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Working Principle of Fan Coil Unit Control

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Author : YESNCER
Update time : 2023-11-22 14:01:47

1. Working principle of the fan coil unit

The fan coil mainly relies on the forced effect of the fan to heat the air as it passes through the surface of the heater, thus strengthening the convection heat exchanger between the radiator and the air and quickly heating the air in the room. The fan coil is the terminal device of the air conditioning system, its working principle is to continuously recirculate the exposed air duct in the unit.

The air in the room is cooled (heated) after passing through the cold water (hot water) coil to keep the room temperature constant. Usually, it is processed by the fresh air unit and sent indoors to meet the demand for fresh air volume in the air-conditioned room.

2. Working principle of fan coil unit control

Fan coil unit control mostly adopts a local control scheme, which is divided into two types: simple control and temperature control:
Simple control of fan coil unit:
Use the three-speed switch to directly manually control the three-speed conversion and start and stop of the fan.
Fan coil temperature control:
Use the thermostat to automatically control the opening and closing of the electric two/three-way valve and the three-speed conversion of the fan based on the comparison and calculation of the set temperature and the actual detected temperature, or directly control the three-speed conversion and start-stop of the fan, thereby controlling The system water flow or air volume reaches constant temperature.

3. Working principle of fan coil system

The fan coil unit is mainly composed of a fan, a heat exchange coil, and a casing. According to the external static pressure of the fan coil unit, it can be divided into standard type and high static pressure type. According to the number of heat exchange coil rows, it can be divided into two rows and three rows. , the heat exchange coil is generally made of copper tubes strung with aluminum fins. The outer diameter of the copper tube is 10~16mm, the fin thickness is about 0.15~0.2mm, and the spacing is 2.0~3.0mm. The fan generally adopts double air inlet front curved blade centrifugal The fan and motor adopt a capacitive 4-pole single-phase motor with three-speed speed, and the casing and condensate pan are insulated.
 

4. Working principle of fan coil air conditioning system

The fan coil unit is used to continuously circulate indoor air so that it can be cooled or heated through the coil to maintain the required temperature and a certain relative humidity of the room. The cold or hot water used in the coil is supplied by centralized cold and heat sources. At the same time, the fresh air after centralized treatment in the fresh air conditioning machine room is sent to each air-conditioned room through special fresh air ducts to meet the hygienic requirements of the air-conditioned room.

Compared with centralized systems, fan coil air conditioning systems have no large air ducts, only water pipes, and smaller fresh air ducts. They have the advantages of easy layout and installation, small building space occupation, and good individual adjustment. They are widely used for temperature and humidity accuracy. It is suitable for comfortable air conditioners with low requirements, many rooms, small rooms, and individual control.

The working principle of a fan coil unit is not as complicated as that of a central air conditioner. In fact, we can think of a fan coil unit as a fan, but the wind blown out by this fan is the temperature we need. There are currently many fan coil units on the market. In order to save costs, many companies will choose domestic fan coil units instead of imported central air conditioning hosts. This will not affect the operation and use of the entire central air conditioning system.

5. Basic knowledge of central air conditioning fan coil units

In order to meet the design and selection of different occasions, the types of fan coil units include horizontal concealed fan coil units (with air box), horizontal exposed fan coil units, vertical concealed fan coil units, and vertical exposed fan coil units, cassette two-outlet fan coil, cassette fan coil, and wall-mounted fan coil, etc. ​
The fan coil unit is mainly composed of a low-noise motor, coil unit, etc. The cold (hot) water in the coil is centrally supplied from the machine room.

Central air conditioning fan coil units are divided into five types according to their forms: horizontal concealed installation, horizontal exposed installation, vertical concealed installation, vertical exposed installation, and cassette fan coil units;

According to whether there is a condensate water pump, it can be divided into ordinary cassette fan coil units and luxury cassette fan coil units;


Fan coil units can be divided into 0Pa, 12Pa, 30Pa, 50Pa, 80Pa, etc. according to the static pressure of the unit. This refers to the static pressure outside the machine;

According to the number of rows of pipes, central air conditioning fan coil units can be divided into: two rows of pipes, three rows of pipes; and two pipes and four pipes:


The two pipes are ordinary fan coil units that use cold water for cooling in summer and hot water for heating in winter;

Four-pipe fan coil units are mostly used in some more luxurious places. They can carry hot and cold water at the same time, that is, they can cool some rooms and heat some rooms as needed.

Two rows of pipes have one pipe in for cold water and one pipe out for cold water in summer, one pipe for hot water and one pipe out for hot water; three rows of pipes have two pipes for water in, one for cold water and one for hot water, and one for hot water at the same time. Pipe out water.
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