LPG vs NG inputs?

Solid_Fuel_Man

Why are L.P. inputs generally higher on the min. input than NG for the same piece of equipment? I know pressure is higher, but wouldn't smaller orfaces make up the difference so the manufacturer could keep the same turndowns for both gasses? Curiosity ya know

Zman

Solid_Fuel_Man said:

Why are L.P. inputs generally higher on the min. input than NG for the same piece of equipment? I know pressure is higher, but wouldn't smaller orfaces make up the difference so the manufacturer could keep the same turndowns for both gasses? Curiosity ya know

Good question! I think @Tim McElwain will have an answer.

Tim McElwain

Could you give me an example from a particular rating plate on a piece of equipment. In most cases it has to do with testing and being able to meet DOE output standards.

Solid_Fuel_Man

Viessmann Vitodens 100-W B1HA 26 specifically. 21-94MBH natural gas, and 31-94MBH input on L.P.

Several other mod/cons from WM and Viessmann also have higher floors on the min for L.P. than for N.G.

Was thinking maybe due to higher BTU per given volume of gas, but seems as though that wouldn't be a factor with modulating gas valves etc.

Thanks! I always appreciate quenching my curiosity of such things.
Taylor

GW

Yes indeed see attachment. One possible explanation is the co2 is set higher on an LP then it is on a nat.

The second attachment is out of a WB1A manual which seems to be the same boiler in this discussion

GW

Oops I wrote wb2b on the manual sheet by mistake

Solid_Fuel_Man

@GW, yes that is the exact spec I was referencing from.

I'm down to a decision of this viessmann or a Weil Mclain ECO series. Both are supported locally, and both are stainless, I feel the radial viessmann is a tried and true design over the WM outsourced fire tube as of now. But the lack of turndown on L.P. on the viessmann still has me thinking.

I don't want all the controls other boilers offer as I already have that all in place for my wood gasification setup this will be integrated into. I want the Chevy options with the Cadillac engine.

Most guys around here are putting in the Bosch mod/cons. I'm just not ready for an aluminum HX, even with lifetime warranty. But their numbers are impressive.

Taylor

Tim McElwain

Keep in mind the ultimate CO2 for natural gas is different than for LP.

Tim McElwain

For what it is worth the Gas Engineers Handbook www.asge-national.org/contents/library/stoichiometry.pdf explains it all.

GW

I like the Viessmann but when I finally learned about its temperature limits I got cold feet. I'm not interested in "it's fine for just about every installation" I've been in three situations that could have gone south... home owner saying the new system wasn't heating as well as the old system in extreme cold weather. I want the ability to crank up the temp if needed. I don't want to go back and add heat emitters, as once was suggested.

GW

Tim, does the higher co2 specs equate to more heat? I would presume so but not sure

Tim McElwain

The CO2 difference does not really mean more heat but the chemical make up of the fuels. Natural Gas has the lowest flame temperature, LP is next highest then Butane and the highest is oil. Keep in mind it takes one btu to raise the temperature of 1 pound of water one degree.

GW

I'm not sure I follow, so hypothetical question- if two boilers are identical and burn the same fuel, one is running a Co2 of 9.0 and the other is 10.0, doesn't the 10 boiler burn the fuel more completely and hotter? I'm trying to understand the OP q myself.

I know this is getting into voodoo economics. Also curious why modern high efficiency furnaces run such meager co2 numbers

Tim McElwain

It has to do with issues with controlled excess air and excessive excess air. High efficiency equipment as to combustion efficiency is about the same as when we remove an oil burner and replace it with a gas conversion burner. the oil efficiency was around 80% the gas will also be 80% but different CO2 and O2 numbers but keep in mind the ultimate CO2 for those two fuels is is different. The
AFUE efficiency of Mod/Cons is then related to low return temps and the modulation of the equipment. For the furnaces it has to do with flue gases passing through the secondary heat exchanger and extracting the latent heat from the condensate. With boilers the heat transfer design of the equipment. That with the lower flue gas temperature will boost the measured efficiency.