Heat pump as one of the main equipment to provide heat, with its environment-friendly and energy-saving features, has been widely used in many fields. in the text. First of all, the history of the heat pump is reviewed. The types, characteristics, use conditions and conditions of the heat pump are introduced. The problems in the application of several main heat pumps are discussed. The research progress, new technology.
1, heat pump and refrigerator
A heat pump is a refrigeration system that heats the conditioned environment with the heat from the condenser. As far as the thermophysical process of a heat pump system is concerned, it is a special type of refrigerator used, from a working principle or from a thermodynamic point of view. It is the main difference with the general refrigerator is:
â‘ the purpose of the use of different. The purpose of the heat pump is heating, the focus of the study is the heat exchange of working fluid between the high-pressure side of the system through the heat exchanger and the external environment; the purpose of the refrigerator is cooling or cryogenic temperature, the focus of study is the working fluid in the system low pressure Side heat exchanger between the heat exchanger and the outside world;
â‘¡ system temperature range of different work. Heat pump is the ambient temperature as a low temperature heat source, the object to be adjusted as a high temperature heat source; the refrigerator is the ambient temperature as a high temperature heat source, the object to be adjusted as a low temperature heat source. Therefore, when the environmental conditions are equivalent, the heat pump system operating temperature is higher than the operating temperature of the refrigeration system.
2, the origin of the heat pump and the main application type
2.1 The origin of the heat pump
With the development of the industrial revolution, there was a keen interest in the issue of whether it was possible to "pump" heat from the cooler medium to the hotter medium in the early 19th century. British physicist JPJoule proposed the principle of "changing the temperature of a compressible fluid by changing its pressure". In 1854, Professor W. Thomson (known as Lord Kelvin) published a paper presenting the concept of Heat Multiplier, which for the first time described the idea of ​​a heat pump.
At that time, the main target of heat pump heating is civil, the total amount of heating demand is small, especially due to the heating mode and its impact on the environment there is not enough awareness. People are mainly heating coal and wood heating, thus, the development of heat pump lags far behind the long-term development of the refrigerator.
In the 1930s, with the development of Freon refrigerators, heat pumps developed rapidly. Especially after World War II, the huge demand for heating supplies and the relative energy shortage brought by the rapid development of the industrial economy have promoted the development of large-scale heat supply and industrial heat pumps. The global energy crisis of 1973 further promoted the worldwide development of heat pumps.
2.2 The main application of heat pump type
According to the heat pump system thermodynamic cycle type, the heat pump is usually divided into the following six categories:
â‘ vapor compression heat pump
Like refrigerators, vapor compression systems are also the main application of heat pumps. According to the combination of low temperature heat source and heating medium, the vapor compression heat pump system is divided into air-air heat pump, air-water heat pump, water-water heat pump, water-air heat pump, geothermal-air heat pump And soil heat - water heat pump and several other major applications.
â‘¡ gas compression heat pump
And vapor compression system heat pump is different in this type of heat pump system, the work area of ​​the working medium for overheating zone. For the gas compression heat pump system, the heat pump system and the related technologies, which mainly use carbon dioxide and humid air as the working medium, are two types of hot topics studied in related fields. Air-conditioning heat pump systems and installations that use moist air as a working medium have traditionally been used primarily for aerospace applications, for example, as air-conditioning cold and heat source equipment for aircraft cabins. For the use of wet air as the working medium of air-conditioning heat pump system in general industrial or civil construction environment regulation application possibilities, the author has essay explored.
â‘¢ steam jet heat pump
Vapor jet heat pump works and the principle of vapor compression heat pump is basically the same, but by the steam ejector instead of the compressor. This heat pump is mainly used for thermal power plant integrated heat utilization, compared with the absorption heat pump, the heat pump is less efficient, less used at present.
â‘£ absorption heat pump
Absorption heat pump is a use of low-grade heat source to achieve the heat from the low-temperature heat pump to high-temperature heat pump cycle system. Common working fluid pair is "water - lithium bromide (which lithium bromide solution as a working medium with lithium bromide as a concentrated solution absorbent"), "ammonia - water (which, as working fluid ammonia, water absorbent) , "Water - calcium chloride (which calcium aluminate dilute solution as working medium, calcium chloride concentrated solution as absorbent)".
⑤ thermoelectric heat pump
Thermoelectric heat pump, also known as temperature difference electric heat pump. It is the use of Peltier effect, that is, when the DC through the two conductors composed of different circuits, it will produce a temperature difference between the two terminals of the circuit.
Thermoelectric heat pump with no moving parts, reliable, long life, easy control adjustment, small vibration, low noise, small environmental pollution, but the higher the cost of thermopiles and less efficient, and therefore mainly used for some special occasions .
