Honeywell CM927 - Optimised Start

[Chris_J]

Does anyone have one of these units? I've had mine for about 2 weeks now and it works great, except I've noticed the optimised start feature often causes the heating to come on very early. In the manual, it states it will adjust this accordingly, dependent on the current temperature in the room, but will limit it to 2 hours maximum.

It is programmed to be at 18C for 6:30am, but I often hear it firing it up at 4:30am (the maximum 2 hours). I've walked down stairs a few times early hours of the morning before the heating comes on and glanced at the temp on the display. The lowest I've ever seen it was 15.5C and that was a particularly cold morning.

As a result, the house will get up to 18C in about 30-45min, since normally overnight temps will only drop to around 16-17C so the rest of the time the stat is just flicking on and off to keep it at 18C.

Will the unit learn how long it needs to increase the room temp, or should I just switch the optimisation off?

 

[D_Hailsham]

There are six time/temperature settings per day on this stat. Optimization works for the first time/temp setting. The sixth setting normally determines the overnight temperature, e.g 2300 hrs 10°C. If you have the overnight temperature set to, say, 16°C and the temp drops below this, the boiler will come on in the middle of the night to maintain the overnight temperature. If this is the case, drop the setting to say 5°C, the problem will go away and the optimization will work as it should.

 

[Chris_J]

Thanks for your reply.

My overnight temperature is set at 10C. It's definately is not going under this and coming on. It comes on exactly 2hs before the programmed temperature, but only takes 45 minutes to get it to the programmed temperature.

I've heared that the CM927 actually learns the efficiency of your particular heating system by working out how long it typically takes to increase the room temperature by 1C, then calculates the time it needs to increase the temperature to the required amount. Not sure how true this is, as Honeywell don't mention it.

Are you sure it only optimises the first temperature in the programme?

 

[D_Hailsham]

My overnight temperature is set at 10C. It's definately is not going under this and coming on. It comes on exactly 2hs before the programmed temperature, but only takes 45 minutes to get it to the programmed temperature.

So that can't be the cause!

I've heared that the CM927 actually learns the efficiency of your particular heating system by working out how long it typically takes to increase the room temperature by 1C, then calculates the time it needs to increase the temperature to the required amount.

How exactly the system works is not divulged by Honeywell; though a trawl through the online European Patent Database may reveal the necessary info.

Is your thermostat near a radiator so it gets false info as to the temperature? As you have the wireless version it might be worthwhile experimenting with different locations.

Have you checked the temperature against another thermometer?

Are you sure it only optimises the first temperature in the programme?

Not 100% certain, but I don't see how it can be otherwise. What happens if you set the temp to 21C at 0700 (get up) and then to 15C at 0830 (leave for work). The boiler will go on at, say 0600, to bring the house up to 21C and then turn off again to allow the house to cool down to 18 by 0830. Somehow, I don't think so! I suspect that the boiler will maintain the temperature at 21C until 0830 and then go off until the temperature has dropped to 15C, at which point it will start to maintain the temp at 15C. If you then set it to go up to 21C at 1830 (return from work), the optimizer may come into play, but I can't quote chapter and verse.

 

[martyc]

I have one of these T-stats aswell (actually its the CM921...the same except 1 day not 7)
Anyway if i remember correctly it states in the instructions that the optimum start is only for the first setting of the day.
I have not enabled the OS though so cannot comment whether or not it "learns" how quickly your house heats.

I am pretty sure though that the instructions only say that the heating comes on earlier depending on the actual temperature @ the sensor which leads me to believe that it is "not intelligent" and simply has a few settings hardcoded into it telling it when to fire the boiler up based on a combination of actual temp/target temp
Marty.

 

[Chris_J]

Is your thermostat near a radiator so it gets false info as to the temperature? As you have the wireless version it might be worthwhile experimenting with different locations.

Have you checked the temperature against another thermometer?

Thermostat is located in the hallway, opposite a radiator and as far away as possible from it. The radiator seems to heat the hall at almost the same rate at which it heats the other rooms. So when my thermometer in the living room reads ~21C, the stat just lags behind slightly at say 20.5C. It was the best place I could locate it really. Didn't want it in the living room, as I have a wood burner in there.

Not 100% certain, but I don't see how it can be otherwise. What happens if you set the temp to 21C at 0700 (get up) and then to 15C at 0830 (leave for work). The boiler will go on at, say 0600, to bring the house up to 21C and then turn off again to allow the house to cool down to 18 by 0830. Somehow, I don't think so! I suspect that the boiler will maintain the temperature at 21C until 0830 and then go off until the temperature has dropped to 15C, at which point it will start to maintain the temp at 15C. If you then set it to go up to 21C at 1830 (return from work), the optimizer may come into play, but I can't quote chapter and verse.

You're right in what you say there. The optimising system only functions during a temperature increase. Where you have programmed a temperature decrease, i.e 15C for when you leave work at 8:00, it will switch off at 8:00 and not try to get it at 15C for 8:00, which would be silly.
However, at the next temperature increase, i.e for when you return from work, I think it will optimse that one.

Sounds like it doesn't learn then and as martyc says, just has presets for particular room temps. Darn.

 

[D_Hailsham]

a trawl through the online European Patent Database may reveal the necessary info.

Are you sure it only optimises the first temperature in the programme?

