How Much Coal Is Wasted Per Day Through a Barometric Damper?

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Carbon12
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Post Wed. Dec. 18, 2013 9:53 am

So true CK!!! I'm estimating burning 6 tons this winter for heat and hot water. I would have to burn 16 tons to equal the $$$ cost of fuel oil and that would be with the thermostat set much lower. Set at 72 degrees with fuel oil??? No way Jose'!!! 72 degrees with coal??? Amen! :D
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Lightning
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Post Wed. Dec. 18, 2013 10:30 am

I made some diagrams and had lots of coffee this morning. :lol:
I'm ready to take another stab at this.
I will probably re state a few things to keep train of thought moving in the right direction :oops:

How much coal is wasted per day thru a barometric damper? When Larry asked this, I assumed the waste of coal would be due to the need for more heat, since the baro would promote excess cold air infiltration into the home. So, it turns out that based on what Carbon12 posted, the amount of air required for the barometric could be much more than anticipated earlier in this thread. Its true that all of the air that the stove and baro uses ultimately comes from cold air infiltration. Its also true that the house has its own cold air infiltration going on due to stack effect. There is warm air pushing against the ceiling making its way out thru gaps, cracks and every unsealed light fixture, attic door and so on, up high in the house. At the same time, cold air is infiltrating the bottom of the house in an equal amount the same way.

Is all of the air that the stove and baro use additional air infiltration? Or could it be that only part of the air that the stove uses is additional air infiltration? And if the latter question is true, where would the other part of the air that the stove uses come from?? These few questions I want to challenge since it very well could be a significant difference..

So here is what I've come up with:
The neutral pressure plane (NPP) is a point in the house where the pressure inside exactly equals the pressure outside. It makes a horizontal line somewhere in the house. A house that is equally sealed on top and bottom will have a NPP somewhere in the middle of it like in the diagram below. In this demonstration, the temperature difference between inside and outside (whatever they may be) causes a stack effect in the house with the pressures I listed on the movable plane.. (Please pardon the crudity I didn't have time to make it to scale lol) You can see we have a -.015 at the floor and a +.015 at the ceiling.
20131218_081231.jpg
Now, lets turn on an exhaust fan or run a heating appliance that requires a chimney that will take air out of the house. Lets say the result is a drop in pressure in the entire house of a -.005 ... Since the NPP always equals exactly the pressure outside look what happens in the diagram below.
20131218_081319.jpg
What happens is, the NPP moves up! So what right? Well, now we have a -.020 at the floor and a +.010 at the ceiling. So what does that mean? Since pressure dictates the volume of air coming in at the floor and also dictates volume of air going out at the ceiling we have more cold air infiltrating than what is leaving the house at the ceiling. Time for another demonstration to explain how all this results.

For simplicity, lets say stack effect by itself in the house is turning over 5000 cubic feet per hour. There is 5000 cf/hour coming in at the floor and 5000 cf/hour leaving the house at the ceiling. Now lets fire up the coal stove. For simplicity lets assume the coal stove with its baro sends 1000 cf/hour up the chimney. Like an exhaust fan, the chimney (with its lighter air instead of rotating blades - same effect) is pumping air out of the house which drops the entire house's pressure and moves our NPP up higher. With our NPP higher, less air is leaving the house at the ceiling and more air is coming in at the floor. How can more air come in at the floor than what is leaving at the ceiling?? (This would violate Air in= Air out). The stove and baro is using it. Only part of the air that the stove is using is additional cold air infiltration to the infiltration that's already happening due to stack effect in the house, the other part is air that would infiltrate regardless if the stove is in use or not. In this demonstration, our house is equally sealed on top and bottom. The stove's usage is 500 cf/hour that is additional cold air infiltration (for a total of 5500 cf/hour coming in at the floor) because of the increased negative pressure there, and the other 500 cf/hour is air that was held back from escaping (total of 4500 cf/hour leaving at the ceiling) due to the equal amount of decreased positive pressure at that location. The part that is held back is the same part that would leave the house when the stove is not being used.

And this is how I have come to the conclusion that half of the total air that the stove and baro use is additional cold air infiltration. Why precisely half? Because the deficient pressure effect caused by the stove and baro would be equally dispersed across the entire house envelope.

I'm gonna go put some coal on the fire now :lol:
Last edited by Lightning on Wed. Dec. 18, 2013 5:14 pm, edited 2 times in total.

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Carbon12
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Post Wed. Dec. 18, 2013 11:00 am

Well, Lightning I suppose I could always do an experiment :D I've been measuring my coal consumption closely on a daily basis and comparing it to Degree Days. I seem to have a consistent formula. This is with the Baro. I SUPPOSE I could foil off the Baro and track consumption for 24 hrs. I'm not sure I can adjust the blower air on the stoker enough to equal the over fire readings of the Baro. Let me take a look and see how close I can get. I'll have to think about it some more too. Not sure the data will be meaningful in any way??? It might fuel the fires of our discussion, however! :lol:
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Carbon12
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Post Wed. Dec. 18, 2013 11:13 am

I'm just going to run a loop of PEX through the sofa and shut off the air handler! That'll teach my evil, air infiltrating boiler a lesson! :lol:
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Post Wed. Dec. 18, 2013 11:28 am

Very interesting addition Lee to a very interesting discussion !!!!!

It would also be interesting to have multiple manometers through out an average house (mine leaks way too much to think about considering) to see if ,and what, numbers are produced for that house stack affect. And, to see what, if any changes occur at each point as a baro is opened, or sealed off at various stove burn rates.

