Full analysis of the operation modes of air-cooled cooling and heating units

As a key equipment in modern air-conditioning systems, air-cooled chillers are widely used in commercial buildings, large residential areas and various places that require centralized air conditioning due to their high efficiency, flexibility and environmental protection. It can switch between multiple operating modes according to different environmental requirements and usage scenarios, thereby achieving functions such as cooling, heating and energy recovery. Next, we will introduce the common operating modes of air-cooled chillers in detail.

Cooling mode

In the hot summer, the cooling mode is one of the common operating modes of air-cooled chillers. Its working process is based on the reverse Carnot cycle principle. First, the compressor, as the "heart" of the entire refrigeration cycle, sucks in the low-temperature and low-pressure gaseous refrigerant from the evaporator and compresses it to turn it into a high-temperature and high-pressure gaseous refrigerant. This process greatly increases the temperature and pressure of the refrigerant, laying the foundation for subsequent heat release.

Subsequently, the high-temperature and high-pressure gaseous refrigerant enters the wind-side heat exchanger (condenser). Here, the fan blows the cold air in the surrounding environment through the condenser fins, and the gaseous refrigerant exchanges heat with the cold air, releasing a large amount of heat, and gradually condenses itself into liquid. The pressure of the condensed liquid refrigerant is still high, and then it flows into the throttling device (such as an expansion valve or capillary tube). The function of the throttling device is to reduce the pressure and throttle the liquid refrigerant, turning it into a low-temperature and low-pressure gas-liquid two-phase mixture, and then enter the water-side heat exchanger (evaporator).

In the water-side heat exchanger, the low-temperature and low-pressure refrigerant evaporates quickly, absorbing the heat of the circulating water passing through the heat exchanger, reducing the temperature of the circulating water. The cooled circulating water is transported to the indoor air-conditioning terminal equipment (such as fan coil units, modular air-conditioning boxes, etc.) through a water pump to exchange heat with the indoor air, thereby reducing the indoor air temperature and creating a cool and comfortable indoor environment for people. The refrigerant that has absorbed the heat becomes gaseous again and is sucked into the compressor, starting a new round of refrigeration cycle.

The cooling mode is widely used in various places that need to be cooled in summer, such as commercial buildings such as office buildings, shopping malls, hotels, hospitals, and centralized air-conditioning systems in residential areas. Its advantage is that it can quickly and efficiently reduce the indoor temperature, and compared with the water-cooled refrigeration system, it does not require an additional cooling water system (such as cooling towers, cooling water pumps and pipes, etc.), reducing installation space and maintenance costs. It is especially suitable for areas where water resources are scarce or it is difficult to install a cooling water system.

Heating mode

When winter comes, the air-cooled heating and cooling unit switches to heating mode to bring warmth to the room. The working principle of heating mode is opposite to that of cooling mode. In essence, the functions of the evaporator and condenser in the refrigeration cycle are interchanged. This process is mainly achieved with the help of a four-way reversing valve.

In heating mode, the high-temperature and high-pressure gaseous refrigerant discharged from the compressor first enters the water-side heat exchanger (which acts as a condenser at this time). Here, the refrigerant transfers a large amount of heat it carries to the circulating water passing through the heat exchanger, raising the temperature of the circulating water. The high-temperature circulating water is transported to the indoor heat dissipation equipment (such as radiators, fan coils, etc.) through a water pump, releasing heat to the indoor air, thereby raising the indoor temperature.

After releasing heat, the refrigerant condenses into liquid, and after being depressurized by the throttling device, it enters the wind-side heat exchanger (which serves as an evaporator at this time). In the wind-side heat exchanger, the liquid refrigerant absorbs heat from the surrounding air and evaporates into gas. Although the ambient air temperature is low in winter, there is still a certain amount of heat in the air. Through efficient heat exchanger design and advanced heating technology, air-cooled chillers can effectively extract heat from the air. The gaseous refrigerant is sucked into the compressor again to complete the heating cycle.

The heating mode is suitable for areas that need heating in winter, especially those places without central heating facilities or with high requirements for heating flexibility, such as small commercial buildings, villas, apartments, etc. Compared with traditional electric heating, air-cooled heating and cooling units have higher energy efficiency ratios, can use free heat in the air, and reduce energy consumption and operating costs. At the same time, compared with gas heating, it is cleaner and more environmentally friendly, without worrying about exhaust emissions from combustion.

