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Post by josephcrawley on Feb 20, 2023 9:25:36 GMT -8
The MHA mail list had a discussion recently about system size to mass ratio. Norbert Senf shared an interesting document with recommendations on the ratio of kcal/hour to mass of the stove. It is an interesting way to look at the sizing of a stove that may have more relevance than just looking at surface area calculations. It also takes into account the climate in which the stove is built. Here's a link to the document hosted by appropedia. www.appropedia.org/File:Grundof.pdf?page=2 |
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Post by fiedia on Feb 22, 2023 7:24:35 GMT -8
Interesting document. For comparison, I scaled a kachelgrundoefen with the same flue diameter as a 200mm/8” batch.
A medium type kachelgrundoefen should have a heating surface of 3.1m2 and supply around 10kW/h with two burns a day.
According to existing batch rocket design rules, a 200mm system can have a heating surface around 9m2. It delivers less than 4.4 kW/h with 2 burns a day (11kg each).
Does it mean that one can load 25kg wood per burn in a kachekgrundoefen? It seems difficult since the firebox surface is smaller than a 200mm batch firebox.
Is there second combustion in the kachelgrundoefen? I see no secondary air and no post-combustion chamber as for batch, DSR or vortex stoves.
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Post by masonryrocketstove on Feb 22, 2023 7:46:42 GMT -8
Does it mean that one can load 25kg wood per burn in a kachekgrundoefen? It seems difficult since the firebox surface is smaller than a 200mm batch firebox. Is there second combustion in the kachelgrundoefen? I see no secondary air and no post-combustion chamber as for batch, DSR or vortex stoves. That document was originally published in 1972 and translated into english a couple decades ago. At the time it was originally published, secondary air was supplied under the fire through the bottom grate. Since then, better testing equipment has shown that secondary air supplied above the fire leads to better efficiency and lower emissions. Austrian and German standards for grundöfen and kachelöfen construction have tightened considerably and improved stove performance dramatically over the last 50 years since that original publication. |
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Post by josephcrawley on Feb 22, 2023 14:00:54 GMT -8
Interesting document. For comparison, I scaled a kachelgrundoefen with the same flue diameter as a 200mm/8” batch. A medium type kachelgrundoefen should have a heating surface of 3.1m2 and supply around 10kW/h with two burns a day. According to existing batch rocket design rules, a 200mm system can have a heating surface around 9m2. It delivers less than 4.4 kW/h with 2 burns a day (11kg each). Does it mean that one can load 25kg wood per burn in a kachekgrundoefen? It seems difficult since the firebox surface is smaller than a 200mm batch firebox. Is there second combustion in the kachelgrundoefen? I see no secondary air and no post-combustion chamber as for batch, DSR or vortex stoves. Regarding the kg would load of a firebox how are these figures calculated? Clearly I could tightly stack wood in my firebox and then weigh it but how does one account for varying density between species? |
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