On Sun, 07 Dec 2003 17:06:25 GMT, "Mike Hibbert"
wrote:

"BillR" wrote in message
...
Mike Hibbert wrote:
Hi all,

I have been thinking about my central heating this morning as it
seems to be getting very toasty at the moment. We have a Combi boiler
(Worcester Bosch Highflow 400) which has a heat setting on it. There
are TRV on all the rads (except the bathroom - I assume to stop the
boiler overheating if the TRV's shut off) , but we dont have a room
stat.

Are the TRV's really temperature controlled or do they simply reduce
the amount of water the rad can get? If that is the case, then with
no room stat, the only way I can control the overall temperature is
by the boiler, so I have to go into the garage and turn it down/up.
Is this a normal set up?
Its normal for installers to fit TRVs on all rads because they can't be
bothered with the hassle of roomstat wiring...
Normally I would leave the heating on 24*7 during the winter and
control it via the room stat so it would get to a reasonable temp and
then switch off, but now if I leave the heating on the boiler tuns
all the time (this must be expensive!!) and the bathroom is like a
sauna. The missus loves it, but I guess the heating bills will be
huge!

Any thoughts?
Fit a programmable room stat. If wiring it up is a problem get one of the
RF
models e.g. CM67 RF.

Thanks Bill, it would still need wiring at the boiler end wouldn't it? Is
that a (relatively) straightforward job?



Mike

I spotted a couple of things from your original post.

TRVs are fairly effective in that they do monitor the room temperature
(albeit they are a little influenced by being near the radiator).
There is a wax or equivalent capsule inside which expands with
temperature and reduces and ultimately stops the water flow. In that
sense they are somewhat more "analogue" than "digital" which is not a
bad thing anyway. Of course, you also have the effect in a house
that there is transfer of heat from room to room so the overall
environment is quite complex. However, they are effective for what
they are.

Adding a room thermostat is a good way to implement overall control of
the house temperature.

I completely agree with Bill, an RF thermostat would probably be a
good solution for you. Apart from the Honeywell CM67RF there is the
Danfoss TP75-RF (about to be superceded by TP7000-RF)

These consist of a remote unit which you can site anywhere, or even
take from room to room if you wanted. There is a clock and a
temperature setting and measuring function and the whole thing is
battery powered.

One useful capability is of night set back. This means that you can
drop the temperature over night by a few degrees rather than turning
off the heating completely. 6 degrees or so setback is fairly
typical. Apart from the improved comfort, depending on the system
and the house, doing this can also result in less use of energy as
well. One of the principles behind this is that in some systems and
houses, when the heating goes on in a cold house, there is an
overshoot past the set point and more energy is used. If the house
is not as cold then the overshoot is less. However this does all
depend on the complete environment of the system and the house thermal
characteristics. Also, with this type of room thermostat, the
temperature sensing is more sensitive and accurate than an old
fashioned bimetal strip type.

Moreover, there is also what is called a proportional control
facility. This basically turns the boiler on and off in proportion
to the heat required when the temperature is a degree or two either
side of the set point. The effect is that overshoot can be
practically eliminated.

Added to this, the boiler that you have is a modulating type which
will adjust heat output according to demand.
Overall, this sounds quite complex. In one sense it is - the
control theory for a system like this and a house is involved.

However, you don't need to be overly concerned.
The main points to achieve are that a) you are getting to the right
temperatures when you want them, b) that there is not significant
temperature overshoot when the system begins the start of a heating
period and c) that the boiler doesn't short cycle (= 30-60 second
burns) because it is producing too much heat.
In reality, you have to experiment a little until you are happy with
the settings.


Regarding installation, at the boiler end you have a receiver which is
connected to the boiler. You can download the installation manual
for the boiler and you will find a wiring diagram. The boiler has a
set of terminals with a permanent live and a switched live for the
heating. At present, these will have a link between them, I would
expect.

After removing the link, you would wire out to the receiver (which
should be located outside the case of the boiler) using the permanent
live and neutral and then the switched live, plus an earth if
required.

It's possible that you might already have a timeswitch on these two
terminals, although I note that some versions of this boiler have one
built in.

The best thing if there is a time switch already would be to set it to
24x7 as you are now and to use the clock function on the remote room
controller.

If you can run the wiring easily, there are non-RF versions of these
two programmers which cost a little less and have the same
functionality.

I hope that that helps. This is not a particularly difficult task
if you are comfortable with doing wiring. Obviously, sketch down
what you have before you start in case you need to revert back for any
reason.





..andy

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