Heat pump is an efficient energy-saving device that makes full use of low-grade heat energy.quantity of heatIt can be spontaneously transferred from a high temperature object to a low temperature object, but not spontaneously in the opposite direction.The working principle of heat pump is a mechanical device that forces heat from low temperature objects to high temperature objects in a reverse circulation way. It only consumes a small amount of reverse circulation net work, and can get a large amount of heat supply, which can effectively use low-grade heat energy that is difficult to use to achieve energy conservation.[1]
Chinese name
heat pump
Foreign name
(Heat Pump)
Status
New energy technologies that have attracted worldwide attention
Heat pump is a device that transfers the heat energy from low heat source to high heat source, and it is also a new energy technology that attracts much attention all over the world.It is different from the familiar mechanical equipment that can improve potential energy - "pump";Heat pumps usually obtain low-grade heat energy from the air, water or soil in nature first, and then work through electricity, and then provide people with high quality heat energy that can be usedgradeThermal energy.[2]
working principle
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It is a natural law that water flows from high places to low places, and heat is transferred from high temperature objects to low temperature objects.However, in real life, for agricultural irrigation, domestic water and other needs, people use pumps to send water from low to high.Similarly, in today's increasingly tight energy, in order to recover the heat from the low-temperature hot gas normally discharged into the atmosphere and low-temperature hot water discharged into rivers, heat pumps are used to transfer the heat from low-temperature objects to high-temperature objects, and then high-temperature objects are used to heat water or heating, making full use of the heat.The working principle of the heat pump system is consistent with that of the refrigeration system.Make sure the heat pumpworking principleFirst, understand the working principle of the refrigeration system.The refrigeration system (compression refrigeration) is generally composed of four parts: compressor, condenser, throttle valve and evaporator.Its working process is: low temperature and low pressure liquidcryogen(For example, Freon), first absorbs heat from high temperature heat source (such as normal temperature air) in evaporator (such as indoor unit of air conditioner) and vaporizes into low-pressure steam.Then the refrigerant gas is compressed into high-temperature and high-pressure steam in the compressor, and the high-temperature and high-pressure gas is cooled and condensed into high-pressure liquid by low-temperature heat source (such as cooling water) in the condenser.Then through throttling element (capillaryThermal expansion valve、Electronic expansion valveThrottle into low temperature and low pressure liquid refrigerant.This completes a refrigeration cycle.The performance of heat pumps is generally evaluated by the coefficient of refrigeration (COP).The refrigeration coefficient is defined as the ratio of the heat transferred from a cryogenic object to a high-temperature object to the required power.Generally, the cooling coefficient of the heat pump is about 3-4, that is to say, the heat pump can transfer 3 to 4 times of its required energy from low-temperature objects to high-temperature objects.Therefore, the heat pump is essentially a heat lifting device, which consumes a small part of electrical energy when it works, but can extract 4-7 times of electrical energy from environmental media (water, air, soil, etc.) to raise the temperature for use, which is also the reason why the heat pump saves energy.Europe, America and Japan are competing to develop new heat pumps.It is reported that the refrigeration coefficient of the new heat pump can be 6 to 8.If this value can be popularized, it means that energy will be used more effectively.The popularity of heat pumps will also be dramatically improved.Ground source heat pump is a kind of heat pump. It is an air-conditioning technology that uses the ground or water as a cold and heat source to warm buildings in winter and cool them in summer. Ground source heat pump only transfers energy between the ground and the room.Use very little electricity to maintain the temperature required in the room.In winter, 1 kilowatt of electricity sends 4-5 kilowatts of heat from soil or water into the room.In summer, on the contrary, the heat in the room is transferred by the heat pump to the soil or water, so that the room can get cool air.The energy obtained underground will be utilized in winter.Such a cycle will integrate the architectural space and nature.Get the most comfortable living environment at the least cost.[2]
Working conditions of heat pump system in winter and summer
Schematic diagram of heat pump system
