Heating oil: effective or real output/yield (per liter)

[courteous]

Heating oil: effective or "real" output/yield (per liter)

http://en.wikipedia.org/wiki/Heating_oil" says that

Heating oil produces 138,500 British thermal units (146,100 kJ) per US gallon ...

which is about 11 kWh/L.

I was given an unbiased (but not necessarily correct) number that the effective output is about 8 kWh/L ...

... and a potentially biased number (from a company that is selling me solar water heating (SWH) system) of 6.5 kWh/L.

Is the last number (6.5 kWh/L) a better approximation than 8 kWh/L for the effective energy yield?

 

[courteous]

Hope I'm allowed to re-ask (after almost 2 months).

 

[russ_watters]

138,500 (10.5, not 11kwh/l) is the higher heating value, which is the total combustion energy. It does not take into account inefficiencies. The max efficiency of a boiler that does not condense water vapor out of the exhaust is about 80%. That is known as the lower heating value and most boilers come in close to it. 8 is 76% of 10.5 which is close enough for me.

 

[meplumber]

I will preface my answer by saying that I am not an engineer. I am a Licensed Master Oil Burner Technician and Master Plumber. I have been a Plumbing, Heating and Cooling contractor for over 20 years.

Mr. Watters is correct in his logic, but slightly off on his numbers.

The average btu content of #2 fuel oil sold in the US and Canada is between 140,000 and 144,000 btus. The most efficient oil fired residential equipment available in North America is 89%. The norm for outdoor reset equipment is around 87%. And the norm for standard single pass cast iron boilers is around 82%.

It is currently not possible to use a condensing oil boiler in North America due to the high sulphur content of the oil. There are a couple of models available in Europe and they are seeing efficiency numbers around 92%.

The descrepancies that you are seeing are listed in North America by the manufacturer as Input BTU and NET. The input btu being determined by the size of the burner nozzle and the pump pressure. I.E. a .85 gallon nozzle with the pump set at 140 psi has an input rating of 140,000 btu. Likewise, a 1.00 gallon nozzle with the pump set at 100 psi is 140,000 btu input. If the boiler has an average 86% efficiency, then the NET is 120,400.

I would be curious of your solar intentions. Good Luck.

 

[courteous]

If the boiler has an average 86% efficiency, then the NET is 120,400.

I would be curious of your solar intentions. Good Luck.

The 120,400 are in btu units, right? So, from this number (presuming 86% efficiency, etc.) it follows that the NET yield is 9.28 kWh/L, correct?

In short, the net yield (using an average boiler) certainly comes closer to 8 kWh/L (than to 6.5 kWh/L)?

The latter number of 6.5 kWh/L was put forward by the solar company (that is trying to sell me their heating system) in order to make their system seem more economically reasonable (than it really is; if their number is indeed way off).

And thank you both for the reply. medplumber, there is no pre-requisite for being an engineer ... otherwise, I shouldn't be writing in this forum either.