Multiple Evohome controllers

[dty]

I’m going to have to add a second EvoHome controller to my house. Does anyone have any experience of operating with two controllers? I’m particularly interested to hear from anyone with multiple controllers AND OpenTherm.

Thanks!

[DBMandrake]

I’m going to have to add a second EvoHome controller to my house. Does anyone have any experience of operating with two controllers? I’m particularly interested to hear from anyone with multiple controllers AND OpenTherm.

Is binding two controllers to a single opentherm bridge even supported ? If so would it just use the higher heat demand of the two demands being sent to it at any given time ?

Presumably only one controller would be configured to control hot water ? Questions, questions...

[dty]

Is binding two controllers to a single opentherm bridge even supported ? If so would it just use the higher heat demand of the two demands being sent to it at any given time ?

I'm reliably informed that it will. No idea how it aggregates the demands. I'd still like to hear from someone who's done it.

Presumably only one controller would be configured to control hot water ? Questions, questions...

Correct. Why would you need two controllers both monitoring the hot water? The hot water is essentially just another type of zone - albeit with slightly different operating parameters.

[DanD]

Hi dty,

It certainly looks like the R8810A Opentherm bridge supports the binding of multiple controllers based upon its installation guide, but unfortunately I can't locate any reference documentation which describes these specifications ie. maximum number of devices unlike the BDR91 which does provide these specifications. The R8810A is also compatible with other Honeywell thermostats e.g. CM727 & DT92E so its plausible that it combines heat demand requests from multiple devices in a similar way to the BDR91. I don't have the R8810A though so can't test it out, but if you have one of the DT92E room thermostats you could try testing out binding it directly to the R8810A as an additional heat demand device (in exactly the same way as your second Evohome controller would be). This might be a quick way of testing the functionality before you invest in another Evohome controller, though it'll obviously be a bit of a pain clearing the bindings on each device and reinstating your previous configuration after testing.

PS are you absolutely certain that you need a second controller? My Evohome set-up has 16 radiators spread across 14 rooms and I find the multi-room zone feature works OK to combine rooms where you are happy to share the same schedule, but allows different heat demands from each radiator.

Regards,

Dan

[GreenGuy]

This may help which says A maximum of four evohome controllers can be bound to one R8810A OpenTherm Bridge. https://ensupport.getconnected.honey...language=en_US

[DanD]

Excellent! Thanks for highlighting that piece of information, it was exactly what I was trying to track down.

[paulockenden]

Shame it doesn't expand on the behaviour when there's multiple inputs. I'm guessing it would be sum, max, avg, or some weighted combination of these.

P.

[DBMandrake]

Shame it doesn't expand on the behaviour when there's multiple inputs. I'm guessing it would be sum, max, avg, or some weighted combination of these.

Almost certainly just max like the heat aggregation in the evotouch itself.

[dty]

PS are you absolutely certain that you need a second controller? My Evohome set-up has 16 radiators spread across 14 rooms and I find the multi-room zone feature works OK to combine rooms where you are happy to share the same schedule, but allows different heat demands from each radiator.

Yes. Range has always been a bit touch-and-go here with the controller placed in an awkward central location. Now we've refurbed one of the furthest rooms from the controller and moved the radiator, it gets no signal at all.

We have 24 rads. Right now, they're spread over 11 zones, but 7 of them are in a multi-room "Downstairs" zone because our downstairs is relatively open-plan. But this means that we can't control that space will wall-mounted thermostats. So we have to use HR92s with offsets. Unfortunately, given the siting of some of the heads, together with some other factors, even a -3C offset isn't enough to get some of the areas within the space up to temperature adequately. (Aside: why limit the offset to +/- 3, I wonder?) The corner of our kitchen where our breakfast table is, for example, is consistently 1-2C below the setpoint because it has two external walls with French doors and a flat roof above. And we can't compensate by raising the setpoint because that would affect all the other rooms in the mega-zone.

TL;DR: yes.

[DBMandrake]

We have 24 rads. Right now, they're spread over 11 zones, but 7 of them are in a multi-room "Downstairs" zone because our downstairs is relatively open-plan. But this means that we can't control that space will wall-mounted thermostats. So we have to use HR92s with offsets. Unfortunately, given the siting of some of the heads, together with some other factors, even a -3C offset isn't enough to get some of the areas within the space up to temperature adequately. (Aside: why limit the offset to +/- 3, I wonder?)

Probably because if you need more than 3 degrees you REALLY need a wall stat.

The corner of our kitchen where our breakfast table is, for example, is consistently 1-2C below the setpoint because it has two external walls with French doors and a flat roof above. And we can't compensate by raising the setpoint because that would affect all the other rooms in the mega-zone.

Actually you can compensate them individually if they need different calibrations. If you have the mega-zone of 7 radiators configured in multi-room mode every HR92 is using its own built in temperature sensor. That means the built in calibration offset will be operational and this offset will be independent for each HR92 and not affect the heating of other radiators in the same zone.

The calibration adjustment of an HR92 only affects other radiators in a single room zone, and only if the HR92 in question is the master HR92 for the zone that is acting as sensor. On other HR92's in a single room zone that are not the designated sensor, the calibrate setting does nothing!