A midtown Manhattan office building's onsite cogeneration system provides improved efficiency and reliability—and, just as importantly, is in sync with the local network grid.
If cost savings is the main reason why the nation's largest publicly held real estate investment trust installed the first onsite combined heat and power (CHP) system in midtown Manhattan that is synchronously interconnected with Consolidated Edison's (ConEd's) midtown network grid, better reliability certainly wasn't far behind, given increasing demands on the local network grid.
Management at Waitsfield, VT—based Northern Power Systems knew that it had more than one customer during the planning and installation of a 1.6-megawatt cogeneration system at Equity Office Properties Trust's 450,000-square-foot 717 Fifth Avenue Class-A office building. Besides Equity Office, Northern had to work closely with ConEd. Extra effort was required to ensure that ConEd's system would not be adversely affected by the local system in the event of a power outage on the grid. A factor driving concern about reliability was the much-publicized blackout that occurred in summer 2003 beginning with a "trip" at an Eastlake, OH, power plant that caused a chain reaction and the loss of power for about 50 million people in eight states and parts of Canada—the biggest power outage in US history. Even without this outage, notes Northern Power, grids in urban areas such as the one in Manhattan are getting routinely stressed to the limit during the summer months.
The 717 Fifth Avenue building experienced power loss during this outage, and Equity Office sought greater system reliability. The benefit of increased reliability compared with the existing ConEd power source has an obvious financial benefit to Equity Office and its tenants, who could stay open for business and remain productive in the event of a power outage. Over the long run, however, the 1.6-megawatt cogeneration system will provide an even greater return on investment than relying solely on ConEd, which results in an efficiency rate of 30% to 40% for the building's energy efficiency. The onsite system, in contrast, will provide an efficiency rate of 60% to 65%. The system, which consists of two 820-kW lean-burn generator sets, heat exchangers, and a 289-ton hot water absorber, will create electric power during on- and mid-peak hours—when purchasing electricity from the utility is most expensive—and is expected to provide 60% of the building's electricity and 65% of its heating and cooling.
Technological Experience Counts
This project proved to be a good fit for Northern Power, which has completed similar CHP projects for Equity Office in Chicago and San Francisco. "They're primarily interested in reliability, using these projects to improve the reliability of their tenants' power supply," notes Chach Curtis, vice president of Northern Power's Onsite Power Systems. "The challenge is that it costs additional money to build in that additional reliability, and they look to recoup that from their tenants—sort of a ‘build-it-and-they-will-come' approach." Curtis adds that Northern's experience with utility interconnections gave the company an edge in its being selected as the provider on this project.
"It was absolutely a big selling point for Northern in that we have significant experience with utility interconnections across the country," he says. "Equity Office has done a number of these projects and has seen how difficult the utility interconnection can be. They wanted to go with someone like Northern that has proven experience doing it."
Curtis adds that Northern Power was held to a higher standard in the planning and installation of the system due to the building's location in relation to ConEd's network grid. "A network grid is primarily in major downtown metro areas; that's where the largest, most vocal customers are, where the utility's major source of revenue comes from," he says. "The last thing they want to do is have a small cogeneration system like this disrupt the network and cause some broader outage. They're going to require a higher level of protection for the downtown grid area.
"What they're looking to protect the grid from is old current that comes from the cogen system in the event of a utility outage. They're going to have a faster disconnect/isolation requirement than on a radial grid. ConEd's grid, for example, is overburdened, particularly during the peak summer months, and it's stressed to the maximum to where any type of fault current could be very disruptive, so they're going to hold you to a higher standard. The ConEd equipment in and around the site—the network protectors are old and outdated. If they don't have the sophisticated controls to react to the cogen system, the utility may ask you to upgrade those."
Less of a challenge for Northern Power was deciding which type of system best suited Equity Office's needs. Amir Yanni, senior project manager for Northern Power, notes that Equity Office wanted a system that could be configured for backup power in the event of a minor outage or a major catastrophe such as the 2003 outage.
