I'm in the process of reviewing my CH system, and have re-calculated all my
heat losses and compared them with the radiators currently fitted. Many of
the rads are over generous - partly because they were fitted a long time ago
when the house was far less well insulated.

I currently have a conventional boiler, and run the system at a mean water
temperature of about 76 degC (82 flow and 70 return), giving a typical
Delta-T of 55 degC. At some point in the future I may replace the boiler
with a condensing model (probably won't have a choice!) and would like to
re-asses the adequacy of my rads for running at a lower Delta-T.

What value should I be using?
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored..
Messages sent to it may not be read for several weeks. PLEASE REPLY TO
NEWSGROUP!

"Roger Mills" wrote in message
...

I'm in the process of reviewing my CH system, and have re-calculated all
my heat losses and compared them with the radiators currently fitted. Many
of the rads are over generous - partly because they were fitted a long
time ago when the house was far less well insulated.

I currently have a conventional boiler, and run the system at a mean water
temperature of about 76 degC (82 flow and 70 return), giving a typical
Delta-T of 55 degC. At some point in the future I may replace the boiler
with a condensing model (probably won't have a choice!) and would like to
re-asses the adequacy of my rads for running at a lower Delta-T.

What value should I be using?

60 flow 40 return. Top quality (expensive) boilers can modulate down to 3
to 5kW, which is still high when the house is up to temp. 90% plus of run
time boiler is on part-load so does not need 82C - 70C.

Assess your DHW, a heat bank may be the better option with TRVs on all rads
and a Smart pump on the CH and also mains pressure DHW. Then a cheaper
simpler boiler can be used to heat the heat bank.

Or a packaged solution: ACV Heat Master (integrated outside weather
compensator), Gledhill Gulfstream or Atmos Multi. These makers will provide
a Smart pump with the units if requested.

On 2007-09-10 10:32:07 +0100, "Roger Mills" said:

I'm in the process of reviewing my CH system, and have re-calculated all my
heat losses and compared them with the radiators currently fitted. Many of
the rads are over generous - partly because they were fitted a long time ago
when the house was far less well insulated.

I currently have a conventional boiler, and run the system at a mean water
temperature of about 76 degC (82 flow and 70 return), giving a typical
Delta-T of 55 degC. At some point in the future I may replace the boiler
with a condensing model (probably won't have a choice!) and would like to
re-asses the adequacy of my rads for running at a lower Delta-T.

What value should I be using?

I did this exercise a few years back to achieve exactly this.

The first thing is that a condensing boiler can manage a much larger
temperature drop - 20 or 25 degrees rather than nominal 12. This
means that for a given flow rate, more heat can be transferred.
Secondly, it means that radiators will output more heat because there
will be a larger temperature drop.

But....... of course, there's a caveat. That is that the mean
water to air temperature, that you had already alluded to is much lower
because the conventional design is to go with 70 degree flow and 50
return.

If you plug that into your radiator data sheet, you will see that the
derating factor falls from about 90% (82/70 case) to about 60% (70/50
case) which makes a huge difference to radiator size if you decide that
you want to use these temperatures.

I did a complete design check for the house and found that over half
the radiators were oversized enough that they would still be OK at
70/50. There was one room which had always been cool in the winter
and it turned out that that had only about 70% of the needed capacity
at 82/70. The remainder were under the requirement for 70/50.

So I changed four radiators (making them double panels with fins) and
put one much larger one in the room that was too cool. I also added
a separate circuit for the conservatory. All of this permitted 70/50
operation.

The boiler that I used is a MAN Micromat, which is a fairly
sophisticated boiler with external weather compensation, continuous
range pump control and temperature sensing. For example, both the room
and cylinder thermostats provide the boiler with temperature figures as
opposed to on/off signalling. There are settings to control the
interaction of the weather compensator vs. the room monitor and their
control effects. In addition, the boiler will modulate down to
about 4kW in heating mode if required. Later in September, it will
start coming on a little in the evenings as the weather cools and runs
with a flow temperature of 40 degrees or so. There is a data logging
output to which I can hook up a PC. In the coldest weather, the flow
temperature has not yet been above 65 degrees. I can have a limit
set on flow temperature of 70 degrees if I wanted to, although I have
actually left it at the default 85 degrees. The HW is handled
separately. When there is demand there, the boiler is wound up to
30kW or so to rapidly heat the cylinder.

It's fair to say that most boilers don't have this sophistication. the
only other that I know that does is Viessmann, although there may be
others. The majority have a thermostat and do some form of
modulation. With these, it may be interesting to set the thermostat
seasonally to prevent the operating temperature going too high,
although generally the boiler ought to optimise for low temperature if
it can.

"Andy Hall" wrote in message
...
On 2007-09-10 10:32:07 +0100, "Roger Mills"
said:

I'm in the process of reviewing my CH system, and have re-calculated all
my
heat losses and compared them with the radiators currently fitted. Many
of
the rads are over generous - partly because they were fitted a long time
ago
when the house was far less well insulated.

