The renovation of a U.S. building overseas could become an example for future government building designs. The U.S. Department of State's Bureau of Overseas Buildings Operations (OBO) has selected the United States Mission to the United Nations in Geneva to become an example of environmental consciousness. The structure would be renovated to showcase sustainability and energy efficiency, and the technology that makes those goals possible.

Hankins and Anderson (H&A), the consulting engineer firm selected to guide the work being done in Geneva, analyzed the building, looking for areas where they could improve energy use, efficiency and sustainability.

Mike Christensen, a senior member at OBO, noted the old building's inefficient chiller. Conventional chillers typically are powered by compressors capable of producing a high volume of chilled air to satisfy a facility's peak demands. However, most buildings do not have 100 percent demand 24 hours a day, so when the massive compressors run, they draw full-capacity power and waste excess energy.

Christensen and H&A had worked with modular-chiller manufacturer Multistack, based in Sparta, Wis., on prior projects, and again looked to the company to solve the old building's problems.

Modular units allow an engineer to specify an assembly of chillers to create enough capacity to meet maximum building demands, and turn units off as demand goes down, creating energy savings, a green building "attitude" and lower installation costs. Multiple units and multiple compressors do the work of a single big unit, producing redundancy, which can eliminate the need for a second full-size back-up unit.

MultiStack's MagLev compressors use magnetic-levitation bearings to support a two-stage impeller shaft in each unit. By "floating" the shaft, there is no need for oil, which can degenerate the compressor refrigerant charge. The design eliminates excess refrigerant changes and because there is no contact, when the shaft begins moving, there is no friction to create additional energy draw. The compressors run at varied speeds that meet the facility's demands.

"Why would we want an air-chiller system that is efficient 365 days a year when we can have peak efficiency all 365 days of the year?" Christensen asks.

Additional equipment used in the project includes a glycol feeder, pair of strainers and tanks, and a pump to move chilled water through the air-cooled machines. The plan is to provide three-, six- and 12-month energy comparisons from the past year to show how much of a savings the system offers.