Adiabatic Evaporative Cooling: Who, When, Where, and How

Sean Convery, Cator, Ruma & Associates
Shannon Horn, University of Colorado

Evaporative Cooling is often used in arid climates as seen in states such as Colorado, New Mexico, Arizona, Utah, Wyoming, Nevada, and areas of California. Many of these areas are considered high-deserts. The benefit of evaporative (adiabatic) cooling in arid climates is very low cost cooling without refrigeration. The methods used to perform evaporative cooling include pad-type media (swamp coolers), high pressure fog systems, ultrasonic humidification/cooling, and cooling towers. The most common for lowering supply air temperature is the use of evaporative pad media due to the simplicity and low first cost. More recently, advancements for indirect evaporative cooling of lab exhaust upstream of energy recovery coils have been utilized which can be applied to many additional climate zones and not just arid climates. Although often thought of as free cooling, there are associated costs due to air pressure drop and water consumption. This presentation would include methods of calculating evaporative cooling, air pressure drop, water consumption, and energy savings using the Psychrometric Chart.

There have been many lessons learned over the years when implementing evaporative cooling. Lessons learned regarding evaporative media pads are: replacement costs of the media, water treatment, controlling bacteria growth, indoor air quality (IAQ), methods for drying out the media and drain down of the sumps to improve IAQ, water carry-over, manufacturer defects of the sumps, and control strategies. For fog systems: water treatment, controlling bacteria growth, control strategies, and high pressure pump maintenance. For ultrasonic humidification and cooling systems: controllability and turndown, absorption distance along with air temperature required for absorption, and implementing droplet filters. Building materials and science experiments can be affected by increasing the moisture content in the air for all systems.

Climate change has been a global concern; however, it has mainly focused on an increase in dry bulb temperature. In the arid states identified above, many have noticed an increase in humidity levels in the summer months. Institutions like Colorado State University and the University of Colorado have been monitoring this increase in moisture for several years. This presentation would show this information graphically for others to understand where the future of evaporative cooling may be heading.

Learning Objectives

  • Participants will be able to identify where ideal locations are in the US for evaporative cooling and the typical methods used to perform evaporative cooling.
  • Participants will explore calculations for heat transfer and water consumption of evaporative cooling systems.
  • Participants will review lessons learned with the various methods of evaporative cooling to be able to best evaluate media, controlling bacteria growth, maintenance, etc.
  • Participants will review data on climate change impacts to evaporative cooling to examine where the future of evaporative cooling may be heading.


Sean T. Convery, PE is a Mechanical Principal at Cator, Ruma & Associates in Denver, CO and a founding Board Member of the Colorado I2SL Chapter. His 20 years of mechanical design experience include energy-efficient mechanical systems for higher education campuses and research labs. Recent projects include the CU Boulder's Sustainability, Energy and Environment Complex (LEED Gold) and Biotechnology Building (LEED Platinum), and Colorado State University's Bioengineering Building (LEED Gold).

Shannon Horn, PE, LEED AP, is a founding Board Member of the Colorado I2SL Chapter and has a passion for reducing energy without compromising form, fit, and function. As a Mechanical Engineer for CU Boulder, her duties range from Commissioning Agent to supporting energy conservation initiatives campus-wide. She also has over 7 years of experience as a consulting engineer focusing on industrial, labs, data centers, hi-tech and educational facilities, and 20 years of institutional experience.


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