In 2001, the University of North Texas (UNT) decided to replace Wooten Hall's original steam boilers, which served as the main junction of a four-building hydronic loop. The challenge was to find a boiler that could increase efficiency, decrease costs, and be maintenance-friendly. After extensive research, Utilities Supervisor David Young discovered AERCO Benchmark boilers at a trade show.
“We ordered three BMK2.0 units for the Wooten building,” Young said. “When they arrived, we nearly fainted. We couldn't believe boilers so small could manage the needs of a 228,000-sq-ft facility.”
The BMK2.0 models replaced two steam boilers that were much larger. Each compact BMK2.0 boiler occupies a 12-sq-ft footprint and can be installed in pairs with zero side-wall clearance.
“Imagine replacing a boiler the size of a pickup truck with one the size of a refrigerator,” Young said.
In January 2001, prior to the installation of the BMK2.0 condensing boilers, the Wooten building used 2,250 Mcf of natural gas. With the BMK2.0 boilers in operation, gas usage dropped to 798 Mcf in January 2003. By January 2007, usage was down to 418 Mcf.
“Another key benefit was that the units required very little maintenance,” Young said.
Based on the success of the Wooten building retrofit, additional Benchmark boilers were installed as replacement equipment and for new-construction projects across the UNT campus. That track record led to three BMK2.0LN boilers being specified for a new chemistry building on campus. However, the engineering firm contracted to design the building switched to lower-cost copper-fin alternatives. Within a few months, energy costs were higher than expected, and the copper-fin units were not up to the overall load requirements.
“Sometimes, engineers don't talk with the maintenance groups,” Young said. “The engineer and the school's building-system board thought money could be saved by switching to the copper-fin boilers. But they only looked at the initial costs, not the bills that come in every month.”
On paper, the two 3.5-million-Btuh atmospheric boilers were enough to satisfy the requirements of the chemistry building. However, “The boilers need to run year-round, for heating in the winter as well as to control humidity in the summer months,” Young said. “Despite higher-than-anticipated fuel costs, the copper-fins did meet the lighter Texas heating loads for most of the year, but once the outside temperature dropped below 50°F, the boilers could not keep up. We pushed them until they couldn't run any harder and one burned out.”
After a year, UNT decided to replace the copper-fin boilers with the three BMK2.0LN boilers that were specified originally. From the moment the 6-million-Btuh-capacity plant came online in February 2008, savings were realized, and all loads were met easily.
“In April of 2007, the copper-fin boilers used 1,638 Mcf of natural gas,” Young said. “In April of 2008, we cut that by more than half — down to just 739 Mcf.”
In addition to their condensing design, the BMK2.0LN boilers feature a 20-1 turndown ratio, minimizing cycling and temperature overshoot. This turndown and condensing operation can deliver operating efficiency of up to 99 percent, creating substantial seasonal fuel savings.
Information and photograph courtesy of AERCO International Inc.