Does anyone know of a way to acurately measure the CFM of the distribution/convection blower? I would like to know what the actual heat output is in BTUH at different settings.
Measure output BTUH
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mepellet said:
There are flow meters that can be used to measure air flow through a vent, the only problem you'll have is that the output doesn't come out in one spot.
Take your 8000 BTU per pound average times your stove efficiency times how many pounds you are burning per hour. The real unknown is a realistic, truthful stove efficiency number. Some say that numbers were ''fudged' to meet the government mandate (kind of like auto MPG) but probably 75% is a good number.
To really get a true value, you need a lab. Last year we had a young guy on here who was charged by his instructor at school to figure out the same thing at a local business that was heated by a pellet stove. You don't have the same assignment, by any chance? %-P
To really get a true value, you need a lab. Last year we had a young guy on here who was charged by his instructor at school to figure out the same thing at a local business that was heated by a pellet stove. You don't have the same assignment, by any chance? %-P
tjnamtiw said:
Haha. No. Just personal assignment. I have a curious mind and just was thinking of a way to figure out the real world heat output. As far as the radiant heat though, thats another story.
If you could measure the airflow somehow or even the air velocity it would be easy to figure out the convection heat output. How about some sort of ductwork and then figuring out the velocity through the ductwork?
mepellet said:
Pretty challenging assignment! What tj suggests will get you real world close, But anything more is gonna hurt!
Before you even start. Your gonna need the the exact BTU amount of the fuel. The pellet you dump in has a wide range in BTU's. Then you can measure whats expelled in the room and also what is expelled out the vent. Lots of work and figures. Some thoughts below.
Some of the stoves out there have EPA'ed certs that have the actual efficiency for the stove at hand. That's really all you need to know. Use the 8000 BTU value(about average for the pellets out there) figure out how many pounds per hour it will feed to the burnpot. Multiply that. Multiply by the stoves efficiency and you will have your BTUH.
Real world pounds per hour will need to be tallied. The stove actually feeds by volume, Not pounds per hour. So you'll have to actually make the stove think its burning and catch the fuel and weight it. This will also very with each brand of fuel used due to size/density variations.
Good luck and keep us posted.
j-takeman said:
Why would I need to know the BTU content of the fuel? If I could measure the cfm and air temperatures going into the distribution blower and exiting the heat exchanger I'd be able to figure out the amount of heat transfered there. Radiant heat, different story.... Theres a lot more radiant heat than I expected.
j-takeman said:
If the OP is interested in only the heat output from the convection system, measuring the air flow, the temperature difference, consulting a table, and doing a simple calculation will do the trick.
If the OP wants the total BTU output of the stove that is a horse of a different pattern and can still be cobbled together, however it becomes non trivial.
I would love to see this work and then compare and see which stove has the most efficient heat exchanger. Been curious about this for a while now.
SmokeyTheBear said:
Correct. I am trying to tackle one item at a time here. Measuring the radiant heat would be much harder. I'll be lucky to figure out the convection heat
mepellet said:SmokeyTheBear said:
Correct. I am trying to tackle one item at a time here. Measuring the radiant heat would be much harder. I'll be lucky to figure out the convection heat
I hope that they factored in the slight partial pressure change ;-) .
You however are still faced with measuring the flow rate.
SmokeyTheBear said:mepellet said:SmokeyTheBear said:
Correct. I am trying to tackle one item at a time here. Measuring the radiant heat would be much harder. I'll be lucky to figure out the convection heat
I hope that they factored in the slight partial pressure change ;-) .
You however are still faced with measuring the flow rate.
How about an easy way to measure the velocity?
If you go through this thread and the one that is referenced in it, you'll see what we did last year to try to improve the heat transfer of the Quads.
https://www.hearth.com/talk/threads/70161/
We addressed heat outputs across all tubes as well as air velocities.
https://www.hearth.com/talk/threads/70161/
We addressed heat outputs across all tubes as well as air velocities.
Each stove is different and lose efficiency as they get dirty at different rates. My stove might perform at its peak for the first say 12 hours and a different model might be able to operate for 24 below really starting to slide on efficiency. I dump my ash pot every day and brush or vacuum out the inside and do a better cleaning at the end of the week to try to get the most bang for my buck out of the pellets. Of course there are a whole ton of factors that go into even figuring this.
mepellet said:SmokeyTheBear said:mepellet said:SmokeyTheBear said:
Correct. I am trying to tackle one item at a time here. Measuring the radiant heat would be much harder. I'll be lucky to figure out the convection heat
I hope that they factored in the slight partial pressure change ;-) .
You however are still faced with measuring the flow rate.
How about an easy way to measure the velocity?
If You already know the fans total cfm at max speed, If you measure the voltage applied, You should be able to get a close CFM at the operating condition. If the controller sets a variable speed for the blower. They do have some flow meters at grainger that measure velocity. I suppose you could do the same for the exhaust. It may help show stoves efficiency?
So you don't really care about the overall BTUH's the stove can produce, You only care about the convection BTUH's?
My theory is its to hard to measure the radiant. But if you knew convection and exhaust BTUH's and the actual input. You could fudge the last number giving you the radiant. Should get close. I am not always right, But I do get into this.
I'm kind of lucky, My stove has some EPA numbers 79.5% so I have a clue on what I have as far as efficiency. I only need to know pounds per hour and I can get a close BTUH my stove is suppling. But its still just close. I am using the average BTU of 8000. Knowing the actual would get me real close! Just saying!
Compounding the problem of total CFM, you will see in last year's experiments that air velocities vary GREATLY across the tubes as does the exit temperatures. The sum of all the tubes' outputs would be needed. Also, the height of the flame varies because of the auger's inability to deliver consistent mass of pellets, which means the exit temperature of the flue gases will vary. Measurements would have to be made almost continuously over a period of time to get good numbers.
Why worry? Pour in a bag of pellets, pour out a glass of beer, tune in a college game, and stay warm!
Why worry? Pour in a bag of pellets, pour out a glass of beer, tune in a college game, and stay warm!
I second the suggestion to pour a brew and enjoy the heat.
I haven't had to do BTU calculations since college physics classes. There are tons of on line tools to do most of that these days.
I haven't had to do BTU calculations since college physics classes. There are tons of on line tools to do most of that these days.
SmokeyTheBear said:
Ha ha. I went for my Thermodynamics physics book but shoved it back where it's been for 46 years
! Nah!
Yeah im thinking that it really isn't worth all the trouble. If I had material to make a sort of duct that could capture the discharge from all the tubes and a device to monitor the temps in and out over a period of time and something to measure air velocity or frm then id do it. Look to be too much foible since I have none of that stuff.... :/ oh well. Curious engineer mind for you I guess.
You could use a duct boot to catch all the convection air. Available at Lowes and HD and relatively cheap.
I'd wish you'd continue. After the beer break maybe? hehe ;-)
I'd wish you'd continue. After the beer break maybe? hehe ;-)
I can assure y'all of one thing.
The efficiency and output are probably less than any amount you are thinking.....
I say this because we usually gloss over many aspects of efficiency. Our fine and advanced car engines, for instance - after BILLIONS of dollars of R&D - are what? Maybe 30% efficient at best - with a controlled fuel.
Best to crack a brew and figure 5,000 BTU output per pound of pellets...if you are lucky.
The efficiency and output are probably less than any amount you are thinking.....
I say this because we usually gloss over many aspects of efficiency. Our fine and advanced car engines, for instance - after BILLIONS of dollars of R&D - are what? Maybe 30% efficient at best - with a controlled fuel.
Best to crack a brew and figure 5,000 BTU output per pound of pellets...if you are lucky.
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