"We initially installed two 2MBtuh Benchmark units to handle the 118,084-sq-ft building," said Stephen Novell, supervisor of mechanical maintenance at the Fort Wayne Community School System. "We kept one of the old boilers because a portion of the building remained on a steam system. In 2002, we pulled the last steam boiler and converted the remainder of the building to hot water. At this point, we also installed a third Benchmark unit. It provided the capacity cushion we wanted while adding to the efficiency profile of the overall heating plant."
Rendering Acid Condensate BenignBecause the Benchmark is designed to condense, Novell was able to simplify the school's heating system. Condensing refers to the release of latent energy, as heat in combustion flue gas when it changes from water vapor to a liquid state. Effective condensing increases the efficiency of the boilers and water heaters by as much as 11% to 12% - turning more of the boiler's fuel into usable heat. Because the Benchmark is designed to drain freely, the acid condensate - a harmful byproduct of this process which can damage and destroy a boiler's heat exchanger over time - is rendered benign. The result is the elimination of cold water temperature and thermal shock limitations. For Novell, this meant that the era of mixing valves, hot water mixing loops, and temperature-averaging components to protect the boilers from thermal shock was over.
To fully leverage the unit's overall efficiency, Novell utilized AERCO's Boiler Management System, which ensures that the three Benchmark units functioned as a single system. The system regulates the units to operate in tandem, providing them with precise firing instructions that ensure maximum efficiency. It is more efficient for the three boilers to run at 30% input than for two to run at 45%, or for one boiler to run at 90% of capacity. The system also consistently rotates the lead boiler in the plant so that each unit receives approximately the same amount of work over the course of the season. This prevents undue wear on any single unit.