Zhang Xinshi
(Zhongyuan Petroleum Exploration Bureau Survey and Design Institute)
Paper abstract: This article introduces the concept and working principle of ground source heat pump, and then details Discusses the characteristics of ground source heat pumps and the restrictions on the development of ground source heat pumps in my country, and introduces the use and development prospects of ground source heat pumps in China. Finally, it is clearly pointed out that ground source heat pump technology is currently the most friendly and effective to human beings. Heating and cooling technology.
1 The concept and working principle of a ground source heat pump
A ground source heat pump is a heat pump that uses shallow underground geothermal resources (including groundwater, soil and surface water) to both provide heat and High-efficiency and energy-saving air conditioning system for cooling. The reverse Carnot cycle is used to transfer low-grade thermal energy to high-grade thermal energy by inputting a small amount of high-grade electrical energy. A heat pump generally consists of four parts: an evaporator, a condenser, a compressor and an expansion valve.
The working principle of the ground source heat pump is: in summer, the heat pump unit takes out the heat from the building, transfers it and releases it into the ground; in winter, it extracts heat from the ground and supplies heat to the building. Usually a ground source heat pump consumes 1kW of energy, and users can get more than 4kW of heat or cooling.
2 Characteristics of ground source heat pumps
We know that the ground temperature at a certain depth below the earth’s surface is relatively constant throughout the year. Ground source heat pumps use shallow geothermal heat as a cold and heat source, which eliminates It eliminates the influence of environmental factors and has the following significant characteristics compared with other heating and cooling systems.
2.1 Renewable energy is used
The ground source heat pump absorbs the heat emitted by the building in the summer and stores it in the shallow underground. Part of the heat is used for heating the building in the winter. The other part of the heat is dissipated directly into the air. Throughout the year, the amount of heat or cooling that buildings utilize shallow geothermal energy is roughly equal. Therefore, ground source heat pumps use renewable energy.
2.2 High efficiency and energy saving
Since the heat source temperature of the ground source heat pump is generally 10-22°C throughout the year, during heating in winter, the water temperature is higher than the ambient temperature, so the evaporation of the heat pump cycle As the temperature increases, the energy efficiency ratio also increases. During cooling in summer, the water temperature is lower than the ambient temperature, the cooling effect is improved, and the unit efficiency is also improved. The cooling and heating coefficient of water source heat pumps can reach more than 4.0, which is about 40% higher than traditional air source heat pumps. Its operating costs are only 50% to 60% of ordinary central air conditioners. It is comparable to electric boilers and electric heating film heating Compared with other methods, it saves about 70% of electric energy.
2.3 Significant environmental benefits
When the water source heat pump is running, all it needs is the heat or cooling of the source water. The water quality does not change, nor does it produce any pollution, and does not consume water. , smoke exhaust, no dust, only consumes a small amount of electricity.
In terms of power consumption, energy saving is environmental protection. The pollutant emissions caused by the use of water source heat pumps are 40% lower than those of air source heat pumps and 70% lower than those of electric boilers. Although ground source heat pumps also use refrigerant, they require 25% less flushing than conventional air conditioners. The ground source heat pump is fully sealed in the factory and will not leak during installation like a split air conditioner.
2.4 One machine for multiple purposes
A set of ground source heat pumps can provide heating, cooling and domestic hot water supply. That is, one set of equipment can replace the original two systems of boiler and air conditioner, so the one-time investment is only 50% to 70% of traditional heating and cooling. Especially during summer cooling, the waste heat generated by the heat pump can be used to provide users with domestic hot water for free. Therefore, ground source heat pumps are particularly suitable for buildings with both heating, cooling and domestic hot water supply.
2.5 Save land resources
Except for the main unit and circulating water pump, the water source heat pump has no other installation equipment. Compared with the boiler room, the water treatment room, fan room, chimney, coal yard and slag yard are omitted, saving land resources.
