Comment

Comment by John Malone on November 27, 2013 at 2:28pm

@Bob

I'm still in trial and error mode at the moment myself.  One of the positives of using the irrigation tubing is that I can move the solar panel around, but I'm quickly coming to the conclusion that I need to get the panel set in a semi-permanent location so that the plumbing can be done 'right'.

I'll be using 1" 200 psi PVC for the in and out pipes because it's super cheap and gives good flow.

First things first, I need to build a frame to mount the solar heater.  Sitting on the ground behind walls robs me of hours of heating time.

Always something to do.  Oooh, look, I've got a 4 day weekend.  That'll do it!

Comment by Bob Wohl on November 27, 2013 at 12:55pm

@John Ha! I figured I'd be doing some head scratching at the Depot for this one :D Looks like I have some work to do this weekend. 

I'll try to do something like this: 1/2" to 3/4" headers(4' long) with T connectors every 6". Could a 1/2" work as a return? trying to think if I can keep this thing modular enough that I can move it around w/o using stationary connectors.

Thanks!

Comment by John Malone on November 27, 2013 at 11:56am

@ Bob Wohl

How is it done?  By standing in the plumbing aisles in Home Depot staring at all the multitude of connectors and adapters and fittings and coming up with something brilliant.  Or, in my case, something that'll work until it doesn't.

My first attempt at the parallel pipes was with irrigation tubing and T barb connectors.   It worked quite well for the first season, but over time the heat got to the tubing and shrank, twisted and distorted it so much that a lot of the joins developed leaks.   This is probably due to the fact that I've got mine under glass to increase the heat capture.  It works. Yesterday the heat inside the solar collector topped out at 120F.   I've changed to using solid PVC pipe and we'll see how that holds up.  I've read that PEX is the way to go, as long as you protect it from UV light, but that would involve buying some tools and learning how to use it.

FYI, my parallel system uses 1/2" PVC with a 3/4" header at each end.  I would have preferred larger headers, but the 3/4 - 1/2 - 3/4 T fitting was available and kept costs down.

This is the fourth version of my solar panel.   It's not an easy thing to get right.

Good luck.

Comment by Bob Wohl on November 27, 2013 at 10:34am

@John Thanks for the write up. I follow your math :). I was expecting more from the bottleneck out in the pressure department. So, with this said, waht is the easiest way tos connect all of these parallel tubes? Trying to think, T joints... But then I'd just be using 1/2 tubing. Are there connectors that I could use to put into/attach to a larger diameter PVC pipe?

Comment by Dr. George B. Brooks, Jr. on November 27, 2013 at 8:08am

@John. An excellent and easy to follow description of a complex process!

Comment by Dr. George B. Brooks, Jr. on November 26, 2013 at 11:28pm

@Stephanie  

Comment by Stephanie Bader on November 26, 2013 at 10:53pm

Dr. Brooks, i see all that space and I'm very jealous! You're going to have fun filling it all up!

Comment by John Malone on November 26, 2013 at 9:41pm

@ Bob Wohl : Pressure in pipes

As a rough rule, for a straight length of single pipe, the pressure required to push water through a pipe is directly proportional to the length of pipe.   i.e. if you double the length of pipe you will double the resistance of the water flow in that pipe.  

It's a simple arithmetic problem to add up all the resistance levels of your pipe to come to the total.   Now to introduce some algebra.  Don't panic, I won't get too complicated.   Let's say that x is the resistance in 1 foot of black irrigation pipe.  I don't know, nor really care what x is.

For a straight 100 feet of black pipe the resistance is going to be 100x.

Now lets say you have a parallel pipe arrangement like in the photos below with 10 rows of 8 feet each.    The resistance of the parallel section is going to be 8/10ths of x.     or 8x/10 or 0.8x.   which is less than 1 foot of straight black pipe.  What length of pipe is used in the parallel section 8 times 10 = 80 feet.

And that leaves the single in and out pipes of 10 feet each.

Now calculate the total resistance in this scenario:

a) 10' of input pipe = 10x

b) 80' parallel pipe = 0.8x

c) 10' of output pipe = 10x

Add them all up to a total resistance of 20.8x.   This is about 1/5 or 20% of the resistance of the straight tube, even with using a single in and out pipe.   Therefore you should be able to push water through this setup with a pump 1/5th the size of one that you would use in the single length.

It gets even better if you use larger diameter pipes for the inlet and outlet pipes.  Double the diameter of those pipes (say from 1/2" to 1") and they can carry 4 times as much water and therefore have a 1/4 of the resistance.  In a simplistic world (and the fluid dynamics world is FAR from simplistic.  Cue choas theory, laminar vs turbulent flow, etc, etc) that reduces you total input and output resistance from 20x to 5x, with a total system resistance of 5.8x.   

100 vs 5.8 : It's not even a fair contest.

This is exactly what Jim Troyer has done and I'm looking to replace my inlet and outlet pipe also for the very reasons calculated above.  

Why is this important?

1) Less resistance means a smaller, cheaper and lower power pump

2) Faster water flow makes the solar heater more efficient.

It's a win-win all around.

 

Comment by Dr. George B. Brooks, Jr. on November 26, 2013 at 8:34pm

With fish & Shrimp and Veggies, a new garden comes soon to south Phoenix.

Comment by Kim Romen on November 26, 2013 at 8:11pm

@ John and Jim, good points.  thx!

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