Honeywell evohome and OpenTherm integration

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Honeywell evohome is unique in the market in offering multizone control of radiator, zone valves and underfloor heating manifold applications
This application capability meets the definitions of ErP Class VIII for multizoning of modulating heaters
The OpenTherm Bridge R8810A1018 enables full modulation control of OpenTherm appliances


Starting a new thread to capture your feedback and to enable any specific cases to be followed up with official Honeywell Tech Support teams as appropriate

If you have any application related questions pre sale or post sale post them here so we can answer on a case by case basis and collate the answers for others to benefit from

[HenGus]

Thanks TB. As suggested by @Rameses, I have raised a case (15186093) via your Technical Support site. My concern - based on just three weeks of heating in April - was the time taken for Evohome/OT to get the boiler into condensing mode. There were only a few zones on and most were at, or close to, their target temperatures, yet the boiler was still showing a flow return temperature of 65+C for a considerable amount of time before starting to fall back. The boiler, an Atag IS24, is set to HW priority and HW was OFF when CH was being demanded. I thought that the idea of OT was to modulate the gas valve to a minimum consistent with keeping set zone temperatures?

[paulockenden]

Can the Honeywell guys confirm whether or not, with OpenTherm, the system still only starts to ramp down demands when all zones are within 1.5 degrees of their setpoint?

Or does OpenTherm make the proportional band a bit wider, which would seem sensible?

P.

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Thanks TB. As suggested by @Rameses, I have raised a case (15186093) via your Technical Support site. My concern - based on just three weeks of heating in April - was the time taken for Evohome/OT to get the boiler into condensing mode. There were only a few zones on and most were at, or close to, their target temperatures, yet the boiler was still showing a flow return temperature of 65+C for a considerable amount of time before starting to fall back. The boiler, an Atag IS24, is set to HW priority and HW was OFF when CH was being demanded. I thought that the idea of OT was to modulate the gas valve to a minimum consistent with keeping set zone temperatures?

Thanks will look into the case and revert

[top brake]

Can the Honeywell guys confirm whether or not, with OpenTherm, the system still only starts to ramp down demands when all zones are within 1.5 degrees of their setpoint?

Or does OpenTherm make the proportional band a bit wider, which would seem sensible?

P.

The control logic is at the evohome controller and either controls the boiler output using the TPI cycle rate/run time or the required flow temp through OT.
This the aggregated demand of all zones.

In either case outside the Proportional Band the boiler demand will be at full rate.

In the case of multizoning the individual HR92 or zone valves or thermal actuators will control the local zone temperatures.

HTH

[paulockenden]

I don't think that really answers the question of whether the proportional band remains at 1.5 degrees when under OpenTherm control, or widens a bit to allow the boiler to modulate down.

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proportional band width is non adjustable and optimised for the application, heating systems are slow reacting so a 1.5 degree control band is fine
The mass flow to the respective zones is modulated locally

The heat demand is aggregated and throttled accordingly

The self learning fuzzy logic control algorithm is the same whether switching a BDR or modulating flow temperatures through OT

It is the steady state control performance and low load operation that is key to achieving maximum condensing effficiency. If the hydronic system is imbalanced or the boiler oversized it will be difficult to achieve thermal equilibrium and sufficient delta T to ensure return temperatures are below 55degC

With a correctly specified and commissioned modulation control system you should see flow temperatures around 45 to 50 degC. My evohome with Vaillant ecotec system at home achieves this easily.

[StephenC]

Several questions from me:

1. Why does EvoHome not (at present) have a max CH water temp config setting when connected to the R8810 OT bridge?

2. Will point 1 above capability ever be added? I can't add R8810 OT bridge back into my system until this is resolved.

3. From my experience, EvoHome asks for max ch temp or very very low (25-30 degrees C), I very rarely saw anything in the middle.This is like a cliff edge, so why when within 1.5 degrees C does it not ramp down the temperature gradually to avoid the possibility of overshoots and allow for the HR92 time for finer control?

4. Data. When will we be able to see the data (somehow, somewhere - in the app maybe?) showing what the system is doing and when? It's very difficult to troubleshoot blind.

For history of my issues with a Viessmann Vitodens 111-W boiler that when EvoHome asks for full rate - that means upwards of 80+ degrees C.....right up to the set point and then ramps down too late, see here:

http://www.automatedhome.co.uk/vbull...1-W-overshoots

Thanks.

Stephen

[top brake]

Several questions from me:

1. Why does EvoHome not (at present) have a max CH water temp config setting when connected to the R8810 OT bridge?

2. Will point 1 above capability ever be added? I can't add R8810 OT bridge back into my system until this is resolved.

3. From my experience, EvoHome asks for max ch temp or very very low (25-30 degrees C), I very rarely saw anything in the middle.This is like a cliff edge, so why when within 1.5 degrees C does it not ramp down the temperature gradually to avoid the possibility of overshoots and allow for the HR92 time for finer control?

4. Data. When will we be able to see the data (somehow, somewhere - in the app maybe?) showing what the system is doing and when? It's very difficult to troubleshoot blind.

For history of my issues with a Viessmann Vitodens 111-W boiler that when EvoHome asks for full rate - that means upwards of 80+ degrees C.....right up to the set point and then ramps down too late, see here:

http://www.automatedhome.co.uk/vbull...1-W-overshoots

Thanks.

Stephen

Hi Stephen

1 - this is not a requirement of the OpenTherm protocol specification
2 - no plans
3 - see 5 below
4 - yes there is a third party OT monitor that alllows this monitoring
5 - the history of your case is long and complex and i recall you having on site support and support from theevohomeshop?

[StephenC]

Hi,

Thanks for the confirmation of point 2.

I shall look at alternatives to OpenTherm (at reducing gas usage and therefore on-going cost saving and emissions savings) at this point now I know.

Re: theevohomeshop - no I worked with my local installer (and seem to be teaching him on this...). No on site support from HoneyWell, but I did have support over the phone from one of your colleagues and they setup data logging etc.


Stephen