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Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1664

Posted: 12:09pm 02 Jan 2017

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Hi All,

Arrived home yesterday after a few days away to an interesting failure of my home made Spa heating system.

Panels consist of 2.4m lengths of corro with 25mm garden poly laying in the down corrugates.

Panels are covered with clear poly carb sheets.

Made them at the end of last summer & they have been up almost a year.

Cloudy overcast conditions when we got in yesterday, & the controller read 33.5�c,
opened the spa cover & I'd lost 6" of water.

kicked the circulation pump in & checked for leaks on the roof & found one to have sprung a few leaks.

3 of the pipes had literally melted & burst, little hard to understand given they have been up for so long, and have endured hotter weather.

Main thing of interest is the data from my weather station, which shows unusual extremes in Solar Radiation & UV indexes.

For the moment I'll replace the 3 blown pipes, but interested in hearing thoughts on alternate "Plan B's".

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 03:51pm 02 Jan 2017

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Hi phil,
that is quite common with exposed poly pipe. it is caused by the water being stationary, hot and under pressure in the pipe.

for example a pipe can be rated for a 100 year life at 150 psi below 30C and 6-12 months at 70 psi at above 70C.

I took this pic on a mild spring slightly breezy morning, when the wind dropped the pipe got to 64.7C with the air temp at 25C, there is a good possibility your pipe could get well into the 90C+ range on a summers day.

PS that is inch rural B class poly not garden pipe.Edited by yahoo2 2017-01-04

I'm confused, no wait... maybe I'm not...

Madness

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Joined: 08/10/2011
Location: Australia
Posts: 2498

Posted: 05:49pm 02 Jan 2017

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That pipe looks like how I have felt with the hot weather we have had in the last week.

There are only 10 types of people in the world: those who understand binary, and those who don't.

Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1664

Posted: 12:26am 03 Jan 2017

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yahoo2 said Hi phil,
that is quite common with exposed poly pipe. it is caused by the water being stationary, hot and under pressure in the pipe.

for example a pipe can be rated for a 100 year life at 150 psi below 30C and 6-12 months at 70 psi at above 70C...

Yeah, mines garden pipe, & have seen 85�C surface temp on a Fluke laser thermometer when there is no water flow.

As far as pressure is concerned the panel has saw stool elevation at the high end & both inlet & outlet have stand pipes.

Operating pressure is about a foot of water heat at the high end.
When the pump stops, the water in the feed & return pipes drains back, but the panels still stay basically full.

The other thing is that several of pipes now have west facing ribs on them, you can sort of make them out in the first pic.

They are basically below the radius on the poly carb sheet where the angled part meets the flat top surface, almost as if the radius of the bend acted as a lens.

Strangely though, the third panel, just visible in the right lower corner of the pic, shows no sign of overheating.

Other thing is it was a broken cloudy day, bight have been extra reflection from the clouds, as on the hottest & clearest days we've hade the weather station showed only a bit over 1100w/m2.

Averages for the day, shown under the curve are not that extreme really, considering what we've had a few weeks earlier.
Edited by Phil23 2017-01-04

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