Home made solar question

[solarboy]

I'm almost finished building a home made solar collector. It is basically an oval lozenge shape on top of a poolside pergola. I've divided up the 2" feed into 20 x 5/8" irrigation pipes that spiral round 4 times before being "collected" together into a 2" pipe together. The spirals range in total length from 130' to 200'. The total collector area is 172sq.feet. The pool surface area is 193sq.feet. This is just under 90% of the pool surface. I understand that it would have been consistent to have had all the pipes the same length.
I have a huge sand filter and currently my pressure there is 12psi with DE (Pool has 1 skimmer,1 main drain and 2 returns)
My question is, I'm reasonably sure with the extra strength of the irrigation unions/clamp brackets/pipe I can run my currently 37 GPM all through the collector without any bypass to get a much higher efficiency than normal. Will the plumbing take this throughput without issue ?

As a side note, it has been said that this type of home made solar isn't worth the effort is it's cheaper to buy retail collectors. These cost me around $2.80/sq.foot and I was able to fit 9 square feet per hour for a total of 20 hours.

 

[iPhone]

Love the picture they always help one see what is going on. Can't help much with the questions but have one of my own.

Have you calculated/thought about how much weight in water you will have on top of your Pergola? Can't see what the underside looks like in the pictures.

 

[solarboy]

Thanks for the reply. The weight is 127lbs which isn't a problem as there are 5x3 joists on 24" centres underneath.

 

[JasonLion]

You should be fine at that flow rate as long as all your joints are good.

Commercial panels on eBay seem to go for around $2/square foot in the US. I also suspect that they would be about twice as efficient as your setup, though that is just a rough estimate. None the less, you should get a significant amount of heat out of your rig.

 

[solarboy]

Thanks for that Jason. I'll be tightening those pipe clips a little bit extra. I think in Europe the panels must be overpriced, the retail price of quality panels is $9.50 ! The eBay ones are about $5.70. I'll be taking extensive measurements when they're up and running so I can get an idea of the inefficiencies.

 

[thunderkyss]

Too cool.

You guys are just way too cool.

 

[gordiec]

Would it be a problem if the weight was between 550 and 700 lbs (or more)? My math, or assumptions, might be wrong but I think 127 lbs is on the low side.

In round, easy to work with numbers you have 20 tubing loops of 150 feet (first assumption) for a total length of 3000 feet of tubing.
If (2nd assumption) the tubing weight is 10 lbs per 100' it the weight is 300 lbs, if it is 15 lbs per 100' it is 450 lbs.

If the inside diameter of the pipe is 1/2" (3rd assumption), the area is about 0.2". Multiply that area by the tubing length in inches and dividing by 231 gives you U.S. gallons. One U.S. gallon of water weights about 8.3 lbs. So 0.2 x (3000 x 12)/231 = 31.1 gallons *8.3 lbs/gal = 259 lbs (of water). Or about 250 lbs, to make it an easy number to work with.

So that is how I came up with a combined weight of 550 to 700 lbs. I don't know the exact specs or length of the hose that you used, or what weight your pergola can carry, but I did want to let you know that I think your weight estimate is on the low side.

I also want to say what a great idea it is! My wife saw the picture and is already thinking that she might want me to do something similar.

Good luck with your project!
Gordon

 

[solarboy]

You're right, it is more than I thought. I had to do it in metric and I got..
6.5mm pipe radius at 1000m gives a volume of 132 liters or 291 lbs. Your estimate is amazingly close considering. The pipe itself weighs (very approximately) 110 lbs so probably a combined weight around 400 lbs. The joists spacing and size are the same as our house roof which was engineer calculated to carry 40kg of tiles per square meter which works out at 936 kg (2000 lbs) over the whole (258 square feet) pergola.
Thanks for your input Gordon, it always makes me feel more confident to know someone else has also pondered.
My granddad always said, "measure twice, cut once".

 

[solarboy]

Well I got bored of doing spirals and connected it all to the pump with only half the eventual pipe "just to see". I connected the 1/2" pipe to the manifolds with irrigation barbed angled connectors with hose clips but they leaked like crazy so I swapped them for 3 part pipe connectors (rubber o-ring,split clamping ring and pipe "nut") and the leaking stopped. In 3 days my end of day temperature has gone up from 73F to 80F while max. daytime temp has dropped 2 so it's obviously working. You can feel the heat at the returns so I'm a very happy bunny. Swimming is balmy ! Only 10 more spirals to go and then I'll post some detailed numbers and hopefully work out the efficiency compared to commercial panels.