Hi - I'm new to this forum but would appreciate some helpful advice.
I live in a flat and am having the kitchen refitted, which means moving
or replacing our existing boiler (Alpha Ocean Style FF - about 12 yrs
old).
I'm told that if we replace it we have to have a condensing boiler (new
building regs), but I understand that there are problems with the plume
from this type of boiler as we have a balcony roof above where the flue
would exit, and it's close to a door and a window.
The cheaper option is to just move the Alpha, but I'm worried this may
affect it (cause leaks). Or can we get a new non-condensing boiler
fitted?
I've spoken to 4 different heating companies (incl BG) and have had
different comments and advice from each.
Any help much appreciated. Thanks.

"CharlieR" wrote in message
oups.com...
Hi - I'm new to this forum but would appreciate some helpful advice.
I live in a flat and am having the kitchen refitted, which means moving
or replacing our existing boiler (Alpha Ocean Style FF - about 12 yrs
old).
I'm told that if we replace it we have to have a condensing boiler (new
building regs), but I understand that there are problems with the plume
from this type of boiler as we have a balcony roof above where the flue
would exit, and it's close to a door and a window.
The cheaper option is to just move the Alpha, but I'm worried this may
affect it (cause leaks). Or can we get a new non-condensing boiler
fitted?
I've spoken to 4 different heating companies (incl BG) and have had
different comments and advice from each.
Any help much appreciated. Thanks.

Look on the odpm site. There is the check list. If the plume is a nuisance,
then a non-condensing boiler can be fitted.

CharlieR wrote:

Hi - I'm new to this forum but would appreciate some helpful advice.
I live in a flat and am having the kitchen refitted, which means moving
or replacing our existing boiler (Alpha Ocean Style FF - about 12 yrs
old).
I'm told that if we replace it we have to have a condensing boiler (new
building regs), but I understand that there are problems with the plume
from this type of boiler as we have a balcony roof above where the flue
would exit, and it's close to a door and a window.

Limitations on proximity to doors and windows are not that different to
existing boilers. There are some issues with distances to neighbouring
properties though since some folks may find the plume objectionable.

What you have been told is correct basically - in that in order to meet
the energy efficiency requirements of the building regulations, you will
need a condensing boiler.

However there are exemptions allowed in certain circumstances. You can
find out if these apply to you by reading this:

http://www.odpm.gov.uk/pub/731/Guide..._id1130731.pdf
http://tinyurl.com/p6n3v

The cheaper option is to just move the Alpha, but I'm worried this may
affect it (cause leaks).

Moving it would count the same as installing - so unless you are
prepared to do it yourself (or can find a CORGI who is prepared to
ignore the regs) then you would be back to requiring the exemption as
above.

Or can we get a new non-condensing boiler
fitted?

See above.

I've spoken to 4 different heating companies (incl BG) and have had
different comments and advice from each.
Any help much appreciated. Thanks.

Hardly surprising - the regulations in this area are a bit of a pigs
breakfast.

--
Cheers,

John.

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

"John Rumm" wrote in message
...
CharlieR wrote:

Hi - I'm new to this forum but would appreciate some helpful advice.
I live in a flat and am having the kitchen refitted, which means moving
or replacing our existing boiler (Alpha Ocean Style FF - about 12 yrs
old).
I'm told that if we replace it we have to have a condensing boiler (new
building regs), but I understand that there are problems with the plume
from this type of boiler as we have a balcony roof above where the flue
would exit, and it's close to a door and a window.

Limitations on proximity to doors and windows are not that different to
existing boilers. There are some issues with distances to neighbouring
properties though since some folks may find the plume objectionable.

What you have been told is correct basically - in that in order to meet
the energy efficiency requirements of the building regulations, you will
need a condensing boiler.

However there are exemptions allowed in certain circumstances. You can
find out if these apply to you by reading this:

http://www.odpm.gov.uk/pub/731/Guide..._id1130731.pdf
http://tinyurl.com/p6n3v

The cheaper option is to just move the Alpha, but I'm worried this may
affect it (cause leaks).

Moving it would count the same as installing

It isn't.

Owain wrote:
CharlieR wrote:
Hi - I'm new to this forum but would appreciate some helpful advice.
I live in a flat and am having the kitchen refitted, which means moving
or replacing our existing boiler (Alpha Ocean Style FF - about 12 yrs
old).
I'm told that if we replace it we have to have a condensing boiler (new
building regs), but I understand that there are problems with the plume
from this type of boiler as we have a balcony roof above where the flue
would exit, and it's close to a door and a window.

Provided the regulations and the manufacturer's instructions re distance
from windows/walls are complied with there is no "problem" with the
plume - it's only water vapour - apart from aesthetically. Personally, I

And financially!

Are there any add-on units that take the exhaust down from ~80C to ~20C,
and use it to warm air to come into the house?

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the exhaust
by using the counter-current priciple to warm the incoming air to the
boiler. Warmer incoming air would surely reduce the work the boiler has to
do to heat the water?

Sounds too simple so there must be something wrong with the idea although I
can't see it.

