Can anyone explain how boiler modulation works, its benefits etc and the
same for weather compensation

Regards Jeff

On Wed, 29 Mar 2006 18:23:53 +0100 Jeff wrote :
Can anyone explain how boiler modulation works, its benefits etc
and the same for weather compensation

In brief (as I'm just going home) modulation means that the boiler
includes a facility for varying the fuel being burnt (and thus the
output) - for example my Glow-worm 24Cxi combi will modulate between
5 and 18kW. When the temperature of the water coming back to the
boiler starts to rise (because the radiators cannot get rid of all
the heat being produced) the burn rate is reduced accordingly.

Think of it as driving a car: if you only had an on/off switch for
the engine you'd have to fire up, then switch off and coast for a
bit, start up again .... instead you ease off the throttle until the
engine is producing just enough power to maintain the desired speed.
Likewise a modulating boiler.

Weather compensation adjusts the boiler's output temperature to suit
the current outside temperature, so the rads will be hotter on cold
days, less hot on milder ones. This makes for greater comfort and
also enhances the boiler efficiency.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

Jeff wrote:
Can anyone explain how boiler modulation works, its benefits etc and the
same for weather compensation

Boiler modulation means that instead of the boiler running flat out for
short periods, it runs for longer, at lower power.
This can improve efficiency, especially with condensing boilers.

"Tony Bryer" wrote in message
...
On Wed, 29 Mar 2006 18:23:53 +0100 Jeff wrote :
Can anyone explain how boiler modulation works, its benefits etc
and the same for weather compensation

In brief (as I'm just going home) modulation means that the boiler
includes a facility for varying the fuel being burnt (and thus the
output) - for example my Glow-worm 24Cxi combi will modulate between
5 and 18kW. When the temperature of the water coming back to the
boiler starts to rise (because the radiators cannot get rid of all
the heat being produced) the burn rate is reduced accordingly.

Think of it as driving a car: if you only had an on/off switch for
the engine you'd have to fire up, then switch off and coast for a
bit, start up again .... instead you ease off the throttle until the
engine is producing just enough power to maintain the desired speed.
Likewise a modulating boiler.

Weather compensation adjusts the boiler's output temperature to suit
the current outside temperature, so the rads will be hotter on cold
days, less hot on milder ones. This makes for greater comfort and
also enhances the boiler efficiency.


So in the above analogy... weather comp varies the 'desired speed' in effect
turning up or down the boiler temp knob ?

The control for the modulation must work on a fixed differential from flow
to return ?

Tony you said 'in brief' - i would love the long and detailed version as i
am trying to get my head around this for a future project.

Regards Jeff



--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

"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.



--

Michael Chare

On Thu, 30 Mar 2006 17:52:05 +0100, Jeff wrote:


"Tony Bryer" wrote in message
...
On Wed, 29 Mar 2006 18:23:53 +0100 Jeff wrote :
Can anyone explain how boiler modulation works, its benefits etc
and the same for weather compensation

In brief (as I'm just going home) modulation means that the boiler
includes a facility for varying the fuel being burnt (and thus the
output) - for example my Glow-worm 24Cxi combi will modulate between
5 and 18kW. When the temperature of the water coming back to the
boiler starts to rise (because the radiators cannot get rid of all
the heat being produced) the burn rate is reduced accordingly.

Think of it as driving a car: if you only had an on/off switch for
the engine you'd have to fire up, then switch off and coast for a
bit, start up again .... instead you ease off the throttle until the
engine is producing just enough power to maintain the desired speed.
Likewise a modulating boiler.

Weather compensation adjusts the boiler's output temperature to suit
the current outside temperature, so the rads will be hotter on cold
days, less hot on milder ones. This makes for greater comfort and
also enhances the boiler efficiency.


So in the above analogy... weather comp varies the 'desired speed' in effect
turning up or down the boiler temp knob ?

The control for the modulation must work on a fixed differential from flow
to return ?

Tony you said 'in brief' - i would love the long and detailed version as i
am trying to get my head around this for a future project.

