Prior to last winter, a 37-year-old, 250-horsepower boiler provided heat to The Lauren, a 168-unit condominium in Washington, D.C. According to Walter Krolman, project manager at The Lauren, the unit functioned well, delivering plenty of heat throughout the 10-story building that was originally constructed in 1972 as an apartment building.

However, Krolman questioned the efficiency of the boiler. “It was built for 80 percent efficiency, but it was probably functioning well below that level,” Krolman explained. “So, in as much as it was scheduled for replacement soon, we decided to move forward and consider replacing the boiler ahead of schedule with a more efficient boiler — one that would immediately allow us to capture energy savings and convert those savings to reduced operating costs.”

The assignment to find a new, more efficient boiler actually fell to Jack McNabb, a consulting engineer who had previously worked with The Lauren on a variety of projects related to the building’s mechanical and electrical systems. McNabb will be the first to say that the original boiler was oversized, which, according to the engineer, was not at all unusual at the time it was installed. Energy costs were low, and the prevailing practice was to over- rather than under-design a system to ensure an adequate heat supply. “Consequently, The Lauren ended up with a boiler that was approximately 8 feet in diameter and more than 20 feet long and operating at about 62 percent efficiency as recently as last year. It was an enormous tank of hot water radiating heat to the world.”

The boiler provided hot water in the building’s pipes for winter heating, and a 220-ton chiller filled these same pipes with cold water in the summer for cooling. In both cases, stack-style fan coil units delivered heat and cooling to the condominium, and separate gas-fired hot water heaters provided domestic hot water.

In his search for a more efficient boiler, McNabb was eventually introduced to pulse combustion technology. A pulse is defined as one cycle of ignition and combustion of a gas/air mixture in a specially designed combustion chamber.

“It definitely makes for an energy-efficient boiler,” said Josh Rossman, sales associate with United Energy Products Inc., the firm that ended up supplying two Fulton Pulse boilers to The Lauren.

“But just as importantly, a pulse boiler significantly reduces electrical consumption associated with the boiler,” he continued. “In fact, the boiler consumes almost no power while in operation.”

That’s because the pulse combustion process is naturally aspirated and does not require a blower motor for operation. An assist fan is used for pre/post purge only and turns off once combustion has been established. In fact, pulse boilers require electricity only for purge cycles, powering fuel valves, control, and other safety features. The pulse combustion process itself requires absolutely no electricity.

Recommended Installation

McNabb recommended the installation of two natural gas-fired 1.4 million Btuh input Fulton Pulse boilers, each rated at 89 to 98 percent efficiency over the majority of load-matching conditions. “The trick in applying these boilers is that the less they’re loaded up, the more efficient they become. By installing two boilers and sharing the load, The Lauren is averaging about 94 percent seasonal efficiency over the load range. And, we have built-in redundancy should we need it, for increased reliability.”

The boilers operate with Fulton’s ModSync control system, which regulates the water temperature leaving the boiler based on the outdoor temperature. “The system turns on the lead boiler when it needs to fire,” McNabb explained. “As long as it can carry this load, it will. But when the temperature drops to a predetermined point, the system automatically turns on the second boiler, allowing both boilers to operate at a lower, more efficient load. That’s the point where efficiency really starts to kick in, because both boilers jockey for a lower load when that second boiler kicks in.”

McNabb’s recommendation to The Lauren included cost estimates as well as an estimate of savings. According to Krolman, the recommendation was thorough. “I knew nothing
about pulse combustion technology,” he admitted. “But, the information Jack provided was detailed and certainly attractive from a cost and energy savings standpoint. Besides, Jack has never steered us wrong in the past, so we took his advice.”

Money and Energy Savings

The boilers were installed at the beginning of the 2009-2010 heating season, and one heating season later, they are performing even better than originally anticipated. The Pulse boilers are definitely wringing more heat from the combustion process, as evidenced by the temperature of flue gases — approximately 150 degrees as compared to 300 degrees in a conventional boiler system.

“The Lauren saved approximately 32 percent in gas consumption or 12,200 therms during the heating season system,” McNabb reported. “To give you a dollar value, The Lauren is paying about $1.50/therm as we speak, so that amounts to about $18,300 saved per heating season.”

He added, “And the electrical savings are substantial, too. The fan associated with the old boiler ran all the time that the boiler burner operated, costing somewhere around $2,000 a heating season. The new system uses a smaller fan, which draws just 4 amps at 120 volts and is only used for a 30-second purge, consuming substantially less electricity and reducing the operating cost of the boilers. When running, the pulse boilers consume about 0.75 amps.”

According to McNabb, the pulse combustion system also contributed to a simpler mechanical design. First, the boilers themselves are much smaller than the one they replaced — approximately 3½ feet wide by 6 feet tall and 4 feet deep — leaving additional unused space in the mechanical room.

“And because the pulse boiler is more efficient, the flue gases take up less volume. As a result, flue pipes are much smaller than with a conventional boiler — as much as two-thirds to 50 percent smaller — which makes the pipes much easier to lay out.”

But it is savings and comfort that have most impressed Krolman and the residents of The Lauren. “We experienced a fairly severe winter last year, but our building was always warm,” remarked Krolman. “It’s also quiet. My office is right next to the mechanical room, and I don’t hear the boilers.

“It’s just a nice, solid installation. The boilers have done what they were projected to do. In fact, they surpassed those projections and have created a good amount of customer satisfaction in the process.”

Publication date: 01/23/2012