2.6 Stable and reliable operation, long service life
Because the water temperature of the ground source heat pump is stable, compared with the air source heat pump, it is free from the effects of frost and defrost. The heat pump has few running parts, basically does not require maintenance, operates stably and reliably, and has a service life of about 20 years.
2.7 High degree of automation
Ground source heat pumps are generally fully computer controlled, which can adjust the working quantity of the compressor according to changes in external load, and are equipped with compressor over-temperature protection, Various protection measures such as water cutoff protection can achieve unattended operation.
3 Composition of ground source heat pump heating system
Ground source heat pump projects generally consist of three parts: ground source water system, heat pump machine room and terminal fan coil cooling system. According to the form of ground source heat exchange system, it is divided into open loop system and closed loop system.
The open loop system pumps water from wells (including lakes and rivers) and sends it to the heat exchange unit for heat exchange. The water after extracting heat or coldness is then poured back into the well. The water used in open loop systems generally only undergoes simple water treatment, which will cause scaling on the surface of the heat exchanger. Open system is the main form of ground source heat pump application at present.
Closed loop systems are further divided into vertical buried loop systems and flat buried loop systems. It exchanges heat with the soil through a loop of polyethylene pipes buried underground. It is usually suitable for installation in larger buildings such as villas.
4 Limitations of Ground Source Heat Pumps
Ground source heat pumps are called by experts the most human-friendly and most effective form of heating and cooling currently available. Research and application have developed rapidly, but due to the limitations of the following objective conditions, the application of this technology is not yet widespread.
4.1 Insufficient publicity and understanding
Although ground source heat pump technology is highly praised by heating experts, to be widely used in projects, it requires the leadership of leaders at all levels, especially those led by project supervisors. recognized. Since this technology has only been developed in recent years with the adjustment of my country's energy strategy, even some heating technicians have insufficient understanding of it. Therefore, in order to gain social recognition, we need to increase publicity efforts.
4.2 Insufficient policy strength
In my country's "Energy Conservation Law", combined heat and power and central heating technology are encouraged and developed, but the comprehensive energy utilization rate is twice that There are still no clear provisions to encourage the development of ground source heat pump technology.
4.3 Limitations on water source conditions
It is important to determine whether the open loop ground source heat pump system has sufficient water sources and whether the local geological and soil conditions can ensure the smooth implementation of tail water recharge. Prerequisites for ground source heat pump application. Generally speaking, when used for community heating, the building floor area ratio should be ≤1. For closed systems, it is subject to environmental conditions such as whether the local geological conditions are suitable for buried pipes and whether there is sufficient site for buried pipes.
4.4 The heat transfer calculation theory of buried pipe system is immature
The current technology for ground source heat pump units and terminal fan coil cooling systems is quite mature. For the open system, the local water conservancy department also has a good understanding of the water source situation; for the buried pipe system, the current calculation theory of soil buried pipe heat transfer is not yet mature, and the design lags behind the engineering application, which makes it difficult to guarantee the quality of the project and makes the project difficult to guarantee. The widespread application of this technology is limited.
4.5 Restricted by local water conservancy department policies
Southern my country has sufficient water resources, while most areas in the north lack water resources. In order to protect limited water resources, each local government has formulated local water resource use regulations. Although the ground source heat pump system does not consume water or pollute groundwater, it requires a large amount of water as a heat carrier. Some local departments charge double fees for water intake and recharge water, so that the energy-saving effect of ground source heat pumps cannot be fully reflected, which limits the development of this technology in these areas.
5 Applications of Ground Source Heat Pumps
5.1 Foreign Applications
Ground source heat pumps are commonly used in Japan, South Korea, the United States, and Central and Northern Europe. According to statistics in 1999, among residential heating devices, ground source heat pumps accounted for 96% in Switzerland, 38% in Austria, and 27% in Denmark. In the United States, ground source heat pump systems accounted for 30% of new buildings in 1998 and are growing steadily at a rate of 10%. One of the most famous ground source heat pump projects is the waterfront office building in Lewisville, Kentucky, with a service area of ??15.8×104m2 and a monthly operating cost saving of US$25,000. As the application of this technology develops, research on its organization has also developed rapidly. According to relevant information, the high-temperature water ground source heat pump developed in Japan has an outlet water temperature of 80 to 150°C and a heating coefficient COP as high as 8.0.
