Home heating automation

Ush1

deezell wrote: »

As a general rule, Opentherm will fire the boiler, while the valves will continue to be opened by the stat or it's receiver SL Relay. Normally the valves combine via their relays contacts to fire the boiler, but these may be disconnected, and the OT digital signal should now fire the boiler, and control it's output according to the thermostat call, either CH and/Or HW. If the boiler OT implementation allows, it should be able to switch to higher temperature flow for HW and HW+CH flow, with finer modulated control for CH only. In all cases this is for a single thermostat CH zone, and a timed HW zone. Adding a second smart thermostat CH zone with OT capability would require a a method of routing two OT sources to one OT boiler input. While this is defined in the OT protocol, I'm not aware of any implementations in current OT equipped smart stats. It is possibly to connect a simple NO contact stat (VOLT FREE!) across the boiler OT termimals, and under the protocol the boiler will now fire in smple on/off mode a la SL. Any OT connected stat will be ignored and its temperature feedback to the boiler will be lost until the volt free contacts open, whence OT modulated control of the heating will resume.

Thanks deezell. EPH actually now do a range of opentherm stats that support zones in a master slave type wiring, I think it aggregates the various temps to regulate the CH water temp efficiency.

https://www.ephcontrols.com/section/progammable-rf-thermostat-receiver/

So my scenario is I have EPH ember wireless stats and the controller which is wiring into the central wiring panel. Also wired into the panel is the motorised valves for the 2 zones and the boiler.

I want to replace the stats and controller with 2 Nest stats which will wire into the central panel and switch the relays to fire the valves, but I also want both nest stats wired directly to the boiler for opentherm so I have two questions.

1.Can you have two Nests(or any Opentherm stats) wired directly into the boiler connections and how will that work, is it clever enough to average the two different temps? Or does it have to be some form of master slave before the boiler.

2.If I'm using Opentherm will that potentially fire the boiler and the relay contacts wont switch and the motorised valves be ignored?(obviously wouldn't be much good).

deezell

Ush1 wrote: »

1.Can you have two Nests(or any Opentherm stats) wired directly into the boiler connections and how will that work, is it clever enough to average the two different temps? Or does it have to be some form of master slave before the boiler.

2.If I'm using Opentherm will that potentially fire the boiler and the relay contacts wont switch and the motorised valves be ignored?(obviously wouldn't be much good).

2. Second question first, there's no reason the relays shouldn't close, the Nest heatlink is a 2 zone receiver, so it's often going to be used in S or Y plan valve switching, regardless of the method used to fire the boiler.

1. If you have 2 stats, you have a problem. I've not come across a wiring schedule for this in OT. An OT switch/router is defined in the OT protocols, to combine 2 OT sources, but I've not seen such a device. As I said in the first post, you can mix 1 OT and 1 Volt free, the second being just closed circuit relay contact. It just bangs the boiler on , no OT refinement while this zone is on. The contacts MUST be volt free so as not to fry the incoming OT signals source from the other stat. I'm assuming the boiler obeys this part of the protocol. As you will have mains voltage on the Nest CH contacts to open the CH valve, you can use the valve microswitch contacts (which currently would provide SL to the boiler) to provide volt free closed contacts to the boiler OT terminals, if you want to experiment. Careful now.

deezell

Further to this, you are correct about the new Ember OT control. They have built the OT routing into the wiser receiver heathub, so only the nominated one connects to the boiler OT terminals. I expect they have an algorithm for OT modulation which takes account of all active CH zones.
I have yet to find any discussion even of dual nest OT connection.
According to Schneider, Drayton wiser OT only works for single CH zone with direct HW, ie, no zone valves, so it will not support 2 stats via OT nor will open the valves on a single CH+HW hub connection.
https://schneider-electric.zendesk.com/hc/en-gb/articles/360033902053-How-to-connect-the-OpenTherm-Module

That just leaves Nest, with an as yet unproven OT/NO combined connection to give OT control on one stat.

