On Tue, 16 May 2006 21:32:17 GMT, John Stumbles
wrote:


I'd have thought a (much cheaper) phosphor-dosing scale inhibitor would
serve this purpose, as it does for other water-heating appliances such as
combi boilers. Do you have some evidence to show that this is not the
case?

"Best practice in water hardness control is more important for direct
than for indirect solar water heating systems. Direct solar water
heating systems may need robust hardness control: and water softeners
may be difficult to install in a few properties. Unless they are
plumbed “indirectly”, water harness control for direct solar is
usually achieved by polyphosphates where the water hardness is
100-200 ppm CaCO3 and by the use of an ion exchange softener above
this figure. Ion exchange water softeners are thus regarded as
essential best practice...

Barry Johnston, MSc
Managing Director, Solartwin.com"

Above 200 mg/l as calcium carbonate equivalent includes most of
Eastern England in an area bounded on the west by Southampton,
Bristol, Birmingham and Lincoln.

http://www.britishwater.co.uk/html/s...water.html#Map



--
Peter Parry.
http://www.wpp.ltd.uk/