What exactly IS chrono-proportional?

[PaulAH]

John, you've made history. This is the first clear working description of chrono-proportional on this site (and, as far as I've managed to search, the www). Thank you.

Moral of the story: Mine's a duffer.

Paul

 

[meldrew's_mate]

At the risk of going over old ground Chrono-proportional is their attempt to use some of the control facilities long used in industrial process control into domestic environments.

A typical domestic heating system uses ON-OFF action.
Control of the floor temperature on the Warm-up brand of UFH is via time proportioned modulation i.e it takes a nominal time period of ,say, 10 minutes. It turns the heating element on for 2 minutes, off for 8, on for 2, etc to give 20% output. Another way to achieve this in electrical heating is phase angle modulation where the current is switched on for only a proportion of its cycle (of which there are 50 per second), clearly too short a period for gas boilers!
Integral action adds to (or subtracts from) the proportional action subject to the temperature error from set-point relative to the length of time the error has been present. It is not used in domestic controls, though I suspect it is integrated (no pun intended) into the control algorithms for some burner modulators judging by their tendancy to overshoot.
Derivative action works on the rate of change of error wrt time, again it's not used domestically.

Proportional action IS a great step forward in controlling domestic comfort levels, though chrono-proportional methods do seem rather crude when we all know a boiler PCB's life is just about limited to a certain number of boiler starts, and most modern ones have gas burner modulaton. Much better IMO to use the control outputs to alter the boiler flow temperature in response to demand, i.e 5 degC below set-point = 70 deg C flow temp; 1 deg C below = 60 deg C flow; 3 deg C above set-point = 50 deg C etc..

There are the rudiments of such a development on the Keston C40 where the CH and HW demands have seperate flow temperatures (not 2-step control), so they are almost ready to have the front panel knob replaced by an external contol signal. External signals from ext. air sensors, or even Michael Fish forecasts can obviously become integrated, but there is still the challenge of making the customer feel in control! (There is a heating system in a foreign ambassador's residence in London that is controlled remotely from the Motherland )

Domestic controls still have a long way to go to even approach those commonplace in industry, the technology is there, the challenge is to make it desireable by the user and maintainable by the plumbers and heating technicians in the field. (Engineers will be fully conversant with PID (3-term) control already). Control Engineering is a seperate subject in its own right, using lots of crazy maths and squiggly symbols, it'll get more and more into boilers so get ready to embrace it.

lots of love and hugs.....MM

 

[PEDANTICVINDICTIVEMAN]

Fitted a fancy all singing dancing system at a customers request once, when finished I asked what settings he wanted and he said, "on and off twice a day will do"

 

[PaulAH]

Another historic moment from Colleague of Meldrew (and I DOOO believe it).

One other thing:

a boiler PCB's life is just about limited to a certain number of boiler starts

Is this really so? How dreadful. A PCB with solid-state components should last indefinitely. What goes on here?

But PVM also hits the button. An aunt of mine had new central heating installed and said: "It's wonderful. It gets so hot I have to open the windows".

 

[meldrew's_mate]

a boiler PCB's life is just about limited to a certain number of boiler starts

Is this really so? How dreadful. A PCB with solid-state components should last indefinitely. What goes on here?

Sadly it also has relays, coils, inductors, spark generators, all of which suffer from mechanical wear or electrical stress (dielectric, etc) or a combination of.

 

[Joatbmon]

I am new to this lot, so hope i'm doing it right.

Dataterm from WarmWorld is technically ahead of the Danfoss
controller (e.g. it looks back at last 5 days and uses fuzzy logic

The Dataterm unit is phenomenally expensive (£360 inc stat and JB) compared with the Danfoss unit, is it really worth it? and are there any other options. I like the idea of separate stat.

Bill

 

[AndrewFalkous]

If useful, this is my response today from Danfoss about the Chrono-proportional function on units such as the TP5000 Si:

------------------------------

When set to chrono-proportional control the thermostat works out a load
percentage when the room temperature is below and within 2 DEG C of the
set temperature.


For example: 100% load equates to a 2 DEG C difference. 50% load equates
to a 1 DEG C difference. 25% load equates to a 1/2 DEG C difference.


It then fires the boiler to achieve 6 cycles per hour based upon the
load percentage.


For example 50% load means that the boiler is fired for 5 minutes and
then kept off for 5 minutes. 25% load means that the boiler is fired for
2.5 minutes and then kept off for 7.5 minutes.


The thermostat recalculates once every minute.


It is possible to deactivate the chrono-proportional control function in
which case the thermostat controls using on/off control with a 1 DEG C
differential.

Some notes comparing chrono-proportional control and on/off control are
attached.

The display can either show the time and to the right in small digits
the required room temperature or it can shown the actual room
temperature in large digits and to the right in small digits the
required room temperature. To switch between the displays you press the
+ and - buttons together. When the display shows the actual room
temperature it is updated every 1 minute. The unit will take some time
to respond to a sudden change in room temperature due to thermal
inertia.


Best Regards

Adrian Wynn

--
Danfoss Randall Ltd.

 

[AndrewFalkous]

If anyone is interested, Danfoss have also sent me a white paper entitled "Domestic Heating Energy Savings with Better Controls" from October 2007.

------------------------------------------------------------

Abstract is as follows: This paper presents results of system testing with 3 different domestic gas boilers (noncondensing, condensing and modulating-condensing) and 3 methods of room thermostatic controller (mechanical bellows, electronic on/off and electronic proportional-integral control). The results of measurements of energy consumption (gas and electricity), carbon emissions and comfort level are presented from tests in a controlled laboratory “test house”. The results suggest significant efficiency benefits can be obtained with the change of a controller from a simple mechanical type to a more sophisticated electronic product. In addition many of the efficiency benefits available from a high efficiency condensing boiler are lost if the controls are not updated to optimise the boiler performance.
The energy consumption of a domestic heating system may be reduced by over 10%, with a similar reduction in carbon dioxide emissions, if the room controls are capable of operating the boiler in its most
efficient mode.

------------------------------------------------------------

This paper has more explanation of Chrono-Proportional control. Can't find this document on Danfoss' website. It has some mroe technical stuff in there with some graphs and tables.
If you want me to send it to you, give me a shout.