What are the aspects of the ground source heat pump system and its advantages and disadvantages?

Today's energy-saving products have already become an important part of people's lives and work, but these are not a good indication that we have already prepared enough to have a good understanding of energy-saving products. Just like the advantages and disadvantages of the ground source heat pump system is not a kind of energy-saving products that every one of us knows.

The ground source heat pump air conditioning system is still in the primary stage in China. It needs to be adapted to local conditions, overall planning, energy characteristics and hydrogeological conditions, and gradually promote the ground source heat pump air conditioning technology, so as to help optimize the energy structure, in the premise of environmental protection. Next, improve energy efficiency. The following is a detailed analysis of the system form of the ground source heat pump and its advantages and disadvantages.
form:

1. Horizontal ground source heat pump

It is exchanged with the soil for cold and heat by a closed heat exchange system horizontally buried below 2 to 4 of the ground surface. This type of system is suitable for buildings with small cooling and heating areas, such as villas and small single-family buildings. The initial investment and construction difficulty of the system is relatively small, but the floor space is large.

2, vertical ground source heat pump

Through the vertical drilling, the closed heat exchange system is buried in the 50-400M deep rock and soil and the soil for cold and heat exchange. This kind of system is suitable for buildings with large heating and heating area, and there are certain open spaces around, such as villas and office buildings. The initial investment of the system is relatively high, and the construction difficulty is relatively large, but the floor space is small.

3. Surface water source heat pump

The ground source heat pump unit exchanges heat and cold with rivers, lakes, seawater, etc. through a closed heat exchange system arranged at the bottom of the water. This system is suitable for small and medium-sized cooling heating areas, buildings near the water. It utilizes the stable temperature and significant heat dissipation of the pool water or the lake underwater, and does not require drilling and trenching, and the initial investment is minimal. But there is a need for deeper, larger rivers or waters around the building.

4, groundwater type ground source heat pump

The ground source heat pump unit exchanges heat and cold with the deep groundwater pumped by the water pump through the closed loop system inside the unit through the heat exchanger. Groundwater is drained or injected into the groundwater layer by a pressurized pump. This system is suitable for large single buildings and small building communities with large construction area and limited open space.

In recent years, breakthroughs have been made in the development of geothermal energy. The Earth's surface water and soil is a huge collector that collects 48% of the energy from the Sun, more than 500 times the energy used by humans every year. According to the heat exchanger carrier partition, the ground source heat pump air conditioner mainly has four forms: one is the buried ground source heat pump; the other is the groundwater ground source heat pump; the third is the surface water ground source heat pump (including the sea water source, rivers, lakes, rivers or surface diving). The fourth is a hybrid ground source heat pump.

The surface is 30 to 130 meters downward, and the temperature throughout the year is relatively constant, generally around 15 to 20 °C. The ground source heat pump utilizes the characteristics of ground energy to realize the conversion from low temperature to high temperature or from high temperature to low temperature by consuming a small amount of electric energy, thereby fully utilizing the ground energy. In the winter, the heat in the low heat source is transferred to the place where heating or heating is needed. In the summer, the residual heat in the room can be transferred to the low heat source to achieve the purpose of cooling or cooling.

Advantages and disadvantages:

First, the advantages of ground source heat pump air conditioning

From the perspective of theory and energy consumption, ground source heat pump air conditioning technology uses the inexhaustible energy stored in the shallow or underground surface to become a form of renewable energy. Ground-source heat pump air conditioners are energy-saving because they use soil, surface water or groundwater as an energy source. Under the same working conditions, they only need to consume about 50% of energy to provide the same energy. Compared with lithium bromide technology, energy saving can reach up to 65. %; up to 40% energy saving than steam compression; heating engineering is equivalent to 2/3 of coal-fired boilers. When the system is in operation, the use of refrigerants and fuels such as Freon, natural gas, and gasoline can greatly reduce the damage to the ozone layer and reduce CO emissions.

Second, the problems that may arise from the use of ground source heat pump air conditioners

The ground source heat pump air conditioning system mainly includes two parts: one is the water loop air conditioning system in the building; the other is the underground part of the ground source heat pump air conditioning system, that is, the underground heat exchanger of the underground coupled heat pump system and the surface water heat pump system. Surface water heat exchanger, water well system of groundwater heat pump system.

(1) Surface water heat pump system: The surface water temperature is greatly affected by the climate. Similar to the air source heat pump, in the surface water source heat pump system that uses deep river water, lake water and sea water for heat absorption and heat release, it must first be emphasized. It is necessary to have a certain depth of water body. Rivers, lakes and sea areas without a depth of 5 m need not be considered. Generally speaking, only the depth of 10 m or less is useful. For water source heat pump units belonging to ground source heat pumps, if they are flowing rivers, rivers, streams, and water temperature is appropriate, they can be used.