â‘¥ solar heat pump
This heat pump to solar collectors as a heat source. Figure 3 shows one of the options for solar heat pump process.
In addition to the above several heat pump, there are chemical heat pump and adsorption heat pump, vortex tube heat pump and other other mainly used in some special occasions, heat pumps.
3, the main problems and application status
Vapor compression heat pump is currently the most widely used commercial heat pump. Mainly air, water or earth as a low-temperature heat source.
3.1 air source heat pump (AirSourceHeatPump)
Heat pump with air as heat source is called air source heat pump or air source heat pump (ASHP). It is usually made into a dual-purpose circulation system capable of cooling and heating.
ASHP needs to be designed for a given climatic conditions, ensuring its capacity and efficiency over a wide range of ambient temperatures. As a result, there is a need to address such a contradiction in terms of performance by minimizing the temperature of the air source when the maximum supply is needed and at the same time, the capacity and efficiency of the unit are also minimized.
In addition, the ASHP unit needs to fully consider the parameter selection of the throttle mechanism and the reasonable match between the two heat exchangers indoors and outdoors under different cycling conditions. With the objective of minimizing the total cost over the life of the unit, the authors recommend air handling parameters as a principle of match between two heat exchangers inside and outside the ASHP system.
In determining the unit capacity, for the general area, because the air conditioning load is greater than the heating load, therefore, according to the air conditioning cooling load can be determined. For users in cold areas, in a certain period of time, the air conditioning load may no longer be greater than the heating load. Under these conditions, two kinds of treatment methods can be taken according to the situation: one is to determine the unit capacity based on the extreme heating load and its corresponding environmental conditions and the operating conditions of the unit; the other is to determine the unit capacity with the cooling load of the air conditioner; Heating can not meet the heating conditions, to take supplementary heating measures. The recommended condition of starting auxiliary heating in [7] is that "the operating efficiency of the heat pump system is about 1.5 to 2.0".
Another problem that needs to be considered in the hot and humid areas in winter and hot in summer is the frosting on the outdoor side heat exchanger of the ASHP unit and a series of problems caused by it. Generally believed that the ambient temperature in the -5 ~ 5 ℃ range, easy to frost area, need special attention.
3.2 water source heat pump (WaterSourceHeatPump)
A heat pump using water as a heat source is called a Water Source Heat Pump (WSHP). Sea water, river water, lake water and well water are usually used as low-temperature heat sources. Due to the small temperature changes of the water, the performance of the water source heat pump is usually better and more stable than that of ASHP. At present, the heat pump system using the water of the sewage pond as the low-temperature heat source has been used in practical projects and the economic performance is good.
To seawater, river water or lake as a low-temperature heat pump, on the one hand, subject to natural conditions, on the other hand, the need for heat pump system, water treatment and anti-corrosion measures taken.
At present, the heat pump system using well water as the low-temperature heat source is a hot spot in the research and application of water source heat pump units and systems. Well water, especially deep well water, the annual temperature is basically stable and good water quality, heat pump system is an ideal low-temperature heat source, used more in the project. However, such systems may have environmental problems such as backwater difficulties, backwater pollution and the destruction of groundwater ecological resources. From a sustainable development point of view, this is a way not to be adopted. Actually, in many countries and regions, corresponding laws prohibit the use of groundwater resources as a low-temperature heat source for heat pump systems.
3.3 soil heat pump (SoilHeatPump)
Soil Heat Pump (SoilHeatPump, SHP) to the earth as its low-temperature heat source. Usually the cooling plate into the underground management, coil and soil heat exchange, heat pump system since its own closed system. According to the different forms of buried pipe, this system is divided into horizontal and vertical buried (also known as buried) in two ways.
SHP has the following deficiencies:
â‘ expensive, harsh construction conditions;
â‘¡ may leak to cause land pollution;
③ may cause a large area of ​​land cracks.
In engineering, one can learn from the pipe is about 100 meters long, about 15 centimeters in diameter as a group of tubes, buried underground. And through a small set of inner tubes to send water to the bottom of a large tube.
3.4 Solar Heat Pump (SolarHeatPump)
SolarHeatPump uses solar collectors as the cryogenic temperature of the heat pump system. Figure 3 is a scheme of solar heat pump system flow diagram. This is a system that efficiently draws heat from a lower temperature environment. When the system is operating as a heat pump, the water in the tank serves as the system's low temperature heat source. If the tank capacity is properly designed, it can still be effectively used even when the water temperature is lowered to 5 ° C, and because of the low water temperature, the solar collector can operate at a lower temperature, thereby increasing its heat absorption rate .
The disadvantage of solar heat pumps is that they can not be effectively used as a single-use system at the same time as an effective refrigeration cycle.
In addition, if the solar heat pump to provide domestic hot water at the same time, you need to consider the distribution and conversion of the two systems. At the same time, when used in high latitudes, there is a possibility that the domestic water temperature is too high. Therefore, measures such as anti-high-temperature water burns must be taken into account in the system.
4, some heat pump new technology introduction
The new heat pump technology mainly focuses on improving the thermodynamic efficiency of the heat pump system, improving the environmental friendliness of the heat pump system and handling the air quality. Some technologies have been applied to related products and systems. Related new technologies include:
â‘ outdoor side heat exchanger frost control, surface nano-materials and surface modification technology
By modifying the outer surface of the outdoor side heat exchanger with nanomaterials, the frost water is spherical and condensed, thereby reducing the chances of frost or condensate freezing on the outer surface of the heat exchanger.
â‘¡ large pressure, non-stable operation of efficient heat pump compressor technology
Including the scroll compressor flexible import structure, the body spray cooling and suction pressure self-identification and adaptive liquid separation adjustment technology, so as to adapt to large pressure, unstable operating conditions.
â‘¢ heat pump adaptive air condition control technology
According to the thermodynamic performance of the heat pump system, the self-diagnosis of the system and the adaptive control of air-condition are determined. From the application of this technology in the ASHP system, it can obviously improve the SEER index of the system. With the new process [11], the technology is effective in ensuring efficient heating of ASHP systems at low ambient temperatures.
â‘£ nano-filler mute technology
Through the nano-materials and micro-nano filler to eliminate the refrigerant in the throttling process, condensation and evaporation process due to phase transition caused by the energy transfer between the phase boundary of the noise and vibration.
⑤ respirable particulate nano-catalytic and decomposition technology
Through air-conditioning in the heat pump and air-conditioning system at the end of the intake and exhaust interface Gang Gang material modification, so that the inhalable particles in the air through nano-catalytic decomposition of the air to be purified.
â‘¥ full air heat pump technology
A transonic expansion heat cycle air-to-air heat pump air conditioning system using wet air. Air at the same time as a working medium and energy exchange medium. The use of oil-free compression equipment and process technology will enable this system to have excellent environmental friendliness.
⑦ nano catalytic high efficiency absorption technology
The use of a low-density, porous nanomaterial having a uniform network structure as a filler for the absorber and the generator can increase the absorption efficiency and the efficiency and the rate at which the miniaturization of the chiller or the absorption heat pump unit during absorption is made possible. Ferric chloride and sodium hydroxide as raw materials, using sol-gel process and supercritical drying technology, through iron-based aerosol basic particles b-FeOOH, and then treated with high temperature into a-Fe2O3-SiO2 matrix Low-density porous nanomaterials are a possible nanocatalytic high-efficiency absorbent filler.
⑧ high efficiency, low pollution combustion technology
After the surface of the burner is modified by titanium-based nano-particles, the catalytic action on the nano-particles can control and adjust the combustion reaction conditions so that the natural gas can be burned faster and more fully, meanwhile, the reaction between the nitrogen and oxygen can be suppressed , So that the combustion reaction intermediates (and pollutants) to reduce, improve combustion efficiency.
⑨ heat pump compressor suction, exhaust mute technology
Compressor refrigeration or heat pump system noise and vibration of the main source. Compressor suction and exhaust aspects of the noise frequency characteristics of its structure and different materials and different. Experiments show that the use of flexible suction and exhaust channel structure can reduce the noise of refrigeration or heat pump units and improve its transmission characteristics in the system.
â‘© reciprocating compressor suction reflow resistance technology.
For reciprocating compressors, the return flow of refrigerant at the suction side of the compressor is one of the main factors that cause the pressure pulsation of the working medium in the suction side of the compressor. The pulsation of the air flow produced by it can be transmitted from the low pressure side to the high pressure side. The use of suction flow resistance structure of the suction channel, you can reduce the compressor noise and vibration, and to improve the efficiency of the compressor.
(11) mineral oil polarity enhancement technology
Mineral oil polarity is weak, and the same weakly polar CFCS working medium compatibility is good, is the replacement of the refrigerant before the advent of refrigeration systems widely used in lubricating oil. As a major alternative to CFCS refrigerants, HFCS refrigerants are more chemically polar and therefore require the use of lubricants having a higher polarity, such as POE oils, which poses a number of problems. The mineral oil polarity enhancement technology has made it possible to use refrigeration systems with HFCS-type refrigerant (and a mixed refrigerant with HFCS-type refrigerant as the main component).
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