Fan-coil air conditioning system
The fan-coil air conditioning system consists of one or more fan-coil units and a cold and heat source supply system. The fan-coil unit consists of a fan, a coil and a filter. As the terminal device of the air-conditioning system, it is installed in each air-conditioned room and can treat the air independently, while the hot and cold water required for air treatment is Centrally prepared by the air-conditioning machine room, it is provided to each fan coil unit through the water supply system.
The application of fan-coil units in air-conditioning projects is mostly combined with a separately treated fresh air system. The structure of the fan coil consists of a coil (ie, surface cooler, generally 2-3 rows) and a fan (forward multi-blade centrifugal fan or cross flow fan), and its air volume is 250-2500m3/h Within range.
The composition of the fan-coil unit: a fan, a motor, a coil, an air filter, a room temperature adjustment device, and a cabinet.
The working principle of the fan-coil unit is: the fan in the unit continuously circulates the air in the room where it is located, so that it is continuously cooled or heated through the coil supplying cold or hot water to maintain the temperature of the room. Among them, the function of the air filter is to filter the dust in the indoor circulating air, improve the sanitary conditions of the room, and at the same time protect the coil from being blocked by dust, and ensure the air volume and heat exchange effect.
The main advantages of the fan-coil air-conditioning system are: low noise, suitable for hotel rooms; it has the advantages of individual control; easy adjustment and control of the system partition; the fan-coil itself is small in size, and the layout and installation are more convenient.
The main disadvantages of fan-coil air-conditioning systems are: because the units are installed indoors, they need to be effectively coordinated with buildings and other types of work; the units are relatively scattered, and the maintenance workload is relatively large; the problem of fresh air must be solved; the static pressure of the fan is small , Can not use high-performance filters, so that the cleanliness of indoor air is not high.
The characteristics of fan-coil units: there are two types of fan-coil units: vertical and horizontal. The installation methods are divided into two types: concealed installation and exposed installation. From the perspective of the structure of the fan coil, its main features are: centrifugal multi-blade fans are mostly used, the diameter of the impeller is generally below 150mm, the static pressure is below 100Pa, and the impeller is made of galvanized steel, aluminum or ABS engineering plastics; Generally, the capacitor type is adopted. The speed of the motor can be changed by the speed control switch during operation to change the air volume of the fan. The ratio of the high, medium and low three gears is about 1:0.75:0.5; the coils generally use copper tube strings. It is made of corrugated or slit aluminum sheet. Generally, the outer diameter of copper pipe is 10mm, the pipe wall thickness is 0.35mm, the thickness of aluminum sheet is 0.12～0.15mm, and the distance between the pieces is 2～2.3mm. The process of expanding the pipe is adopted. , To ensure close contact between the copper tube and the aluminum fins, improve the thermal conductivity, the number of rows of coils is two or three rows; the filter material of the air filter is made of coarse-pore foam plastic, fiber fabric or nylon braid. In actual projects, fan coil units are widely used in guest rooms, offices and other buildings due to their control flexibility and low noise. The fan-coil unit mainly provides indoor heat and humidity load, and the fresh air is processed by other equipment.
The components of the fan-coil air-conditioning unit are as follows:
(1) Fan The fan is one of the main components in the fan-coil air conditioner, and it plays a role in conveying air. At the same time, it is the driving force that causes the forced convection heat exchange in the coil to enhance the heat exchange capacity. The fans used in the fan coil include multi-blade centrifugal fans and cross-flow fans.
(2) Coil The coil is a heat exchanger and an important part of the fan coil unit. Nowadays, copper tubes are mostly used in series with aluminum sheets, and the tubes are mechanically expanded to eliminate contact thermal resistance. There are also made of rolled sheet tubes, generally two-row tubes or three-row tubes.
(3) Air filter The filter material is made of coarse-pored foam plastic or fiber fabric, which can be cleaned or replaced.
(4) Fan motors generally use capacitive circuits and oil-impregnated bearings, and no oil is usually added. Note that if it is not an oil-impregnated bearing, it should be oiled regularly. Usually there are three gears to adjust the air volume, the air volume adjustment range is about 50%.
(5) Cabinet The concealed cabinet is usually made of galvanized iron plate. The surface of the exposed cabinet shall be sprayed with paint or plastic, and the iron plate shall be treated by pickling and phosphating before spraying. There must be good heat preservation measures inside the cabinet, so that the unit can maintain a good heat preservation effect when operating in wet conditions to prevent condensation on the outer casing.
Two pipe and Four pipe
The general air-conditioning water system adopts double pipes, that is, the hot water supply in winter and the cold water supply in summer are carried out in the same system. The fan coil corresponding to this water system is a single coil. There are two rows and three rows of single coils, which are used for cooling in summer and heating in winter. The advantage of this air conditioning system is that the system is simple and the initial investment is small; the disadvantage is that in the transition season, when some areas need heating and some areas need cooling, it cannot meet the requirements.
The cold water and hot water of the four-pipe air conditioning system are transported separately by two pipes, and the return pipe is also one for cold water and one for hot water. The fan coil corresponding to such an air conditioning system is in the form of a double coil, which has two coils, a cold coil and a hot coil. This system can supply hot and cold water at the same time throughout the year, flexibly adjust the room temperature, and ensure the temperature of the indoor air; but the initial investment is large, the area of the pipe well occupied is large, the water pipe line is complicated, and there may be cold, The disadvantage of heat offset. For air use, if air accumulates in the coil, it will affect the heat transfer effect at a slight degree, and it may cut off and lose its effect. The return air enters the unit from the bottom, and some are arranged in the lower half of the panel. The air outlet can be opened upward or sideways, and the direction of the air outlet is changed.
