There is significant scope within present-day irrigation design guidelines to improve both water efficiency and pumping system energy efficiency, thereby contributing meaningfully to the objectives of EU Taxonomy. EU Taxonomy frames sustainability within economic activities and supports those who make substantial progress toward sustainability criteria.
Sustainable Pumping is classified as a “green traffic light” in an Extended Taxonomy, meaning it substantially contributes to at least one of the six objectives without harming the others. It directly supports:
- Climate change mitigation
- Sustainable use of water
- Preservation of water resources - indirectly aids
1- What is Sustainable Pumping?
Sustainable Pumping is measured by Specific Energy, defined as the energy a pump uses to move a specific volume of fluid.
Equation:
kWh/Megalitre = 2.73 x TDH (metres) / (pump efficiency × motor efficiency × drive efficiency)
Each component contributes to sustainable pumping, so let’s examine each component for significance:
Total Dynamic Head (TDH)
TDH must overcome:
- Static lift (usually constant)
- System resistance (main variable factor)
In the design phase, pipe diameter is key to sustainable pumping. Balancing the pump electricity operating cost (OPEX) with the cost of pipe (CAPEX) is fundamental to sustainable pumping.
Optimising System resistance is crucial to sustainable pumping, but needs to be considered in two steps:
Optimizing system resistance involves:
- Design phase: Pipe diameter selection to balance Capitalised Cost of Power (OPEX) with supply and installation costs (CAPEX).
- Maintenance phase: Managing pipeline performance deterioration over time.
Key points:
- Traditional irrigation guidelines specify water velocities at 1.5 metres per second. The United States of America’s Irrigation Association design criteria for irrigation pipeline specifies water velocity limit at 5 feet/sec (1.5 metres per second).
- However, 5 feet per second (1.5m/s) was never intended as an energy design parameter but originally intended only as an irrigation design parameter for acceptable CU’s and DU’s (the resulting water application uniformity).
- WATER PUMPING INSTITUTE research shows lower velocities are needed for both pumping and irrigation energy efficiency, especially on submains where pipe diameters are typically 100mm and less.
- So, what is the water velocity for optimum pumping energy efficiency?
Optimal water velocity depends on several factors:
-
- Pipe diameter
- Energy cost
- Volume pumped per year
- Pipe C Value
- Flow rate
- Pump and Motor efficiency
- Electricity cost index
Example:
Mainlines (300mm and above) perform well at 1.5 m/s, but smaller submain pipes (100mm down to 32mm) require velocities at or below 1 m/s for true sustainable pumping.
Lower submain velocities improve both pumping system efficiency and water application uniformity (DU’s and CU’s), leading to potential 15% irrigation efficiency improvements.
Pump Efficiency
- Modern pumps are already highly efficient.
- Differences among brands are minimal due to competitive marketing.
- Major energy losses can occur mainly when operating OFF Best Efficiency Point (OFF-BEP), not because of pump condition, but because of poor system design.
- While relevant, pump efficiency is not a critical element for sustainable pumping
Drives
- Variable Frequency Drives (VFDs) allow pumps to match varying system resistance.
- VFDs do not directly save energy but allow pump output to match system resistance.
- Typical VFD efficiencies range from 95% to 98%.
- While relevant, VFD efficiency is not a critical element for sustainable pumping
Motor
- Motor efficiency variations are minimal (less than 1% across top 50% load range).
- While relevant, motor efficiency is not a critical element for sustainable pumping.
2- Sustainable Pumping Improves Sustainable Irrigation
Lowering submain water velocities can:
- Improve DU by up to 15%
- Enhance field water use efficiency
- Provide additional benefits beyond energy savings
Case Studies
WPI has audited numerous large scale irrigation projects, finding significant improvements in sustainable pumping, based on energy costs, with average hydraulic sustainability improvements of 33% but average pump efficiency improvement potential of only 16%, as shown in the table below.
Case Studies Summary:
- Average hydraulic sustainability improvements: 33%
- Average pump efficiency improvement: 16%
Hydraulic efficiency gains are mainly due to optimized pipe diameters. Identified potential pump efficiency gains, however, are limited and subject to manufacturing tolerances, and in some cases may never be achievable.
Legacy irrigation designs focused solely on water delivery, not energy savings, result in poor hydraulic and energy efficiency today.
Case Study: Pipe Replacement in Dairy Irrigation
In southeast Australia, a dairy farmer replaced a 150mm rising main with a 200mm pipe:
- Water velocity dropped from 2.1 m/s to 1.1 m/s
- Annual pumping costs reduced by $18,000
- CO₂ emissions dropped by 68 tonnes per year
This highlights the second phase of sustainable pumping: optimizing existing systems to reduce costs and greenhouse gas emissions.
There are many outdated irrigation systems where pipe duplication or replacement would significantly improve sustainability.
Maintenance Phase
Over time, all pipelines suffer hydraulic efficiency losses. Based on extensive WPI experience:
- Groundwater iron hydroxide can reduce C Values dramatically (e.g., from C=150 to C=60 within months).
- Raw water and recycled water can cause severe pipe performance deterioration.
- Smaller pipes suffer disproportionately from biofilm and fouling.
If not addressed in design or maintenance, such degradation undermines sustainable pumping efforts.
Case Study:
A recycled water system with 10 km of 450mm pipe saw a 15% drop in pump output over 18 months. Pigging restored the pipeline’s performance and efficiency.
Who Pays the Extra Cost?
Optimizing systems through larger pipes raises CAPEX costs. However:
- EU Taxonomy offers financial mechanisms to support investments in sustainable irrigation improvements.
- Green financing schemes could cover the additional costs where substantial environmental benefits can be demonstrated.
The European Irrigation Association (EIA) has proposed a draft Taxonomy for irrigation activities that incorporates these sustainable efficiency concepts.
Summary :
Designing irrigation systems with:
- Optimized water velocities
- Anticipated pipeline performance degradation
has clear benefits for sustainable energy use and irrigation efficiency.
EU Taxonomy can assist projects by providing access to green finance for demonstrated improvements in sustainability.
Training Courses
The WATER PUMPING INSTITUTE provides professional training courses to help irrigation professionals:
- Improve new irrigation designs with optimised hydraulic losses
- Retrofit existing systems with optimised hydraulics, saving OPEX and CO2 emissions
- Achieve higher hydraulic and energy efficiency, with improved irrigation efficiency
Face-to-face classes will be offered in Europe in October 2025.
More information is available at www.waterpumping.institute/sustainable-pumping-for-irrigation-europe.
Want more information on the presenter? https://www.waterpumping.institute/about
Rob Welke
Managing Director, WATER PUMPING INSTITUTE
Adelaide, South Australia
April 2025
