Re: Real HA - central heating control by the radiator

[Kevin Hawkins <lists@xxxxxxxxxxxxxxxxx>]

Lehane Kellett wrote:
>
> I have my doubts, for a domestic install anyway, whether full
> proportional on a single rad is worth the
> £40-50 quid a go extra. For DHW mixing, definitely.
>
For me - with very large cast iron radiators the hysteresis was too
large without proportional control.   Some of my controlled valves
control 3+ radiators as well which helps cost wise.   I was getting
oscillations of nearly 3 degrees C in my room temperature using ONOFF
switching. this was quite noticeable. I tried three approaches to fix
this, I'm sure there are others,,

1) Getting the flow temperature reduced and hence more 'balanced',
worked quite well but this had problems in satisfying any sudden heat
demand elsewhere.

2) Trying a calculated 'pulsed' on period that would estimate the heat
required and avoid overshoot. Never got far with this.

3) Using proportional (TRV's - with remote sensors as a lot of my rads
are encased) which I found achieves the best results as the system
settles into a stable state with each rad staying fairly constant in
temp. I currently use Danfoss proportionals with a remote sensor that
has a small heater element underneath it. These were a commercial
offering from Danfoss but are not manufactured anymore, You apply a
small current to this element and it offsets the TRV's operation
accordingly, at full voltage it turns off the radiator effectively.  I'm
hoping that those 0-10V proportionals might be able to replicate this.

Having said that the 0-10V proportionals are proving very difficult to
source (seems not available in the UK) and I do suspect that with fairly
light modern radiators the proportional may not be needed.

Kevin