What exactly IS chrono-proportional?

[PaulAH]

In my last post on thermostats (now buried) the question of thermo-proportional setting arose, courtesy CH4.

Danfoss describe it as an "energy saving" feature where the boiler is told to fire in cycles (3 or 6), thereby keeping the room at a more constant temperature.

But what exactly is going on here? Cycles of what? For how long and what period? In what conditions? At what temperature and what limits? Only on Tuesdays or bank holidays too?

And, more to the point, WHY? Turning the boiler on and off in bursts isn't my idea of fuel efficiency.

Could some kind soul explain what's behind all this? Thanks

Paul

 

[megawatt]

From the Danfoss programmers manual:

If the optional Chrono-proportional feature has been enabled, then the
heat emitters will be switched on at regular intervals to prevent the
large swings in room temperature caused by heat emitters alternating
between very hot and cold. In mild weather and when the system is up
to temperature the heat emitters wiil be switched on regularly but for
only short periods. This is not a fault, and will provide increased
comfort.

I agree with you ... Sounds like a right load of old moody to me ... Probably sells loads more programmers to unsuspecting gadget freaks though

 

[oilman]

Alright, I admit I don't really KNOW (do I ever?) but it's to do with temperature control algorithms (which you've probably come across) called PID (Proportional Integral Derivative).

If you have a thermostat which the boiler responds to, it will switch on as the temperature drops and switch off as the temperature rises. Analogue thermostats have that resistor that attempts to compensate for over/under shoots, but the temperature swings from the required temperature are still noticable. I often get people complaining their radiators keep going cold, surprise, surprise, the thermostat's telling them it's hot enough.

It's possible to get the temperature closer to the required set point, but wilh an oil boiler especially, it's either on or it's off, but giving it a number of sort of semi-premptive kicks the temperature is nuged a bit. The end result is that people COULD have their set point a bit lower than they might have otherwise. They don't because they want the house warm and as it gets warmer the humidity drops, they feel colder and so up goes the temperature. They will stop this in a few years when the fuel price gets much higher and they have to make economies.

For furthur reading you could look here

So chrono-proportional is varying mark:space ratio of the boiler's operation.

Here's another bit I found on diybanter

For me the Dataterm from WarmWorld is technically ahead of the Danfoss
controller (e.g. it looks back at last 5 days and uses fuzzy logic to
predict the future with a built in memory that learns the thermal
characteristics of your house/heating system. You set the temperature
you want at a particular time and Dataterm just does what it takes to
ensure that this is met winter, spring, summer, autumn).

Danfoss is a bigger company with everything that entails from that
(e.g. more customers, more marketing clout, better support?). But the
product does not seem as good, the Optimal Start will bring the
heating on up to 2 hours before the required time depending on ambient
temperature, but that's it. The chrono-proportional control cannot be
used if you have motorised valves.

 

[PaulAH]

Well if you two bugg$rs don't know I might as well look it up in the Bible.

Thank you for saying what I thought all along. It's either marketing hogwash or there is some sense behind it that only they understand and are not prepared to share with our pretty little heads.

...the product (Danfoss) does not seem as good, the Optimal Start will bring the heating on up to 2 hours before the required time depending on ambient temperature, but that's it.

This is all very odd. I've never noticed the heating coming on at any time other then when the stat kicks in as expected.

The chrono-proportional control cannot be used if you have motorised valves.

Wierder still. Are they saying the cycle is so short that it will switch off before the MV has travelled? Call for Prescott.

We still haven't got to the bottom of this - barely the middle. More investigation required. Thanks MW, Oilman, and his mate Proportional Integral Derivative Esq. I think I'll just swing the DIP to the on/off setting.

If you can find any more info I'd be grateful, as perhaps would all the others who didn't reply to this post.

EDIT: Just had a closer look at your link, Oilman. Some of the formulae test my creaky maths to beyond the limit but I get the broad picture.

It would seem a lot of this is designed to achieve critical temperature stability, such as you might need in a lab. But where does Danfoss's "energy efficiency" come into it?

 

[Agile]

I am surprised that no one has mentioned the controller which communicates with the met office and listens to the weather forecast.

It then provides heating according to the weather forecast to ensure the occupants have the most comfortable environment.

For example if a huricane is predicted it stands by to relight the pilot if it gets blown out by the high wind speed.

Tony

 

[PaulAH]

Does it have a Michael Fish filter?