There is also Tado. These stats are highly configurable, and Tado support would know more than anyone what is possible, but remember, they already support boiler firing via OT from multiple stats if these are the stats built into their TRVs. All TRVs can fire the boiler via the main stat. An additional wall stat might also be able to trigger the boiler thus, and provided it's NO relay contacts remain active it can also operate it's respective zone valve.
As you can add an unwired extra stat to a Tado installation to act as the temperature measurement device for a TRV, the TRV now effectively becoming a single rad zone valve, and the main OT connected stat controls the boiler on behalf of another Tado stat, albeit one acting on behalf of a TRV. I expect that perhaps you should be able to do the same with an additional stat not TRV related. Furthermore, I know that a stat used for TRV measurement can have it's unused relay disabled to save battery power, so this implies that it if left undisabled it should close NO contacts during calls for heat. If you want to consider Tado, a question to tado support would be in order. I might ask it myself.

Ush1

What I think I will do is go with the two nests and just have OT on the downstairs one since that is the zone we use heating far more often in.

So have the nest stat relays wired into the valves which will in turn fire the boiler and the temp be only modulated by the downstairs zone.

Even if I was to go with the ember system the only thing I could keep would be the valves, you even need a new internet gateway for the app for their new OT stats combipack. Their support was very helpful but I'm leaning towards the nest.

Possibly will go with an ultra cheap seperate smart TRV system in the future, AliExpress type job.

deezell

Just remember that if you connect one Nest via it's OT terminals to the boiler OT in, generally it's normal to leave SL terminals bridged. If you leave your existing valve contacts across these, the boiler might only fire when they are bridged AND a signal comes through on the OT terminals. I'd predict that you will only get firing for zone one. You would normally have to bridge the SL terminals, connect one stat OT to the boiler OT, and connect the other zones Volt free valve relay accross the boiler OT terminals, which will revert the boiler to standard on off when zone 2 is on.

deezell

What is the make and model of your boiler? I'll retrieve and take a look at its connection diagrams to see if it uses bridged terminals when operating in SL or OT mode, to see if the hybrid OT mode is supported.

Ush1

deezell wrote: »

What is the make and model of your boiler? I'll retrieve and take a look at its connection diagrams to see if it uses bridged terminals when operating in SL or OT mode, to see if the hybrid OT mode is supported.

Thanks a mill, Ideal Logic Combi C24.

Ush1

deezell wrote: »

Just remember that if you connect one Nest via it's OT terminals to the boiler OT in, generally it's normal to leave SL terminals bridged. If you leave your existing valve contacts across these, the boiler might only fire when they are bridged AND a signal comes through on the OT terminals. I'd predict that you will only get firing for zone one. You would normally have to bridge the SL terminals, connect one stat OT to the boiler OT, and connect the other zones Volt free valve relay accross the boiler OT terminals, which will revert the boiler to standard on off when zone 2 is on.

Interesting, so you reckon the OT connections can be pulsed by a relay to fire heating(without the modulation I'm guessing)?

deezell

H

Ush1 wrote: »

Interesting, so you reckon the OT connections can be pulsed by a relay to fire heating(without the modulation I'm guessing)?

Yes, that's in the OT protocol document, a simple short across the OT terminals turns the boiler on old school style. If another stat was connect via OT, it's feedback and control is now shorted out. If it were requesting the boiler to fire, it will have to make do with a non modulated full on flow until the other stat's volt free relay which shorted the terminals releases them, then the OT stat can re-set up comms with the OT boiler input.
I've had an idea that would use the volt free contacts on the valves to divert the OT signal from Nest 2 to the OT terminals of the boiler. If your zone valves are 5 wire, the relay will have NO, NC and Com contacts, Grey, White and Orange respectively. This extra contact could be used to select the OT source to the boiler, so when Nest 1 is not calling, a call from Nest 2 will divert the OT from 2 in place of 1. Would it work? I don't know. Nest 2 will have no OT comms with the boiler until the moment it opens its zone valve. How long it takes to establish contact, I'm not sure, it would effectively be a new device hooking up. I'd need to read the protocol more to see, but if it can recover Instantly from a short and re-establish connection, then a different OT source should be able to drop in. If there are stored strings or ids from the original OT connection, it might not work. It's an idea nonetheless, which might give you 2 zone OT control with priority for one when both are active. Meantime, I'll search for that boiler manual later, better do a bit of WFH.

