Viessmann boiler with weather compensator.

[Tristar]

Having trawled through the advice offered, I am replacing a faulty boiler with a Viessmann 26KW Vitodens 200-W system boiler, and including a weather compensator from day one in anticipation of yet further gas price rises.

I am somewhat puzzled as to the way it is to be installed, according to Viessmann technical department, with no room thermostat fitted, this being taken care of by the boiler itself.

We currently have a timed room thermostat in the lounge which suits us, as evening use/temperature is thus easily controlled. I would prefer the heating demand to be still controlled by the temperature in the lounge, and I assume, with the Viessmann setup, that this will have to be taken care of by TRV's.

If anyone has any experience of the proposed setup who can advise or comment on its performance, I would be grateful.

 

[simond]

You can fit a Viessmann WC controller remotely, your installer should know about this and advise you accordingly.

 

[Tristar]

You can fit a Viessmann WC controller remotely, your installer should know about this and advise you accordingly.

Thanks Simon, I was aware of the external remote WC installation, I am just interested as to how the set-up works without a roomstat, as this would seem to be a step backwards technologically, similar to systems fitted 30 years ago with boiler thermostats and no roomstat. I appreciate that, with WC, this system will also be dependent on the OAT, but why not take the internal temp from a room in use rather than a boiler room?

 

[simond]

Heat loss across the boiler flow and returns has to occur in the house from the emitters.

Therefore you can deduce the room temperature from the heat loss and the outside temperature.

By trimming the curve you can prevent overheating in a uniformly insulated house. WC is not going to work properly in a house which has been extended over different periods.

My point was that a remote WC station will take into account room temperature if this is what you desire. Your Viessmann installer should be telling you this stuff. I haven't been on a course there for 5 years but this is pretty basic.

 

[Norcon]

Simond wrote

WC is not going to work properly in a house which has been extended over different periods.

Why not ?.
You can set the curve for the older uninsulated part of the building with trv,s trimming the temperature in the newer part.
The amount of throttling required by the trv's is now reduced and overall control improved.

My point was that a remote WC station will take into account room temperature if this is what you desire

Can the compensator controller be removed from the Vitodens 200-W and if so , why would anyone want a bulky WC station sited in their home in order to capture the space temperature ?.
Is the compensator controller for the Vitodens 200-W compatible with a space sensor and if so what type is used ?.

Viessmann wrote

According to the Energy Savings Order [Germany], the temperature in each room must be individually controlled, e.g. through
thermostatic radiator valves.

 

[Tristar]

Thanks,

spooky that you knew the house had been extended, the lounge is in the oldest part, and due to thermal building requirements in the 70's, and therefore less well insulated blockwork, is usually the coldest part of the house. The whole property has cavity wall insulation, the lounge has argon filled DG, the loft has 15" of insulation.

If I read the comments correctly, the TRV's take care of localised room temps.

 

[Tristar]

By trimming the curve you can prevent overheating in a uniformly insulated house. WC is not going to work properly in a house which has been extended over different periods.

Simon, I have recently added a conservatory with two 2K radiators, so from what you say above, a WC setup is not going to cope too well with that and the other new(ish) extension, I can only hope that we can trim it all in the old fashioned way through TRV's.

I am wondering whether to skip the WC.

 

[Tristar]

Heat loss across the boiler flow and returns has to occur in the house from the emitters. Therefore you can deduce the room temperature from the heat loss and the outside temperature.

This assessment of temperature must based on the overall average house
(emitters) temperature. This is fine if your house is 100% insulated as in Scandinavia, but our building standards lag way behind theirs, and therefore I would prefer the system to identify the temperature in a more localised area by use of a roomstat, otherwise I will be running around adjusting TRV's for different times of the day. On that issue, I have still been unable to identify a suitable digital timer TRV to replace manual ones.

 

[simond]

Honeywell Hometronic.

Not cheap but state of the art in heating. Can be linked to a Viessmann WC system if you require.

 

[Tristar]

Honeywell Hometronic.

Not cheap but state of the art in heating. Can be linked to a Viessmann WC system if you require.

Thanks, yes I have seen that system, but it seems very pricey. I would prefer individual battery controlled digital TRV's. I believe they are available in Germany.

 

[simond]

I would be interested to see the ones you prefer, can you post a link?

Bear in mind they can't turn the boiler on, or off, like Hometronic does. Which is rather key to having a programmable radiator.

PS: Hometronic was a Honeywell Germany launched product.

 

[Tristar]

I would be interested to see the ones you prefer, can you post a link?

I can't remember where I saw them discussed, may have been in this forum. I'll have a look tomorrow.

 

[Tristar]

Bear in mind they can't turn the boiler on, or off, like Hometronic does. Which is rather key to having a programmable radiator.

However the setup that I (may) get with WC/Viessmann will be exactly like that. i.e. No roomstat, room temps controlled by TRV's, and the boiler will not know that the TRV is turned off by a digital timer or a rise in room temp.

 

[Agile]

However the setup that I (may) get with WC/Viessmann will be exactly like that. i.e. No roomstat, room temps controlled by TRV's, and the boiler will not know that the TRV is turned off by a digital timer or a rise in room temp.

But the boiler might be able to work that out if the return is about the same as the flow !

It could turn off and then try again a few minutes later to see if the situation has changed!

Tony

 

[namsag]

Oh be honest FFS its not worth the hassle just stick a normal control system in. Far easier to use and understand so will save you money instead of complicated sh#te you wont be able to set up