OpenTherm with Multiple nests on underfloor heating

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Nick Slatter

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I'm in the process of upgrading the controls of my heating system. (Unvented S plan with 2 heating zones)

So far I have swapped the old fashioned room stat for a nest/heat link to control the zone valve for the upstairs zone which is a trad radiator system. That all works BRILLIANTLY!

So the next stage is to upgrade the downstairs zone which is a wet UFH split into 3 manifold zones on an ancient JG speedfit wireless wiring centre with 3 wireless room stats.

Because I LOVE the nest so much, I am willing to buy 3 more to get individual learning on the 3 downstairs zones and hopefully, all 4 (inc upstairs) will all talk and auto away together etc.

My question is around opentherm control:

How do I connect the Opentherm terminals to the heatlink(s)?

Will the modulation control take into account requirements from the other nests? I.e. If the one nominated nest that controls Hot water needs the flow temp to be hotter, will this override the Opentherm control from another heat link that might call for a lower flow temp.

Also does anyone have any experience with UFH and nest? I'm attracted to opentherm to take advantage of a very low flow temp to stop the boiler short cycling when heating just the UFH zones.

Thanks for any help or stories to share.
 
I am not an expert on nest or opentherm but I am assuming you have a mixer valve on your ufh manifold so I cant see how modulating the boiler flow temp will work, apart from the fact you have a mix of rads and ufh.
 
Ok, another suggestion then - is there a UFH system that can use one nest as an overall master controller but still have individual zone temp control?
 
Nest is designed for one zone only, and whilst it can sort of work with multiple zones, you'd be much better off with a purpose-designed multizone system such as Genius Home, EvoHome, Heatmiser Neo or the new Delta Dore system.
 
The Nest can provide on/off control of individual zones.

It can provide opentherm control of a boiler. But your boiler does not know where it's heat is going and so only one opentherm control can be used on it. But with multiple zones you would not want to use opentherm flow temp control as what is required for one zone will not be what is required on another zone.

Your boiler only provides one flow temperature and so different flow temps to different zones are not possible without remotely activated blending valves which become expensive !

Tony
 
Thanks guys. I've looked into all of those and they just don't look as good on your wall!!

I might have to live with 2 separate independent zones with different manufacturers controllers and maybe link them together with IFTTT or something
 
There is no point in heating an unoccupied area. Just a waste of heat.

So multiple zones are very good.

Weather compensation ( WC ) where the flow temperature is varied only adds a very small saving, probably 3-6%, although it can give a nice well controlled temperature if set up well.
 
I'll try to keep independent control of the 3 downstairs zones but I find with UFH that it needs to be 'on' for large parts of the day due to the thermal mass in the screed and tiles etc. I wanted OT so that I could reduce the flow temp (and thus the return) so that it would take advantage of condensing mode more often.
 
UFH is only supplied at about 40-50 C and at that flow temp the boiler will be condensing as much as the design allows.

So WC will not increase efficiency any more.

And due to the long time lag of UFH any WC needs to be very cleverly controlled.
 
Mine works great with UFH radiators and an unvented cylinder. But what would I know. I'm only a manufacturers part swapper. ;) :(
 
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