For example, the water temperature in shallow water lakes such as Wuhan East Lake is higher than the wet bulb temperature, and there is no use value. The winter water temperature is slightly higher than the temperature and can be used as heat source water; Ningbo Fenghua River water is 7m deep 31.2°C, and the Pearl River bottom layer is 31.8°C. The heat pollution of the river is very high, and the utilization value is not great. The Yangtze River water can be used as the heat source of the surface water heat pump system, but the water level in the winter is very low. From the perspective of economical and flood control, the actual use is extremely difficult.

The cooling and heat load that a certain surface water body can bear is related to various factors such as area, depth and temperature, and needs to be calculated according to specific conditions. Whether the heat transfer of such a heat pump has an impact on the ecological environment in the water body should be considered in advance. The deep water lake will produce temperature stratification in the summer, and the bottom of the lake will maintain a lower temperature; the winter lake surface will limit the temperature drop of the lake after freezing. From the current actual project situation, the naturally formed shallow water lake is greatly affected by the external climate or thermal pollution. Because it is a non-flowing lake water, it depends on whether the heat discharged into the lake water can pass the self-stability of the lake water. Recovery, if you can not recover, you can not use, otherwise change the temperature of the lake, endangering the lake creatures; even if the seaside buildings can consider the sea source heat pump, but must pay attention to the impact on the ocean current, pay attention to whether it affects the survival of marine life.

The project where the project location and the groundwater heat exchanger site are more than 500m away from the site must be carefully and comprehensively analyzed. If the application conditions are neglected, the surface water source heat pump system will be promoted, and at the same time, the water pumping and distribution energy consumption of river water, lake water and sea water may be offset to the energy saving benefits obtained on the water source heat pump.

In order to economically and feasiblely use the cold and heat sources of rivers, rivers and seawater, only the river, river and seawater can be used for rough pretreatment to solve the problem of blockage of the flow surface by a large amount of sediment and suspended matter, but the water still contains small particle size. The solid matter will affect the flow heat transfer characteristics of the heat exchanger, which also increases the cost of operation and warranty.

(2) Groundwater source heat pump (surface diving) and groundwater source heat pump are two methods of extracting water containing ground temperature from the well, taking out heat, and then re-injecting it into other wells; The form of the buried pipe. Many domestic colleges and universities have carried out relevant experimental research and small-scale engineering application of buried pipes, and established a heat transfer model of buried pipes. The geological conditions vary from place to place, and the soil temperature and thermal properties are different. Therefore, the application of groundwater heat pump needs further experimental verification and accumulation of experimental data. In addition, this shallow geostrophic acquisition technique involves the exploitation of groundwater or surface water, with three disadvantages:

1) While pumping and recharging in other wells, it will cause the movement of sand in the well. When a large amount of well sand is removed, it will often cause the collapse of the pumping well, and also cause the blockage of the return well and shorten the life of the well. ;

2) Under most geological conditions, many projects have not actually reached 100% recharge. The number of recharge wells and production wells and the need for winter and summer swap rotation, whether single well recharge is reasonable and effective, whether it will destroy underground aquifers. The recharge of well water is often unsmooth, which is easy to cause waste of groundwater resources. Although the recharged water will be recharged after pumping, this is not a completely reversible process. The water quality and quantity in the soil after recharge Can not be exactly the same as before pumping, a large amount of groundwater extraction and recharge will inevitably lead to imbalance of groundwater level, affecting the local geological structure, and may damage the buildings on the ground.

3) The ground source heat pump unit requires a basic balance between the cooling load and the heat load throughout the year, so that the underground thermal environment does not deteriorate, and the energy efficiency ratio of the unit is reduced or even cannot be used normally. In the underground of 30 to 300 m deep, as long as the total calorific value of the whole year is equal to the total calorific value, the state of the constant temperature zone can be maintained for a long time; if the constant temperature zone is regarded as an inexhaustible low temperature that can be continuously regenerated Geothermal resources, which can be supplemented by deep geothermal resources or surface solar energy, will make a principled mistake.

In fact, the heat transfer of underground soil, pebbles and rocks, and the thermal migration of underground aquifers are very slow. If we do not follow the principle of annual heat balance, if the actual amount of heat discharged to the ground every summer is greater than the amount of heat absorbed in winter, Even if the underground thermostatic belt in the area only rises by 0.5 °C per year, the ground source heat pump system will not work normally after 10 years. The ground source heat pump used in the mouth is a closed system, but the vertical buried pipe system has a small footprint, the water system consumes less power, but the drilling cost is high; the horizontal buried pipe installation cost is low, but the floor space is large. The water system consumes a lot of power. Although surface water and groundwater have not been extracted, it has changed the temperature inside the ground, affecting geology and even plant growth.