Regards Jeff


I seriously suggest you read all the FAQs available on heating, plumbing
and boilers. (Sorry if you have done that already).

The mechanism for modulation is essentially one of two forms:

On conventional burners the gas pressure is varied typically over a range
of about 5:1. Giving a power range of about 2.5:1

On a premix burner the fan speed is adjusted thus changing the flow rate
through the burner. Typically the fan speed would alter over a range of
2:1 or even as much as 3:1 giving a power range of 4:1 or even as much
as 9:1.

The gas valves for conventional modulation usually are fed with 230V for
one/off and a signal of 0-9V DC which alters between the lowest and
highest rates.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

In an earlier contribution to this discussion,
Ed Sirett wrote:


I seriously suggest you read all the FAQs available on heating,
plumbing and boilers. (Sorry if you have done that already).

The mechanism for modulation is essentially one of two forms:

On conventional burners the gas pressure is varied typically over a
range of about 5:1. Giving a power range of about 2.5:1

On a premix burner the fan speed is adjusted thus changing the flow
rate through the burner. Typically the fan speed would alter over a
range of 2:1 or even as much as 3:1 giving a power range of 4:1 or
even as much as 9:1.

The gas valves for conventional modulation usually are fed with 230V
for one/off and a signal of 0-9V DC which alters between the lowest
and highest rates.


OK - that tells us *how* it does it - but what's actually driving it? In
other words what feedback parameter(s) - e.g. water outlet temperature,
return temperature, temperature differential, etc. - is it setting out to
control by modulating the burner?
--
Cheers,
Roger
______
Please reply to newsgroup.
Reply address IS valid, but not regularly monitored.

On Thu, 30 Mar 2006 22:05:22 +0100, Roger Mills wrote:



OK - that tells us *how* it does it - but what's actually driving it? In
other words what feedback parameter(s) - e.g. water outlet temperature,
return temperature, temperature differential, etc. - is it setting out to
control by modulating the burner?

Most boilers seem to govern the flow temperature. This is usually where
the NTC is placed.

A few seem to monitor both flow and return temps and some alter the
pump settings as well.
I strongly suspect that on my Keston C25 the front knob controls the flow
temp and that affects the burner power but the boiler senses the return
temp to adjust the pump in an attempt to get the differential higher.

Quite a few models seem to have a "cruise-before-decision" approach, in
which they operate at middling lowish power after ignition for around a
minute or so then ramp up (usually) to the required power.

In almost every boiler I've fiddle with, the algorithm/electronics is
usually sensitive to the rate of change of temperature as well as the
temperature. For instance if you move the control quickly down the burner
may cut out but if you move it slowly down the flames just reduce.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

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

Thanks for the input, that last link was very interesting. There is very
little on the 'net about weather compensation which is what prompted the
question here.

So here is my list of current assumptions :-

1. I need to keep the return temp as low as possible below 57 degrees.

2. A low temp, long burn is more efficient than a high temp short burn

and here's the long shot

3. Weather compensation does the same as turning the temp knob up or down
relative to the outside temp.

If point 3 is correct then why have an outside temp sensor, surely you could
just monitor the return temp to keep it constant thus compensating for
different losses due to different outside temps.

I'm still struggling to fit modulation into this

Regards Jeff

On Fri, 31 Mar 2006 19:05:45 +0100, "Jeff"
wrote:

Thanks for the input, that last link was very interesting. There is very
little on the 'net about weather compensation which is what prompted the
question here.

So here is my list of current assumptions :-

1. I need to keep the return temp as low as possible below 57 degrees.

That's somewhat true, but don't get the impression that there is some
magic step change in efficiency when condensing commences. What
actually happens is that the rate of change of improvement in
efficiency increases below the dew point.

In essence, the lower the better. This can most effectively be
achieved for more of the time by having the radiators adequately sized
such that they can produce enough output to meet worst case outside
temperatures at 70 degree flow (or lower if you like) rather than the
conventional 82 degree design.



