[OpenTRV-interest] Question from Steve R

Marko Cosic marko at coheat.co.uk
Sun Nov 22 12:58:32 GMT 2015

On 22 November 2015 at 11:20, Simon Hobson <linux at thehobsons.co.uk> wrote:

> Mark Wigmore <mawigmore at gmail.com> wrote:

> My goal would be (eventually) to have feedback from each TRV as to it's
> valve position, and regulate the flow temp accordingly. That way, under
> light heating load, the flow can stay up a bit but at low temperature -
> avoiding the "rad cold but for a small (very) hot spot at one end" effect.
> Or depending on the setup, avoiding the noisy system pumping water round
> through the bypass because the stupid boiler design* can't cope with normal
> heating loads.

You have feedback from TRVs already: hydraulic resistance. Fit a modulating
pump and it'll sense differential pressure and can respond as you wish it

Weather compensation addresses your high flow temperature/low return
temperature/bouncing around on the bypass issue.

* Which is universally the case unless someone can tell me otherwise. I've
> never found a boiler designed for other than a  flow rate that gives around
> 20˚C delta-T.

A 20C dT (as opposed to the 11C dT that most Uk designers still use) is a
very good compromise between flow rates, radiator mean water temperatures,
and flow/return temperatures.

11C dT means you can't get very high mean water temperatures without
dropping out of condensing mode.

30C dT is too low a flow rate usually and ends up sludging things up and is
tricky to control with a TRV.

A boiler with weather compensation of flow temperature, anti-cycling
controls, and no bypass (or thermal store - use the rads) works very well
indeed at 20C dT.

What is the purpose of the thermal store in your application?

Marko Cosic
Technical Director

+44 7774 524 114


COHEAT Ltd is a company registered in England and Wales. Registered number:
Registered office: Future Business Centre (RS10), Kings Hedges Road,
Cambridge CB4 2HY
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