[Stoves] [MHAtech] Re: Top lit updraft combustors
Frank Shields
franke at cruzio.com
Mon Dec 18 12:19:48 CST 2017
Dear Crispin,
You are not exactly building up our confidence in convincing us to use
the LHV calculations for our small stoves by pointing out all the
problems. Ha But a very good learning tool.
But I have a question: Say you do a WBT using biomass having, say -10%
moisture and calculated in the LHV based on time and temperature
increase and water loss etc. Could you then just calculate the time it
would take to heat water using the same biomass but having 15% moisture?
or perhaps 5% moisture by plugin in the data? And if you were to
actually use biomass with 15 and 5 percent moisture find your
calculation were spot-on? I'm guessing not close.
That because; take a small active burning and task producting stove and
'place it on a platform' and plot XYZ one centimeters apart, Every
cubic cm will be changing in temperature, gas flow and pressure every
second. And every square cm of surface area will be changing in heat
holding and temperature every second = too variable to reliably use LHV.
Unlike a commercial biomass boiler.
If you cannot use the LHV calculations to predict happening at a
different temperature then the calculations just create an error. I'm
thinking a better way is to run tests using the HHV and just report the
moisture of the biomass used along with the findings.
But I will be VERY happy to be proven wrong.
Regards
Frank
On 12/18/17 9:42 AM, Crispin Pemberton-Pigott wrote:
>
> Note to all:
>
> I caution that when calculating the HHV using either the EPA’s formula
> or, if in the Far East, the Chinese method in their national
> standards, both are using a constant for fuel moisture compensation in
> the HHV formula that is incorrect (and in disagreement). This was
> discussed in an analysis of several test methods in Zhang, Y et al
> 2014 p.7/11 and a correction proposed.
>
> “KEY DIFFERENCES OF PERFORMANCE TEST PROTOCOLS FOR HOUSEHOLD BIOMASS
> COOKSTOVES”
>
> *DOI: *10.1109/DUE.2014.6827753 <https://doi.org/10.1109/DUE.2014.6827753>
>
> The proposed correction concerns the constant used to adjust the
> cooling of condensed water vapour from 100˚C to normal temperature.
> The EPA and Chinese methods in essence have it that room temperature
> is 52 and 60.5˚C respectively.
>
> For the LHV there is a second issue: many calculated Lower Heating
> Values include a value for the condensation of water vapour to liquid
> but omit the cooling of the water to normal temperature. The
> difference is about 60kJ. One of the most accessible tables of
> biomass, HHV and LHV values is at the back of the Water Boiling Test,
> versions 3.x to 4.x. All the values in the back are based on a
> ‘standard deduction’ not a calculation from the analysis of the fuel.
> The “standard deduction” from the HHV is 1.32 MJ per kg. Not only is
> the value almost always not correct for the condensation energy, it
> also omits the 60kJ from the deduction.
>
> This omission was noted in Sam Baldwin’s book in 1987 but was never
> incorporated into the WBT calculations.
>
> Regards
>
> Crispin
>
> ++++++++++++
>
> *ABSTRACT*
>
> *In this study, different ways of testing household*
>
> *biomass cooking stoves are compared and analyzed.*
>
> *The differences between test methods relate to the stove*
>
> *operation and data analysis methods, the fueling*
>
> *procedure, the end point selection, the choice of metrics*
>
> *and others factors. The influences of these differences*
>
> *were analyzed by using an induction heater. The results*
>
> *show the use of a pot lid or not, and the selection of the*
>
> *end point of the test have the greatest influence on the*
>
> *rated performance. Consequently test results provided*
>
> *by laboratories using different test methods will place*
>
> *the same stove-plus-fuel combination on significantly*
>
> *different performance ‘tiers’. Also the results show*
>
> *some metrics in popular tests should be reviewed. Some*
>
> *recommendations are provided for improving the*
>
> *accuracy and repeatability of test*
>
> +++++++
>
> Thanks, Steven. That's great.
>
> Our experience with domestic-scale cordwood in masonry heaters (50 lb
> batches @20% moisture) is that the "boiling of water" or latent heat
> loss is typically in the 13% range, using the Condar spreadsheet HHV
> calculation heatkit.com/docs/condar.PDF
> <https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fheatkit.com%2Fdocs%2Fcondar.PDF&data=02%7C01%7C%7C9d752582db6d47f6399f08d546367aa5%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636492122151013754&sdata=asRt6%2FrP3ifNJ%2FMqKKXwWHGyOBbjxzV4xMjitTc6Sqs%3D&reserved=0>
>
> On Mon, Dec 18, 2017 at 11:24 AM, Law, Steven (MOECC)
> <Steven.Law at ontario.ca <mailto:Steven.Law at ontario.ca>> wrote:
>
> Hello all,
>
> I have finally completed a proper study of reporting efficiency
> using LHV and HHV. It was much more complicated than I thought it
> would be, and now I know why this is such a mess!
>
> Just remember that HHV is always less than LHV, and anything above
> 100% is WRONG and cannot possibly conserve energy or mass and is
> therefore unscientific.
>
> When an LHV efficiency from Europe is 90% (which is actually a
> reasonable number), the HHV efficiency is a maximum of 84% or
> usually less, depending on the moisture content of the wood fuel
> and is more typically 75-80%. This is important, HHV efficiency is
> extremely dependent on fuel moisture whereas LHV is less so, but
> only for non-condensing boilers.
>
> Again, this is for non-condensing combustion devices, because when
> you throw in high efficiency condensing heat recovery all the
> numbers get screwy and LHV no longer applies. Everything has to be
> re-done for condensing boilers and only HHV can be used, I will
> repeat LHV cannot be used for anything where condensation of the
> flue gas occurs in the heat recovery device!
>
> I think I have a proper engineering calculation procedure mapped
> out to deal with all of the above issues and I will begin to roll
> this out a little bit at a time since I need to review it again
> before sending anything out. It is a scientific method that is
> based on conservation of mass and energy and I hope that this new
> calculation procedure will help to solve some current problems in
> the industry.
>
> Best regards, Steven
>
> --
>
> Norbert Senf
> Masonry Stove Builders
> 25 Brouse Road, RR 5
> Shawville Québec J0X 2Y0
> 819.647.5092
> www.heatkit.com
> <https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.heatkit.com&data=02%7C01%7C%7C9d752582db6d47f6399f08d546367aa5%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636492122151013754&sdata=gxkaGDly5HpdqTu6bxTy6HZRAO67QM8XRp%2BVftSLG4E%3D&reserved=0>
>
> __._,_.___
>
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--
Frank Shields
444 Main Street Apt. 4205
Watsonville, CA 95076
(831) 246-0417 cell
franke at cruzio.com
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