Ush1

I can understand when you mean switching the OT connection through the aux relay on the valve, but I don't see how that would get around when both valves are active won't both be trying to connect to the boiler OT thermals? I must be getting lost somewhere in the description.

championc

Maybe it might be easier to go with the likes of Tado, having Smart TRV's on all rads, essentially turning rads into their own zones (if the TRV's are linked to a single central Smart Thermostat). Up to 10 rads can be linked to a Smart Thermostat, to allow rads to turn the boiler on and off, irrespective of the setting on the main Smart Thermostat. So you could add Smart TRV's everywhere, or everywhere that you currently control with Zone valves

deezell

Ush1 wrote: »

I can understand when you mean switching the OT connection through the aux relay on the valve, but I don't see how that would get around when both valves are active won't both be trying to connect to the boiler OT thermals? I must be getting lost somewhere in the description.

What I was suggesting, without any proof, is that it might be possible to change the source OT stat connected to the boiler on the fly, such that if either stat 1 alone or stat 2 alone is active, then this is the one connected to the OT terminals on the boiler. If neither or both are active, then the default is stat 1. The boiler will always be modulating, and with both zones active, according to the information from stat 1.
Problems with this scenario would be if zone 1 was near target, the boiler might be modulating and producing a flow whose temperature would be efficient for condensor purposes, but may not be sufficient for zone 2 to reach target temperature. Only when zone 1 reaches target will it's relay actually close, handing control over to stat 2.
The problem really is that by its very nature, boiler modulation will always reduce the firing to a point where the heating flow reduces in temperature to achieve a steady state, but never or rarely cutting off completely, and closing the zone valve.
At least with the other wiring scheme there is no conflict. Stat 2 comes on and shorts the terminal, the boiler fires at full capacity until zone 2 hits target, thereby returning control to zone 1 stat 1.
My suggestion was also predicated on the ability of the boiler to recognise the digital signal from a different OT source, crudely switched by a relay. It may not be able to do this instantaneously. There's also the small matter of wiring. OT sources are two wire balanced, for my suggestion both stat OT connections would have be combined on one wire into the boiler, say terminal OT1, while the other terminal OT2 from both stats, would be switched by the changeover relay. There are issues of non termination and impedance which could render such as circuit unreliable, as unterminated OT signals from one of the stats energise the cables, but analysing this is well beyond the scope of this thought experiment. If you had 2 nests already wired and working in SL mode, and then connected one only by its OT terminals, removing all SL connections, you could mock up a change of stat using an old double pole light switch. I'll put together a wiring diagram to explain the logic, probably tomorrow, but like I said, it's a bodge at best if it works, and may have odd effects as a result of the way modulated heating works, especially when both zone valves are open but only one stat is sending temperature info.

deezell

I'll also talk to you about the nature of smart stats, and how they use integral modelling over time to generate their own version of modulation on a standard on/off boiler, mimicking OT modulation. The Tado does this really well

championc

I'm getting more and more impressed with the Tado by the day. The better half wanted the sitting room a bit warmer this evening. I increased the temperature by 1°. The boiler came on, but only for a few minutes. It went off without the temperature being anywhere near having been increased by 1°.

However, the TRV has obviously learned as to how long it takes to increase the temperature in the room and so, low and behold, the room temperature gradually increased to the required level, and no higher, so not a single bit of gas is wasted.

