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Nonresidential Cooling Towers

Proposal Description

This CASE Report presents justifications for code changes to cooling towers and blowdown controls that refine and build on prior code changes to Title 24, Part 6 approved by the CEC. The proposed code changes would apply to nonresidential and multifamily new construction, new systems serving additions, alterations (except for existing buildings), and both open-circuit and closed-circuit cooling towers 150 tons and larger.

Cooling Tower Efficiency

This measure proposes an increase of the prescriptive requirement for efficiency of axial fan, open-circuit cooling towers in condenser water systems of 900 gallons per minute (GPM) or greater established in 140.4(h)5 and 170.2(c)4Fv. This measure would apply to nonresidential and multifamily new construction and new systems serving additions. This measure also impacts alterations, except where the equipment is being mounted to an existing building.

The current 2022 Title 24, Part 6 Standards’ prescriptive minimum efficiency for axial fan cooling towers is 60 gallons per minute per horsepower (GPM/HP) (except for Climate Zones 1 and 16, which are exempted and subject to the mandatory minimum of 42.1 GPM/HP). The intent of this proposal is to update the prescriptive efficiency requirement from the statewide minimum of 60 GPM/HP in Climate Zones 2 through 15to climate zone specific values, increasing the requirement where cost effective. The code change would be implemented by introducing a table that establishes climate zone specific minimum efficiencies based on cost effectiveness, ranging from the current mandatory efficiency of 42.1 GPM/HP for Climate Zones 1 and 16, to 90 GPM/HP for Climate Zones 8, 10, and 15. The proposed code change applies to cooling towers in condenser water systems serving condenser water loops of 900 GPM or greater. The proposed code change does not recommend modifications to the existing mandatory minimum efficiency requirements.

Blowdown Controls

This measure would update the mandatory language in Section 110.2(e) which currently requires all open- and closed-circuit cooling towers 150 tons and larger to:

  • Be equipped with either conductivity or flow-based controls that automate system bleed and chemical feed in order to maximize cycles of concentration and reduce cooling tower blowdown.
  • Be equipped with a makeup water flow meter and overflow alarm that alerts to a makeup water valve failure.
  • Have efficient drift eliminators installed.
  • Document the maximum achievable cycles of concentration achievable given local water quality conditions and a Langelier Saturation Index (LSI) of 2.5 or less.

The proposed measure would revise Section 110.2(e) and associated cycles of concentration compliance document as follows:

  • Require the use of conductivity-based controls (eliminate the option to use flow-based controls).
  • Require the designer to document target maximum cycles of concentration in the NRCC-MCH-E compliance document based on the recirculating water properties established in ANSI/ASHRAE Standard 189.1-2020.
  • Require that controls be programmed to not allow blowdown until one or more of the recirculating water parameter limits set in ANSI/ASHRAE Standard 189.1-2020 is met.
  • Add an acceptance test to verify installation and programming of controls to achieve documented cycles of concentration and overflow alarms.

Cooling towers in nonresidential and multifamily buildings represent a significant opportunity to reduce energy and water use in California. Cooling towers account for an estimated 20 to 40 percent of water demand in buildings that include water-cooled chillers. In recent years, water consumption has come to the forefront of concerns in the state of California. According to the State of California Water Year 2021 report, the water year ending on September 30, 2021 was the second driest year on record based on statewide runoff, following 2020 which was the fifth driest year. As such, methods for achieving water savings in California are of prime importance.

Title 24 Part 6 has included updated requirements for cooling towers previously in 2005, 2013, and 2019. The measures under consideration in this CASE Report build upon and update these current requirements.

Relevant Documents

CASE Report

Round One Utility-Sponsored Stakeholder Meeting Materials

Provide Feedback

Submit feedback and view the Energy Commission's proceedings and available proposed code language by visiting their 2025 Building Energy Efficiency Standards page.

This measure page will be updated as the 2025 code cycle progresses. For questions or suggestions, email [email protected]. Please include the measure name in the subject line.

Give Us Your Feedback

The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

  • Use the form above to provide feedback on this measure.

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