Energy Efficiency Considerations in Pumps and Pump Stations

Transcription

1 Energy Efficiency Considerations in Pumps and Pump Stations Jeff Foray, P.E. WSU Extension Energy Program 14 March 2014

2 How Do You Save Energy? Don t design it wrong Operate smart Fix stuff Thanks for your time, any questions me at [email protected]

3 Energy in a Pumping System

4 Pumps and Other Fluid Movers Centrifugal pumps are the most common End suction Split case Turbines Submersibles Positive displacement pumps Other devices Fans Compressors

5 Some Basic Stuff Flow: 1 mgd = 694 gpm Head: 1 psi = 2.31 feet Head Loss: liquid friction, velocity 2 Power: 1 hp =.75 kw Money ($.07/kwhr) 1 mgd at 100 feet (22 hp) for a year is about $10,000 2 mgd in same pipe is about $18,000 a year 1 hp for a year about $500

6 What is Efficiency? Good divided by the total Energy Losses in Pumps: Mechanical (friction in bearings, etc.) Volumetric (recirculation) Hydraulic (liquid friction)

7 Calculating Pump Horsepower hp = Q x h eff X 3,960 Q = flow in gpm h = head (pressure) in feet (1 psi = 2.31 feet of head) eff = efficiency Water horsepower: ignore efficiency Brake horsepower: pump efficiency only (size the motor) Wire-to-water horsepower: pump x motor efficiency (size the electrical service)

8 Typical Pump Efficiencies Pump only (brake, no motor) Non-clog centrifugal, 25 hp: 65% Submersible wastewater, 34 hp: 75% Vertical turbine, water, 30 hp: 81% End Suction, water, 30 hp: 75% Bigger is better: add about 5 points at 200 hp Slower is better: add a couple points below 1200 rpm

9 Pump Curve: Superbasics Head (feet or psi) Operating Point Pump curve System curve Dynamic Losses Static Pressure Flow

10 Pump Curve: Less Basic Nerdy but crucial Best Efficiency Point (BEP) Typically drops off about 20% from BEP How pump is applied determines how efficient it will be

11 Minimum/Maximum/Normal

12 Pump and System Curves System Curve Normal High Static Head Low Static Head

13 Dynamic Losses May Vary High Dynamic Head System Curve Normal Low Dynamic Head

14 Operation at Low End of Pump Curve High Dynamic Head System Curve Normal Low Dynamic Head

15 Operation at High End of Pump Curve High Dynamic Head System Curve Normal Low Dynamic Head

16 Variable Speed Pumping Variable Speed Drives (VFD s) Vary motor speed from about 50% to 100% Drive is about 98% efficient 2 to 4 times cost of starter Why? Moving water slower reduces friction

17 Why VFD s? Throttling Stinks ,800 RPM curve 1,125 gpm 2,250 gpm throttling valve 70 hp 90 hp Head (feet) 150 1,200 RPM curve VFD: 36 hp System curve System curve: throttled ,000 1,500 2,000 2,500 Flow (gpm)

18 Pump Selection Seems Easy Looks great for peak design conditions Head (feet) System curve rpm Flow (gpm)

19 Not So Fast.. 70 Pumps are often unstable and inefficient at average/ minimum conditions Efficiency is just 40% at 500 gpm Head (feet) System curve rpm 460 rpm 500 rpm Flow (gpm)

20 Follow Standards Hydraulic Institute Pump Intake Design (9.8) Allowable Operating Region (9.6.3) Read Pumping Station Design (Sanks)

21 Electric Motors Most applications: NEMA standard Enclosure type: TEFC, open dripproof, weather protected 1992 Energy Act Submersibles use special motors Inverter Duty: improved cooling, insulation

22 Electric Motor Efficiency Standard efficiency motors: 90% Premium efficiency: 10% more expensive, 5% more efficient Efficiency is constant to about 50% load % full load efficiency Hp Hp Hp % full load

23 Improving Pump Efficiency Don t Design it Wrong Invest in a good predesign Decide how it will operate before messing around with layouts and equipment selection Pick pumps to operate efficiently operate at conditions where the pump will actually operate most of the time Consider variable speed drives or smaller pumps to improve efficiency at low flows

24 Improving Pumping Efficiency Operate Smart Pump as slowly as possible Utilize storage to level out pumping rate Eliminate throttling Fix Stuff Test pumps regularly (inc electrical measurements) Visual inspection of interior Modify or replace impeller to match conditions Replace old motors (pre Energy Act, 1992 to 1997)

25 Example: Big Water Pump Station Figure 3 - Projected Average Day Power Usage, 2011 Projected Average Day Flow Average Power (kw) January February March April May June July August September October November December Month Average Power Consumption Current Condition Pumps kw After PS 1 Upgrade kw Average Flow (mgd) After PS 1 Upgrade Current Condition Pumps Projected Average Daily Flow

26 Energy Before and After Upgrade Current Condition Pumps 76 kw After PS 1 Upgrade 39 kw 16 kw 91 kw 614 kw 190 kw 611 kw 123 kw Average Hydraulic Power Loss Average Hyd Power Average Motor Loss Average Hydraulic Power Loss Average Hyd Power Average Motor Loss AFD Loss Savings Compared to Current Pumps