Boiler control using the Drayton Wiser and opentherm.

[chris_x]

Has anyone had success using the Drayton Wiser controller to communicate with a combi boiler through the opentherm protocol i.e. to modulate the boiler output? This will exclude Worcester Bosch who use ems and Vaillant.

 

The Viessmann 100-W is supposedly opentherm compatible but does it work in reality?

[SimonD]

Yes, Opentherm does work and I'm sure that the Drayton wiser system will work providing it's installed correctly

[billt]

I have a Viessman 100, allegedly Opentherm compatible and a Drayton Wiser also allegedly Opentherm compatible. They don't talk to each other.

 

Also tried an Opentherm to Arduino adapter which didn't talk to the boiler either.

 

I get the impression that Opentherm has lots of different dialects which don't necessarily communicate, a bit like Zigbee.

 

 

[MJNewton]

There have been quite a few variations of the 100-W over the years so probably worth being more specific when discussing them and referencing their model code (e.g. BK1F).

[Radian]

4 hours ago, chris_x said:

This will exclude Worcester Bosch who use ems and Vaillant.

 

FYI Vaillant is well covered by ebusd which is a linux daemon for handling communication with eBUS devices connected to the 2-wire bus system used by Vaillant/Glowworm. It can be set up to talk over MQTT and used for reading/writing pretty much everything.

[chris_x]

The Viessmann boiler I was looking at is the B1KF which is a combi. 

The problem I have found is getting real evidence that a Drayton Wiser will work using opentherm on different boilers. When you talk to the various manufacturers such as Viessmann, Baxi, Ideal and Intergas they all say that they are opentherm compatible but have not tested the Wiser controller on their boiler.

 

The only real data has come from an online supplier of boilers and controllers who say that Wiser does work with Intergas boilers using opentherm. The man has it running in his house.

 

Maybe the answer is to get the Viessmann 200-W which has a 1:17 modulation ratio and run it in weather compensation mode (it does not offer opentherm) and switch it on and off using 240V. The only problem is, will the rooms take much longer to warm up as the central heating water temp is determined by the weather comp curve and not the current room temp? I get the impression weather comp is more suited to 24/7 operation and not having rooms going on and off during the day using smart TRVs.

[JohnMo]

Most if not all Viessmann products are designed to run weather compensation via their own controllers, and can run two zones at different flow temps if required via a fully open system without thermostats or trvs.  So why mess with that?  By putting a third party thermostat that will give less control or worse efficiency.

 

Run as the Germans intended

[mk1_man]

I have installed a Wundasmart heating controller with my Viessmann 100-W and it works great using Opentherm.  It controls the water and underfloor heating and allows full modulation.  I have plumbed the boiler in a 4 pipe configuration, one circuit for cylinder and the other for heating.  Heating is set at 40 degrees and water at 60.  I am very impressed with the system.

[nashant]

@mk1_man does the wunda actually modulate the flow temp as the Delta T of the heating reduces? I've called them and they say that it doesn't. I'm really hoping that it does because the local API is super attractive

Edited April 5 by nashant

[SimonD]

5 hours ago, nashant said:

@mk1_man does the wunda actually modulate the flow temp as the Delta T of the heating reduces? I've called them and they say that it doesn't. I'm really hoping that it does because the local API is super attractive

 

https://support.wundasmart.com/en/question,64/open-therm

[marshian]

On 24/01/2023 at 14:53, JohnMo said:

Most if not all Viessmann products are designed to run weather compensation via their own controllers, and can run two zones at different flow temps if required via a fully open system without thermostats or trvs.  So why mess with that?  By putting a third party thermostat that will give less control or worse efficiency.

 

Run as the Germans intended

 

I know this an old post and I agree with the point made about using Viessmann controls I don't think there is a huge saving to be made.

 

I've fully invested in the Wiser system and since Sep 22 I've replaced all the rads and optimised the sizes to allow me to run much lower flow temps. The individual room temp settings and the scheduled heating times are now spot on for what I need. I don't have any UFH just rads and one heating zone.

 

However with a house heat loss of 4.5 kWh at -2 and a 24 kW glow worm boiler with a min output of 10 kW it's rather over sized for the house and I don't have weather compensation on the boiler so I currently manually set the flow temp for the weather conditions - I run anywhere between 42 Deg C and 58 Deg C flow temps but for HW requirements I have to manually increase the flow temp and turn off the CH whilst HW requirements are met.