 

[ChrisR]

Bit of a yawn, this. Boiler energy management systems have been trying to get it right for a lot longer than I can remember. I've been trying to get it right since modelling the output of a nuclear reactor 30 years ago - as controlled by lowering in the control rods, which has all sorts of other problems.
The idea IS to limit the overtemperature excursion ("wasted energy") and get the control as near as possible to "Critical Damping".
Go to the interactive demonstration on oilman's link page two, and click the graph. Then change the "Simulation Parameters" from ON/OFF to PID and you'll see the objective.

You get the ideal , "Critical" damping by applying heat as shown by the blue line at the bottom.
Trouble is, you can't DO IT with conventional boiler controls because they don't turn up and down, they ONLY go on and off.

So what you have to do is turn the boiler on and off rapidly - like if it's on for a minute, off for a minute that's half power, right? Yeah sure -
unless it's a Netaheat which takes a minute to light, then you're screwed, or -
similar sort of problem with the motorised valve, though in practice they often stay in the position where they were last used (makes another long post) so it isn't such a problem. Or,-
the boiler takes a while to ramp up, get warm or whatever, and also will keep putting energy into the system after you've turned it off.

The answer doesn't lie in conventional controls but in modulating boilers. They OUGHT to know what their own parameters are, can "learn" to refine them anyway, and can be made to react to changing temperature readings coming from sensors in the house, with a varying heat output. They can learn the response of the house with changing outside temp, and all that. Some are going that way (WB for one, there must be others) but nowhere near as fast or as loudly as I would have expected. I daresay before long this sort of proportional feedback will be mandatory under the building regs.

For anyone who doesn't understand what the hell this is all about, try flying the helicopter round the obstacles in "Chopper 2", 8 down the list, here:
http://www.trustedtradesmen.com/forum/arcade/arcade.asp
You don't have proportional control, only on/off. By clicking the mouse constantly you can get a horizontal-ish flight, but when you go round an obstacle you have to go early and control the overshoot...

 

[oilman]

Well if you two bugg$rs don't know I might as well look it up in the Bible.

Then you can have any meaning you want, for anything

Thank you for saying what I thought all along. It's either marketing hogwash or there is some sense behind it that only they understand and are not prepared to share with our pretty little heads.

Your thoughts were correct then, well done. As for your pretty (cough) little (cough, cough) head, most people can't understand the technical background to making a light work, what's the point of going into detail that the manufacturers technical help line can't understand. Certainly most plumbers don't understand it.

...the product (Danfoss) does not seem as good, the Optimal Start will bring the heating on up to 2 hours before the required time depending on ambient temperature, but that's it.

This is all very odd. I've never noticed the heating coming on at any time other then when the stat kicks in as expected.

Perhaps you could have it set up by an expert when you get your boiler done.

The chrono-proportional control cannot be used if you have motorised valves.

Wierder still. Are they saying the cycle is so short that it will switch off before the MV has travelled? Call for Prescott.

He doesn't know, you may have a parameter you can alter. Call for an expert.

We still haven't got to the bottom of this - barely the middle. More investigation required. Thanks MW, Oilman, and his mate Proportional Integral Derivative Esq. I think I'll just swing the DIP to the on/off setting.

If you can find any more info I'd be grateful, as perhaps would all the others who didn't reply to this post.

I see you've had a session with the bottle again.

EDIT: Just had a closer look at your link, Oilman. Some of the formulae test my creaky maths to beyond the limit but I get the broad picture.

It would seem a lot of this is designed to achieve critical temperature stability, such as you might need in a lab. But where does Danfoss's "energy efficiency" come into it?

Go back to my earlier post when the alcohol has worn off.

 

[PEDANTICVINDICTIVEMAN]

Do we actually need to understand it to use it, it's like having to know the constituants of natural gas, why, if it dont come in from the street the right mix there is fek all I can do about it.

 

[PaulAH]

Alright, I admit I don't really KNOW

Certainly most plumbers don't understand it.

detail that the manufacturers technical help line can't understand

Call for an expert.

And you chide me for asking? Who is this 'expert'? Forget booze - you must wean yourself off the grumpy pills.

If my questions are stupid, or you think I'm incapable of understanding the answers, then by all means say so.

I thought that by raising this issue, others who have scratched their heads at chrono-proportional - and there must be quite a few - might welcome an explanation too.

