In Sept 2013, Tallemenco was contracted by the Victorian Dept Primary Industries to conduct a detailed pumping energy efficiency audit on a modern vegetable farm in the Gippsland District.

A 6 yr old 656’ long Lateral Move (LM) irrigated mixed vegetables on the privately owned farm. A 50 HP direct driven electric pump pumped 666 gpm from the Mitchel River and delivered it to the LM approx 1650’ away via an 8” PVC pipe.

The audit measured pump efficiency plus friction losses across each major pipe and irrigation equipment sector. The system had 81 AF/yr usage, approx $5,500/yr electricity cost at ave 25c/kWh and pumped head was 167’.

Findings

Excessive residual pressure (36.2 psi) was found at the end of the LM, plus high hydraulic losses on the layflat hose, and the well maintained 35yr old pump, in otherwise good condition, was running left of BEP.

The 656’ long Lateral Move was supplied with 328’ of 4” layflat hose. Misting was evident at the nozzles, potentially indicating high residual pressure.

Whilst the pump was satisfactory, the hydraulic losses were a combination of the layflat hose and excessive residual pressure.

In this case, the 4”is the optimal size lay flat connection from rising main to LM.

However, the residual pressure was excessive and could be reduced by 14.5psi (33’).

This would result in an annual energy saving of $1,080pa.

In this case, a trimmed impeller would achieve the required pressure reduction, with minimal cost.

By reducing LM residual head, the system could run at 134.4’ TDH and $54.3/AF, with a $1,080 pa savings and a payback period of 1 year.

However, with 68% pump efficiency, there would be no economic advantage from pump overhaul.

If a simple pump test only had been carried out on this property, approx. $1.080 of annual electricity savings would have been overlooked, or 16% of annual electricity usage.

An impeller reduction would cost about $1000 in labour, resulting in a ROI of about 1.0 yr.

An alternative would be to fit a VFD to the pump to reduce the pumped head. This would cost about $5,000, with a ROI of 5 yrs.

However, the VFD has a 5% energy efficiency penalty, negating the advantage of using a VFD in this case.

Quantifying pumping energy efficiency in an irrigation system has long been understood to be made with a simple pump test. Ignored was the significant additional potential energy savings available in irrigation system pipelines due to poor hydraulics.

The WATER PUMPING INSTITUTE’s aim is to educate water engineers in the art and science of identifying hydraulic in-efficiencies in irrigation (and other water) systems. This is achieved through its training course “Pumping System Master Class (US)” with “Fit for Purpose” software which comes with the training course.

These case studies have been compiled as living proof of the feasibility and practicality of identifying (or incorporating into new systems) up to 50% hydraulic savings from pumping system energy audits. These case studies demonstrate the importance and savings advantages of quantifying hydraulic efficiencies when conducting pumping energy audits.