It appears to me that the recommended ISA is based on a necessary output temperature of the exhaust flow, about 80 degrees C. ,with a totally cold mass heat extractor. In a bell the pressure will be the same every where so flows out of the bell will be proportional to flow area approximately. I propose a small opening to inject hot gases into the chimney flow After a while the two flows will mix and become the proportional average temperature. this flow is what exits the chimney. With the recommended ISA and no bypass the gas flow will be cooled to 80c. But if we increase the ISA more cooling will occur. For example let's assume we oversized the bell and our output temperature is 43C. our flue is 7" rectangular and we add a 1 1/2 dia. hole injecting un cooled gas at 1000C, the flow out of the chimney will be about 80C. What I don't know is how much ISA will cool the output of my 8" system to 43C. It seems to me that more cooling followed by hot gas injection can actually increase efficiency and result in dryer exhaust.
I'm no expert, but it seems to me that the efficiency of heat recovery between the core and the stack will determined by temperature into bell vs. temperature out top of stack. If you cool some portion of the gases to 43 C in a bell and then add heat to get the stack to 80 C, I don't think you have gained any efficiency. Smarter folks here may correct me if I am wrong.
Also consider that to "capture the heat of vaporization" will require condensation (inside the bell). That creates a whole new problem. Again, I could be wrong, but I suspect you are overthinking this.
My reason for suspecting efficiency could be greater by using hot gas bypass is that the greater cooling of most of the flow will capture the heat of vaporization from more moisture in the gas.
As I understand it, it may be possible to extract the latent heat of vaporisation by the codensation of the water vapour in the exhaust gases, but if that condensate is not removed, then it will eventually have to evaporate, and then absorb the same amount of heat it previously deposited. In which case, for this to work you'd need to have a condensate drain of some kind, just as in a condensing gas boiler.
I can easily add a condensate drain as part of my base slab. Would be interesting to collect and measure the water out. Ordinary fire brick would not be the best choice for the lower portion of the bell as their surface gets wetted and holds the moisture however soapstone brick or slabs or ceramic tile would capture much less water.
TexasGonzo: Sooooo glad I found this site! Its always rewarding to find such a super group of folks! To any and all, feel free to PM me anytime. Thanks for having me!
Mar 11, 2019 18:56:41 GMT -8
jlmtech: GADGET: CONSIDER USING A JET PUMP INSTEAD OF A BLOWER FAN TO INDUCE DRAFT; NO CLOGGING.
Mar 26, 2019 8:19:28 GMT -8
michaelegan: i am unable to open the sketchup files on my mac. I used sketchup a few years back but apparently the company now requires a subscription. does anyone have any advice/instructions on how to use the program or how to view pictures without spending money?
Aug 20, 2019 18:41:48 GMT -8
mannytheseacow: michaelegan: download AutoCAD student version for free... import .SKP
Aug 23, 2019 13:33:44 GMT -8
topbaza: hi everyone, been searching all over net and this is were i need to be i think!!
Sept 28, 2019 6:16:25 GMT -8
anounaki: Hi, why I cant upload photos when I make new tread to this forum?
Feb 28, 2020 2:09:40 GMT -8
ahansen: photos under 1 mb not possible?
Jun 4, 2020 0:09:21 GMT -8
belgiangulch: Photo's are possible. They must be downloaded elsewhere and the image url (adress) is copyied.
Sept 14, 2020 7:26:15 GMT -8
belgiangulch: While creating a thread click on the small picture in the banner above the reply. A box pops up, paste the image url in the box. Pay no attention to the huge list of numbers and such.When you finish and hit reply your post with pictures will come up.
Sept 14, 2020 7:29:27 GMT -8
deadstarsstillburn: Hi there. I was directed this way by folks on the Permies.com website and am hoping I can get some information on how a total newbie can get started designing, siting, building, and not-dying-in-a-horrible-house-fire with a new RMH in a 160-year old home
Oct 21, 2020 6:52:10 GMT -8
deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
Oct 21, 2020 6:53:59 GMT -8
BenAlexanderT: Happy new year everybody. I wish you the best
Dec 31, 2020 15:06:14 GMT -8
Solomon: Anybody in Southern Oregon, in Jackson or Josephine counties?
Jan 16, 2021 21:54:43 GMT -8
gnomedome: i realsie this is from 2009
Apr 14, 2021 8:30:44 GMT -8
gnomedome: i realize this is from 2009 id love to see the photos from this ..as im looking to build a sauna soon similar to this .... if anyody sees this post email@example.com..... the photos in this post did not show up
Apr 14, 2021 8:32:00 GMT -8