Talking about combined cooling and heating and water source heat pump in residential areas in northern China

1 Introduction
    According to statistics, as of the end of 2000, the country’s annual construction area was 36 billion square meters, of which 7.3 billion square meters in urban areas were mostly residential dwellings. With the continuous improvement of people’s living standards, the requirements for living comfort have become higher and higher. Especially in the north, heating in winter and cooling in summer have become necessary means to improve the living environment. In particular, with the further improvement of housing loans and other policies, the scale of individual housing purchases will continue to increase, and a series of mid-to-high-end residences suitable for medium and high-income families have appeared, including many luxurious villa residences. The proportion of houses over 100 square meters in newly built houses is also increasing. In this type of residence, it is also a basic requirement to be equipped with heating equipment and air conditioning equipment. As a real estate developer, to equip such mid- and high-end residences with heating and air-conditioning equipment does not account for a high proportion of the total cost of the initial investment, but it can greatly improve the quality of the residence. Therefore, from the above analysis, it can be seen that the residence The heating and air-conditioning industry not only has a broad market prospect, but also has many articles to write.
    This article makes a rough comparison of the various cooling and heating methods of residential communities in the northern area, and combines the domestic actual situation to propose a water-source heat pump-based combined cooling and heating mode, which is currently the most practical and feasible method in the market. A trend of future development.
    2 Cooling and heating modes in northern areas
   With the continuous improvement of people’s living standards, residential air conditioners have developed rapidly. At present, split air conditioners are still the mainstream in the market. However, with the development of technology, new residential air conditioners continue to emerge. Multi-split air conditioning system, VRV/MRV air conditioning system, air source/water source heat pump cold and hot water air conditioning system, lithium absorption cold and hot water air conditioning system, etc.
    In northern China, residential heating in winter is one of the necessary conditions for people’s lives. In the past, the main methods of residential heating were coal-fired central heating (regional boilers and combined heat and power) and coal-fired decentralized heating (small boilers and domestic heating stoves). In recent years, with technological progress and the improvement of people’s living standards, new and different heating and cooling methods have gradually entered people’s homes.
     In our country, especially in recent years, the domestic integrated heat and cold source machine has developed rapidly. According to the medium that transports the cold capacity, it can be divided into the following three types: (1) The direct expansion system with R22 in the pipeline, such as Japan’s VRV system, Haier’s MRV system, American MDV system, split wall-mounted machine, cabinet machine, etc.;
(2) Ducted system, which uses air as the conveying medium. Its principle is similar to that of large-scale all-air systems. The principle is basically the same. It uses the outdoor unit to centrally generate cold/heat, and then cools/heats the mixed air of the return air or the return air and fresh air from the room, and then sends it to the room;
(3) Cold/hot water unit, cold/hot water unit delivery The medium is usually water or glycol solution. It produces cold/hot water through the outdoor host, which is transported to the indoor terminal device by the pipeline system, and exchanges heat with the indoor air through it. The indoor terminal device of the system is usually a fan coil. These three systems have their own advantages and disadvantages, but according to different national conditions, the degree of development is also different. In Japan, the “fluorine system” air conditioner is mainly developed, while the “wind system” is developing more rapidly in the United States. According to China’s national conditions, which type of air-conditioning system is our future development direction? In response to this issue, several teachers from Tsinghua University published an article titled “Analysis and Prospects of the Industry Status Quo of Household Small Central Air Conditioning” in the “Refrigeration and Air Conditioning” magazine. This article gave a very detailed description of the above problems. analyze. They believe that from the perspective of technological maturity, the national economic development level, and the structural type of the building, the development of cold/hot water units should be the main consideration. Practice has proved that it is true.
    According to the heat source medium, the cold/hot water unit can be divided into three types: water/water heat pump (water source heat pump), air/water heat pump (air source heat pump), and lithium absorption chiller and hot water unit.
2.1 Direct-fired lithium cold and hot water unit This heating method uses a lithium absorption chiller to achieve heating. In summer, the chiller produces 7/12°C (outlet water temperature/return water temperature) chilled water to meet building air conditioning needs ; In winter, the refrigerator provides a water supply temperature of 60~80℃ for heating. When needed, domestic hot water (60℃) can be provided throughout the year
    Lithium absorption refrigerators can be divided into three types: direct-fired type, steam type, and hot water type. The hot-water lithium absorption chiller that uses solar energy for cooling in China is still in the experimental research stage. Due to the instability and intermittentness of solar energy, and the current solar collectors on the market cannot match the chiller, and cost issues All seriously hinder the promotion and application of this energy-saving refrigerator.
    When the local power supply is short, there is a thermal power station for heating or enough winter heating boilers, especially when there is waste heat and waste heat available, lithium absorption chillers should be preferred; but when the local supply of cheap natural gas and technology When the economy is more reasonable, because the direct-fired machine has the characteristics of higher thermal efficiency, less fuel consumption, better safety, and dual use than other types of water-absorbing refrigerators, it should be preferred.
    Direct-fired lithium hot and cold water units for heating and cooling, in terms of environmental protection, comprehensive utilization of energy, operating costs and comprehensive cost, are not advantageous compared with cogeneration mode heating, but because it is a cold and heat source Integration can be considered comprehensively in communities with air-conditioning requirements.
2.2 Air source heat pump air source heat pump performs a refrigeration cycle in summer, transferring the waste heat of the room and the input power of the unit to the outdoor air together to achieve the purpose of cooling the room; in winter, a heating cycle is used to extract heat from the outdoor air. Together with the input power of the unit, it is transferred to the room to achieve the purpose of heating the room. When it is in refrigeration operation, its energy efficiency ratio (EER) value is as high as 3.0 or more; in heating operation, its coefficient of performance (COP) value is also above 3.0, so its power consumption is only 25% to 50% of electric heating type , And one machine has two functions, which improves the utilization rate of the equipment. However, when the outdoor temperature is lower than -5°C, the heat supply is reduced, the energy-saving benefit is reduced, and the unit malfunctions increase, and the room temperature is easy to change.
2.3 Water source heat pump Compared with air source heat pump, due to the improvement and stability of its working conditions, the water source heat pump not only improves the efficiency of the unit, but also runs stably and reliably; there is no frosting problem and the service life is prolonged. Its EER value and COP value are as high as 4.3 to 4.6. The power consumption is only 60 to 70% of the air source heat pump; it also has a heat recovery function and has significant energy-saving benefits. Therefore, the water source heat pump is the best solution to the heating and air conditioning of urban buildings in the northern region.
    Water source heat pumps are classified according to the medium of their heat sources, including water/air heat pumps and water/water heat pumps;
    if water source heat pumps use the earth (soil, strata, groundwater) as the heat source, they can also be called ground source heat pumps.
    The ground source heat pump is a heat pump air-conditioning system that uses land as a low-level heat source. The ground source heat pump has the advantages of environmental protection, energy saving, and good thermal stability, and has a good market prospect. However, due to the incomplete equipment (such as land heat exchangers, pipes) and process equipment associated with the ground source heat pump, its application is still at the stage of theoretical discussion.
   The price of the water source heat pump is equivalent to that of the room air conditioner. As long as the heat dissipation problem of the water source is solved, it will be a strong competitor of the room air conditioner.
3 The new model of combined cooling and heating explores the air source heat pump chiller/hot water unit. It is widely used in the Yangtze River Basin and the south of China, the Yellow River Basin and other regions, and the technology is also very mature. , Inner Mongolia and other regions are relatively rare. Can air source heat pump chillers/hot water units be used for heating and cooling in these cold regions? Cooling is undoubtedly possible, but what about heating? Several professors such as Ma Zuliang of Harbin Institute of Technology believe that the air source heat pump hot and cold water units cannot operate normally in the coldest period in the north, because the compression ratio of the units is greater than 10 or even more than 20. Therefore, Professor Ma proposed the joint operation of air source heat pump chillers and hot water units and water source heat pumps to solve this contradiction. At this time, the COP value of the system can also reach about 2.0. But because of its high cost, it will hinder the popularization and use of the system. The author believes that it is better to use the city’s heating pipe network to make an article, and it is more convenient and effective to use the cogeneration of waste heat, waste heat + water source heat pump chiller and hot water unit + fan coil mode. Set up a small thermal station in the community, with water/water heat exchangers and cooling towers. The heat exchanger is used for the 20℃~25℃ normal temperature water generated by heat exchange with the cogeneration waste heat and waste heat for the cold water source heat pump chiller/hot water unit for heating operation, to ensure the constant low-pressure water temperature measurement. The cooling tower is used to ensure the constant high-pressure water temperature measurement when the water source heat pump is in refrigeration operation, and the heat pump can also provide hot water to the user, so the expensive domestic hot water pipe network is naturally omitted.
    In summary, the author believes that in terms of the planning and construction of a community in the northern region, this kind of dual-use, environmentally friendly and energy-saving cooling and heating combined supply mode should be vigorously promoted. Of course, in the southern region, due to its soil superiority, ground source heat pumps should be promoted vigorously.

