Smart thermostar: 2 x Zones and HW and Opentherm.

[GoodDIYjob]

Hello and good evening.

I’m trying to help out a friend, part way through some house extension work.

Their CH system has been altered from a y plan with a unvented cylinder and radiators to an s plan with 3 no. zone valves 1. Rads, 2. CH, 3. HW Cylinder and is operational on the old timer controls and stat.

He wants to update the old thermostat and timer control. OK so far so good.

1. He wanted to use nest. Which would require 2 x thermostats, incl 2 heatlinks. I said I think it will work, with relay switching through the zone valves BUT not with Opentherm to give modulation of flow temperature as both relays would have an opentherm connection and there would need to be something that determines priority and one comms stream to boiler. Am I right or are the thermostats able to determine priority amongst themselves and only send the same set of opentherm comms from either relay?


2. How much could wireless comms be a problem? There is lots of steel work as well as steel undertrays, and foil insulation in ceilings now. The boiler and zone vlaves are on the 2nd floor in a cupboard in the converted loft straight line maybe 12M but a lot of obstruction in between. He had thought the nest would allow hard wiring but I said I don’t believe so in Euro versions, it is only the DC power to the nest that can be wired.

So, assuming the nest will not allow open therm modulation in a 2 zone setup and HW:

3. Is there any smart thermostats, that allow either wired comms to the boiler / at least 2 x zone valves and hot water or a mixture of wireless and wired smart stats for 2 zones, and will allow opentherm to operate across the 2 zones and HW?

I didn’t imagine it would be terribly hard with all the tech out there. 2 Zones and Hotwater doesn’t seem like cutting edge does it? Most of the wiring diagrams for all the major start stats show y plan or s plan or opentherm. Not in combination....

Thanks for any guidance.

 

[ericmark]

Not sure about 2 zones, mine has 4 zones, or TRV heads which are clearly motorised valves. I don't have an opentherm boiler so don't know how that would work, however my wall thermostat is connected to the heat link with the 12 volt DC option and it reports as being hard wired so I assume the data is sent down the pair as well as the 12 volt DC supply!

I can't really work out why central heating is split into zones using an on/off valve. OK I can see one point, my TRV heads have a minimum setting of 12°C rather than completely off. But other than that if going analogue then go analogue, can't really mix digital and analogue.

I am not impressed with the way Nest and Energenie interconnect, I have used the follow command and at moment I have 4 TRV heads with target of 19°C and the Nest wall thermostat is set to 18°C this should not happen, but it has, the TRV heads should have been at 18°C target.

To my mind the link between Nest and Energenie is the wrong way around, the TRV head should tell the wall thermostat to what heat is required which in turn tells the boiler what is required, not the other way around.

I did not like Hive, however although it does not have opentherm I can see the simple beauty in its design, it allows the boilers own modulation software to control boiler output, and the TRV head sends a signal to wall thermostat to switch on for ½ hour if the target is above current, so simple yet so effective.

There are some thermostats that use a pulse width modulation control, seems that's another way to use digital control to simulate an analogue control, I do question how this will work with all boilers however I suppose one could hold a motorised valve in a part open position, but I would not expect the micro switches to last long.

I think I would look at EvoHome with the opentherm add on, or Tado in spite of having Nest myself, I am not a great fan of the system. Yes it uses internet to work out what the weather is going to do and works out in off/on mode how long of a burn is required. However back the basics the TRV head controls each room, the wall thermostat is more of a hub than a thermostat collecting the information.