Pluming, and condensing boiler efficiency.
Donwill
less efficient than a condensing boiler that hardly plumes at all. Is
this statement true? If a proportion of the water vapour condenses
outside the boiler then surely you are losing some energy? I'm not sure,
what do others think?
Don
Dave Liquorice
> Is it related? I feel that a condensing boiler that plumes a lot may be
> less efficient than a condensing boiler that hardly plumes at all. Is
> this statement true?
Pluming is a function of the external air temp and humidity. If it's
cold a wet you get a plume, hot and dry and you won't.
As an indicator of efficency I suspect it's the other way round to
what you say. My reasoning being the the exiting flue gases on the
boiler that plumes a lot are cooler (ie the heat has been retained in
the boiler) than the one that doesn't. Cooler flue gases will get
below the dew point quicker than hotter ones. Thus the cooler gases
stand more chance of forming a visible plume before becoming
dispersed.
--
Cheers
Dave.
John Rumm
> Is it related? I feel that a condensing boiler that plumes a lot may be
> less efficient than a condensing boiler that hardly plumes at all. Is
> this statement true? If a proportion of the water vapour condenses
I think you will find it is actually the other way around...
> outside the boiler then surely you are losing some energy? I'm not sure,
> what do others think?
The pluming is related to the temperature of the flue exhaust - the
cooler it is (i.e. the more heat extracted, hence the lower the return
temperature to the boiler, the greater the condensing efficency), the
more pluming you are likely to see.
Remember that the condensing is designed to recover the latent heat of
vaporisation - i.e. the energy given up on the state change from gas
(i.e. steam) to liquid. What you see at the boiler flue is not steam but
water vapour already well below steam temperatures.
--
Cheers,
John.
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Ronald Raygun
> What you see at the boiler flue is not steam but
> water vapour already well below steam temperatures.
That's not quite correct. Water vapour *is* steam, and
is invisible (except for its refractive characteristics).
What you see isn't water vapour, it's a fog of water
droplets which have already condensed from the vapour
into the liquid state.
Pete Zahut
> On 21/11/2010 12:02, Donwill wrote:
>> Is it related? I feel that a condensing boiler that plumes a lot may
>> be less efficient than a condensing boiler that hardly plumes at
>> all. Is this statement true? If a proportion of the water vapour
>> condenses
>
> I think you will find it is actually the other way around...
>
>> outside the boiler then surely you are losing some energy? I'm not
>> sure, what do others think?
>
> The pluming is related to the temperature of the flue exhaust - the
> cooler it is (i.e. the more heat extracted, hence the lower the return
> temperature to the boiler, the greater the condensing efficency), the
> more pluming you are likely to see.
>
> Remember that the condensing is designed to recover the latent heat of
> vaporisation - i.e. the energy given up on the state change from gas
> (i.e. steam) to liquid. What you see at the boiler flue is not steam
> but water vapour already well below steam temperatures.
What does this all mean in a 'real-world' situation though, and if it's not
pluming 'correctly' what can you do about it? For instance, we have an Alpha
CD32C that feeds 6 rads, a towel rad and a kickspace heater. The boiler has
a control for heating (numbered 1 to 9 and set at 7 by the installer 3 years
ago) and the normal rads have TRVs, all fully open apart from the two spare
rooms where they are about 50%. The programmer/stat in the hallway is
normally set to about 18C.
The house is the correct temp for us and the way we like it but the boiler
doesn't plume very much at all, so is that 'wrong' and if so, what do we do
about it?
Roger Chapman
> On 21/11/2010 12:02, Donwill wrote:
>> Is it related? I feel that a condensing boiler that plumes a lot may be
>> less efficient than a condensing boiler that hardly plumes at all. Is
>> this statement true? If a proportion of the water vapour condenses
>
> I think you will find it is actually the other way around...
>
>> outside the boiler then surely you are losing some energy? I'm not sure,
>> what do others think?
>
> The pluming is related to the temperature of the flue exhaust - the
> cooler it is (i.e. the more heat extracted, hence the lower the return
> temperature to the boiler, the greater the condensing efficency), the
> more pluming you are likely to see.