Tim

On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the exhaust
by using the counter-current priciple to warm the incoming air to the
boiler. Warmer incoming air would surely reduce the work the boiler has to
do to heat the water?

Sounds too simple so there must be something wrong with the idea although I
can't see it.

Cars often have a temperature controlled flap that diverts the
incoming air via the radiator in order to warm it up.

sponix

On 17 Mar 2006 07:28:43 GMT, Ian Stirling
wrote:

Owain wrote:
CharlieR wrote:
Hi - I'm new to this forum but would appreciate some helpful advice.
I live in a flat and am having the kitchen refitted, which means moving
or replacing our existing boiler (Alpha Ocean Style FF - about 12 yrs
old).
I'm told that if we replace it we have to have a condensing boiler (new
building regs), but I understand that there are problems with the plume
from this type of boiler as we have a balcony roof above where the flue
would exit, and it's close to a door and a window.

Provided the regulations and the manufacturer's instructions re distance
from windows/walls are complied with there is no "problem" with the
plume - it's only water vapour - apart from aesthetically. Personally, I

And financially!

Are there any add-on units that take the exhaust down from ~80C to ~20C,
and use it to warm air to come into the house?

In effect, this is what some early UK designs of condensing boiler did
- manufacturers added a secondary heat exchanger. The trouble was
that the whole set up was not well designed to cope with the acidic
condensate and corrosion resulted; leading to a poor reputation in the
trade for condensing technology in general. German and Dutch designs
which were made from the ground up as condensing, did much better and
have been in use for many years.

The second aspect is that balanced flue boilers with no fan are not
designed to have an extended flue because they use natural draught to
bring in air and expel exhaust. Even those with a fan may not be
designed to run with a long flue since the fan may have been selected
to run with a designed and limited length flue.


--

..andy

On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the exhaust
by using the counter-current priciple to warm the incoming air to the
boiler. Warmer incoming air would surely reduce the work the boiler has to
do to heat the water?

Sounds too simple so there must be something wrong with the idea although I
can't see it.


There are several issues:

- People may not *want* to have a long flue even though the boiler may
be able to support it.

- Condensing boilers have a low exhaust temperature. Since the rate
of heat transfer would depend on the temperature difference between
incoming and outgoing air, this would be a lot less than on a
conventional boiler in the first place.

- Plastic flues are not good conductors of heat

Because of these first issues, to make this worthwhile whould probably
need something similar in concept to a plate heat exchanger where
there is a lot of contact area between the incoming and outgoing
flows. There needs to be good conductivity as well. There would be
additional condensation from outgoing flue gases and this condensate
would be acidic. There would be an increased resistance to flow for
gases in and out, and the fan would need to cope with that.

The net of all of this is that I suspect a physically large heat
exchanger with quite large stainless steel plates would be needed in
order to make much differene as well as standing up to the conditions.

I don't suppose that this would be inexpensive.





--

..andy

Sponix wrote:
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the exhaust
by using the counter-current priciple to warm the incoming air to the
boiler. Warmer incoming air would surely reduce the work the boiler has to
do to heat the water?

Sounds too simple so there must be something wrong with the idea although I
can't see it.

Cars often have a temperature controlled flap that diverts the
incoming air via the radiator in order to warm it up.

Cold air is denser so you get more air per unit volume to support
combustion so they also fit intercoolers to cool the air before it
enters the engine.

MBQ

wrote:
Sponix wrote:
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer
insulated co-axial flue. This would reclaim much more of the heat
lost in the exhaust by using the counter-current priciple to warm
the incoming air to the boiler. Warmer incoming air would surely
reduce the work the boiler has to do to heat the water?

Sounds too simple so there must be something wrong with the idea
although I can't see it.

Cars often have a temperature controlled flap that diverts the
incoming air via the radiator in order to warm it up.

Cold air is denser so you get more air per unit volume to support
combustion so they also fit intercoolers to cool the air before it
enters the engine.

Yeah but cars are internal combustion engines, not CH boilers so I'm not
sure the argument's the same. Intercooling in a car maximises the power
output which isn't the desired object of pre-warming the air in a CH boiler.

Tim

MBQ

wrote in message
oups.com...

Sponix wrote:
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the
exhaust
by using the counter-current priciple to warm the incoming air to the
boiler. Warmer incoming air would surely reduce the work the boiler has
to
do to heat the water?

Sounds too simple so there must be something wrong with the idea
although I
can't see it.

Cars often have a temperature controlled flap that diverts the
incoming air via the radiator in order to warm it up.

Cold air is denser so you get more air per unit volume to support
combustion so they also fit intercoolers to cool the air before it
enters the engine.

On start up better warm, after the engine is warm the colder the better.

Andy Hall wrote:
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:
Sounds too simple so there must be something wrong with the idea
although I can't see it.


There are several issues:

- People may not *want* to have a long flue even though the boiler may
be able to support it.

True but they might be convinced if the savings were worthwhile.


