Post by fiedia on Aug 8, 2021 0:46:52 GMT -8
It started 3 years ago with a very optimistic design to heat 3 rooms with a single batch box. At that time, uncertainty regarding bell thermal behavior was too high to move forward on this project. Today, after testing 4 different prototypes, though lot of question remain, I feel more comfortable to move forward.
The design remains roughly the same, it still aims to heat three rooms with a 200mm batch box but the heat flow has been modified as well as the firebox position. Several features for day to day use and cooking have been added.
Overview:
Kitchen + sleeping room above:
Living room:
HR:
- HR scaling: according to spreadsheets, I should use a 250 mm HR to heat my house. The problem is that it requires to load 30 kg wood in the firebox… Well it is a lot of wood to carry and handle. During the last 2 heating seasons, I weighted day after day wood loads to heat the kitchen above 20°C and warm up the living room around 16°C. With my old dirty stove, the max wood consumption was 32kg a day. Therefore, I hope a 200 mm design (14kg wood per load) should be a good compromise. I may have to burn three or four loads a day when the weather is getting really cold but one to two loads a day should be sufficient for the rest of the season.
- HR shape and material: I did some trials with an aerated concrete prototype. I noticed that round shape HR insulated with vermiculite provide faster clean smokes than non insulated square shaped HR. My last prototype was built out of dense refractory bricks. It was warming quite slowly and I wish to try light refractory bricks this time. The octagonal shape is copied from batchrocket.eu from Peterberg.
Firebox :
- Firebox orientation: the best radiating input is coming from the fireplace window. Everybody is instinctively standing in front of that door to get warm. The firebox door should face the center of the kitchen. With the firebox perpendicular to the wall, a sidewinder will optimize stove footprint.
Bell scaling:
- Scaling bell1: my last prototype (125 mm batch) had 2.2 m² radiating surface. It was sufficient when outside temp was above 10°C. In contrary, kitchen temp did not get above 13°C when outside temp dropped down to -7°C. Bell1 radiating surface needs to be significantly increased (6.2 m² in this new design and 4 m² SIA).
- Scaling bell2: 2 years ago, I tested a bell with 2.1 m² radiating surface. It was sufficient to warm up the living room around 16°C. It was fed with 600°C smokes from my 125mm old dirty stove. For this new bell2, I am targeting a radiating surface greater than 2.1m².
- Bell2 height: Surface temperature of my former living room bell was much warmer on the upper half. Reducing the effective bell height by half did not impact significantly heating performances. Heat extraction is apparently more efficient with a wide and short bell than a narrow and tall one. Therefore, I will reduce bell2 height to 1.1m in my new design. The width will be increased to get 3.6m² radiating surface (SIA = 3.3m²).
- Bell2 feed: Last winter, chaining the second bell to my 125mm batchbox was clearly not efficient. Smokes coming out the kitchen bell were too cold (below 200°C) and did not heat sufficiently the second bell. In this new design, bell2 is linked to bell1 both on top and bottom by two pipes. As temperatures measured on top of my present kitchen bell are between 400 and 500 °C, I expect smokes running through this new bell2 to be much hotter than 200°C.
- Scaling bell 3: In a coming project this batch rocket will heat water during winter. Bell 3 is here to add some water pipes on top of the kitchen bell. Its dimensions are given by the kitchen bell cross section and a reasonable height for cleaning access (SIA: 3.2m²).
Heat flow:
- Bell1 top: hot smokes from the heat riser spread inside a large space on top of bell1 (9 x HR CSA). The rear cavity on the left side will be filled with clay and stones for heat storage. The middle cavity is a duct for smokes rising from bell1 bottom. The right cavity is a secondary duct. Its purpose will be described later.
Bell1 middle: cooling smokes from bell1 top fall down on the left side(2.2 x HR CSA). The CS gets bigger above the bench. Smokes should flow both on the right and left thirds of the bench.
Bell1 bottom: Smokes flow from right and left to the middle and rise in the rear duct up to the top of the bell towards bell3. We will see if it is warm enough to get a comfortable bench temperature.
- Bell2 feed: bell2 is linked to bell1 by 2 pipes. Bell2 top pipe collects hot smokes from bell1 top. The lower pipe is needed to extract cold smokes out of bell2 towards bell1 bottom. I will try to insulate them as much as possible (I do not want to waste heat in the wall between kitchen and living room).
Bypasses:
ecologie-pratique.org/mediagallery/album.php?aid=1882&page=1
This 3 bell design has a SIA above recommended value (~ 9m² max). I added different bypasses to shunt bells and balance heat flow between them.
- Bell1 bypass: it shunts bell1 bottom as well as bell2. Smokes will flow directly into bell3. Opening partially this bypass should balance heat flow between bell1 and bell3.