I know I have appeared as particularly thick of late but I don't see
that at all. Surely extraction of latent heat requires no more of a
temperature change than conversion into latent heat. (ie none). Thus
what matters with the exhaust is its relative humidity at any given
temperature which is determined by the amount of condensation that has
occurred within the boiler. Water vapour turning to mist outside the
boiler is latent heat lost to the system.
> Remember that the condensing is designed to recover the latent heat of
> vaporisation - i.e. the energy given up on the state change from gas
> (i.e. steam) to liquid. What you see at the boiler flue is not steam but
> water vapour already well below steam temperatures.
But surely still with some latent heat.
dennis@home
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:B9GdnUAgcsLyiHTR...@brightview.co.uk...
> On 21/11/2010 12:02, Donwill wrote:
>> Is it related? I feel that a condensing boiler that plumes a lot may be
>> less efficient than a condensing boiler that hardly plumes at all. Is
>> this statement true? If a proportion of the water vapour condenses
>
> I think you will find it is actually the other way around...
>
>> outside the boiler then surely you are losing some energy? I'm not sure,
>> what do others think?
>
> The pluming is related to the temperature of the flue exhaust - the cooler
> it is (i.e. the more heat extracted, hence the lower the return
> temperature to the boiler, the greater the condensing efficency), the more
> pluming you are likely to see.
>
Are you sure, non condensing boilers plume a lot.
The exhausts may be hotter but they cool very quickly in cold air.
> Remember that the condensing is designed to recover the latent heat of
> vaporisation - i.e. the energy given up on the state change from gas (i.e.
> steam) to liquid. What you see at the boiler flue is not steam but water
> vapour already well below steam temperatures.
It may well be droplets that have condensed but if they haven't condensed on
the heat exchanger they probably haven't transferred the energy to the heat
exchanger so its has been wasted.
If the steam was condensing on the heat exchanger it wouldn't be in the air
to form a plume.
Its not at all obvious which is true as the observations can be made to fit
either theory, someone needs to measure the things to decide.
Roger Chapman
>> >> Is it related? I feel that a condensing boiler that plumes a lot
>> may be
>> >> less efficient than a condensing boiler that hardly plumes at all. Is
>> >> this statement true? If a proportion of the water vapour condenses
>> >
>> > I think you will find it is actually the other way around...
>> >
>> >> outside the boiler then surely you are losing some energy? I'm not
>> sure,
>> >> what do others think?
>> >
>> > The pluming is related to the temperature of the flue exhaust - the
>> > cooler it is (i.e. the more heat extracted, hence the lower the return
>> > temperature to the boiler, the greater the condensing efficency), the
>> > more pluming you are likely to see.
>>
>> I know I have appeared as particularly thick of late but I don't see
>> that at all. Surely extraction of latent heat requires no more of a
>> temperature change than conversion into latent heat. (ie none). Thus
>> what matters with the exhaust is its relative humidity at any given
>> temperature which is determined by the amount of condensation that has
>> occurred within the boiler. Water vapour turning to mist outside the
>> boiler is latent heat lost to the system.
>
> Who says its happening *outside* the boiler? I'd have thought that if
> things are working properly, it'll all condense *within* the boiler,
> giving up its latent heat and turning to water. Presumably this is the
> water that has to be run off. Some of the *condensed* water stays as
> water droplets (i.e., mist) and that is what you see as a plume.
I read John's explanation (the cooler it is ... the more pluming you
see) as suggesting the transformation from water vapour to mist was
occurring outside the flue.
>> > Remember that the condensing is designed to recover the latent heat of
>> > vaporisation - i.e. the energy given up on the state change from gas
>> > (i.e. steam) to liquid. What you see at the boiler flue is not steam
>> but
>> > water vapour already well below steam temperatures.
>>
>> But surely still with some latent heat.
>
> No, because it's not *steam* any longer. The mist is *water*. It won't
> give up more latent heat unless it freezes.
I focused on the 'water vapour' not on the 'what you see'. Are you
saying that water vapour, as opposed to mist, has no latent heat?
harry
Not all the water vapour present is condensed in the boiler. Some is
condensed when the combustion gases hit cold air outside. The visible
plume is water droplets. These evaporate into invisible vapour. Takes
longer for this to happen in cold weather hence the plume appears
bigger. The vapour can turn back into droplets too as it cools below
dewpoint. All to do with relative humidity in the plume.
