Closed circuits of drip laterals versus open circuits: hydraulic performance and energy-saving potential

Drip irrigation systems are usually designed according to open circuits, characterised by branching pipe networks with many drip laterals and one manifold. However, the closure of the circuits with a secondary manifold connecting lateral ends makes it possible to apply a lower inlet pressure head than open circuits, with important implications in energy-saving. In this paper, a comprehensive comparison between the hydraulic performance of open and closed circuits of drip laterals is carried out. The open circuits (op) were analysed by using IrriLab software, which requires two arbitrarily set pressure head tolerances, one for the laterals (δ_L) and one for the manifold (δ_M), determining the pressure tolerance of the unit (δ_op). Meanwhile, the closed circuits were analysed using the well-known Hardy Cross method (HCM). For #3800 drip irrigation units characterised by different geometric and hydraulic parameters, an approximated relationship is derived to accurately predict the energy saving associated with the closure of the open circuits. Results showed that open circuits are recommended when designing for low δ_M (low-pressure head variability in the manifold), since energy can be saved, although higher inside manifold diameters are required in this case. Contrarily, for high δ_M, the closure of the circuit is more appropriate to save energy, since the inlet pressure head is much lower than that required by open circuits.