In the Harford County Public School System, northeast of Baltimore, every possible penny goes into educating students. Money for capital improvements is hard to get. Although the district needed a new administration building, the school board didn't approve the project until school administration officials demonstrated that a sustainable building would pay for itself.
The school board approved the 74,000-square-foot administration building project when they learned how cost-effective it could be. Key to the efficiency of the HVAC system is a McQuay® 150-ton dual frictionless compressor chiller, which contributed to the LEED® Gold designation from the U.S. Green Building Council (USBGC). The HVAC system is expected to save 46 percent on energy compared to the requirements of ASHRAE 90.1, the nationally accepted standard on energy efficiency.
It wasn't just that the existing 119-year-old administration building had inadequate lighting, major ADA deficiencies and poor indoor air quality. It also had an inefficient HVAC system-plus the old building simply wasn't big enough. The district leased space in four additional buildings around the city of Bel Air, which made it hard to get to meetings and meant the district was paying rent without gaining equity.
"If we had gone on as we were, we would have seen our leasing costs and our energy costs go up," said Chris Morton, the district's assistant supervisor for planning and construction. "A new building solved both problems. We estimate we will break even within seven years. After that, we're ahead of the game. In 25 years, we'll be saving money because we'll own the building and have no lease payments."
Frictionless chiller: efficient, quiet and oil-free
"The McQuay chiller is by far the most efficient piece of equipment in the entire building," said Bradley Salemie, lead HVAC engineer with Spears/Votta and Associates, Inc., in Baltimore.
The key to the chiller's efficiency is the compressor's digitally controlled magnetic bearing system. The drive shaft is suspended in midair by a system of permanent magnets and electromagnets. Positioning signals received by the electromagnets hold the shaft precisely in position within a tolerance of 0.000005 inch. Shaft position is sampled and adjusted 10,000 times each second.
The frictionless chiller's efficiency allows it to be continuously adjustable down to 10 percent of full load. "Because of the increased chiller water temperature differential," said Salemie, "we were able to design smaller pumps and distribution piping. That saves money for first cost and operational cost." The chiller's efficiency also allowed Salemie to specify lower-than-standard temperature for the water produced by the chiller. "When you make the largest and most efficient system component work harder," he said, "the rest of the building's mechanical system doesn't have to work as hard."
While a typical screw-type compressor can draw as much as 500 to 600 amperes at start-up, the compressor in the frictionless chiller's permanent-magnet motors requires only 2 amps per compressor at start-up. Also, when running with a partial load, the frictionless chiller can consume less than 0.2 kW/ton of cooling capacity at certain conditions-the most efficient performance of all available chillers in their tonnage range.
The fringe benefits of frictionless technology
Though the school system's bottom line benefits greatly from the frictionless chiller's efficiency, most building occupants never think about the chiller-which turns out to be yet another benefit of frictionless design. "It's the quietest chiller I've ever been around," said Morton. "The chiller is immediately adjacent to a training space, but when you stand in that room, it's impossible to detect whether the chiller is on or off." Since the compressor rotor and impeller shaft are levitated on a magnetic cushion, there is almost none of the vibration or noise produced by conventional bearing systems.
Another considerable benefit of frictionless compressor technology is that no oil is needed to lubricate the WMC's bearings, so there are no oil pumps, filters, coolers or heaters-and no need to dispose of used oil. That significantly reduces maintenance, mess, odor and costs.
Green means overall building synergy
Even with its many benefits, the frictionless chiller could not win a LEED Gold certification by itself. The key to a green building is synergy among all building components and systems. Engineers and architects must design each system as part of the whole and understand how that system affects all others. The Harford County Schools Administration Building's synergistic green features are extensive:
- An airflow sensor and a motor-operated damper are installed in a mechanical room on each floor. Only the amount of outside air needed for good indoor air quality is allowed into the building.
- Light sensors positioned all around the building perimeter are connected to electric light dimmers. This reduces the amount of heat produced, which in turn helps to control the size, initial cost and operating cost of the air-conditioning system.
- A high-efficiency boiler operates with lower-than-typical water temperatures-between 100 and 140 degrees Fahrenheit.
- About 30 percent of the building's windows are operable, so occupants can choose "free" air conditioning in cool weather.
- Low-e glass and a white TPO (thermoplastic polyolefin) roof reject heat from sunlight, further reducing the load on the HVAC system.
Objective requires high level of teamwork
Despite all these green features, the building does not have the distinctive design of other LEED Gold certified buildings, according to Morton. "We met the requirements without being flashy," he said. "The building is built with public money, and we wanted to show taxpayers we were good stewards of their money. Everyone involved in this project was focused on providing a great finished project. People showed that they cared and were out to do the right thing because it meant more money for education."
McQuay International delivers engineered, flexible solutions for commercial, industrial and institutional HVAC requirements with reliable products, knowledgeable applications expertise and responsive support. McQuay products and services are provided through a worldwide network of dedicated sales and service offices. For more information or the name of your local McQuay representative, call 1-800-432-1342 or visit www.mcquay.com.