I currently have a conventional boiler, and run the system at a mean
water
temperature of about 76 degC (82 flow and 70 return), giving a typical
Delta-T of 55 degC. At some point in the future I may replace the boiler
with a condensing model (probably won't have a choice!) and would like to
re-asses the adequacy of my rads for running at a lower Delta-T.

What value should I be using?

I did this exercise a few years back to achieve exactly this.

The first thing is that a condensing boiler can manage a much larger
temperature drop - 20 or 25 degrees rather than nominal 12. This means
that for a given flow rate, more heat can be transferred. Secondly, it
means that radiators will output more heat because there will be a larger
temperature drop.

But....... of course, there's a caveat. That is that the mean water
to air temperature, that you had already alluded to is much lower because
the conventional design is to go with 70 degree flow and 50 return.

If you plug that into your radiator data sheet, you will see that the
derating factor falls from about 90% (82/70 case) to about 60% (70/50
case) which makes a huge difference to radiator size if you decide that
you want to use these temperatures.

I did a complete design check for the house and found that over half the
radiators were oversized enough that they would still be OK at 70/50.
There was one room which had always been cool in the winter and it turned
out that that had only about 70% of the needed capacity at 82/70. The
remainder were under the requirement for 70/50.

So I changed four radiators (making them double panels with fins) and put
one much larger one in the room that was too cool. I also added a
separate circuit for the conservatory. All of this permitted 70/50
operation.

The boiler that I used is a MAN Micromat, which is a fairly sophisticated
boiler with external weather compensation, continuous range pump control
and temperature sensing. For example, both the room and cylinder
thermostats provide the boiler with temperature figures as opposed to
on/off signalling. There are settings to control the interaction of the
weather compensator vs. the room monitor and their control effects.
In addition, the boiler will modulate down to about 4kW in heating mode if
required. Later in September, it will start coming on a little in the
evenings as the weather cools and runs with a flow temperature of 40
degrees or so. There is a data logging output to which I can hook up a
PC. In the coldest weather, the flow temperature has not yet been above
65 degrees. I can have a limit set on flow temperature of 70 degrees
if I wanted to, although I have actually left it at the default 85
degrees. The HW is handled separately. When there is demand there,
the boiler is wound up to 30kW or so to rapidly heat the cylinder.

It's fair to say that most boilers don't have this sophistication. the
only other that I know that does is Viessmann, although there may be
others. The majority have a thermostat and do some form of modulation.
With these, it may be interesting to set the thermostat seasonally to
prevent the operating temperature going too high, although generally the
boiler ought to optimise for low temperature if it can.

Best put a stand alone weather compensator in. They it winds the flow
temperature up and down to suit.

On 2007-09-10 12:28:59 +0100, "Doctor Drivel" said:

Best put a stand alone weather compensator in. They it winds the flow
temperature up and down to suit.

Only if it is able to provide an analogue or equivalent signal to the boiler.

If it is handling the boiler by simply turning its burner on and off,
it is not a good solution by comparison with a boiler that has full
external temperture sensing and acts upon that.

"Andy Hall" wrote in message
...
On 2007-09-10 12:28:59 +0100, "Doctor Drivel" said:

Best put a stand alone weather compensator in. Then it winds the flow
temperature up and down to suit.

Only if it is able to provide an analogue
or equivalent signal to the boiler.

Nope. It maintain the flow temperature to what the weather compensator
controller dictates. I used one for years and years.

If it is handling the boiler by simply turning its burner on and off, it
is not a good solution

It is a good solution. It has anti-cycling circuitry.

On 2007-09-10 13:40:25 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...
On 2007-09-10 12:28:59 +0100, "Doctor Drivel" said:

Best put a stand alone weather compensator in. Then it winds the flow
temperature up and down to suit.

Only if it is able to provide an analogue
or equivalent signal to the boiler.

Nope. It maintain the flow temperature to what the weather compensator
controller dictates. I used one for years and years.

The flow temperature will fluctuate up and down as the burner is turned
on and off because the thermal intertia of the heat exchanger is small.


If it is handling the boiler by simply turning its burner on and off,
it is not a good solution

It is a good solution. It has anti-cycling circuitry.

This is incorrect.

A boiler with built in weather compensation by virtue of measuring
temperature directly will achieve a better controlled result than an
external device that turns the burner on and off even if there is anti
cycling.

You are suggesting breaking the control loop with on/off switching, and
that, by definition, is inferior to full analogue measurement.


If, on the other hand, the boiler has no weather compensation at all,
an external device *may* be interesting .

However, if anticycling also has to be brought into the equation in
order to avoid the inefficiency introduced by turning the burner on and
off, you will have introduced two discontiguous control elements into
the system thus making the control even worse.