Because the working principle of the heat pump device is consistent with the compression refrigeration;Therefore, in order to give full play to its efficiency, the same set of equipment is used to cool the air conditioner in summer or warm it in winter.When heating in winter, the evaporator and condenser in the air conditioner are exchanged through a reversing valve, as shown in the schematic diagram of heat pump system on the left.It can be seen from the figure that when the air conditioner cools down in summer, it operates according to the refrigeration condition. The high-pressure steam discharged from the compressor enters the condenser through the reversing valve (also known as four-way valve). The refrigerant steam is condensed into liquid, enters the evaporator through the throttling device, absorbs heat in the evaporator, cools the indoor air, and the evaporated refrigerant steam is sucked into the compressor after passing the reversing valve,In this way, the refrigeration cycle is realized.When heating in winter, first turn the reversing valve to the working position of the heat pump, then the high-pressure refrigerant steam discharged from the compressor flows into the indoor evaporator (used as a condenser) after passing the reversing valve. The latent heat released when the refrigerant steam condenses heats the indoor air to achieve the purpose of indoor heating. The condensed liquid refrigerant,From the reverse flow through the throttling device, it enters the condenser (used as the evaporator), absorbs the external heat and evaporates. The evaporated steam is sucked by the compressor after passing through the reversing valve to complete the heating cycle.In this way, the heat in the outside air (or circulating water) is "pumped" into the room with higher temperature, so it is called "heat pump".For a split heat pump air conditioner, the outdoor unit is used as the condenser and the indoor unit as the evaporator when cooling in summer, and the indoor heat is delivered to the outdoor when running.In winter, the indoor unit is used as the condenser and the outdoor unit is used as the evaporator, so that the outdoor heat is transmitted to the indoor. Usually, these are transmitted throughfour-way reversing valve To achieve.There is a four-way reversing valve in the heat pump air conditioner.Under refrigeration conditions, the indoor heat exchanger is the evaporator, and the outdoor heat exchanger (the thing that exhales hot air in summer) is the condenser.When heating in winter, the four-way reversing valve switches to change the flow direction of refrigerant. At this time, the indoor heat exchanger is the condenser, and the outdoor heat exchanger (the thing that exhales cold air outside in winter) is the evaporator.As the cold air goes out in winter, the heat exchanger will frost, so when the frost reaches a certain degree, the four-way reversing valve will be switched, and the air conditioner will become a summer cooling condition. The outdoor heat exchanger will get heat and defrost. After defrosting, the four-way valve will be switched to the heating state.During defrosting, the fan of the indoor unit stops to prevent cooling air from blowing into the room.(Of course, this reverse defrosting has a certain impact on comfort, so there are hot gas bypass defrosting, thermal storage defrosting and other modes that do not need to switch working conditions)[2]
energy analysis
In the heat pump cycle, from the low-temperature heat source (outdoor air or circulating water, the temperature is higher than the evaporation temperature tzero）Get Q inzeroThe heat of kcal/h consumes the mechanical work of ALkcal/h and supplies Q to the high temperature heat source (indoor heating system)oneKcal/h, and the relationship between these heats is consistent withFirst law of thermodynamicsIs Qone=Qzero+AL kcal/h If a heat pump device is not used, but the heat converted from mechanical work (or electric energy is used to directly heat the high-temperature heat source, the heat obtained is ALkcal/h, while after the heat pump device is used, the high-temperature heat source (heating system) gains more heat: Qone-AL=Qzerokcal/h。This heat is obtained from a low temperature heat source. If a heat pump device is not used, this heat cannot be obtained.Therefore, the heat pump device can not only save fuel, but also utilize waste heat.The working cycle of the heat pump is just the opposite of that of the heat engine. The heat engine uses the energy of the high temperature heat source to generate mechanical work, and the heat pump uses the mechanical work to transfer the heat of the low temperature heat source to the high temperature object.The heat pump has two identical heat source temperatures, so the relationship between them is: φ=Qone╱AL=（Qzero+AL)/AL=ε+1, ε is the refrigeration coefficient of the refrigerator.It can be seen that,Heat conversion coefficientThe minimum value of is φ=1, in this limit case ε=0, Qzero=0, that is, no heat is absorbed from the low temperature heat source.[2]
Energy conversion of heat pump
As a natural phenomenon, just as water flows from high places to low places, heat always flows from high temperature areas to low temperature areas.But people can create machines, just as water pumps are used to lift water from low to high, heat pumps can pump heat from low to high temperature.So the heat pump is essentially a heat lifting device. The function of the heat pump is to absorb heat from the surrounding environment and transfer it to the heated object (the object with high temperature). Its working principle isrefrigeratorSame, all according toInverse carnot cycleThe only difference is that the working temperature range is different.When the heat pump is working, it consumes part of its energy, and the energy stored in the environmental medium
Principle of heat pump system
