I've tried a few but they seem to give wildly differing numbers (and one
gave the same answer regardless of the inputs!), can anyone suggest one
that works?

--
Dave S
(The return email address is a dummy)

On Thu, 30 Dec 2004 22:01:09 +0000, Dave
wrote:

I've tried a few but they seem to give wildly differing numbers (and one
gave the same answer regardless of the inputs!), can anyone suggest one
that works?



The Myson and Barlo ones are OK.

The Myson one is not on their site at present, but I have a copy and
will happily send it to you if you drop me a mail.

One of the problems with some of these programs is that they have
incorrect U values for given object types - so it's always as well to
check the numbers against the list in the Building Regulations
Approved Documents.

The other factors that can introduce error are that some programs do
not account for floor heat loss correctly. The reasonably correct
approach is based on the combination of outside wall lengths and floor
area and there are correction tables of modified U values to cope with
it. Computer programs should do all of this as well, but if not,
there will be an error. Some programs have correction factors for
whether the heating is on all day, exposure of the house and so on.
The defaults may not be sensible.

Finally, you do need to make sure that heat loss by air exchange is
reasonably accounted for. This is a big chunk of heat requirement in
most properties.



--

..andy

To email, substitute .nospam with .gl

Andy Hall wrote:
On Thu, 30 Dec 2004 22:01:09 +0000, Dave
wrote:


I've tried a few but they seem to give wildly differing numbers (and one
gave the same answer regardless of the inputs!), can anyone suggest one
that works?




The Myson and Barlo ones are OK.

The Myson one is not on their site at present, but I have a copy and
will happily send it to you if you drop me a mail.

One of the problems with some of these programs is that they have
incorrect U values for given object types - so it's always as well to
check the numbers against the list in the Building Regulations
Approved Documents.

The other factors that can introduce error are that some programs do
not account for floor heat loss correctly. The reasonably correct
approach is based on the combination of outside wall lengths and floor
area and there are correction tables of modified U values to cope with
it. Computer programs should do all of this as well, but if not,
there will be an error. Some programs have correction factors for
whether the heating is on all day, exposure of the house and so on.
The defaults may not be sensible.

Finally, you do need to make sure that heat loss by air exchange is
reasonably accounted for. This is a big chunk of heat requirement in
most properties.



Thanks Andy, email sent.

Do you happen to know whether the U values in the myson software are
correct?
Estimating air exchange is tough, any suggestions on how to approach it?

--
Dave S
(The return email address is a dummy)

On Thu, 30 Dec 2004 23:20:20 +0000, Dave
wrote:



Thanks Andy, email sent.

On its way.


Do you happen to know whether the U values in the myson software are
correct?

The ones that I used were, but I didn't check all of them and had to
add a couple.

Estimating air exchange is tough, any suggestions on how to approach it?

I used the standard numbers given in the program, which are an
industry standard. If the house is exposed or the windows are older
sash types or you have gaps in the floorboards then it would be an
idea to up the numbers a bit.

You can also look at the various correction factors and adjust to your
pattern of use and location.

You don't need to include the typical 3kW or so for the hot water.
This is used for older cylinders with basic coil.

Are you going for a condensing boiler? If so, you can design the
radiator provision around a 70 degree flow and 50 return. This will
keep the boiler at the efficient end of the scale and also give you
plenty of head room for very cold weather. It does imply larger
radiators of course. Don't forget the correction factors from the
manufacturer data tables. These are normally 0.89 for 82/70 degree
operation and 0.6 for 70/50.




--

..andy

To email, substitute .nospam with .gl

"Dave" wrote in message
...
Do you happen to know whether the U values in the myson software are
correct?
Estimating air exchange is tough, any suggestions on how to approach it?

I use Myson V1.05, not sure if that is the latest version or not. Noticed
recently that there is a design program available at
http://www.centralheating.co.uk for £15.

Find the Myson useful for the maths because it takes into account your mean
water temperature and the room temperature but then transfer the results to
a spreadsheet. There is a "funny" with this version. The required outputs
are presented on a Dt60 basis but with a confusing product reference comment
to Dt50 and so have to be factored down to Dt50 before they are useable with
current rad data.

Jim A

Andy Hall wrote:
On Thu, 30 Dec 2004 23:20:20 +0000, Dave
wrote:

.... snipped

Are you going for a condensing boiler? If so, you can design the
radiator provision around a 70 degree flow and 50 return. This will
keep the boiler at the efficient end of the scale and also give you
plenty of head room for very cold weather. It does imply larger
radiators of course. Don't forget the correction factors from the
manufacturer data tables. These are normally 0.89 for 82/70 degree
operation and 0.6 for 70/50.


