Brooklyn rec center is off to a fast start to saving millions in power costs.
By David Engle
Consolidated Edison’s term for it was “reconductoring.” That’s what would be needed to upgrade a 2-mile span of 1930s-era high-voltage lines running to the old airport known as Floyd Bennett Field in Brooklyn, NY. Reconductoring was the only way to deliver peaking power there, on the shores of Jamaica Bay—power critical to achieving two local developers’ vision of unusual and ambitious rehab.
First, some background.
Long ago, in 1931—when electricity was almost as novel as commercial flight—Floyd Bennett Field had opened as New York’s first and only municipal airport.
That distinction lasted but a short while, though, as the site found itself relegated to reduced roles in local aviation. Since 1972 or so, more kite-flyers and joggers have touched down there than aircraft.
These days, the onetime airfield from the glory days of early aviation is a national park drawing a million-plus visitors yearly.
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| Bennet Field was New York City’s first municipal airport. |
Astride its tarmac all this time has stood a block of four aging but still reasonably serviceable brick hangars. In 2004, developers Kevin McCabe and Steven Gluckstern got the idea of renovating them, remodeling all four into a single structure and turning it into a gleaming sports complex. Skating rinks, gymnasiums, exhibition galleries, playing courts, and even rock-climbing would be featured in a new 170,000-square-foot community rec center for Brooklyn and Queens—every day, year-round—to be known as Aviator Sports and Recreation (ASR).
First, though, there was Con Ed’s inauspiciously negative assessment of the infrastructure. Reconductoring would cost the considerable sum of $1.5 million, an investment spent solely to gain access to electricity, thereby enabling ASR to buy peaking power.
The project’s consulting engineer, David Ahrens of Energy Spectrum, recalls: “We found out that the service to this part of Brooklyn was overextended and could not support any additional load.”
It’s an increasingly common situation in built-up areas of several US cities.
Ahrens thought the $1.5 million could obviously be better spent on getting onsite energy—high-efficiency combined heating, cooling, and power that ASR would own outright.
Assorted generous incentives and credits are offered to such power project developers—incentives coming primarily from the New York State Energy Research and Development Agency (NYSERDA), which is keen on solving New York’s energy production and transmission bottlenecks.
Ahrens realized that with these subsidies an onsite power investment could be recouped in four or five years, after which the owners would realize hundreds of thousands of dollars in annual savings.
But energy self-reliance is still uncharted territory, according to Ahrens. “This type of approach had never been tried in this area before. It was kind of new to all parties involved, both on the federal level and with the owners and investors, along with the engineering and architectural teams,” he says.
But the owners had a vision that they wanted to use cogen—in part to save money, but also, Ahrens adds, to realize environmental benefits from using fuel combustion three times over to yield electricity, warmth, and cooling.
ASR general manager Tom Wells adds: “When we began exploring alternative types of source of electricity, we began realizing the many possibilities, and how interesting and ‘eco-friendly’ these could be,” he says. “It was a project that just blossomed.”
Flight Plan
To make it happen, a first step was to do predictive modeling of electrical needs, hour-by-hour and annually. Such projections will dictate the plant’s size, energy yield, and operation.
Ahrens thus went to work, researching and gathering data, then applying modeling software (DOE2) to explore numerous possible impacts. He compared trigeneration (cooling, heating, and power) with cogeneration (heating and power alone). He also gauged the potential of natural light as a conservation measure and investigated automatic lighting controls and variable-speed drives on air handlers, pumps, and compressors. Calculations were broken into sub-components for each physical place in the facility and respective sporting function. All were assessed in assorted interactive scenarios to determine resulting loads and peaks and to sketch a system design.
Here, most unexpected, was the discovery that, based on the estimation of maximum usage, electrical load peaks “would be so much higher than the normal [base] load,” Ahrens recalls. He and his associates became most concerned about peak days, because the facility would have two indoor ice rinks producing quite a surge at startup. Chillers capable of making subfreezing temperatures drain lots of power; in this case they would yield 300 tons of ammonia-based refrigeration, relying on three 75-horsepower compressors and six auxiliary 20-horsepower motors, notes ASR’s Director of Operations Don Acton.
When spectators are enjoying the figure-skating competition or rooting for hockey teams, comfort-control loads add to the challenge.
On that score, room heating and summer cooling naturally required close load calculations. Ahrens assumed that all of the cogenerated exhaust heat would be available for producing hot water, year-round; added to this was an estimate, he says, of “what would be the maximum requirement ... for the coldest days.” Accordingly, he specified adding a 2-million-Btu-per-hour boiler as a heating supplement to the cogen heat on the hot water loop.
Likewise, for summer cooling, most of this would be cogenerated from a high-efficiency, exhaust-heat-fired absorption chiller.