The whole heat pump device consumes only a small part of the output work, so the use of heat pump technology can save a lot of high-grade energy.In operation,evaporatorAbsorb heat from the surrounding environment to evaporate the heat transfer working medium, the temperature and pressure of the working medium steam will rise after being compressed by the compressor, and the high-temperature steam will pass throughcondenserWhen condensed into a liquid, the heat released is transferred to the water in the storage tank.The condensed heat transfer working medium returns to the evaporator through the expansion valve, and then is evaporated, and so on.[2]
Heat pump working medium
The working medium of heat pump used to be Freon, butFreonIt has a destructive effect on the ozone in the earth's atmosphere. In order to protect the earth's ecological environment, in addition to improving the cooling coefficient of heat pumps and effectively using energy, science in various countries is also committed to the development of new working fluids, and the working fluids that have replaced Freon have been applied.However, the working medium used by most manufacturers in China today is R22, and the era of using environmental friendly working medium R417A and 134A has not yet arrived.Japan and other countries have taken the lead in adopting COtwoAs working medium, so as not to cause damage to the ozone layer.（Therefore, the copper pipe must be tightly connected during installation to prevent R22 leakage.）In addition, R22, R417A, 134A and CO2 mentioned above do not cause harm to human body. Even if there is leakage, the whole set of equipment is still safe.[2]
Development history
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In the early 19th century, Sadi Karnot, a French scientist, first proposed the theory of "Carnot cycle" in 1824, which became the origin of heat pump technology.In 1852, British scientist L. Kelvin proposed that the refrigeration device could be used for heating, and the reverse Carnot cycle could be used for heating.He was the first to propose a formal heat pump system, which was called "heat multiplier" at that time.After that, many scientists and engineers carried out a lot of research on heat pumps, which lasted for 80 years.In 1912, Zurich, Switzerland, successfully installed a set of heat pump equipment with river water as the low level heat source for heating. This is the early water source heat pump system and the first heat pump system in the world.The heat pump industry developed rapidly from the 1940s to the early 1950s. The heat pumps for household and industrial buildings began to enter the market, and the heat pumps entered the early stage of development.Since the 1970s, the heat pump industry has entered a golden age, and countries around the world have attached great importance to the research work of heat pumps. For example, the International Energy Agency and the European Community have formulated large-scale heat pump development plans. New heat pump technologies have emerged in endlessly, and the use of heat pumps has been constantly expanding, and they are widely used in air conditioning and industrial fields,It plays an important role in energy conservation and environmental protection.In the 21st century, with the emergence of the "energy crisis", the fuel price has suddenly risen. With the characteristics of efficient recovery of low-temperature environmental heat energy, energy conservation and environmental protection, the improved and developed heat pump has stepped onto the historical stage again and become the most valuable new energy technology at present.The former International Heat Energy Agency specially set up an international heat pump center and set up a heat pump program to promote coordination to countries around the worldHeat pump technologyApplication and development of.The governments of the United States, Canada, Sweden, Germany, Japan, South Korea and other countries have issued special official guidelines to promote the social application of heat pump technology.Compared with the development of heat pumps in the world, the research of heat pumps in China started about 20-30 years later.After the founding of New China, with the arrival of a new upsurge in industrial construction, heat pump technology began to be introduced into China.After entering the 21st century, due to the rapid urbanization of China's coastal areas, the growth of per capita GDP2008 Beijing Olympic GamesAnd the 2010 Shanghai World Expo and other factors have driven the development of China's air conditioning market, promoting the application of heat pumps in China more and more widely. The development of heat pumps is very rapid, and the research of heat pump technology continues to innovate.Since the start of heat pump in 2001, after five years of cultivation, the heat pump industry in China has shifted from the introduction period to the growth period.The rapid development of the heat pump industry, on the one hand, benefits from the energy shortage that makes the advantages of heat pump energy saving more and more obvious, on the other hand, has a great relationship with the participation of various forces to promote technological innovation in the industry.[2]
classification
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It can be divided into air source heat pump, water source heat pump, ground source heat pump, and dual source heat pump (water source heat pump and air source heat pump combined) according to different types of heat sources.
