Meaning of several parameters of fan coil units
While fan coil units may seem to have many parameters, the core logic is simple: airflow determines ventilation and air delivery capacity, heating and cooling capacity determines load handling ability, external static pressure determines whether ductwork can be connected, water resistance affects water pump selection, and noise affects user experience . When selecting a fan coil unit, one should not only look at nominal values, but also pay attention to its degradation under actual operating conditions. Below, we clarify the significance of several key parameters and common pitfalls associated with fan coil units :
I. Air volume (m³/h)
This is the most basic parameter of a fan coil unit, referring to the volume of air delivered into the room per unit time. The air volume directly affects the air exchange rate, the supply air temperature difference, and the uniformity of room temperature.
Note : The "nominal air volume" on the sample is usually measured under specific conditions where the coil is not flowing water and the outlet static pressure is zero. After actual installation, the air volume will often decrease after adding a return air box, filter, or short duct. In actual use, the air volume of domestic units in cooling mode may be 20% to 30% lower than the nominal value , and may even be more than half lower in long-term operation. Therefore, the nominal air volume should not be strictly adhered to when selecting a model.
II. Cooling Capacity / Heating Capacity (kW)
This indicates the unit's ability to handle air cooling/heating loads under rated operating conditions. Cooling capacity determines how long it takes for a room to cool down, and the same applies to heating capacity.
Note : These values also have "nominal operating conditions" (such as specific inlet dry and wet bulb temperatures, water temperature, etc.). If the actual water temperature and air temperature do not match the sample conditions, the heating and cooling capacity needs to be adjusted. In addition, the rated heating capacity of a single-coil unit is generally about 1.5 times the rated cooling capacity .
III. External Static Pressure (Pa)
This parameter is easily overlooked, but it is crucial. It refers to how much pressure remains at the air outlet after the fan overcomes its own resistance to "push" air through the duct, air outlet, or filter.
Low static pressure type : The outlet static pressure is usually 0 or 12 Pa , which is suitable for the air outlet to blow directly into the room, or only connected to a very short section of the air outlet.
High static pressure type : The outlet static pressure is not less than 30 Pa , which is suitable for occasions where a section of duct is needed to distribute the air supply. If a low static pressure model is selected when duct is actually connected, the air volume will be greatly reduced, resulting in a poorer room performance.
IV. Water Resistance (kPa)
This refers to the resistance encountered by water as it flows through the inside of the coil. This parameter directly affects the head selection of the air conditioning water system pump—the greater the water resistance, the higher the pressure the pump needs to provide. Ignoring water resistance during selection may result in insufficient actual water flow, thus hindering the output of cooling and heating.
V. Noise (dB(A))
This refers to the A-weighted sound level noise level of the unit during operation. Fan coil units are usually installed in the ceiling or near areas where people move around, and noise is an important indicator of comfort. Within the same series of units, the noise level is usually higher at high static pressure or high fan speed. When selecting a model, the appropriate noise limit should be checked according to the room's purpose (e.g., bedroom, office, hall), and not just whether the cooling capacity is sufficient.
VI. Input Power (W)
This refers to the electrical power consumed by the fan motor, mainly used in power distribution design and operational energy consumption assessment. It is directly related to air volume and static pressure: the higher the required air pressure and the larger the air volume, the higher the input power is usually required.
In short: First, select a general model based on the room's cooling load, then check if the air volume is sufficient under actual installation conditions (considering static pressure and accessory resistance), and finally check if the water resistance and noise are within acceptable ranges .
