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Take the Chiller Challenge: Energy Efficiency

Key Points
  • There are a number of strategies available to improve chiller system performance.
  • Use variable frequency drives and sequencing to maximize chiller efficiency in part-load operation.
  • Install water-side economizers to provide free cooling when weather conditions permit. 

Source: iStock
Chiller plant
Chiller plants are widely used in commercial and institutional building air conditioning systems. For many facilities, they are the largest single user of electricity. As such, chillers present a significant opportunity to save energy and reduce summer demand charges. Despite this, many organizations are simply not aware of the full range of chiller optimization strategies available. Let's take a look at some of the most effective upgrades and techniques for improving chiller performance.

Install variable frequency drives. Retrofitting chilled-water pumps, condensers and air handling units with variable frequency drives (VFDs) helps to save energy at part-load operation. VFD pumps use sophisticated controls to adjust water temperature and flow rate to meet varying demand more efficiently.

Use controls to sequence chillers. Chillers rarely operate at full capacity and their efficiency drops as the load decreases. The ideal capacity for maximum chiller efficiency is between 60 to 80 percent. Efficiency drops significantly at loads below 50 percent. Monitor the capacity of all chillers in the plant and switch them on or off to keep them operating in their most efficient zone.

Take advantage of free cooling. Install water-side economizers to allow cooling towers to produce chilled water when weather conditions permit. Under the right circumstances, free cooling can save a lot of energy. In dry, cool climates, water-side economizers can provide up to 35 percent of cooling needs; in warmer climates, they may provide up to 10 percent.

Replace standard valves with low-friction models. This helps minimize flow-resistance for the chilled water, which reduces pump energy use and returns less heat to the chiller.

Insulate chilled-water pipes. Insulation keeps the chilled water at the right temperature by ensuring that it only absorbs heat from areas where it is intended to do so.

Rightsize pumps. Replace standard or oversized pumps with high-efficiency units sized correctly for your needs. Induction motors that drive pumps reach peak efficiency when they are roughly 75 percent loaded and are less efficient at full capacity. Size pumps so that much of their operating time is spent at their most efficient part-load operation.

Looking for more cost-saving ideas? See our Commercial Energy Efficiency Recommendations for tips and suggestions tailored to your facility.