- Bell2 bypass: it blocks bell2 upper pipe or direct access to bell1 bottom. When set on the upper position, smokes will flow directly towards the lower part of bell1. When set on the lower position, smokes will flow through bell2 before going through bell1 bottom. Opening it partially should balance heat flow between bell1 bottom and bell2.
- Bell3 bypass: smokes coming from bell1 will flow through bell3 when set in the upper position.
- Cooking: A white oven sits on top of the firebox. There is a hot surface for soup or stew in front of the oven.
- Ashtray: there is a hole behind the p-channel to reduce dust while cleaning. Ashes will be pushed towards the rear of the box instead of shoveling them through the front door. Ashes will fall into an ashtray underneath the firebox.
Firebox bypass: HR port opening being lower than the firebox top, smokes flow inside the kitchen every time I open the firebox door. It is really a problem while lighting a new fire. Besides, during this phase, smokes are really dirty. The less they flow through bells and HR, the better. I designed an ‘escape way’ at the top rear of the firebox to extract smokes from the firebox without running through Hrn bell1 and bell2. There is a bypass to open and close this shunt.
Cooking hood bypass: Stews cooking for hours smell in the whole house. I will try to use the firebox ‘escape way’ as a secondary flue for a cooking hood above the oven. I planned to use it when the fire is definitely over and no smokes remain in the bells. The hood bypass will block the hood duct.
Cleaning and maintenance:
- Bell1 access doors: there are 2 doors on the left side of bell1 to clean respectively the upper and lower pipes leading to bell2 as well as the top and bottom of bell1. There is also a door above the hood entry to clean the HR top and the right hand side of bell1. There is a lower front door below the bench for cleaning bell1 floor.
- Bell2 access door: A single door should be enough to clean the whole bell.
Bell3 access doors: The front door is here to clean the secondary duct as well as bell3, the side door for sweeping exit flue as well as bell1 rear duct.
Dimensions (in mm):
HR: 1210 x 200
Firebox: 290 x 420 x 730 port at 614 from the door
Port: 316 x 72
Floor channel: 654 x 80 x 50
Channel stub: 50 x 50 x 160
Frame bottom primary air inlet: 74 x 44 (two per frame)
Frame inner CS: 74 x 44
Frame upper inlet: 160 x 20 (two per frame)
I do not know if it is better to put two openings on each side of the door frame or to add a third opening on the top of the same frame.
I am eager to read your comments on this design. Please tell me if you see any problem that could occur.
Sketchup file here
The design remains roughly the same, it still aims to heat three rooms with a 200mm batch box but the heat flow has been modified as well as the firebox position. Several features for day to day use and cooking have been added.
Overview:
Kitchen + sleeping room above:
Living room:
HR:
- HR scaling: according to spreadsheets, I should use a 250 mm HR to heat my house. The problem is that it requires to load 30 kg wood in the firebox… Well it is a lot of wood to carry and handle. During the last 2 heating seasons, I weighted day after day wood loads to heat the kitchen above 20°C and warm up the living room around 16°C. With my old dirty stove, the max wood consumption was 32kg a day. Therefore, I hope a 200 mm design (14kg wood per load) should be a good compromise. I may have to burn three or four loads a day when the weather is getting really cold but one to two loads a day should be sufficient for the rest of the season.
- HR shape and material: I did some trials with an aerated concrete prototype. I noticed that round shape HR insulated with vermiculite provide faster clean smokes than non insulated square shaped HR. My last prototype was built out of dense refractory bricks. It was warming quite slowly and I wish to try light refractory bricks this time. The octagonal shape is copied from batchrocket.eu from Peterberg.
Firebox :
- Firebox location: I measured that the firebox sides can be an interesting heat source. Curves below show that firebox sides are warmer than any other surface of the bell (blue curve in the last box). I want firebox sides to radiate as much as possible directly towards the kitchen, not inside the bell.
Bell scaling:
- Scaling bell1: my last prototype (125 mm batch) had 2.2 m² radiating surface. It was sufficient when outside temp was above 10°C. In contrary, kitchen temp did not get above 13°C when outside temp dropped down to -7°C. Bell1 radiating surface needs to be significantly increased (6.2 m² in this new design and 4 m² SIA).
- Scaling bell2: 2 years ago, I tested a bell with 2.1 m² radiating surface. It was sufficient to warm up the living room around 16°C. It was fed with 600°C smokes from my 125mm old dirty stove. For this new bell2, I am targeting a radiating surface greater than 2.1m².
