On Sat, 13 Dec 2003 18:20:50 -0000, "stuart noble"
wrote:


Andy Hall wrote in message ...
From all of this, I would conclude that room thermostats may be good
practice and used as part of demonstrating compliance with Part L1,
but I can see nothing in the Approved Document that mandates them and
it is certainly a long stretch to say that not having one in a new
installation is specifically illegal.


Thanks for the wider view, Andy. What concerns me is, I assume a room stat
can't do any harm, unless of course it fights with the TRVs in such a way
that the boiler doesn't know what the hell it's doing.

Even then it won't do any harm as such. The fighting comes from a
few scenarios which can be avoided:

- Room stat is in a place where the radiator(s) have TRVs. As the
temperature rises, the room stat may switch off first. If this
happens then there is no more heat to there or the rest of the house.
Alternatively, the TRV may start to close down, effectively reducing
the heat contribution into the space and preventing the room stat from
operating unless the temperature goes much higher for other reasons
such as solar gain or heat gain from other rooms.

- Room stat in place where there is other heating - e.g. a living room
with gas fire or a kitchen. These contribute heat which is
effectively outside of the control loop and the room stat will react
by turning off the boiler early making the rest of the house cold.

By having the room stat where there is a non-TRV-controlled radiator
you create a control loop between temperature of that space and the
boiler firing. Ignoring the rest of the house for a moment, this
space will attain and be maintained at the room stat setting.

When you add in the TRVs for the other rooms, the trick is to ensure
that the radiator sizes and water flows are such that the TRVs are
starting to shut down before the room stat cuts off the boiler.

All of this is somewhat imprecise because the radiator water flows are
inter-related and of course heat passes from room to room.

You may want to think about using a radio linked room stat. These
have the advantage that apart from not needing to be wired all the
way, you can try different locations until happy with the results.
The sensor/control piece is battery powered and the receiver is fitted
near the boiler.



Why the installers
should bother to disconnect the old stat is a mystery.

It doesn't make a lot of sense, although if it was an old bimetal one,
using an electronic one would giver better control sensitivity.


The other thing that would concern me is the reliability of the TRVs. I've
never had a stat fail but I've known plenty of TRVs seize up if they're not
adjusted from one year to the next.

I've always used Invensys/Drayton ones and have never had the plunger
of one sieze up. I have had failures of the head part after 7-8
years but I have a couple that are still fine after 15.



..andy

To email, substitute .nospam with .gl