water heat pumps (GWHP) is a branch of ground source heat pumps (GSHP). This technology began in 1912, when zoelly of Switzerland put forward the concept of "ground heat source heat pump". In 1948, the first ground water source heat pump system was put into operation in the federal building in Portland, Oregon. In the following decades, groundwater source heat pumps have been more widely used. In the past 10 years, the annual growth rate of groundwater source heat pumps in the United States has been 12%. Now about 500000 sets of groundwater source heat pumps (each equivalent to 12KW) are in operation, and about 50000 sets of groundwater source heat pumps are installed every year. China's underground water source thermal measurement after fracture length and cross-sectional area pump from improving the energy utilization efficiency of the plastic granulator process and preventing and controlling environmental pollution are complementary. In 1997, China began to learn and introduce European products, and a large-scale underground water source heat pump heating project appeared. By the end of 1999, there were about 100 underground water source heat pump heating or cooling systems in China [1]

in China, coal, as the main energy, has occupied an absolutely dominant position in production and consumption for a long time. Although the proportion of coal has decreased slightly in recent years, it remains above 65% and shows signs of rising again [2]. Only by reducing the use of coal can the problem of air pollution be solved. China's urban and rural buildings have developed rapidly. In recent years, the residential area built every year has reached 400-500 million square meters in cities and towns, and 700-800 million square meters in rural areas, of which the construction area of heating and air conditioning is as high as 650million square meters. Compared with developed countries with similar climatic conditions, the heating energy consumption per unit area of residential buildings in China is about three times that of them [3]. Now, the use of heating in winter and air conditioning in summer in these high-energy buildings is becoming increasingly common, and it has become an urgent need to solve the problems of energy waste and environmental pollution caused by them. At present, China prohibits the construction of small and medium-sized coal-fired boiler houses in cities and towns. Therefore, in addition to the type of central heating, there is an urgent need to develop other alternative heating methods. Heat pump (including ground water source heat pump) is such a new heating and air conditioning technology that can effectively save energy, reduce air pollution and CO emissions

1. Basic working principle

the low-level heat source of groundwater source heat pump system is groundwater extracted from wells or abandoned mines. The heat pump unit absorbs heat from the underground water provided by the production well in winter. After improving the grade, it heats the building, transfers the heat from the low-level heat source to the place where heating and humidification are needed, and the underground water after heat extraction returns to the ground through the reinjection well. In summer, the production well is exchanged with the reinjection well, and the indoor waste heat is transferred to the low-level heat source to achieve the purpose of cooling or refrigeration. In addition, it can also play the role of well maintenance

if it is groundwater with good water quality, it can directly enter the heat pump for heat exchange. Such a system is called open loop. In practical projects, the heat pump circulating water system in the form of closed loop is more used, that is, the plate heat exchanger is used to separate the groundwater from the circulating water through the heat pump, so as to prevent the influence of sediment and corrosive impurities in the groundwater on the heat pump unit [3]

because the deeper stratum will not be disturbed by the change of atmospheric temperature, it can maintain a constant temperature all year round, which is much higher than the outdoor air temperature in winter and lower than the outdoor air temperature in summer, and has a large heat capacity. Therefore, the efficiency of groundwater source heat pump system is higher than that of air source heat pump. The COP value is generally between 3 and 4.5, and there is no frost and other problems. In addition, in winter, the heat pump absorbs the heat in the earth, increases the air temperature, and then heats the building. At the same time, it reduces the temperature in the earth, that is, it stores the cooling capacity, which can be used in summer; In summer, the heat of the building is transferred to the earth through the heat pump to cool the building. At the same time, heat is stored in the earth for winter use. In this way, it plays the role of energy accumulator in the ground water source heat pump system, and further improves the energy utilization efficiency of the air conditioning system throughout the year

the ground water source heat pump system can also produce domestic hot water, and there are roughly four ways to connect its waterways. The simplest way is to completely separate and associate the air conditioning water system and the domestic hot water system, and connect the well water system in series. However, the former has a small condensation temperature difference, and the latter can not solve the problem of reducing the capacity of the air conditioning system when the water source heat pump unit for domestic hot water is shut down. Therefore, the electric three-way valve is added on the basis of the latter, which not only reduces the installed capacity and initial investment, but also makes the configuration of the unit more reasonable and improves the total energy efficiency ratio of the system. In addition, there is a connection mode of domestic hot water using heat recovery water source heat pump units [4]. The latter two methods make full use of the energy of well water, and prepare domestic hot water by recycling the condensation heat of the air conditioning system, which improves the energy efficiency ratio of the whole system, which is more reasonable and energy-saving

domestic groundwater reinjection basically adopts the original artificial reinjection method, which is mainly divided into pressure reinjection and vacuum reinjection. Pressure reinjection is applicable to aquifers with high water level and low permeability, as well as underground aquifers with low water level and good permeability; Vacuum reinjection is only applicable to aquifers with low water level and good permeability. At present, most systems in China adopt the groundwater recharge method that users can test new materials by using three predefined structures to understand how to deposit empty recharge on the print bed. In addition, groundwater recharge is usually maintained by means of uplift and cleaning in China. The number and time of reinjection depend on the permeability of the aquifer, and then consider the characteristics of the well, water quality, reinjection volume and Reinjection Technology. These are very professional work, which greatly increases the maintenance workload of users. In this way, the gauge length clamped by the extensometer is the original gauge length of the sample in the free state, and this operation also causes great damage to the well, which will reduce the service life of the system [5]

2. Engineering application examples

in 1997, the Ministry of science and technology of China and the Department of energy of the United States signed the Sino US energy efficiency and renewable energy cooperation protocol, one of which is the development strategy of ground source heat pump. In 1998, China and the United States decided to establish a joint venture in Beijing (representing the northern cold zone) and Ningbo (representing

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