In an earlier contribution to this discussion,
Andy Hall wrote:



http://content.honeywell.com/uk/homes/files/pag113.pdf

http://tinyurl.com/2yc23


If you look at Adaptive Intelligent Recovery, it is basically doing
what you describe in your third point - i.e. if you turn that feature
on, the controller measures the rate of rise of temperature and uses
it to calculate the next heating period's start time also accounting
for the starting temperature. This is a relatively simple
controller, so it appears that it only does this session by session.
A really intelligent controller would store the temperature points by
time over more days because the rate of change of temperature is not
absolutely linear, although it is to a first approximation. Hence
the method used is a lot better than doing nothing at all.
All of that has to do with optimised starting.

The proportional band has to do with the behaviour of the controller
(it is a proportional plus integral controller)

Proportional control is that the heat contribution over a period of
time is adjusted to match the heat loss and maintain the temperature
accurately. There are controllers that will do this in a genuinely
analogue way by modulating the boiler output to match the requirement.

However, many boilers can only be controlled in an on/off fashion aand
indeed this is also true of most zone valves if you were using that as
a means of control. In order to control this type of device, the
controller does so by using time proportions. A simple example
might be that if you want 50% of the average output, the boiler is
turned on for 5 minutes and off for 5 minutes. For 80%, it would be
on for 8 and off for 2.

The CM67 does this but allows some additional settings.

- There is an cycle rate setting of 3,6,9,12 cycles per hour. If the
entity being controlled can react quickly without any disadvantages
(e.g. if you were controlling electric heating), then you could set 12
cycles per hour. At the other extreme, devices that show
inefficiency or might have other problems if cycled too frequently
would be run at three cycles per hour. In between you have typical
gas heating, which is run at 6 cycles/hour i.e. cycles last ten
minutes. So the behaviour would be as in my example above.
Note that the minimum on time is set to 1 minute, which in effect will
be 10%.


- Proportional bandwidth is the temperature range about the set point
where proportional control operates. Within this range, the
controller operates in this cycling mode. Below it, the output will
always be on and above it will always be off.

Adjustment for this will depend on the heating system and thermal
inertia of the house. Ideally what you want to have happen, is that
when starting from cold, if the current temperature is below the
proportional lower limit, then the optimisation should time operation
to fire the boiler at 100%. However, as the temperature rises into
the proportional band, the cycling control should begin to take
effect. If possible, you want to avoid the temperature overshooting
above the proportional band because a) you use more energy than needed
and b) the temperature may tend to oscillate for a long time before
settling. This is most likely to happen in well insulated properties
with oversized heating. It is really a trade off between achieving
the set point quickly and not overshooting.
On this controller, you can vary the proportional bandwidth to help
with that, in that it will enter cycling operation earlier on the rise
and begin backing off the average heat output of the system.

The proportional bandwidth may be taken into account in the optimised
start. That's not clear.

The best thing to do is to check the temperature rise behaviour by
recording temperature readings (say) every ten minutes during start up
for a few days. Plot a graph if you like.
You can then experiment with proportional bandwidth if needed.




.andy

To email, substitute .nospam with .gl


Many thanks for your very full asnwer, Andy - and for the links. My CM67 is
the hard-wired rather than RF model, and the leaflet which came with it is
slightly different. The "Adaptive Intelligent Recovery" section in the RF
model leaflet does say fairly explicitly that it uses the start-up
performance this time around to decide what to do next time. My leaflet is a
lot less explicit. Its equivalent paragraph is entitled "Optimisation
(Variable Start Time)" and says:
"The Programmable Thermostat will delay the start time to the last possible
moment, so that the desired temperature is reached by the start of the
program (sic) period. Simply set the times at which you would like to be
warm and the Programmable Thermostat will switch on when required up to a
maximum of 3 hours early."

I assume that the hard-wired version works in the same way as the RF version
in this respect, but it seems strange that they use different words to
describe it.

As you say, it appears that it bases its temperature rise rate value on what
happened at the most recent startup period - rather than averaging it over a
number of periods.

Thankyou for explaining cycles per hour too. Presumably with the default 10
minute cycle (6 per hour) once it has done its thing within the current
cycle, it won't turn the boiler on again until the start of the next 10
minute cycle even if the house has cooled rapidly in the meantime because
(say) some fool has opened all the doors and windows? Presumably also, the
minimum ON time only applies once it has decided to turn the boiler on. That
is, it never runs the boiler for less than a minute. However, it may - and
often does - decide not to run it at all within a particular cycle - e.g.
when the actual temp is way above the target temp, as in over-night
conditions.
--
Cheers,
Set Square
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