With the continuous development of the automotive industry, people's requirements for comfort, reliability, and environmental friendliness of cars are also increasing, and car air conditioning also needs to make technological innovations and changes accordingly; This article mainly elaborates on the current technology and development trends of automotive air conditioning HVAC assemblies. Finally, the existing problems in current research and technology and future development directions are proposed.
HVAC is the abbreviation for Heating Ventilation and Air Conditioning. The automotive air conditioning HVAC assembly is an important component of the automotive air conditioning system, and its power consumption and noise are indicators for evaluating the overall economy and comfort of the vehicle. The optimization of its performance ensures the thermal comfort of the occupants inside the vehicle and the quality of the air intake; With the increasing depletion of traditional energy and the unfavorable atmospheric environment, automotive air conditioning HVAC technology is developing towards greater efficiency, energy conservation, and environmental friendliness. At the same time, more and more attention is being paid to effective prevention, control, and filtration of harmful gases and particles outside the vehicle; At the same time, research on automotive air conditioning HVAC both domestically and internationally aims to analyze the mechanisms of existing technologies and identify performance optimization methods that are insufficient.
1. Composition and Structure of Automotive Air Conditioning HVAC
The automotive air conditioning HVAC assembly, also known as the air conditioner assembly, refers to the unit installed under the dashboard with heating, ventilation, and air conditioning functions, including the blower assembly (including filters), evaporator core, heater core, mixing air door, mode air door and other main components; Structurally, it includes five parts: inlet section, evaporator section, middle section, heating core section, and outlet section, with three modes: blowing surface, blowing feet, defrosting and defogging; On different vehicle models, the HVAC structure varies and there is a certain degree of autonomy in design.
2.Development Trends and Technologies of Air Conditioning HVAC
2.1 HVAC overall structure
The automotive air conditioning HVAC assembly contains three major components (blower, evaporator, heater), which are divided into three box structure, two box structure, and one box structure according to the overall structure of the three components. Currently, the air conditioning assembly has a trend of developing from the former to the latter. The three box structure is rarely used due to its disadvantages such as occupying a large space and increasing the weight of the vehicle, which emphasizes energy conservation and economy, The interface of a one box structure no longer has the limitations of multiple boxes, so the installation of the heat exchanger core is more flexible and free. At the same time, it reduces the overall components, shortens the length of the air duct, and reduces costs. However, it also increases the difficulty of replacing and repairing the heat exchanger core. In addition, the process design of the cross-section is also more difficult, and the advantages and disadvantages of the two box structure are in between, Most recommend using a two box or one box structure.
2.2 Evaporators and heating devices
The evaporator is a key part of HVAC to achieve refrigeration function. After being depressurized by the expansion valve, the liquid refrigerant evaporates inside the evaporator to absorb the heat on the surface of the evaporator and achieve the cooling of the surrounding air. The evaporator is structurally divided into tube type, tube belt type, stacked type, and parallel flow type. The latter two have high refrigeration efficiency, low material consumption, and light weight, so stacked and parallel flow types are widely used. With the development of evaporators towards lightweight and high efficiency, microchannel structured evaporators (such as parallel flow evaporators) have good prospects for use. In terms of optimizing the volume of evaporators, microchannel structures can reduce space by 35% compared to traditional structural forms. In addition, finding new refrigerants with high refrigeration coefficients and no damage to the atmospheric ozone layer is also a research topic in modern automotive air conditioning.
Heating devices are divided into two types according to their working process: wind heating and water heating. Currently, the more widely used type is water heating, which means that a part of the engine's cooling water is introduced into a heat exchanger (heater core, also known as warm air core) to raise the temperature of the cold air blown by the fan and enter the car. But with the high efficiency of the engine and the reduction of waste heat, this heating method also faces problems and challenges. In order to solve the problem of insufficient heating sources in winter, some supplementary heating technologies have emerged: using an independent fuel heater to burn fuel can increase the temperature of the engine antifreeze and improve the heating effect; The auxiliary electric water pump can send hot water into the heat exchanger core when the engine stops running; The method of using friction heating is to add a Viscous heater. Its principle is that the disc connected to the engine shaft and the high viscosity oil rotate and rub to generate heat to supply the heating system; Some new energy vehicles such as electric vehicles use heat pump air conditioning systems, which can achieve efficient and lightweight effects that traditional heating methods cannot achieve, thereby increasing the driving range of electric vehicles.
2.3 Ventilation and air purification devices
The air conditioning filters are the main ones that filter and purify the air outside the vehicle in the HVAC system. Currently, the development trend of automotive air conditioning filters tends to be towards composite filtration, which combines traditional fiber based particulate filters with activated carbon filters. In addition, many electrostatic adsorption filters have a significant effect on filtering fine particles and are widely used. With BYD's green purification technology, The electrostatic generator located in the ventilation system charges particles in the air, changing their direction of movement. After colliding with the filtering material, it is intercepted and subjected to triple filtration (ionization plate, electrostatic cotton, HAF filter element) to reduce PM2.5 in the car.
Contrary to actively filtering out harmful substances, passive prevention and control ventilation systems can also effectively ensure the cleanliness and safety of the air inside the vehicle. Vzleo has developed a new type of air conditioning system, which adopts an automatic internal circulation mode controlled by environmental pollution sensors. When the sensor detects toxic gases (such as carbon monoxide) in the outside air, it will automatically activate the internal circulation mode to isolate the outside air from the passenger compartment; Volvo's Air Quality System (IAQS) is similar to it, but the difference lies in the sensor sensing the content of air pollutants in the car. When it exceeds a certain value, the air intake is automatically closed, and multiple filters (including components soaked in activated carbon) filter and cycle the air inside the car to reduce the content of excessive harmful substances.
Traditional ventilation systems generally suffer from significant heat loss during winter ventilation. The reason is that in order to avoid fogging of the windows, car air conditioners adopt an external circulation method for the return air, which introduces fresh air from the outside into the car and releases humid air outside the car, resulting in significant heat loss. As a result, a new type of double-layer air supply system has emerged. The return air system is divided into two layers, with the upper layer blowing fresh air into the windows for defogging, Then export the car outside, blow the lower layer towards the feet, and use internal circulation to flow in the lower layer inside the car, which can greatly reduce heat loss and reduce fuel consumption.

