On Sun, 8 Feb 2004 15:22:09 -0000, "Set Square"
wrote:




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.

I think that if you poke around on the sites a little, you will find
the CM61 or CM67. There are possibly a few differences in the RF
version to save battery power, but functionally from when I looked
them they are basically the same as the wired one.

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."


It is a bit vague isn't it. Probably written by a technical author
who didn't understand the product.

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?

That would be true unless the temperature has fallen so rapidly that
you reach the edge of the proportional band. At that point, the
controller will go to 100% on. Obviously this is another factor that
you could trade in deciding on the bandwidth setting. If the sudden
loss of heat situation happens a lot, then setting the bandwidth
narrower might be in order.


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.

If you set it to the 10 minute cycle, yes. Depending on the nature
of the house and system, setting a longer cycle might be worth doing -
e.g. if it's an older (say cast iron) boiler and not overpowered for
the house.

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.

Correct. But that is where you have gone outside the proportional
band anyway. On the way down, as you come into the band, the boiler
would begin firing as soon as 10% heat or more is demanded.

Another factor that I should have mentioned is the boiler thermostat.
If the boiler is oversized or the heat is not being disposed of
quickly enough, that will come into play and have an impact on the
system. You would notice this if the boiler has a tendency to short
cycle without the controller in operation. Ideally, when starting
from cold, the boiler thermostat shouldn't come into play until you
are getting towards the set point if at all.




..andy

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