I can size the rads for a 70 flow but can't see how to achieve a 50
return. If the house is heating from cold (and all TRVs are open) the
return will presumably be much cooler than when the house is up to
temperature and all/most TRVs shut; is it really possible to design for
a specific return temperature?

--
Dave S
(The return email address is a dummy)

Jim Alexander wrote:
.... snipped
Find the Myson useful for the maths because it takes into account your mean
water temperature and the room temperature but then transfer the results to
a spreadsheet. There is a "funny" with this version. The required outputs
are presented on a Dt60 basis but with a confusing product reference comment
to Dt50 and so have to be factored down to Dt50 before they are useable with
current rad data.

Jim A


Thanks for the warning, where does it say that it's on a Dt60 basis?

--
Dave S
(The return email address is a dummy)

On Tue, 04 Jan 2005 09:19:53 +0000, Dave
wrote:

Jim Alexander wrote:
... snipped
Find the Myson useful for the maths because it takes into account your mean
water temperature and the room temperature but then transfer the results to
a spreadsheet. There is a "funny" with this version. The required outputs
are presented on a Dt60 basis but with a confusing product reference comment
to Dt50 and so have to be factored down to Dt50 before they are useable with
current rad data.

Jim A


Thanks for the warning, where does it say that it's on a Dt60 basis?

That's part of the EN 442 test standard. Normally it is mentioned in
the radiator data sheet as well. You can deduce it anyway, because
there is an accompanying table of correction factors for different dT
values. For 60 degrees it is 1.0





--

..andy

To email, substitute .nospam with .gl

On Tue, 04 Jan 2005 08:55:27 +0000, Dave
wrote:

Andy Hall wrote:
On Thu, 30 Dec 2004 23:20:20 +0000, Dave
wrote:

... snipped

Are you going for a condensing boiler? If so, you can design the
radiator provision around a 70 degree flow and 50 return. This will
keep the boiler at the efficient end of the scale and also give you
plenty of head room for very cold weather. It does imply larger
radiators of course. Don't forget the correction factors from the
manufacturer data tables. These are normally 0.89 for 82/70 degree
operation and 0.6 for 70/50.


I can size the rads for a 70 flow but can't see how to achieve a 50
return. If the house is heating from cold (and all TRVs are open) the
return will presumably be much cooler than when the house is up to
temperature and all/most TRVs shut; is it really possible to design for
a specific return temperature?

OK.

The radiator calculation is to first of all determine heat loss using
-3 degrees as the outside temperature (considered worst case)
inlcuding air change losses etc. and correction factors for exposed
position, intermittent use (needs more during start up) etc.

You will have figures in watts for each room.

If you work on 70 degrees flow and 50 return, then the mean water
temperature is going to be 60 degrees. Let's say you want 20
degrees in the room. The Mean Water To Air temperature will be 40
degrees. Most radiator manufacturers give a correction factor of 0.6
for that. You could be a purist and use slightly different numbers
for temperatures in different rooms but it probably isn't worth it.

From this, you pick your radiators. So for example, if you needed
1200W in a room, then you would need a 2kW nominal radiator.

A condensing boiler, by virtue mainly of its heat exchanger design,
can manage a dT of 20, sometimes as much as 25 degrees.

If everything were precisely matched (i.e. radiators and boiler
exactly matching heat loss), then the boiler would reach a steady
state of 70/50 degrees and would be operating in the condensing range
as well.

In practice, as you say, you won't have these levels of heat loss
because the system will have a design margin and weather will
typically be warmer.

Under those circumstances, when the system is heating from cold, it
will go flat out to begin with. Some boilers will allow you to set
the maximum flow temperature and you could set that to 70 degrees and
keep the return under 50. This is good from the efficiency point of
view (lower return temperatures, especially below the condensing dew
point are more efficient) or you could set the control at 82 degrees
and the system will heat more quickly.

With a modulating boiler, the burn rate will reduce accordingly.

If the heat demand reduces (e.g. because TRVs start to close, then the
boiler detects the load reduction by monitoring of the temperatures
and again reduces burn rate.

The point of designing around 70/50 is that you can operate the boiler
in a more efficient range. Efficiencies of condensing boilers tend
to be better than many non condensing types anyway since the heat
exchanger is usually larger. The efficiency increases as return
temperature reduces, but in the condensing range the *rate* of
improvement of efficiency increases with falling temperature.





--

..andy

To email, substitute .nospam with .gl

The message
from Dave contains these words:

I can size the rads for a 70 flow but can't see how to achieve a 50
return. If the house is heating from cold (and all TRVs are open) the
return will presumably be much cooler than when the house is up to
temperature and all/most TRVs shut; is it really possible to design for
a specific return temperature?

You are looking at this from the wrong perspective. The 70 flow, 50
return is an element you use in calculating the required radiator sizes.
In operation you won't initially get the 70 flow as the boiler has to
heat the return from cold but you should get (ignoring any losses in the
pipework) a 20 degree rise across the boiler.

