Brief analysis case of fan coil selection and layout in central air conditioning

Brief analysis case of fan coil selection and layout in central air conditioning

With the continuous improvement of high-end office and office environment, the air-conditioning system has become more and more widely used in daily life. How to make the selected air-conditioning system have the best effect, in addition to the rationality of the design, has also attracted more and more thoughts from field engineers.

　　As the terminal device of the central air conditioning system, the fan coil unit is widely used in many public places. Its main advantages are as follows:

　　 1. Self-contained unit, flexible adjustment. The fan coil is three-speed variable speed, and the water system can automatically control the temperature adjustment valve with cold and hot water according to the user's room temperature setting, so that each room can independently adjust the room temperature to meet the needs of customers using different air conditioners. It can be turned off manually or automatically when used by people, and it can prevent developers from investing too much at a time, facilitate their rolling development, and open different rooms according to the situation of the customers. Thereby reducing the operating cost of the overall system.

2. The partition control of the entire system is relatively easy. It can be divided into several areas according to the orientation, floor, purpose, use time, etc. of the room, and the partition control is carried out according to different customer needs, thus avoiding the unreasonable side of the large air duct system that must be controlled centrally .

　　 3. The fan-coil unit has a small body, flexible layout, convenient installation, and takes up less building space, which is convenient for interior construction. However, how to choose a better fan coil unit and apply it to the Longsheng Building project according to the different needs of the owners and combined with the design drawings, the author has fully considered the following points:

　　 (1) Check of cooling capacity

　　 Generally, the product is selected according to the calculated cooling load, but it should be noted that different fresh air supply methods will cause the load cooling capacity of the fan coil to be different. When fresh air is directly sent to the room through the external wall, without heat and humidity treatment, the cooling capacity of the fan coil = indoor cooling load + fresh air cooling load; when an independent fresh air system is set up, the cooling capacity of the fan coil = indoor Cold load. The current products on the market are generally nominal cooling capacity and the cooling capacity in actual operation should be cooling capacity × average operating time per unit time, that is, changing the operating time or air volume will affect the input cooling capacity of the unit. Therefore, it is not that the higher the nominal cooling capacity is, the better. If only the high cooling capacity is selected, the cooling capacity will be too large, resulting in too low operating rate, reduced air changes, increased room temperature gradient, and increased system capacity and Equipment investment, air-conditioning energy consumption increased, and air-conditioning effect decreased. Therefore, cooling capacity is only one of the necessary conditions for selecting equipment, and other factors should be taken into consideration.

　　 (2) Air volume check

　　 Mainly check the air change frequency according to the room quality requirements. The smaller the supply air temperature difference and the more air changes, the better the air quality and the more comfortable it is. Why does some air-conditioned rooms feel peculiar smell and stuffiness? The air volume check is not handled properly. Since the nominal air volume of the fan coil is measured under the conditions of no water flow and zero pressure difference between the air inlet and outlet, there are some unrealistic factors, so the actual determination of the air volume should be the value of the air volume in the ideal state. Excluding, the author calculated through the actual calculation of the Longsheng Building project, this part of the supplementary air volume should account for 20-30% of the nominal air volume.

　　 (3) Sending and returning wind

　　 Sending and returning air forms the so-called airflow organization. Whether it is reasonable or not directly affects the uniformity and stability of the temperature field and velocity field of the air-conditioned room, that is, the quality of the air-conditioning effect. Reasonable airflow organization requires a certain air supply speed to avoid short circuit of airflow to ensure a certain jet length. The wind speed depends on factors such as the static pressure outside the machine, the air supply volume, and the air supply opening. If the static pressure outside the machine is too low, the air volume will decrease, the range will be reduced, and the room will be unevenly cooled and heated. There is a big difference between the designed airflow organization and the actual operating state on the graph. Therefore, it should be based on the actual building pattern and the structure of the room. For conditions such as depth and height, select mid-range air volume and wind speed indicators to select the fan coil model accordingly. For fan coil units currently on the market, the external static pressure values ​​of various manufacturers are not uniformly calibrated, and the differences are large. In addition, the Longsheng Building uses a horizontal concealed unit with external short air ducts, filters, and inlet and return air. The grid resistance value is relatively large, so when the actual order is determined, the external static pressure value is selected as 30Pa, and some rooms even choose a unit with a 50Pa external static pressure value, which is greater than the conventional resistance value of about 20Pa, so in actual operation It ensures a good uniform field and achieves the expected air withering effect.

　　 (4) Other factors

　　A. The noise index is controlled below 40dB. For fan coils with large noise, a noise reduction device is installed, and the resistance value is not more than 10Pa.

　　B. During installation and construction, pay attention to the quality of heat preservation, the discharge of condensate, the slope direction, the pipe fittings, and the clean system.

　　C. The setting method of the water system is horizontal or vertical.