 

Later this year I will replace the boiler with a Viessmann 100 W in DHWP mode, Allow the CH Temp controlled by a Viessmann Weather Compensation module and leave the Wiser system and all the smart TRV's in place. I'm pretty confident that this will work nicely provided I get the curve right.

 

If I find that it doesn't work as well as I expect I'll dump all the TRV's and run fully open system but I think my plan will work just fine.

 

I don't see that the Viessmann Controls for CH give me any advantage over the Wiser and I have no intention of trying to use the Wiser OT to control the boiler flow temps as I don't think it's as accurate as a WC temp sensor on my house wall.

 

[MrPotts]

6 hours ago, marshian said:

 

I know this an old post and I agree with the point made about using Viessmann controls I don't think there is a huge saving to be made.

 

I've fully invested in the Wiser system and since Sep 22 I've replaced all the rads and optimised the sizes to allow me to run much lower flow temps. The individual room temp settings and the scheduled heating times are now spot on for what I need. I don't have any UFH just rads and one heating zone.

 

However with a house heat loss of 4.5 kWh at -2 and a 24 kW glow worm boiler with a min output of 10 kW it's rather over sized for the house and I don't have weather compensation on the boiler so I currently manually set the flow temp for the weather conditions - I run anywhere between 42 Deg C and 58 Deg C flow temps but for HW requirements I have to manually increase the flow temp and turn off the CH whilst HW requirements are met.

 

Later this year I will replace the boiler with a Viessmann 100 W in DHWP mode, Allow the CH Temp controlled by a Viessmann Weather Compensation module and leave the Wiser system and all the smart TRV's in place. I'm pretty confident that this will work nicely provided I get the curve right.

 

If I find that it doesn't work as well as I expect I'll dump all the TRV's and run fully open system but I think my plan will work just fine.

 

I don't see that the Viessmann Controls for CH give me any advantage over the Wiser and I have no intention of trying to use the Wiser OT to control the boiler flow temps as I don't think it's as accurate as a WC temp sensor on my house wall.

 

Wiser user here as well. I like the Wiser hub and room thermostat but the Wiser smart TRV’s don’t work very well in my house. I just can’t see how running my gas boiler to service a single radiator can possible be good for boiler efficiency and hence gas usage. I started out with smart TRV’s on all my radiators but am now down to just 3 and they are all controlled by a single room thermostat. The rest of the radiators have manual TRV’s.

[JohnMo]

19 minutes ago, MrPotts said:

. I just can’t see how running my gas boiler to service a single radiator can possible be good for boiler efficiency and hence gas usage. I started out with smart TRV’s on all my radiators but am now down to just 3 and they are all controlled by a single room thermostat. The rest of the radiators have manual TRV’s.

@Post and beam should read this.

[nashant]

On 05/04/2024 at 11:54, SimonD said:

 

https://support.wundasmart.com/en/question,64/open-therm

Thank you! I cannot understand why they would tell me that it doesn't. I'm wondering whether the technical person I spoke to was actually just a receptionist who overheard some tech support talking one day

[marshian]

5 hours ago, MrPotts said:

Wiser user here as well. I like the Wiser hub and room thermostat but the Wiser smart TRV’s don’t work very well in my house. I just can’t see how running my gas boiler to service a single radiator can possible be good for boiler efficiency and hence gas usage. I started out with smart TRV’s on all my radiators but am now down to just 3 and they are all controlled by a single room thermostat. The rest of the radiators have manual TRV’s.

Whats the difference between a smart TRV and a manual one - they do the same thing

 

Always happy to learn something new

[JohnMo]

8 hours ago, marshian said:

Whats the difference between a smart TRV and a manual one - they do the same thing

 

Always happy to learn something new

A smart TRV is just internet connected, a marketing ploy to make things sound better than they really are.

[marshian]

7 minutes ago, JohnMo said:

A smart TRV is just internet connected, a marketing ploy to make things sound better than they really are.

