[Stoves] [MHAtech] Re: Top lit updraft combustors

Mon Dec 18 11:42:06 CST 2017

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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