4 Characteristics of combined heat and power generation, waste heat, waste heat + water source heat pump + fan-coil cooling and heating mode 4.1 Cogeneration of waste heat and waste heat utilization At present, all large and medium-sized cities in northern China use combined heat and power, and regional boiler houses are used as heat sources. The central heating method is based on heat and electricity. The high-temperature and high-pressure steam from the thermal power plant undergoes two to three-stage heat transfer processes to generate heating hot water at 85~95℃, and domestic hot water at 50~60℃ at the same time, which are sent through two different heat pipe networks. Into thousands of households.
    At present, the average power generation efficiency of large-scale thermal power plants in China is 33%, while the power generation efficiency of thermal power plants is 20%, and more than 70% of the remaining 80% heat can be used for heating. The use of cogeneration waste heat and waste heat will greatly improve the power generation efficiency of thermal power plants, and when the water source heat pump is in heating operation, the water temperature required for low pressure measurement is only normal temperature, so there is no need to set up multi-stage thermal power stations to deliver the temperature of the water. It is not too high (30-40°C), which not only reduces the investment in the heating station and the pipe network, but also reduces the energy transmission loss, and the associated water treatment equipment is also reduced.
4.2 water source heat pump system water source heat pump system in front of the brief overview has been done, and here we are by comparison with other systems to once again look at its advantages and disadvantages
4.2.1 source heat pump split air-conditioning system and civil Comparison Table 1
number Water source heat pump system civil split air conditioner 1 High energy efficiency ratio (4.3~4.6), low energy efficiency ratio (3.0), no energy saving 2 Wide blowing area, uniform cooling capacity, easy to decorate, single air volume, uneven cooling capacity, unfavorable room decoration 3 It can recover heat and provide domestic hot water. It cannot provide domestic hot water. 4 It will not damage the appearance of the building. If it does not form a heat island effect on the environment, it will destroy the appearance of the building and form a heat island effect. The internal and external units are installed separately, which is greatly affected by the installation and is easy to leak. 6 It is convenient to introduce fresh air and cannot introduce fresh air in time. 

4.2.2 lithium source heat pump system and the absorption water chiller system Comparison Table 2
Number source heat pump system using a centralized cooling and heating system water at room temperature, can make full use of waste heat, waste heat using steam or hot water, is not sufficiently Utilize waste heat

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