"Andy Hall" wrote in message
...
On 2007-09-10 13:40:25 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...
On 2007-09-10 12:28:59 +0100, "Doctor Drivel" said:

Best put a stand alone weather compensator in. Then it winds the flow
temperature up and down to suit.

Only if it is able to provide an analogue
or equivalent signal to the boiler.

Nope. It maintain the flow temperature to what the weather compensator
controller dictates. I used one for years and years.

The flow temperature will fluctuate up and down as the burner is turned on
and off because the thermal intertia of the heat exchanger is small.


If it is handling the boiler by simply turning its burner on and off, it
is not a good solution

It is a good solution. It has anti-cycling circuitry.

This is incorrect.

Matt, it is correct, mine has anti-cycling circuitry.

A boiler with built in weather compensation by virtue of measuring
temperature directly will achieve a better controlled result than an
external device that turns the burner on and off even if there is anti
cycling.

Matt, no one is arguing with you.

You are suggesting breaking the control loop with on/off switching, and
that, by definition, is inferior to full analogue measurement.

Matt, read back, a simple cheaper boiler can be enhanced by using stand
alone weather compensator.

If, on the other hand, the boiler has no weather compensation at all, an
external device *may* be interesting .

Matt. very interesting indeed.

However, if anticycling also has to be brought into the equation in order
to avoid the inefficiency introduced by turning the burner on and off, you
will have introduced two discontiguous control elements into the system
thus making the control even worse.

Nope. the flow temperature remains low and the boiler does not continually
cycle. Best of a buffer tank is used, or a heat bank, which the weather
compensator controls the temperature of, then no to little cycling.

On 2007-09-10 14:11:09 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...
On 2007-09-10 13:40:25 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...
On 2007-09-10 12:28:59 +0100, "Doctor Drivel" said:

Best put a stand alone weather compensator in. Then it winds the flow
temperature up and down to suit.

Only if it is able to provide an analogue
or equivalent signal to the boiler.

Nope. It maintain the flow temperature to what the weather compensator
controller dictates. I used one for years and years.

The flow temperature will fluctuate up and down as the burner is turned
on and off because the thermal intertia of the heat exchanger is small.


If it is handling the boiler by simply turning its burner on and off,
it is not a good solution

It is a good solution. It has anti-cycling circuitry.

This is incorrect.

Matt, it is correct, mine has anti-cycling circuitry.


A boiler with built in weather compensation by virtue of measuring
temperature directly will achieve a better controlled result than an
external device that turns the burner on and off even if there is anti
cycling.

Matt, no one is arguing with you.


You are suggesting breaking the control loop with on/off switching, and
that, by definition, is inferior to full analogue measurement.

Matt, read back, a simple cheaper boiler can be enhanced by using stand
alone weather compensator.

If, on the other hand, the boiler has no weather compensation at all,
an external device *may* be interesting .

Matt. very interesting indeed.

However, if anticycling also has to be brought into the equation in
order to avoid the inefficiency introduced by turning the burner on and
off, you will have introduced two discontiguous control elements into
the system thus making the control even worse.

Nope. the flow temperature remains low and the boiler does not
continually cycle. Best of a buffer tank is used, or a heat bank,
which the weather compensator controls the temperature of, then no to
little cycling.

Except that by the time one has bought all that lot, one can have
bought a boiler with the proper controls and sensing, so the exercise
in adding an external compensator plus the bits to make it work is
pointless.

If one already had the boiler and wished to add an external box of
tricks, then it may be interesting. It certainly isn't if one is
starting with a clean sheet of paper as in the case. The decision
would be to go for a boiler with the functionality built in or not to
bother with any means of weather compensation.

"Andy Hall" wrote in message
...
On 2007-09-10 14:11:09 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...
On 2007-09-10 13:40:25 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...
On 2007-09-10 12:28:59 +0100, "Doctor Drivel"
said:

Best put a stand alone weather compensator in. Then it winds the flow
temperature up and down to suit.

Only if it is able to provide an analogue
or equivalent signal to the boiler.

Nope. It maintain the flow temperature to what the weather compensator
controller dictates. I used one for years and years.

The flow temperature will fluctuate up and down as the burner is turned
on and off because the thermal intertia of the heat exchanger is small.


If it is handling the boiler by simply turning its burner on and off,
it is not a good solution

It is a good solution. It has anti-cycling circuitry.

This is incorrect.

Matt, it is correct, mine has anti-cycling circuitry.


A boiler with built in weather compensation by virtue of measuring
temperature directly will achieve a better controlled result than an
external device that turns the burner on and off even if there is anti
cycling.

Matt, no one is arguing with you.


You are suggesting breaking the control loop with on/off switching, and
that, by definition, is inferior to full analogue measurement.

Matt, read back, a simple cheaper boiler can be enhanced by using stand
alone weather compensator.

