Effect of Different Collector Designs on Water Pressure Loss and Experimental Investigation of the Fan Coil Heat Exchanger

The aim of this study is to experimentally investigate the influence of collector design parameters on water-side pressure loss in fan coil heat exchangers. Pipe diameters (Ø16, Ø22, Ø25 mm), collector lengths (180 and 240 mm), and circuit numbers (2NC and 4NC) were evaluated through laboratory tests conducted on five different configurations over a flow range of 0.150–2.000 m³/h. The results show that for 2NC configurations, increasing pipe diameter led to a rise in pressure loss (ΔP), whereas in the 4NC configuration the same diameter increase resulted in a reduction in ΔP due to improved flow distribution. The 4NC design exhibited the lowest pressure losses, approximately one-third of those observed in comparable 2NC designs. Main-effect analysis revealed a clear sensitivity hierarchy among the investigated parameters: number of circuits (NC) >> diameter (D) > length (L). While the circuit number produced an average ΔP difference of approximately 35 kPa between 2NC and 4NC levels, the diameter effect remained within 1–3 kPa and the length effect below 1.5 kPa across the investigated range. The findings indicate that hydraulic performance in fan coil collectors is governed primarily by flow redistribution associated with circuit configuration rather than by simple geometric scaling of pipe diameter. These results provide quantitative support for optimizing collector design based on flow balance and cost-performance considerations.