Air conditioning, referred to as air conditioning for short, is a special technology that sends the treated air into the room in a certain way, so that the temperature, humidity, cleanliness and flow rate of the indoor air are controlled in an appropriate range to meet the needs of life comfort and production technology. Central air-conditioning system is an air-conditioning system in which a host computer (or refrigeration system or air supply system) supplies air through a duct or drives multiple terminals with cold and hot water sources to achieve indoor air conditioning.

5.2 air conditioning system classification

According to different classification standards, air conditioners can be divided into the following categories:

5.2. 1 Classification by conveying working medium.

5.2. 1. 1 all-air air conditioning system

The air conditioning system in which the treated air bears all the heat and humidity loads in the air-conditioned room is called all-air air conditioning system, also known as duct air conditioning system. All-air air conditioning system uses air as transport medium. It uses the cold/heat generated by the outdoor host to cool/heat the return air (or the mixed air of return air and fresh air) brought back from the room, and then sends it into the room to eliminate the cold/heat load of the air conditioner.

Fig. 5. 1 ducted central air conditioning system

The advantages of all-air air conditioning system are simple configuration, small initial investment, introduction of fresh air, and improvement of air quality and human comfort. However, its shortcomings are also obvious: it is difficult to install, the air distribution system occupies a large building space, and generally requires a large floor of the house, and the problem of air duct passing through the wall should also be considered. Moreover, it is difficult to meet the different air conditioning load requirements of different rooms without VAV terminal by using unified air supply mode.

5.2. 1.2 air conditioning system of hot and cold water units

An air conditioning system in which all the hot (cold) and wet loads of an air-conditioned room are borne by water is called a cold/hot water air conditioning system. The conveying medium of cold/hot water air conditioning system is usually water or glycol solution. It generates cold/hot water of air conditioner through outdoor host computer, and sends it to indoor terminal equipment through pipeline system, where the cold/hot water exchanges heat with indoor air to generate cold/hot air, thus eliminating the cold/hot load of room air conditioner.

Figure 5.2 Central air conditioning system of cold and hot water units

The indoor terminal equipment of the system is usually a fan coil unit. At present, the fan coil can generally adjust its fan speed (or adjust the water flow through the coil through the bypass valve), thus adjusting the cold/heat of the delivery room, so it can meet the different needs of each room and has good energy saving. In addition, its power transmission and distribution system occupies a small space and is generally not limited by the height of residential buildings. However, this system is generally difficult to introduce fresh air, so its comfort is poor for usually closed air-conditioned rooms.

5.2. 1.3 air-water air conditioning system

The air-conditioning system in which the heat and humidity load of an air-conditioned room is shared by water and air is called air-water air conditioning system. Its typical device is fan coil plus fresh air system. Air-water air conditioning system uses fan coil or inducer to heat and humidify the air in the air-conditioned room. The air needed in the air-conditioned room is treated by the central air conditioning system and then sent to each air-conditioned room through the air supply pipeline.

Air-water air conditioning system solves the problem that cold/hot water air conditioning system can't be ventilated, and overcomes the shortcomings that all-air system needs large air duct area and takes up more building space.

5.2. 1.4 refrigerant air conditioning system

Refrigerant central air-conditioning system, referred to as VRV (Variable Refrigerant Volume) system, takes refrigerant as the conveying medium, the outdoor host is composed of outdoor heat exchanger, compressor and other accessories, and the terminal device is an indoor unit composed of direct evaporative heat exchanger and fan, and the refrigerant directly evaporates and absorbs heat in the fan coil. An outdoor unit can transport refrigerant liquid to several indoor units through pipes. By controlling the refrigerant circulation of the compressor and the refrigerant flow into the indoor heat exchanger, the indoor cooling/heating load demand can be met in time.

Figure 5.3 Refrigerant Central Air Conditioning System

Refrigerant air conditioning system has many advantages, such as energy saving, comfort, stable operation and so on. Each room can be adjusted independently to meet the needs of different air conditioning loads in different rooms. However, the control of the system is complicated, which requires high pipe material, manufacturing technology and on-site welding, and its initial investment is also relatively high.

Depending on the host.

According to the host type, air conditioners can be divided into compression type and absorption type.

Compression type

Including piston type, screw type (single screw and twin screw), centrifugal type and scroll type.

5.2.2.2 absorption type

(1) Classification by purpose

(1) water chiller, which provides cold water for air conditioning or process. There are four kinds of cold water outlet temperatures: 7℃, 10℃, 13℃, 15℃.

(2) Hot and cold water units, supplying air conditioning and domestic hot and cold water. The inlet and outlet temperature of cold water is12℃/7℃; The inlet and outlet temperature of heating hot water is 55℃/60℃.

(3) Heat pump unit, which relies on the energy of driving heat source to raise the heat from low potential energy to high potential energy for heating or technological process. The temperature of output heat is lower than the temperature of driving heat source, and the heat pump unit used for heating is called the first kind of absorption heat pump; The temperature of the output heat is higher than that of the driving heat source, and the heat pump unit with the purpose of heating up is called the second kind of absorption heat pump.

