Variable-Speed Direct-Drive Screw Chiller

Green Proving Ground (GPG) evaluated a variable-speed direct-drive screw (VSS) chiller against a baseline state-of-the-art chiller technology, the variable-speed magnetic bearing chiller (MBC). Results showed similar performance for both chillers.

Agencies should consider both VSS and MBC for new or end-of-life chiller replacements. Individual site characteristics will determine the most cost-effective chiller technology for a particular application.

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GPG Findings 031, November 2017, Variable-speed direct-drive screw chiller. Opportunity: What is the impact of improved chiller operations on GSA? Most large commercial buildings (> 100,000 ft2) use water-cooled chillers. 80% of GSA floor space is in large buildings. Technology: How does this Variable-Speed Screw (VSS) Chiller work? capacity controlled by regulating motor speed alone. three screw rotors and a variable-speed motor are the only moving parts; there are no unloader. Measurement and Verification: Where did M and V occur? oak ridge NATIONAL LABORATORY assessed a variable-speed direct-drive screw (VSS) chiller against a baseline variable-speed magnetic bearing chiller (MBC). The chillers were installed at the Sidney R. Yates Building in Washington, D.C. and connected to the same chilled water and condenser water loops, creating operating conditions as close to identical as possible within a real-world environment. Results: How did the Variable-Speed Screw Chiller perform in M&V at the test bed location? High EFFICIENcy energy use comparable to baseline mbc. VSS savings over baseline MBC could range from +24% to -4% due to field measurement uncertaint. Range of operating conditions met. Condenser water temperature ranged from 55°F to over 95°F. Quiet performance. 77-83 DECIBELS. For both VSS & MBC. Deployment: Where does M&V recommend deploying the Variable-Speed Screw Chiller? consider VSS & MBC for end-of-life replacement. Both chillers performed effectively and have rated energy consumption that is more than 35% better than FEMP standards for water-cooled chillers. Individual site characteristics will determine the most cost-effective chiller for the application [PDF - 454 KB]


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Last Reviewed: 2022-06-14