Two types of systems suit backup power generation in a situation such as the 717 Fifth Avenue project, Yanni notes. Induction generators absorb power from the utility grid at startup before producing power on their own. A disadvantage to this type of system is that it stops generating power once it gets disconnected from the signal on the utility grid. A synchronous generator, in contrast, is equipped with its own internal signal, so it does not depend on the utility's signal in order to continue operating.
"One of the disadvantages of a synchronous generator is that it adds additional full current to the utility that is connected to it," says Yanni. "Unless the utility has the capability of absorbing the additional full current coming from the generator, they do not allow any synchronous systems to be on the grid because it affects their network protectors, and it can cause severe damage to their system. In the past, ConEd was adamant about not allowing any synchronous system to be connected to them until recently, when the combined power theory and the lack of power and the shortage of power in the area came about and they started addressing this situation. We were lucky because the Equity Office building is being fed by a substation that was recently upgraded by ConEd to have the ability to withstand additional full current from a synchronous generator without the need for an additional device between the two systems."
Among the available prime mover technologies available, Northern Power opted for the proven reciprocating engine. "The type of technology to be considered for CHP depends on the location and the application," Yanni notes. "For industrial applications where they need something that can run around the clock and that can produce a lot of steam for the process, turbines are steady, the load doesn't change, and the turbine becomes a little more efficient. In a commercial office building, the building shuts down at 7, 8 o'clock in the evening, and the load becomes almost minimal. So in any commercial office application, the reciprocating engine became the dominating technology used, unless you had a situation where the building is 24/7, running around the clock, and there is not much change in the load between the morning and night. Then you can consider the turbine.
"The other factor you look at is that you have two different types of rates you pay: the on-peak and the off-peak," he continues. "If you look at the off-peak rate here in New York, it's very cheap considering the gas cost at this time, so it's cheaper to turn the system off at night than to continue producing power with a low load and a high gas cost. The on-peak period is very expensive, and it does save a lot of money, so that's why a lot of commercial office buildings run during the off-peak period and shut down at night. Looking at all of these factors, it puts the engine at the top of the list."
In a typical system, Yanni notes, about one-third of the fuel fed into it becomes exhaust steam, with the other two-thirds converting into electricity and heat, respectively. Rather than allow the exhaust steam to simply escape, he says, the system at 717 Fifth Avenue captures it and adds it to the system's heat production. In the summer, the heat is directed to an absorption chiller and converted into cool air for the building.
Installation of the system posed a considerable challenge. An entire city block in busy midtown Manhattan had to be closed down while a 600-ton crane placed the system on top of the building's lower roof, 17 stories up. In order to minimize operational noise, the system is contained within a sound-attenuated housing enclosure and mounted on steel dunnage that uses vibration isolators to reduce noise. The entire system will not be louder than cooling towers located there previously. Benefits such as energy savings and noise minimization are expected to make the property more attractive to potential tenants.
A Positive Environment
Another reason for Northern Power's success on this project is that the State of New York and New York City are pioneers in the acceptance of CHP. Energy conservation is one environmental factor driving New York's advocacy of CHP. Air quality is another. Systems that capture and utilize exhaust also reduce greenhouse gas emissions.
In 2001, Governor George Pataki issued Executive Order 111 requiring state agencies to utilize more CHP technologies and other forms of distributed generation. Specifically, agencies were to generate a minimum of 10% of their energy from renewable sources such as fuel cells by 2005 and 20% by 2010. For its part, the New York Power Authority instituted a peak load management incentive program in which the authority pays its customers based on an amount of energy use reduction they agree upon during peak summer months. The customers achieve the reductions via conservation measures or onsite power generation. The 717 Fifth Avenue building's $4.1 million system was supported by a $745,000 grant from the New York State Energy Research and Development Authority (NYSERDA).
"NYSERDA actually provides funding up to 30% of the installed cost of the project or a cap of $1 million," notes Curtis. "Why have they done that? A number of reasons: One would be environmental, air-quality concerns, trying to reduce emissions through the improved efficiency of the cogen system. The second would be that in a place like Manhattan, where they understand that grid congestion is very severe and the grid is actually at risk of failing on a peak summer day, the more onsite generation they can get locally, the more they can alleviate the congestion problem."