If, on the other hand, the boiler has no weather compensation at all, an
external device *may* be interesting .

Matt. very interesting indeed.

However, if anticycling also has to be brought into the equation in
order to avoid the inefficiency introduced by turning the burner on and
off, you will have introduced two discontiguous control elements into
the system thus making the control even worse.

Nope. the flow temperature remains low and the boiler does not
continually cycle. Best of a buffer tank is used, or a heat bank, which
the weather compensator controls the temperature of, then no to little
cycling.

Except that by the time one has bought all that lot, one can have bought a
boiler with the proper controls and sensing, so the exercise in adding an
external compensator plus the bits to make it work is pointless.

Nope, A heat bank brings many, many advantages.

If one already had the boiler and wished to add an external box of tricks,
then it may be interesting. It certainly isn't if one is starting with a
clean sheet of paper as in the case. The decision would be to go for a
boiler with the functionality built in or not to bother with any means of
weather compensation.

Nope. Best for a heat bank (this is the buffer) and a simple cheaper more
reliable boiler.

On 2007-09-10 14:32:24 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...

Except that by the time one has bought all that lot, one can have
bought a boiler with the proper controls and sensing, so the exercise
in adding an external compensator plus the bits to make it work is
pointless.

Nope, A heat bank brings many, many advantages.

Which are separate to the point being discussed here and may or may not
be relevant.




If one already had the boiler and wished to add an external box of
tricks, then it may be interesting. It certainly isn't if one is
starting with a clean sheet of paper as in the case. The decision
would be to go for a boiler with the functionality built in or not to
bother with any means of weather compensation.

Nope. Best for a heat bank (this is the buffer) and a simple cheaper
more reliable boiler.

That argument doesn't really hold weight.

Consider the differences between the so called "cheap and reliable"
boiler and the more expensive one such as the MAN or Viessmann.

The firmware of the more sophisticated boiler will be more complex.
Does this lead to greater unreliability? I don't think so. More to
the point would be boards used in cheap boilers engineered down to a
cost. One thinks of certain Potterton models here which are notorious.

The burner and heat exchanger in the more sophisticated boiler are of
better quality. That has been said many times, even by you.

Therefore what is it precisely in one of these "simpler boilers" that
makes it more reliable?

How does adding a heat bank, with extra controls, valves, relays and
thermostats result in a more reliable system overall?

Short answer is that they don't.

"Andy Hall" wrote in message
...
On 2007-09-10 14:32:24 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...

Except that by the time one has bought all that lot, one can have bought
a boiler with the proper controls and sensing, so the exercise in adding
an external compensator plus the bits to make it work is pointless.

Nope, A heat bank brings many, many advantages.

Which are separate to the point being discussed here and may or may not be
relevant.

He wants an effcient system.

If one already had the boiler and wished to add an external box of
tricks, then it may be interesting. It certainly isn't if one is
starting with a clean sheet of paper as in the case. The decision would
be to go for a boiler with the functionality built in or not to bother
with any means of weather compensation.

Nope. Best for a heat bank (this is the buffer) and a simple cheaper more
reliable boiler.

That argument doesn't really hold weight.

It does.

Consider the differences between the so called "cheap and reliable" boiler
and the more expensive one such as the MAN or Viessmann.

Yes, two are expensive and the others cheaper.

The firmware of the more sophisticated boiler will be more complex. Does
this lead to greater unreliability? I don't think so. More to the
point would be boards used in cheap boilers engineered down to a cost.
One thinks of certain Potterton models here which are notorious.


Other boilers are reliable and not expensive.

The burner and heat exchanger in the more sophisticated boiler are of
better quality. That has been said many times, even by you.

But they cost a lot more.

Therefore what is it precisely in one of these "simpler boilers" that
makes it more reliable?

Less on them

How does adding a heat bank, with extra controls, valves, relays and
thermostats result in a more reliable system overall?

A neutral point, a buffer, mains pressure DHW and a superior hydraulic
environment in which the boiler operates.

Short answer is that they don't.

Matt, you need therapy.

On 2007-09-10 17:05:32 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...

Consider the differences between the so called "cheap and reliable"
boiler and the more expensive one such as the MAN or Viessmann.

Yes, two are expensive and the others cheaper.

Once the total cost of installation and ownership of something like
these vs. your collection of bits and pieces are added up, there is
likely to be very little in it.



The firmware of the more sophisticated boiler will be more complex.
Does this lead to greater unreliability? I don't think so. More to
the point would be boards used in cheap boilers engineered down to a
cost. One thinks of certain Potterton models here which are notorious.


Other boilers are reliable and not expensive.

The burner and heat exchanger in the more sophisticated boiler are of
better quality. That has been said many times, even by you.

But they cost a lot more.

Therefore what is it precisely in one of these "simpler boilers" that
makes it more reliable?

