Effect of different collector designs on water pressure loss and experimental investigation of the fan coil heat exchanger

This study aims to analyse the effects of different pipe diameters (Ø16, Ø22, Ø25 mm), circuit numbers (2NC, 4NC), and pipe lengths (180 mm, 240 mm) on water differential pressure (ΔP). The widely accepted hypothesis that "an increase in pipe diameter leads to a decrease in pressure loss" was not validated in Groups A, B, C, and D, but was confirmed only in Group E. The experimental studies were conducted in an air enthalpy laboratory under water temperature conditions ranging from 7 to 15 °C and air temperatures from 15 to 25 °C. The relationship between volumetric water flow rate (Q, m³/h) and differential pressure (ΔP, kPa) was graphically analysed. Each group (A, B, C, D, E) was tested with three samples per diameter (Ø16, Ø22, and Ø25 mm), resulting in a total of 15 samples. The group configurations are as follows: Group A has centrally positioned circuits with a pipe length of 180 mm; Group B also has centrally positioned circuits but with a pipe length of 240 mm; Group C has circuits located at the corner edges with a pipe length of 180 mm; Group D has circuits at the corner edges with a pipe length of 240 mm; and Group E has circuits positioned both centrally and at the corner edges (4NC) with a pipe length of 180 mm. According to the experimental results: In the flow rate range of 0.150–0.500 m³/h, changes in pipe diameter and length did not show a significant effect on differential pressure/pressure drop (ΔP). In the range of 0.500–1.000 m³/h, in Group A, ΔP increased by up to 1 kPa as the diameter increased. In Group B, compared to Group A, ΔP for Ø16 changed by less than 1 kPa and decreased, while no significant changes were observed for the other diameters. In Group C, ΔP decreased by up to 0.5 kPa as the diameter increased. In Group D, ΔP increased compared to Group C; for Ø16, the change was less than 0.5 kPa, and for Ø25, it was less than 2.5 kPa. In the range of 1.000–1.500 m³/h, in Group A, ΔP increased by up to 2 kPa with increasing diameter. In Group B, compared to Group A, ΔP for Ø16 changed by less than 2.5 kPa, and no significant change was observed for other diameters. In Group C, ΔP decreased by up to 1 kPa as the diameter increased. In Group D, ΔP increased compared to Group C, with an increase of up to 5 kPa observed for Ø25. In the range of 1.500–2.000 m³/h, in Group A, ΔP increased by up to 3.5 kPa as the diameter increased. In Group B, compared to Group A, ΔP for Ø16 changed by less than 5 kPa, and by less than 0.5 kPa for the other diameters. In Group C, ΔP decreased by up to 1.5 kPa with increasing diameter. In Group D, ΔP decreased compared to Group C, with a reduction of up to 7.5 kPa for Ø25. In Group E, with an increased number of circuits, the pressure drop was observed to be approximately three times lower than in Groups A, B, C, and D. Additionally, the traditional expectation that ΔP decreases with increasing pipe diameter was confirmed in this group, with the maximum ΔP difference observed being 1.5 kPa. In conclusion, increasing pipe diameters can significantly reduce pressure loss in laminar flow and balanced distribution systems. Instead of considering only diameter changes, other parameters such as the number of circuits (NC) and pipe length should also be considered during the design process. By implementing more balanced flow structures—such as the 4NC configuration—the effect of diameter increase on pressure loss can be optimized. In low water flow rate ranges, since increasing the diameter does not cause a notable change, cost-effective copper pipe selections can be preferred. Additionally, considering the relationship between pipe diameter and pressure loss during pump selection can improve overall system efficiency. Configurations that provide lower pressure loss can enable the pump to operate with reduced energy consumption, thereby lowering operational costs. Keywords: Collector / Pipe Geometry, Number of circuits (NC), Pressure loss (ΔP), Flow regime, Fan coil