"Andy Hall" wrote in message
...
On Wed, 14 Jan 2004 15:51:05 -0000, "Christian McArdle"
wrote:

Do you have a feeling as to whether this is because the bottom
modulating point is less or because it's condensing more internally
and delivering to the condensate drain?

I'm not quite sure. We were going to pull the condensate drain apart and
take a peek, but never got round to it, as I needed the cooker point
moved
the same day.

I put a tundish under mine to be able to see the flow.

I had a bucket under the Isar I did a few weeks back, and got a steady
dribble of condensate (it was a cold night, in a cold house, and we'd fired
up the system for the first time). But we couldn't see the flue.


One major difference is that the flue is much longer. Not very long,
mind.
However, it does have a couple of bends, an extension piece and a
vertical
flue terminal. This would give a much greater chance of flue condensing.

Could have an influence, I suppose. I have a flue kit which is a bend
and straight out through the wall, with a downward slope back to the
boiler.



I still don't know if it isn't pluming because the flue gas is too hot,
or
too cold for major condensing at the terminal. If anything, there are
more
wisps at higher return temperatures than lower ones.

Given the current conditions, it's probably because it is modulated
down. Don't forget that the volume of condensate produced depends on
the burn rate as well as the low temperature - i.e. less gas, less
water. Also, it looks like this boiler modulates by varying fan
speed. This influences the velocity of the flue gases, and I would
assume that the longer time spent inside, the greater the amount of
condensation inside.



It seems a shame really, having gone to all the trouble of having the
terminal in a place where pluming wouldn't be a problem! (It goes out
through the roof).

It would appear that different designs have different characteristics.

The Greenstar seems to have a minimum power level of 7.5kW vs. the
Ideal's 9kW, although that doesn't suggest a huge difference.
Perhaps the heat exchanger arrangement - although both seem to be
downfiring types, the Greenstar looks like it has a tall heat
exchanger at the side, whereas the Ideal has a shallower one at the
top.

My boiler drops down to about 3kW on CH output, and under those
conditions, there is very little visible from the flue and a steady
drip of condensate - perhaps 2-3/second.
The only time when there is a more substantial plume is when the
boiler starts a hot water cycle with a totally cold cylinder. Then it
is wound up to about 28kW with full fan speed and a temperature
difference across it of 25 degrees plus. Under those circumstances
there is a fairly hefty stream of condensate into the drain. That
only lasts for a few minutes, though. There is a temperature sensor
on the cylinder, and as the water temperature approaches the set
point, the boiler modulates down

When I measured the gas rate it was approx .01 m^3 in 15s immediately the
boiler fired up (not measured over the usual 2 minutes for a digital meter
as the boiler modulates down too soon) indicating a heat input of 25.73kW.
After about 30s(?) the boiler modulated down to half that, staying at that
sort of rate for several minutes until it turned off. (It was too cold, late
and dark to take more gas rate samples, but when Christian gets a webcam set
up on the meter and we can OCR the readings I'm sure we'll get some really
interesting data :-)


--
John Stumbles
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The astronomer married a star