"Set Square" ...
In an earlier contribution to this discussion,
Neil Jones wrote:


I have gas fired central heating with a non-modulating conventional
cast iron boiler which is rated at about double the worst-case heat
loss for the house. I have a programmable room stat, with TRVs on 10
radiators and one bypass.

How much would it cost to add individual time/temp control to the
system with a view to increasing efficiency without the disruption
of
moving or reconfiguring pipework?

If you recall, I mentioned that I had been looking at the CM67z and
HR80 solution yesterday becasue it appeared to do what I wanted,
although at the price indicated I would want more - interfaces to
house control system, that kind of thing.

Neil


Hi Neil,

The CM67z sounds interesting to me as a way of retrofitting some
measure of
individual room control to an existing system without a lot of
plumbing and
wiring changes. The main drawback seems to me (apart from the
batteries!) to
be the fact that each CM67z only controls 2 zones. So if you have
(say) 10
rooms, and want each room to do something different by way of
temperature
profile, you need 5 CM67z's - which could get a bit expensive.

I think that if I were to upgrade my system - which is similar to
yours
except that I haven't got any TRVs - I would probably fit a 2-port
zone
valve in the feed to each rad, and have each of these controlled by a
programmable room stat. [Ok, I would need 10 stats, but they could be
a lot
less exotic than a CM67z]. Installing zone valves would not
necessitate
converting to a manifold system (contrary to IMM's inference) as long
as you
can get at the feed pipe to each rad in some suitable location.
Bringing
them all together in a central point would simplify wiring up all the
volt-free contacts on the zone valves to control the boiler - but is
by no
means essential. In my case, at any rate, all the zone valves could be
under
the upstairs floorboards, and the only exposed wiring would be that
going to
each room stat - which I would cover with small section white square
trunking until the room is next decorated, when I would chase it into
the
plaster.

Good point, although I'm not sure I have room under the floorboards to
house the zone valves, and having them exposed in each room would not
have sufficient WAF to obtain budgetary approval :-)

When I first saw the CM67z I considered 2 zones (being nominally 'living
rooms' and 'bedrooms'.) Clearly if one room calls for heat the whole
system will be switched on, but unless I *actually* zone the system that
will happen whatever I do. Battery life looks a definite disadvantage -
these valves must be making adjustements on a fairly regular basis. On
the other hand it would probably be simple to use a mains transformer
instead.

At the end of the day, if it starts getting too expensive I'd be better
off replacing the boiler, although that is no simple job either, given
the layout of the house.

Neil