2. A low temp, long burn is more efficient than a high temp short burn

That is true.




and here's the long shot

3. Weather compensation does the same as turning the temp knob up or down
relative to the outside temp.

If point 3 is correct then why have an outside temp sensor, surely you could
just monitor the return temp to keep it constant thus compensating for
different losses due to different outside temps.

I'm still struggling to fit modulation into this

Yes and no. External monitoring provides for increased comfort
because both the temperature as well as the rate of change of
temperature outside become known to the controller more accurately
than by the other means. think of it this way. Changes in outside
temperature (eventually) affect the heat loss through the building
surfaces and air changes. However, the boiler, if it has return
temperature sensing only learns about this indirectly as a result of
TRVs adjusting flow rates through radiators. In most systems the
only additional monitor is an on/off room control.

There are room thermostats which will do things such as optimised
starting to start the boiler based on rate of temperature rise during
previous heating periods. However, these can't be as accurate as
being able to measure the actual conditions.

If the boiler has that information, then being able to adjust the heat
output finely and continuously will produce far better control
tracking leading to greater comfort and saving of fuel.








Regards Jeff


--

..andy

"Andy Hall" wrote :-
External monitoring provides for increased comfort
because both the temperature as well as the rate of change of
temperature outside become known to the controller more accurately
than by the other means. think of it this way. Changes in outside
temperature (eventually) affect the heat loss through the building
surfaces and air changes. However, the boiler, if it has return
temperature sensing only learns about this indirectly as a result of
TRVs adjusting flow rates through radiators. In most systems the
only additional monitor is an on/off room control.

There are room thermostats which will do things such as optimised
starting to start the boiler based on rate of temperature rise during
previous heating periods. However, these can't be as accurate as
being able to measure the actual conditions.

If the boiler has that information, then being able to adjust the heat
output finely and continuously will produce far better control
tracking leading to greater comfort and saving of fuel.


Bingo !

So, you can do it by monitoring return temp, but with outside temp
monitoring the system is more accurate and responsive

Regards Jeff

On Fri, 31 Mar 2006 22:36:56 +0100, "Jeff"
wrote:


"Andy Hall" wrote :-
External monitoring provides for increased comfort
because both the temperature as well as the rate of change of
temperature outside become known to the controller more accurately
than by the other means. think of it this way. Changes in outside
temperature (eventually) affect the heat loss through the building
surfaces and air changes. However, the boiler, if it has return
temperature sensing only learns about this indirectly as a result of
TRVs adjusting flow rates through radiators. In most systems the
only additional monitor is an on/off room control.

There are room thermostats which will do things such as optimised
starting to start the boiler based on rate of temperature rise during
previous heating periods. However, these can't be as accurate as
being able to measure the actual conditions.

If the boiler has that information, then being able to adjust the heat
output finely and continuously will produce far better control
tracking leading to greater comfort and saving of fuel.


Bingo !

So, you can do it by monitoring return temp, but with outside temp
monitoring the system is more accurate and responsive

Regards Jeff


This is a simplification, because of course there are all kinds of
complexities if one really wanted to produce an accurate model and
control system.

A temperature sensor is an electronic component costing a few tens of
pence. The electronics on the boiler controller to interface it are
not a lot more. The complexity comes in the algorithms in the
firmware. In one way it is surprising that more manufacturers don't
give their boilers the ability to sense more information and to do so
more accurately - the component cost isn't high and the firmware is
initial development cost (which can be substantial of course.

Nevertheless, I suspect that part of the story is that this strategy
allows manufacturers to have optional features for which much more
money can be charged than the unit cost. I suspect that another part
is that setting up of some of the mopre sophisticated capabilities is
deemed to be beyond what the manufacturer believes the capabilities of
the average installer to be.

If you want to look at more general information, look for references
to industrial control and the techniques used for that. Some of
these are borrowed in simplified form.

e.g. http://en.wikipedia.org/wiki/PID_controller

and links from it is a place to start.




--

..andy