Classification of air conditioning systems
Air conditioning systems are electromechanical systems that regulate indoor air parameters such as temperature, humidity, cleanliness, and airflow. Based on multiple core dimensions, including the target user, air handling method, equipment installation type, media delivery method, and airflow regulation method, they can be categorized into different types. Each type of system is adapted to different building scenarios and usage requirements. The specific classifications are as follows:
I. Classification by service recipients and usage scenarios
This classification method is based on the service scope, environmental requirements, and usage scenarios of air conditioners, and is the most basic classification method in engineering.
1. Comfort air conditioning system
With the core objective of meeting human comfort needs, the system requires moderate precision in controlling air parameters, focusing on creating a comfortable living, working, and leisure environment. It operates with a reasonable temperature difference, low noise, and uniform airflow, without strict standards for precise temperature and humidity control. Ordinary air conditioners are widely used in residential, office, shopping mall, hotel, school, passenger car, and rail transit vehicles, among other civilian applications.
2. Process air conditioning system
Designed to meet the process requirements of industrial production, precision equipment operation, and experimental testing, these systems have strict and fixed precision requirements for parameters such as indoor temperature, humidity, cleanliness, airflow velocity, and pressure difference, and are not limited by human comfort needs. Some scenarios require year-round constant temperature and humidity, dust prevention, and sterilization. Data center air conditioners are mainly used in electronic cleanrooms, precision instrument laboratories, pharmaceutical workshops, operating rooms, archives, and industrial production plants.
II. Classification by the location of air handling equipment
Based on the installation layout of the core air handling equipment (evaporator, heater, filter, fan, etc.), air conditioning systems are divided into three categories: centralized, semi-centralized, and decentralized. This is the core classification method for HVAC engineering.
1. Centralized air conditioning system
All air handling units, fans, and chiller/heater equipment are centrally located in a dedicated air conditioning room. The treated air is then distributed to each room via ductwork, while return air is centrally collected and treated. This system handles large air volumes, provides excellent air purification, and facilitates maintenance and management due to its centralized equipment. The room occupies a dedicated space, and there is no noise from large equipment inside. However, the ductwork system is complex, requires significant ceiling height, and is prone to dust accumulation in the ducts. It is suitable for large public buildings, such as large shopping malls, stadiums, airports, office buildings, theaters, and other large-area, multi-room unified air conditioning scenarios.
2. Semi-centralized air conditioning system
Combining the advantages of centralized and decentralized systems, the cold and heat source equipment is centrally located, while the air terminal handling equipment is distributed throughout each air-conditioned room. Common equipment includes fan coil units and a fresh air system. Fresh air is centrally processed and delivered from a central equipment room, while indoor temperature and humidity are independently regulated by the fan coil units within each room. The system features simple piping, minimal floor height requirement, independent temperature control for each room, and high flexibility. It is widely used in small to medium-sized buildings with high demands for independent temperature control, such as hotel rooms, office buildings, apartments, and hospital wards.
3. Decentralized air conditioning systems (local air conditioning systems)
need for a centralized server room, integrating all equipment for cooling, heating, air supply, and temperature control into a single unit. This unit is directly installed within the air-conditioned room, independently handling air processing. Common equipment includes split-type wall-mounted/floor-standing units, portable air conditioners, and window air conditioners. The system is easy to install, low-cost, allows for flexible start-up and shutdown, and requires no ductwork or water pipes. However, individual units have a small coverage area, overall energy efficiency is relatively low, and indoor equipment can generate noise. It is suitable for small spaces and decentralized air conditioning scenarios such as homes, small offices, and single-room shops.
III. Classification by Media Delivery Method
The classification of air conditioning systems based on the different media used to transport heat and cold determines the system piping configuration, heat exchange efficiency, and applicable scenarios.
1. All-air conditioning system
Using air as the sole transport medium, this system delivers treated air (both hot and cold) through ductwork to control indoor air conditioning. It boasts strong air purification capabilities, a large fresh air volume, and excellent ventilation, offering multiple air treatment functions including humidification, dehumidification, and purification. The absence of water pipes eliminates the risk of leaks. However, the ductwork has a large cross-sectional area, occupies significant building height, and exhibits considerable airflow resistance. It is primarily used in large spaces with high air quality requirements, such as shopping malls, exhibition halls, stadiums, and cleanrooms.
2. Air-water air conditioning system
Simultaneously, using air and water as transport media, centrally processed fresh air is delivered indoors through ducts, and indoor terminal equipment achieves heat exchange through water circulation. The most typical example is the fan coil unit + fresh air system . Water's heat exchange efficiency is far higher than that of air, the ductwork is small in size and occupies little space, and the temperature control speed is fast. Balancing fresh air quality and space utilization, it is currently the most widely used system type in civil buildings.
