Remeha boilers and Honeywell CM9XX thermostats

[ALEC1]

gosh these type of controls should not be used with conventional cast iron boilers or with modulating condensing boilers....great product honeywell....

why they don't just bring out the OT version that can only be used with an OT boiler beats me...

 

[D_Hailsham]

That maybe the case but the green light on receiver box would be on obviously due to power via terminal B , ie: MV or boiler powered.

You are assuming that the green light is connected directly to terminal B.

In laymens terms green light on reciever will always be on when flame signal is showing on CM controller , or in the case of the 907 MV/boiler will be powered. You have one so why not carry out some R&D.

Just done that

Result

CM927: Flame showing on controller - green light not showing on receiver. Boiler not lit.

 

[D_Hailsham]

Why would the wireless be any different to the wired? , whenever i've encountered the green light illuminated on reciever the boiler/MV are powered.

IF the wireless version worked exactly the same way as the wired, the transmitter would have to transmit continually and the receiver receive continually. This would reduce the battery life of the transmitter continually.

By separating the functions, all the transmitter has to do is send a brief signal every time there is a change in requirements and leave it to the receiver to carry out the instructions.

 

[MJN]

It does seem odd that in the wireless version they split the control function between thermostat and receiver. They must have had some good reason.

In a wireless communications system there are benefits to be had by shifting some of the 'intelligence' from the transmitter to the receiver, most notably battery saving and resilience to communications failure.

In this case battery saving can be achieved by virtue of the transmitter only having to periodically send an update when a change in control strategy (duty cycle) is required. Thus, rather than sending an on and off signal every, say, 10 minutes it can simply tell the receiver to maintain a particular duty cycle until further notice. It thus simply has to transmit the particular parameters required (cycle length and duty cycle) and let the receiver do the rest (send the on/offs as required). Under steady state conditions once the control strategy is perfectly balancing the heat loss it could feasibly not have to send any update for hours at a time (chances are it'll repeat an instruction periodically however for reliability - see below).

The transmission of duty cycle instead of discrete on/offs also makes the system more resilient to transient communication failures because little will change if it simply misses a duty cycle update (given the parameters won't be changing significantly each time ie. there usually isn't a step change in duty cycle given the reduced under/overshoot of TPI) whereas with a simple on/off transmission if it missed one of these then the boiler will be left on or off until the next transmission is made (and received).

Such a shift of intelligence to the receiver in a wireless system also easily allows other functionality such as 'if you don't hear from me at all in a 24 hour period then assume I've run out of battery or other serious problem so maintain a duty cycle of x in case of frost, or just exercise the pump every so often', for example.

Mathew

[Apologies D_Hailsham, didn't read your post where in part you'd pretty much said the same thing but as I've typed this post on my phone I'll be damned if I'm deleting it now!! ]

 

[D_Hailsham]

Just carried out another experiment.

I set the target temperature to 25C, well above the current value, so the boiler would run continuously. The fan started at 25 and then dropped to 13 (min output) it took about six minutes for the speed to increase to 35 (max output). The flow temperature had risen in that time from about 45C to 60C (max 70C).

Obviously if the duty cycle is only asking for the boiler to be on for one minute out of 10, the boiler will be running at near minimum output for that times, so instead of providing 1.8kW over 10 minutes it would have provided about 0.6kW, a third of what was expected. The effect of this is that, once the system enters the proportional band, it will take longer to actually achieve the target temperature.

 

[D_Hailsham]

Only observation by comparing the OT version with the on-off version . Compensation controllers have the same TPI logic as the 9xx versions but send different signals...so there is a difference in the signal, one asks for temperature the other sends an on-off signal..

Perhaps I was over enthusiastic in the use of the word "same"

Maybe you are correct after all.

I have a Honeywell FAQ sheet on Opentherm (It doesn't seem to be available anymore.) which says:

An example would be to replace a wireless ... programmable room thermostat ... , such as a Honeywell CM927, with a similar CM957. In fact, both are wireless and the thermostat part would be exactly the same, just the wireless receiver would be different.

