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Home » Energy Efficient Products » Ways to Reduce IT Energy Costs » 12 Ways to Save Energy in the Data Center » Water-Side Economizer

Water-Side Economizer

Description

  • For data centers with water- or air-cooled chilled water plants, a water-side economizer uses the evaporative cooling capacity of a cooling tower to produce chilled water and can be used instead of the chiller during the winter months. (A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.)
  • Water-side economizers offer cooling redundancy because they can provide chilled water in the event that a chiller goes offline. This can reduce the risk of data center down time.
  • Water-side economizers are best suited in climates where the wet bulb temperature is lower than 55°F for 3,000 hours or more. This describes the majority of the United States barring areas in the extreme Southwest and portions of the Southeast. (See Figure 15 below.)
     
    Figure 15: Hours of ideal water-side economizer conditions in the United States. (Courtesy of DOE and The Green Grid)

    Figure 15: Hours of ideal water-side economizer conditions in the United States. (Courtesy of DOE and The Green Grid)

  • Unlike air-side economizers, water-side economizers can be economically retrofitted.

Savings and Costs

  • During water-side economizer operation, costs of a chilled water plant are reduced by up to 70%.46
  • Water-side economizer retrofits in California have shown one- to four-year paybacks.47
  • Water side economizer retrofits can sometimes be costly.

Considerations

  • Water-side economizers can be integrated with the chiller or non-integrated. Integrated water-side economizers are the better option because they can pre-cool water before it reaches the chiller. Non-integrated water-side economizers run in place of the chiller when conditions allow.
  • A variable speed drive should be used on the fan motor in the free cooling tower.
  • Like air-side economizers, this technology depends on design and controls to work optimally.
  • Data centers that use containment, along with a cold aisle or hot aisle configuration, usually have much higher server inlet temperatures. These higher temperatures can be produced using a higher chilled water set point. With intermixing eliminated, data center operators may be able to achieve their desired server inlet temperature with a 55°F or warmer chilled water supply. With these higher temperatures, water-side economizers can be used more often.
  • Physical space is a major concern. Oracle attempted a retrofit and concluded that the additional parts–new "pipes, valves, and controls"–required physical space that existing facilities simply did not have.48
46 High Performance Data Centers, January 2006, PG&E, p. 38.
47 Data Center Energy Practitioner HVAC Specialist Training Day 2.
48 https://www.energystar.gov/sites/default/files/asset/document/MKhattar_Case_Study.pdf (PDF, 123.27 KB)

Top Twelve Data Center Energy Efficiency Strategies

IT Opportunities

  1. Server Virtualization
  2. Decommissioning of Unused Servers
  3. Consolidation of Lightly Utilized Servers
  4. Better Management of Data Storage
  5. Purchasing More Energy-Efficient Servers, UPSs, and PDUs

Airflow Management Strategies

  1. Hot Aisle/Cold Aisle Layout
  2. Containment/Enclosures
  3. Variable Speed Fan Drives
  4. Properly Deployed Airflow Management Devices

HVAC Adjustments

  1. Server Inlet Temperature and Humidity Adjustments
  2. Air-Side Economizer
  3. Water-Side Economizer 

Quick Links

  • Data Center Equipment
  • 5 Simple Ways to Cut Energy Waste
  • More Ways to Save in Data Centers
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