Tado OpenTherm S plan

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Tado OpenTherm S plan

Post by navdra » Wed May 16, 2018 5:05 am

Hi there,

I stumbled upon this forum while trying to find some info on wiring up my future Tado system.
My intended setup is based on boiler Viessmann Vitodens 100-W B1HA. I'm also installing Viessmann Vitocell 100-W (120 L) DHW tank.

I intend to organize and control two central heating zones wired in S plan and hot water preparation
System schematics
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Tado setup would consist of Extension Box (for HW control), Internet Bridge, 2x Smart Thermostat

Zone S: Living room, kitchen and hallway (openspace with three radiators) + three bedrooms (another three radiators). Smart Thermostat T(s) positioned in living room should control zone valve 2P(s). I may add TRV to bedrooms later on for complete control.

Zone K: Two bathrooms. Mixed underfloor heating and one radiator in each bathroom. Smart Thermostat T(k) positioned in one of the bathrooms should control zone valve 2P(k).
This setup should allow me to fine tune bathroom UFH control to enjoy warm floor in bathrooms independently and keep bathrooms at controlled higher temperature than rest of the apartment.

I want to utilize Tado and Viessmann OpenTherm capabilities to fine tune heating temperature, comfort and energy efficiency.

I'm stuck with wiring.... I have prepared generic concept based on standard S plan system wiring
Standard S Plan wiring
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I'm not sure what to do with low voltage OpenTherm connections and 220V wiring that obviously needs to go from each thermostat to corresponding zone valve? I guess each thermostat needs to be wired. Am I supposed to connect each Smart Thermostat to Extension Box?
Will I be able to separately control hot water demand?
Should I use Switched Live or Potential Free Extension Box interface?
Please try to help me out with this. It seems like good idea to me, but I'm not sure how to finalize it and have limited trust in local heating installers - I'd prefer to figure everything out before placing Tado order and organize intended S plan setup.

Beside intended scheme and generic S plan wiring I'm attaching technical documentation needed for wiring everything up:
Vitodens 100-W Installation and Service
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(see p.37)
Tado Manual & Technical Documentation v1.1
(1.04 MiB) Downloaded 84 times
(see p.8 and p.11)
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Re: Tado OpenTherm S plan

Post by ericmark » Thu May 31, 2018 6:30 am

I have read instructions and looked on web site and I also can't see the products required to make it work. For any system to work using OpenTherm you need something to tell the hub when and how much heat is required. The electronic thermostatic radiator valves and room thermostats will clearly tell the system when and how much heat is required by the rooms to heat them.

However I can't find any device that fits to the cistern to tell the system when hot water is required. I would have expected to find at least two thermostats on the cistern one to say there is hot water over 60 degs C at top, and one to say when there is enough hot water to fill a bath, it would depend on plumbing the Willis system heats from top of cistern so can either heat a section or all of cistern, but more basic systems have less control.

Using non Opentherm simple enough, but as far as I can tell reading the instructions there is no sensor for hot water which measures temperature, all that can be done is use a standard thermostat which simply switches on/off at a pre-set temperature.

I suspect it only uses OpenTherm with combi-boilers? I expect it does not have an option to adjust heat levels with use of cistern? the problem is with a combi very little water is kept hot, so chance of legionnaires is low, but with a cistern you need to ensure temperature is over 60 degs C for safety.

I am just an electrician, I did look at Tado and EvoHome and Nest for use in my mothers house, however it turned out the boiler did not support OpenTherm so I just fitted the electronic thermostatic radiator valves down stairs only. I did get it to work, however as far as geo-fencing goes it was a flop.

The major problem was reaction time, in my own house with Myson radiators from boiler switching on to house getting heat is minutes, so half an hour after boiler goes on, house is getting warm, however with mothers house the radiators hold that much water it was taking half an hour just to warm radiators never mind pump that heat into the house. So in real terms there is an hour or more lead in time required before the house gets warm, so unless you work over an hours travelling time from home geofencing does not work. It needs you to either use a fixed time, or manually switch it on before you set off for home.

Although the new Myson has three or more speeds to vary output and heat home quickly, the problem is Tado, EvoHome, and Nest will not work with the Myson radiators, it needs a far more expensive system, building management its called, and it can control both heating and cooling with Myson radiators. However although good idea for a hotel or hospital far too expensive for domestic.

So although Myson will work well with simple times set, with fast heat and cool, the geofencing is far too expensive.

So in real terms geofencing is a pipe dream, theory may be good, but in practice it fails, and in real terms you don't need to alter the temperature of each room remotely anyway, all you need is simple on/off and I realised in real terms I did not need to control each room from PC, once times and temperatures were set that was it, I would turn whole system off and on, but never changed settings on each radiator valve. So why pay for expensive wifi valves, electronic yes, but no need for wifi, so £25 per valve not £80 per valve. Also if house rented then you don't really want to provide internet and hubs as part of rental price, so I ended up ripping it all out again.

I am looking at adding a thermostat to my old Myson so it runs at two different speeds one to maintain temperature and one as boost when very cold, making it more like the new design, but since boiler in my house not modulating in hind sight the Myson is not ideal, with old boilers you want heat retained in radiators.

This is of course the problem, in the UK we try to mix and match, and it does not really work, with a hot air central heating system as used in USA the simple cheap Hive works well, one single thermostat for whole house. But our water system unless using fan assisted radiators is not suited for variable temperatures through the day.
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