Less on them

What exactly is absent that makes for more reliability on these
"simpler boilers"?




How does adding a heat bank, with extra controls, valves, relays and
thermostats result in a more reliable system overall?

A neutral point, a buffer, mains pressure DHW and a superior hydraulic
environment in which the boiler operates.


Did you read that in a book?

"Andy Hall" wrote in message
...
On 2007-09-10 17:05:32 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...

Consider the differences between the so called "cheap and reliable"
boiler and the more expensive one such as the MAN or Viessmann.

Yes, two are expensive and the others cheaper.

Once the total cost of installation and ownership of something like these
vs. your collection of bits and pieces are added up, there is likely to be
very little in it.



The firmware of the more sophisticated boiler will be more complex.
Does this lead to greater unreliability? I don't think so. More to
the point would be boards used in cheap boilers engineered down to a
cost. One thinks of certain Potterton models here which are notorious.


Other boilers are reliable and not expensive.

The burner and heat exchanger in the more sophisticated boiler are of
better quality. That has been said many times, even by you.

But they cost a lot more.

Therefore what is it precisely in one of these "simpler boilers" that
makes it more reliable?

Less on them

What exactly is absent that makes for more reliability on these "simpler
boilers"?

On the fixed rate boilers there is no modulation control.

How does adding a heat bank, with extra controls, valves, relays and
thermostats result in a more reliable system overall?

A neutral point, a buffer, mains pressure DHW and a superior hydraulic
environment in which the boiler operates.

Did you read that in a book?

Well you just read it, so take note. Best to rip out that system you have,
and fit a heat bank. and an accumulator because your mains is crap.

On 2007-09-10 19:28:20 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...

What exactly is absent that makes for more reliability on these
"simpler boilers"?

On the fixed rate boilers there is no modulation control.

Which on a modulating boiler consists of a fan with variable speed
control operated by the electronics. Are you now going to tell me
that this alone worsens reliability, or would it more likely be the
****ty bearings in the cheap boiler's fan?

You're going to have to do better......




How does adding a heat bank, with extra controls, valves, relays and
thermostats result in a more reliable system overall?

A neutral point, a buffer, mains pressure DHW and a superior hydraulic
environment in which the boiler operates.

Did you read that in a book?

Well you just read it, so take note. Best to rip out that system you
have, and fit a heat bank. and an accumulator because your mains is
crap.

Riiiiggghhhtt........

"Andy Hall" wrote in message
...
On 2007-09-10 19:28:20 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...

What exactly is absent that makes for more reliability on these "simpler
boilers"?

On the fixed rate boilers there is no modulation control.

Which on a modulating boiler consists of a fan with variable speed control
operated by the electronics. Are you now going to tell me that this
alone worsens reliability, or would it more likely be the ****ty bearings
in the cheap boiler's fan?

You're going to have to do better......

Cheaper boilers? The boilers are cheaper because they have less on them.

How does adding a heat bank, with extra controls, valves, relays and
thermostats result in a more reliable system overall?

A neutral point, a buffer, mains pressure DHW and a superior hydraulic
environment in which the boiler operates.

Did you read that in a book?

Well you just read it, so take note. Best to rip out that system you
have, and fit a heat bank. and an accumulator because your mains is crap.

Riiiiggghhhtt........

On 2007-09-10 20:31:37 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...
On 2007-09-10 19:28:20 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...

What exactly is absent that makes for more reliability on these
"simpler boilers"?

On the fixed rate boilers there is no modulation control.

Which on a modulating boiler consists of a fan with variable speed
control operated by the electronics. Are you now going to tell me
that this alone worsens reliability, or would it more likely be the
****ty bearings in the cheap boiler's fan?

You're going to have to do better......

Cheaper boilers? The boilers are cheaper because they have less on them.

The boilers are cheaper because they use cheaper components

"Andy Hall" wrote in message
...
On 2007-09-10 20:31:37 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...
On 2007-09-10 19:28:20 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...

What exactly is absent that makes for more reliability on these
"simpler boilers"?

On the fixed rate boilers there is no modulation control.

Which on a modulating boiler consists of a fan with variable speed
control operated by the electronics. Are you now going to tell me
that this alone worsens reliability, or would it more likely be the
****ty bearings in the cheap boiler's fan?

You're going to have to do better......

Cheaper boilers? The boilers are cheaper because they have less on them.

The boilers are cheaper because they use cheaper components

Matt, you have never seen inside one of them.

On 2007-09-10 20:51:12 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...
On 2007-09-10 20:31:37 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...
On 2007-09-10 19:28:20 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...

What exactly is absent that makes for more reliability on these
"simpler boilers"?

On the fixed rate boilers there is no modulation control.

Which on a modulating boiler consists of a fan with variable speed
control operated by the electronics. Are you now going to tell me
that this alone worsens reliability, or would it more likely be the
****ty bearings in the cheap boiler's fan?