- Condensing boilers have a low exhaust temperature. Since the rate
of heat transfer would depend on the temperature difference between
incoming and outgoing air, this would be a lot less than on a
conventional boiler in the first place.

Again true but there is still wasted heat going out that could be regained.
I've no idea of the amount but there's no technical reason why the exhaust
temperature couldn't be cooled right done the the incoming air temperature.
Surely that's got to be worth something?


- Plastic flues are not good conductors of heat

Which would be good for the outer intake pipe. The inner exhaust pipe could
be made of stainless steel.


Because of these first issues, to make this worthwhile whould probably
need something similar in concept to a plate heat exchanger where
there is a lot of contact area between the incoming and outgoing
flows.

I think that without testing designs it would be premature to dismiss a
simple coaxial counter-current heat exchanger. Keeping it straight &
relatively long would keep it cheap making the payback period proportionally
shorter.

There needs to be good conductivity as well.

Duh...

There would be
additional condensation from outgoing flue gases and this condensate
would be acidic.

So the stuff that condenses at the moment and trickles back through the
boiler isn't acidic? I would presume that the boiler's materials already
take that into account.

There would be an increased resistance to flow for
gases in and out, and the fan would need to cope with that.

Well that's true and might limit what can be retro fitted to an existing
boiler but many boilers can already accept quite long flue extensions.

The net of all of this is that I suspect a physically large heat
exchanger with quite large stainless steel plates would be needed in
order to make much differene as well as standing up to the conditions.

I don't suppose that this would be inexpensive.

Maybe. I remain unconvinced.

Tim

"Ian Stirling" wrote in message
...
Are there any add-on units that take the
exhaust down from ~80C to ~20C,
and use it to warm air to come into the house?

Yep.

A company in Plymouth, Zenex, has come out with a "top box" that fits on a
condensing boiler's flue - out of the boiler into the box and out again to
outside. Not new as Johnnson & Starley has one for their forced air units
converting them to condensers. This appears a leap though making condensers
more efficient.

They announced it pre-Xmas, but now it is on sale.

It extracts even more latent heat from the flue of a condensing boiler. They
claim, with some independent validation, that a "condensing" boiler can
improve fuel consumption by 30%. Currently the best non-condensing boiler
is 80% SEDBUK, and the best condensing 92% - only 12% leap. They claim it
will go to the near 109% available (yes you can get 109% efficiencies from a
condensing boiler). There are no moving parts.

They claim that a combi can deliver 50% more water flow for the same input -
so a 12 litres per min job will be 18 litres, a big hype that fills a bath
pretty fast instead of a leisurely fill.

They are developing a 15kW combi that delivers 12 litres/min - a little
better than the average combi around. 12 litres is normally only achieved
by a 28kW boiler. So, at 15Kw it is not oversized for the CH in flats, and
the case size can be kept down.

They plan one for a non-condensing boilers too, that will bring non-
condenser into condesning territory.

They claim the price will fall from £595 as production gears up. If it get
to half, and it does what they say, then this can save a lot of fuel, the
bigger the house the more fuel saved.

They may have versions available for oil and LPG boilers. The version
available may suitable for LPG boioers. This box may well make an LPG boiler
equal, or better, than an oil boiler to run and with £600 on top probably
still lower capital costs of installation.

Worth looking at and assessing.
http://www.zenexenergy.com/downloads/HVR10-REPRINT.pdf
http://www.zenexenergy.com/

Buy here for alimted flue implementation. More flues to come.:
http://www.discountedheating.co.uk/shop/acatalog/Zenex_Gas_Saver.html

Another way of eliminating a plume and yet have higher efficiencies than
non-condensing boiler is to intall a bledning valve on the boiers
flow-return, set to 60C. The returning wtaer will always be about dew-point.

"Andy Hall" wrote in message
...
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the
exhaust
by using the counter-current priciple to warm the incoming air to the
boiler. Warmer incoming air would surely reduce the work the boiler has
to
do to heat the water?

Sounds too simple so there must be something wrong with the idea although
I
can't see it.


There are several issues:

- People may not *want* to have a
long flue even though the boiler may
be able to support it.

A long plastic mPVC flue can have a pipe around it. A pipe in pipe
arrangement. This is legal as the inside of flue is not touched at all.
It could run for 10 to 15 foot across a loft and have water in the gap
between the pipes. Feed cold mains water through this and it pre-heats the
water. Zenex, pre-heat water this way with their top boxes and claim 50%
greater flow rate through a combi. So, a 12 litres/min combi can be zipped
up to 18 litres/min. Big jump.

Using a pipe in pipe means it is cheaper than their top box. But they are
incorporating it all inside one combi box. They are talking to the big
boiler manufacturers to licence their technology. If a 12 l/min combi gives
18 litre/min for the same kW input then this combi will sell like hot cakes.
Also, the plume is eradicated.

Councils are now having to deal with complaints of nuisance pluming. This
appear to be the answer.

Doctor Drivel wrote:
"Andy Hall" wrote in message
...
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer
insulated co-axial flue. This would reclaim much more of the heat
lost in the exhaust
by using the counter-current priciple to warm the incoming air to
the boiler. Warmer incoming air would surely reduce the work the
boiler has to
do to heat the water?

