New Pellet Burner

[fadippides]

New pellet burner (long time lurker) and had a couple of questions I havent seen in the forum (only did a quick search).

I have a Harman Accentra Insert in a 2650 sqft home with a very open floor plan. The stove sits on the far edge of a great room and puts out enough heat to turn the ceiling fan at a decent rate (I'd love to calculate why one of these days).

Two questions:

Is the unit more efficent with the blower on high (do I lose heat if it is lower)?
What effect does the feed rate have on efficency?

So far I am able to heat the entire house on it but we haven't been below 30 degrees yet, and I havent left it on at night yet. We also have geothermal heat and hope for the stove to be a nice augment and able to heat the house when the power is out. (still need to connect the generator).

I have 5 tons of pellets in the garage and hope to be a pellet pig some day.

 

[imacman]

Welcome to the forum, Fadippides.

IMO, the higher the room blower is set, the more heat you get from the pellets, and less goes up the exhaust so I'd have to say higher blower =higher efficiency, heat output wise.

That said, running on high all the time probably lowers the life expectancy of the blower motor, and it also is louder. I used to run my Astoria blower at 75% all the time.

I don't think pellet feed rate has anything to do w/ efficiency, unless I'm missing something.

With 5 tons, I think you already qualify as a Pellet Pig...OINK OINK!

 

[burrman]

I have 5 tons of pellets in the garage and hope to be a pellet pig some day.

some day?....welcome to the pellet pig chapter my friend.....

 

[MCPO]

I`d have to go with macman on this since the object is to remove as much heat as possible from the heat exchanger as fast as you can. It has to minimize the amount of heat escaping up the chimney. You don`t want heat to linger in the stove longer than necessary.
A Harman stove (accordian type exchanger) or most others with tubes for heat exchangers is what gets heated first and the faster you remove the heat off them the more heat the exchanger can absorb and consequently the more effective the heat transfer. Obviously the distribution fan is the primary method to accomplish just that. Running it on low seemingly would allow for more extraneous heat to go up the chimney especially when set on medium + burns .
Of course there is a point during a burn when the heat exchanger reaches a static temperature and you lose some heat up the flue anyway but the object is to remove as much heat as possible with the blower fan on high .

 

[countk]

Welcome to the forum, Fadippides.

IMO, the higher the room blower is set, the more heat you get from the pellets, and less goes up the exhaust so I'd have to say higher blower =higher efficiency, heat output wise.

That said, running on high all the time probably lowers the life expectancy of the blower motor, and it also is louder. I used to run my Astoria blower at 75% all the time.

I don't think pellet feed rate has anything to do w/ efficiency, unless I'm missing something.

With 5 tons, I think you already qualify as a Pellet Pig...OINK OINK!

Question, does it really lower life expectancy that much. The reason I ask, is that on my empress, which is not as powerful as others, I run on high, at least when I fire it up to get the chill off. Also, during cold months, I will be on 5 a lot.

One thing for sure, at least with the empress, even on high it is still a relatively quiet stove, compared to others

 

[stoveguy2esw]

great question. the actual answer would depend on the physical ability of the heat exchanger to transfer thermal energy to the air circulating through it. the higher the surface area of the exchanger the higher the ability to transfer to an extent, the velocity of which air flows through the exchanger determines transfer as well. in most modern pellet stoves you will likely not reacha "tipping point" where you start to lose transfer energy due to velocity. unless an extreme low burn rate and an extreme high blower speed were used. so , running a higher blower speed while it may lower the air temp coming out may well increase the actual transfer ratio into the room.

look at it this way (now the numbers im using are not an actual representatioon of your stove but to give an idea how it works)

say you create input 10,000 BTU into a heat exchanger at 0 velocity which allows the exchanger to reach say 500F with no air movement (this wouldnt hapen but just for example)

say you move 10CFM through this chamber and the air coming out is 300F at 10 cfm
if you move 20CFM through the air coming out may be at say 250F at 20CFM in which case you would have a lower air temp but more overall heat released.
now if you moved say 50CFM and only got say 50F at that 50CFM , you would be past the "tipping point" and less heat would be released.

so a moderately higher blower speed would actually increase heat output but too much would decrease it.

 

[SmokeyTheBear]

Welcome to the forum, Fadippides.

IMO, the higher the room blower is set, the more heat you get from the pellets, and less goes up the exhaust so I'd have to say higher blower =higher efficiency, heat output wise.

That said, running on high all the time probably lowers the life expectancy of the blower motor, and it also is louder. I used to run my Astoria blower at 75% all the time.

I don't think pellet feed rate has anything to do w/ efficiency, unless I'm missing something.

With 5 tons, I think you already qualify as a Pellet Pig...OINK OINK!

Question, does it really lower life expectancy that much. The reason I ask, is that on my empress, which is not as powerful as others, I run on high, at least when I fire it up to get the chill off. Also, during cold months, I will be on 5 a lot.

One thing for sure, at least with the empress, even on high it is still a relatively quiet stove, compared to others

I think the answer about life expectancy is really about how well the motor is constructed, keeping it properly lubricated, and away from excessive heat.

I currently am on my second convection blower, it is supposed to be oiled every six months of use, it has yet to make it to six months. I started having problems with the second blower after three months of actual use, so now I plan on oiling it every month.

I'm firmly convinced that part of the issue is the proximity to heat. It would be better if it was back several inches from where it is.

This is also one instance where a sealed self lubricating bearing would help.

Then again I don't design these things, so what would I know.

 

[gbreda]

Great question and welcome to the forum !

From the answers, I think I need to increase my fan speed off of low.

 

[SmokeyTheBear]

Heat extraction will increase with the temperature difference between the heat exchanger and the air being moved. So running on high should extract the most heat because it will increase the temperature difference.

The limiting factor will be once the air inlet temperature starts to rise (as when all of the air in the container the stove is heating becomes hot enough so that the temperature difference drops), the transfer efficiency will begin to drop.

I doubt that you would be able to push air through the exchanger fast enough for it to reach that point given normal blower capacities and normal building heat loss.

 

[gbreda]

OK, there is alot of talk about lowering the temp of the heat exhanger from a higher fan speed. With this in mind, should we be using the stove temp mode over room temp mode to keep the exhanger at a higher temp for heating?

 

[stoveguy2esw]

kinda what i meant, i did state that its unlikely that an extereme would be reached allowing too much velocity for effective heat transfer, stove design involves ensuring that the blower fits the heat exchanger system for optimal performance, it would be hard indeed to find a stove out there which had a stock blower capable of exceeding the tipping point