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Water-Side Economizers

What Is a Water-Side Economizer?

A water-side economizer is a high-efficiency option for buildings that generate cooling through the use of water or air chillers.  A traditional chiller works by extracting heat from liquids through a vapor-compression or refrigeration absorption cycle, then running that chilled liquid through a heat exchanger to provide cooling to heat-sensitive equipment or to building spaces.  For facilities with air- or water-cooled chilled water plants, a water-side economizer is able to harness the power of cooler outdoor air temperatures during certain parts of the year to provide the same chilled water cooling benefit, but at a significant energy savings.

Who Can Consider a Water-Side Economizer?

Facilities located in climates where the wet bulb temperature is below 55 degrees Fahrenheit for at least 3,000 hours annually ( which is virtually everywhere in the US except the edges of the southwest and select areas in the southeast.)

Locations with adequate physical space to retrofit the necessary controls, pipes, valves, and other parts to ensure a properly working economizer.

Is It Worth It?

While water-side economizers can be cost-effectively retrofitted (unlike air-side economizers), it is still important to examine the specific economics of every potential site.  Generally speaking, chilled water plant costs have been found to be reduced by up to 70% during water-side economizer operation, and California has found these energy-saving systems to show payback from one to four years.  In every case, a value-engineering study should be performed to determine whether the energy savings and other benefits will outweigh the added costs.

What Else Is Important to Know?

  • An important benefit of including or retrofitting a water-side economizer to a building is the security of a redundant system in the event of a chiller service interruption.  For high-capital housing such as data centers, this is a very desirable advantage as it can keep the data center Online in the event of a chiller outage.

  • Data center facilities using containment will usually have markedly higher server inlet temperature rates.  These higher temperatures will allow a water-side economizer to be used more often as data centers may be able to use a chilled water supply of 55 degrees or warmer to regulate their optimum server inlet temperature.

  • Integrating the water-side economizers with the chiller allows the system to cool the water before it reaches the chiller, making this the preferred layout.  A non-integrated economizer will operate in lieu of the chiller during suitable conditions.

  • Optimal performance of a water-side economizer relies on the design and controls installed.  The fan motor in the free cooling tower should utilize a variable speed drive.


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