Sounds too simple so there must be something wrong with the idea
although I
can't see it.


There are several issues:

- People may not *want* to have a
long flue even though the boiler may
be able to support it.

A long plastic mPVC flue can have a pipe around it. A pipe in pipe
arrangement. This is legal as the inside of flue is not touched at
all. It could run for 10 to 15 foot across a loft and have water in the
gap
between the pipes. Feed cold mains water through this and it
pre-heats the water. Zenex, pre-heat water this way with their top
boxes and claim 50% greater flow rate through a combi. So, a 12
litres/min combi can be zipped up to 18 litres/min. Big jump.

Using a pipe in pipe means it is cheaper than their top box. But
they are incorporating it all inside one combi box. They are talking
to the big boiler manufacturers to licence their technology. If a 12
l/min combi gives 18 litre/min for the same kW input then this combi
will sell like hot cakes. Also, the plume is eradicated.

Councils are now having to deal with complaints of nuisance pluming.
This appear to be the answer.

On Fri, 17 Mar 2006 08:19:35 -0000 Tim Downie wrote :
I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the
exhaust by using the counter-current priciple to warm the incoming air
to the boiler. Warmer incoming air would surely reduce the work the
boiler has to do to heat the water?

I'm not sure that warmer air would improve combustion efficiency - cars
are reputed to run better in cool weather as the air is denser. Re the
flue, ISTM that the problem is that if heat can easily migrate from the
flue into the room then the reverse will be true too, and when the boiler
isn't running the flue would act as a heat sink losing heat from the
room.

Are there any scientists here who can tell us how much heat could
potentially be recovered if you could condense all the water vapour in
the combustion gases. I remember enough school chemistry to know that
it's CH4+ 4O = CO2+ 2H2O - so every 12g of gas burned makes 36g of water
vapour. And the latent heat of water is easy to find. But I couldn't find
what gas weighs given that it is under pressure when metered.

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

"Tony Bryer" wrote in message
...
On Fri, 17 Mar 2006 08:19:35 -0000 Tim Downie wrote :
I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the
exhaust by using the counter-current priciple to warm the incoming air
to the boiler. Warmer incoming air would surely reduce the work the
boiler has to do to heat the water?

I'm not sure that warmer air would
improve combustion efficiency - cars
are reputed to run better in cool weather
as the air is denser.

The denser air means more oxygen. The same for any combustion process.

"Tony Bryer" wrote in message
...
On Fri, 17 Mar 2006 08:19:35 -0000 Tim Downie wrote :
I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the
exhaust by using the counter-current priciple to warm the incoming air
to the boiler. Warmer incoming air would surely reduce the work the
boiler has to do to heat the water?

I'm not sure that warmer air would
improve combustion efficiency - cars
are reputed to run better in cool weather
as the air is denser.

In co-axial flues the incoming air is heated by the exhaust air. Two pipe
flue systems are more efficient as the incoming cold stays cold until burnt.

On large trucks there were experiments to us heat pumps to cool the incoming
air. The larger the engine, and more fuel used, the more cost effective
these things are.

The message ews.net
from "Doctor Drivel" contains these words:

Councils are now having to deal with complaints of nuisance pluming.

Hah, I read that as plumbing and had visions of gangs of unruly plumbers
fitting a bathroom on the street corner and giving the wife a loutish
plungering.

--
Skipweasel
Pay no attention to the man behind the curtain.

The message ews.net
from "Doctor Drivel" contains these words:

In co-axial flues the incoming air is heated by the exhaust air. Two pipe
flue systems are more efficient as the incoming cold stays cold until burnt.

On large trucks there were experiments to us heat pumps to cool the
incoming
air. The larger the engine, and more fuel used, the more cost effective
these things are.

I'm fairly sure that the coolth of the incoming charge is only of
consequence on an expansion engine, where the idea is to get the
smallest most dense charge into the engine, then expand it to the
maximum amount practicable to extract the most energy possible.

Boilers are different - provided the fuel is fully burnt at the
stochiometric point or better (leaner), then all the thermal energy will
have been liberated and now the task it to extract as much as
practicable. This means that the closer the exhaust temperature is to
ambient (above, of course) the more energy has been retained for useful
purposes.

If you look at the design of boiler systems for power stations you'll
see that they take great trouble to preheat the imcoming air for
combustion to the maximum practicable. This is a much closer analogy to
a domestic boiler than an internal combustion engine.

--
Skipweasel
Pay no attention to the man behind the curtain.

On Fri, 17 Mar 2006 11:00:19 -0000 Tim Downie wrote :
Yeah but cars are internal combustion engines,

What with twiddling screws to get the gas-air mix right, poking
things in the exhaust pipe and spark plugs that don't they are
going that way!

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

"Guy King" wrote in message
...
The message ews.net
from "Doctor Drivel" contains these words:

In co-axial flues the incoming air is heated by the exhaust air. Two pipe
flue systems are more efficient as the incoming cold stays cold until
burnt.