If the rise is too low decrease the pump speed, too large increase the
pump speed. Unless you have a continuously variable pump (do such
animals exist?) you are not going to get this exact and as the TRVs
start closing off the circuit resistance will increase mimicking the
effect of decreasing the pump speed so I think you should aim low* if
you have a condensing boiler and want to benefit by recovering any of
the latent heat out of the steam in the flue.

Not having a condensing boiler myself I haven't had to deal with the
practicalities of this but ISTR from long ago that to get any condensing
effect the return must be below 53C and that it is not an on/off effect
but develops over a temperature range.

*This may not necessarily be correct but keeping the return temperature
low is critical in getting the best out of a condensing boiler. No doubt
someone more knowledgeable will be along in a minute to pull my
contribution apart but don't take any notice of dIMM unless he is backed
up by a good majority.

--
Roger

"Dave" wrote in message
...
Jim Alexander wrote:
... snipped
Find the Myson useful for the maths because it takes into account your
mean water temperature and the room temperature but then transfer the
results to a spreadsheet. There is a "funny" with this version. The
required outputs are presented on a Dt60 basis but with a confusing
product reference comment to Dt50 and so have to be factored down to Dt50
before they are useable with current rad data.

Jim A


Thanks for the warning, where does it say that it's on a Dt60 basis?

It doesn't, you need to check the data sheets to find out.

Jim A

Andy Hall wrote:
On Tue, 04 Jan 2005 08:55:27 +0000, Dave
wrote:


Andy Hall wrote:

On Thu, 30 Dec 2004 23:20:20 +0000, Dave
wrote:

... snipped


Are you going for a condensing boiler? If so, you can design the
radiator provision around a 70 degree flow and 50 return. This will
keep the boiler at the efficient end of the scale and also give you
plenty of head room for very cold weather. It does imply larger
radiators of course. Don't forget the correction factors from the
manufacturer data tables. These are normally 0.89 for 82/70 degree
operation and 0.6 for 70/50.


I can size the rads for a 70 flow but can't see how to achieve a 50
return. If the house is heating from cold (and all TRVs are open) the
return will presumably be much cooler than when the house is up to
temperature and all/most TRVs shut; is it really possible to design for
a specific return temperature?


OK.

The radiator calculation is to first of all determine heat loss using
-3 degrees as the outside temperature (considered worst case)
inlcuding air change losses etc. and correction factors for exposed
position, intermittent use (needs more during start up) etc.

You will have figures in watts for each room.

If you work on 70 degrees flow and 50 return, then the mean water
temperature is going to be 60 degrees. Let's say you want 20
degrees in the room. The Mean Water To Air temperature will be 40
degrees. Most radiator manufacturers give a correction factor of 0.6
for that. You could be a purist and use slightly different numbers
for temperatures in different rooms but it probably isn't worth it.

From this, you pick your radiators. So for example, if you needed
1200W in a room, then you would need a 2kW nominal radiator.

A condensing boiler, by virtue mainly of its heat exchanger design,
can manage a dT of 20, sometimes as much as 25 degrees.

If everything were precisely matched (i.e. radiators and boiler
exactly matching heat loss), then the boiler would reach a steady
state of 70/50 degrees and would be operating in the condensing range
as well.

In practice, as you say, you won't have these levels of heat loss
because the system will have a design margin and weather will
typically be warmer.

Under those circumstances, when the system is heating from cold, it
will go flat out to begin with. Some boilers will allow you to set
the maximum flow temperature and you could set that to 70 degrees and
keep the return under 50. This is good from the efficiency point of
view (lower return temperatures, especially below the condensing dew
point are more efficient) or you could set the control at 82 degrees
and the system will heat more quickly.

With a modulating boiler, the burn rate will reduce accordingly.

If the heat demand reduces (e.g. because TRVs start to close, then the
boiler detects the load reduction by monitoring of the temperatures
and again reduces burn rate.

The point of designing around 70/50 is that you can operate the boiler
in a more efficient range. Efficiencies of condensing boilers tend
to be better than many non condensing types anyway since the heat
exchanger is usually larger. The efficiency increases as return
temperature reduces, but in the condensing range the *rate* of
improvement of efficiency increases with falling temperature.


This is one of those aha! moments - light has dawned and, as usual, the
answer's pretty obvious once you look at it from the right direction.

Many Thanks to Andy and Roger (below)

--
Dave S
(The return email address is a dummy)

On Tue, 4 Jan 2005 10:39:00 GMT, Roger
wrote:

The message
from Dave contains these words:

I can size the rads for a 70 flow but can't see how to achieve a 50
return. If the house is heating from cold (and all TRVs are open) the
return will presumably be much cooler than when the house is up to
temperature and all/most TRVs shut; is it really possible to design for
a specific return temperature?

