The Future of Hydronics: Combustion Technology

FROM THE TIME that man started a fire in a pit in a cave, the process of combustion has intrigued mankind. He has taken it upon himself to make the smaller, more efficient and as clean as possible. In this process, the technology has moved us from the Stone Age fire pit, to todays computer-driven, lightweight, highly efficient, fully condensing technologies. The road between the fire pit and the computer

FROM THE TIME that man started a fire in a pit in a cave, the process of combustion has intrigued mankind. He has taken it upon himself to make the “fires” smaller, more efficient and as clean as possible. In this process, the technology has moved us from the Stone Age fire pit, to today’s computer-driven, lightweight, highly efficient, fully condensing technologies.

The road between the fire pit and the computer pit was strewn with boilers of all materials, good and bad, and of all combustion technologies, some better than others. There have been cast-iron vessels, copper vessels, steel vessels, copper finned-tube vessels, steel finned-tube vessels, stainless steel vessels, aluminum vessels and partially finned stainless vessels.

The combustion technology as it pertains to solid fuels has been from wood to coal back to pelletized wood and a mention of pelletized coal, including some corn-powered combustion processes. Many of the new solid-fuel appliances offer an inexpensive alternative to the higher cost of propane and other gaseous fuels. In some cases, you can “grow your own” fuel. Most of the newer technology uses a variable-speed combustion fan to ensure that the fuel is controlled and burned as efficiently as possible with claims of efficiency approaching 99%.

Gaseous fuels have come a long way on their journey to ultimate efficiency. Many solid fuel-burning appliances were converted to natural gas during the middle of the last century. The men who set these burners up took their secrets with them to the grave. I’m sure there was a method to their madness, I just haven’t figured it out quite yet.

For the most part, the coal grates were removed and were replaced by a single flower-shaped burner. Directly above this, firebricks were placed to absorb the radiant energy transmitted by the intense flame and reflect it to the water jackets directly adjacent to the combustion process. In many cases, these burners are still out there, doing a grand job of keeping the utility people in business delivering gas. They are obviously inefficient, but at the time they were introduced, efficiency was the least of their concerns. Comfort and convenience won out over efficiency.

As the distribution systems changed, so did the heat generators. Hydronic heating was becoming more of a science than an art, and attention was being paid to the actual demands imparted on the system and on fuel efficiency. Boilers got smaller and combustion efficiency increased. Eventually, the cost of fuel reached a level that efficiency started taking over as the primary concern of the end user.

Programmable thermostats dating back to the 1900s have been found, and some are still in working order. While they did nothing to address combustion efficiency, they did provide for more comfortable sleeping conditions and caused the system as a whole to be more efficient.

Meanwhile, back in the laboratory, the boiler manufacturers were experimenting with multi-stage burners and even variable flame-height burners in their never-ending search for the ultimate in efficiency. Even today, two-stage burner options are available on atmospheric burner assemblies. While this would appear to be an efficient means of converting gaseous fuels to thermal energy, it has been proven that this technology leaves a lot to be desired as it pertains to overall thermal efficiency.

It has always been known that in order to control the combustion process completely, you must control all the variables of combustion, including but not limited to: fuel; oxygen needed to mix with the fuel to get complete combustion (primary air); the air necessary to establish and maintain draft action through the combustion zone (secondary air); and the draft pressures associated with the operation of multiple-story flues.

All of them have an influence over the other and, if left unchecked, they can create havoc with the combustion process. Too much secondary air and you’ll cool the flame and retard the thermal conversion/transfer process. Not enough draft and the flame will burn back on itself, dousing itself with carbon dioxide and generating unsafe levels of carbon monoxide.

This led to the use of “power burners.” They allowed the manufacturer to control all the variables and increase thermal performance of their appliances. The only problem was that this technology required a large boiler (150,000 Btuh and larger) in order to accommodate the large flame assemblies. Due to the lack of variable-speed technology, the burner was basically two position, on or off. It’s the equivalent of driving a tack with a sledgehammer for the majority if the heating season, until your home is exposed to design conditions. The burner assembly is much larger than necessary. Because of its size, it was limited in application to those jobs where its potential could be utilized.

Tune in next month as we continue to discover new advances in combustion technology. Until then, Happy Efficiently Combusted Hydronicing!

Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.

TAGS: Hydronics