For very hot days needing a boost beyond this, a single Carrier 40-ton direct-exchange compressor air conditioner would suffice, he says, “as a peaking type of unit, if you will.”
After tallying and double-checking projections, Ahrens came up with “a little reverse logic” on plant sizing, he recalls. “We determined in this case that a bit smaller was better than larger, to try to achieve maximum efficiency of the cogen equipment throughout the year.”
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| UTC Carrier heat-exchange chillers were provided as part of a turnkey package. |
A more usual approach would have been to specify a plant perhaps 10% larger than the peak calculation, to provide a reserve. However, at ASR the reserve could be supplied instead by a low-emissions 800-kW Cummins diesel genset that Ahrens also proposed. In addition, this would serve as an emergency power backup should the Con Ed grid go down, and it could fire up automatically for demand curtailment or peak shaving (when grid power is both taxed by demand and most expensive to buy and, again, not reliably deliverable over that archaic wiring).
Thus, the presence of this standby 800-kW resource enabled building a smaller base-loading trigen plant.
Meanwhile, as Ahrens was weighing such issues, Con Ed came back with a second access proposal for the old circuitry. Even though the utility had decided that it could not guarantee peaking power without reconductoring, at other, non-peak times Con Ed could provisionally supply it via the existing line; this was available under a tariff provision called an “excess distribution service.” The essential difference between this and reconductoring was the lack of any guarantee.
In this second proposal, Ahrens notes, ASR “would still need to pay the utility’s ... ‘lateral cost’ [amounting a couple hundred thousand dollars] across from the high-voltage line” into the facility, plus annual maintenance fees in five figures.
“It’s a somewhat different approach,” says Ahrens, who, along with ASR’s owners, gave Con Ed’s offer due consideration. Ultimately, though, they decided “no deal.” Again, the money would be better spent on power trigeneration (and on the 800-kW backup). So, the existing old wiring would remain as is.
Taxiing for “Takeoff”
With load projections in hand, in early 2005 Ahrens and ASR crafted a request for proposals (RFP) from the onsite power industry.
Rather than spelling out specific hardware, his RFP simply presented prospective contractors with the rec center’s operational schedules and loads in each area, along with anticipated usage by system—“Say, by lighting or by HVAC,” he recalls. Then he invited creative solutions. “We kind of left it up to bidders’ expertise to understand what they could offer economically and what would be the best fit for the site,” he says. Contractors could decide what they wanted to provide, up to and including 100% of the electrical load, in grid-parallel—so long as their plan met the overall need.
Bidders were also asked for a five-year, fixed-price schedule for operation and maintenance.
Responses (five in number), says Ahrens, “ranged everywhere from a very large 2.5-megawatt reciprocating engine proposal, down to multiple turbines with double-effect absorption chillers in about the 600-kilowatt range.” This diversity reflected varied thoughts on heating and cooling solutions.
Bids were compared on a cost-benefit basis. In-person presentations followed.
One in particular quickly stood out: the double-effect PureComfort system from the power division of the United Technology Corp. (UTC Power). This system, using microturbines in series, offered “a turnkey installation in a minimal timeline,” Ahrens says, along with an attractive availability guarantee
Packaged, Skidded Integration
Technologically, pre-engineered and pre-assembled trigeneration systems are now the state of the art.
Microturbines are a mature technology, boasting high reliability, minimal maintenance, quiet running, a small footprint, and emissions low enough for exemption from air-quality restrictions. UTC Power’s PureComfort package builds on a Capstone C-65 natural gas-fueled microturbine yielding 65 kW of electric power. At 600°F, the engine’s exhaust warms a water loop for heating—or, in summer, fires an integrated absorption chiller made by sister UTC division Carrier Corp.
The latter chiller and heat-exchangers come in a pre-engineered, dual-action bundle, and this tight integration is another major plus. When it first arrived on the market several years ago, the PureComfort system was the first such packaged combined cooling, heating, and power (CHP) to do so. Since then, 20 systems have been installed nation-wide, and several more are pending, says UTC Power’s George Angelescu, who was project manager for the ASR job.
Resulting fuel-energy efficiencies reach “upwards of 80% or 90%, if you capture all the waste heat and utilize it in the facility,” adds PureComfort Product Manager John Fox.
With nearly double the fuel efficiency of a single-function power-plant or boiler and air conditioner, paybacks on equipment can come in five to seven years or fewer if the application utilizes 100% of the thermal (waste) energy.
To match a facility’s loads, a plant can be sized in 60-kW increments as needed. Thus, at ASR’s four hangars, calculations indicated 10 increments would be optimal, configured in two shed-enclosed mini-plants at opposite ends of the complex—one yielding 360 kW and the other at 240 kW, for a total of 600 kW.
A design using Ingersoll Rand’s 250-kW microturbine is also being investigated, Fox says. This would obviously enhance the usability options and improve the economics.
