The hottest solar heat pump technology and its hea

2022-08-19
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Solar heat pump technology and its heating application

abstract heat pump technology is a good energy-saving air conditioning refrigeration and heating technology. The combination of heat pump technology and solar heat utilization technology can improve the efficiency of solar collectors and the performance of heat pump systems, and solve the problem of all-weather heating at the same time. Therefore, the research and development of solar heat pump is receiving increasing attention. This paper discusses the technical principle and characteristics of solar heat pump, as well as its application and research status in providing hot water

key words: technical characteristics of solar heat pump cop energy saving

0 introduction

with the economic development and scientific and technological progress, energy and environment are the two prominent social problems in the world today, which makes people more aware of the importance of energy to mankind, and pay more and more attention to the utilization of solar energy and energy-saving heat pump technology. At present, the heat utilization of solar energy in China mainly focuses on passive solar room heating and domestic hot water provided by water heaters, while the development and utilization of active solar heating system is relatively backward. Adopting the system mode of connecting the energy-saving device heat pump with the solar heat collection equipment and heat storage mechanism can not only effectively overcome the rarity and intermittency of solar energy itself, but also achieve the purpose of saving high energy and reducing environmental pollution, which has great development and application potential

heat pump technology is a good energy-saving air conditioning refrigeration and heating technology, which uses a small amount of high-grade electric energy as the driving energy, efficiently absorbs low-grade heat energy from the low-temperature heat source, and transmits it to the high-temperature heat source, so as to achieve the purpose of pumping heat, so as to convert the energy with low energy quality coefficient into the energy with high energy quality coefficient (save high-grade energy), that is, the technology to improve the energy grade. With the increasing demand for access to domestic hot water, solar energy with intermittent characteristics is difficult to meet all-weather heating. To solve this problem, the combination of heat pump technology and solar energy utilization is undoubtedly a good choice

1 basic principle and type of heat pump, but because the steel market transaction is not smooth, the pressure on the raw material end is not reduced

heat pump is a refrigerator used in reverse, and what is different from the refrigerator is the working temperature range. Working principle of the heat pump system: after the evaporator absorbs heat, the high-temperature and low-pressure superheated gas of its working medium changes into high-temperature and high-pressure gas through adiabatic compression in the compressor, and then condenses into low-temperature and high-pressure liquid through the constant pressure of the condenser (discharging the gasification heat of the working medium, etc., and exchanging heat with the condensed water, so that the condensed water is heated into hot water for users to use). The liquid working medium changes into low-temperature and low-pressure liquid after adiabatic throttling by the pressure reducing valve, Enter the evaporator to absorb the heat of the heat source at constant pressure, and evaporate into superheated steam to complete a cycle process. In this cycle, the heat energy of the heat source is continuously transferred to the condensate

according to the first law of thermodynamics, there are: qg= QD + A. according to the second law of thermodynamics, the electric power a consumed by the compressor plays a compensation role, so that the refrigerant can continuously absorb heat (QD) from the low-temperature environment and release heat (QG) to the high-temperature environment, and cycle again. Therefore, the energy consumption of the compressor is an important technical and economic index. Generally, the energy efficiency of the device is measured by the coefficient of performance (COP), which is defined as:

cop=qg/a = (qd+a)/a=1+qd/a

obviously, the cop of the heat pump is always greater than 1. Therefore, heat pump is a high-efficiency energy-saving device, and it is also an important way to implement building energy conservation in the field of refrigeration and air conditioning. It plays a positive role in saving conventional energy, alleviating air pollution and greenhouse effect

all types of heat pumps have two temperature levels of evaporation and condensation. Expansion valves or capillary tubes are used to reduce the pressure and throttle the refrigerant, but there are different forms of pressure increase, mainly mechanical compression, thermal compression and steam injection compression. Among them, mechanical compression heat pump, also known as electric heat pump, has been widely used in building heating and air conditioning, occupying a leading position in the heat pump market; The heat energy compression heat pump includes absorption type and adsorption type. Among them, the water lithium bromide absorption type and ammonia water absorption type hot water units have gradually embarked on the road of commercial development, while the adsorption type heat pump is still in the research and development stage, and the problems of intermittent operation, low system performance and low cooling weight ratio must be overcome before it can be truly applied to practice

according to the different forms of heat sources, heat pumps can be divided into air source heat pumps, water source heat pumps, ground source heat pumps and solar energy heat pumps. Foreign literature generally refers to groundwater heat pump, surface water heat pump and ground source heat pump as ground source heat pump

1 basic principle and type of heat pump

heat pump is a refrigerator with reverse use, which is different from the refrigerator only in the working temperature range. The working principle of the heat pump system is shown in Figure 1 [1][2]. After the evaporator absorbs heat, the high-temperature and low-pressure superheated gas of its working medium is transformed into high-temperature and high-pressure gas through adiabatic compression in the compressor, and then condensed into low-temperature and high-pressure liquid through the constant pressure of the condenser (releasing the gasification heat of the working medium, etc., and exchanging heat with the condensed water, so that the condensed water is heated into hot water for users to use). The liquid working medium is transformed into low-temperature and low-pressure liquid after adiabatic throttling by the pressure reducing valve, and enters the evaporator to absorb the heat of the heat source at constant pressure, And evaporate into superheated steam to complete a cycle process. In this cycle, the heat energy of the heat source is continuously transferred to the condensate

