Programmable Room Thermostat Optimum Start

[James_H]

I am going to change my ordinary mechanical stat for for one of these. I have acquired a Sunvic TLX6501 although it is relatively crude and doesn't have as much functionality as I would have liked (the instructions for the TLX6501 on Sunvic's website are for a more sophisticated model but with the same name). The Sunvic has optimum start on the first 'comfort' switch-on of the day.

However, the Honeywell CM67 seems the be the 'daddy' of programmable thermostats with enough set-points and features such as holiday, party and day off buttons, although they seem to be in the £50 to £60 range. It seems well recommended on here.

Does anyone know whether the CM67 optimum start operates on all higher temperature periods or just the first one of the day?

How does the CM67 determine when to start the heating? Does it start a fixed amount of time earlier dependent on the difference between current and required temperature or would it learn how long my system takes to heat up? I can't see anything in the installer guide on Honeywell's website.

After doing a forum search, I found someone said that they disable the optimum start feature on a lot of their installations as a lot of people find is disconcerting or they are sitting in the cold while the stat thinks no heat is needed (I can't find the post now). I can't see a reason for this. If people are cold then surely the time settings are wrong? The primary reason for a programmable stat in my opinion is comfort, with little to be made in efficiency savings (or the reverse). Surely the room stat should, on most days, just provide a set and forget operation where you let it do the job and the house is warm when you have set it to be.

Then again, I'm sure many people in general don't understand the principle of a thermostat, turning it up and down unneccesarily. I moved the limit pegs when in a houseshare, to stop a housemate upping it to 25 degrees because he was cold. The reason for it being cold was that the house would only about 18 and still warming up!


Thanks,

James

 

[wilhelm]

i think you might need the other bit, for it to work.

 

[kevplumb]

wot the boiler

 

[wilhelm]

 

[kevplumb]

alright marra

 

[wilhelm]

aye, but tonight mathew i will mostly be on 14% vol

 

[kevplumb]

wimp get on the 40 mate somebodys putting water in your tank

 

[James_H]

Willhelm, what do you mean by 'other bit'?

I'm going for the hard-wired CM67, not the wireless CM67 RF if you were thinking about the relay box. In particular, the T66671085 is the optimum start hard-wired version (replaicing 85 by 69 gives the non-optimum start model).

The add-ons for the CM67 are:
1. An automatic time set
2. Outside temperature sensor
3. Remote temperature sensor
2 is for display only and for me dealt with by my Oregon weather station in the same room. I'm happy to set the time myself, not needing 1, although the Oregon uses the same Rugby time signal for accuracy. 3 is hardwired and just means turning the heating on/off according to the temperature somewhere else, not at the CM67. You can't have 3 and 2 together.

Not sure what I'm mssing here.

 

[wilhelm]

well, you started with acquired tlx......etc
you didnt say you had put it in the bin.

 

[wilhelm]

ahh. i have just found out what an oregon wx station is.

and i just put on an extra fleece.

 

[ChrisR]

Does anyone know whether the CM67 optimum start operates on all higher temperature periods or just the first one of the day?

All.

How does the CM67 determine when to start the heating?

It learns from the response of the house to the On periods.

Does it start a fixed amount of time earlier dependent on the difference between current and required temperature

No

or would it learn how long my system takes to heat up?

It learns total response. Dependency is on the proportonal, integral, and differential differences in temperature over the learning period. Also known as PID control or 3 term control, standard control engineering stuff.

I can't see anything in the installer guide on Honeywell's website.

Not surprising, its A level/Uni level calculus. Incongrous in an instruction sheet. Easy when you know how it works.

The object of it all is to get the house to the required temp at the required time without overshooting. Sometimes while the house is still getting hotter the heating would be off and perplex the uninitiated. But if it was on UNTIL the house was up to temp, there would be an inefficient overshoot.

If you feel cold you got the times/temperatures wrong!

 

[James_H]

Willhelm, sorry to confuse. My reference to the Sunvic was just was just because I wanted something better and there's no financial loss from replacing it.

ChrisR, thanks, that's what I wanted to hear.

I agree that the full technical gubbins will go over the heads of most users/installers but them simply stating that it learns how much to heat by would be sufficient.

Thanks, an online visit to RKM is on the cards now.

 

[croydoncorgi]

As a matter of interest, what was the price difference between the 'optimum start' type and the all-bells-and-whistles version?

The problem with outside temp sensors in most systems is how to connect them effectively. The easiest way to compensate for low outside temperature is to increase the temp of the rads. In the case of BOILERS with outside temp sensors (there are some), the effect is just to increase the Flow temperature a bit. But making an optimum start room thermostat that also factors-in changes in outside temperature WITHOUT raising the boiler temperature sounds 'quite challenging' and no doubt results in lots of extra ££££ in the price.