Post by jcfougere on Oct 29, 2018 11:31:37 GMT -8
Hey all,
I've been spending some time reading through the forums, reading the Wisner's book 'the rocket mass heater builders guide' and now I'm working out logistics and considering what size system is best for my application. Of course a few questions have come up. I haven't been able to find the specific math involved for determining ideal bell ISA in a batch rocket design. Ive got Peters spreadsheet on proper dimensions of the batch box, riser, port size etc but I'm only familiar with traditional J tube designs when it comes to the thermal mass ducting part.
Ive attached a few drawings that show the building dimensions and an overhead of 2 design concepts. Also some pics of the actual greenhouse. The graph paper sketches are more or less to scale, each box 6"x6".
Build specifics:
-Greenhouse with a floor space of 178" x 94"
-primary purpose is to heat a horizontal mass that runs the length of the greenhouse in order to provide heat to seedling trays via conduction and convection
-secondary purpose to heat the air in the greenhouse via radiation from thermal mass and barrel on the heat riser
-will be fired in spring from Feb - April when overnight lows range between -5f and 25f
-also fired in fall during the months of sept-oct when lows hover around 25f
-batch rocket design to reduce feeding frequency
-horizontal bench with a series of bell chambers to maximize heat capture to thermal mass
We have 8 45gal drums to work with but I haven't seen them yet to measure sizes. I'm working with the assumption they are 2'x3'. I'm currently working out what size batch rocket we can fit, given that the ratios are very strict and we do have a bit of a space bottle neck vertically. The glass part of the roof is pretty low until it's 2-3' away from the wall, which puts the riser out 2-3' and the burn box another 1-2' further in to the greenhouse space.
If we can get away with a 6" system that will be roughly 72" of vertical (including a 3" gap at top of riser, a brick foundation, and 2' above the barrel for a kettle etc) which will require the back edge of the barrel to be 2' from the south wall. Then if the barrel is 2' in diameter and we have a batch box 17" long the entire burning unit will be about 6' from the south wall. Aligning the burn box towards the middle of the greenhouse will avoid blocking the door but as you can see we're a bit space limited even with a 6" riser. For a 7" system we're about an extra foot off the south wall, 8" system 2 more feet. Perhaps there is another easier way to fit this system in the footprint? The owners (I'm consulting and helping them build) want the chimney on the east side so it's not obvious from the road, and would prefer the thermal mass be on the south side.
Personally I think the easiest way to fit a batch system would be to stick the riser in the north east corner facing west, and then run the thermal mass in an L south and west, and vent out the west side(and not worry about who's seeing the flue). More heated bench run, easier to get in and out the door. Also easier to build a 7" or 8" sized system with the roof pitch on the north wall.
With all those variables I'd love to get the communities opinion on feasibility or if there are any glaring mistakes being made here.
Aside from the actual sizing and functionality, a couple big questions:
-how can I figure out the optimal Isa of a bell/pipe system, in order to figure out how big a bell can be, or how many bells I can have etc? I know draw is important and I'd like to get this right right off the bat. From my understanding too much ISA in the heat exchange area will reduce draw and cause issues firing up? Too small ISA and I'm losing heat out the chimney and wasting wood?
-when using a bell chamber system, can I link multiple barrels in to one giant bell chamber, or should they be sectional with a low port for cooler gas to pass through to the next bell? My idea was to have a run of brick under the bench, build up a 1' wide channel with brick about 6" high, then cut the 3' long barrels in to quarters and lay 3 of them down length wise to create a 9' long, 1' high and 1' wide bell, then cob it all in and finish the bench 2' high. Will this work? Of course all 6" ducting work being down low to allow cool air to pass.
-more basic question, in your opinion what size batch rocket is ideal for this design? 6, 7, 8? I know most designs look at heating a space but we really only need the seedling trays to stay warm, not the entire volume of the greenhouse.
-lastly, is 6" of space between the thermal mass and the flammable wall adequate? How much space would you allow behind the heat riser barrel? Just get a fire plate for the wall?
Thanks in advance for any help, feedback and comments.
If this is a success I'll be building another one on our farm next year and hosting a series of workshops to teach the basics!
Cheers,
James.
ibb.co/ceWdAq
ibb.co/bNSUGV
ibb.co/kZK4iA
ibb.co/n23Qqq
ibb.co/kj6dAq
ibb.co/n8r6wV
![](https://thumb.ibb.co/n8r6wV/IMG-20181027-101712.jpg)
I've been spending some time reading through the forums, reading the Wisner's book 'the rocket mass heater builders guide' and now I'm working out logistics and considering what size system is best for my application. Of course a few questions have come up. I haven't been able to find the specific math involved for determining ideal bell ISA in a batch rocket design. Ive got Peters spreadsheet on proper dimensions of the batch box, riser, port size etc but I'm only familiar with traditional J tube designs when it comes to the thermal mass ducting part.
