23 April 2015, 12:00AM
Pumping efficiency tests have found that many pumps are operating inefficiently and costing growers more than is required. The most common reasons for inefficient pump operation included worn impellers, poor pump selection, improper motor size and changes to the application system.

Many growers are unaware that the initial purchase price of a pump typically represents 5% of the total cost over a 10 year period for electrical driven units. The results of pump assessments have highlighted significant savings to be made through improved pump efficiency. Pump efficiency is often represented as a percentage and is a measurement of how well a pump converts input power into water delivery (both pressure and volume). The electricity consumption, discharge rate, pump operating pressure and electricity tariff are then used to determine the pumping cost and the pump's efficiency.

A recent audit report published in The Journal for Irrigation Professionals - Irrigation Australia, outlines the results of an audit on a 25ha banana farm in the wet tropics, where the pump was found to be oversized and performing below 50% efficiency of a possible 79%. The audit was conducted on a Southern Cross 100x65-250 centrifugal pump fitted to a 55kW motor. Together they deliver a flow rate of 17.5L/s and a total dynamic head (TDH) of 86.6m, consuming 34.6kW per hour. This equates to 6.34 kWh/ML/m, which is above the target of 5 kWh/ML/m. 

Energy consumption per hour. 36kW - Off peak $104.61 ML, Peak Cost $189.93 ML.

Annual operating cost $15,112.80

Based on the irrigation schedule in place on the day of the assessment, the pump unit is oversized for the required duty. The high head and low flow rate delivered by the existing pump unit sits well outside the efficient operating range according to pump performance data. The pump selection chart for this range of pumps shows these conditions (flow rate and TDH) can be met with a smaller pump and motor that consumes 22kW instead of the current 34kW. By replacing the current pump unit (pump & motor) with a more efficient unit that matches the duty, the grower can expect a 2 year payback period through reduced electricity consumption and resultant energy cost savings.

How Can TEAM Irrigation Help?

Contact TEAM Irrigation to explore your options. We will investigate your irrigation design, current systems and irrigation schedule to improve system efficiency. We will work through pump manufacturer curves to ensure that the combination of pump and impeller size will give you the best efficiency for the required operating conditions.