Atag and Intergas - New to me

[Dan Robinson]

It won't need to.

 

[D_Hailsham]

My understanding is that OT + Evohome learns the house and then optimises the gas supply regardless of how many rooms are on and off and what temp each individual room is calling for.

With WC + Evohome, all Evohome can do is tell the boiler to switch on or off - it can't tell it how hard to work. Yes WC would control the boiler dependant on the outdoor temp, but it won't know if I'm trying to heat 1 room or 10 rooms.

Although OT can do many things -mainly reading info from the boiler - its main task is to tell the boiler what flow temperature it needs to produce. This can be achieved in two ways: (1) Room temperature control (compares actual temp with required temp and calculates flow temp); or (2) Outside temperature control aka Weather compensation (flow temp depends on outside temperature). Once the boiler has been given that information it is up to the boiler how it maintains that temperature. If the boiler needs to modulate up/down it will do so; and if it needs to turn on/off, because it has reached the low limit of modulation, it will do so.

As for knowing how many rooms are being heated, the boiler "learns" this by the amount of heat used, i.e the change in return temperature. Say all rooms are being heated and then one room is turned off. The return temperature at the boiler will automatically rise as less heat has been extracted from the water. This will cause the boiler to modulate down as less heat will be required to bring the water back to the required flow temperature. When the rad is turned back on the opposite will take place.

Different temperatures in different rooms is the responsibility of the TRV in that room.

 

[fergie_]

Thanks, that seems to be the piece of information I was missing.

So it would mean that in laypersons terms opentherm is proactive where as the boiler is reactive? Both get to the same place - just the route taken to get there is different.

When I researched evohome and spoke to Honeywell it was stressed opentherm would allow me to get the most out of the system.

I'd still prefer that option, but makes sense that WC on the correct boiler could be just as effective.

Still leaves me struggling to find the right boiler though...

 

[Dan Robinson]

Honeywell it was stressed opentherm

They assume that the everything works as intended. It is not always the case though. Hence my advice about the Intergas and OpenTherm.

 

[D_Hailsham]

So it would mean that in laypersons terms opentherm is proactive where as the boiler is reactive? Both get to the same place - just the route taken to get there is different.

Not really. I don't see the stat being proactive as that would imply it knows what to do in advance. Both are reactive: the stat reacts to room/outside temperatures and calculates the required flow temperature; the boiler reacts to instructions from the stat telling it what flow temperature to maintain.

In OT parlance the thermostat is the Master and the boiler is the Slave.

 

[fergie_]

Maybe it's being over hyped, but I thought evohome would know the temp of each zone (from 92s or extra senors), know what temp is being asked for in each zone and can therefore govern how much heat it needs to a) reach that temp and b) hold that temp.

I.e. If you are using it as a controller it is simply telling the boiler to switch on or off, but if you add opentherm it can then help the boiler do what it should to its optimum.

 

[Dan Robinson]

The stat has optimization routines. It works together with the boiler based on past performance.

 

[D_Hailsham]

Maybe it's being over hyped, but I thought evohome would know the temp of each zone (from 92s or extra senors), know what temp is being asked for in each zone and can therefore govern how much heat it needs to a) reach that temp and b) hold that temp.
I.e. If you are using it as a controller it is simply telling the boiler to switch on or off, but if you add opentherm it can then help the boiler do what it should to its optimum.

Evohome cannot control directly the distribution of heat to each room, that is down to system design, balancing and the thermostat/TRV in each room. The amount of heat necessary at an one time will depend on the change in flow temperature: if it drops, more heat is required and vice versa; the boiler takes care of that. All OT does is tell the boiler the required flow temp. Thermostats with TPI can achieve similar results to OT by varying the on/off ratio to produce a variable mean flow temperature. The difference is that with TPI the boiler is always trying to reach a fixed temperature, not a changeable one as provided by OT. The standard Evohome controller uses TPI.

 

[fergie_]

Maybe I'm hoping for too much from evohome, but I thought it would know what each electronic TRV is doing and then calculate if the demand should be higher or lower.

It should know the set temp of each room, the actual temp and whether it is trying to add heat or cool down or hold the current temps.

My logic says that if it is also controlling the demand, it is much easier to keep the temps consistent rather than having to react to changes from the boiler.

I would agree that there is not much point to OT in a single zone house, but where there are multiple zones, it would appear to make a lot more sense.

In conclusion though, it means I have alternative options to achieve my wanted result if I can't find a boiler that will work correctly with OT evohome.

 

[Dan Robinson]

Maybe I'm hoping for too much from evohome, but I thought it would know what each electronic TRV is doing and then calculate if the demand should be higher or lower.

It should know the set temp of each room, the actual temp and whether it is trying to add heat or cool down or hold the current temps.

My logic says that if it is also controlling the demand, it is much easier to keep the temps consistent rather than having to react to changes from the boiler.

I would agree that there is not much point to OT in a single zone house, but where there are multiple zones, it would appear to make a lot more sense.

In conclusion though, it means I have alternative options to achieve my wanted result if I can't find a boiler that will work correctly with OT evohome.

Why don't you reread what has been posted