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Determining combustion efficiency health

May 1, 2011
Are you properly commissioning your new gas fired high-efficiency equipment? If you are not, you just might be voiding any warranty on the consumers' equipment...

Are you properly commissioning your new gas fired high-efficiency equipment? If you are not, you just might be voiding any warranty on the consumers' equipment...

Although testing and commissioning of gas fired equipment has always been a requirement for most all gas fired equipment, it is one of those grey areas that really has no enforcement. It has always been the recommendation of gas fired appliance manufacturers to request annual service check ups. And in a lot of cases, many contractors do provide minimal preventative maintenance procedures on the gas fired appliances on an annual basis, however, they are not addressing the issue of combustion health/efficiency of the appliance.

As Ross Perot once said, "If you don't look under the hood, how are you going to know if it's broken or not?"

Other than the obvious significant accumulations of carbon, without having a combustion analyzer you would not know the general combustion efficiency of the gas fired appliance you are dealing with. And this is not something that can be judged with the naked human eye. It requires the use of a combustion flue gas analyzer, of which there are many available on the open market.

As I have stated publicly before, just having an analyzer is the first step in understanding the actual process and application. Unfortunately, many people own this equipment, but do not understand how to read and interpret the output of the analyzer. Most people focus on the percent efficiency number, and ignore the other critical numbers that pertain to the efficiency of the combustion and heat exchange process. Not only is this dangerous, but it can lead to a loss of life and or equipment, and possibly your livelihood.

There are numerous components to the flue gas analysis that are critical in determining combustion efficiency health. These constituents are generally dictated by the appliance manufacturer and vary from appliance efficiency to appliance efficiency, with the most critical being in the sealed combustion, modulating/condensing categories. There are some new controls coming out on European boilers that are supposed to be able to adjust fuel and air ratios to optimize the combustion process. This doesn't mean that you can sell your combustion analyzer on E-Bay. You will still be required to test the appliance to make certain that nothing is out of whack. The very first one of these new class of boilers that I encountered required an intervention by the local manufacturer's representative in order to bring the appliance in to conformance. So, contrary to misguided belief, it is not a plug-and-play world. It never has been, and never should nor will be a plug-and-play world as it pertains to combustion processes.

The process is fairly straight forward. You have a fuel, and you have air. You mix these two and expose it to the presence of heat and establish flame, I like to think of it in terms of an automobile, and fuel carburetion. Sure, I understand that most automobiles of today don't even have a carburetor on them, but most service technicians remember when fuel injection was not an option.

Back to the combustion process, we mix air and fuel and set it on fire. As air and fuel are mixed and burned, it generates heat, light energy, a reduction in oxygen (o2) content, and correlating increase in carbon dioxide (CO2), the presence of carbon monoxide (CO), and some other soon to be regulated byproducts, like nitrous oxides (NOX) and residual moisture (H20).

Theoretically, the presence of carbon monoxide can be eliminated down to zero under perfect, ideal conditions. This condition is referred to as being "stoichiometric." In all of my years of traveling and testing appliances, I have personally seen two natural gas appliances that had zero carbon monoxide in their flue gas stream, and both of these appliances were atmospherically vented appliances. This atmospheric type of appliance is notorious for having a lot of combustion issues, because of the lack of control over, primary/secondary dilution air and draft, but for whatever reason, at the time of my test, the two appliances came in at a perfect burn.

With the proper amount of heat exchange area, the flue gas will initially go through a significant increase in fluid temperatures in the "source" side of the heat exchange process, but those temperatures are also dictated by the optimum combustion process. As the flue gas travels through the heat exchanger, the flue gas temperatures drop because they are giving up their heat to the load side of the heat exchanger. If the heat exchange area is properly sized, the load side of the heat exchanger should go through a significant increase in fluid temperature. Conversely, you could have an optimum combustion process, but if your heat exchange process is weak or undersized, then it too will affect the appliance’s overall thermal efficiency.

Tune in next month as we continue to look at what is necessary to set these highly technical pieces of equipment up to insure safe and proper operation. Until then, happy combustion efficiency hydronicing.

All Mark Eatherton material on this website is protected by Copyright 2011. Any reuse of this material (print or electronic) must first have the expressed written permission of Mark Eatherton and CONTRACTOR Magazine. Please contact via email at: [email protected].

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