This only applies to the latest version of the CM927, which is supplied with the BDR91 receiver. The earlier versions with the HC60NG are one-way communication - the stat transmits and the receiver receives. The version with the BDR91 is two way communication.

I did email Honeywell about a year ago asking why the Opentherm versions were not available. They replied saying it was because they were not suitable for the two-zone requirements laid down by Building Regs! They have now produced the Evohome system which covers multiple zones with or without Opentherm.

 

[Dan Robinson]

Plus there is the two zone controller.

There are also multiple versions of the BDR box. Some are not fully forwardly compatible.

 

[D_Hailsham]

Plus there is the two zone controller.

Are you thinking of the Sundial RF2 Pack 5? If so, that is not Opentherm, it's TPI/On-off.

There are also multiple versions of the BDR box. Some are not fully forwardly compatible.

I know about the HC60NG, originally used with the CM67 and in the original version of the CM92X, which was replaced by the BDR91 on the current CM92X. I didn't know there are several versions of the BDR91. Do you have any info, links etc?

 

[Dan Robinson]

Are you thinking of the Sundial RF2 Pack 5? If so, that is not Opentherm, it's TPI/On-off.

I didn't know there are several versions of the BDR91. Do you have any info, links etc?

I don't make this stuff up you know

Not only have i fitted pack 5's (and was given a write up in PHAM about it )

There is a firking great bit OT logo on the first page of the manual.

I also have Evolution Home running HR80uk valves off an unvented thermal store using the EH as the store controller. Honeywell said it couldn't do it - but it does a very good job.

Next stage is to try and implement OT and weather ccomp into the TS system


As for different BDR's.... it is not a published thing. But newer ones have different software to enable tighter 2-way communication amongst other things.

 

[D_Hailsham]

There is a firking great bit OT logo on the first page of the manual.

Thanks for putting me right. I see it's a wired OT connection to the boiler, though they also suggest you contact Tech Support if you want to have a wireless OT connection.

Things are looking up, though I do wonder why they have not incorporated OT connectivity in the other Packs.

As for different BDR's.... it is not a published thing. But newer ones have different software to enable tighter 2-way communication amongst other things.

Thanks. A quick search found that CM92X uses the BDR91 and Evohome uses the BDR91A. Sundial Packs can use the BDR91T if remote boiler control is required.

 

[ALEC1]

I do wonder why they have not incorporated OT connectivity in the other Packs

It would be tempting to say that they don't understand the benefits of OT..but I am sure thats not the case...

the truth is that the manufacturers use the regs to determine what to sell or not...to honeywell we are a market only...as long as they make money it matters not one iota what they sell..

until the rule writers wake up and smell the coffee I am afraid we are stuck with an antiquated way of controlling heating...unless of course you use boiler manufactures controls...

 

[mysteryman]

... which are so easy and so effective.

 

[MJN]

...and pricey, not to mention severely limited in choice.

The sooner OT, or similar, becomes the de facto standard and ubiquitous the sooner we can cut the monopolising and allow natural market competition to produce the most effective, in terms of capability, usability and cost - products for installers and consumers to choose from.

Perhaps it is unfair to pin the blame solely on the manufacturers; there is afterall a whole generation of fitters who's understanding of technology options stretches little beyond bimetallic stats and who think that weather compensation is something the government pay out if we don't get a barbecue summer.

Mathew

 

[ALEC1]

the manufacturers do little to promote the technology, so it is the manufacturers who must carry the can on this one...

 

[ALEC1]

on the behest of boiler manufacturers, OT on boilers has been dropped as a requirement by th EU...

boilers do though have to accept compensation controls...opening the way for another monopoly...

Honeywell runs a very active PR campaign...promoting the use of on-off thermostats..so much so that all the reports that guide the government never mention compensation controls...