On large trucks there were experiments to us heat pumps to cool the
incoming
air. The larger the engine, and more fuel used, the more cost effective
these things are.

I'm fairly sure that the coolth of the incoming charge is only of
consequence on an expansion engine, where the idea is to get the
smallest most dense charge into the engine, then expand it to the
maximum amount practicable to extract the most energy possible.

Yep.

Boilers are different

Not really, although external combustion is far more efficient than internal
explosions.

- provided the fuel is fully burnt at the
stochiometric point or better (leaner),

A pre-mix fan can only deliver a ratio of air/gas because of the fan design.
Put more oxygen insthe air and more efficient combustion. Cold air is denser
containing more oxygen.

then all the thermal energy will
have been liberated and now the task
it to extract as much as
practicable.

All the sensible heat has been liberated, not to recover the latent heat.

This means that the closer the
exhaust temperature is to
ambient (above, of course) the
more energy has been retained for useful
purposes.

It means more latetent heat has been extracted

If you look at the design of boiler
systems for power stations you'll
see that they take great trouble to
preheat the imcoming air for
combustion to the maximum practicable.
This is a much closer analogy to
a domestic boiler than an internal
combustion engine.

It depends on the engines being used. Turbines are different again.

Doctor Drivel wrote:

A long plastic mPVC flue can have a pipe around it. A pipe in pipe
arrangement. This is legal as the inside of flue is not touched at
all. It could run for 10 to 15 foot across a loft and have water in the
gap
between the pipes. Feed cold mains water through this and it
pre-heats the water. Zenex, pre-heat water this way with their top
boxes and claim 50% greater flow rate through a combi. So, a 12
litres/min combi can be zipped up to 18 litres/min. Big jump.

Yes *but* the Zenex design looks to be very much optimised for gas to water
heat exchange, not gas to gas. Now, what proportion of a typical domestic
combi boilers gas consumtion goes on heating hot water for the taps and how
much on heating for the radiators? 5%, 10%, 20%?

The water to gas heat exchange is going to do absolutely diddly if you're
not drawing hot water and would be useless on a non-combi boiler. (Okay,
you could run the SH return through it but the gains are going to be small).
A gas/gas heat exchanger would improve the efficiency *all* the time the
boiler is running.


Tim

"Tim Downie" wrote in message
...
Doctor Drivel wrote:

A long plastic mPVC flue can have a pipe around it. A pipe in pipe
arrangement. This is legal as the inside of flue is not touched at
all. It could run for 10 to 15 foot across a loft and have water in the
gap
between the pipes. Feed cold mains water through this and it
pre-heats the water. Zenex, pre-heat water this way with their top
boxes and claim 50% greater flow rate through a combi. So, a 12
litres/min combi can be zipped up to 18 litres/min. Big jump.

Yes *but* the Zenex design looks to be very much optimised for gas to
water heat exchange, not gas to gas. Now, what proportion of a typical
domestic combi boilers gas consumtion goes on heating hot water for the
taps and how much on heating for the radiators? 5%, 10%, 20%?

The water to gas heat exchange is going to do absolutely diddly if you're
not drawing hot water and would be useless on a non-combi boiler.

Read their web site and HV article again.

Tony Bryer wrote:

Are there any scientists here who can tell us how much heat could
potentially be recovered if you could condense all the water vapour in
the combustion gases. I remember enough school chemistry to know that
it's CH4+ 4O = CO2+ 2H2O - so every 12g of gas burned makes 36g of water

If you take the density in its gaseous state at 1.82 kg/m^3 - your 3:1
water to gas weight ratio above would yield 5.46 L of water vapour.
Which seems a bit much...

Are you sure that 36g is the mass of just the water? If it were the
total mass of the combustion product (i.e. inc CO2) that would make more
sense with a water vapour yield of 3.64 L

(if you take the latenet heat of vapourisation of water as 2.26 MJ/kg
the 5.46L figure would give you a total of 12.3MJ as oposed to 8.23MJ
for the lower figure)

Since the figures are normally quoted at about 36 / 43MJ for the nett /
gross energy yield of natural gas the latter one seems closer.

vapour. And the latent heat of water is easy to find. But I couldn't find
what gas weighs given that it is under pressure when metered.

It is under very little pressure when metered (0.021 Bar) so you can
probably discount that.


--
Cheers,

John.

/================================================== ===============\
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\================================================= ================/

On Fri, 17 Mar 2006 11:14:30 -0000, "Tim Downie"
wrote:

Andy Hall wrote:
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:
Sounds too simple so there must be something wrong with the idea
although I can't see it.


There are several issues:

- People may not *want* to have a long flue even though the boiler may
be able to support it.

True but they might be convinced if the savings were worthwhile.

and that the logistics of running the flue worked.



- Condensing boilers have a low exhaust temperature. Since the rate
of heat transfer would depend on the temperature difference between
incoming and outgoing air, this would be a lot less than on a
conventional boiler in the first place.

