OpenTherm RF Stat available in the UK?

[D_Hailsham]

I don't think the cycling approach adopted by the CM927 works well with the modulating approach of the Avanta.

There may be something in what you say. I have just come across a report produced for the Energy Saving Trust by an Gastec last September entitled "In-situ monitoring of efficiencies of condensing boilers – TPI control project extension". It is the second phase of a long study in real homes of condensing boilers efficiency.

In the summary it says:

It is acknowledged that there could be potential conflicts between the logic of the TPI controller and the in-built logic of a modulating boiler.

I haven't read the whole report - it's 117 pages long - but it seems to concentrate on "efficiency", while I think the main reasoning behind TPI controls is comfort, i.e maintaining a stable temperature.

Except that in the case of the Avanta range they don't. The start up fan speed is set to 22 against a max of 35.

The only speeds quoted in the manual are the min and max. So is the start up speed set to 22 or is the boiler clever enough to know that 22 is the most appropriate start up speed for your system? It would be interesting to know what other Avanta boilers do.

Their iSense stuff is good but oh my gawd their technical guys are clueless.

That's because the tech side has been taken over by Heateam.

I recently emailed Remeha for advice about using an iSense with an 18V open-vent boiler. This was because it is shown as an option in their wiring manual for System boilers but not for OV boilers, which I thought very strange as there is no real difference between System and OV.

The reply I got came from someone in Baxi Group Sales and it was obvious that he had just looked at the wiring book and concluded that it was not possible. No explanation as to why it can't be used.

 

[dumbrill]

Except that in the case of the Avanta range they don't. The start up fan speed is set to 22 against a max of 35.

The only speeds quoted in the manual are the min and max. So is the start up speed set to 22 or is the boiler clever enough to know that 22 is the most appropriate start up speed for your system? It would be interesting to know what other Avanta boilers do.

Parameter 'p20' is the one that sets the start-up fan speed, but it's not supposed to be changed. It's not 22, but that was a guess from memory. The value changes for each size of boiler, but its never full speed.

 

[dumbrill]

I don't think the cycling approach adopted by the CM927 works well with the modulating approach of the Avanta.

There may be something in what you say. I have just come across a report produced for the Energy Saving Trust by an Gastec last September entitled "In-situ monitoring of efficiencies of condensing boilers – TPI control project extension". It is the second phase of a long study in real homes of condensing boilers efficiency.

In the summary it says:

It is acknowledged that there could be potential conflicts between the logic of the TPI controller and the in-built logic of a modulating boiler.

I haven't read the whole report - it's 117 pages long - but it seems to concentrate on "efficiency", while I think the main reasoning behind TPI controls is comfort, i.e maintaining a stable temperature.

I don't see this as surprising really. The TPI control has to be based on the boiler output always being the same each time it cycles on. If the CH is cycling on so many times per hour for a given set of conditions then its no good the boiler varying what output its giving every time it comes on.

In my case I could see that the boiler would come on, but wouldn't give 100% output initially. It slowly ramped up and more often than not the CM927 would turn off the CH before it got near to 100%. Also the house felt warmer with the old boiler/CM927 combination than with the new boiler/CM927.

 

[D_Hailsham]

Parameter 'p20' is the one that sets the start-up fan speed, but it's not supposed to be changed. It's not 22, but that was a guess from memory. The value changes for each size of boiler, but its never full speed.

I had forgotten about P20. I've just checked my copy of the manuals and it's 25 for all versions; the min is always 13. It's only the max which varies, according to the boiler output.

Unless the installer fiddled with the setting, the only possible reason for your boiler always starting at 22 is that the logic of the boiler has determined that 22 is the optimum start up speed for your boiler.

 

[dumbrill]

22 was just a guess from memory. It's set to whatever it's suposed to be.

 

[D_Hailsham]

22 was just a guess from memory. It's set to whatever it's supposed to be.

Got it!

In my case I could see that the boiler would come on, but wouldn't give 100% output initially. It slowly ramped up and more often than not the CM927 would turn off the CH before it got near to 100%.

