In article ,
Brian A writes:
Currently I don't have a central heating system.
I want a system which allows me to control each radiator separately.
This will then allow me to only have rooms heated when they are likely
to be occupied and to properly control the temperature with wall
thermostats.
Rather than employ 2 port motorised valves I thought about trying a
different system of control.
What would happen if a standard thermostically controlled radiator
valve was set to full temperature and then a resistor placed in the
vicinity to facilitate temperature control. By applying a voltage to
the resistor it would heat up and, hopefully, cause the valve to
close.
Has anyone tried this method of control?

I did it with a Grugasar gas wall heater which had a capilliary/bulb
providing modulating/proportional control, but no timeswitch or remote
control capability built in.

I taped 3 resistors to it. I had originally intended to drive these
directly from the alarm/home-automation system, but found I needed
more power than I wanted to drain from its battery backed supply,
so I used a wall-wart to power it, controlled by the HA system.

You can callibrate it by driving the resistors at a certain power,
and measuring the corresponding setback in room temperature. This
then scales linearly to increase or decrease the setback temperature
required. Then you set the thermostat (TRV in your case) to the
normal room temperature, and drive the resistors to create the
appropriate setback. I had two setback levels -- one for night
time of a few degrees setback, and one for frost/damp protection.

One thing is I'm not conviced by the accurancy of TRV's. The
Drugasar I had would maintain the room temperature to an accuracy
of 0.1C (it had a very long bulb, which made it both accurate and
responsive), but I don't think TRVs come close to that, which might
make the calibration difficult, and the final result a bit more hit
and miss.

I vaguely recall finding a web page somewhere showing how someone
had done this with TRVs, so you could try searching that out.

--
Andrew Gabriel