Vicodens with zoned heating AND weather compensator?

[tstaddon]

Hi

Assuming we have an odd house with lots of different rooms of different sizes and ages (ranging from Victorian parlours and reception rooms with bay windows and fireplaces, to 21st century open plan) what's the right setup?

Looking to replace an underpowered WB 24i boiler and its single Alltech wireless thermostat with a Vicodens 111-W and weather comp. The house has 3 showers, one bath, and six occupants who're all at home almost all day every day thanks to COVID.

We need zoned heating because of the huge variation in room temperature - without the heating on we've currently got one reception room at 24 degrees (because the fire's on), another reception room is reading 8 degrees, two bedrooms are reading around 18 degrees and two others are more like 11 degrees. That's all by using the same thermostat, moving it from room to room.

Rough guess: R8810A1018 (OpenTherm kit) + https://theevohomeshop.co.uk/honeywell- ... -deal.html (not OpenTherm) might be the right combination to start with, but frankly I can't tell if we should be going with a non-OpenTherm setup and rely on firmware updates, or get the OpenTherm bits and bodge one of these: https://www.automatedhome.co.uk/tutoria ... ohome.html

It's all very confusing!

[tstaddon]

Bit more info...

Our existing heating controls work like Honeywell's single zone, but we can literally have one downstairs room five degrees hotter than another in summer, and the reverse problem in winter. If we move the thermostat from room to room downstairs, the temperature variance is so much that a single thermostat indoors is next to useless.

In this floor diagram, I've marked the downstairs radiators in blue. The family rooms are old Victorian rooms with bay windows, chimneys and multifuel stoves, each has one radiator. On a cold day with the fires lit these rooms don't need radiator heat at all, but the other rads need to be able to maintain the temperature evenly otherwise the reception room heat just escapes out through the kitchen and hallway/porch and fools the thermostat into thinking the rooms are warm when actually they're just getting a warm draught.

The connecting hall and stairway has two small radiators in the porch, which is glass - even with both radiators on, the hallway doesn't hold the heat so it is dependent on both reception rooms being warmer.
The downstairs bedroom and wet room are in the modern rear extension, with a radiator and a towel rail both on the heating circuit.
The pantry and kitchen is open plan with 3 radiators.

So I'm thinking BDR91 and a single zone for the upstairs circuit controlled entirely by the boiler and weather comp, and at least four rad zones downstairs controlled by OpenTherm - bedroom/wet room, kitchen/pantry, each reception room. There's no point having the hall rads on unless both the reception rooms are warmer than it is.

All I need is a sanity check - if I do this, will it work the way I think it will and if not, what else do I need to buy?

[Richard]

Some of the issues with Viessmann 100 on OpenTherm, are well documented in our own forum - viewtopic.php?f=5&t=477

I think some of the guys had a successful result after recoding the gateway to add a temperature limit for the boiler. You can obviously ask questions to the guys that were involved in the above link. But out the box, OpenTherm won't work properly on a 100 series.

[tstaddon]

Thanks - I've read those posts extensively both here and elsewhere and some of those posts might relate to an older edition of the 111-W.

Best I can tell there are three versions of 111-W in circulation. This is reflected in some of the parts - for example, when ordering weather comp you need to choose from two packs, one designed for B1LA or B1LB and the other designed for B1LD.

For now I've ordered the Honeywell Home evohome Essentials Pack (ATP926G3001) and the Wall Mounting Pack ATF600, I just need the installer to confirm what's going in on the boiler side of things. At the minute I am steering away from an OpenTherm setup as it looks like three extra parts are needed: ZK04327: Vitoconnect OT2 with Vitotrol 100 OT1, and the bridge (R8810A1018) and I'm struggling to see the benefit.

I saw a mention of firmware testing for weather comp inside the evohome - what does that mean in practice? Does that mean the weather comp can natively talk to evohome?

[Bart]

I did give weather compensation a try on my opentherm controlled viesmann, but it gave poor results for low CHW temperature requests and low heating demand due to the way that the boiler behaves in this situation.
What I did was limit the max chw temperature to a certain value, the opentherm controller would then scale its requests between 20 and my max value, let's say to 35 degrees. The boiler would start heating, turn off because the actual CHW value would rise way above 35, and then it would heat again for a long time, waiting for the temperature going significantly below 35. Like it has a hysteresis.
In the end I just fixed the max CHW to 60C and let the evohome controller do its thing.

I don't know if the behavior on your boiler would differ, but I suspect that Viesmann (as many other companies) will not re-write what they consider to be working software for each new boiler.

You can TPI with weather compensation, if you really want, it seemed to work ok on mine, but opentherm is considered the better solution (not sure if I blindly agree).