System Boiler (Y-plan) with Google Nest 3rd Gen and OpenTherm?

[albert85]

Hi

I've got an Ideal Logic+ System Boiler (installed by my plumber as a Y-plan currently in the simple on/off mode) with Google Nest 3rd Gen.

Is it possible to upgrade my system so that the Nest 3rd Gen controls the boiler via the OpenTherm protocol for both the heating and for the hot water tank?

The Google Nest installation manual doesn't contain a wiring diagram for my situation. It only contains the on/off Y-plan setup I've got currently running (page 23) and an OpenTherm setup (page 24) that doesn't show how the Y-plan valve might be controlled to divert water between either heating or hot water tank in my setup once the boiler is controlled via OpenTherm.

Is this possible if I purchase additional equipment? My goal is to have both the hot water and heating controllable via the Nest app, and have the heating temperature controlled via OpenTherm to get a more even room temperature.

 

[hometech]

the protocol works by deciding how much input you need at a point in time. There is a very simple logic to the operation and is often referred to incorrectly as intelligent. So imagine that the 2 zones you have need different inputs so zone 1 needs 10Kw and zone 2 only needs 5Kw. What does the boiler decide is best to turn the boiler up or down? How can it even do that? Then add the hot water needs and the variable input. Which does it give priority to and in which order? The other thing worth a mention. The opentherm protocol is a set of standards that CAN be implemented but DON'T HAVE TO BE implemented. This will vary by brand as many have their own versions of the standard. Compatibility and interoperability are different

 

[albert85]

Thanks for the reply!

I'm interested to know if specifically the Ideal Logic+ System Boiler can be made to work in OpenTherm mode (for both controlling heating and hot water) with Google Nest 3rd generation and a Y-plan setup, and if so, how?

My plumber had not installed OpenTherm before and so if I want him to do it I need to give him some more pointers

 

[hometech]

Thanks for the reply!

I'm interested to know if specifically the Ideal Logic+ System Boiler can be made to work in OpenTherm mode (for both controlling heating and hot water) with Google Nest 3rd generation and a Y-plan setup, and if so, how?

My plumber had not installed OpenTherm before and so if I want him to do it I need to give him some more pointers

What are you expecting to happen? control zones without closing the valve but instead turn the water temp down?
on that individual circuit...while keeping the other circuit(s) operating at a higher or lower flow temp?
but with the water coming from the same feed/return?
Then add DHW control...so does the boiler switch the valve to heat the coil in the tank...while keeping the heating circuits in operation or does it heat the water to the temp you want...while deciding how much water needs heating....and how much you are using..
Do you see the complexity of what you are suggesting?

Opentherm modulates the burner to adjust CH flow temp to prevent stop/start and create a slow, steady heating profile.
Imagine you have a car that only has full throttle or no throttle as a means of controlling speed in traffic.

So it will operate S or Y plan and modulate the CH flow temp (opentherm) but the S/Y valves will be either open or shut as will the case with the DHW valve. So you fill a bath, water needs heated, max power applied, no CH in operation. HW store up to temp, CH back on line and working with opentherm. Close a valve, less flow, higher return temp, modulation kicks in etc...

My personal home system has CH and DHW as different needs/demands so has different boilers. I removed the zones S plan) and TRV's and sized the rads based upon heat loss of the room based on 45 degree temp flow.
The heating is automated (on 24/7) so I have no room thermostats, it works on air intake temp and return temp.
It controls the CH flow temp directly. Result is the house has a constant temp and humidity in every single room and landing and the gas reduction is around 50% less than it was with a storage system with zones.
Unlimited hot water on demand is great...

 

[albert85]

Your two boiler setup sounds nice

What I wanted to happen was for the hot water cylinder heating to take priority always, so any time the hot water cylinder temperature drops below target the system should try to heat that immediately (even stopping central heating if sending the very hot water towards central heating is not asked for at that time)

And then for the central heating flow temp to be modulated to keep the room temperature contained in a 0.5 degree range or better (currently my on/off system manages to keep it in a 1 degree range)

Also I was hoping for the radiators to not get as hot as they currently do and instead stay on for longer on a lower temperature (because I think it might create a more pleasant humidity level that way, could be wrong on that)

From your answer it sounds like maybe I'm expecting entirely too much out of a single boiler, and I either accept the limitations of a traditional on/off system, or I go for a two boiler setup like you have

p.s. i've attached the temperature profile my on/off system is able to achieve over a 24 hour period for other interested readers (target temp for day is 2.5 degrees, night is 19 degrees which is why it drops down to that)

 

[Jerry]

Hi Albert85,

As far as I am aware, only combi boilers seem to work with opentherm.

The nest controls the heating directly on an opentherm combi boiler by low voltage. If you have two heating zones (e.g heating and hot water), then you have zone valve/s. The only way the Nest can control this is via mains voltage. This is then your normal on/off type controls. As opposed to modulating via opentherm.

I believe that with Ideal boilers, if any mains voltage is detected on the switch live to the boiler (i.e the bit that turns it on/off), then the opentherm is ignored.

However, there may be a way of doing it. You may be able to run low voltage through the brown and orange or two 2 port valves with 2 seperate Nests etc. There may be a aftermarket gadget that can do this but....its a lot of time and money for a small improvement.

You also stated that you want to keep the temperature within 0.5 degrees. i dont beleive you can obtain this. Think about the solar gain from the north and south facing aspects of your property. Think about the movement of air within the property when you cook, open windows, open doors etc. I doube you can maintain a 0.5 degree difference between the ceiling and the floor.

 

[albert85]

Thanks for the replies. I think I'm beginning to see why OpenTherm hasn't taken off more. The extra complexity doesn't seem to be worth it for the small improvement it can offer over the simple on/off system

 

[hometech]

Thanks for the replies. I think I'm beginning to see why OpenTherm hasn't taken off more. The extra complexity doesn't seem to be worth it for the small improvement it can offer over the simple on/off system

it makes a massive improvement (being able to modulate the boiler) but like all de facto standards, companies want to control things.
Like Linux and windows. Use Linux and you have no security concerns, it is always up to date and it costs nothing as its opensource. Its older than windows but it requires a higher level of understanding (well it used to) to use and manage it. Why don't people use Linux then? Because MS spends a fortune to convince you otherwise.

What you want to achieve can be put together but you would use valve control rather than gas burner control.
A few raspberry pi zeros or arduion's and relays and temp probes would work and you will find a massive community who have already done this and will show you how to do it.

 

[Jerry]

I have one customer who has done the above. He has used his professional technical knowledge to access the Honeywell Evohome wireless network that controls his wireless TRV's. He built an app that allows him to track everything. It must have taken him a very long time and he was rightly proud.

However, 99.9999% of people just want it to work, maybe save them some money and not have to think about it.

Boilers modulate, controls do their thing and manufacturers are always concerned about giving access to their products. Especially if it can turn into a bomb or poison you in your sleep.

 

[Basher]

Thanks for the replies. I think I'm beginning to see why OpenTherm hasn't taken off more. The extra complexity doesn't seem to be worth it for the small improvement it can offer over the simple on/off system

To attempt to answer your original post regarding the circuit for opentherm, my immediate reaction on reading the Nest manual you linked, was that the opentherm connections on P24 are to be used in addition to all the other connections for the system (in your case Y-plan on P23). This seems to be borne out by a thread (but S-plan) I've seen, but some people who have done this have had trouble with demand for hot water only not firing the boiler. Might be worth looking through this (admittedly from a few years ago):

Nest and Opentherm - Page 1 - Homes, Gardens and DIY - PistonHeads UK