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Post by chrisb on Dec 20, 2016 14:12:13 GMT -8
Okay - I'm sure this is answered somewhere, but I'm struggling to find it and it is a fairly fundamental question, so please bear with me ... I have been looking at the spreadsheets and calculations for sizing the firebox, vents and also the bell based on a 6" diameter riser. The most common bell we see elsewhere is a 55 gallon drum which has an internal surface area of approximately 20 square feet (excluding one end). This seems to be a common choice for a bell in many designs though ... are we to assume that all the piping which runs under the benches, for example, is also classed as part of the bell for purposes of the calculation of bell ISA? So - to achieve 5.3 square metres of ISA (57 square feet) we need the 55 gallon drum (20 square feet) and 24 linear feet of 6" pipe under the bench - ISA of 24 linear feet at 6" diameter is approximately 37 square feet ... all numbers fairly rounded Or - am I missing something fundamental here? All answers which don't include the word "idiot" gratefully received
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Post by peterberg on Dec 20, 2016 14:33:48 GMT -8
Hi ChrisB, welcome to the boards. The general rule here is "be nice", so when somebody calls another forum member an idiot that post will be deleted without further ado.
And yes, you are missing something fundamental here. The bell calculation based on the riser csa (not the diameter!) is valid for batch box rockets and bells only. So not for Evans' style J-tubes and not for pipe runs in benches. The pipe in a bench can't be classified as part of a bell, for that it should sport at least a csa of 5 times that of the riser. Bells are relying on gravity to do the heat extraction and therefor the forward velocity of the gas stream need to be slowed down greatly.
This doesn't mean you can't build a batch box with a barrel and a piped bench. It has been done before but there are no calculations available for such a setup.
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Post by chrisb on Dec 20, 2016 15:10:52 GMT -8
Ahhh ... yep, pretty fundamental . Thank you for your quick response Peter. I actually ended up here after seeing a youtube video by a gentleman who had that setup, a batchbox firebox linked to a bench for residual mass heating and I had assumed it was a common practice so was looking for information on the combination ... I guess I need to rethink that part of the budding plan rolling around in my grey matter . I have to say I really like the way discussions seem to roll in here and I look forward to learning more, and hopefully contributing, as time goes on. Stay warm out there ... it was -30C here (Southern Saskatchewan) last week and I'm looking for a better alternative to heating my acreage workshop than a gas furnace that Noah rejected
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Post by peterberg on Dec 21, 2016 2:55:03 GMT -8
Chris, is a mass bench for your workshop really what you need? In my view, a mass heater in a workshop is only viable when that space is in use for at least 12 hours a day and every day of the week. When it's not, you'd do better to look for a mass-less heater like the one in my former workshop, the three-barrel tower. No mass to speak of, getting warm in 5 minutes and that's it. In that same workshop I've had different mass heaters for almost 30 years, partly because it has been my hobby all that time. The moment we had to move house I'd need a quick heater for the last winter season there because all the bricks and casted parts were brought to the tip.
So, in short: it isn't particulary efficient to have a mass heater in a space that isn't occupated at least half of every 24 hours. Most of the warmth is dissipated when you're not there. And on the other hand you have to fire it every day to keep the space comfortable, irrespective whether you are using it or not.
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