Is there a boiler that preheats the incoming air?

[The Natural Philosopher]

which shows that the heat exchange bit is less important than the condensing bit.

Or they simply dont like visible plumimg for some reason.

[The Natural Philosopher]

one canm usually assume that the working fluid inlet and outlet pressures eventually become the same, and teh poaahse cahnges are a function of temeprture anyway.

OK its more true for a heat engine than a boiler, because boilers make their own gases as it were, as well as simply heating the bulk of the air (nitrogen) and exchanging that heat with colder water. but its still the dominant factor.

That's the beauty of systems approaches to things. You don't need to know how its working internally.Calories go in, and calories come out., Some in the water that is to be heated, some into the room the boiler sits in, and some in the flue. They HAVE to add up to a balance.

The less calories come out, the more some have ended up heating the house in some way.

HOW you get less to come out, is the detail.

Arguably a conventional boiler with a heat pump on the exhaust might be a complex, but every efficient way to boost efficiency.

Certainly a conventional power station plus heat pump uses less energy than an in-house boiler. Sadly it tends to cost the same, or more..

[Doctor Drivel]

In cities condensing boilers have become a nuisance. Cowboy plumbers fit them in flats and the plumes are a cause of problems. The plumes look horrible coming out of the sides of buildings.

[<me9]

But that's completely different to a heat *engine* which is a heat to mechanical power conversion. In that case it is more to do with how close to absolute zero, not ambient, you can get the output fluid.

[<me9]

There is!

Each CH4 produces one CO2 molecule and two H2O molecules.

CH4 + 2O2 = CO2 = 2H2O.

Condensing the water is the equivalent of cooling it through 540 degrees. so well worth it.

[Andy Champ]

Trouble is they all quote efficiency based on 50 degree or so return temp. And mine is a lot more than that - I'd guess 65 at worst case - which will take off a lot of efficiency.

Andy

[The Natural Philosopher]

well you didn't even get that right.

CO2 doesn't equal 2H20

not when its less than 1% of the total mass

>

[The Natural Philosopher]

ER, no.

[<me9]

Typo. Have you never made one?

CH4 + 2O2 = CO2 + 2H2O.

11.8% more likely! A worthwhile contribution.

[The Natural Philosopher]

cant be even close to that.

21% of air is oxygen. Even if you are exactly at the whatever its called ratio to use ALL the oxygen, only one third of it, so 7% of the incoming, will be in the H20.

so that's 7% of the incoming AT BEST. BUT you have added methane as well, and that essentially dilutes the mix still further. with CO2

The more carbon to hydrogen ratio there is in the gas the less water and the more CO2, which reduces water content still further. butane and propane have a much higher carbon to hydrogen ration.

And you never would run a boiler at critical fuel-air tratis. You run it well over to ensure complete combustion. And full use of teh fuel.

[Andrew Gabriel]

It's not _well_ over as that knocks the efficiency too much. When my Keston is tuned spot-on perfect, the O2 exhaust is

5.7% and the excess air (over that used for combustion) is 37%, which results in around 40ppm CO. (CO output climbs as the excess air reduces, because it gets harder to find enough O2 molecules to oxidise the carbon fully to CO2. You are balancing CO production against the inefficiency of heating up excess air.)

A non-condensing boiler doesn't control the air flow, and they are typically between 100% and 170% excess air.

[mark]

stoicheiometric ratio

mark

[Andy Champ]

21% oxygen by volume. Let's keep with volume, and remember that the volume is roughly proportional to the number of molecules. Andrew's Keston burns 15% and leaves 6%. Given Methane fuel you end up with 1xCO2 and 2xH2O for each Methane, and use 2xO2 to make them. (By chance the burnt mixture has the same number of molecules as the unburnt one).

So: Incoming: 79% inert gasses, 21% O2; add 7.5% methane (it's not percent anymore but YSWIM)

Outgoing: 79% inert gasses 6% O2 7.5% Co2 15% H2O (If you want true percent; 73, 6, 7, 14 to the nearest integer). So one seventh of the outgoing mix is water. Well worth condensing out.

I'm on mains. Mostly methane.

I'll admit I was surprised how "lean" a mixture is used. I'm more used to IC petrol engines and they run very close to stoichiometric mixtures.

It may be that the wet exhaust holds too much energy for the dry intake to recover a significant amount of energy. Must crunch the numbers some time.

Andy