In 2007, after nearly ten years in service, countless repairs, deteriorating efficiency, and four consecutive increases in annual natural gas consumption, OFS Fitel, LLC (OFS) needed to replace its five, one million Btuh copper-fin boilers or face the possibility of a total system failure. Installation of two AERCO Benchmark 2.0 Low NOx (BMK2.0LN) boilers has not only kept the facility operational, but it has enabled the Avon, CT-based fiber optic manufacturing company to reduce energy consumption by 25% in the first year. Monthly tracking by OFS reveals the role that the high turndown and condensing operation of the new system play in the energy savings.    

While the decision to make a change was simple, other aspects of the project were challenging. The new boilers needed to fit into a very small space on an equipment mezzanine, there was a strict timeframe for installation, and the budget was tight. OFS management worked with its HVAC contractor Tradesmen of New England (TNE, Bloomfield, CT) and Ed Adajian of Adajian Engineering to aid with the solution.

Efficiency is Key

Considering all the requirements set forth by OFS, the TNE team began researching boilers that could match the peak output of the old boiler plant while providing greater efficiency and savings and fitting in the allotted space. The solution was two of AERCO’s condensing and fully modulating BMK2.0LN boilers and the company’s multi-unit controller, the AERCO Boiler Management System (BMS).

 “During the selection process, the standout characteristic of the Benchmark boilers was the efficiency. Their condensing design and 20:1 turndown was very attractive,” said Marc Riccardi from TNE. “Even though the initial cost was higher than a direct replacement would have been, we felt confident that the savings from the lower energy requirements of the boilers were going to be significant.”

Although original copper-fin boilers were listed as Category IV condensing appliances, the limitations of the equipment became evident almost immediately. Upon the first exchanger corrosion failure, the manufacturer advised that only >140°F be returned to the boiler plant. Consequently, OFS’ 20°ΔT hydronic heating loop was operated based on 180° supply setpoint/160° return to protect the copper-fin boilers from the corrosive impact of condensing operation. For fear of voiding the remaining warranties by returning cooler water to the copper-fin boilers, OFS never varied these operating parameters.

In conjunction with the BMK2.0LN retrofit, OFS was able to employ an outside air reset schedule to vary supply water temperatures between 180° and 120° based on changes in outside air temperature. On the coldest winter night, when local temperatures dipped to -5°, the system delivers 180° supply water to ensure that there is adequate heat in the building. However, on days when temperatures exceed 65°, the system can deliver adequate heat and humidity control with just a 120° boiler supply setpoint.

Turndown Reduces Cycling Waste

While the benefit of the new boiler’s condensing design is greatest during the warmest weather, savings from the new system’s turndown are realized all year.

Each of the original, one million Btuh, copper-fin boilers was equipped with an “On/Off” burner. Units in the plant were operated sequentially. The result was an inefficient system whose lowest operating level was one million Btuh. Since only four of the units were needed at peak load, the plant had 4:1 staged turndown. It could meet loads of one, two, three, or four million Btuh effectively - but units would cycle on and off repeatedly to meet other demands. Cycling wastes energy. 

In contrast, the BMK2.0LN boiler delivers 20:1 turndown to perfectly match any load from 100,000 to 2 million without cycling. Managed by AERCO’s multi-unit, BMS controller, the new four million Btuh boiler plant has 40:1 infinite turndown. Cycling only occurs when loads dip below 100,000 Btuh. During the majority of the heating season, the boiler plant’s input is at perfect equilibrium with the building’s fluctuating load. 

“Energy savings from reduced cycling are obvious during colder New England weather when there are far fewer opportunities to condense,” said Riccardi, “but I think that it’s actually during the summer months, when loads are at their very lowest, that the new equipment really shines.  Rather than responding to demand with repeated blasts of one million Btuh, the Benchmarks can steadily deliver as little as 100,000 Btuh without shutting down.”

Out with the Old, In with the New

Installation was scheduled to be done over Thanksgiving weekend, between Friday and Monday morning when the plant would re-open to resume manufacturing. TNE coordinated the efforts of its personnel, as well as the work of electricians, riggers, roofers and pipe fitters required for the job. The boiler flat was positioned off a main stairwell, and the two BMK2.0LN boilers were housed there side by side. The delivery of fully wired, factory-tested equipment helped the installation to come off without a hitch. The new boiler plant was online before the building ever became cool.    

The AERCO BMS, a multiple unit boiler controller, coordinates operations of the two units to maximize operating efficiency of the boiler plant. The BMS was easily integrated into the building’s existing EMS via Modbus communications protocol at no additional expense to OFS.

Conclusion

After a calibration and adjustment period used by TNE, OFS began to experience savings. Tracking monthly gas consumption clearly demonstrated the combined power of turndown and condensing operation. Overall, the company reduced its natural gas consumption by 25% during the first year. ES