Thank you ChrisR and Oilman for having a stab at it. But it still doesn't answer the very real question of what settings 3 and 6 mean. There's a hint in the literature where it denotes "cycles per hour". It also says

ON/OFF - boiler switches ON when below set temperature and OFF when above.
CHRONO - energy saving feature which fires the boiler at regular intervals to maintain a set temperature, achieving a constant ambient environment for the user.
- use 6 Cycles for radiator systems
- use 3 Cycles for underfloor heating

The trouble is, when mine is set to chrono-proportional it behaves in every way as if it was in on/off mode but with a very small hysteresis, which doen't match the description above. I needed to understand what was going on in order to build a case for sending the thing back.

Yes Chris, it's a yawn but please don't spank me for asking (not you; The virtuoil entity).

Paul

 

[Agile]

That controler is just making a somewhat feeble attempt to give a modulating effect to boilers which dont modulate like the early Kestons.

The technique is called "pulse width modulation". It was famously used by Clive Sinclair to produce an audio amplifier which would give lots of watts of audio power with a tiny amplifier. It was technically a perfectly sound principle but like all his other inventions it failed to deliver. ( Remember the C5 ? )

A simple explanation of the principle is to obtain 15 kw for a 30 kW boiler by switching it on for a minute and then off for a minute so it is on for half the time. Integrating the heat output using the long thermal time constant of the radiators you then get 15 kW.

By varying the proportion of " on" to "off" times any power output can be obtained between 0 and 30 kW. It still has an application for indutrial heating but is largely superceeded for domestic applications because most boilers are now condensing and give smooth analogue power output control.

Tony Glazier

 

[oilman]

So you've got a duffy and need an excuse to get rid of it. As I read your original question, most of the info to answer is in my first post, which seems to have met resistance and given rise to some derision, you then quote parts several of my sentences completely out of context. ChrisR and Agile have also divulged relevant information.

The best people to resolve your problem is the manufacturers, as with your previous problem.

And you chide me for asking? Who is this 'expert'? Forget booze - you must wean yourself off the grumpy pills.

If my questions are stupid, or you think I'm incapable of understanding the answers, then by all means say so

For this sort of stuff, I think the right move would be to start a topic on the General Chat forum.

 

[PaulAH]

That seems to be the case, Tony (rough analogy might be a slow version of AC waveform chopping, right?). If so, it beats me what this "6 cycles per hour" means.

No resistance, Oilman. I read it and was grateful. But "six cycles per hour..."

 

[oilman]

According to the Honeywell blurb, 6 is ok for gas boilers, and 3-4 for oil boilers as their time constant is longer. Though it's all a bit iffy when the boiler gives out so much heat it is always switching on its control stat.

 

[CH4]

Paul,

As mentioned above, your thermostat's Chrono-Proportional control simply adjusts the duty cycle (On to Off ratio) of the boiler, in proportion to the heating demand. The period of the duty cycle is set to 10 or 20 minutes with DIP switch 3.

I do not know the actual parameters used by Danfoss, but a simplified algorithm might be something like this:

• When the room temperature is 2°C or more below set temperature, the boiler duty cycle would be 100% (continuously on)
• When the room temperature is 1.5°C to < 2°C below set temperature, the boiler duty cycle could be 75% (7.5 minutes on, 2.5 minutes off)
• When the room temperature is 1°C to < 1.5°C below set temperature, the boiler duty cycle could be 50% (5 minutes on, 5 minutes off)
• When the room temperature could be 0.5°C to <1°C below set temperature, the boiler duty cycle could be 25% (2.5 minutes on, 7.5 minutes off)
• When the room temperature is at or above set temperature, the boiler duty cycle would be 0% (continuously off)

NB the above figures are made-up and for the 6 cycles per hour setting (a period of 10 minutes).

A better algorithm would take into account any temperature changes between consecutive cycles, and adjust the duty cycle accordingly. If done well, temperature overshoot and undershoot could be all but eliminated, achieving near constant room temperature and improving the heating efficiency (as maximum heat loss occurs during periods of overshoot, when the inside to outside temperature difference is greatest).

Your thermostat is designed for use in a domestic central heating system. Its Chrono-Proportional control is only intended as an improvement over simple On/Off control. Danfoss does not, therefore, need to go anywhere near very low duty cycles - except for 0% (Off), of course. So, if your thermostat is switching on and off rapidly, it has to be faulty.

John