Heat recovery mode

As people's requirements for energy efficiency and environmental protection continue to increase, the heat recovery mode of air-cooled chillers is gaining more and more attention. The heat recovery mode aims to recycle the heat that was originally discharged to the environment during the cooling or heating process, thereby improving the comprehensive utilization rate of energy and reducing energy waste.

During the refrigeration process, the workflow of the heat recovery mode is as follows: part of the high-temperature and high-pressure gaseous refrigerant discharged from the compressor enters the air-side heat exchanger (condenser) for conventional condensation and heat dissipation, and the other part enters the heat recovery device. The heat recovery device usually adopts an efficient heat exchange structure to exchange heat with domestic water or other heat users that need to be heated. In the heat recovery device, the refrigerant transfers heat to the heated medium and partially condenses itself. The refrigerant after passing through the heat recovery device merges with the refrigerant coming out of the air-side heat exchanger, and together they enter the evaporator after being reduced in pressure by the throttling device to complete the refrigeration cycle. By monitoring and controlling the temperature of the domestic hot water tank or the needs of other heat users, the system can automatically adjust the refrigerant flow entering the heat recovery device and the condenser to achieve a better heat recovery effect.

The heat recovery mode can also play a role in the heating process. When the unit is in the heating state, the water-side heat exchanger (condenser) can release heat to the circulating water while transferring part of the heat to the heat recovery system for preheating domestic water or meeting other low-grade heat needs. This heat recovery method in the heating process further improves the overall energy efficiency of the unit and realizes the cascade utilization of energy.

The heat recovery mode has significant energy-saving and environmental benefits. In some places where there is a demand for both refrigeration and hot water, such as hotels, hospitals, sauna and bath centers, the heat recovery mode can produce domestic hot water for free or at low cost while providing refrigeration services, greatly reducing the energy consumption of hot water heating equipment. According to statistics, under normal air-conditioning conditions, the heat recovery mode can recover 30%-80% of the cooling capacity, which not only improves energy efficiency, but also reduces thermal pollution to the environment. At the same time, the heat recovery mode helps to reduce the overall energy consumption of buildings, which is in line with the current concept of green buildings and sustainable development, and brings long-term economic and environmental benefits to users.

Cooling + Heating Mode

In some special building scenarios, such as different functional areas of large commercial complexes, different departments and laboratories in hospitals, there may be a demand for both cooling and heating. The cooling + heating mode of air-cooled chillers can well meet such complex needs.

Air-cooled cooling and heating units with cooling + heating modes usually use advanced system design and control technology. For example, dual compressor or multi-compressor design is adopted to provide cooling and heating for different areas or different needs through independent cooling and heating circulation loops. During operation, the control system of the unit will accurately adjust the operating parameters of the cooling and heating cycles according to the temperature set value and actual temperature feedback of each area, ensuring that the temperature of the cooling area is maintained at a low level, while the temperature of the heating area is maintained at a high level.

Taking a large commercial complex as an example, the dining area of a shopping mall usually requires a large amount of cooling to maintain a comfortable ambient temperature due to the dense crowds and heat dissipation of cooking equipment; while some stores (such as clothing stores, bookstores, etc.) may need a certain amount of heat to increase the indoor temperature in winter due to factors such as closed space and heating of lighting equipment. At this time, the cooling + heating mode of the air-cooled chiller can cool the dining area and heat other stores at the same time, realizing differentiated temperature control in different areas of the same building.

The advantage of this model is that it can flexibly respond to complex building cooling and heating needs, and improve the comfort and satisfaction of the indoor environment. At the same time, compared with installing refrigeration equipment and heating equipment separately, the use of air-cooled cooling and heating units with cooling + heating modes can reduce the equipment footprint, reduce initial investment costs and operation and maintenance costs, and improve the overall reliability and stability of the system.

The various operating modes of air-cooled chillers enable them to adapt to a variety of application scenarios and user needs, creating a comfortable indoor environment for people while achieving efficient use of energy and sustainable development. With the continuous advancement of science and technology, the operating mode of air-cooled chillers will become more intelligent and efficient, making greater contributions to building energy conservation and environmental protection. Whether in the commercial center of a bustling city or a quiet and comfortable residential area, air-cooled chillers are silently playing an important role and becoming the guardian of the comfortable environment of modern buildings.