On Wed, 30 Jul 2003 08:44:05 +0100, "Jonathan@Home"
wrote:

Andy,

What thermostat are you using? I have an outside sensor for my CM67 but
haven't got round to connecting up, I do though have a natty little module
that gets the time from the Rugby radio clock signal; so I never ahve to
worry about the spring and autimn time changes. It connects via a couple of
pins internaly and I'm wondering if I can slave the other zone controllers
off this one with a bit if wiring to share it via a terminal box.


Cheers
Jonathan


My boiler (MAN Micromat) has its own control system and sensors.

The boiler itself modulates the burner via use of the fan speed and
will give an output from 4kW up to full power. THe pump is internal
and it modulates that as well, linearly. There are sensors for the
flow and return water temperatures and it will run quite well just
using those if you have a system with TRVs. As they adjust, it will
vary heat output accordingly.

The manufacturer supplies an outside temperature sensor with the
boiler which can be used to provide feedforward control. Since a
house as a fairly substantial thermal time constant, sensing a change
in outside temperature (especially if there is a relatively sudden
one) allows the boiler to begin to adjust for it rather than waiting
for the disturbance to show up in the house. This results in better
temperature control and economy than can be achieved with an inside
sensor alone.

One can also add an internal controller that is specific to the
boiler, (but made by Siemens (Landis & Gyr) ). This hooks into the
boiler and allows it to measure the actual room temperature. A
conventional on/off thermostat or a proportional control type work by
turning the heat demand on and off, albeit to good effect with a
proportional type if adjusted correctly.

On this controller, it's possible to do all of the normal setback
adjustments, and the boiler microprocessor begins to learn the heating
behaviour of the house. You can also adjust the relative sensitivity
and effect of the inside control and the outside control if you want
to optimise further. One effect, for example is that sometimes the
boiler will fire up at very low output just after sunset and the
radiators will become tepid - about 40 degrees - increasing if need
be. The boiler will also accept a conventional or proportional
controller, although control is then not as fine.

This article explains a little about the principles of feedforward in
a control system, albeit an industrial process. The concept is
similar for a CH system of this type.

http://www.pc-education.mcmaster.ca/...arlin_2002.pdf

There's an optional bullet type sensor for DHW cylinders which goes
into a pocket in the cylinder. This hooks directly to the boiler,
allowing it to sense water temperature directly rather than from an on
off thermostat. This allows it to detect rate of change of
temperature among other things. For example if the set point is 60
degrees and I am just drawing off little bits of water, the boiler
ignores it until the temperature reaches 55 degrees, at which point it
fires up and does a water reheat cycle at full power, cylinder only.
If I run a shower or draw a bath, it sees a rapid drop in temperature
and responds more quickly. There is also a mechanism whereby the
boiler begins to throttle back as the set point is approached so that
it doesn't overshoot.

The manufacturer even supplies optional PC software so that you can
log its every move and even display temperature, power level etc
graphs should you be so minded. I take the data from mine and use it
for energy consumption recording among other things.


For the CM67, have a look at this application note.

http://content.honeywell.com/uk/homes/files/pag106.pdf

It rather looks as though the outside sensor is there to display
temperature on the room thermostat as opposed to taking it into
account for control purposes. It may be worth asking Honeywell
though.

As regards sharing the clock module, I think it will depend on how it
interfaces with the rest of the logic of the controller.
If the module simply outputs the time based on the MSF signal (which
it could) then it may work. OTOH, if the main microprocessor has to
program the chip in the time module or send commands to tell the chip
to provide the time then it probably won't work to drive multiple
controllers from one time module.


..andy

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