You're going to have to do better......

Cheaper boilers? The boilers are cheaper because they have less on them.

The boilers are cheaper because they use cheaper components

Matt, you have never seen inside one of them.

You really aren't doing well at all, are you....

"Andy Hall" wrote in message
...
On 2007-09-10 20:51:12 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...
On 2007-09-10 20:31:37 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...
On 2007-09-10 19:28:20 +0100, "Doctor Drivel"
said:


"Andy Hall" wrote in message
...

What exactly is absent that makes for more reliability on these
"simpler boilers"?

On the fixed rate boilers there is no modulation control.

Which on a modulating boiler consists of a fan with variable speed
control operated by the electronics. Are you now going to tell me
that this alone worsens reliability, or would it more likely be the
****ty bearings in the cheap boiler's fan?

You're going to have to do better......

Cheaper boilers? The boilers are cheaper because they have less on
them.

The boilers are cheaper because they use cheaper components

Matt, you have never seen inside one of them.

You really aren't doing well at all, are you....

Matt, I am. I know how to get the cases off.

On 2007-09-10 21:59:36 +0100, "Doctor Drivel" said:

Matt, I am. I know how to get the cases off.

Do you know how to get the donkey hind legs out of your freezer for
dinner? It must be full of them.

Roger Mills wrote:

I currently have a conventional boiler, and run the system at a mean water
temperature of about 76 degC (82 flow and 70 return), giving a typical
Delta-T of 55 degC. At some point in the future I may replace the boiler
with a condensing model (probably won't have a choice!) and would like to
re-asses the adequacy of my rads for running at a lower Delta-T.

What value should I be using?

You would usually balance for a wider flow/return differential. So if
you were to run the boiler at say 60/40 nominal[1] then that would give
an average dT to the room of 30. So scale the rad outputs by 30/55.

[1] The concept of nominal becomes rather elusive with a system that has
a modulating boiler and and TRVs on nearly every rad. You will probably
not often be running in the flat out conditions that match your calcs.
The other thing to consider is that with a conventional boiler you can
chose your own return temperature by virtue of the selected flow
temperature and how you balance the system. With a modern modulating
boiler, you can probably specify a maximum flow temperature, but not do
much more than that. The boilers closed loop control system will adjust
down from that maximum to optimise the return temperature, and the
nested control loop elements that are the TRVs will in effect try to
lower the flow/return differential as they throttle the water passed
through each rad.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
...
Roger Mills wrote:

I currently have a conventional boiler, and run the system at a mean
water temperature of about 76 degC (82 flow and 70 return), giving a
typical Delta-T of 55 degC. At some point in the future I may replace the
boiler with a condensing model (probably won't have a choice!) and would
like to re-asses the adequacy of my rads for running at a lower Delta-T.

What value should I be using?

You would usually balance for a wider flow/return differential. So if you
were to run the boiler at say 60/40 nominal[1] then that would give an
average dT to the room of 30. So scale the rad outputs by 30/55.

[1] The concept of nominal becomes rather elusive with a system that has a
modulating boiler and and TRVs on nearly every rad. You will probably not
often be running in the flat out conditions that match your calcs. The
other thing to consider is that with a conventional boiler you can chose
your own return temperature by virtue of the selected flow temperature and
how you balance the system. With a modern modulating boiler, you can
probably specify a maximum flow temperature, but not do much more than
that. The boilers closed loop control system will adjust down from that
maximum to optimise the return temperature, and the nested control loop
elements that are the TRVs will in effect try to lower the flow/return
differential as they throttle the water passed through each rad.

This is where a heat bank scores very well. The items are separated. The
CH circuit is run off the cylinder with a modulating Smart pump (Wilo Smart
or Grundfos Alpha). TRVs can be on all rads with any affect on the boiler.
The rads can be set to 60-40 temp differential. The boiler (pref
non-modulating) heats the cylinder. A weather compensator dictates the
temperature of the CH section of the cylinder. This ensures a low return
temperature and no cycling as the boiler heats up a mass of water to the
exactly the right temperature. If a warm day the water will be warminsh,
cold day will be very hot. The boilers is in an ideal hydraulic environment
with full flow through at all times and far less activation of the controls
prolonging longevity.

Doctor Drivel wrote:

What value should I be using?

You would usually balance for a wider flow/return differential. So if
you were to run the boiler at say 60/40 nominal[1] then that would
give an average dT to the room of 30. So scale the rad outputs by 30/55.

[1] The concept of nominal becomes rather elusive with a system that
has a modulating boiler and and TRVs on nearly every rad. You will
probably not often be running in the flat out conditions that match
your calcs. The other thing to consider is that with a conventional
boiler you can chose your own return temperature by virtue of the
selected flow temperature and how you balance the system. With a
modern modulating boiler, you can probably specify a maximum flow
temperature, but not do much more than that. The boilers closed loop
control system will adjust down from that maximum to optimise the
return temperature, and the nested control loop elements that are the
TRVs will in effect try to lower the flow/return differential as they
throttle the water passed through each rad.