You are looking at this from the wrong perspective. The 70 flow, 50
return is an element you use in calculating the required radiator sizes.
In operation you won't initially get the 70 flow as the boiler has to
heat the return from cold but you should get (ignoring any losses in the
pipework) a 20 degree rise across the boiler.

If the rise is too low decrease the pump speed, too large increase the
pump speed. Unless you have a continuously variable pump (do such
animals exist?) you are not going to get this exact and as the TRVs
start closing off the circuit resistance will increase mimicking the
effect of decreasing the pump speed so I think you should aim low* if
you have a condensing boiler and want to benefit by recovering any of
the latent heat out of the steam in the flue.

There are a few approaches here.

a) There are pumps like the Grundfos Alpha, which will detect
increased flow resistance from TRVs starting to close, and will back
off accordingly. These are outside of boiler control though and are
responding mechanically.

b) There are boilers with integral pump where the typical three pump
settings are controlled by the boiler electronics. The Keston Celsius
25 has this, for example, and is able to roughly match pump oomph with
boiler heat output.

c) Version of b) where the boiler electronics control the pump on a
continuously varying basis. The MAN Micromat does this and can vary
the pump oomph between 20 and 100% of full power.




Not having a condensing boiler myself I haven't had to deal with the
practicalities of this but ISTR from long ago that to get any condensing
effect the return must be below 53C and that it is not an on/off effect
but develops over a temperature range.

Yes. There isn't a sudden condensing efficiency orgasm that happens
at the dew point. Efficiency increases with falling return
temperature and exhibits a greater *rate* of this below the dew point.
Ergo, the objective is to get the temperature as low as possible for
as much of the time as possible.



*This may not necessarily be correct but keeping the return temperature
low is critical in getting the best out of a condensing boiler. No doubt
someone more knowledgeable will be along in a minute to pull my
contribution apart but don't take any notice of dIMM unless he is backed
up by a good majority.


--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
Yes. There isn't a sudden condensing efficiency orgasm that happens
at the dew point. Efficiency increases with falling return
temperature and exhibits a greater *rate* of this below the dew point.

Hmmm. Preparing for "compulsory" replacement condensing boilers in May 2005
(two jags bombshell No2) had a holiday project trying to find some hard data
on this. Failed miserably. Any links to actual data over the full
operating temperature ranges?

Ergo, the objective is to get the temperature as low as possible for
as much of the time as possible.

Yep, unfortunately my radiator system is designed for 70deg mean water
temperature. Works well but has little margin for condensing operation.

Jim A

The message
from "Jim Alexander" contains these words:

"Andy Hall" wrote in message
...
Yes. There isn't a sudden condensing efficiency orgasm that happens
at the dew point. Efficiency increases with falling return
temperature and exhibits a greater *rate* of this below the dew point.

Hmmm. Preparing for "compulsory" replacement condensing boilers in
May 2005
(two jags bombshell No2) had a holiday project trying to find some
hard data
on this. Failed miserably. Any links to actual data over the full
operating temperature ranges?

ISTR that this was raised on the ng several years ago, possibly during
one of the interminable arguments with dIMM and maybe even back in the
days when he was pretending to be Adam. However finding that item is
beyond me.

Ergo, the objective is to get the temperature as low as possible for
as much of the time as possible.

Yep, unfortunately my radiator system is designed for 70deg mean water
temperature. Works well but has little margin for condensing operation.

Think yourself lucky. I am not sure mine was designed at all but when it
falls to 10 below outside I have to run mine continuously to have any
chance of the temperature approaching 19C at the times I want it to. I
have a round tuit buried quite a long way down the pile that had the
materials necessary for insulating the walls (without robbing me of too
much room space) priced at £1000 with the cost of plastering throughout
on top of that. Not sure if the payback point would be anywhere short of
infinity.

--
Roger

In article , Jim Alexander
wrote:
Hmmm. Preparing for "compulsory" replacement condensing boilers
in May 2005 (two jags bombshell No2) had a holiday project
trying to find some hard data on this. Failed miserably. Any
links to actual data over the full operating temperature
ranges?

Does the graph on http://www.keston.co.uk/products/celsius25.htm help?

--
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

On Tue, 4 Jan 2005 13:21:27 -0000, "Jim Alexander"
wrote:


"Andy Hall" wrote in message
.. .
Yes. There isn't a sudden condensing efficiency orgasm that happens
at the dew point. Efficiency increases with falling return
temperature and exhibits a greater *rate* of this below the dew point.

Hmmm. Preparing for "compulsory" replacement condensing boilers in May 2005
(two jags bombshell No2) had a holiday project trying to find some hard data
on this. Failed miserably. Any links to actual data over the full
operating temperature ranges?