Ive attached a few drawings that show the building dimensions and an overhead of 2 design concepts. Also some pics of the actual greenhouse. The graph paper sketches are more or less to scale, each box 6"x6".
Build specifics:
-Greenhouse with a floor space of 178" x 94"
-primary purpose is to heat a horizontal mass that runs the length of the greenhouse in order to provide heat to seedling trays via conduction and convection
-secondary purpose to heat the air in the greenhouse via radiation from thermal mass and barrel on the heat riser
-will be fired in spring from Feb - April when overnight lows range between -5f and 25f
-also fired in fall during the months of sept-oct when lows hover around 25f
-batch rocket design to reduce feeding frequency
-horizontal bench with a series of bell chambers to maximize heat capture to thermal mass
We have 8 45gal drums to work with but I haven't seen them yet to measure sizes. I'm working with the assumption they are 2'x3'. I'm currently working out what size batch rocket we can fit, given that the ratios are very strict and we do have a bit of a space bottle neck vertically. The glass part of the roof is pretty low until it's 2-3' away from the wall, which puts the riser out 2-3' and the burn box another 1-2' further in to the greenhouse space.
If we can get away with a 6" system that will be roughly 72" of vertical (including a 3" gap at top of riser, a brick foundation, and 2' above the barrel for a kettle etc) which will require the back edge of the barrel to be 2' from the south wall. Then if the barrel is 2' in diameter and we have a batch box 17" long the entire burning unit will be about 6' from the south wall. Aligning the burn box towards the middle of the greenhouse will avoid blocking the door but as you can see we're a bit space limited even with a 6" riser. For a 7" system we're about an extra foot off the south wall, 8" system 2 more feet. Perhaps there is another easier way to fit this system in the footprint? The owners (I'm consulting and helping them build) want the chimney on the east side so it's not obvious from the road, and would prefer the thermal mass be on the south side.
Personally I think the easiest way to fit a batch system would be to stick the riser in the north east corner facing west, and then run the thermal mass in an L south and west, and vent out the west side(and not worry about who's seeing the flue). More heated bench run, easier to get in and out the door. Also easier to build a 7" or 8" sized system with the roof pitch on the north wall.
With all those variables I'd love to get the communities opinion on feasibility or if there are any glaring mistakes being made here.
Aside from the actual sizing and functionality, a couple big questions:
-how can I figure out the optimal Isa of a bell/pipe system, in order to figure out how big a bell can be, or how many bells I can have etc? I know draw is important and I'd like to get this right right off the bat. From my understanding too much ISA in the heat exchange area will reduce draw and cause issues firing up? Too small ISA and I'm losing heat out the chimney and wasting wood?
-when using a bell chamber system, can I link multiple barrels in to one giant bell chamber, or should they be sectional with a low port for cooler gas to pass through to the next bell? My idea was to have a run of brick under the bench, build up a 1' wide channel with brick about 6" high, then cut the 3' long barrels in to quarters and lay 3 of them down length wise to create a 9' long, 1' high and 1' wide bell, then cob it all in and finish the bench 2' high. Will this work? Of course all 6" ducting work being down low to allow cool air to pass.
-more basic question, in your opinion what size batch rocket is ideal for this design? 6, 7, 8? I know most designs look at heating a space but we really only need the seedling trays to stay warm, not the entire volume of the greenhouse.
-lastly, is 6" of space between the thermal mass and the flammable wall adequate? How much space would you allow behind the heat riser barrel? Just get a fire plate for the wall?
Thanks in advance for any help, feedback and comments.
If this is a success I'll be building another one on our farm next year and hosting a series of workshops to teach the basics!
Cheers,
James.
ibb.co/ceWdAq
ibb.co/bNSUGV
ibb.co/kZK4iA
ibb.co/n23Qqq
ibb.co/kj6dAq
ibb.co/n8r6wV
![](https://thumb.ibb.co/ceWdAq/IMG-20181029-102930.jpg)
![](https://thumb.ibb.co/bNSUGV/IMG-20181029-104435.jpg)
![](https://thumb.ibb.co/kZK4iA/IMG-20181029-124545.jpg)
![](https://thumb.ibb.co/n23Qqq/IMG-20181027-102343.jpg)
![](https://thumb.ibb.co/kj6dAq/IMG-20181027-101723.jpg)
![](https://thumb.ibb.co/n8r6wV/IMG-20181027-101712.jpg)