Recently announced by UTC Power is a fully integrated, factory-assembled skid design, which, for CHP engineering, could be revolutionary. “By being built at the same factory by the same workers,” the skid concept reduces the onsite assembly headaches that may arise from “different contractors trying to deal with each location.”
Absent the factory-assembly concept, connecting the parts onsite involves as many as 30 or 40 components, “all in different boxes,” shipped separately to the project—“still needing ductwork, conduits, controllers, fuel gas boosters, microturbines—all of that,” Fox explains. Now, though, nearly all of these can come pre-assembled. The microturbines are premounted, with plumbing, hardwiring of controls, fuel compressors, and some ductwork. The only remaining assembly, he says, “is to bolt the skids together and connect plumbing and electrical ties, which takes less than one day. It has very much simplified the siting of our units.”
“It cuts down the installation time from weeks to hours,” Angelescu adds.
The first “skidded” project, in fall 2006, was in East Hartford, CT, at East Hartford High School. Others are in progress.
As for ASR—even without the skid—the entire process, from the date of the order to design, delivery, construction, integration with the building management system (BMS), and commissioning on September 1 took an exceptionally short time frame of less than four months.
Linkup With Con Ed
A shakedown run and commissioning brought it all to life uneventfully. ASR facility staff received “classroom” training in the new power system’s operation, care, and feeding.
Next, parallel interconnection to the grid was still desirable and needed, delivering minimal electrical service on the old wiring—as a convenience, as a potential backup, and as a power complement.
As noted at the story’s beginning, interconnection would entail splicing new onsite power circuitry to a “rickety” 75-year-old infrastructure, with or without reconductoring. This hookup now occurred at switchgear junctures located a mile or two from the hangars—“an interesting experience,” says Ahrens, describing the challenge of marrying systems several generations removed.
Grid power arrives on a 4.16-kV line. The sports complex operates at 480 V, so a transformer was applied.
To parallel the grid, a 4,160-V cable runs from the cogen plant to the transformer and into the old switchgear.
What’s tricky here, says Ahrens, is protecting the grid from receiving power that might flow out from the turbines. “A reverse power relay was added in there ... and control signals, so that if there’s any reverse power, the [microturbines] can modulate down to follow the load in the facility and not create an excess power situation.”
Capstone microturbines come equipped with built-in power modulation features, but Con Ed required some added measures—not an uncommon demand in paralleling.
Prep work spanned several months, Ahrens remembers. “We put a lot of effort into the up-front part of ... electrical engineering issues, such as short-circuit rating on the system; how best to interface with utility; upgrading to add protection above and beyond what was even in the base equipment; and adding a circuit type of reverse power relay, beyond the normal inverter safety approach in accords with IEEE.”
Paperwork showing Energy Spectrum’s calculation was submitted to Con Ed; Ahrens eventually corralled the utility’s engineer, program manager, and service manager “all at the same time for the witness test,” he says—not an easy task in itself. Once the lengthy preparations were done, he says, the interconnection itself worked flawlessly.
Unlike the grid hookup, gas hookup via a lateral line was a cinch. For advanced control and monitoring, a pulse signal in the meter integrates into the new BMS. The new mini-power-plant operator (primarily Acton) can see, says Ahrens, “in real time, exactly how much gas he’s using and compare that to the estimates.”
Smooth Flight So Far
The new plant’s overall performance is working out well, says ASR General Manager Wells. “We’re very pleased with the results.”
The hands-on guy, Operations Director Acton, amplifies. Apart from a few bugs early on, he says, the system is basically running nonstop” at full capacity for baseload power—mostly serving the ice-rink compressors.
When the PureComfort generators are baseloading, he adds, “We’re pulling almost nothing off the grid.” At peak times, the grid supplies the needed 100- to 115-kW load.
As for the Cummins backup and peaking generator, he adds, this hasn’t been required yet, and the need for it isn’t anticipated until perhaps summertime, when demand may occasionally exceed the utility allotment.
During the past winter, says Ahrens, the Capstones’ exhaust heat supplied fully 95% of the building’s warmth. At summer’s end in 2006, just as the system was first switched on, the exhaust-fired chiller met 92% of the need.
As the first winter arrived, Acton preset the exhaust-fired warm-water coils to 140°F for comfort heating. If the water temp should drop below 126°F, the supplemental 2-million-Btu boiler fires up. After three months of winter operation it’s come on briefly only once—due to a minor control issue that Acton easily corrected.
Thus, in effect, the predicted match between heat output and load came out right on target.
Domestic hot water for services like locker-room showers and resurfacing the ice rinks must, of course, be heated in dedicated boilers, Acton says.