Ergo, the objective is to get the temperature as low as possible for
as much of the time as possible.

Yep, unfortunately my radiator system is designed for 70deg mean water
temperature. Works well but has little margin for condensing operation.

Jim A


Several things here.

1) There are to be some exemptions which will basically operate if
replacement of an existing conventional boiler with a condensing one
will be too disruptive. This will be cases related to flue
arrangements, condensate drain etc., and a points scoring system is
used. Thus if you have a backboiler with conventional flue in the
middle of the house, then you may score sufficient points not to need
to replace with a condensing model. However, if it's a wall mount in
the kitchen, you would be pretty unlikely to meet exemption criteria.
Details are at www.2jags.com (www.odpm.gov.uk)

2) There are some typical curves for condensing boilers on the Keston
web site.

3) It doesn't matter if you have an existing radiator design for the
more typical 82/70 boiler arrangement. When the weather is really
cold, the boiler will wind up to these temperatures. When it's
warmer, less heat will be needed and it will modulate down and try to
operate at as low a temperature as possible. So for much of the year,
you would still be operating in the more efficient range below the dew
point. Obviously if you take the situation over the whole year it
won't be *as* good, but still worthwhile.












--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Tue, 4 Jan 2005 13:21:27 -0000, "Jim Alexander"
wrote:


Several things here.

1) There are to be some exemptions which will basically operate if
replacement of an existing conventional boiler with a condensing one
will be too disruptive. This will be cases related to flue
arrangements, condensate drain etc., and a points scoring system is
used. Thus if you have a backboiler with conventional flue in the
middle of the house, then you may score sufficient points not to need
to replace with a condensing model. However, if it's a wall mount in
the kitchen, you would be pretty unlikely to meet exemption criteria.

Guess we have both read the rules but for the education of anyone who hasn't
my gripe is that although the guidance claims to avoid situations which are
"too costly" the cost is NOT taken into account, only theoretical
disruption. Not only that but the acceptability of the lowest cost assessed
position to the householder and existing furniture and fittings are totally
ignored in the assessment. Not a gripe about the installer but he will get
his money. Absolutely a stealth tax on the hard-up. An election looms does
it not?

2) There are some typical curves for condensing boilers on the Keston
web site.

Thanks for the Keston link. Seems to me that the main efficency advantages
acrue from the larger heat exchanger.

3) It doesn't matter if you have an existing radiator design for the
more typical 82/70 boiler arrangement. When the weather is really
cold, the boiler will wind up to these temperatures. When it's
warmer, less heat will be needed and it will modulate down and try to
operate at as low a temperature as possible.

How exactly does it do that? Maybe I have got this wrong but I thought the
modulation worked by reducing the gas rate to control the flow temperature
to its setting. I would have to manually adjust the temperature according
to the weather to achieve lower flow temperatures?

So for much of the year,
you would still be operating in the more efficient range below the dew
point. Obviously if you take the situation over the whole year it
won't be *as* good, but still worthwhile.

OK, I've turned the temperature down, doesn't the water heating take an age
now and give me legionnaires disease?

Not if its a condensing combi but I'm not going there.

Jim A

On Wed, 5 Jan 2005 10:31:27 -0000, "Jim Alexander"
wrote:


"Andy Hall" wrote in message
.. .
On Tue, 4 Jan 2005 13:21:27 -0000, "Jim Alexander"
wrote:


Several things here.

1) There are to be some exemptions which will basically operate if
replacement of an existing conventional boiler with a condensing one
will be too disruptive. This will be cases related to flue
arrangements, condensate drain etc., and a points scoring system is
used. Thus if you have a backboiler with conventional flue in the
middle of the house, then you may score sufficient points not to need
to replace with a condensing model. However, if it's a wall mount in
the kitchen, you would be pretty unlikely to meet exemption criteria.

Guess we have both read the rules but for the education of anyone who hasn't
my gripe is that although the guidance claims to avoid situations which are
"too costly" the cost is NOT taken into account, only theoretical
disruption. Not only that but the acceptability of the lowest cost assessed
position to the householder and existing furniture and fittings are totally
ignored in the assessment. Not a gripe about the installer but he will get
his money. Absolutely a stealth tax on the hard-up.

A stealth tax on everybody - just like all the rest.

An election looms does
it not?

Yes indeed. Whether all of these intrusions into people's lives and
the stealth taxes will be sufficient to influence how they vote is
another thing though.




2) There are some typical curves for condensing boilers on the Keston
web site.

Thanks for the Keston link. Seems to me that the main efficency advantages
acrue from the larger heat exchanger.

Until you get down below the dew point.....



3) It doesn't matter if you have an existing radiator design for the
more typical 82/70 boiler arrangement. When the weather is really
cold, the boiler will wind up to these temperatures. When it's
warmer, less heat will be needed and it will modulate down and try to
operate at as low a temperature as possible.

