After more than 20 years in business, SAS Institute is the largest privately owned software company in the world and one of the top 10 largest independent software vendors. SAS Institute delivers an integrated suite of software for business decision-making that addresses the unique needs of business users and information technologies departments. SAS software is widely used for data warehousing, data mining, business intelligence, and analysis at more than 30,000 business, government, and university sites, including an overwhelming majority of Fortune 100 companies.
The ChallengeThe SAS Institute campus includes 16 buildings, most of which were built using split-system heat pump hvac systems. Thomas explains, "As the campus grew, each succeeding building got a little larger. The last building, which we did entirely with heat pumps, had about 500 offices in it. It was a bit of a stretch to do that building with heat pumps and we did have some problems with comfort and zoning.
There are about 75 rooftop-condensing units on that building. That's a lot of maintenance work to do." Thomas says that when planning began for the new Research and Development Building, SAS wanted to go with a central system that provided good reliability, redundancy, efficiency, and low life-cycle costs. The Building R design called for 1,000 10- by 12-ft offices arranged in four wings around a central glass-covered atrium. Thomas says, "It was obvious that we couldn't do this building with heat pumps; at least not very efficiently. We began reviewing all the latest hvac technology.
"We had worked with Trane on Building V, which is our video production facility. Single-source responsibility for both equipment and controls was a big factor in working with Trane. It became simply an issue of evaluating and selecting the best technology system for this building," Thomas adds.
"From an efficiency standpoint, a centrifugal chiller central plant offered the best results," says Thomas. However, because redundancy was a critical requirement, SAS had to consider purchasing a second chiller, and that would have a negative impact on the economics of the project.
Thomas says, "The building has a large internal heat gain every day, because in addition to the central data center, every office has two or three PCs in it. We considered building a central chiller plant, but redundancy was a big issue. We've got a nominal 750-ton load. How do you make that redundant? You buy another 750-ton chiller. That would have driven the first cost through the roof, creating a higher life-cycle cost as well."
Economic analysis also showed that while heat pumps were the low first-cost solution, their overall efficiency and maintenance costs made the life-cycle costs unfavorable.
The SolutionThe solution that best satisfied all four requirements was commercial self-contained air conditioning units with a vav distribution system on each floor and a Tracer(r) direct digital controls (ddc) automation system. Four commercial self-contained units, of 20- to 80-tons capacity each, are installed on each of Building R's seven floors, providing excellent zone control and comfort. In addition to lower first cost compared to a centrifugal chiller plant, the self-contained units render nearly the same efficiency as a central chilled water plant. With two to four scroll compressors in each unit, each with separate refrigerant circuits, redundancy needs are more than met.
Says Thomas, "With four units on each floor, if there is a unit failure, we can isolate it without compromising the comfort of everyone in the building. The odds of a major portion of the building being without air conditioning are very, very slim. Even if one circuit fails, the unit will bring on a second compressor with its own refrigerant circuit. The chance of a zone being completely down is also very slim. And because we can centrally control energy use with the Tracer automation system, a waterside economizer system provides even more energy savings. We felt like we got a 'Cadillac' system at a very reasonable cost."
Thomas reports that even with an additional 400,000 sq ft in Building R, SAS Institute had to hire only one additional facilities technician. "With our facilities tracking system, we can immediately address more than 50% of hvac inquiries using the Tracer system and without having to dispatch a technician to that building for typically a minimum of 20 minutes. ES
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