- Bell2 height: Surface temperature of my former living room bell was much warmer on the upper half. Reducing the effective bell height by half did not impact significantly heating performances. Heat extraction is apparently more efficient with a wide and short bell than a narrow and tall one. Therefore, I will reduce bell2 height to 1.1m in my new design. The width will be increased to get 3.6m² radiating surface (SIA = 3.3m²).
- Bell2 feed: Last winter, chaining the second bell to my 125mm batchbox was clearly not efficient. Smokes coming out the kitchen bell were too cold (below 200°C) and did not heat sufficiently the second bell. In this new design, bell2 is linked to bell1 both on top and bottom by two pipes. As temperatures measured on top of my present kitchen bell are between 400 and 500 °C, I expect smokes running through this new bell2 to be much hotter than 200°C.
- Scaling bell 3: In a coming project this batch rocket will heat water during winter. Bell 3 is here to add some water pipes on top of the kitchen bell. Its dimensions are given by the kitchen bell cross section and a reasonable height for cleaning access (SIA: 3.2m²).
Heat flow:
- Bell1 top: hot smokes from the heat riser spread inside a large space on top of bell1 (9 x HR CSA). The rear cavity on the left side will be filled with clay and stones for heat storage. The middle cavity is a duct for smokes rising from bell1 bottom. The right cavity is a secondary duct. Its purpose will be described later.
Bell1 middle: cooling smokes from bell1 top fall down on the left side(2.2 x HR CSA). The CS gets bigger above the bench. Smokes should flow both on the right and left thirds of the bench.
Bell1 bottom: Smokes flow from right and left to the middle and rise in the rear duct up to the top of the bell towards bell3. We will see if it is warm enough to get a comfortable bench temperature.
- Bell2 feed: bell2 is linked to bell1 by 2 pipes. Bell2 top pipe collects hot smokes from bell1 top. The lower pipe is needed to extract cold smokes out of bell2 towards bell1 bottom. I will try to insulate them as much as possible (I do not want to waste heat in the wall between kitchen and living room).
Bypasses:
ecologie-pratique.org/mediagallery/album.php?aid=1882&page=1
This 3 bell design has a SIA above recommended value (~ 9m² max). I added different bypasses to shunt bells and balance heat flow between them.
- Bell1 bypass: it shunts bell1 bottom as well as bell2. Smokes will flow directly into bell3. Opening partially this bypass should balance heat flow between bell1 and bell3.
- Bell2 bypass: it blocks bell2 upper pipe or direct access to bell1 bottom. When set on the upper position, smokes will flow directly towards the lower part of bell1. When set on the lower position, smokes will flow through bell2 before going through bell1 bottom. Opening it partially should balance heat flow between bell1 bottom and bell2.
- Bell3 bypass: smokes coming from bell1 will flow through bell3 when set in the upper position.
- Cooking: A white oven sits on top of the firebox. There is a hot surface for soup or stew in front of the oven.
- Ashtray: there is a hole behind the p-channel to reduce dust while cleaning. Ashes will be pushed towards the rear of the box instead of shoveling them through the front door. Ashes will fall into an ashtray underneath the firebox.
Firebox bypass: HR port opening being lower than the firebox top, smokes flow inside the kitchen every time I open the firebox door. It is really a problem while lighting a new fire. Besides, during this phase, smokes are really dirty. The less they flow through bells and HR, the better. I designed an ‘escape way’ at the top rear of the firebox to extract smokes from the firebox without running through Hrn bell1 and bell2. There is a bypass to open and close this shunt.
Cooking hood bypass: Stews cooking for hours smell in the whole house. I will try to use the firebox ‘escape way’ as a secondary flue for a cooking hood above the oven. I planned to use it when the fire is definitely over and no smokes remain in the bells. The hood bypass will block the hood duct.
Cleaning and maintenance:
- Bell1 access doors: there are 2 doors on the left side of bell1 to clean respectively the upper and lower pipes leading to bell2 as well as the top and bottom of bell1. There is also a door above the hood entry to clean the HR top and the right hand side of bell1. There is a lower front door below the bench for cleaning bell1 floor.
- Bell2 access door: A single door should be enough to clean the whole bell.
Bell3 access doors: The front door is here to clean the secondary duct as well as bell3, the side door for sweeping exit flue as well as bell1 rear duct.
Dimensions (in mm):
HR: 1210 x 200
Firebox: 290 x 420 x 730 port at 614 from the door
Port: 316 x 72
Floor channel: 654 x 80 x 50
Channel stub: 50 x 50 x 160
Frame bottom primary air inlet: 74 x 44 (two per frame)
Frame inner CS: 74 x 44
Frame upper inlet: 160 x 20 (two per frame)
I do not know if it is better to put two openings on each side of the door frame or to add a third opening on the top of the same frame.
I am eager to read your comments on this design. Please tell me if you see any problem that could occur.
Sketchup file here