Welcome to Keep Your Cool - a series tackling simple cooling optimization strategies for the busy data center operators by former busy data center operator, Gregg Haley.

When it comes to taking measurements in the Data Center, we tend to focus on the white space. We’ve spent a lot of time in this blog, exploring how regularly measuring your inlet and outlet temperatures can improve efficiency and prevent major server breakdowns. Yet, we have not explored the importance of measuring the air coming INTO the data center, specially at the rooftop chiller. 

Rooftop chillers play a vital role in managing the temperature of large buildings by rejecting heat into the atmosphere. These units work by using refrigerants to absorb heat from the building's internal environment and then expelling it outside. The refrigerant absorbs heat from the evaporator, which is then transferred to the condenser coils on the rooftop chiller. Here, the heat is released into the atmosphere, allowing the refrigerant to cool down and repeat the cycle.

To ensure optimal performance, it's essential to monitor your rooftop chillers continuously. While sensors typically measure the temperature difference between supply and return temperatures at the evaporator, few sensors are placed to measure the actual ambient air temperature being drawn into the chiller coils and the exhaust temperatures. This “chiller” delta T calculation is crucial because chillers, like AHU/CRAC units, are subject to recycled. 

Recycled (or recirculating) hot air can significantly reduce the efficiency of your chillers, making fan motors run hotter and reducing their Mean Time Between Failures (MTBF), leading to premature failures. This inefficiency affects the overall Power Usage Effectiveness (PUE) and electricity consumption, as chillers must work harder to reject heat. The placement of chillers and the design of the building's rooftop can strongly influence how effectively chillers reject heat. Prevailing winds can cause air turbulence or create barrier layers, leading to the recirculation of hot air and reducing chiller efficiency. 

Of course, the best way to manage your existing chiller operation is to conduct a baseline measurement to see where you are. You should simultaneously measure the air going into the chiller and the exhaust air to see what your Chiller delta-t looks like. You can then identify where recirculation may be happening and lead to effective solutions, such as adding barriers, hoods, additional fans, or changing the overall control algorithm. 

Take for example, this static temperature map that we measured at a rooftop chiller. This is a profile view of a chiller, where we took temperature measurements at four different heights every couple of feet across the Chiller profile. The map shows that the area to the right of the chiller is significantly hotter than the left side — indicating that warm air is recirculating back to the Chiller – instead of away. 

Monitoring your rooftop chillers with a thermal survey or continuously sensors is the best way to ensure that your chillers operate at peak efficiency.

About Purkay Labs

Purkay Labs specializes in thermal surveys for efficient data center management. We offer practical solutions to optimize performance and sustainability. Partner with Purkay Labs for streamlined data center efficiency. You can learn more at www.purkaylabs.com.

If you want to learn more about why you need a thermal survey or need someone to come and conduct one for you, please contact us today.

About the Author

Gregg Haley is a data center and telecommunications executive with more than 30 years of leadership experience. Most recently served as the Senior Director of Data Center Operations - Global for Limelight Networks. Gregg provides data center assessment and optimization reviews showing businesses how to reduce operating expenses by identifying energy conservation opportunities. Through infrastructure optimization energy expenses can be reduced by 10% to 30%.
In addition to Gregg's data center efforts, he has a certification from the Disaster Recovery Institute International (DRII) as Business Continuity Planner. In November of 2005, Gregg was a founding member and Treasurer of the Association of Contingency Planners - Greater Boston Chapter, a non-profit industry association dedicated to the promotion and education of Business Continuity Planning. Gregg had served on the chapter's Board of Directors for the first four years. Gregg is also a past member of the American Society of Industrial Security (ASIS). Gregg currently serves as the Principal Consultant for Purkay Labs.