Not 100% certain, but I don't see how it can be otherwise. What happens if you set the temp to 21C at 0700 (get up) and then to 15C at 0830 (leave for work). The boiler will go on at, say 0600, to bring the house up to 21C and then turn off again to allow the house to cool down to 18 by 0830. Somehow, I don't think so! I suspect that the boiler will maintain the temperature at 21C until 0830 and then go off until the temperature has dropped to 15C, at which point it will start to maintain the temp at 15C. If you then set it to go up to 21C at 1830 (return from work), the optimizer may come into play, but I can't quote chapter and verse.

Just done a Patent Trawl Honeywell filed a patent in 1996 for "A thermostat system having an optimized temperature recovery ramp rate". Reading through it says that, while the technique could be used for cooling, the main field of use is for heating up a spce so it reaches the required temperature whenthe space will start being occupied, e.g. office blocks. It relies on learning how quickly the space gains and looses heat.

The CM927 has a reset facility, which clears everything, presumably including what it has learned. It might be worth resetting the programmer and then inputting the time/temp data again. Start from fresh!

 

[D_Hailsham]

comes on earlier depending on the actual temperature @ the sensor which leads me to believe that it is "not intelligent" and simply has a few settings hardcoded into it telling it when to fire the boiler up based on a combination of actual temp/target temp
Marty.

The Honeywell literature says:

The thermostat will adjust the start time in the
morning/afternoon so the desired temperature is
reached by the start of the program period e.g. Time
7:00, Temp 21 oC. The thermostat will monitor the
accuracy of the start up and use this information to
modify the calculation for the following day by changing
the ramp rate (initial 3 K/hr) .The system will restrict the
start time to a max of 2 hours.
Note: Optimisation will not work in cooling mode.

 

[Chris_J]

I was thinking about resetting it to let it re-learn, but didn't want to have to re-programme it again! (I'm a lazy ar5e). I wonder if removing the batteries would do it?

Going off your second post, it sounds like the stat doesn't actually learn, but bases it on the previous day's accuracy.

What you think, shall I start fresh?

 

[martyc]

D_hailsham,
I have read what you posted there before..most likely on honeywells site,but it does not say that on the literature that comes with the stat.
It says..............

This is an energy efficiency system that adjusts the start time of your system depending upon how cold it is. Eg on cold days your system will be started earlier and on warm days your system will be started later to save energy

(that was page 14 of user manual)


And then on page 8 of installation guide
the thermostat will adjust the start time in the morning so the desired temperature is reached by the start of the program period.The system will restrict the start time by a max of 2 hours.


I had also read the blurb before i bought mine about how it "learns" how its environment reacts etc etc...however there is NO mention of this in the literature that comes with it which leads me to believe its all bull!!

Im sure they have the technology(not exactly rocket science)...but I really dont think it comes with the CM900 series for the reasons stated above.
Ill do another quick scan of the literature though in case im wrong.
marty

 

[D_Hailsham]

I was thinking about resetting it to let it re-learn, but didn't want to have to re-programme it again! (I'm a lazy a**e). I wonder if removing the batteries would do it?

Going off your second post, it sounds like the stat doesn't actually learn, but bases it on the previous day's accuracy.

What you think, shall I start fresh?

Removing the batteries should clear the stat, but how is that different from using the reset option in the programming menu?

Don't forget that, once you have set up one day, you can copy that to all the other days of the week. You can also disable time settings if you only need on or two a day.

I think the stat is a bit more sophisticated than just basing today's setiings on yesterday's. In one leaflet they talk about "fuzzy logic programming". I presume that means it keeps on adjusting the "ramp rate" until it gets it right.

 

[Chris_J]

I thought if you remove the batteries, it would reset everything except the user program. A factory reset would wipe the whole thing, including all the installer parameters.

If it's always recalculating, it should eventually tune itself to it's environment. I'll try resetting it anyway...

 

[martyc]

Right,ive read the CM900 literature again cover to cover...and no mention of learning/intelligence/fuzzy logic whatsoever...just what i said in my last post.

I googled the text that D_Hailsham posted above and it is on the manual for the CM61 and the cm907
here
http://www.honeywell.be/DocsAdobePDF/EN/Chronotherm/CM61_pd.pdf
Page 4
And here
http://europe.hbc.honeywell.com/products/pdf/en0h8547uk07r0906.pdf
Page 4 also......

They call it
"Optimisation(variable start time)
adaptive intelligence recovery"

And give a nice explanation as per D_hailshams earlier post

However there is a slightly different text on the CM927 literature and im pretty sure it was changed for a reason.....

Have a look here its the 927 blurb...page 4
http://europe.hbc.honeywell.com/finland/pdf/en0h8556uk07r1006.pdf

they just call it optimisation and no mention of intelligence or ramp rates etc....
This is not a coincidence...the 927 does NOT have this technology.

I must say when i got mine i was disappointed that i could not find any blurb on it as i was certain it had this technology...how as ever its a class piece of kit!!

Marty.

 

[Chris_J]

I did hear stories of the CM927 predecessor (CM67) having an even worse optimisation function - sometimes making the heating come on up to 4hrs before the set time.

So maybe Honeywell got rid of the crazy fuzzy learning function for good reason, as I guess it didn't work.

Having said that, your searches prove it is present in the CM907. Maybe it's more relevant for a single day programmer..?

Anyhow, I've reset the unit and programmed it back up for morning. See how it goes eh.

Thanks for all your very useful input!

 

[martyc]

Do let us know...be interested to see how you get on.
Marty.