Automation of virtually every system function, thanks to the Carrier BMS, makes for a smooth-running system, says Acton. He logs on to monitor a total of 50-plus indices, including things like kilowatt output per turbine, total kilowatts, revolutions per minute, coefficients of performance, inlet and exhaust temperatures, fueling, and operational hours. Since having established his baselines, he’s found it’s easy to see whether anything is out of whack. “I just watch it and make sure it’s doing what it’s supposed to be doing,” he says.
Ahrens adds that the many readings are “trended and analyzed for efficiency and used in a predictive maintenance program.”
Fox notes, too, that the PureComfort supervisory controller chipset already has built-in peak-shaving capability. This will prove to be, he adds, a huge advantage during summer periods.
At that time, Con Ed grid’s net per-kilowatt cost will soar to around 25 cents per kilowatt-hour, Ahrens says. Even nonpeak rates have been averaging 20–22 cents per kilowatt-hour, he adds.
By comparison, far lower production costs, in the range of 12 to 14 cents per kilowatt-hour, are now being realized at ASR’s onsite plant.
In addition to Acton’s access to these displays, remote monitoring occurs around the clock at UTC Power’s customer support center in North Carolina (via the Carrier Corp. relationship), says Angelescu. Under a five-year contract, a hotline connects Acton with expert technicians as needed.
Acton’s and Ahrens’s biggest operational challenge thus far, they say, has probably been to juggle the load-following of the turbines for three 75-horsepower ice-rink compressors. Initially, all the icemakers were sometimes coming on almost simultaneously, “jumping the system around too much,” says Ahrens.
Compressor starts were subsequently staggered to five- to 15-minute intervals. Shutdowns were also made gradually.
Another correction was done to improve load-following: Initially, the six turbines in the 360-kW plant were designated as the primary pack and were to be kept running for baseloading; the other 240-kW setup was programmed to derate and/or turn on or off to follow loads.
This resulted in the 240-kW array sometimes shutting itself down (to save power).
Actually, though, too many unwanted stops and starts resulted; this was corrected simply by reversing the two mini-plants’ roles. Acton explains: “The 360 kilowatt can vary down to as low as 15 or 20 kilowatts per unit” for very good load-following, which keeps the operation from going into a full shutdown.
“It was a learning curve,” Acton sums up. “Once you get your baseline established and see what’s going on, everything levels right out.”
Future “Discount Fares”
This story began with a couple of million dollars sought for reconductoring, but it ends with a potential of several million dollars saved on utility billings. More specifically, the advantages being anticipated by Ahrens and Steve Flatlow, Aviator’s chief financial officer, work out as follows:
- Total cogen plant cost, Flatlow and Ahrens report, comes to about $3 million. But rebates and tax credits have already whittled this down by over $1 million—to a net cost below $2 million.
- Ahrens and Flatlow thus expect payback in about four or five years. After this, in the long term, several million dollars probably will be saved.
Ahrens also describes the various credits and tax allowances:
- The Energy Policy Act of 2005 (EPAC) offers microturbine cogeneration (and certain other generation technologies) the lesser of 10% of project cost or $200 per kilowatt. Total value comes to $120,000 as a tax credit.
- Under EPAC, a first-year depreciation credit of $1.80 per square foot is allowed—a reward for investing in high-efficiency systems vis-à-vis more conventional ones. Total value comes to $306,000 ($1.80 x 170,000 square feet) as a one-time depreciation allowance.
- NYSERDA incentives for microturbines (at this writing, anticipated though not yet fully worked out) figure in the neighborhood of $200,000 as a cash rebate.
- Also from NYSERDA comes the New Commercial Building Incentive given to projects that achieve a 50% efficiency improvement over conventional systems. The cash-rebate value is expected to be more than $400,000.
- And atop these, the gas tariffs that ASR will be paying should come out 10%–20% less per unit volume because the customer will be burning fuel ultra-efficiently for trigeneration.
Finally, regarding day-to-day savings that may come, Fox offers some cautionary words. First, he underscores the critical importance of “correct integration of supplemental chillers or supplemental boilers—and how they turn on and turn off.” Failure at the operational management stage may well mean that “the value [of trigeneration] to the customer is not seen ... You don’t get the efficiencies that you desire. And, therefore, you don’t get the savings that you desire.”
Thus, full automation becomes critical. “The building-management system and integration to our system is the key,” he says, describing a two-way communication between facility systems and power production. In a sense, the PureComfort’s onboard logic and controllers are “actually ‘talking’ to the building. We ‘ask’ the BMS to ‘tell us’ ... before things are going to happen. The building will say, ‘I need to turn this compressor on or off.’”
Signals are sent at, say, five minutes and at 30 seconds in advance, telling the microturbines to “either spool up—knowing that something large is going to turn on—or start spooling down, knowing that there’s going to be a step change.”
This tight interaction, he sums up, “is critical for our operation.” And no doubt it will be, increasingly, for others.
Writer David Engle specializes in construction-related topics.
DE - July/August 2007
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