Hydoelectric Calculations: Friction Head Losses in Pipe

Submit your own Letteror Article: Let Us Know!

Hydroelectric Calculations
Friction Head Losses in Pipe

Hi Meg,

Thanks for getting back to me. I'd tried emailing you some info but didn't seem to be getting through. Now that I am I'll do a rewrite and send later.

Found your site when I was doing a search on small hydro. The chart on pressure drop is way off ("Pressure Drop & Flow Rate Charts" Good charts & information on hydro systems. Pressure varies with pipe length & flow rate can be varied with different sized nozzles.)

It's the same chart AEE uses in their catalog and I'd talked with Dave Katz (AEE owner) about it this week after I'd gotten their new catalog. Anyhow, I'll try to put together a decent explanation and get back to you.

Went through some of the rest of your site. It's GREAT. Downloaded all your editorials but haven't had a chance to read them all. Will write more later.

Nick.

[LATER...]

Okay, this is probably more than you want to get into (I read your first editorial). But for people who are going to go hydro, it's important. In some cases, using the wrong figures for head losses due to pipe friction can mean the difference between happiness and disappointment. I've included the "real" loss figures so, if you want, you (or someone else), can compare them with AEE's.

Here are two examples.
Suppose someone has a stream that has a reliable flow of 18 gallons per minute (GPM) and that can have a head of 75' using 300' of pipe. Looking at AEE's chart, using 1" pipe, they would expect to have a head loss due to friction of 21', giving a net head of 54'. Assuming 35% efficiency (typical) they would expect to get an output of 64 watts or 1500 watts per day. This is enough for many folks without refrigerators.

However, the real head loss is 49', which results in a net head of 26'. At 35% efficiency they'd get 31 watts, or 745 watts a day. Depending on their expectations (and how much they'd spent) this could be a real disappointment.

In another case, suppose someone has a stream that can put out 40 GPM with an overall head of 150' using 1000' of pipe. They might decide that (using AEE's figures) a head loss of 46' for 1 1/2" pipe was acceptable because the money they'd save on pipe would help buy a refrig and a bunch of other stuff. Using 35% they would expect 275 watts or 6500 watts/day - this is hog heaven livin off the grid.

Instead, what happens is the head loss is 90' with a net head of 60'. This results in 160 watts and 3800 watts/day - still pretty much hog heaven, but I hope they didn't rush out and spend a bunch of money on appliances before they got the system up and running.

I'm sending this overload to you because I've been around this scene for awhile and I want to see the stuff we're up to succeed, and the people that get into it be happy, in spite of what at times may seem hardship.

Take care, Nick

Here's the loss chart. It's from a spreadsheet I wrote based on the Williams and Hazen formula, which is used by pipe manufacturers and distributors. The table I sent is for PVC pipe. Steel pipe has head losses about twice as great as those shown, but most people doing residential hydro use PVC. Nick

You might add an email link to me for those who are confused or want to comment.
hansn@midcoast.com Hans Nicolaisen

NOTE: This info was "tabled" in HTML by MEG. Jose has instructed me on how to fix the headings, so I think it's right now. I can make the wheels go round & round, and laugh like a kid when it seems to be working, but coefficients and logarithms, et.al., tend to confuse me greatly.<G>I'm pretty sure it's fixed.

Hydroelectric Calculations: Friction Head Losses in Pipe
HEAD LOSS per 100 FEET (of pipe)

PIPE SIZE

GPM	1.00"	1.25"	1.50"	2.00"	2.50"	3.00"	4.00"
3	0.59	0.16	0.07	0.02	0.01	0.00	0.00
4	1.01	0.27	0.13	0.04	0.02	0.01	0.00
5	1.53	0.40	0.19	0.06	0.02	0.01	0.00
6	2.14	0.57	0.27	0.08	0.03	0.01	0.00
7	2.85	0.75	0.36	0.11	0.04	0.02	0.00
8	3.65	0.97	0.46	0.14	0.06	0.02	0.01
9	4.54	1.20	0.57	0.17	0.07	0.02	0.01
10	5.52	1.46	0.69	0.20	0.09	0.03	0.01
12	7.74	2.05	0.97	0.29	0.12	0.04	0.01
14	10.29	2.72	1.29	0.38	0.16	0.06	0.01
16	13.18	3.49	1.65	0.49	0.21	0.07	0.02
18	16.39	4.34	2.05	0.61	0.26	0.09	0.02
20	19.92	5.27	2.49	0.74	0.31	0.11	0.03
22	23.77	6.29	2.97	0.88	0.37	0.13	0.03
24	27.92	7.39	3.49	1.03	0.44	0.15	0.04
26	32.39	8.57	4.05	1.20	0.51	0.18	0.05
28	+	9.83	4.64	1.38	0.58	0.20	0.05
30	+	11.17	5.28	1.56	0.66	0.23	0.06
35	+	14.86	7.02	2.08	0.88	0.30	0.08
40	+	19.03	8.99	2.66	1.12	0.39	0.10
45	+	23.66	11.18	3.31	1.40	0.49	0.13
50	+	28.76	13.59	4.03	1.70	0.59	0.16
55	+	34.32	16.21	4.81	2.02	0.70	0.19
60	+	+	19.04	5.65	2.38	0.83	0.22
65	+	+	22.09	6.55	2.76	0.96	0.26
70	+	+	25.34	7.51	3.16	1.10	0.29
75	+	+	28.79	8.54	3.60	1.25	0.33
80	+	+	32.44	9.62	4.05	1.41	0.38
85	+	+	+	10.76	4 5.0	1.58	0.42
90	+	+	+	11.96	4.53	1.75	0.47
95	+	+	+	13.22	5.57	1.94	0.52
100	+	+	+	14.54	6.13	2.13	0.57
200	+	+	+	+	22.11	7.68	2.05
300	+	+	+	+	+	16.28	4.34
400	+	+	+	+	+	27.74	7.39
500	+	+	+	+	+	+	11.18

You might add an email link to me for those who are confused or want to comment.
hansn@midcoast.com Hans Nicolaisen

RETURN to Informational Articles

Please Read The Website Disclaimer!
Copyright 2006, The Survival & Self-Reliance Studies Institute (SSRsi), All Rights Reserved
Site conceptualized, designed, created & maintained by MEG Raven
Snail Mail: SSRsi, PO Box 2572 Dillon, CO. 80435-2572