Air source heat pump
principle
Air source heat pumpDuring operation, the evaporator absorbs heat from the environmental heat energy in the air to evaporate the heat transfer working medium. The pressure and temperature of the working medium steam rise after being compressed by the compressor. When the high-temperature steam passes through the special annular tube bonded on the outer surface of the water storage tank, the condenser condenses into a liquid and transfers the heat to the water in the water storage tank of the air source heat pump.[2]
The heat transfer working medium of the air source heat pump is a special substance. Under normal pressure, its boiling point is minus 40 ℃, and its freezing point is below minus 100 ℃. When the substance is cold, it is liquid, but it is easy to evaporate into gas, and vice versa.In actual operation, the evaporation limit temperature of the heat transfer working medium in the air source heat pump is about - 20 ℃, so the ambient temperature of 5 ℃ is also "hot" for such a low temperature, even the temperature of snow, such as 0 ℃, is also hot in comparison, so some heat can still be exchanged.[2]
Water source heat pump
principle
The shallow water sources on the earth's surface (generally within 1000 meters), such as groundwater, surface rivers, lakes and oceans, absorb a considerable amount ofRadiant energyAnd the temperature of the water source is generally very stable.The working principle of water source heat pump technology is to input a small amount of high-grade energy (such aselectric energy）And realize the transfer of low temperature potential heat energy to high temperature potential.Water is used as heat source for heat pump heating in winter and air conditioning in summerCold sourceThat is, the heat in the building is "taken out" in summer and released into the water body. Because the water source temperature is low, the heat can be taken away efficiently to achieve the purpose of cooling the building indoor in summer;In winterWater source heat pump unitThe heat energy is "extracted" from the water source and sent to the building for heating.[2]
advantage
Compared with the heating system of boiler (electricity, fuel) and air source heat pump, water source heat pump has obvious advantages.Boiler heating can only convert 90%~98% of electric energy or 70%~90% of internal energy of fuel into heat for users, so ground source heat pump is better thanElectric boilerThe heating saves more than two-thirds of the electric energy, which is more than half of the energy of the fuel boiler;Since the heat source temperature of water source heat pump is relatively stable throughout the year, generally 10~25 ℃, its refrigeration and heating coefficient can reach 3.5~4.4, which is about 40% higher than that of traditional air source heat pump, and its operating cost is 50%~60% of that of ordinary central air-conditioning.Therefore, in recent decades,Water source heat pump air conditioning systemRapid development has been achieved in North America, Central Europe, Northern Europe and other countries. The market of water source heat pump in China is also increasingly active, making this technology widely used and becoming an effective heating and cooling air-conditioning technology.[2]
Ground source heat pump
Ground source heat pumpIt can provide heat and cooling by using shallow geothermal resources (also called geothermal energy, including groundwater, soil or surface water)Energy efficient air conditioningEquipment.By inputting a small amount of high-grade energy (such as electric energy), the ground source heat pump realizes the transfer from low potential heat energy to high potential heat energy.The ground energy is used as the heat source for heat pump heating in winter and the cold source for cooling in summer, that is, in winter, the heat in the ground energy is taken out, and after the temperature is raised, it is supplied for indoor heating;In summer, take out the indoor heat and release it into the ground energy.Generally, ground source heat pump consumes 1kWh of energy, and users can get more than 4kWh of heat or cooling capacity.[2]
High temperature air energy heat pump
high temperatureAir energy heat pumpLiterally, it refers to the heat pump whose heating water outlet temperature is higher than 60 ℃ (i.e. high temperature hot water) or whose air outlet temperature can reach more than 80 ℃ (i.e. high temperature drying heat pump).Compared with the popular conventional heat pumps in the market today, the temperature of conventional hot water is generally below 55 ℃, while the new generation of high temperature air energy heat pumps can produce high temperature hot water up to about 85 ℃, which can be used for electroplating, pasteurization, slaughtering,Glass cleaning, printing and dyeing and other industries.[2]
working principle
The working principle of high temperature air energy heat pump is to use the reverse Carnot cycle principle to obtain a low temperature heat source through natural energy (air heat storage), and become a high temperature heat source after the efficient heat collection integration of the system, which is used to obtain (supply) warm, dry or supply hot water.[2]
advantage