3. All-water air conditioning system
Using water as the sole transport medium, hot and cold water are delivered to indoor terminal devices ( fan coil units , radiators, etc.) through water pipes. Indoor temperature is regulated solely by water circulation and heat exchange, with no centralized fresh air supply. The system features extremely simple piping, minimal floor height requirements, and low cost, but it lacks active ventilation, resulting in poor indoor air quality, stuffiness, and oxygen deficiency. It is typically used in conjunction with window ventilation or simple fresh air systems and is commonly found in older buildings, ordinary residences, and small office spaces.
4. Refrigerant direct evaporation system
Using refrigerant (such as Freon) as the heat exchange medium, the outdoor and indoor units are directly connected by copper pipes. The refrigerant evaporates directly within the pipes for heat exchange, eliminating the need for water or air intermediaries. Common equipment includes multi-split systems (VRF/VRV) and split-type air conditioners . The system boasts high heat exchange efficiency, excellent energy saving, flexible installation, precise temperature control, and independent operation for each room. It is suitable for small to medium-sized office buildings, villas, shops, and renovated buildings.
IV. Classification by air volume adjustment method
For centralized and semi-centralized all-air systems, they are classified according to whether the air volume is adjustable during operation.
1. Constant air volume air conditioning system
During system operation, the air volume supplied to the room remains constant, and the supply air temperature is adjusted to adapt to changes in indoor heating and cooling loads. The system has a simple structure, stable operation, low failure rate, and convenient maintenance, but its energy consumption is high when the load is low, and it cannot save energy as needed. It is mostly used in fixed scenarios with stable loads and low energy-saving requirements, such as factories, public corridors, and ordinary exhibition halls.
2. Variable Air Volume (VAV) Air Conditioning System
It maintains a constant supply air temperature and automatically adjusts the air volume supplied to the room based on real-time changes in indoor heating and cooling loads and the number of people. It reduces air volume and energy consumption during low loads and increases air volume during high loads, resulting in significant energy savings and higher temperature control accuracy. The system boasts a high degree of intelligence, but also higher equipment costs and control complexity. It is suitable for scenarios with large load fluctuations, such as large high-end office buildings, business centers, and intelligent public buildings.
V. Classification by source of heating and cooling load
1. Electric compressor air conditioning system
Relying on electric power to drive the compressor to complete the refrigeration cycle, and with heating mostly achieved through electric auxiliary heating or heat pump heating, this is currently the most widely used system type, including residential air conditioners, multi-split systems, screw chillers, and centrifugal chillers . It is suitable for the vast majority of civil and industrial applications.
2. Absorption air conditioning system
Powered by thermal energy sources such as hot water, steam, and natural gas, refrigeration is achieved through lithium bromide absorption chillers, utilizing industrial waste heat, natural gas, and other energy sources. Electricity consumption is extremely low, energy utilization is high, and it is energy-saving and environmentally friendly; however, the units are large and require high initial investment. They are primarily used in industrial parks, large factories, and public buildings with well-developed energy infrastructure, where there are stable waste heat sources.
VI. Classification by Fresh Air Supply Method
1. DC air conditioning system (fresh air system)
All outdoor fresh air is treated before being supplied indoors, absorbing excess heat and moisture before being directly exhausted, with no return air circulation. Air cleanliness is extremely high, with no cross-contamination of indoor air, but energy consumption is extremely high. Suitable for special industrial workshops, laboratories, infectious disease wards, and other scenarios involving toxic, harmful, or dusty environments where return air is strictly prohibited.
2. Closed-loop air conditioning system (full return air system)
It does not introduce fresh outdoor air, but recirculates and processes the existing indoor air throughout the entire process, only regulating temperature and humidity without ventilation. Energy consumption is extremely low, but indoor air quality is poor, bacteria easily grow, and oxygen levels are insufficient. It is only suitable for enclosed spaces where no one stays for extended periods and fresh air is not required, such as underground equipment rooms, warehouses, and special sealed storage tank spaces.
3. Hybrid air conditioning system
Combining the advantages of both fresh air and return air systems, this system employs a hybrid "fresh air + return air" approach. It introduces some outdoor fresh air to ensure indoor air quality while utilizing indoor return air to reduce air conditioning energy consumption. This is the fresh air mode currently used in the vast majority of buildings, balancing comfort, health, and energy conservation.
