Brown to Green: Town of Hempstead Uses Solar Energy to Power Town Hall HVAC System
The Town of Hempstead, Nextek Power Systems and Rockwell Automation Use Clean Air Act Settlement to Set National ‘Green’ Precedent
Home to more than 750,000 residents, the town of Hempstead, N.Y., is setting an example for money- and energy-saving “green” innovation in local government. Answering a challenge from Town Supervisor Kate Murray to find alternative energy solutions that create savings for taxpayers, the town hired Hauppauge, NY based Nextek Power Systems to bring its advanced grid-connected smart power platform to the installation of a 40 –KW solar photovoltaic system on the southern face of the Hempstead Town Hall. The solar PV system will power part of the building’s HVAC system.
As energy prices continue to increase, individuals and organizations alike are identifying different ways to control energy costs. The Town of Hempstead officials recognized the opportunity to innovatively work with Nextek Power Systems to set a green precedent locally and nationally. The solar transition also gave the town an opportunity to better match the HVAC system motors with adjustable frequency drives improving operational efficiencies.
Energy Savings Challenge Met with Innovation
Answering Murray’s challenge, town officials chose the town hall site for its central role in community affairs and its ability to showcase solar power use to power not just the return air fans for the building, but also the DC lighting in the supervisor’s office and a conference room. Ron Masters, commissioner of conservation and waterways for the town, was familiar and confident with Nextek Power Systems, a leader in DC power networks and experienced in facilitating alternative energy projects.
Nextek Power Systems worked with the local Allen-Bradley® distributor, Mid-Island Electrical Supply of Commack, NY, to integrate the Nextek Power Gateway and 40-kW of PV photovoltaic (PV) panels on the southern face of the town hall. The Power Gateway is also Direct Coupled® to two Allen-Bradley PowerFlex® AC drives from Rockwell Automation, creating a direct pathway for the clean DC power generated at the panels into the building’s HVAC system. Nextek’s Power Gateway eliminates the need for an inverter and bypasses the rectifier on the front end of the drives, improving energy capacity by approximately 10 percent.
“We wanted reassurance in this new application that the technology used was high quality and trusted,” said Paul Savage, president, Nextek Power Systems. “Rockwell Automation was a natural first choice, and the results were great.”
At night or during periods of low solar output, the Nextek Power Gateway seamlessly reverts back to grid power until the renewable source is available again. Because the system is Direct Coupled®, it is not subject to anti-islanding regulations which require conventional grid-tied solar systems to shut down in the event of a grid failure. The Power Gateway also enables load shaping and peak mitigating with its advanced metering, monitoring, and controls capabilities. During daytime peak usage, the HVAC system will be powered primarily by the solar PV array, reducing the burden on the local utility.
Settling for Green
The solar energy system was funded through $260,000 from the settlement of a clean air lawsuit against a power company in 2003. Under the settlement, the power company was required to pay $2.1 million for air pollution mitigation projects in New York State. The $2.1 million is being administered by the New York State Energy Research and Development Authority (NYSERDA) to install solar energy equipment on government-owned buildings in the state.
“Many people aren’t aware of commercial HVAC operations and the energy-saving opportunities with these motor-driven applications,” said Masters. “Demonstrating the value of these types of installations is important to furthering public understanding, and we see many other flat-roofed buildings that could be using and benefiting from this technology.”
AC drives, which act as controllers to protect motors and improve motor performance, have long benefited HVAC fan and pump applications, but Hempstead’s solar-power supply is unique. Rockwell Automation has a 100-year legacy in controlling motors in virtually every conceivable application, including HVAC, but pulling DC power off solar panels was a first. Masters is convinced that the three-phase Allen-Bradley PowerFlex AC drive with the DC source gave the town the ability to win the NYSERDA award. In addition, the accessibility of the DC bus made it simple to Direct Couple the drive to Nextek’s equipment.
“The success we’ve had with Allen-Bradley PowerFlex drives is an efficiency we didn’t anticipate when we started the project,” said Masters. “With the variable frequency drives, we can set and throttle back to idle the system to match our energy needs, and the exposed front end of the drive adds additional economy to the system.”
Townspeople and officials are pleased with the new system and it is setting an example across Long Island.
“To date, it has been a tremendous success,” said Masters. “It has performed beautifully.”
With the success of the town hall installation, Masters anticipates future successes in upcoming “green” applications.
Added Murray, “The Town of Hempstead continues to lead the way in implementing environmentally friendly technology, and we are proud to have installed a solar-energy system at town hall that will reduce our reliance on fossil fuels.”
This commitment to incorporating alternative energy systems in this town’s overall power scheme will continue to be met by innovative partners, including Nextek Power Systems and Rockwell Automation.
Intelligent Motor Control
Allen-Bradley PowerFlex® 700 AC drives from Rockwell Automation were DirectCoupled® with Nextek Power Systems’ own Power Gateway to deliver precise motor torque and speed when powering the HVAC system.
By using the PowerFlex 700 AC drives with the exposed DC bus, energy savings were increased by 10 percent since the DC power from the solar panels avoided the DC to AC excursion usually imposed by inverter-based systems.
The drives allow the motors to become a DC load for the Nextek system, seamlessly transitioning between the grid and solar PV.
The system can be throttled back to idle to match the energy needs of the HVAC system. In full sun, the drives are 100 percent solar-powered.