At present, in China, the groundwater heat pump system is relatively mature in technology, and the feasibility of using it is relatively large. In order to cater to the new technology of ground source heat pump air conditioner, one-sided pursuit of its energy-saving effect, the number of domestic production of water source heat pump units has reached two or thirty. Because the production technical standards of water source heat pump units have not been promulgated in China, the quality of products produced by domestic manufacturers is quite different. Some manufacturers' products have incomplete and inaccurate technical parameters. Many manufacturers do not have actual measurement methods, and the water source heat pump units are required. A lot of data can't be provided, and it doesn't even rule out that some manufacturers with poor technical strength simply don't understand the technical difference between water source heat pump units and conventional water chillers. They directly use conventional chillers as water source heat pump units for market use. In this way, neither the energy-saving advantages of the water source heat pump unit nor the environment is destroyed.

(3) Some ground source heat pump air conditioning projects carried out geological surveys at the beginning of the completion of the work, and concluded that ground source heat pump air conditioners have no effect on geology, but such conclusions seem premature. There is no monitoring well, and regular and long-term monitoring of groundwater production, recharge, water temperature, water quality and aquifer thickness changes are not carried out. The well company can complete the task as long as it can extract the groundwater with the water temperature and water volume specified in the design. For the groundwater heat pump system, there are very few complete hydrogeological data. After most of the projects are put into operation, there is no regular monitoring of the basic parameters of groundwater, let alone the data of groundwater migration.

Hydrogeological analysis and calculation results show that it is extremely irresponsible to take only water without effective recharge or recharge to cause groundwater pollution, and the damage caused by such irresponsible behavior is irreparable. For example, the over-exploitation of groundwater in Tanggu, Tianjin led to the infiltration of seawater, causing serious damage to the ecology; the North China region formed a 40,000-square-kilometer large funnel in North China; due to over-exploitation of groundwater in Xi'an, the Giant Wild Goose Pagoda tilted nearly 1 m and formed thirteen Vertical and horizontal cracks, up to 50 kilometers, the clock tower is 135 rot / 1.

We cannot ignore or intentionally downplay and cover up the possibility that the ground source heat pump system will pollute urban groundwater resources, the damage to the surrounding buildings and the entire urban stratum structure, and the risk that the project may fail. In administrative management, drilling wells to extract groundwater, geology and mineral resources, land and resources, urban environmental protection, water supply companies and other departments seem to have jurisdiction. There is no unified management regulation and organization to manage the use of groundwater. A small amount of ground source heat pump air conditioners may have little impact on geology during a short period of operation. However, if a large number of ground source heat pump air conditioners are used for a long time, the consequences are not difficult to imagine. Perhaps humans are trying to reduce damage to the earth's surface. At the same time, the underground has been destroyed by ground source heat pump air conditioning, and once this damage is caused, it may be more difficult to repair.

(4) From the perspective of economy and technology, the construction of ground source heat pump system, whether it is buried pipe, well drilling, or underwater heat exchangers or water intake devices for lakes, rivers and oceans, Well site selection must carry out some highly specialized operations such as soil and groundwater exploration, and it requires a certain degree of hydrogeology and marine expertise. This is not good for air-conditioning professional technicians; its above-ground part, whether it is The annual cold and heat load calculation and annual distribution of the building are also the design of indoor and outdoor water systems, and it is not the expertise of hydrogeology, geology and mineral exploration, and marine harbor technicians.

In order to make the ground source heat pump system develop healthily, it is extremely important to strengthen communication and cooperation between the air conditioning industry and hydrogeology, geology and mineral exploration, and marine seaport industry. On the other hand, some highly specialized operations such as soil quality and groundwater exploration for site selection of energy storage wells and a large number of underground constructions have increased the scale of investment, resulting in high system cost and installation costs, and cost recovery. The long cycle has also become the biggest obstacle to the application of ground source heat pump air conditioning technology.

Conclusion:

Similar to the saying that “the ground source water passes through the heat pump unit, it only exchanges heat, the water quality has hardly changed, and it will not cause pollution to the original water source after being recharged to the stratum or re-discharged into the surface water body”. For example, in Guangdong, Guangzhou, Shenzhen and other places, the climatic conditions are long in the summer, and the cooling load is relatively large, while the winter heating demand is small, the cooling load is much larger than the heat load, and the cooling and heating load is very uneven. There is not enough heating needs to offset the summer cold load and achieve a cold and heat balance. It is not recommended to use ground source heat pump units for cold and heat sources.

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Label: Ground source heat pump system

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