This is where a heat bank scores very well. The items are separated.
The CH circuit is run off the cylinder with a modulating Smart pump
(Wilo Smart or Grundfos Alpha). TRVs can be on all rads with any affect
on the boiler. The rads can be set to 60-40 temp differential. The
boiler (pref non-modulating) heats the cylinder. A weather compensator
dictates the temperature of the CH section of the cylinder. This
ensures a low return temperature and no cycling as the boiler heats up a
mass of water to the exactly the right temperature. If a warm day the
water will be warminsh, cold day will be very hot. The boilers is in an
ideal hydraulic environment with full flow through at all times and far
less activation of the controls prolonging longevity.

Which is a lot of extra "stuff" to achieve what the modulating control
system of the boiler will do quite well for you in the first place,
especially if you choose one with a wide modulation range.

What you describe above has more merit with a oil boiler since they tend
to have far more restricted modulation ranges.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
...
Doctor Drivel wrote:

What value should I be using?

You would usually balance for a wider flow/return differential. So if
you were to run the boiler at say 60/40 nominal[1] then that would give
an average dT to the room of 30. So scale the rad outputs by 30/55.

[1] The concept of nominal becomes rather elusive with a system that has
a modulating boiler and and TRVs on nearly every rad. You will probably
not often be running in the flat out conditions that match your calcs.
The other thing to consider is that with a conventional boiler you can
chose your own return temperature by virtue of the selected flow
temperature and how you balance the system. With a modern modulating
boiler, you can probably specify a maximum flow temperature, but not do
much more than that. The boilers closed loop control system will adjust
down from that maximum to optimise the return temperature, and the
nested control loop elements that are the TRVs will in effect try to
lower the flow/return differential as they throttle the water passed
through each rad.

This is where a heat bank scores very well. The items are separated.
The CH circuit is run off the cylinder with a modulating Smart pump (Wilo
Smart or Grundfos Alpha). TRVs can be on all rads with any affect on the
boiler. The rads can be set to 60-40 temp differential. The boiler (pref
non-modulating) heats the cylinder. A weather compensator dictates the
temperature of the CH section of the cylinder. This ensures a low return
temperature and no cycling as the boiler heats up a mass of water to the
exactly the right temperature. If a warm day the water will be warminsh,
cold day will be very hot. The boilers is in an ideal hydraulic
environment with full flow through at all times and far less activation
of the controls prolonging longevity.

Which is a lot of extra "stuff" to achieve what the modulating control
system of the boiler will do quite well for you in the first place,
especially if you choose one with a wide modulation range.

No. The boiler on heat bank is always on full flow and may be a cheaper
simpler boiler.

What you describe above has more merit with a oil boiler since they tend
to have far more restricted modulation ranges.

Nope. The boiler is an ideal hydraulic environment with a heat bank.
Easier on the controls and no boiler cycling. The CH circuit can just drip
feed 0.5 kW from the beat store at just the right temperature. Zoning is
easy and can taken off the cylinder too.

Modulating boilers are poor compromise fix to retrofit boilers into existing
systems that were not design for condensing boiler systems.

On 2007-09-11 12:03:02 +0100, "Doctor Drivel" said:

No. The boiler on heat bank is always on full flow and may be a
cheaper simpler boiler.

You still haven't justified the "cheaper, simpler boiler" point.



What you describe above has more merit with a oil boiler since they
tend to have far more restricted modulation ranges.

Nope. The boiler is an ideal hydraulic environment with a heat bank.
Easier on the controls and no boiler cycling. The CH circuit can just
drip feed 0.5 kW from the beat store at just the right temperature.
Zoning is easy and can taken off the cylinder too.

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

If you refer back to the original question, it was about potentially
changing the radiators to match a condensing boiler that may be
installed in the future. Hence this point is not relevant.

Doctor Drivel wrote:

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

you are spouting rubbish again...

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Andy Hall" wrote in message
...
On 2007-09-11 12:03:02 +0100, "Doctor Drivel" said:

No. The boiler on heat bank is always on full flow and may be a cheaper
simpler boiler.

You still haven't justified the "cheaper, simpler boiler" point.



What you describe above has more merit with a oil boiler since they tend
to have far more restricted modulation ranges.

Nope. The boiler is an ideal hydraulic environment with a heat bank.
Easier on the controls and no boiler cycling. The CH circuit can just
drip feed 0.5 kW from the beat store at just the right temperature.
Zoning is easy and can taken off the cylinder too.

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

If you refer back to the original question, it was about potentially
changing the radiators to match a condensing boiler that may be installed
in the future. Hence this point is not relevant.