Maybe I've missed something but from what I've experienced, a Tado will certainly save money by giving full room to room flexibility. I cannot see how a Nest can really save much, unless in conjunction with other controls

Ush1

championc wrote: »

Maybe it might be easier to go with the likes of Tado, having Smart TRV's on all rads, essentially turning rads into their own zones (if the TRV's are linked to a single central Smart Thermostat). Up to 10 rads can be linked to a Smart Thermostat, to allow rads to turn the boiler on and off, irrespective of the setting on the main Smart Thermostat. So you could add Smart TRV's everywhere, or everywhere that you currently control with Zone valves

Thats fine but it doesn't get around the issue of 2 zones and Opentherm.

snowstreams

I got a tado starter kit on an Amazon deal last week. The extension kit with a smart thermostat.
I have a 3 zone controller at the moment, upstairs downstairs and water.
So I have connected in the smart thermostat to upstairs for now and wanted to use the extension kit to control the hot water on cloudy days (I have solar hot water).
But tado support then told me that I can't use the extension kit since my controller is 3 zones.
I still think I could replace my controller and wired the old stat and water to the extension kit. Then leave the new smart thermostat in a hardwired ON state since that's the state it needs to be left in for tado to work.
Has anyone here tried doing something like this? Or are there any reasons not to do this?

championc

Ush1 wrote: »

Thats fine but it doesn't get around the issue of 2 zones and Opentherm.

The point I was making was that you basically set those permanently open and allow individual rooms beyond the zone valves to be the Zones. If all rads TRV's in that zone are closed, it's the same thing as having the zone closed.

championc

snowstreams wrote: »

I got a tado starter kit on an Amazon deal last week. The extension kit with a smart thermostat.
I have a 3 zone controller at the moment, upstairs downstairs and water.
So I have connected in the smart thermostat to upstairs for now and wanted to use the extension kit to control the hot water on cloudy days (I have solar hot water).
But tado support then told me that I can't use the extension kit since my controller is 3 zones.
I still think I could replace my controller and wired the old stat and water to the extension kit. Then leave the new smart thermostat in a hardwired ON state since that's the state it needs to be left in for tado to work.
Has anyone here tried doing something like this? Or are there any reasons not to do this?

That's somewhere where I was. I had a zone for Upstairs. I have a Kingspan thermomax solar tubes system for hot water, but because I have a Combi Boiler, I don't have any need for a hot water "zone" so I have just the two zones - Downstairs and Whole house (when upstairs valve is opened.

But as I said to Ush1, I think you could make a far more effective setup with Smart Radiator Thermostats on all of your upstairs rads, which would essentially do away with your upstairs zone value.

As I said in my post last night, I cannot really see how an individual (or two) Smart thermostats can make any great amount of savings to your heating bill but I can absolutely see now how the Smart Radiator Thermostats can save money by only heating rooms to the temperature required and not wildly fluctuating above and below the thresholds set in a traditional TRV. So if I set my sitting room for 22, it pretty much stays within the 22 deg range for the period it's set for, rather than swinging between 21 and 23 or whatever.

snowstreams

I don't have trvs on my radiators yet. I'll install them over the summer and stock up on tado radiator valves on the next sale.
But I wanted to be able to remotely turn off on hot water for cloudy days etc if we had been away.
I'll play around with the extension kit at the weekend anyway since I don't think it's worth returning it.
It should do what I want, then I'll use some other thermostat to check the tank temperature remotely too.

deezell

Ush1 wrote: »

Thats fine but it doesn't get around the issue of 2 zones and Opentherm.

I've had a look at the logic combi installation, it's standard setup. For normal firing the link across the stst/timerL terminals is removed and these terminal connected to a stat/ timer relay. For OT firing, this link remains and the OT link is removed and connected to the stat' s OT terminals. A short across these terminals will fire the boiler in normal mode.

Ush1

championc wrote: »

The point I was making was that you basically set those permanently open and allow individual rooms beyond the zone valves to be the Zones. If all rads TRV's in that zone are closed, it's the same thing as having the zone closed.

