In message , Bob Minchin
writes
Tim Lamb wrote:
Confused....

Either my known to be suspect mathematics is wrong or there is something
amiss with sites recommending pressure vessel sizes.

Under my new floors I have carefully:-) laid 820m of 16mm pex-al-pex
piping.

Sadly absent from the mainly American sites offering pipe volume
calculations. My vernier gives a bore of 11.5mm and Pi x r2 x L comes to
85L. A more agile brain may kindly care to check!

Could that length of pipe bore conceivably squash into an 18 gallon
container? Probably.

The underfloor heating systems suppliers suggest a 4L vessel is adequate
for 1000m of 16mm pipe yet most sites marketing PVs are wildly in excess
of this. Surely they know that the system is run at a much lower
temperature than 85C boiler output!

Any thoughts?


Coefficient of expansion of water is 0.000214/degree c or for your 85
litres is 18ml per degree c
I'd allow for a max temperature assuming your mixing valve had failed
and a minimum of + a few degree assuming the system was filled on a
cold day. But even if you assumed 5 degrees to 85degrees you only get
1.5 litres so I'd reckon a 4l should be more than adequate unless I've
done my sums wrong.

Thanks Bob. Coincides with other posts but I still say there is
something awry with the PV sites.

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