3. Existing problems and suggestions

1. At present, the research conditions for HVAC systems are relatively single, and static experiments have limitations, ignoring the dynamic changes of external environmental factors during vehicle driving on its internal flow field. Therefore, it is possible to study the influence of different external conditions on the internal flow field characteristics of HVAC systems; Furthermore, current research generally treats the evaporator and heating core sections as porous media, and the simulated data obtained is similar to the experimental data, but there is still a large error compared to the actual process. Therefore, efforts need to be made to find optimized experimental and simulation plans that can reduce the error with the actual situation.
2. Most research on automotive air conditioning ventilation focuses on the central air duct after the HVAC assembly, which independently studies the airflow flow in the central air duct to improve airflow distribution and enhance interior comfort. However, in reality, the HVAC box assembly is connected to the air duct, and their internal flow is closely related. Therefore, studying the ventilation situation from the HVAC system inlet section to the central air duct outlet section is more practical.
3. In terms of air purification, especially particle purification research, there is currently little research in China that focuses on the gas-phase flow field or gas-solid two-phase flow field in automotive HVAC systems. Through CFD analysis, the internal structure is optimized to make the flow field near the filter more uniform to improve filtration efficiency, or to make particles stay as much as possible inside the HVAC flow channel and allow air to flow smoothly into the cabin.
4. The current technology of automotive HVAC systems mostly improves on the existing traditional structure, retaining traditional refrigeration and heating equipment. However, it has not yet fundamentally solved the defects of refrigerant pollution in the environment and reduced engine power caused by air conditioning operation. Therefore, it is necessary to consider theoretically innovating air conditioning technology and designing new and feasible air conditioning systems.

This article introduces the structural composition of automotive air conditioning HVAC assemblies, the development trends of overall and partial structures, as well as the current emerging technologies and research concepts. Overall, automotive air conditioning HVAC is developing towards a trend of lightweight, compact, efficient, energy-saving, and environmentally friendly, while also adapting to the higher demands of modern society's passengers for automotive comfort, safety, and economy.
At present, research on various parts and performance of HVAC systems has become increasingly mature, and a conventional theoretical system and research approach have gradually formed. However, there is still a certain distance from complete system research. Analyzing the shortcomings and shortcomings of current research can provide reference for future research directions.