As the terminal component of HVAC system, fan coil units(FCUs) are widely used in various public places for the following reasons:

1. Self-Contained Units and Flexible Regulation:
   • Fan coil units (FCUs) operate independently, allowing flexible temperature adjustments for each room. Water circuits automatically control temperature valves based on user-set room temperatures. This independence ensures that rooms can be individually regulated, meeting diverse air conditioning needs. When rooms are unoccupied, manual or automatic shutdown is possible, allowing developers to avoid excessive initial investment and adapt to different room requirements. Overall, this reduces system operating costs.
2. Zone Control and Easy Implementation:
   • FCUs facilitate straightforward system zoning. Rooms can be divided into zones based on orientation, floor, purpose, and usage time. This approach avoids the impractical centralized control associated with large duct systems.
3. Compact Design and Installation Convenience:
   • FCUs have small footprints, making them suitable for interior construction. However, selecting the right FCU for practical engineering involves considering several factors:
   a. Cooling Load Calculation:
   • Calculating cooling loads typically guides product selection. Note that different fresh air supply methods affect FCU cooling loads. When fresh air directly enters rooms through external walls without heat and humidity treatment, the FCU’s cooling load equals indoor load plus fresh air load. If an independent fresh air system is established, the FCU’s cooling load equals the indoor load. Market products often specify nominal cooling capacity, but actual operational cooling depends on average runtime (considering changes in operation time or airflow). High nominal cooling capacity alone isn’t ideal; oversized cooling capacity leads to low utilization, reduced ventilation frequency, wider temperature gradients, increased system capacity, higher equipment investment, and elevated energy consumption.
   b. Airflow Calculation:
   • Air exchange rates are determined by room quality requirements. Smaller temperature differences between supply and return air result in more frequent air exchanges, improving air quality and comfort. Proper airflow calculation is crucial to prevent unpleasant odors or stuffiness. The nominal airflow specified for FCUs assumes zero water flow and zero pressure difference at air inlets and outlets. Therefore, practical airflow should deduct this idealized value. Empirical estimates suggest adding 20–30% to the nominal airflow.
   c. Supply and Return Air Arrangement:
   • Proper airflow organization directly impacts temperature and velocity uniformity in air-conditioned rooms. Achieving a balanced temperature field and stable velocity requires appropriate supply air speed to prevent short-circuiting. External static pressure, supply airflow, and outlet design influence airflow speed. Low external static pressure reduces airflow and range, leading to uneven room temperatures. When selecting FCU models, consider building layout, room structure, depth, height, and opt for medium airflow and velocity indicators. Note that manufacturers’ external static pressure values vary significantly. Some sites use concealed horizontal units with additional short ducts, filters, and higher-than-usual resistance (e.g., 30 Pa or even 50 Pa). This ensures uniform airflow and the desired air conditioning effect during actual operation.