Derek Broughton wrote:

There is no such thing as zero risk. It's OK for you to not worry about
freezing. We just had two weeks at -10C and lower.

At no time have I stated that there is no need to worry about freezing.
Its quite obvious that a solarthermal system in Britain will need to be
safe in freezing conditions.


I'm not risking
exposing water pipes to that.

Lots of people round the country expose hosepipes to subzero temps day
in day out. Does this make them burst? No, because theyre not full of
water.


The idea of a draindown system is to _not_
permit that - but how do you guarantee that it's always sufficiently
drained?

by designing the system so it drains itself when the pump stops. As
long as its partly drained, all is well. The expansion of water on
freezing can be accomodated by a small percentage of air in the pipe.
With draindowns they are almost completely empty every time the pump
stops. Its how they work.

I could install a drain-down system, but (a) I'm not confident I won't have
a flood, (b) nobody in this area will sell or service them (because _they_
aren't confident, either), and (c) I'm _definitely_ not confident that _I_
could build, or even install one, that would be low-risk. otoh, I can get
a glycol-loop system, built locally, installed professionally, with proven
reliability - and still save money over heating water with propane.

Its not because theyre not confident, but thats another story.


NT