Key points of selection for FCU

Fan Coil Units has only fan and coil apart from the filter section, are the ideal solution to meet the air treatment needs of systems including distribution through ducting or directly into the room and installation in false ceilings or in service rooms. Fan coil units can be wall-mounted, freestanding or ceiling-mounted and may be concealed in ceiling voids. They may be controlled by local thermostats or by a building management system (BMS). Where fan coil units are supplied with chilled water and hot water from central boilers and chillers they are generally referred to as two pipe (either heating or cooling) or four pipe (both heating and cooling) units.

The following points should be fully considered in how to select a better fan coil unit for practical engineering according to the different needs of the owner and the design drawings:

1. Check the cooling capacity

Generally, the products are selected according to the calculated cooling load, but it should be noted that different fresh air supply modes will lead to different load cooling capacity of fan coil units. When the fresh air is sent to the room directly through the outer wall, the cooling capacity of the fan coil unit = indoor cooling load+fresh air cooling load without heat and humidity treatment; When an independent fresh air system is set up, the cooling capacity of fan coil unit = indoor cooling load.

At present, the products on the market are generally nominal refrigerating capacity, but the refrigerating capacity in actual operation should be the refrigerating capacity x the average running time per unit time, that is, changing the running time or air volume will affect the input refrigerating capacity of the unit.

Therefore, the higher the nominal cooling capacity, the better. If only the high cooling capacity is selected, the cooling capacity will be too large, resulting in low starting rate, reduced air changes, increased room temperature gradient, increased system capacity and equipment investment, increased air conditioning energy consumption and decreased air conditioning effect.

Therefore, cooling capacity is only one of the necessary conditions for selecting equipment, and other factors should be taken into account.

2. Check the air volume

Check the air changes mainly according to the room quality requirements. The smaller the air supply temperature difference and the more air changes, the better the air quality and the more comfortable it is. Why do some air-conditioned rooms feel peculiar smell and sulk, that is, the air volume check is not handled well?

Because the nominal air volume of fan coil unit is measured under the condition that there is no water and the pressure difference between air inlet and outlet is zero, there are some unrealistic factors. Therefore, the air volume in this ideal state should be deducted when the air volume is actually determined. Through empirical calculation, this supplementary air volume should account for 20~30% of the nominal air volume.

3. Delivery and return air modes

The so-called airflow organization is formed by the way of sending and returning air, which directly affects the uniformity and stability of temperature field and velocity field in air-conditioned rooms, that is, the air-conditioning effect is good or bad.

Reasonable air distribution requires a certain air supply speed to avoid air short circuit and ensure a certain jet length. Wind speed depends on external static pressure, air supply volume, air supply outlet and other factors.

If the static pressure outside the machine is too low, the air volume and range will decrease, and the room will be cold and hot unevenly. There is a big difference between the design air distribution and the actual running state on the graph. Therefore, the fan coil model should be selected according to the actual building pattern, the structural form of the room, the depth and height, etc.

At present, the external static pressure values of fan coil units in the market are not uniformly calibrated by different manufacturers, which is quite different. In addition, some construction sites use horizontal concealed units, which are connected with short air ducts and filters, and have large inlet and return air grille resistance values. Therefore, the external static pressure value is determined to be 30Pa when actually ordering, and some rooms even choose units with an external static pressure value of 50Pa, which is greater than the conventional resistance value of about 20Pa, thus ensuring good uniformity in actual operation.

4. Other factors

(1) the noise index shall be controlled below 40dB, and the fan coil units with large noise shall be equipped with silencing treatment device, and the resistance value shall not be greater than 10Pa.

(2) Pay attention to heat preservation quality, condensed water discharge, slope direction, pipe joint and system cleaning during installation and construction.

(3) The setting mode of water system is horizontal system or vertical system, and vertical system is selected for some construction sites, which can better ensure the discharge of condensed water and ensure the height requirement of the room.