Condensing boilers boost efficiency

In this installment of "What Works," gas consumption is cut 25% in Connecticut.

In 2007, after only 10 years in service but countless repairs, deteriorating efficiency and four consecutive increases in annual natural gas consumption, OFS Fitel, LLC (OFS, www.ofsoptics.com) replaced five, one million BTU/hr copper-fin boilers with two Benchmark 2.0 Low NOx (BMK2.0LN) boilers from AERCO (www.aerco.com). The new boilers’ high turndown and condensing operation reduced the Avon, Conn.-based fiber optic manufacturing company’s energy consumption by 25% in the first year.

The new boilers needed to fit into a 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, www.tradesmanofne.com), and Ed Adajian of Adajian Engineering (www.aeipe.com) to aid with the solution.

TNE researched boilers that could match the peak output of the old boiler plant while providing greater efficiency and savings, as well as fit in the allotted space. They chose two condensing and fully-modulating BMK2.0LN boilers and the company’s multi-unit controller, the AERCO Boiler Management System (BMS).

Annual gas consumption decreased 25% from 153,000 CCF to 114,000 CCF in only one year.

Although the original copper-fin boilers were listed as Category IV condensing appliances, upon the first exchanger corrosion failure, the manufacturer advised a minimum of 140°F be returned to the boiler plant. Consequently, OFS’ 20°ΔT hydronic heating loop was operated year-round based on 180°F supply setpoint/160°F return to protect the copper-fin boilers from the corrosive effect of condensing operation.

With the BMK2.0LN retrofit, OFS was able to vary supply water temperatures between 180°F and 120°F based on changes in outside air temperature. On the coldest winter night, when local temperatures dip to -5°F, the system delivers 180°F supply water. However, on days when ambient temperatures exceed 65°F, the system can deliver adequate heat and humidity control with a 120°F boiler supply set point. Varying supply water temperatures according to outside air temperatures reduces energy consumption because it promotes condensing. The new plant should operate in condensing mode whenever the outside air temperature rises above 45°F.

The five original, one million BTU/hr boilers were equipped with on/off burners and operated sequentially. Only four of the units were needed at peak load, so the plant had 4:1 staged turndown. It could meet loads of one, two, three or four million BTU/hour effectively, but units would cycle on and off to meet any other demand. Cycling wastes energy.

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Each new BMK2.0LN boiler delivers 20:1 turndown to match any load from 100,000 BTU/hr to 2 million BTU/hr without cycling. Managed by the BMS controller, the four million BTU/hr boiler plant has 40:1 infinite turndown. During the majority of the heating season, the boiler plant’s input matches 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,” says TNE’s Marc 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 BTU/hr., the Benchmarks can steadily deliver as little as 100,000 BTU/hr without shutting down.”

The new boilers’ high turndown and condensing operation reduced the Avon, Conn.-based fiber optic manufacturing company’s energy consumption by 25% in the first year.

The new units occupy a small footprint (12 sq. ft.) and can be installed in pairs with zero side-wall clearance. 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 delivery of fully wired, factory-tested equipment helped the installation to come off without a hitch, and the new boiler plant was online before the building ever became cool.

The AERCO BMS controller was easily integrated into the building’s existing Energy Management system via Modbus communications protocol at no additional expense to OFS.

After calibration and adjustment by TNE, OFS began to enjoy 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.

As an added benefit, the new system emits less NOx than the copper-fin boiler plant. The BMK 2.0LN boilers are designed with low-NOx burners that consistently measure less than 30 ppm of NOx corrected to 3% excess oxygen.

“Overall, the end result has proven to be a great success. Everyone associated with the project worked together to ensure that the new boiler system would maximize efficiency and savings. Thanks to the BMK2.0LN boilers, we have achieved that goal,” says Riccardi.

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