In Lev Nelik’s September column (“Quiz: Why Did Water Flow Reduce So Drastically?”), he explored issues of watering a garden at an apartment complex. To see Nelik’s solution to the quiz, check out his column in the October issue of Pumps & Systems. The following is a response from Mike Dominik, PhD, PMP, PE, senior project manager at Orbital Engineering, Inc.
Original Case
Case 1
Watering from a 150-foot garden hose (3/8-inch opening) for 30 minutes, with a supply pressure of approximately 60 pounds per square inch of pressure (psig). The cost of water is approximately $1 per 100 gallons.
Case 2
Watering from the same hose attached to a 3rd-floor shower room water spigot.
Quiz Question
Make a rough estimate of the cost of watering the garden in each case. Make any simplifying assumptions for your calculations. Hint: Shower room water is supplied from the same main water line via approximately 500 feet of pipe (assumed to be roughly the same diameter as a garden hose).
MIKE’S RESPONSE
Case 1
2.5 gallons per minute (gpm)
Case 2
1.25 gpm
Rough Answer
All equations are pulled directly from Crane’s Flow of Fluids.
So, you can ignore the inlet and outlet conditions.
Assume the hose does not have many turns:
- L is 150 inches
- Assume f is constant cases
Case 2
More exact:
