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 o One kilowatt is 1.34 horsepower o 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 Stuffing Box Impeller Balance Line Discharge Volute Inlet Wearing Rings Deep Well Turbine Deep Well Turbine Submersible Pump Terms Total head or lift Capacity Brake horsepower Input horsepower Overall efficiency Motor Ground Surface Discharge Pressure Gauge Discharge Pipe Pump Head 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 Discharge Pressure Intake Pressure Pump Discharge Pipe Pump Intake Total Head or Lift of Booster Pumps Difference between pump intake pressure and pump discharge pressure Multiply difference (psi) x 2.31 Example o o o o 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 o o o o Total Head or Lift - Capacity Pump Efficiency - Capacity Brakehorsepower - Capacity Net Positive Suction Head - Capacity (centrifugal pumps) Total Head - Capacity 250 Worn Pump New Pump TOTAL HEAD (feet) 200 150 100 50 0 200 250 300 350 PUMP CAPACITY (gallons per minute) 400 PUMPING PLANT EFFICIENCY (%) Efficiency - Capacity 60 50 40 30 20 10 Worn Pump New Pump 0 200 250 300 350 400 PUMP CAPACITY (gallons per minute) Horsepower - Capacity BRAKE hORSEPOWER 10 8 6 4 2 New Worn 300 400 0 0 100 200 CAPACITY (gpm) 500 600 700 100 100 9 Total Head 80 70 8.5 80 82 8 60 83 83 60 82 80 40 40 83.5 Brake Horsepow er 20 20 0 0 200 400 600 800 1000 PUMP CAPACITY (gpm ) 1200 0 1400 BRAKE HORSEPOWER TOTAL HEAD (feet) 80 How Do You Use Performance Curves? o Selecting a new pump o 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 Selecting a New Pump Design: Total Head = 228 feet, Capacity = 940 gpm A Capacity (gpm) Total Head per Stage (feet) No. Stages Actual Total Head (feet) Pump Efficiency (%) Pump or Brake Horsepower Annual Energy Cost ($) B C 940 940 940 57 73 37 4 3 6 228 219 223 84 69 76 64 73 69 7162 8225 7721 Common Causes of Poor Pumping Plant Performance Wear (sand) Improperly matched pump Changed pumping conditions o Irrigation system changes o Ground water levels Clogged impeller Poor suction conditions Throttling the pump Improving Pumping Plant Performance Impeller Adjustment Effect of Impeller Adjustment Capacity (gpm) Total Overall Input Head Efficiency Horsepower (feet) (%) Pump 1 Before After 605 910 148 152 54 71 42 49 Pump 2 Before After 708 789 181 206 59 63 55 65 Pump 3 Before After 432 539 302 323 54 65 61 67 Pump 4 Before After 616 796 488 489 57 68 133 144 Effect of Impeller Adjustment on Energy Use Pump Pump Pump Pump 1 2 3 4 Same Operating Same Volume Time of Water +16.7% -22.8% +18.2% +5.0% +9.8% -12.3% +8.3% -16.8% Repair Worn Pump Effect of Pump Repair Before 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 Efficiency (%) Matched Pump Improperly Matched Pump 0 0 Capacity (gpm) Mismatched Pump Pumping Plant Test Data Pumping Lift (feet) 113 Discharge Pressure (psi) 50 Total Head (feet) 228 Capacity (gpm) 940 Input Horsepower 112 Overall Efficiency (%) 48 Multiple Pump Tests Test 1 Test 2 Test 3 (Normal) Capacity (gpm) 940 870 1060 Pressure (psi) 50 79 15 Pumping Lift (feet) 113 112 112 Total Head (feet) 228 295 147 IHP 112 112 104 Overall Efficiency (%) 48 57 38 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 8 PIPE DIAMETERS 2 PIPE DIAMETERS FLOW FLOW METER Input Horsepower Is a pump worn or mismatched? Multiple pump tests Compare pump test data with manufacturer’s pump performance curves 200 TOTAL HEAD (feet) REPAIRED PUMP Pumping Lift = 102 ft Capacity = 537 gpm Input Horsepower = 28 Overall Efficiency = 50% Kwhr/af = 211 150 Small Difference 100 Large Difference WORN PUMP Pumping Lift = 45 ft Capacity = 624 gpm Input Horsepower = 19 Overall Efficiency = 39% Kwhr/af = 123 50 0 0 100 200 300 400 500 600 700 PUMP CAPACITY (gpm) 800 900 1000 1100 100 TOTAL HEAD (feet) 80 60 1984(54%) 1983 (64%) 1985 (62%) 40 20 0 2000 2400 2800 PUMP CAPACITY (gpm) 3200 3600 100 TOTAL HEAD (feet) 80 1983 (64%) 1984 (66%) 60 1985 (55%) 40 20 0 2000 2400 2800 PUMP CAPACITY (gpm) 3200 3600 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 Horsepower Standard 10 20 50 75 100 125 86.5 86.5 90.2 90.2 91.7 91.7 Energy Efficient 91.7 93.0 94.5 95.0 95.8 96.2 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 o 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 differentlysized 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 Acres Pressure (psi) Capacity (gpm) Input Horsepower RPM Overall Efficiency (%) Unthrottled 80 80 1,100 128 1770 40 Throttled 50 64 600 90 1770 24 VFD 50 60 700 55 1345 44 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. 200 167 173 BRAKE HORSEPOWER 157 144 150 128 110 100 50 0 1200 1400 1600 1800 ENGINE RPM 2000 2200 FUEL CONSUMPTION (lb/bhp-hr) 0.40 0.39 0.38 0.38 0.38 0.37 0.37 1600 1800 0.37 0.36 0.34 0.32 0.30 1200 1400 ENGINE RPM 2000 2200 40 ENGINE EFFICIENCY (%) 38 36 35.1 35.1 34.7 34.2 33.9 34 33.2 32 30 1200 1400 1600 1800 ENGINE RPM 2000 2200 160 PUMP HP CONTINUOUS ENGINE HP 140 HORSEPOWER 120 100 80 60 40 20 0 1400 1500 1600 1700 1800 RPM 1900 2000 2100 2200 RPM 1500 1600 1700 1800 Fuel Use Versus RPM Pump Flow Gallons of Diesel Rate (gpm) per Hour 1228 1731 2161 2486 9 11 15 19 Gallons of Water per Gallon of Diesel 8187 9617 8644 8019 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 Capital Cost Unit Energy Cost Total Cost ($/af) Electric Motor $5,500 $0.14/kwhr 60.5 Diesel Engine $11,500 $0.95/gal 37.8 $16,500 $0.95/gal 39.9 $16,500 $1.25/gal 48.5 That’s All, Folks