VAG_dude
From what I have seen the plume is very large and thick when the
boiler is on full tilt i.e producing hot water at full flow rate
(37kw), on heating the plume is also large when the boiler is on full
power and not yet modulated down.
Roger Chapman
As far as condensing mode is concerned ISTR that condensing doesn't
occur at all unless the return temperature to the boiler is below
something in the region of 53 degrees C and even lower temperatures are
required to get extract anywhere near all the latent heat. In a house
that was originally plumbed for a conventional boiler it may be that the
radiators are too small to allow such a low return temperature for much
of a cold winter.
chris French
<no....@localhost.localdomain> writes
Well yes, though this is one of those situations where the
non-technical/colloquial use of a word conflicts with the more precise
definition.
--
Chris French
chris French
<den...@killspam.kicks-ass.net> writes
>
>
>"John Rumm" <see.my.s...@nowhere.null> wrote in message
>news:B9GdnUAgcsLyiHTR...@brightview.co.uk...
>> On 21/11/2010 12:02, Donwill wrote:
>>> Is it related? I feel that a condensing boiler that plumes a lot may be
>>> less efficient than a condensing boiler that hardly plumes at all. Is
>>> this statement true? If a proportion of the water vapour condenses
>>
>> I think you will find it is actually the other way around...
>>
>>> outside the boiler then surely you are losing some energy? I'm not sure,
>>> what do others think?
>>
>> The pluming is related to the temperature of the flue exhaust - the
>>cooler it is (i.e. the more heat extracted, hence the lower the
>>return temperature to the boiler, the greater the condensing
>>efficency), the more pluming you are likely to see.
>>
>
>Are you sure, non condensing boilers plume a lot.
No so much I'd say. We had a standard balanced flue boiler, as did our
old neighbours. They had a condensing boiler installed. The condensing
boiler produced much bigger plumes ISTM than the standard boiler.
>The exhausts may be hotter but they cool very quickly in cold air.
>
I've always assumed that being hotter, the exhaust can disperse more
before it condenses, so producing a less obvious plume
--
Chris French
John Rumm
Indeed, I was being imprecise...
What I wanted to distinguish between is the "fog" you can see - that
people think of as steam, but in reality is not, as opposed to the
transparent gas that steam actually is! ;-)
John Rumm
> John Rumm wrote:
>> On 21/11/2010 12:02, Donwill wrote:
>>> Is it related? I feel that a condensing boiler that plumes a lot may
>>> be less efficient than a condensing boiler that hardly plumes at
>>> all. Is this statement true? If a proportion of the water vapour
>>> condenses
>>
>> I think you will find it is actually the other way around...
>>
>>> outside the boiler then surely you are losing some energy? I'm not
>>> sure, what do others think?
>>
>> The pluming is related to the temperature of the flue exhaust - the
>> cooler it is (i.e. the more heat extracted, hence the lower the return
>> temperature to the boiler, the greater the condensing efficency), the
>> more pluming you are likely to see.
>>
>> Remember that the condensing is designed to recover the latent heat of
>> vaporisation - i.e. the energy given up on the state change from gas
>> (i.e. steam) to liquid. What you see at the boiler flue is not steam
>> but water vapour already well below steam temperatures.
>
> What does this all mean in a 'real-world' situation though, and if it's not
> pluming 'correctly' what can you do about it? For instance, we have an Alpha
There are no right and wrongs here. Plume visibility will vary with
weather and also how hard the boiler is working.
> CD32C that feeds 6 rads, a towel rad and a kickspace heater. The boiler has
> a control for heating (numbered 1 to 9 and set at 7 by the installer 3 years
> ago) and the normal rads have TRVs, all fully open apart from the two spare
> rooms where they are about 50%. The programmer/stat in the hallway is
> normally set to about 18C.
>
> The house is the correct temp for us and the way we like it but the boiler
> doesn't plume very much at all, so is that 'wrong' and if so, what do we do
> about it?