 

I know that - the question was directed to MrPotts as he's reverted to manual TRV's having had smart ones

 

From my perspective a smart TRV does have a one advantage over a manual TRV - If a member of the household (I'm looking at Mrs Marshian here) turns it up because she thinks the room will warm up faster...... after 1 hr it reverts to it's previous set point (a Manual TRV stays there till I realise a. the room is too hot or b. I've burnt a lot more gas than normal)

 

 

[MrPotts]

12 hours ago, marshian said:

Whats the difference between a smart TRV and a manual one - they do the same thing

 

Always happy to learn something new

The Wiser smart trv can request the boiler to fire whereas a manual trv can’t.

 

i found that having individual radiators firing the boiler was very inefficient, I prefer to control the heating for the house as a whole rather than on a room by room basis.

Edited April 7 by MrPotts

[marshian]

6 minutes ago, MrPotts said:

The Wiser smart trv can request the boiler to fire whereas a manual trv can’t.

 

i found that having individual radiators firing the boiler was very inefficient, I prefer to control the heating for the house as a whole rather than on a room by room basis.

 

Ahhhh now that makes perfect sense - it did that once so I've set up my wiser so the "base" temp is only 7.5 deg. Unless a room reaches that temp when it's not scheduled for heating it won't fire the boiler and it's only the front entrance hall that's ever likely to hit that temp so for that TRV it's set to "off"

[MrPotts]

16 minutes ago, marshian said:

 

Ahhhh now that makes perfect sense - it did that once so I've set up my wiser so the "base" temp is only 7.5 deg. Unless a room reaches that temp when it's not scheduled for heating it won't fire the boiler and it's only the front entrance hall that's ever likely to hit that temp so for that TRV it's set to "off"

I found that when heating setpoints were set to say 20c if any single radiator trv detected even a slight decrease from setpoint the boiler would fire and keep firing when any of the 11 TRV’s requested it. This is not an efficient way to heat a home IMO.

[billt]

14 hours ago, marshian said:

Whats the difference between a smart TRV and a manual one - they do the same thing

 

Always happy to learn something new

 

You can change the room temperature from outside the room.

You can set an actual temperature, rather than a vague number.

You get a reading of the actual room temperature (and humidity).

You can link multiple radiators in one room together.

When used in a suitable setup system the boiler will fire when any room is demanding heat, not just the room where the thermostat is situated.

 

Of course, if you have a near passivhaus where all the rooms are the same temperature and that temperature doesn't change much it's moot.

 

My Drayton Wiser system is now retired as the Wiser system isn't suited to heat pump control. Reverted to the old fashioned system of setting and balancing emitters to match each rooms heat loss with one temperature sensor in the living room. It works OK but has to run 24/7.

[JohnMo]

1 hour ago, billt said:

suitable setup system the boiler will fire when any room is demanding heat,

Is that really a good thing, short cycling comes to mind.

[MrPotts]

10 minutes ago, JohnMo said:

Is that really a good thing, short cycling comes to mind.

It seems wasteful when my boiler only modulates down to 7kw and my house heating requirement is 8kw. Think of the amount of boiler cycling for one 500w radiator!

[MrPotts]

1 hour ago, billt said:

 

You can change the room temperature from outside the room.

You can set an actual temperature, rather than a vague number.

You get a reading of the actual room temperature (and humidity).

You can link multiple radiators in one room together.

When used in a suitable setup system the boiler will fire when any room is demanding heat, not just the room where the thermostat is situated.

 

Of course, if you have a near passivhaus where all the rooms are the same temperature and that temperature doesn't change much it's moot.

 

My Drayton Wiser system is now retired as the Wiser system isn't suited to heat pump control. Reverted to the old fashioned system of setting and balancing emitters to match each rooms heat loss with one temperature sensor in the living room. It works OK but has to run 24/7.

The manufacturers extol the virtues of being able to micro control heating on a room by room basis, and be able to change temps via an app remotely but is that really necessary? I don’t think it is.

 

THe other issue I was having is with the inaccuracy of the radiator TRV’s, they read too low when heating is off and too high when it’s on. This causes the boiler to fire up unnecessarily or to turn off prematurely.

 

Wiser TRV’s don’t nt read humidity but being so close to the heat source it wouldn’t be accurate anyway.

Edited April 7 by MrPotts

[billt]

1 hour ago, JohnMo said:

Is that really a good thing, short cycling comes to mind.

That rather depends on the nature of the building. In my case there were few occasions when only one room would call for heat, so short cycling wasn't particularly an issue.

I was merely pointing out the reasons for having "smart" TRVs, not recommending them.