Irrigation Pumping Plants By Blaine Hanson University of California, Davis

Questions How do pumps perform? How can I select an efficient pump? What causes a pump to become inefficient? How can I determine my pump’s performance? How can I improve my pump’s performance? Will improving my pump’s performance reduce my energy bill?

Basic Concepts Definition Energy = kilowatt-hours One kilowatt is 1.34 horsepower Hours = operating time Energy cost is based on kwhr consumed and unit energy cost ($/kwhr) Reducing energy costs Reduce Input Horsepower Reduce Operating Hours Reduce Unit Energy Cost

Improving Pumping Plant Efficiency Adjust pump impeller Repair worn pump Replace mismatched pump Convert to an energy-efficient electric motor

Centrifugal or Booster Pump Shaft Frame Impeller Discharge Inlet Stuffing Box Balance Line Volute Wearing Rings

Deep Well Turbine

Deep Well Turbine

Submersible Pump

Terms Total head or lift Capacity Brake horsepower Input horsepower Overall efficiency

Pumping Lift Discharge Pressure Gauge Motor Discharge Pipe Pump Head Ground Surface Static or Standing Water Level Pumping Lift Ground Water Pumping Water Level Pump

Discharge Pressure Head Height of a column of water that produces the desired pressure at its base Discharge pressure head (feet) = discharge pressure (psi) x 2.31 Note: a change in elevation of 2.31 feet causes a pressure change of 1 psi

Total Head or Total Lift = Pumping Lift (feet) + Discharge Pressure Head (feet) Example Pumping Lift = 100 feet Discharge Pressure = 10 psi Discharge Pressure Head = 10 psi x 2.31 = 23.1 feet Total Head = 100 +23.1 = 123.1 feet

Total Head or Lift of Booster Pumps Difference between pump intake pressure and pump discharge pressure Multiply difference (psi) x 2.31 Example Intake pressure = 20 psi Discharge pressure = 60 psi Difference = 40 psi Total Head = 40 x 2.31 = 92.4 feet

Brake Horsepower = Shaft Horsepower of Motor or Engine Input Horsepower = Power Demand of Motor or Engine

Overall Pumping Plant Efficiency = Gallons per minute x Feet of Total Head 3960 x Input Horsepower

Pump Performance Curves Total Head or Lift - Capacity Pump Efficiency - Capacity Brakehorsepower - Capacity Net Positive Suction Head - Capacity (centrifugal pumps)

Total Head - Capacity

Efficiency - Capacity

Horsepower - Capacity

How Do You Use Performance Curves? Selecting a new pump Evaluating an existing pump

Selecting an Efficient Pump Information needed Flow rate (gallons per minute) Total Head (feet) Consult pump catalogs provided by pump manufacturers to find a pump that will provide the desired flow rate and total head near the point of maximum efficiency

Design: Total Head = 228 feet, Capacity = 940 gpm Selecting a New Pump Design: Total Head = 228 feet, Capacity = 940 gpm

Common Causes of Poor Pumping Plant Performance Wear (sand) Improperly matched pump Changed pumping conditions Irrigation system changes Ground water levels Clogged impeller Poor suction conditions Throttling the pump

Improving Pumping Plant Performance

Impeller Adjustment

Effect of Impeller Adjustment  

Effect of Impeller Adjustment on Energy Use

Repair Worn Pump

Effect of Pump Repair Before After Pumping lift = 95 feet Capacity = 1552 gpm IHP = 83 Efficiency = 45% After Pumping lift = 118 feet Capacity = 2008 gpm IHP = 89 Efficiency = 67%

Summary of the Effect of Repairing Pumps 63 pump tests comparing pump performance before-and-after repair Average percent increase in pump capacity – 41% Average percent increase in total head – 0.5% (pumping lift only) Average percent increase in pumping plant efficiency – 33% IHP increased for 58% of the pumping plants. Average percent increase in input horsepower – 17%

Adjusting/Repairing Pumps Adjustment/repair will increase pump capacity and total head Adjustment/repair will increase input horsepower Reduction in operating time is needed to realize any energy savings More acres irrigated per set Less time per set Energy costs will increase if operating time is not reduced

Replace Mismatched Pump A mismatched pump is one that is operating properly, but is not operating near its point of maximum efficiency

Matched Pump Efficiency (%) Improperly Matched Pump Capacity (gpm)

Mismatched Pump

Multiple Pump Tests

Replacing this pump with one operating at an overall efficiency of 60% would:  Reduce the input horsepower by 19%  Reduce the annual energy consumption by 34,000 Kwhr  Reduce the annual energy costs by $3,400 (annual operating time of 2000 hours and an energy cost of $0.10/kwhr)

Replacing a Mismatched Pump Pumping plant efficiency will increase Input horsepower demand will decrease Energy savings will occur because of the reduced horsepower demand

How do I determine the condition of my pump? Answer: Conduct a pumping plant test and evaluate the results using the manufacturer’s pump performance data

Pumping Lift

Discharge Pressure Pump Capacity

Input Horsepower

Is a pump worn or mismatched? Multiple pump tests Compare pump test data with manufacturer’s pump performance curves

Recommended Corrective Action Eo greater than 60% - no corrective action 55% to 60% - consider adjusting impeller 50% to 55% - consider adjusting impeller; consider repairing or replacing pump if adjustment has no effect Less than 50% - consider repairing or replacing pump

Energy-efficient Electric Motors

Efficiencies of Standard and Energy-efficient Electric Motors

Variable Frequency Drives

What is a Variable Frequency Drive? Electronic device that changes the frequency of the power to an electric motor Reducing the power frequency reduces the motor rpm Reducing the motor rpm, and thus the pump rpm, decreases the pump horsepower demand A small reduction in pump rpm results in a large reduction in the horsepower demand

When are Variable Frequency Drives Appropriate? One pump is used to irrigate differently-sized fields. Pump capacity must be reduced for the smaller fields Number of laterals changes during the field irrigation (odd shaped fields) Fluctuating ground water levels Fluctuating canal or ditch water levels

Centrifugal pump used to irrigate Both 80-and 50-acre fields

Note: Pumping plants should be operated at the reduced frequency for at least 1,000 hours per year to be economical

Convert To Diesel Engines

Options for Converting From Electric Motors to Engines Direct drive (gear head) Engine shaft to pump shaft efficiency = 98% Diesel-generator Engine shaft to pump shaft efficiency less than about 80%

Considerations Brake Horsepower = Shaft Horsepower Engines and motors are rated based on brake horsepower ( 100 HP electric motor provides the same horsepower as a 100 HP engine Input horsepower of an engine is greater than that of an electric motor for the same brake horsepower

Engine Horsepower Maximum horsepower Continuous horsepower About ¾’s of the maximum horsepower Derated for altitude, temperature, accessories, etc.

0.40 0.39 0.38 0.38 0.38 0.37 0.37 0.37 0.36 FUEL CONSUMPTION (lb/bhp-hr) 0.34 0.32 0.30 1200 1400 1600 1800 2000 2200 ENGINE RPM

Electric Motors vs Diesel Engines: Which is the Best? Unit energy cost Capital costs, maintenance costs, etc Hours of operation Horsepower Cost of pollution control devices for engines

Comparison of electric motor and diesel engine 100 HP 1,100 gpm 2,000 hours per year

That’s All, Folks