He is engaging in major work. This requires a re-think. He asked something
and now clearly has pro advice on different approaches.

"John Rumm" wrote in message
...
Doctor Drivel wrote:

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

you are spouting rubbish again...

You don't even understand what I wrote.

On 2007-09-11 20:36:46 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message ...
On 2007-09-11 12:03:02 +0100, "Doctor Drivel" said:

No. The boiler on heat bank is always on full flow and may be a
cheaper simpler boiler.

You still haven't justified the "cheaper, simpler boiler" point.



What you describe above has more merit with a oil boiler since they
tend to have far more restricted modulation ranges.

Nope. The boiler is an ideal hydraulic environment with a heat bank.
Easier on the controls and no boiler cycling. The CH circuit can just
drip feed 0.5 kW from the beat store at just the right temperature.
Zoning is easy and can taken off the cylinder too.

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

If you refer back to the original question, it was about potentially
changing the radiators to match a condensing boiler that may be
installed in the future. Hence this point is not relevant.

He is engaging in major work. This requires a re-think. He asked
something and now clearly has pro advice on different approaches.

Really?

Doctor Drivel wrote:

"John Rumm" wrote in message
...
Doctor Drivel wrote:

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

you are spouting rubbish again...

You don't even understand what I wrote.

See, we can agree on something.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Andy Hall" wrote in message
...
On 2007-09-11 20:36:46 +0100, "Doctor Drivel" said:


"Andy Hall" wrote in message
...
On 2007-09-11 12:03:02 +0100, "Doctor Drivel" said:

No. The boiler on heat bank is always on full flow and may be a
cheaper simpler boiler.

You still haven't justified the "cheaper, simpler boiler" point.



What you describe above has more merit with a oil boiler since they
tend to have far more restricted modulation ranges.

Nope. The boiler is an ideal hydraulic environment with a heat bank.
Easier on the controls and no boiler cycling. The CH circuit can just
drip feed 0.5 kW from the beat store at just the right temperature.
Zoning is easy and can taken off the cylinder too.

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

If you refer back to the original question, it was about potentially
changing the radiators to match a condensing boiler that may be
installed in the future. Hence this point is not relevant.

He is engaging in major work. This requires a re-think. He asked
something and now clearly has pro advice on different approaches.

Really?

No. O'Really.

"John Rumm" wrote in message
...
Doctor Drivel wrote:

"John Rumm" wrote in message
...
Doctor Drivel wrote:

Modulating boilers are poor compromise fix to retrofit boilers into
existing systems that were not design for condensing boiler systems.

you are spouting rubbish again...

You don't even understand what I wrote.

See, we can agree on something.

We clearly do!!

On Tue, 11 Sep 2007 02:28:21 +0100, John Rumm wrote:

Roger Mills wrote:

I currently have a conventional boiler, and run the system at a mean water
temperature of about 76 degC (82 flow and 70 return), giving a typical
Delta-T of 55 degC. At some point in the future I may replace the boiler
with a condensing model (probably won't have a choice!) and would like to
re-asses the adequacy of my rads for running at a lower Delta-T.

What value should I be using?

You would usually balance for a wider flow/return differential. So if
you were to run the boiler at say 60/40 nominal[1] then that would give
an average dT to the room of 30. So scale the rad outputs by 30/55.

I don't think the output is a simple proportion of the "Delta T".
The radiation output is very non linear and will be next to nothing
at all but the highest temperatures where it becomes a significant
minority aspect. The unforced convection is also non-linear. Both of these
effects are in the "unhelpful" direction in that 1/2 Delta-T will be
much less than 1/2 output.




--
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:

On Tue, 11 Sep 2007 02:28:21 +0100, John Rumm wrote:

Roger Mills wrote:

What value should I be using?

You would usually balance for a wider flow/return differential. So if
you were to run the boiler at say 60/40 nominal[1] then that would
give an average dT to the room of 30. So scale the rad outputs by
30/55.

I don't think the output is a simple proportion of the "Delta T".
The radiation output is very non linear and will be next to nothing
at all but the highest temperatures where it becomes a significant
minority aspect. The unforced convection is also non-linear. Both of
these effects are in the "unhelpful" direction in that 1/2 Delta-T
will be much less than 1/2 output.

Thanks Ed. I was actually only asking what Delta-T to use. I can work out
the effect on the output using tables such as those which appear on a
Stelrad radiator brochure, and am aware that it's not a simple linear
relationship.

Based on the answers received, a mean rad temp of 60 degC (70/50) seems a
reasonable thing to go for, giving a Delta-T of around 40 rather than 55.
Taking the ratio of the factors for 40 and 55, the output of my rads will be
reduced to about 0.605/0.898 - i.e. about 67% of their current output
(whereas scaling the Delta-T values would erroneously give about 72%.)
--
Cheers,
Roger
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