No it isn't the same. The zone valves stop hot water from getting to the upstairs pipework, TRVs only stop water getting to the rad.

championc

Ush1 wrote: »

No it isn't the same. The zone valves stop hot water from getting to the upstairs pipework, TRVs only stop water getting to the rad.

Eh ? If no TRV is open, then no water can flow around that whole section of the pipework, from the point where that whole section branches off from active sections.

So it absolutely can indeed turn all of that whole section into a "zone" - yes ?

Ush1

deezell wrote: »

I've had a look at the logic combi installation, it's standard setup. For normal firing the link across the stst/timerL terminals is removed and these terminal connected to a stat/ timer relay. For OT firing, this link remains and the OT link is removed and connected to the stat' s OT terminals. A short across these terminals will fire the boiler in normal mode.

Thanks a mill deezell, legend. So worse case it looks like I'll at least to able to have downstairs OT and upstairs just standard firing.

I'll do some tests when I get the Nest stats and let you know how I get on.

deezell

Ush1 wrote: »

Thanks a mill deezell, legend. So worse case it looks like I'll at least to able to have downstairs OT and upstairs just standard firing.

I'll do some tests when I get the Nest stats and let you know how I get on.

That would be best, it's within the protocol and allows the boiler to fire at full tilt when zone 2 kicks in, returning to modulation for zone 1 only . The other scenario is unproven, whereby you use the valve contacts to switch the OT source depending on zone valves state.. Using both valve contacts would allow you to select OT1 for Zone1 ON only, both Zones ON and both zones OFF, (system idle), with OT2 connected only for Zone 2 ON only.

Zone 1 |Zone 2 |OT Source
OFF |OFF |Zone1
ON |OFF |Zone1
ON |ON |Zone1
OFF |ON |Zone2 See if you can figure the wiring to satisfy this logic using the terminals of the two zone valve relays! Answer tomorrow.

comfort

Hi guys, just a quick question as I seem to have a brain freeze. I have the Hive System (3 Zone - DS, US & HW). Now that Hive is HomeKit compatible has been a nice improvement albeit small as the HW zone is not HomeKit compatible. Anyway my question is this, with hive can I install TRV's and both work or does one override the other ? I would not be installing TRV on all the rads at once.

Many thanks

Ush1

deezell wrote: »

That would be best, it's within the protocol and allows the boiler to fire at full tilt when zone 2 kicks in, returning to modulation for zone 1 only . The other scenario is unproven, whereby you use the valve contacts to switch the OT source depending on zone valves state.. Using both valve contacts would allow you to select OT1 for Zone1 ON only, both Zones ON and both zones OFF, (system idle), with OT2 connected only for Zone 2 ON only.

Zone 1 |Zone 2 |OT Source
OFF |OFF |Zone1
ON |OFF |Zone1
ON |ON |Zone1
OFF |ON |Zone2 See if you can figure the wiring to satisfy this logic using the terminals of the two zone valve relays! Answer tomorrow.

Might be being silly here but I actually can't see how I can do it even with just one zone opentherm.

I presume the Opentherm connection is supposed to be permanent, otherwise it just fires heating normally as you said before. I spoke to Nest and they said when the stat is in Opentherm mode it won't click the relay. This causes an issue where I have nothing to drive the valve, as far as I can see.

deezell

Ush1 wrote: »

Might be being silly here but I actually can't see how I can do it even with just one zone opentherm.

I presume the Opentherm connection is supposed to be permanent, otherwise it just fires heating normally as you said before. I spoke to Nest and they said when the stat is in Opentherm mode it won't click the relay. This causes an issue where I have nothing to drive the valve, as far as I can see.