How exactly does it do that? Maybe I have got this wrong but I thought the
modulation worked by reducing the gas rate to control the flow temperature
to its setting. I would have to manually adjust the temperature according
to the weather to achieve lower flow temperatures?

There are a couple of ways.

If you have TRVs, they will respond to the rooms becoming warm and
reduce the flow. The boiler is monitoring the resulting changes in
temperature of the water and will respond to it by adjusting output.
Since the heat required to be put into the room to maintain a given
temperature varies with outside temperature (plus a lag), there is
going to be a correlation between burn rate and outside temperature.

Some boilers have outside temperature monitoring and weather
compensation. The effect here is that the boiler now knows directly
what the heat requirement is going to need to be.

You can always adjust the water temperature down. Obviously, the
upper limit needs to be enough to provide adequate heat under cold
conditions. Other than that, cooler water means longer warm up time.




So for much of the year,
you would still be operating in the more efficient range below the dew
point. Obviously if you take the situation over the whole year it
won't be *as* good, but still worthwhile.

OK, I've turned the temperature down, doesn't the water heating take an age
now and give me legionnaires disease?

It depends on the boiler and its connection arrangements. If it has
a way of knowing that the heat demand is for a water heating cycle,
then it can go to a higher temperature for that. If not, even if the
flow temperature is reduced to 70 degrees, it will be enough to
maintain a cylinder at 60 degrees.



Not if its a condensing combi but I'm not going there.

Quite. The point is though that the boiler does then know the
difference between HW and CH.


Jim A





--

..andy

To email, substitute .nospam with .gl

On Tue, 04 Jan 2005 15:41:24 GMT, Tony Bryer
wrote:

In article , Jim Alexander
wrote:
Hmmm. Preparing for "compulsory" replacement condensing boilers
in May 2005 (two jags bombshell No2) had a holiday project
trying to find some hard data on this. Failed miserably. Any
links to actual data over the full operating temperature
ranges?

Does the graph on http://www.keston.co.uk/products/celsius25.htm help?

Interesting, but 100% efficiency at 20C could do with some explanation.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me

On Fri, 07 Jan 2005 23:53:52 GMT, Phil Addison
wrote:

On Tue, 04 Jan 2005 15:41:24 GMT, Tony Bryer
wrote:

In article , Jim Alexander
wrote:
Hmmm. Preparing for "compulsory" replacement condensing boilers
in May 2005 (two jags bombshell No2) had a holiday project
trying to find some hard data on this. Failed miserably. Any
links to actual data over the full operating temperature
ranges?

Does the graph on http://www.keston.co.uk/products/celsius25.htm help?

Interesting, but 100% efficiency at 20C could do with some explanation.


There's a better graph at

http://www.keston.co.uk/downloads/pdf/cel25-b.pdf

showing the knee in the efficiency curve at the dew point and the
resulting increased rate of change with temperature.

They should have probably dotted the curve below about 25-30 degrees,
since that is generally about the minimum modulated down temperature
in steady state.

It's also possible that they have included the latent heat in the
figures...





--

..andy

To email, substitute .nospam with .gl

On Sat, 08 Jan 2005 00:14:05 +0000, Andy Hall wrote:

On Fri, 07 Jan 2005 23:53:52 GMT, Phil Addison
wrote:

On Tue, 04 Jan 2005 15:41:24 GMT, Tony Bryer
wrote:

In article , Jim Alexander
wrote:
Hmmm. Preparing for "compulsory" replacement condensing boilers
in May 2005 (two jags bombshell No2) had a holiday project
trying to find some hard data on this. Failed miserably. Any
links to actual data over the full operating temperature
ranges?

Does the graph on http://www.keston.co.uk/products/celsius25.htm help?

Interesting, but 100% efficiency at 20C could do with some explanation.


There's a better graph at

http://www.keston.co.uk/downloads/pdf/cel25-b.pdf

showing the knee in the efficiency curve at the dew point and the
resulting increased rate of change with temperature.

But it still shows 100% efficiency.

ISTR some discussion about an EU way of measuring that could result in
more than 100%. I didn't take much notice at the time, thinking that was
nonsense. Is there something I'm missing or should the ASA, or at least
the CA, look into this? (the CA have been having a go at the ASA in the
latest "Which?").

They should have probably dotted the curve below about 25-30 degrees,
since that is generally about the minimum modulated down temperature
in steady state.

Hmmm... if you extrapolate their straight line it implies well over 100%
during warm up of an empty house on a cold day.

It's also possible that they have included the latent heat in the
figures...

I hope British Gas, et al, don't get wind of that or they'll be upping
the price of gas to include the value of the 'free' latent heat...
err... not!