Again true but there is still wasted heat going out that could be regained.
I've no idea of the amount but there's no technical reason why the exhaust
temperature couldn't be cooled right done the the incoming air temperature.
Surely that's got to be worth something?

It depends on how much and the context of the rest of the house. The
amount of surface area required to achieve this amount of temperature
drop could become quite substantial.





- Plastic flues are not good conductors of heat

Which would be good for the outer intake pipe. The inner exhaust pipe could
be made of stainless steel.

Although the contact area is then not that substantial in comparison
to something with baffles etc.




Because of these first issues, to make this worthwhile whould probably
need something similar in concept to a plate heat exchanger where
there is a lot of contact area between the incoming and outgoing
flows.

I think that without testing designs it would be premature to dismiss a
simple coaxial counter-current heat exchanger. Keeping it straight &
relatively long would keep it cheap making the payback period proportionally
shorter.


It comes back to whether people would want the extra cost and hassle
of running a long flue for the small amount of energy involved.

There needs to be good conductivity as well.

Duh...

There would be
additional condensation from outgoing flue gases and this condensate
would be acidic.

So the stuff that condenses at the moment and trickles back through the
boiler isn't acidic? I would presume that the boiler's materials already
take that into account.

We were looking originally at conventional boilers.



There would be an increased resistance to flow for
gases in and out, and the fan would need to cope with that.

Well that's true and might limit what can be retro fitted to an existing
boiler but many boilers can already accept quite long flue extensions.

Generally those that are already condensing models.



The net of all of this is that I suspect a physically large heat
exchanger with quite large stainless steel plates would be needed in
order to make much differene as well as standing up to the conditions.

I don't suppose that this would be inexpensive.

Maybe. I remain unconvinced.

I would look elsewhere first


Tim


--

..andy

On Fri, 17 Mar 2006 11:10:08 -0000, "Doctor Drivel"
wrote:

wrote in message
roups.com...

Cars often have a temperature controlled flap that diverts the
incoming air via the radiator in order to warm it up.

Cold air is denser so you get more air per unit volume to support
combustion so they also fit intercoolers to cool the air before it
enters the engine.

On start up better warm, after the engine is warm the colder the better.

Wrong (partly) again. I guess you've never experienced "carb" icing
then?


--

On Fri, 17 Mar 2006 11:15:58 -0000, "Doctor Drivel"
wrote:

A company in Plymouth, Zenex, has come out with a "top box" that fits on a
condensing boiler's flue.

As you seem to have such a close relationship with this company, would
you care to locate the relevant patents that they claim to have?

The mumbo jumbo quoted on their website, together with the performance
"test" that has more holes in it than a colander hardly inspire
confidence in the claimed performance.


--

Doctor Drivel wrote:

A company in Plymouth, Zenex, has come out with a "top box" that fits on
a condensing boiler's flue - out of the boiler into the box and out
again to outside. Not new as Johnnson & Starley has one for their forced
air units converting them to condensers. This appears a leap though
making condensers more efficient.

Sounds like you have been reading glossy brosures again, get ready for
the incoming barrage of dodgy statistics....

It extracts even more latent heat from the flue of a condensing boiler.
They claim, with some independent validation, that a "condensing" boiler
can improve fuel consumption by 30%. Currently the best non-condensing

What did I say! What does that mean exactly? 30% of what?

From the description it sounds like the best that would be able to
achieve would be recovery of 30% or the un-recovered heat remaining in
the flue gasses - or put it another way, for a top efficiency boiler you
are only talking about perhaps 3% over and above what the boiler can
extract anyway. Note also the gain is only applied to HW use and not CH
- so again there is a proportionate reduction in return there.

boiler is 80% SEDBUK, and the best condensing 92% - only 12% leap. They

100% - 92% = 12% hmmm...

The idea looks ok in priniple, but I can't see how you will ever achieve
any payback given its £800 cost (probably more like £1100 once fitted
for most buyers). Unless you have a gerriatric old boiler with very poor
efficiency - in which case the cost of the top box would buy you a whole
new boiler.

claim it will go to the near 109% available (yes you can get 109%
efficiencies from a condensing boiler).

Only if you put the wrong calorific value (i.e. the nett value) for gas
into the equations... do the sums correctly and you can't.

They claim that a combi can deliver 50% more water flow for the same
input - so a 12 litres per min job will be 18 litres, a big hype that
fills a bath pretty fast instead of a leisurely fill.

Hype is certainly the word....

They are developing a 15kW combi that delivers 12 litres/min - a little
better than the average combi around. 12 litres is normally only

(I suppose we are talking about 35 degree rise over incoming temp here)

Are you sure that is not 12 lpm *peak* rate - i.e. by dumping its
reserve of stored heat into the first few litres demanded?

Otherwise where is the other 14.4kW coming from if you are talking about
susstained performance?

and the case size can be kept down.

"Straws", clutching at perhaps ;-)

Another way of eliminating a plume and yet have higher efficiencies than
non-condensing boiler is to intall a bledning valve on the boiers
flow-return, set to 60C. The returning wtaer will always be about
dew-point.

