[Stoves] Stoves Digest, Vol 95, Issue 3

Crispin Pemberton-Pigott crispinpigott at outlook.com
Fri Jul 6 09:15:17 MDT 2018

Dear Nikhil

These units are convertible if one makes either certain assumptions, or using the assumptions that are in the background of the various organisations’ methods. These assumptions have to do with the efficiency of the device, or minimum efficiency, and the burn rates.

The conversions are ‘legitimate’ insofar as the assumptions are made clear. For example when comparing the emissions per MJ delivered, and there is no efficiency stated for the device, it is common to assume that the device is approved and that the required minimum (70% for example) has been met. There are EPA conversions that apply this in principle.

Some metric targets are created on the basis of such an assumed minimum efficiency. When looking at the ‘residential’ emissions rate of 2 g per hr, then there is in fact buried in there an expected mass burn rate, and an efficiency minimum of 70% (HHV).

Airshed and dispersion modelers want to know the total mass of PM they are tracking so using PM mass per ton burned, and knowing roughly the number of tons burned gives them their input number. Using time series analysis they can also generate 1 or 2-hr concentrations forecasts. JICA has been able to show measurements are within 50% of predicted value, (or better most of the time). It is quite a feat.

So if wood is assumed to burn at a rate of 25 pounds per hr, for example, and the emission rate is 2 g per hr, then that is 88 hours and 176 g/ton (0.176 kg/ton). If the expectation is 10 pounds per hr (22.7 kW) burn rate and the emission permitted is 2 g/hr then it is

1000/(10/2.2046) hrs x 2g/hr = 440g/ton = 0.44 kg/ton

Clearly, this is circumstance-dependent, so how much is actually emitted per hr is strongly dependent on the combination of the burn rate and the cleanliness of the burn. This approach is based on the ‘shared resource’ approach to the airshed’s ability to be contaminated. Everyone can contribute their bit.

More: If the burn rate is 50 lbs per hr (250 kW) and the emission rage 2 g/hr, then a ton lasts 1000/(50/2.2046) = 44 hrs and the rate is 88 g/ton. (0.088 kg/ton). That is unrealistic because houses don’t have 250 kW fireplaces running flat out 24/7. Being more realistic and choosing 10 kW continuous would look like this:

10 kW = 2.0 kg per hr @ 2 g/hr = 1 g/kg = 1kg/ton.  (assumption 18 MJ/kg)

That looks very different from what I calculated earlier for the JICA numbers (13 kg/ton). I cannot explain the difference, that is what they told me. Perhaps they have low expectations for coal combustion.

So: How does the crossdraft coal stove line up?

At 10 kW it uses 1.8 kg/hr of Nalaikh coal emitting at an average at a rate of 0.006 g/MJ delivered at full power = 0.1 g/kg (including ignition).  I don’t have a separate number for 10 kW, but it is considerably less because there is a lot less flyash (nearly no BC at all).  Let’s say it converts to something like 0.033 x 1.8 = 0.06 kg per ton. That is a 1/17th of the new EPA limit.

Altanzul, using the Hebei Province test sequence, (ignores ignition because they only light once per year) consistently obtained a value of 0.0004 to 0.0003 g/MJ which converts: 0.0046 – 0.0035 kg/ton burned (Shenmu raw coal). That is 1/288th of the new EPA target.  In Kyrgyzstan this is the value most likely to be witnessed as they run the stoves a very low power all the time and only light once or twice per season. We can assume the same for water heating low pressure boilers.

So the values are convertible using either the actual performance numbers or assumptions about what minima must be met.



EPA NSPS are in g/hr basis, not g/t or kg/t. See https://www.gpo.gov/fdsys/pkg/FR-2015-03-16/pdf/2015-03733.pdf<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.gpo.gov%2Ffdsys%2Fpkg%2FFR-2015-03-16%2Fpdf%2F2015-03733.pdf&data=02%7C01%7C%7C5ad351e92f78434b76c408d5e2de6fb4%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636664367332975097&sdata=6YHK2aMvI2XCXLm7ZJ2hIW9xeLIWvCXChPQtWtGCyy0%3D&reserved=0>.

I suppose for Single Burn Rate Heaters, g/hr can be converted to kg/t assuming kg/hr. See https://www.hearthandhome.com/news/2016-03-08/single_burn-rate_wood_stoves_new_again.html<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.hearthandhome.com%2Fnews%2F2016-03-08%2Fsingle_burn-rate_wood_stoves_new_again.html&data=02%7C01%7C%7C5ad351e92f78434b76c408d5e2de6fb4%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636664367332975097&sdata=tRQzqFu3YX864F9G%2FMuFtBwGgG%2BLkcxdeYRlXBHSURg%3D&reserved=0>.

The target emission rate for new stoves beginning 2020 is 2 g/hr.  The House passed a bill<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.congress.gov%2Fbill%2F115th-congress%2Fhouse-bill%2F1917%2Ftext&data=02%7C01%7C%7C5ad351e92f78434b76c408d5e2de6fb4%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636664367332975097&sdata=9sumlou8Mvl80l4Yl%2BBzcSYBJLbK5orrOAnJshjF09U%3D&reserved=0> to extend the date to 2023; the Senate is yet to act, and I doubt it will become the law this year.

Also, the practical effect is to drive up the cost of forced air furnaces and hydronic heating systems. See Table 9, p. 13696.

With that kind of cost increase, either the old systems will continue to be in use (in existing buildings) or people will switch to gas and electric heating (for new homes).

And that too if states agree to implement the EPA NSPS on the original schedule.

In short, the whole multi-decadal exercise was a bureaucratic career project with negligible air quality impacts except in a few counties of the US.  See Table 6, p. 13694. Annual reduction in PM2.5 emissions from wood heaters is expected to be measly 34 tons, and that from Single Burn Rate heaters 684 tons.

Wood is coming under attack in the UK as well. Burning issue: Are wood-burning stoves going to get the chop?<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.theguardian.com%2Fmoney%2F2018%2Fmay%2F26%2Fwood-burner-open-fire-pollution-cleaning-up-air-quality&data=02%7C01%7C%7C5ad351e92f78434b76c408d5e2de6fb4%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636664367332975097&sdata=1%2BYc8048BAIOR2c4QmxHrzOpK5jr82Ro%2BJXQa9dF3io%3D&reserved=0> Guardian (UK) 26 May 2018


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