[OpenTRV-dev] Using TELE-temperature to add on radio-TRVs

[Damon Hart-Davis]

Hello!

On 20 Mar 2013, at 12:22, Thomas Hood wrote:

> Hi. First let me briefly introduce myself. I am an electrical engineer living in the Netherlands. I am trying to reduce my energy consumption and I think that the next best thing for me to do is to add time-programmable TRVs to my radiators. There are systems on the market that allow ("radio-")TRVs to be programmed wirelessly and to be controlled by wall-mounted sensors — OK — and even a few (Honeywell Evohome; Danfoss Living Connect; RWE Smarthome are the ones I have found so far) that can control the boiler as well as the radio-TRVs so that if a room needs heat when the living room doesn't, the boiler will be switched on. But these systems are all expensive, imperfect and closed, so I am interested in the OpenTRV project which could provide a better, open, alternative.

I'm on a client site today so cannot respond in detail,.

Note that that minimum requirement was modelled on my own house and shouldn't be construed as cast in stone for all OpenTRV installs!  I needed a concrete goal to work towards.

> OK, now for my first thought. On the OpenTRV website the initial list of minimum requirements includes the following.
> 
> > The boiler end end, ideally, should be a two-wire volt-free
> > 240V switch that can be paralleled with an existing room
> > thermostat to control an existing non-modulating combi,
> > and that will call for heat when any of our TRVs do.
> 
> I have a Honeywell Chronotherm Modulation T8851M1000. This thermostat has a "TELE-temperature" feature such that when two terminals on the thermostat are connected, the target temperature changes to a defined static value. With such a thermostat the radio-TRVs could perhaps be added to the system in the following way.
> 
> 0. Assume the living room thermostat is set to 20°C.
> 1. Add radio-TRVs to radiators except the one in the living room.
> 2. On the radiator in the living room put a dumb (non-radio-controlled) TRV set to 21°C.
> 3. Set up the system so that if any radio-TRV calls for heat, the thermostat is put in TELE-temperature mode.
> 4. Set the TELE-temperature to 22°C.
> 
> When the radio-TRVs are not used or need no heat, the thermostat will keep the living room at 20°C.
> 
> When a radio-TRV calls for heat the thermostat switches on the boiler to try to get the temperature up to 22°C. The living room dumb-TRV keeps the temperature from exceeding 21°C. Once other rooms have heated up sufficiently, the radio-TRVs withdraw the call for heat and the living room thermostat is taken out of TELE-temperature mode.
> 
> Advantage: radio-TRVs can be added on to an OpenTherm system without an OpenTherm bridge.
> 
> Danger: If the dumb TRV is set too low then the living room thermostat will keep the boiler on with all radiator valves closed.

My understand is that my local building regulations, ie for England, (a) require the boiler to have an automatic bypass if necessary so that this situation cannot do any damage and (b) forbid the use of a TRV in a room with the "house" thermostat to prevent those two stats "fighting" in the way that you allude.

Rgds

Damon