[OpenTRV-interest] getting hands on some valves

Simon Hobson linux at thehobsons.co.uk
Sun Nov 27 20:20:39 GMT 2016

Jason Pearce <jason at pearce.org.uk> wrote:

> I would need 7 (unless you no longer need a central thermostat with this solution, in which I would need 8)

You want 8 then.

The basic idea is that a single thermostat is actually very poor at controlling the system. Using these, you have individual control for each room - each head determines if the room it is in is occupied - and controls that radiator accordingly. The control is to the set temperature when occupied, and to 18˚C when not - 18˚C is generally considered a suitable temperature for sleeping in and avoiding condensation in empty rooms.

For the boiler, there's a relay unit. Each TRV head transmits information on what it's doing, and the relay unit will switch on when any paired TRV is telling it it needs heat. Thus you get the effect of having a thermostat and zoneing for each room - with night/unoccupied setback.
Without the relay unit, you'd have to leave the boiler running just about full time - and it would just fire up when the water circulating round the pipes & bypass valve cools off, either because there's a rad using heat, or just heat loss in the pipes.

For us techies, we can hook up a receiver to a computer and log data. There's an example graph somewhere on the OpenTRV site showing what's available. IIRC it includes setpoint (ie the user setting), occupancy, current setpoint, actual room temp, valve position.
This can also be used for supporting vulnerable people - perhaps elderly relatives or tenants by sending the data up to a server so you can keep an eye on things - this is one of the use cases for social housing use of the system you'll find on their site.

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