(2) according to the driving heat source classification

① Steam type, with steam as the driving heat source. The working steam pressure of single-effect unit is generally 0. 1MPa (table); The working steam pressure of the double-effect unit is 0.25 ~ 0.8 MPa (table).

(2) Direct-fired, with the combustion heat of fuel as the driving heat source. According to the type of fuel used, it can be divided into fuel type (light oil or heavy oil) and gas type (liquefied gas, natural gas and city gas).

③ Hot water type, with sensible heat of hot water as the driving heat source. The hot water temperature range of single-effect unit is 85 ~150℃; Hot water temperature of double-effect unit > 150℃.

(3) According to the utilization mode of the driving heat source.

(1) single effect, the driving heat source is directly used once in the unit.

② Double-effect, the driving heat source is directly used in the high-pressure generator of the unit, and the generated high-temperature refrigerant vapor is indirectly used in the low-pressure generator.

③ Multi-effect, which drives the heat source to be directly and indirectly used for many times in the unit.

5.2.3 According to the use requirements

Air conditioners commonly used in production or scientific experiments are called "process air conditioners", and air conditioners used to ensure human comfort are called "comfort air conditioners". Process air conditioning not only meets the special requirements of special processes, but also often meets the comfort requirements of staff. So the two are closely related.

Comfortable air conditioning

The task of comfortable air conditioning is to create a comfortable working environment, ensure people's health and improve work efficiency. Widely used in office buildings, conference rooms, exhibition halls, theaters, libraries, gymnasiums, shopping malls, hotels, restaurants and so on.

5.2.3.2 craft air conditioning

Process air conditioning mainly depends on process requirements, and different departments vary greatly. Generally speaking, it is mainly divided into cooling air conditioning and constant temperature (constant humidity) air conditioning.

(1) air conditioning system is essential in textile industry, printing industry, watch industry, film industry, food industry, cigarette industry and grain depot. The task of some refrigeration and air conditioners is to keep the operator's hands from sweating, not to affect the production process and product quality, and to prevent the products from getting wet.

⑵ Indoor environments such as control rooms, measuring rooms, inspection rooms and computer rooms in electronic industry, instrument industry, synthetic fiber industry and scientific research institutions require constant temperature and humidity.

⑶ Some technological processes closely related to modern industry and cutting-edge technology not only require a certain temperature and humidity, but also have strict requirements on the dust content and particle size of air, such as "industrial clean rooms" in precision machinery industry and semiconductor industry; "Biological cleanrooms" such as pharmaceutical workshops, aseptic laboratories, burn wards and operating rooms also stipulate the number of bacteria in the air per unit volume.

5.2.4 Classification according to the situation of air handling equipment.

5.2.4. 1 central air conditioning system

Central air conditioning system refers to the air conditioning system that purifies, cools (or heats), humidifies (or dehumidifies) the air in the same building, and then transports and distributes it.

The central air conditioning system is characterized in that air handling equipment, air supply and return fans are concentrated in the air-conditioned room, which is connected with the air-conditioned place through the return air pipeline to centrally treat and distribute the air; Centralized central air conditioning system has centralized cold source and heat source, which are called freezing station and heat exchange station respectively; Large air handling capacity, safe and reliable operation and convenient maintenance and management, but the computer room occupies a large area.

Semi-centralized air conditioning system in 5.2.4.2

Semi-centralized air conditioning system, also known as hybrid air conditioning system, is developed on the basis of centralized air conditioning system. In addition to the air handling equipment of central air-conditioning system, there are also air handling equipment scattered in air-conditioned rooms to treat indoor air locally or supplement air from central air-conditioning equipment, such as inducer system and fan coil system. This kind of air conditioner is suitable for buildings with many air-conditioned rooms, and the air parameters of each room need to be adjusted independently.

Centralized air conditioning system and semi-centralized air conditioning system can usually be called central air conditioning system.

Decentralization in 5.2.4.3

Decentralized systems are also called local or independent air conditioning systems. It is characterized by dispersing air treatment equipment in each room. People's common window air conditioners and split air conditioners belong to this category.

5.2.5 According to the condensation mode of the condenser

According to the cooling mode of condenser, the main engine can be divided into air-cooled and water-cooled. The main difference is that water cooling has a cooling circulation system, a cooling pump and a cooling tower fan.

Figure 5.4 Schematic diagram of water cooling refrigeration

The main structural features of common water-cooled chillers are that the condenser and evaporator are shell-and-tube heat exchangers, and equipped with cooling water system equipment (cooling water pump, cooling tower, water treatment device, water filter and cooling water system pipeline, etc.). ), so the cooling effect is better.

Figure 5.5 Schematic Diagram of Air-cooled Refrigeration

Air cooled chiller refers to equipment (cooling water pump, cooling tower, water treatment device, water filter and cooling water system pipeline, etc. The cooling fan of the condenser replaces the cooling water system in the water-cooled chiller, which makes the huge chiller simple and compact.

Air-cooled units can be installed in outdoor open spaces or roofs, and there is no need to build a machine room.