Condensing boiler efficiency will improve with lower flow and return
temperatures. You also get an increase in the rate of improvement of
efficiency at about 54 degrees C. So a condensing boiler running at
50/30 will tend to perform a little better than one running at 80/60
John Rumm
> On 21/11/2010 12:49, John Rumm wrote:
>> On 21/11/2010 12:02, Donwill wrote:
>>> Is it related? I feel that a condensing boiler that plumes a lot may be
>>> less efficient than a condensing boiler that hardly plumes at all. Is
>>> this statement true? If a proportion of the water vapour condenses
>>
>> I think you will find it is actually the other way around...
>>
>>> outside the boiler then surely you are losing some energy? I'm not sure,
>>> what do others think?
>>
>> The pluming is related to the temperature of the flue exhaust - the
>> cooler it is (i.e. the more heat extracted, hence the lower the return
>> temperature to the boiler, the greater the condensing efficency), the
>> more pluming you are likely to see.
>
> I know I have appeared as particularly thick of late but I don't see
> that at all. Surely extraction of latent heat requires no more of a
> temperature change than conversion into latent heat. (ie none). Thus
Indeed - you recover the latent heat on the state change...
> what matters with the exhaust is its relative humidity at any given
> temperature which is determined by the amount of condensation that has
> occurred within the boiler. Water vapour turning to mist outside the
> boiler is latent heat lost to the system.
The main change is with a conventional boiler the exhaust temp will be
in excess of a couple of hundred degrees C. The water (manufactured
during the combustion process) will be expelled as steam (in the true
sense) in the flue gasses. They will condense later but are usually too
dispersed by the time they have cooled enough to be particularly visible.
On the condenser, the state change will have mostly happened in the
boiler - leaving liquid water in the flue gas rather than steam.
>> Remember that the condensing is designed to recover the latent heat of
>> vaporisation - i.e. the energy given up on the state change from gas
>> (i.e. steam) to liquid. What you see at the boiler flue is not steam but
>> water vapour already well below steam temperatures.
>
> But surely still with some latent heat.
Heat yes, but not latent heat. What you see in the flue gas on a modern
boiler is already liquid water. You only recover the latent heat once on
the state change from gas to liquid. So a lower return temp will allow
you to extract a bit more heat from the flue gasses, but its not a big
gain like that from the initial condensation.
John Rumm
> Are you sure, non condensing boilers plume a lot.
> The exhausts may be hotter but they cool very quickly in cold air.
Non condensers are designed not to condense (and hence plume) if
possible - since condensation in the boiler was in those days a "bad
thing" - it quickly caused corrosion of cast iron heat exchangers etc.
You typically see condensing occurring on a conventional boiler when it
first fires up and all the cold metalwork absorbs a proportion of the
heat dropping the flue temperature to lower than normal. Atmospheric
conditions effect matters a fair bit as well.
>> Remember that the condensing is designed to recover the latent heat of
>> vaporisation - i.e. the energy given up on the state change from gas
>> (i.e. steam) to liquid. What you see at the boiler flue is not steam
>> but water vapour already well below steam temperatures.
>
> It may well be droplets that have condensed but if they haven't
> condensed on the heat exchanger they probably haven't transferred the
> energy to the heat exchanger so its has been wasted.
> If the steam was condensing on the heat exchanger it wouldn't be in the
> air to form a plume.
Some will condense directly on the HE, and some will do do in the air
flow adjacent to it.
A better assessment of the condensing efficiency is to look at the rate
of liquid water discharged from the condensate pipe than at the amount
of plume visible (which is effected by to many external factors to be a
reliable indicator)
> Its not at all obvious which is true as the observations can be made to
> fit either theory, someone needs to measure the things to decide.
I think you will find studies have been done....
There was a link Andy Hall used to post that contained one IIRC.
Donwill
swamped by " what colour shall I paint my Gran's front door" type questions.
I knew that question would draw you out, I think I shall have to turn my
pump down a tad so I can present a cooler temp on the return.
Cheers
Don
Jeremy Brown
--
For full context, visit https://www.homeownershub.com/uk-diy/pluming-and-condensing-boiler-efficiency-669751-.htm
Fredxx
> Roger is one of the very few who understands condensing boilers.
>
http://wiki.diyfaq.org.uk/index.php/Home_owners_hub