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]

"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]

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

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.

"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