5.2 Domestic Applications
Professor Lu Canren from the Institute of Thermal Energy of Tianjin University carried out the earliest research on heat pumps in my country in 1954, and successfully developed the first water-cooled heat pump unit in China in 1965. . Currently, many universities and research institutions are conducting research on water source heat pumps.
The earliest domestic manufacturers of water source heat pumps include Tsinghua Tongfang Artificial Environment Equipment Company and Shandong Ocean Fulda, and their products have been serialized. At present, the outlet water temperature of the heat pump unit has reached 65°C, and the cooling coefficient COP can reach 6.7. At present, the more typical domestic users include Shenyang Northeast Electric Power Residential Community, with a service area of ??8×104m2; Beijing Friendship Hospital, with a service area of ??7.1×104m2, saving about 9 yuan/m2 in heating and cooling operating costs throughout the year.
The water source heat pump demonstration project in the office building of Zhongyuan Oilfield Drilling Company No. 3 is our first ground source heat pump system. Two ZYRB240 heat pump units jointly developed and produced by the Drilling Integrated Engineering Department and Tsinghua University were selected, with a service area of ??6000m2. The successful implementation of this project will surely play a strong role in promoting the promotion and application of ground source heat pumps in Zhongyuan Field.
6 Development Prospects of Ground Source Heat Pumps
6.1 Comply with the requirements of relevant government departments
Ground source heat pumps are highly energy-saving, environmentally friendly and in line with my country’s energy policy and environmental protection policies, the comprehensive energy utilization rate of heat pump technology is about 120% to 180%. Therefore, the state regards combined heat, electricity and cooling technology as a general energy-saving technology to encourage the development and promotes the development of ground source heat pump technology.
6.2 In line with the interests of the owners
Ground source heat pumps can provide both heating and cooling. One system can replace the original two systems with low investment. In addition, ground source heat pumps occupy less space, have low operating costs, and are easy to manage, which are in line with the fundamental interests of the owners.
6.3 In line with the interests of users
The heating cost of a ground source heat pump is half of the heating cost of a coal-fired centralized boiler room, and the cooling cost in summer is about 60% of that of a chiller. This means It reduces users’ heating and cooling expenses, which is in line with users’ vital interests.
6.4 Wide range of applicable areas
Chillers can only be used for cooling in summer, air-cooling units are only suitable for heating and cooling in the Yangtze River Basin, and ground source heat pumps are not suitable for other applications. Except for a few areas where groundwater can be used but pipes cannot be buried, it is applicable to most other areas.
6.5 Application scope continues to expand
Ground source heat pumps have not only developed rapidly in building heating and cooling, but are currently used in chemical industry, food, papermaking, agriculture, metallurgy, wood drying, pharmaceuticals It has also been widely used in other industries. It is predicted that more than 1,200 ground source heat pumps will be used in these industries in 2000, and the development momentum is strong.
To sum up, ground source heat pump technology has developed rapidly in China in recent years due to its unique advantages. With the adjustment of my country's energy structure policy, my country's traditional forms of coal-fired boiler heating and air source heat pump cooling will be replaced by more efficient ground source heat pumps. With the research and development of ground source heat pump technology, it will become the most common and effective heating and cooling technology in the 21st century.
References
[1] Liu Xingzhong. Introduction to water source heat pump system. 2001
[2] Wu Zhanhao. Ground source heat pump air conditioning system. 2001
Note: This article is quoted from the Proceedings of the National Urban Geothermal Development and Utilization Experience Exchange Conference in Oil Regions, Metallurgical Industry Press, 2003