Is that combustion efficiency for oil or coal? Is that temperature measured on the flue pipe exterior or in it's center? All important details. The A-A boiler in the two year study published by the Bureau of Mines in 1952 had the following temperature ranges: Boiler water 150-225 deg F. with corresponding center flue gas temperatures of 150-450 deg F. The AHS boiler because it's virtual clone would be very similar. If the Hartman has 84-85% combustion efficiency I'd like to know how they do it with only 300 deg. F flue gas temperature. Perhaps it's an average flue gas temperature.Highlander wrote:I'm not sure where you guys are getting your efficiency numbers from, the Harman boiler I saw ran the flue gas cool enough to lay your hand on the pipe. If you purchase the oil gun option, Harman rates the efficiency as 84-85% with a 300deg flue temp, not too bad in my book.
But the stoker with a combustion blower should not make heat when the blower is off. That's a fundamental design feature. I don't know the construction details of other brands but the AHS or A-A will only make appreciable heat when the blower is running. That's when the coal gases are really flaming above the coal bed and are being drawn into the boiler tubes, transferring the heat from the flue gas to the water. When the blower is not running the coal bed is just idling. Since it is not burning much during this time there is only a small volume of flue gas. No matter how insulated a chimney liner might be by the time any flue gas gets to the chimney thimble it will be cold. Perhaps even at the temperature where the flue gas temperature is below its dew point temperature. I have operational experience that this is true. When there is a no demand for heat for many hours, say 8-12 hours and the wind is still you get the characteristic sulfur smell. This means there are sulfur compounds being produced. Under the right still wind conditions it can be quite noticeable outside. I have to keep telling my wife, "it wasn't me dear". The reduction of heat production during the transition from the blower running to not running is not a step function. There is still some heat being produced and this is what causes temperature overshoot at the aquastat high set point. With a AHS or A-A boiler an insulated chimney would be a waste of money. What you want is resistance to sulfur compounds, i.e. a clay tile lined chimney.jpen1 wrote:Coal stokers still require draft to operate even though they have a forced air draft. A coal stoker operates on positive draft and requires a drafting chimney or power vent to operate. For a chimney to draft effectively the flue gas temperature at the top of the chimney must be higher than the ambient air temperature. Yes a stoker requires less draft to operate than a hand fired appliance does but it can't operate with no draft like a pellet appliance which uses a exhaust blower which creates its own draft. that being said an external masonary chimney can be insulated as well and would be mroe effective and draft better than a metal one even in warm weather.
Where can I view a copy of the 1952 Boiler tests,I see this test referred to many times but have not been able to find it on the internet.I would like tosee it and see how many boilers were tested at this time.
Thank You: BigBarney
The report is not on the Internet. It's 13 pages of text, one huge table of data and 23 pages of photos and plots. I'm converting it to electronic form. All of the difficult stuff is done, the table is now an Excel spreadsheet, the text was run through a optical character reader and the errors corrected. What I need to do is scan the remaining pages and then assemble it all in a single pdf file. I'm busy with many projects now, but I will get it done, surely by this fall. I believe it's a historically important document and should be more widely distributed. It's only about the A-A boiler, but much of the data applies to any residential boiler. Testing was done in 1949 and 1950 by the Bureau of Mines.BigBarney wrote:Yanche:
Where can I view a copy of the 1952 Boiler tests,I see this test referred to many times but have not been able to find it on the internet.I would like to
see it and see how many boilers were tested at this time.
Thank You: BigBarney
Hi Berlin , I have to agree with you on the masonary chimney for coal. I have the stainless metal chimney. From the top of the chimney , down about 12 inches , I had corrosion on the surface. I cleaned it up , and sprayed with high temp aluminum paint. The chimney cap had corroded apart , and also alowed rain water to activate the acid. I now have 36 inch diameter copper cap , which keeps the rain out. You can bet I'll be keeping an eye on it. Never had that problem with masonary chimney.Berlin wrote:yup and if you get it the 316ti is the best, however i would still reccomend strongly against stainless if you can do masonry.