The air source heat pump water heater is a kind of equipment which transfers heat from low temperature object to high temperature water through medium by using reverse Carnot principle. It is mainly composed of compressor, heat exchanger, axial fan, heat preservation water tank, water pump, liquid storage tank, filter, electronic expansion valve and electronic automatic controller. When the power supply is turned on, the axial fan starts to run, and the outdoor air exchanges heat through the evaporator. The air with lower temperature is discharged from the system by the fan. At the same time, the working medium inside the evaporator absorbs heat and vaporizes into the compressor, which compresses the low-pressure working medium gas into high-temperature and high-pressure gas and sends it to the condenser, and 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, and the working medium is cooled into liquid, which flows into the evaporator again after throttling and cooling by the expansion valve. In this way, the heat energy in the air is continuously "pumped" into the water, so that the water temperature in the heat preservation water tank gradually rises to about 55 ℃, which is just suitable for people to take a bath, This is the basic working principle of air source heat pump water heater.

The structural change of air source water heater promotes the progress of heat pump technology, and the main problem affecting the development of heat pump technology is the product structure. According to the evolution process of heat pump technology and the difference of product internal structure, the development of heat pump products can be roughly divided into four different types.

1、 In order to improve the thermal efficiency of the static immersion heat pump, the original structure is improved on the basis of the early products. The heat exchange copper tube is directly placed in the water tank to contact with the cold water. By subtracting the heat conduction loss of the middle layer of the inner tank, the thermal efficiency of the static immersion heat pump is greatly improved, the heating time is shortened, and the heating water temperature is faster and higher. Although the built-in heat exchange copper tube solves the main contradiction of thermal efficiency, it also causes another problem, which is the scaling problem on the outer wall of copper tube caused by long-term immersion in water. Because the water flow in the water tank depends on the pressure of the tap water itself, the water in the water tank does not flow when the hot water tap is closed, so the second generation heat pump is also known as the static type.

2、 The early heat pump water heater used the structure of water tank outer wall coil. The main feature of the structure is that the heat exchange copper tube is located in the foaming layer between the inner tank and the shell of the water tank, and the heat exchange of the heat exchange copper tube is transmitted to the inner tank of the water tank first, and then to the cold water in the water tank by the inner tank. Because there is a layer of heat conduction medium in the tank, the disadvantages of the structure are self-evident, such as low efficiency, long heating time, more heat loss and low heating water temperature. Because the thermal efficiency of the external wall coil heat pump water heater can not catch up with the traditional water storage water heater, and the structure is complex and the cost is higher, the improved products appeared in the market soon.

3、 The fourth generation of dynamic shell and tube type is actually an improved version of dynamic casing type. The stainless steel vessel was expanded from stainless steel tube to larger canned vessel, and more than 10 thin copper tubes in the vessel were changed into a single thick coiled copper tube with a wall thickness of 2mm. How much the thermal efficiency of dynamic shell and tube is improved remains to be further studied. JiuHeng new energy represents the enterprise. Through the above process of heat pump product technology evolution, it can be seen that the structure update and improvement is the key to promote the progress of heat pump technology.

4、 Dynamic casing heat pump is not only the static immersion type, but also the dynamic casing heat pump. In order to improve the heat exchange efficiency, the heat exchange process is carried out in a thick stainless steel tubular container. More than 10 thin copper tubes with wall thickness of 1.0 mm were bent in the stainless steel tubular vessel. Inside the copper tube is the flowing refrigerant, and between the stainless steel tube and the copper tube is cold water, which is connected to the water tank. The dynamic casing structure also achieves the purpose of reducing the heat conduction link and improving the thermal efficiency. Because the water flow in the stainless steel pipe is recycled by shielded water pump, the scaling is reduced to a certain extent. However, due to the small volume of stainless steel pipe, poor water flow and limited flow, the problem of scaling has not been completely solved. Moreover, the small volume also affects the full play of thermal efficiency. At the same time, the thin copper pipe wall is easy to be damaged, leading to refrigerant leakage. Therefore, the thermal efficiency of the third generation dynamic casing type is different from that of the second generation static immersion type, but there are also some defects.

5、 Water tank technology is another bottleneck affecting the development of air energy water heater technology. In addition to structural problems, water tank technology is another key technology affecting the service life of water heater. This seems to be an unavoidable stumbling block for the water heater industry. According to the different materials of water tank, the heat pump water tank on the market can be divided into three categories: Enamel tank, stainless steel tank and polymer tank (commonly known as crystal tank). The enamel tank is made of carbon steel with enamel coating inside. The water tank has good anti-corrosion and pressure bearing performance, but the cost is high.