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Microhydro

Learn about microhydro flow assessment techniques including the use of nozzles, float methods, and weir measurement methods. Calculate flow rates using different measurement techniques and determine the appropriate size and number of nozzles for your microhydro system.

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Microhydro

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  1. Microhydro Flow, nozzles

  2. Site Assessment: Flow • 5-gallon bucket • Small stream, small waterfall • Float • Larger, flat, uniform stream • V-notch Weir • Rectangular Weir

  3. 5 gallon bucket Most typical method for microhydro Small stream, little waterfall This may be tricky…

  4. 5 gallon bucket • If the measured flow using a 5 gallon bucket and a stop watch was 5 gallons in 1.5 seconds, how many GPM would this be?

  5. 5 gallon bucket • If the measured flow using a 5 gallon bucket and a stop watch was 5 gallons in 1.5 seconds, how many GPM would this be?

  6. Float method Big, flat, uniform creek

  7. Float method Flow (ft3/s) = Velocity (ft/s) x Cross Sectional Area (ft2)

  8. Float method • Calculate the average depth Lay a board across the stream, measure the depth every foot, average the depths

  9. Float method • Calculate the cross sectional area Area (ft2) = Average depth (ft) x Width (ft) If XS is too irregular, divide into rectangles and sum em’ up

  10. Float Method • Calculate velocity Measure where you measured the area, an orange makes a good float, start well upstream, a 10’ span is good, average multiple measurements

  11. Float method • Correct for Friction Flow (ft3/s) = Velocity (ft/s) x Cross Sectional Area (ft3) x .83 Multiply x 0.83 to correct for friction on the bottom of the stream

  12. Float Method So, if these guys measure this 3’ wide stream and get an average depth of 8” and it takes an orange an average 5 seconds to go 10 feet, what is the flow in GPM? 1 ft3 = 7.48 gallons

  13. Float Method So, if these guys measure this 3’ wide stream and get an average depth of 8” and it takes an orange an average 5 seconds to go 10 feet, what is the flow in GPM? • Area = 3’ x 8” x (1’/12”) = 2 ft2 • Velocity = 10 ft/5 s = 2 ft/s • Flow = 2 ft2 x 2 ft/ s = 4 ft3/s • 4 ft3/s x 7.48 gal/1 ft3 x 60s/1 min = 1795 gpm • Correct for friction, 1795 gpm x .83 = 1490 gpm Complicated but easier than this…

  14. Weir Method • For larger flows or more accurate measurements • Small • V-notch • Larger • Rectangular • All you needs is depth and the table

  15. With V-notch or Rectangular weirs, drive a stake in the ground level with the bottom of the weir for depth measurement The stake should be behind the weir about 4x the depth of water through the weir Weir depth measurement

  16. V-notch Weir

  17. V-notch Weir Using the V-notch weir chart, determine what a stream’s flow rate would be in GPM if the depth of the water was 5.5 inches.

  18. Rectangular Weir Using the Weir chart, determine what a stream’s flow rate would be in GPM if the depth of the water above the weir notch was 3 inches and the weir notch was 4" wide.

  19. Nozzles Generally, single nozzle systems with under 2000 feet of penstock require a 2" pipe. A two nozzle system needs a 3" pipe and 4 nozzle systems require a 4" pipe. This will keep pipe losses under 25%.

  20. Nozzles • What size nozzles and how many would you recommend if one wants to use about ½ of a stream with 260 GPM of measured flow with 100 ft of head (pelton wheel)?

  21. Nozzles

  22. Nozzles

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