Dear Ron
2. Re the use of 18 vs 15 - I agree. I have just gotten used to working with nice easy divisible numbers so folks could easily follow the math. I apologize; I should have put in a warning to that effect. Any idea how the energy value of char should be similarly devalued by humidity? The char coming out of a stove will have no moisture init. If it is kept around (under shelter) it will still pick up 3-5% over a period of weeks. If it a really humid place like Maputo it can reach 10% but that is not so common. The devaluation is then (for 5% WWB) is about 1.5%. You can probably use 29 MJ/kg if you are assuming a pyrolyser and not be too far wrong. IF it is char recovered from a fire, anything goes. Perhaps Jim Jetter is the best to talk about that because he tested so many samples recently. There is not much published on the subject. A piece of fireplace charcoal might be mostly ash or contain some wood in the centre. Hard to know. It is reasonable to assume that the volatiles content of charcoal is 15% if it is intended for sale as fuel (i.e. from a forest) because if it is a lot lower it is hard to light. Old char can be added to an existing fire but has unpredictable heat content. >I have been amazed at how uniform power levels can be once one has set a >desired power level; that converts to saved time.(and therefore another >income aspect of a cost comparison. The problem I have seen is virtually no control over the power level at all. It is a big minus for cooking and a plus for home industry. >I give a talk at ETHOS on the handling of char in stove efficiency >computations - that will take issue with some of your thoughts below. Let's >revisit this after you have heard my view on this topic. Great. It needs to be discussed. Also please see the talk/paper by Prof Harold Annegarn and yours truly where metrics are discussed because it is directly related: different players want different metrics out of a test and ‘efficiency’ has different meanings to different stakeholders representing different (and all valid) aspects of stove performance. Regards Crispin
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