On Thu, 30 Mar 2006 21:53:05 +0100, "Roger Mills"
wrote:

In an earlier contribution to this discussion,
Michael Chare wrote:

"Jeff" wrote in message
...
Can anyone explain how boiler modulation works, its benefits etc and
the same for weather compensation

Modulation is like a light dimmer, the level of output can be
varied, so the boiler can be on at a low level continously.

The alternative is like a normal light switch which can be off or on.
You just keep the boiler on for long enough to generate the amount of
heat that you need.

Indeed - but I think the OP is looking for a slightly more in-depth
explanation - like what algorithm the controller uses when deciding what
power setting to select.



I researched this quite a bit when I was selecting a boiler. You can
deduce quite a bit from looking through the installation and
maintenance manuals.

Factors I found we

- Outside temperature sensor? yes/no

- Boiler water temperature sensor(s). Flow, return, both?

- Method of modulation i.e. gas pressure or fan speed

- Pump control. Fixed speed, 2-3 speeds controlled by boiler,
variable speed controlled by boiler.

- Room temperature thermostat. On/off or sensing temperature.

- Settings of boiler behaviour for outside temperature changes.

- Settings of boiler for different types of heating load - e.g.
radiators sized for conventional boiler, radiators sized for better
efficiency from condensing boiler, underfloor heating.

The number and amount of detail with these has an influence on what it
is possible for the boiler's controller to do to optimise its
operation. Unsurprisingly, the more expensive boilers tend to have
more sensing and more ability to control.

Examples of these are MHG and Viessmann.

http://www.mhg.de/en/products/gas_un...cromat_ec.html
http://www.mhsboilers.com/boilers/premix/strata1.htm

http://www.viessmann.co.uk/products/...itodens200.php

This one has a document explaining condensing operation and controls.

http://tinyurl.com/54aqs






--

..andy