how much condensate per therm NG?

Dale Pickard

Thanks

for going through the stoichiometry. (sp?) My chemistry was some time ago.

Dale

Dale Pickard

I don't think so.

I just think that you discovered experimental error. I'd trust the measurement that you are taking at the boiler outlet as correct, especially if you have calibrated the thermometer. The copper tube wall is almost transparent thermally, (less than 1 deg drop).

Dale

Kal Row

Ok lets try expansion…its one of the refrigeration cycles…

There is quite an increase in area from the combustion to exit. So the stuff cools, the h2o drops out of the mix, and gives up its latent heat, the three inch exit is a lot larger than the 1.5 inch gas valve venturi – so you have a net cooling

so perhaps, the are getting cool, outlet temps, and lots of water removal, but maybe they are not recovering quite as much latent heat – as they would have you believe – but they are definitely doing better than the munchkin or the vidoden on high temp loads

I have to look at Buderus’s docs, their new wall mount is aluminum also – have to see what it can do

Dale Pickard

OK

That sounds more plausible....but still skeptical.

Dale

.

> Try 60 degrees and 55 degrees.


(a) We are now getting several days when the number of ddays is the same as in November. But the Munchkin is consuming 20% more gas. Changing the baseline can't possibly change that result.

(b) The previous (CI) boiler did not show the deteriorating trend, using the same (65F) baseline.

Dale Pickard

Do Propane

Hello Micheal,

Can you flesh out propane for us in a similar way? Great education, information for all.

Thanks,

Dale

Dale Pickard

Seems unreasonable though

Don't you think? To what do you attribute the difference in fuel consumption. Is the munchkin running poorly? Do you suggest they all run this way?

I think the difference must be in the experimental technique. (not to diss your efforts at all). It's just that Comparing one installation to another by way of DD seems fraught with potential error. One wants something harder with which to check or correlate the DD data. Like a btu/meter on both boiler outlets.

If it were a Vitodens, I would definitely check the technique before I questioned the boiler.

Dale

michael_15

propane

Propane is C₃H₈.

C₃H₈ + 5O₂ -> 3CO₂ + 4H₂O

Releases 2292 kJ/mol if the water is allowed to condense. Since 1 therm = 105500 kJ, this reaction must happen to the (105500/2292)=47.5 molar equivalent level.

47.5 molar equivalents * 4 H₂O per equivalent = 190 moles of water = 3422 grams at 18 grams/mole.

3422 grams = 0.904 gallons.

Goodness, this sounds like what I did all through college.

-Michael

Chuckles_3

> Don't you think? To what do you attribute the

> difference in fuel consumption. Is the munchkin

> running poorly? Do you suggest they all run this

> way?


If I knew, I wouldn't have started this thread.

> I think the difference must be in the

> experimental technique. (not to diss your efforts

> at all). It's just that Comparing one

> installation to another by way of DD seems

> fraught with potential error.


I have no idea what you mean. I can't compare the gas consumption of an old boiler to that of a new boiler? Isn't that the bottom line?

Dale Pickard

Sure but,

There are other uncontrolled variables, among them the actual DD experienced at your house and the use and occcupancy of the house. Hard to account for 20% Is the munch driving dhw as well?

Bummer if the new munchkin is not doing as well as your old CI boiler. Have you done the flue gas analysis? Is it running well? Is there something that you suspect in the Munch design that accounts for the difference?

Dale

Chuckles_3

> Is the munch driving dhw as well?


No.

> Bummer if the new munchkin is not doing

> as well as your old CI boiler.


I didn't say that. It's doing slightly better in moderate weather, no difference in 0F weather (design is -10F, which we didn't reach this year).

>Have you done the flue gas analysis?


Yes, it's just fine.

> something that you suspect in the Munch design

> that accounts for the difference?


This is beyond my expertise. But it was doing fine in the fall, maybe 30% better than the CI boiler.

Chuckles_3

another calculation of interest

If I put condensate per therm (1.1 gals) together with the latent heat of vaporization for water (970 BTU/lb) and the weight of one gallon of water (8.3 lb), I come up with a theoretical saving due to full condensing of 9000 BTU per therm, or 9%.

YMMV; in fact I am currently condensing only half this amount (i.e. about half a gallon per therm), even though my return water never exceeds 120F.

This calculation has also made me realize that any problems with the condensing process can't possibly explain a 20% increase in usage per degree-day. In other words I didn't need to start this thread at all...I will have to look elsewhere for the explanation, as some people have already told me in posts above.

Mike T., Swampeast MO

Experimental Error

CERTAINLY accept the possibility.

However, I'm using the supply temp reported by the boiler itself and the flue temp I measure in that port. Guess I could add a bit of slack and put the sensing element an nth away from the HX (instead of 3-4" away), but wouldn't that cause another problem with radiant energy from the HX inflating the air temp?

Guess it's possible that the Vitodens isn't reporting the proper temp, but I try to believe that such an appliance isn't prone to that sort of error.

Kal Row

hard science is soooo soothing to the mind!!! tnx

Kal Row

true - at the end of the day....

Condensing boilers are more efficient, not because of condensing, but rather good combustion and modulation

Mike T., Swampeast MO

Gotta Love the Chemists...

..who exercise their learning.