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
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On Sat, 08 Jan 2005 22:38:00 GMT, Phil Addison
wrote:



But it still shows 100% efficiency.

ISTR some discussion about an EU way of measuring that could result in
more than 100%. I didn't take much notice at the time, thinking that was
nonsense. Is there something I'm missing or should the ASA, or at least
the CA, look into this? (the CA have been having a go at the ASA in the
latest "Which?").

It's all kosher and has to do with how the calorific value of the fuel
is considered - i.e. whether it is on a net or gross basis, taking
account of the latent heat recovered from the water vapour in the
combustion products of the condensing boiler or not.

The UK uses the gross value (including the possible latent heat) which
is why efficiencies never exceed 100%.

The rest of Europe uses net calorific value and so if there is latent
heat contribution through condensing, efficiencies do go abover 100%.

There is a good technical note written by Viessmann on this and the
principles of condensing technology in general.

http://tinyurl.com/54aqs




They should have probably dotted the curve below about 25-30 degrees,
since that is generally about the minimum modulated down temperature
in steady state.

Hmmm... if you extrapolate their straight line it implies well over 100%
during warm up of an empty house on a cold day.

It's also possible that they have included the latent heat in the
figures...

I hope British Gas, et al, don't get wind of that or they'll be upping
the price of gas to include the value of the 'free' latent heat...
err... not!

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me


--

..andy

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The message
from Andy Hall contains these words:

The rest of Europe uses net calorific value and so if there is latent
heat contribution through condensing, efficiencies do go abover 100%.

Which of course is semantic nonsense and leads dumbos like dIMM to think
they are getting something for nothing.

--
Roger

On Sun, 9 Jan 2005 09:19:36 GMT, Roger
wrote:

The message
from Andy Hall contains these words:

The rest of Europe uses net calorific value and so if there is latent
heat contribution through condensing, efficiencies do go abover 100%.

Which of course is semantic nonsense and leads dumbos like dIMM to think
they are getting something for nothing.

Yes of course, because charging is related to the given calorific
value.

What you can say is that condensing captures the latent heat, plus in
general lower flue gas temperatures lead to less heat loss.





--

..andy

To email, substitute .nospam with .gl

Roger wrote:

The message
from Andy Hall contains these words:


The rest of Europe uses net calorific value and so if there is latent
heat contribution through condensing, efficiencies do go abover 100%.


Which of course is semantic nonsense and leads dumbos like dIMM to think
they are getting something for nothing.

That would happen irrespective of anything else.

On Sun, 09 Jan 2005 00:08:00 +0000, Andy Hall wrote:

On Sat, 08 Jan 2005 22:38:00 GMT, Phil Addison
wrote:



But it still shows 100% efficiency.

ISTR some discussion about an EU way of measuring that could result in
more than 100%. I didn't take much notice at the time, thinking that was
nonsense. Is there something I'm missing or should the ASA, or at least
the CA, look into this? (the CA have been having a go at the ASA in the
latest "Which?").

It's all kosher and has to do with how the calorific value of the fuel
is considered - i.e. whether it is on a net or gross basis, taking
account of the latent heat recovered from the water vapour in the
combustion products of the condensing boiler or not.

The UK uses the gross value (including the possible latent heat) which
is why efficiencies never exceed 100%.

The rest of Europe uses net calorific value and so if there is latent
heat contribution through condensing, efficiencies do go abover 100%.

OK, I'll just have to accept that is the way the specs are written, but
I don't like it - it seems the UK has got it right this time.

One can ask where the heat that converts the generated H2O into vapour
came from. Surely from the energy created by burning the gas? It's
rather like defining a coal fire as 100% efficient if burnt in an open
grate, and then claiming 110% in a system that extracts the tar from the
smoke and re-burns it. Or saying a jet engine is 110% when the
afterburner is on. It's not compatible with the physics I learnt to
claim over 100% just because at some point in history it was not thought
realistic to utilise energy that was known to be present. One might as
well say a light bulb is 100% efficient because all the light is
emitted.

There is a good technical note written by Viessmann on this and the
principles of condensing technology in general.

http://tinyurl.com/54aqs

Thanks for that - an interesting update on the technology - I didn't
realise so much thought had gone into it.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me

On Sun, 09 Jan 2005 18:33:07 GMT, Phil Addison
wrote:

On Sun, 09 Jan 2005 00:08:00 +0000, Andy Hall wrote:



The rest of Europe uses net calorific value and so if there is latent
heat contribution through condensing, efficiencies do go abover 100%.

OK, I'll just have to accept that is the way the specs are written, but
I don't like it - it seems the UK has got it right this time.

Well...... if you consider the situation prior to condensing boilers
(say 25 years ago if one considers mainland Europe) then using the net
value was quite reasonable. The UK, using gross values would show
figures less than those.



