Yesncer’s knowledge about fan coil units
What is this article talking about？
In daily central air conditioning systems, the most common air conditioning method should be a fan coil plus fresh air system. This is almost universally recognized. The fan coil air conditioning system is a unit composed of a fan and a coil placed directly in the room. During operation, hot or cold water flows through the coils as needed. This machine draws indoor air into the unit, and after filtering, it is cooled or heated by the coil. Then it is sent back to the room, where the indoor temperature and humidity are cyclically adjusted. The fresh air required indoors is usually outdoor air. After centralized treatment by the fresh air treatment unit, it is sent indoors through pipes. Since the refrigerant and heat medium used by fan coil units are also centrally supplied, most fan coil air conditioning systems are semi-centralized air conditioning systems. In this system, cold or heat is brought into the air-conditioned room through air and water respectively, so it is an air-water system.
The system is widely used in high-end multi-story buildings such as hotels, apartments, hospitals, and office buildings. This air conditioning system is also more suitable for older buildings with smaller areas and more rooms that require additional air conditioning, because it occupies a small area and is easy to install and construct.
- Characteristics of fan coil air conditioning system
① Compared with the centralized air conditioning system, only fresh air air conditioning is needed in the computer room. The computer room occupies a small area and has a low floor height. Fan coil units are placed in air-conditioned rooms with limited space.
② Only fresh air system is required, the cross-sectional area of the air duct is small and easy to arrange.
③The coil can pass both cold water and hot water, and can be used in winter and summer. However, coils are prone to scaling, which affects the heat transfer effect.
④ Flexible operation, the load of each room can be adjusted by itself, and the energy-saving effect is good, but it cannot achieve energy-saving operation adjustment under various working conditions throughout the year.
⑤Easy installation, short construction time and long service life.
⑥The fan coil layout is scattered, and the layout of air ducts, water pipes, condensate pipes and other pipelines is complicated. Water systems are prone to leaks and maintenance and management are cumbersome.
⑦It is difficult to meet the strict requirements of temperature, humidity and cleanliness.
⑧Fan coil units generally use low-noise fan coil units.
- Structure and type of fan coil unit
The unit is mainly composed of the main engine, motor, coil, air filter, condensate pan and box. In addition, there is an automatic indoor temperature adjustment device. Its structure is as shown in the figure:
The unit box is made of steel plate frame and thin steel plate, and the air outlet grille can be fixed or adjustable. The housing panels can be removed to provide easy access to internal equipment. The surface of the surface-mounted unit box is sprayed with colorful paint to coordinate with the architectural decoration and can also be used as indoor furnishings. There are two types of air outlet locations: upper air outlet and front air outlet.
The fan is a double-inlet centrifugal fan. The impeller is molded from an aluminum plate, has low noise, and is driven by a low-noise motor with adjustable speed. It has three wind speeds: high, medium and low, which can change the air volume of the fan.
Coils generally use fin heat exchangers, with copper tubes enclosed in aluminum sheets. The copper tube and aluminum sheet are closely combined and have good heat transfer performance. There is a drain pan underneath to collect condensation water.
The air filter is usually located at the bottom or side of the unit and is used to filter dust in the return air. Generally, coarse-pore foam plastic is used as the filter material, and the filter is made into a drawer type for easy replacement and cleaning.
The fan coil room temperature automatic adjustment device is shown in the figure.
It consists of a temperature sensing element, a two-position room temperature regulator and a small motor three-way reversing valve. Under the action of the temperature sensing element, the water quantity valve is adjusted to provide intermittent water supply to the unit and adjust the room temperature.
Fan coil units come in various forms, such as vertical exposed installation, vertical concealed installation, horizontal exposed installation, and horizontal concealed installation. The selection and arrangement of air conditioning coils are related to the nature of use of the air conditioner and the architectural form. Room. For hotel rooms, they are generally arranged on the ceiling of the corridor at the entrance, using horizontal concealed units, as shown in the figure:
This kind of arrangement is beautiful, does not occupy the effective area of the room, and has low noise. From the perspective of indoor air flow organization and uniform temperature distribution, this method is particularly suitable for summer use.
For rooms with no ceiling installation space, such as offices and hospital wards, vertical exposed or concealed units are generally used and placed under the exterior wall.
Vertical units are mostly used in rooms with larger spaces and indoors in winter and summer. It has good temperature uniformity and is especially suitable for air supply in winter. The vertical unit is easy to install and maintain, but it takes up the effective use area of the room.
In recent years, my country has begun to produce and use ceiling-mounted (also known as cassette-type four-side air outlets) exposed/concealed units. The main advantages of this type of unit are that it does not occupy the usable area of the room and is simple to install, inspect and maintain. However, when this kind of unit is used in winter, the indoor temperature gradient will be larger, and it is generally not suitable for places where heating is the main focus in winter.
- Fresh air supply method for fan coil air conditioning system
① Rely on the natural penetration of outdoor air through gaps such as indoor doors and windows and the mechanical exhaust of bathrooms and toilets to supply fresh air. At this time, the air processed by the unit is internal circulation air.
This solution has low initial investment and operating costs, but it is difficult to guarantee the supply of fresh air and the indoor sanitary conditions are poor. In addition, the unorganized penetration of fresh air makes it difficult to distribute indoor temperature and humidity evenly. Therefore, this method is only suitable for installing fan coil air conditioning systems in old buildings, and it is difficult to arrange new air ducts.
② Drill holes in the outer wall of the room to introduce fresh air directly into the fan coil unit. The fresh air outlet adopts an adjustable form and operates according to the minimum fresh air volume in winter and summer. Use as much fresh air as possible during transitional seasons.
Although this method can better ensure fresh air, the indoor temperature is greatly affected by the outside temperature. Outdoor noise will also enter the room directly from the fresh air outlet, which will also affect the beauty of the building.
③Fresh air is provided by an independent fresh air system. The fresh air after centralized treatment is sent to each air-conditioned room through the air supply duct. The air supply outlet of the air supply duct can directly supply fresh air from the upper part of the room, or it can be shared with the fan coil air supply outlet through a louver to supply air. Fresh air can also be sent into the return air box of the fan coil and heated together with the coil. After the exchange is completed, you will be sent to the room. For air-conditioned buildings with strict sanitary conditions, an independent fresh air system is very suitable. Many hotels have adopted this approach in recent years. This fresh air supply method can be adjusted according to changes in outdoor air conditions to ensure the stability of indoor air condition parameters. In addition, the fresh air volume in the room can be guaranteed all year round. At present, the fresh air supply of fan coil air conditioning systems mostly adopts this method.
