Mainstream technical solutions for heat pump air conditioners
for new energy vehicles
A heat pump is an air conditioning device that can forcefully transfer heat energy from a low-level heat source to a high-level heat source, similar to a "water pump" that can pump water from a low place to a high place. The use of a four-way reversing valve can interchange the functions of the evaporator and condenser of a heat pump air conditioner and change the direction of heat transfer, thereby achieving the effect of cooling in summer and heating in winter.
The theoretical basis of heat pumps comes from the thermodynamic reverse Carnot cycle. The refrigeration and heating of heat pump air-conditioning systems use dedicated electric compressors to drive the refrigeration or heating cycle. In winter, heating is no longer the same as existing electric air conditioners. PTC heating uses electric compressor drive to achieve heating.
At present, research on electric vehicle heat pump air conditioning is mainly divided into three types: 1) heat pump systems based on the existing refrigerant R134a; 2) heat pump technology using refrigerant CO2; 3) solar heat pump air conditioning systems. According to the number of heat exchangers, these systems can be divided into two types: single heat exchanger and double heat exchanger; according to the different compressors, the system can be divided into two different types: sliding vane compressor and scroll compressor.
According to the refrigerant, heat pump air conditioning systems mainly include R134a type and CO2 type. Although CO2 has good thermophysical properties and the global warming potential (GWP) of CO2 is one thousandth that of R134a, since various automotive air conditioning systems currently mainly use refrigerant R134a, parts design, production and after-sales Service and maintenance are designed based on the physical properties of R134a refrigerant, and R134a heat pump air conditioning systems have become the mainstream technology currently being developed.
Using R134a as the refrigerant, there are usually two options for the structure of electric vehicle heat pump air conditioning systems.
1. Option 1: The system consists of an electric air conditioning compressor, a gas-liquid separator, an HVAC assembly (including an in-car condenser, evaporator, evaporator fan, and auxiliary heating PTC), an exterior heat exchanger, and multiple solenoid valves. Generally speaking, it is based on the electric air conditioner commonly used in existing electric vehicles, using an electric compressor, the external heat exchanger is a vertical "V"-shaped fin parallel flow heat exchanger, and increasing in-vehicle condensation inside the HVAC assembly and auxiliary heating PTC, add multiple solenoid valves to the air conditioning pipeline, and control the refrigerant flow direction by controlling the opening and closing of multiple solenoid valves. The combination of multiple solenoid valves can not only switch the flow direction of the refrigerant, but also expand the refrigerant.
2. Option 2: Use an electric compressor to change the flow direction of the refrigerant through a four-way reversing valve. Use an electronic expansion valve to achieve two-way flow of refrigerant. The exterior heat exchanger uses vertical "V" shaped fins for parallel flow exchange. Heater, add auxiliary heating.
In the heat pump air conditioning system of Scheme 2, the cooling and heating principles are similar to Scheme 1. The difference is that the four-way reversing valve can simultaneously switch the refrigerant of the refrigeration TXV valve and the heat pump TXV valve of Scheme 1. The electronic expansion The valve functions as an expansion refrigerant for both the refrigeration TCV and the heat pump TXV. The operation of the system is controlled by a dedicated heat pump controller.
There are differences in the components involved between the above two solutions
The components involved in option one are relatively mature and reliable, and it is less difficult to achieve the cooling and heating functions. However, the system has many components. In order to realize the refrigerant switching and expansion functions, a solenoid valve, a reversing valve and an electromagnetic expansion valve are added. In order to realize the heat exchange function in the car, an in-car condenser is added to the evaporator. It is difficult to arrange the pipeline space, and the air conditioning main unit needs to be redesigned. Because the plan involves many valve bodies, too many pipe joints, the refrigerant flow resistance is large, and the efficiency and energy saving are slightly insufficient. In terms of control accuracy, it is difficult to control accurately and the overall development cost is high.
Option 2 has a simple system structure and involves fewer parts. The core is the four-way reversing valve and the electronic expansion valve. Since the in-car heat exchanger functions as both a condenser and an evaporator in the car, the air-conditioning main unit can be directly borrowed and the pipeline complexity is low. In terms of control accuracy, there are relatively few domestically mature products for electronic expansion valves and four-way reversing valves, and mainstream valve parts manufacturers are currently working on key developments. Special heat pump air conditioning controllers are needed to achieve precise control, which is why various host companies are looking for Key implementation tasks in air conditioning development. At this stage, development and calibration costs are relatively high, and the system cost is equivalent to that of Solution 1. However, as the product becomes more popular and the volume increases, the price will drop significantly. At present, all host companies at home and abroad adopt this solution.
In order to realize the mass industrialization of heat pump systems under the existing industry background, it is a trend to develop the heat pump air conditioning system shown in Plan 2. The industry needs to cultivate core components such as high-speed and high-efficiency electric compressors, exterior and interior heat exchangers, four-way reversing valves, and electronic expansion valves, and promote the components to become mature and reliable as soon as possible. Host companies must improve control over heat pump system integration. Development capabilities.
