On Fri, 10 Mar 2006 09:54:57 +0000 someone who may be AJH
wrote this:-

Thanks I was considering a more simple open vented system. In general
I have a preference for sealed systems

In general I have a preference for open vented systems, in small
installations. In such installations the advantages of a "sealed"
system largely fall to the installer and maintainer. The occupier
gains little with such systems, in many/most cases. Large
installations (I have been responsible for some very large heating
systems) are a different matter.

However, for solar water heating the disadvantages of an open vented
system include the trouble of placing the header tank high enough,
then maintaining it and the inability to heat water above 100C. In
this case I think the advantage lies with a "sealed" system.

Once the option for sealed
system is taken I can see little advantage in drainback over a glycol
or food grade antifreeze system.

The system at http://www.imaginationsolar.com/system.htm has a
number of advantages. One of these is that it does not use mains
electricity, which can exterminate 20% of the savings gained by
using solar hot water heating [1]. The control system is very
simple, if the sun is shining it pumps water into the panel and
starts warming up the cylinder. If the sun is not shining, or there
is snow on the PV panel, then the pump is not running and the panel
is drained of water.

The system at http://www.navitron.org.uk/solar_collector_panel.htm
is more sophisticated and so will extract more heat from the sun. On
the other hand it needs mains electricity 24 hours a day, because
the controller might need to turn on the pump occasionally to warm
up the panel header a bit on cold nights (assuming it is run without
anti-freeze). Mains failure means possible freezing in winter and
overheating in summer, though these are rare in most of the UK.

The system at http://www.solartwin.com/easy_to_plumb_in.htm involves
much less plumbing, so is easy to fit and has simple PV powered
controls. Provided that the existing hot water cylinder is well
insulated and of an adequate size this has great advantages.

These are just three possibilities, but they do show a range of
possible solutions in one small part of the world.

[1] - "Side by Side Testing of Eight Solar Water Heating Systems"
DTI/Pub URN 01/1292
http://www.dti.gov.uk/energy/renewab...bs_solar.shtml



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54