One can ask where the heat that converts the generated H2O into vapour
came from. Surely from the energy created by burning the gas

That would assume that the H20 product of combustion was in the liquid
phase at the instant of combustion. It isn't - it's in the gaseous
phase. The initial amount of energy created is the same regardless
of whether the boiler is condensing or not.

When the water in the flue gases condenses, the latent heat is
released. In the case of the conventional boiler, this happens
outside, whereas for the condensing boiler it happens (mainly) inside.

I think that this appears strange because the energy considered on the
input side is not directly measured (as it can be with electricity,
for example), but is derived indirectly via the calorific value.



It's
rather like defining a coal fire as 100% efficient if burnt in an open
grate, and then claiming 110% in a system that extracts the tar from the
smoke and re-burns it. Or saying a jet engine is 110% when the
afterburner is on. It's not compatible with the physics I learnt to
claim over 100% just because at some point in history it was not thought
realistic to utilise energy that was known to be present.

I don't disagree. It's intuitively odd to think of efficiencies of
100% anyway. The alternative would have been to switch from using
the net calorific value to the gross one so that everything became
calibrated to 100%. The trouble is that the numbers for existing
products would then have to change, leading to a different kind of
confusion.

It does make things look as though people are getting something for
nothing, which of course they aren't. They are simply getting a
greater proportion of what they paid for.



One might as
well say a light bulb is 100% efficient because all the light is
emitted.

There is a good technical note written by Viessmann on this and the
principles of condensing technology in general.

http://tinyurl.com/54aqs

Thanks for that - an interesting update on the technology - I didn't
realise so much thought had gone into it.

There's about 20 years of history at least with condensing technology
in Germany and Holland especially, which is one reason why the
products coming from those countries tend to be good.








Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me


--

..andy

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On Sun, 09 Jan 2005 20:04:39 +0000, Andy Hall wrote:

On Sun, 09 Jan 2005 18:33:07 GMT, Phil Addison
wrote:

OK, I'll just have to accept that is the way the specs are written, but
I don't like it - it seems the UK has got it right this time.

Well...... if you consider the situation prior to condensing boilers
(say 25 years ago if one considers mainland Europe) then using the net
value was quite reasonable. The UK, using gross values would show
figures less than those.

I'm not sure that 25 years ago anyone considered the difference between
net and gross - I don't recall hearing the terms used. Efficiencies were
so low, and measurements so crude (compared to the method in the
Viessmann report) that the latent heat effect was probably lost in the
noise.

One can ask where the heat that converts the generated H2O into vapour
came from. Surely from the energy created by burning the gas

That would assume that the H20 product of combustion was in the liquid
phase at the instant of combustion. It isn't - it's in the gaseous
phase. The initial amount of energy created is the same regardless
of whether the boiler is condensing or not.

It is only in the vapour phase because we run the CH4+O2 reaction very
hot (in a flame). That is done deliberately in a boiler by igniting the
gases with a spark to get them to react. Another way (the precise method
may not have been invented yet!) would be to react them with a catalyst
below 100C. In either case isn't it possible to compute the energy
released using basic physical chemistry laws?

When the water in the flue gases condenses, the latent heat is
released. In the case of the conventional boiler, this happens
outside, whereas for the condensing boiler it happens (mainly) inside.

I think that this appears strange because the energy considered on the
input side is not directly measured (as it can be with electricity,
for example), but is derived indirectly via the calorific value.

AIUI the calorific value is defined as the total heat obtained by
complete burning, so it should be immaterial whether we react in a flame
or below 100C - so long as we capture all the heat produced. In an ideal
calorific heat measurement, all the material of combustion would be
captured, and the before and after temperatures would be the same. This
definition implies capturing the latent heat, though I admit to not
having checked to see if it is the accepted definition.

Anyway, I don't want to take on the task of putting the EU right, so its
all academic now.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me

The message
from Phil Addison contains these words:

AIUI the calorific value is defined as the total heat obtained by
complete burning, so it should be immaterial whether we react in a flame
or below 100C - so long as we capture all the heat produced. In an ideal
calorific heat measurement, all the material of combustion would be
captured, and the before and after temperatures would be the same. This
definition implies capturing the latent heat, though I admit to not
having checked to see if it is the accepted definition.

My 'Mechanical Engineers Handbook' claims to have been completely
revised in 1973 and that distinguishes between Higher and Lower
Calorific Values.

The following is based on the section on combustion.

On Combustion Efficiency (in engine or combustor) may be defined 3 ways:

In non flow combustors
- Actual volumetic %age of CO2/
Max. possible

In flow combustors
- Actual temp. rise in the combustion chamber/
Max poss. rise with same air/fuel ratio

In heating devices
- Actual heat transfer to working substance/
Max. poss. heat transfer in an isothermal reaction

--
Roger