Why not leave it up to the control systems in the boiler? They seem to
do a pretty good job of modulating the gas rate to achieve best
efficiency anyway, and the efficiency ought to take precedence over the
visibility of the plume.

--
Cheers,

John.

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

Andy Hall wrote:
On Fri, 17 Mar 2006 11:14:30 -0000, "Tim Downie"
Maybe. I remain unconvinced.

I would look elsewhere first


Andy, I don't *know* if my idea would be viable but you seem to be taking
the position "It hasn't been done so it can't work" which may be right most
of the time but certainly not all of the time.

There's nothing logically wrong with my idea that you've pointed out. I see
no reason why a cheap co-axial flue extension shouldn't reclaim a
significant amount of waste heat. It doesn't need to be complicated and if
the bore diameters were reasonably dimensioned, it seems unlikely that it
would greatly increase the amount of backpressure over what a modern fan
flues boiler can cope with.

Tim

"Matt" aka Lord Hall wrote in message
...
On Fri, 17 Mar 2006 11:10:08 -0000, "Doctor Drivel"
wrote:

wrote in message
groups.com...

Cars often have a temperature controlled flap that diverts the
incoming air via the radiator in order to warm it up.

Cold air is denser so you get more air per unit volume to support
combustion so they also fit intercoolers to cool the air before it
enters the engine.

On start up better warm, after the
engine is warm the colder the better.

Wrong (partly) again. I guess you've never experienced "carb" icing
then?

Lord Hall, the point is combustion. I doubt the penny will drop.

"Matt" aka Lord Hall wrote in message
...
On Fri, 17 Mar 2006 11:15:58 -0000, "Doctor Drivel"
wrote:

A company in Plymouth, Zenex, has
come out with a "top box" that fits on a
condensing boiler's flue.

As you seem to have such a close
relationship with this company, would
you care to locate the relevant patents
that they claim to have?

Lord Hall, I have no direct relationship with them.

The mumbo jumbo quoted on their
website, together with the performance
"test" that has more holes in it than a
colander hardly inspire
confidence in the claimed performance.

GasTec, a testing house in Holand, confirnen their claims.

"Tim Downie" wrote in message
...
Andy Hall wrote:
On Fri, 17 Mar 2006 11:14:30 -0000, "Tim Downie"
Maybe. I remain unconvinced.

I would look elsewhere first


Andy, I don't *know* if my idea would be viable but you seem to be taking
the position "It hasn't been done so it can't work" which may be right
most of the time but certainly not all of the time.

There's nothing logically wrong with my idea that you've pointed out. I
see no reason why a cheap co-axial flue extension shouldn't reclaim a
significant amount of waste heat. It doesn't need to be complicated and
if the bore diameters were reasonably dimensioned, it seems unlikely that
it would greatly increase the amount of backpressure over what a modern
fan flues boiler can cope with.

Johnson & Starley sell a unit that converts a non-condensing conventional
flued forced air unit into a condenser doing what you proposed. It is a box
in the flue pre-heating air.

The message
from Tony Bryer contains these words:

Are there any scientists here who can tell us how much heat could
potentially be recovered if you could condense all the water vapour in
the combustion gases. I remember enough school chemistry to know that
it's CH4+ 4O = CO2+ 2H2O - so every 12g of gas burned makes 36g of water
vapour. And the latent heat of water is easy to find. But I couldn't find
what gas weighs given that it is under pressure when metered.

ISTM you don't need be a scientist to solve the problem. Being an
engineer is quite sufficient. The key is the difference between the
Higher and Lower Calorific Values of North Sea Gas. 38500 - 34500 = 4000
or about 10.4% of the higher value.

I could be wrong but I thought the figures usually bandied about for
boiler efficiency were based of the HCV. Dribble says different but he
can't be trusted at that level of competence.

As Tim pondered it should be worthwhile reducing exhaust gases to input
air temperature and while that would appear impossible in an gas to air
heat exchanger surely if achieved that would mean a fuel efficiency of
100%. But if that is the case then in the manner of heat engines if some
way was used to reduce the temperature of the exhaust gasses to less
than that of the incoming air then efficiency in excess of 100% does
become a possibility. Not technically true of course but on a par with
using the LVC to calculate boiler efficiencies.

--
Roger Chapman

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

A company in Plymouth, Zenex, has come out with a "top box" that fits on
a condensing boiler's flue - out of the boiler into the box and out again
to outside. Not new as Johnnson & Starley has one for their forced air
units converting them to condensers. This appears a leap though making
condensers more efficient.

Sounds like you have been reading glossy brosures again, get ready for the
incoming barrage of dodgy statistics....

Chav, this is your way of envy of my knowledge, as you tend to know sweet FA
about thsis game.

It extracts even more latent heat from the flue of a condensing boiler.
They claim, with some independent validation, that a "condensing" boiler
can improve fuel consumption by 30%. Currently the best non-condensing

What did I say! What does that mean exactly? 30% of what?

