[OpenTRV-interest] getting hands on some valves

Simon Hobson linux at thehobsons.co.uk
Mon Nov 28 11:03:15 GMT 2016

Kairos <kairosmedia at swissmail.org> wrote:

> -- Susceptibility to sticking - they age, things get less smooth, depending on the valve construction this may be an issue
> -- Longevity of seals....


> -- Susceptibility to scaling and flow reduction


> -- Resilience to customer abuse (over-tightening of compression joints etc).

All these are down to the valve body you use. OpenTRV only does the actuator head - the idea being that you unscrew the existing head off your valves and pop this in it's place. No plumber (or DIY skills) needed, no draindown - and if you move on, easy to reverse.

This latter feature is particularly useful for those in rented accommodation where the heating often has "poor controls". Speaking as a landlord, there's little financial incentive to spend money past "it works reliably" as it realistically doesn't make any difference to the rent you'll get. Looking at some of the properties relatives have been living it, it's clear that "not all landlords are equal" in details like this - I like to think I'm on the better end of the scale.

If you are fitting new valve, you just buy a basic TRV from the local plumbers merchant and leave the head in it's box. Seems a bit wasteful, and I guess if OpenTRV does manage to take off, they'll come up with a source of "bare" valve bodies. I know in the past (different hat, different job) I've been able to buy valve bodies and actuators separately - but this was in a commercial/industrial environment where you are picking from a selection of different valve bodies (2/3/4 port) and actuators (2 wire thermal hydraulic (wax)/3 wire motor/0-10V proportional) according to needs.

As an aside, we had to get some controllers modified (add a dwell time) because of overshoot. The actuator heads we were using could take as long as 2 minutes to start opening when starting from cold. When "heat soaked" after a period of being full open, they could take up to 5 minutes to close. The impact on control loops of such lags is "interesting" 8-O
These were thermo-hydraulic actuator heads - similar to the wax capsule heads on normal TRVs, but with a small electric heater. Apply power, wax heats up, valve opens; turn off power, wax cools down, valve closes. In between, they could actually modulate if you turns the supply on/off over a fairly short cycle.

> -- Ergonomics - some TRVs look down right ugly and needlessly bulky!

I get the impression that these are "fairly large", but it's really hard to get the scale from a picture on a website.

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