PRESSURE DISTRIBUTION ON CENTER-PIVOT LATERAL LINES: COMPARATIVE RESULTS AND ENERGY CONSERVATION WITH A VARIABLE SPEED DRIVE
Center pivot irrigation; Pressure distribution; Head loss correction factor. Hydraulic model. Energy consumption. Variable speed.
Pressure distribution detailed description and adequate knowledge of the minimum pressure
point position along the center pivot lateral is required to define strategies to reduce energy
consumption in this equipment. The use variable speed drives to rotation control on the
irrigation pumping station it is one of the strategies among the proposed in other researchers to
reduce energy consumption. In addition, the use of computational tools for hydraulic simulation
using numerical solutions enables comparison with analytical models and analysis of energy
use. In this sense, this research aimed to study the spatial pressure distribution along center
pivot lateral line in plots with variable topography, and from this to analyze the energy
conservation within the use of variable speed drives in the pumping station. As described in
article 1, the pressure distribution along center pivot lateral line was determined by four models
with different analytical solutions and compared with the numerical solution obtained through
the EPANET hydraulic simulator for different lateral line configurations (lateral line with one
and two pipe diameters, different values of the gross irrigation depth per time of operation,
different values of the pipe wall roughness coefficients, different values of the ground slope, and
lateral line operating with and without end gun). For the different center pivot lateral line
configurations considered in this study, two different sets of values were compared: the Darcy-
Weisbach equation was used in the first set, while the Hazen-Williams equation in the second
set. Results showed that in both sets, the four analytical solutions evaluated presented estimates
of head loss values similar to those calculated with the EPANET hydraulic simulator. These
results indicate that the detailed description of the flow distribution along the center pivot lateral
line required by the numerical method did not improve the accuracy of the head loss
distribution. In addition, the process of editing the input data required by EPANET may be
limiting for its use. In this sense, in article 2, the VSPM (Variable Speed Pivot Model) tool was
developed to, besides facilitating the process of editing the input data in EPANET, to perform
the hydraulic behavior simulation, integrating the pumping station energy characteristics and the
topographic characteristics. This study presented a proposal to vary the pressure supplied to a
center pivot irrigation system according to the angular position of the lateral line by adjusting
the speed of the pumping station with a variable speed drive (VSD). For this, a simulation of the
possible reduction in energy consumption was performed by using a VSD at a center pivot
pumping station in Albacete (Spain). The present study showed a saving of 12.2% of energy
when using speed control at the pumping station in comparison with the commonly used fixed
speed. This reduction in energy allowed economic savings close to 2,821.47 €, in an area
irrigated by a center pivot with a difference in maximum elevation of 15.3 m.