عنوان مقاله [English]
Introduction: The energy crisis has led the world toward the reduction of energy consumption. More than 70 percent of the energy in agriculture sector is used by pumps. In our country, there is no clear standard and guideline and also no adequate supervision for the design, selection, installation and operation of pumping systems appropriate to the circumstances and needs. Consequently, these systems operate with low efficiency and high losses of energy. While more than 20 percent of the world's electricity is consumed by pumps, average pumping efficiency is less than 40%. So evaluation of pumping stations and providing some solutions to increase efficiency and pumping system’s life time and to reduce energy consumption can be an effective in optimization of energy consumption in the country. The main reasons for the low efficiency of pumping systems comparing to potential efficiency are using unsuitable techniques for flow control, hydraulic and physical changes of pumping system during the time, using pumps or motors with low efficiency and poor maintenance. Normally the amount of flow is not constant over the time in a pumping system and needed flow rate is changed at different times. Designing of pumping system should be responsible for peak requirements as well as it must suggest the suitable flow control method to achieve least energy losses for minimum flow requirements. Also one of the main capabilities to reduce energy consumption in pumping stations is improving the flow control method. Using the flow control valves and bypass line with high energy losses is very common. While the use of variable speed pumps (VSPs) that supply water requirement with sufficient pressure and minimum amount of energy, is limited due to lack of awareness of designers and (or) high initial costs.
Materials and Methods: In this study, the operation of the pumping stations under four scenarios (for discharge control) in a drip irrigation system was analyzed and evaluated: A) Pumping station equipped with VSPs, in this case it is possible to regulate energy consumption due to the required discharge and pressure for irrigation system , B) Pumping stations equipped with constant speed pumps (CSPs) and flow control valve maneuver in every decade of irrigation, C) Pumping stations equipped with CSPs without any flow control and D) Pumping stations equipped with CSPs and flow control valve maneuver per month of irrigation. Pumping stations equipped with CSPs was designed for a 100 hectares irrigation area for peach and apple trees in the South West of Isfahan province. The produced pressure under four types of flow control were determined. Then pump performance and energy consumption were evaluated under three operation scenarios (B, C and D) and afterward compared with the performance of VSP stations that was designed for this irrigation system.
Results and discussion: The most important point in the design of pumping stations is energy consumption, because the cost of energy supply is high and the operation should be able to save more energy. Using the output values of pressure and flow rate from developed model, the amount of energy consumption for each pump was calculated. It was observed that the energy consumed in pumping stations equipped with VSPs is significantly less than other stations. Regarding to the total energy consumption and the amount of energy that each scenario can save, the percentage of energy savings were calculated. The results show that the highest percentage of energy savings are belonging to scenario (a) (using VSPs).
Conclusion: The results of this study show that application of VSPs at pumping stations than commonly pumping stations with CPSs, depending on the type of CSP operation, saves 44 to 54 percent of energy. Using VSPs, which save a lot of energy compare to other methods, can be an important phase in optimizing energy consumption and minimizing the cost operation of the agriculture pumping station. So the type of operation that discussed in the present study and also the type of irrigation system, pump selection, cultivated area and irrigation scheduling are effective at saving energy during VSPs employment. In a recent case, reduction in energy cost should be independently calculated for each irrigation system and be considered in the lifetime costs of pumping system. Regarding the results of this research and also latest studies, it can be said that the study design and implementation of variable speed pumps in irrigation projects should be considered in national scale. Because development of pressurized irrigation schemes that inevitably need to pump, is the country's main policies for efficient use of water.