From the description it sounds like the best that would be able to
achieve would be recovery of 30% or the un-recovered heat remaining in the
flue gasses - or put it another way, for a top efficiency boiler you are
only talking about perhaps 3% over and above what the boiler can extract
anyway. Note also the gain is only applied to HW use and not CH - so
again there is a proportionate reduction in return there.

boiler is 80% SEDBUK, and the best condensing 92% - only 12% leap. They

100% - 92% = 12% hmmm...

The idea looks ok in priniple, but I can't see how you will ever achieve
any payback given its £800 cost (probably more like £1100 once fitted for
most buyers).

£600 and they hope to half this price once production is up.

Unless you have a gerriatric old boiler with very poor
efficiency - in which case the cost of the top box would buy you a whole
new boiler.

claim it will go to the near 109% available (yes you can get 109%
efficiencies from a condensing boiler).

Only if you put the wrong calorific value (i.e. the nett value) for gas
into the equations... do the sums correctly and you can't.

They claim that a combi can deliver 50% more water flow for the same
input - so a 12 litres per min job will be 18 litres, a big hype that
fills a bath pretty fast instead of a leisurely fill.

Hype is certainly the word....

Chav, tell that to GasTec in Holland who did the testing

Why not leave it up to the control systems in the boiler?

Chav, you clearly haven't got it.

You could buy a two pipe plastic flue combi and make you own pipe in pipe
flue, mains water pre-heater. Totally legal to do so. These plastic flue
boilers are expensive. Or buy one of these top-boxes for an Ariston and
the total cost is less than the Keston, Eco-Hometec, etc. And you claw back
a hell of a lot of wasted energy, converting 12 l/min combi to an 18
litres/min combi and fill your bath pronto

Then, add a GFX drain water heat reclaimer, solar panels too and DHW will
not cost too much at all. Have all this in a highly insulated and pretty
air-tight house, where DHW is the bulk of heating energy used, and your
overall gas bills will be very, very, low.

Doctor Drivel wrote:

Chav, this is your way of envy of my knowledge, as you tend to know
sweet FA about thsis game.

You probably are self deluded enough to believe that...

The idea looks ok in priniple, but I can't see how you will ever
achieve any payback given its £800 cost (probably more like £1100 once
fitted for most buyers).


£600 and they hope to half this price once production is up.

+VAT + the adaption kit for connecting to the boiler gets you to £788.
Still 'kin expensive at half the price.

If there are worthwhile gains to be had then you can expect a boiler
manufacturer to include the same concept in the box without needing
anything like the price jump proposed here.

Chav, you clearly haven't got it.

Chump, if it is what you have, then I clearly don't want it!

--
Cheers,

John.

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

"John Rumm" wrote in message
...


"Straws", clutching at perhaps ;-)

Chav, you really are a dumbo. Here is the GasTec report:
http://www.zenexenergy.com/downloads/Final%20GasTec%20report%20for%20Zenex.pdf

On Fri, 17 Mar 2006 15:54:23 -0000 Doctor Drivel wrote :
Chav, you really are a dumbo. Here is the GasTec report:
http://www.zenexenergy.com/downloads/Final%20GasTec%20report%20for%20Zenex.pdf

Which says that during the summer season you can expect to cut your
DHW energy usage by 12%. On a modern house DHW is responsible for about
one third of energy use and most of this will be during the heating
season (greater part of year and colder water coming in).

"Added to this figure should be the instantaneous saving of ~2.47% that
this achieved whilst the boiler is operational in DHW mode. The total
saving is thus projected to be ~(38+2.47) % ie fractionally in excess
of 40%. This figure will only be valid if the boiler operates for
sufficient hours to release the required amount of flue gas energy. If
this amounts to 2.47%, then energy that the boiler must consume is:-
2.24/0.0247 = 91kWh

This is equivalent to about 3 hours operation per day for a ~30kW Combi,
although this period should be reasonably uniformly distributed through
the day. This operational period and such an operational profile is not unreasonable during the winter months."

For most people this assumption is totally unreasonable. If you have a
30kW combi it's almost certain that this is determined by DHW needs. For
the typical house we use as a model (108m2 built to 2002 standards) the
annual heating energy is 7325kWh - averaging about 30kW/day across the
heating season. You can't recover what's not going out the flue.

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

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

Chav, this is your way of envy of my knowledge, as you tend to know
sweet FA about thsis game.

You probably are self deluded enough to believe that...

Chav, it is clear you are very lacking.

£600 and they hope to half this price once production is up.

+VAT + the adaption kit for connecting to the boiler gets you to £788.
Still 'kin expensive at half the price.

Payback could be 3 years. They aim to get it into mass produced combis as
an integral part of the combi. Many makers are assessing it, and a housing
associtions in Liverpool is testing out a number of them. Chav, tell them
they are all wrong, as you know better.

If there are worthwhile gains to be had then you can expect a boiler
manufacturer to include the same concept in the box without needing
anything like the price jump proposed here.

See above.

Chav, you clearly haven't got it.

Chump, if it is what you have, then I clearly don't want it!

Chav, you reall want it, but I never dance in Essex.