You say that you have a Remeha 18S, which is an 18kW boiler. Who decide what size boiler you should have and how?

 

[dumbrill]

22 was just a guess from memory. It's set to whatever it's supposed to be.

Got it!

In my case I could see that the boiler would come on, but wouldn't give 100% output initially. It slowly ramped up and more often than not the CM927 would turn off the CH before it got near to 100%.

You say that you have a Remeha 18S, which is an 18kW boiler. Who decide what size boiler you should have and how?

I did and the boiler is not oversized.

 

[tourcd]

I've been using an iSense RF with an Avanta 18S for about 6 months now and it works very well.

Did you have to power the transmitter unit using a separate DC transformer? Or can the iSense be driven off the PCB of a Avanta Plus 39C?

 

[D_Hailsham]

Did you have to power the transmitter unit using a separate DC transformer? Or can the iSense be driven off the PCB of a Avanta Plus 39C?

All UK versions of Avanta boilers use the same PCB, so none of them are able to provide the necessary power to drive the iBase. You have to use a separate DC power supply.

 

[dumbrill]

Did you have to power the transmitter unit using a separate DC transformer? Or can the iSense be driven off the PCB of a Avanta Plus 39C?

All UK versions of Avanta boilers use the same PCB, so none of them are able to provide the necessary power to drive the iBase. You have to use a separate DC power supply.

The iBase will work without the 5V supply, but I've never left it like this for long. I don't know what capability the boiler PCB has to supply the iBase.

The PCB for the boiler is made by SIT Controls who are an Italian company. I don't know if they are part of the Remeha group. It interesting that when you look at the components in the boiler it's really only a combination of components from other manufacturers. Is the UK Avanta the same or different to the Dutch Avanta?

 

[D_Hailsham]

The iBase will work without the 5V supply, but I've never left it like this for long.

That sounded interesting, so I have done a bit of digging. The latest version of the OT Protocol introduced a feature called "SmartPower". This is described in one of the Newletters as follows:

Basically OpenTherm SmartPower consists of 3 power levels; low power (existing protocol specification), medium power and high power. The use of these power levels can best be described with an example.

A thermostat (master) with a large display and backlight function, is powered via OpenTherm by a boiler (slave). The display and especially the backlight of the thermostat demand more power in order to function. Only this demand is not constantly and depends of the use the thermostat.

With OpenTherm SmartPower this problem is now solved. When the master needs more power (for the backlight), it will ask the slave to provide more power. The slave will then switch to a higher power level. When there is no longer a need for more power, again a request will go to slave to switch back to a lower power level. Which power level is being used, depends of the functionality.

So SmartPower is a way for the boiler to provide more power to the connected unit when the backlight is on. But the iBase doesn't have a backlight, so why would it need the extra power? Possibly to power the wireless side?

 

[dumbrill]

With OpenTherm SmartPower this problem is now solved. When the master needs more power (for the backlight), it will ask the slave to provide more power. The slave will then switch to a higher power level. When there is no longer a need for more power, again a request will go to slave to switch back to a lower power level. Which power level is being used, depends of the functionality.

I remember reading this before and it doesn't really make sense to me. When a device 'uses' more power it draws more current. There is no switching involved. I have never left the iBase powered solely off the boiler because I am not sure if its up to supplying the necessary current.

 

[D_Hailsham]

I remember reading this before and it doesn't really make sense to me. When a device 'uses' more power it draws more current. There is no switching involved.

OpenTherm works by sending signals between the Master (iBase or wired iSense) and the Slave (boiler) and from slave to master.

Signals from Master to Slave are generated by switching between two closely defined voltage levels; those from Slave to Master by switching between two current levels. So there is a very sophisticated control system within both Master and Slave. The ability temporarily to provide a higher current to power the backlight is therefore quite feasible.

Looking at the OT Association's list of approved products it would appear that it may not be a change of PCB but a revised version of the software which provides SmartPower.

Here is a link to version 2.2 of the OpenTherm Protocol. The current version is version 3, but newer version are always backwards compatible to earlier versions.