Four advantages of high temperature air energy heat pump: First, energy saving is conducive to the comprehensive utilization of energy. High temperature air energy heat pump absorbs the low temperature heat energy in the air and converts it into high temperature heat energy after being compressed by the compressor. Its energy-saving effect is quite remarkable;Second, it is conducive to environmental protection;Third, the combination of cold and hot, high equipment application rate, saving investment, fourth, because it is electrically driven, regulation is more convenient.Compared with the electric boiler, it can save more than 50% of the power consumption, and reduce the trouble of frequently replacing the electric heating tube;Compared with traditional coal boiler andOil fired boilerIt is pollution-free, emission free, and safe. It saves routine security inspection every year, professional boiler workers, fully automatic temperature control, and greatly reduces operating costs by more than 50%.High temperature heat pumpA heat pump capable of supplying heat and cooling in a particular field.Generally speaking, high temperature air energy heat pump uses special heat pump compressor, special refrigerant and system.[2]
Heat pump water heater
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type
On the marketHeat pump water heaterThere are many kinds, mainly including solar energy boost type, water source and air source.Solar assisted heat pump is a heat pump technology that combines heat pump and solar energy technology;The water source heat pump uses the water source with a certain temperature (above 20 ℃) as the heat source and the refrigerant as the medium, absorbs the heat in the water source and compresses it to heat through the compressor, and exchanges heat with the cold water through the heat exchanger to achieve the purpose of heating and producing hot water. The water source heat pump must have a water source with a certain temperature and flow;Air source heat pump heats water by obtaining heat from air in a similar way to water source heat pump.Among the three types of heat pumps, the air source heat pump has the smallest constraints and the largest development space.[2]
Air source heat pump water heater
Air source heat pump water heaterMainly composed of compressor, heat exchangerAxial fan、thermal insulation water tank, water pump, liquid storage tank, filter, electronic expansion valve, electronic automatic controller, etc.After the power supply is connected, the axial flow fan starts to run, the outdoor air is heat exchanged through the evaporator, and the air with reduced temperature is discharged from the system by the fan. At the same time, the heat absorption vaporization of the working medium inside the evaporator is sucked into the compressor, which compresses the low-pressure working medium gas into high-temperature and high-pressure gas and sends it to the condenser. The water forced to circulate by the water pump also passes through the condenser,After being heated by the working medium, it is sent to the user for use, while the working medium is cooled into a liquid, which flows into the evaporator again after being throttled and cooled by the expansion valve. In such a repeated cycle, the heat energy in the air is constantly "pumped" to the water, so that the water temperature in the thermal insulation tank gradually rises, and finally reaches about 55 ℃, which is just suitable for people to bathe.[2]
heat pump
Air source heat pump is one of the most advanced energy utilization products in the world today.With the rapid development of economy and the improvement of people's living standards, domestic hot water has become a necessity. However, traditional water heaters (electric water heaters, fuel oil and gas water heaters) have many disadvantages, such as high energy consumption, high cost and serious pollution;andEnergy saving and environmental protectiontypesolar heaterIts operation is restricted by meteorological conditions.The heating principle of the air source heat pump is different from that of the traditional solar water heater. The air source heat pump uses air, water, solar energy, etc. as the low-temperature heat source. The air source heat pump uses electric energy as the power to draw heat from the low-temperature side to heat domestic water. Hot water is directly sent to users through the circulation system as hot water supply or utilizationFan coilSmall area heating.Air source heat pump is the best solution for the centralized supply system of large, medium and small hot water in school dormitories, hotels, bath centers and other places.[2]
Heat pump market sales mode
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The sales channels of the heat pump market in China are mainly enterprise self operation mode, agent mode and the mixed mode of the two.The direct operation mode is that enterprises set up branches or send business personnel to operate directly in various places. This mode is mainly commercial computers, and this mode is less for home computers.The direct marketing mode is influenced by the strength of enterprises andabilityIt is difficult to be stronger and larger.The distribution system model is that the manufacturer sets up representative offices in various places to expand channels. In the early stage, it sends business personnel to carry out counseling work, and in the later stage, the dealers independently complete market operations. The problem with this model is that the result of the interest game between the enterprise and the dealers is often the separation of the two, and the channels are unstable.The third is the hybrid mode.Intelligent research consultingAccording to the data, some enterprises adopt the direct sales mode in the surrounding markets and the distribution system in the foreign markets.In the industry, the dealer model accounts for a large proportion.In general, the sales channel construction of the heat pump industry is still in the initial stage, and the very suitable channel model and channel management mode are still uncertain.[2]
