[Stoves] "78% Efficient"

Frank Shields franke at cruzio.com
Thu May 7 15:08:40 CDT 2015


Frank Shields
franke at cruzio.com


> On May 7, 2015, at 11:24 AM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
> 
> Dear Frank
> 
> Interesting question. The EPA has some strange test methods that are not really based on matching performance in use. They mace other methods that are extremely precise and accurate. There is a real mix. 
> 
> The manufacturers of wood stoves have been complaining for years that the test was so divorced from actual use that there was no real correlation between lab tests (official tests) and performance in use. The new regulations are supposed to address this. If you recall the discussion a while ago about Alexander in Russia, he was complaining about the new test and the way it averaged the efficiency numbers. 
> 
> There are two groups now: those who have compliant stoves (tested in the new way) and the rest. 
> 
> It is not clear yet how close the new test is to typical use. The way measurements are made for PM is reasonable, I feel. The method is not utterly precise ‎because it uses a hood with volume and pitot tube velocity with compensations for temperature and pressure. When emissions are low, fixed flow systems have difficulty measuring anything. 

I’m thinking the accuracy of measuring velocity of a gas moving through a pipe would be highly suspect. That because taking a cross section finds the flow differs from the outside to the center. A slight movement of probes and one gets a different reading that when multiplied up to determine the amount of gas per hour (for example) will differ a lot. I would like to see this replaced with the surrogate helium standard I mentioned before. 


> The alternatives are carbon mass balance or chemical mass balance. The former is used by the EPA for vehicles and the latter is used by SeTAR methods. 
> 
> The efficiency (as a heater) can be determined using the Siegert Formula which is a chemical mass balance approach with various iterations depending on the ‎data available. 

Neither will work as I see it. Like measuring temperature or CO2 produced in a compost pile to determine if the pile has stabilized only works with a properly formulated and working compost. But the entire purpose of testing is to find the piles that are poorly made and not stabilized and these methods will give false positive readings. So the test methods we now have for determining if a compost is stabilized is poor and meaningless. Same with stoves as I see it. The energy coming out of a stack of a properly run stove can be determined with CO and CO2 and carbon soot. But poorly run stoves will also contain wide ranges of unburned organics gases. Unless these are determined we do not know the energy value to assign. That was the purpose of my idea of the heated tube with oxygen input. Measuring CO2 before and after to get an idea (not exact) of the energy remaining in the outflow gas from the combustion chamber. . 



> 
> If you look deep into the origin of that assumption of 78% efficient, it is used to set emissions rates. It is a bit difficult to explain in a short method but this might help. 
> 
> In the Indian Standard 13152 which is a Chula test, there is an implied thermal efficiency, something the EPA has stated for various calculations. In the Indian test there is a chart of pot sizes that one selects from based on the firepower. If a stove has a firepower of 5 kW then it is assumed it can 'cook a pot' of a certain size. If it is 10 kW it is assumed it can cook a pot of twice the capacity. 

In this case is the ‘fire power’ defined from the rate the fuel (of known energy)  is consumed and without heating water in the pot? 
Do the chart of pot sizes really display a linear response? 

> 
> Think about this for a moment: what does 'cook' mean?
> 
> It means adequately heat and service the cooking needs in a pot of that capacity. 
> 
> If you make a stove with 5 kW and say that it can cook the pot of the 10 kW rating according to the chart.
> 
> Now, should the stove be tested with the larger or smaller pot specified in the 5 kW ‎column of the Standard?
> 
> The assumption in the test method is that no one will ever make a stove that is twice as efficient. So creating a stove that will cook the larger pot with the smaller power is not anticipated by the Standard. 
> 
> You see? So creating a stove that will cook an 80 litre pot with a '20 litre' fire is unexpected. 
> 
Interesting. There are so many variables in our small combustion chambers relating to stove construction, design and air flow that these test methods seem to provide no room for improvement - if I understand this?



> So in the EPA methods there is in the background calculations some things to do with emissions and performance that are based on a 78% efficiency. 

Really? What could these possible be? And why?

> 
> The ad was misusing the default number and, in my view, the logo of the EPA. I do not know the rules they have for the use of their logo. For SABS markings you have to pay per label. 
> 
> ‎The US uses a non-Siegert method that is also, at root, a chemical balance method that uses only the carbon (as I understand it). It gives a different answer from the European method because one can deal with condensing furnaces and the other can't. 

Biomass combustion is used in many different applications and, as I see it, they need to be grouped with each group having their own set of tests. Do we stovers care about condensing furnaces? 

Thanks

Frank



> 
> Regards 
> Crispin
> 
> Dear Crispin,
> 
> I wonder how many more years it will take to do such a simple job.
> 
> Frank
> 
> 
> 
> 
> 
> Frank Shields
> franke at cruzio.com <mailto:franke at cruzio.com>
> 
> 
>> On May 6, 2015, at 12:27 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com <mailto:crispinpigott at outlook.com>> wrote:
>> 
>> Dear Friends of Efficiency
>>  
>> Here is the “Ad of the month” from the Alliance for Green Heat
>> <image001.png>
>> The problem starts with the EPA having a ‘default’ estimated heating efficiency based on a fuel type. No one has any idea what the heating efficiency is, apparently. Even if there was a set of measurement that came to the 78% figure, that would only apply to the stoves measured, not future stoves that might work much better.
>>  
>> Note the ‘firepower’ is based on the theoretical heat available from the fuel. Oh wait, there are two fuels listed but only one heat ‘input’.  Heat input means the heat that could be generated from the fuel burned, not the heat actually generated.
>>  
>> So, there are all sorts of problems in the stove industry, not just the cooking stoves.
>>  
>> Makers of compliant stoves are suing the EPA to speed up the implementation of new lower emissions limits. Makers of non-complaint stoves are suing the EPA to have the new limits delayed. Some states are ignoring the new regs, some are applying them.
>>  
>> At least the test method is an improvement over the old one, though no one is yet claiming that the test predicts performance in the field. The main purpose of the testing is outdoor air quality.
>>  
>> Regards
>> Crispin
>>  
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