[Stoves] change heading - stove tests

[Frank Shields]

Dear Crispin,

I'm thinking; Ideally;  When testing biomass stoves what we want is the 
info between  - START at once the fuel has been ignited and conditions 
we want to look at have been achieved (low power, full power) then 
measurements taken until an agreed TIME has passed when the tests ENDS. 
Problem is getting accurate measurements of the energy in the fire box 
at the START point and again at the END point.

So we measure the energy of the fuel (water, biomass) we place in the 
fire box and energy we remove (water, biomass, torified wood, char, ash 
) from the fire box to determine the energy used from the fuel during 
the time of testing. The starting fuel and, especially, the ending fuel 
has a lot of room for error.  If we ran a cord of wood through Pauls 
TLUD without stopping the error percent at the ends would be much 
smaller than when we just run a few Kg of fuel. Thats my point. We still 
need the effects of loading fuel included in the test and longer runs 
would help average this also. No more failed tests because a little dust 
went up the stack one time. That because longer runs one needs to add 
fuel lots of times that average the particle emission value etc..

One might think we could better determine thermal efficiency of a stove 
using a gas heat source rather than biomass fuel because that is a 
constant controlled heat supply. But we can't because where to you point 
the flame(?).. Since different biomass fuels have different burn 
patterns the fuel needs be included and the fuel type used specified.  
To reduce the tallest noise peaks when testing stoves I think longer 
runs and fuel characteristics described (when we know how to do that) 
are most important. Once that is done we look for the next highest peaks 
to reduce and that may be your .

"If the losses from the water (radiation) the pot
(radiation, convection, conduction and the lid (ditto) are large compared
with the heat lost from water evaporation then the calculated result is in
(large) error."


It sounds like what you are doing (many hours per run and using coal(?) 
as a constant fuel)  is just what I am talking about. And now its time 
to look at radiation, convection etc.as you are. Not so with other stove 
testing.



Frank (on his soap box)
 


Crispin Pemberton-Pigott wrote:

>Dear Frank
>
>  
>
>>A part of the testing I would like to see changed is going from testing the
>>    
>>
>stove as 'we think it will be used'  to 'a continuous run for hours' 
>
>I am all in favour of that. The point of running any test is to get useful
>information. After a while, no new information is gained so continued
>testing is pointless.
>
>  
>
>>...to lower the percent errors when determining energy of remains fuel and
>>    
>>
>time a temperature reads simmer to boiling.  
>
>If the point of a test is to find out what the thermal efficiency is at low
>power, run the stove at low power and put on a pot of cold water. Between
>30-70 degrees C the thermal efficiency will be obvious, especially at the
>lower end of that range.
>
>  
>
>>These errors in their measurements will be the same if we run the stove for
>>    
>>
>an hour or for 20 hours but it will be a larger percentage of the one hour
>and a much small percentage a 20 hour run. 
>
>The error is not caused by the duration of the test, it is from measuring
>only a small portion of the energy that passes through the pot and declaring
>that to be the total. Only a small percentage of heat passing into a pot at
>low power disappears as evaporated water, even less if the lid is off.
>
>  
>
>>And the increase in fuel burned will more represent an average of the fuel
>>    
>>
>and changing conditions when loading. We can then do a simmer test for 20
>hours and keep the results separate.
>
>This repeats the error. If the losses from the water (radiation) the pot
>(radiation, convection, conduction and the lid (ditto) are large compared
>with the heat lost from water evaporation then the calculated result is in
>(large) error.
>
>  
>
>>I realize 20 hours is too long ...
>>    
>>
>
>We are doing some very long tests in UB to see what there is to learn.
>Basically nothing. We have reduced the fuel burned from 95% to 90% of that
>loaded for two reasons: there is nothing of interest to learn and because
>too many stoves are unable to burn 95% of the fuel in a reasonable time (say
>12 hours). Most stoves can burn 90% of a fuel load in a few hours, including
>a refuelling episode. Let's say 6 or 7. That is a reasonably long and
>accurate test yielding 1500-2500 data points. The mass corrected thermal
>efficiency and the emissions (similarly corrected) are the results of
>interest. The accuracy is high and the result meaningful when expressed in
>emissions per unit of heat potentially produced.
>
>We did some tests for 20 or more hours and learned nothing at all. We did
>several to prove that there was no new information to be gained in relation
>to emissions and efficiency, then stopped. We can pretty accurately predict
>daily and monthly emissions and the fuel savings/use of a variety of stoves
>with tests lasting no more than 7 or 8 hours. As UB is primarily a PM
>reduction project, that is enough.
>
>Regards
>Crispin
>
>
>
>_______________________________________________
>Stoves mailing list
>
>to Send a Message to the list, use the email address
>Stoves mailing list
>
>to UNSUBSCRIBE or Change your List Settings use the web page
>http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
>for more Biomass Cooking Stoves,  News and Information see our web site:
>http://www.bioenergylists.org/
>Stoves at lists.bioenergylists.org
>http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
>
>  
>