according to the first law of thermodynamics, there are: qg= QD + A. according to the second law of thermodynamics, the electric power a consumed by the compressor plays a compensation role, so that the refrigerant can continuously absorb heat (QD) from the low-temperature environment and release heat (QG) to the high-temperature environment, and cycle again. Therefore, the energy consumption of the compressor is an important technical and economic index. Generally, the energy efficiency of the device is measured by the coefficient of performance (COP), which is defined as:

cop=qg/a = (qd+a)/a=1+qd/a

obviously, the cop of the heat pump is always greater than 1. Therefore, heat pump is a high-efficiency energy-saving device, and it is also an important way to implement building energy conservation in the field of refrigeration and air conditioning. It plays a positive role in saving conventional energy, alleviating air pollution and greenhouse effect

all types of heat pumps have two temperature levels of evaporation and condensation. Expansion valves or capillary tubes are used to reduce the pressure and throttle the refrigerant, but there are different forms of pressure increase, mainly mechanical compression, thermal compression and steam injection compression. Among them, mechanical compression heat pump, also known as electric heat pump, has been widely used in building heating and air conditioning, occupying a leading position in the heat pump market; The heat energy compression heat pump includes absorption type and adsorption type. Among them, the water lithium bromide absorption type and ammonia water absorption type hot water units have gradually embarked on the road of commercial development, while the adsorption type heat pump is still in the research and development stage, and the problems of intermittent operation, low system performance and low cooling weight ratio must be overcome before it can be truly applied to practice

according to the different forms of heat sources, heat pumps can be divided into air source heat pumps, water source heat pumps, ground source heat pumps and solar energy heat pumps. Foreign literature generally refers to groundwater heat pump, surface water heat pump and ground source heat pump as ground source heat pump

2 principle and characteristics of solar heat pump technology

solar heat pump generally refers to the heat pump system using solar energy as the heat source of evaporator, which is different from the heat pump unit driven by solar photovoltaic or thermal power generation. It combines heat pump technology and solar energy heat utilization technology organically, which can improve the efficiency of solar collector and the performance of heat pump system at the same time. The heat absorbed by the collector is used as the low-temperature heat source of the heat pump. In rainy days, the direct expansion solar heat pump is transformed into an air source heat pump, and the non direct expansion solar heat pump is used as the auxiliary heat source of the heating system. Therefore, it can work all day and provide hot water or heat

2.1 classification of solar heat pump

according to the combination form of solar collector and heat pump evaporator, it can be divided into direct expansion soar assisted heat pump (DX-SAHP) and non direct expansion type. In the direct expansion system, the solar collector and the heat pump evaporator are combined into one, that is, the refrigerant absorbs the solar radiant energy directly in the solar collector and evaporates (as shown in Figure 2). In the non direct expansion system, the solar collector is separated from the heat pump evaporator. The solar energy is absorbed in the collector through the heat collection medium (generally water, air and antifreeze solution), and the heat is transferred to the refrigerant in the evaporator, or directly to the air or water that needs to be preheated through the heat exchanger. According to the connection form of solar collector loop and heat pump loop, the indirect expansion system can be further divided into series, parallel and double heat source systems. Series type means that the collector loop and the heat pump loop are connected in series through the evaporator, and the heat source of the evaporator is all from the heat absorbed by the solar collector loop (as shown in Figure 3); Parallel type means that the solar collector loop and the heat pump loop are independent of each other. The former is generally used to preheat the heating object of the latter, or the latter is used as the auxiliary heat source of the former (as shown in Figure 4); The double heat source type is basically the same as the series type, except that the evaporator can use two low-temperature heat sources including solar energy at the same time (as shown in Figure 5) [3]

2.2 technical characteristics of solar heat pump

solar heat pump organically combines solar energy utilization technology with heat pump technology, and has the following technical characteristics [4]:

1) compared with the traditional solar direct heating system, the biggest advantage of solar heat pump is that it can adopt a simple structure collector, and the cost of heat collection is very low. In the direct expansion system, the working temperature of the solar collector is consistent with the evaporation temperature of the heat pump, and close to the outdoor temperature. In the non direct expansion system, the solar collector loop is often used as the low-temperature heat source of the evaporator, and the temperature of the collector medium is usually 20 ℃ ~ 30 ℃. Therefore, the heat dissipation loss of the collector is very small, and the efficiency of the collector is correspondingly improved. Studies have shown that even if ordinary flat plate collectors with simple and cheap structure are used in non cold areas, the collector efficiency is as high as 60% - 80%, and even bare plate collectors without cover plate and insulation can be used

2) due to the shortcomings of low density, intermittency and instability of solar energy, conventional solar heating systems often need to adopt large heat collection and storage devices, and equipped with corresponding auxiliary heat sources, which not only causes high initial investment of the system, but also makes it difficult to arrange large-area heat collectors. Based on the energy conservation of the heat pump and the efficiency of the collector, under the same heat load conditions, the collector area and accumulator volume required by the solar heat pump are much smaller than those of the conventional system, making the system structure more compact and the layout more flexible

3) under the condition of good solar radiation, solar heat pump can often obtain higher evaporation temperature than air source heat pump, so it has a higher heating performance coefficient (COP can reach more than 4), and the heating performance is less affected by the decline of outdoor temperature

4) because solar energy is everywhere and inexhaustible, the application range of solar heat pump is very wide, which is not limited by local water source conditions and geological conditions, and has little impact on the natural living environment

5) like other types of heat pumps, solar heat pumps also have the advantage of "one machine for multiple purposes",

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