One assumption is that air leakage in/out of a house can easily change to adapt to changes of feeding leaks out, plus a stove with (or without a baro).

But, as I mentioned to you with your pipe secondary air supply experiment, openings don't flow air proportionally to their size. Especially so with the usual small openings that make up air leakage in many houses. The smaller a leak, the sooner it's resistance to air flow starts requiring a greater pressure drop to flow more air through that same small opening.

So, is there a point in some houses that leakage will switch over from more easily leaking cold air lower in the house, to maxing them out (without a change in pressure drop ) and starting to pull cold air from warm air leakage points up higher in the house (cold then coming in where warm was going out), and how that would affect where that NPP point is ?

All theories that I think would be very interesting to see numbers for.

Paul
So many stoves - so few chimneys. I must be coal-stone crazy.

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Post Wed. Dec. 18, 2013 11:28 am

Carbon12 wrote:I'm just going to run a loop of PEX through the sofa and shut off the air handler! That'll teach my evil, air infiltrating boiler a lesson! :lol:
:D You show 'em C12 ! :D

Paul
So many stoves - so few chimneys. I must be coal-stone crazy.

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Post Wed. Dec. 18, 2013 12:03 pm

Carbon12 wrote:I've been measuring my coal consumption closely on a daily basis and comparing it to Degree Days. I seem to have a consistent formula. This is with the Baro. I SUPPOSE I could foil off the Baro and track consumption for 24 hrs. I'm not sure I can adjust the blower air on the stoker enough to equal the over fire readings of the Baro.
If I understand correctly, wouldn't you want to have outside air piped to your combustion blower to see the difference foiling the baro would have on coal consumption?

It seems to me that with combustion air piped in before and after foiling the baro, it isolates the effect of the baro on coal consumption making it easier to quantify. Without piped combustion air don't you have other variables introduced from the cooler air infiltration that muddy the impact of the baro?

Or is the idea to try to come up with a 'net' coal usage impact for a given installation including all variables whether they are quantifiable or not?

I think I've just max'ed out my threshold of thinking about this!! :wacko:
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Carbon12
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Post Wed. Dec. 18, 2013 12:12 pm

Somewhere in the world there must have been a study done about this! I just can't find a published scientific study using coal as a heat source! Does anyone's kid need a college level science project???
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Carbon12
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Post Wed. Dec. 18, 2013 12:17 pm

Of course, letting the dog in and out all morning has me thinking that the repeated rush of cold air into a home when an exterior door is opened probably makes any and all calculations about a Baro null and void. Who cares, as long as it's warm and I'm paying a lot less for coal than fuel oil,.....and having fun doing so!!! :D
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Post Wed. Dec. 18, 2013 12:19 pm

Hell C12, in this day & age, that would be a Elementary School level science project--ya think?
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Post Wed. Dec. 18, 2013 12:41 pm

Sunny Boy wrote:So, is there a point in some houses that leakage will switch over from more easily leaking cold air lower in the house, to maxing them out (without a change in pressure drop ) and starting to pull cold air from warm air leakage points up higher in the house (cold then coming in where warm was going out), and how that would affect where that NPP point is ?

If an exhaust fan pumped air out of the house at a high enough rate the NPP would go above the ceiling. It makes sense to me also that opening an attic way in the ceiling that would vent out thru the roof could do this too. At that point the entire house would have a negative pressure as compared to pressure outside. And then yes, air would come in from everywhere to try to equalize the negative pressure in the house.. :D

This condition would also cannabalize the draft in the chimney and cause a reversal.

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Post Wed. Dec. 18, 2013 12:49 pm

This issue exists regardless of the fuel....coal, oil, gas...they all need air to burn, and if the appliance is connected to a chimney it usually requires a draft control...which will pull air from the mechanical room that needs to be replaced.

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Post Wed. Dec. 18, 2013 1:00 pm

Lee,
I was thinking more steady state for that heated indoor space. Adding variables such as fans on, or off, windowstats in use :roll: or chopping holes in roofs like a fireman :shock: while they add to the complexity, would they get us any closer to an answer for, or against a baro ????

Paul
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Post Wed. Dec. 18, 2013 1:13 pm

Rob R. wrote:This issue exists regardless of the fuel....coal, oil, gas...they all need air to burn, and if the appliance is connected to a chimney it usually requires a draft control...which will pull air from the mechanical room that needs to be replaced.
Good point.

But, then if we get away from just coal use, there may be another question with that. Is there any bearing on the baro's job if the fuel choice is a constant heat output like coal and wood, or intermittent output like oil and gas ?

If that doesn't mater, then I think it gets back to the simple question of, . . does it waste more heat to pull that warmer indoor air through a baro, or without a baro, putting more draft pressure on the heating appliance and possibly pulling more warm room air through it (depending also on how air tight it is) ?

Paul
So many stoves - so few chimneys. I must be coal-stone crazy.

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Post Wed. Dec. 18, 2013 1:20 pm

Sunny Boy wrote: would they get us any closer to an answer for, or against a baro ????
The answer is if you have fluctuating draft only a baro will smooth it out. A thermostat on the air intake will also work but slower in response.

The advantage of a baro over a manual damper is that it never obstructs the flue passage. Under low draft conditions I don't think an obstruction is good though testing might prove otherwise since low draft does not need a large opening and the smaller opening might not result in lower draft. A disadvantage of the Field RC is that it makes a permanent leak in the smoke pipe owing to the gap around the flap which is also not good with weak draft.. Others seal better.


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