Well that's that then. The same goes for the Drayton Wiser. It seems like it's more trouble than it's worth, and your only other option is single Zone, with smart TRVs on a schedule to give you back a zoned system, but that can be expensive. I've found the tado excellent in mimicking modulation. What you are trying to achieve is tight control of temperature, where the stat behind to cut the boiler in advance of the target, to prevent overshoot, and ditto as it measures the temperature dropping. The second element is when it pulses the boiler around this point, short bursts, cooled return flow to optimise condensor boiler efficiency. At the same time it will respond to a sudden increase request, say from 15° or lower in away mode to 22° when it detects you're on the way. This will require the boiler to pump well heated water to geta rapid rate of change of temperature, but it is constantit measuring this rate, and also the lag in response, so can work out when to cut and pulse, greeting you with an almost exact temperature on arrival. Consider the Tado or Drayton wired on/off. Both have integrated TRVs as part of their kit.

Ush1

deezell wrote: »

Well that's that then. The same goes for the Drayton Wiser. It seems like it's more trouble than it's worth, and your only other option is single Zone, with smart TRVs on a schedule to give you back a zoned system, but that can be expensive. I've found the tado excellent in mimicking modulation. What you are trying to achieve is tight control of temperature, where the stat behind to cut the boiler in advance of the target, to prevent overshoot, and ditto as it measures the temperature dropping. The second element is when it pulses the boiler around this point, short bursts, cooled return flow to optimise condensor boiler efficiency. At the same time it will respond to a sudden increase request, say from 15° or lower in away mode to 22° when it detects you're on the way. This will require the boiler to pump well heated water to geta rapid rate of change of temperature, but it is constantit measuring this rate, and also the lag in response, so can work out when to cut and pulse, greeting you with an almost exact temperature on arrival. Consider the Tado or Drayton wired on/off. Both have integrated TRVs as part of their kit.

One last thing I found looks interesting but pretty tricky:
https://www.domoticaforum.eu/viewtopic.php?f=75&t=11419&p=80759&hilit=2+zones#p80816

That guys post contradicts what Nest told me though about the relay clicking, but the post is from 2016 so maybe the firmware changed or something.

Other options would be the Ember system which does what I want but its expensive and no integrated smart TRVs.

Final one is no Opentherm and an integrated smart TRV system, auch as the Drayton or Tado. Really want to make use of Opentherm though!:pac:

deezell

Ush1 wrote: »

One last thing I found looks interesting but pretty tricky:
https://www.domoticaforum.eu/viewtopic.php?f=75&t=11419&p=80759&hilit=2+zones#p80816

That guys post contradicts what Nest told me though about the relay clicking, but the post is from 2016 so maybe the firmware changed or something.

Other options would be the Ember system which does what I want but its expensive and no integrated smart TRVs.

Final one is no Opentherm and an integrated smart TRV system, auch as the Drayton or Tado. Really want to make use of Opentherm though!:pac:

You could partially, by having only the main zone on OT, with it's zone valve always open, then zone 2 will jump in and out as required. You won't be able to turn off zone 1 while 2 is calling though, so the temperature of zone 1 will increase regardless of its stat. Not a great option. There's almost no hard information out there on the Nest and OT connection, but then Nest was never positioned as a zoned system, what with each heatlink box having a HW relay, you end up with two when you buy 2 nests. In fact the heatlink only exists because of the European market, with live mains switching of boilers and plumbed HW tanks. US Nest connects straight to the boiler low current trigger terminals, often from a legacy boiler which is passively powered by a millivolt thermopile. Zoning in the US is often the opening and closing of warm air baffles rather than redirecting hot water flows. Tado might be your best bet for zoned OT, with a query to Tado support your first move.

deezell

Ush1 wrote: »

One last thing I found looks interesting but pretty tricky:
https://www.domoticaforum.eu/viewtopic.php?f=75&t=11419&p=80759&hilit=2+zones#p80816

......Final one is no Opentherm and an integrated smart TRV system, auch as the Drayton or Tado. Really want to make use of Opentherm though!:pac:

Missed this comment, readng in the sunshine. Tado and Drayton with their respective TRVs can still be connected by OT afaik. Drayton OT is an add in module into the relay box, Its included in the Tado stat or its wireless ext kit, no extra bits. OT modulation will work just as well while individual TRVs open and close.