The Cascading impact of Recirculated Air at the Chillers
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.
In last week's Blog “Who is watching the Chillers?, we introduced the concept of recirculated air at the chiller and how it has a negative impact on efficiency. This week, I’d like to discuss the cascading effects the recycled air has on operations.
A very simplistic description of the chiller’s function is to draw in ambient air and as it passes across the coil fins (where the heat is), it absorbs heat and rejects that heat into the atmosphere out of the top of the chiller. In a nutshell, chillers remove heat from the air helping to maintain desired temperatures in buildings. The design and location of rooftop chillers can significantly influence their efficiency due to turbulence and barrier layers that may cause air recirculation.
We’ve observed as much as a twenty degree Fahrenheit difference of recorded inlet temperatures from one end of a chiller lineup to the other end due to recirculated air caused by the aerodynamics of the building. Obviously the Chillers at the end with the higher inlet temperatures not operating as efficiently as those with the lower inlet temperatures.
So what are the Cascading Impacts of Recirculated Air?
Recirculated air being drawn back into the chiller is both hotter and drier than the ambient air, thus the chiller cannot achieve the same cooling efficiency it would normally produce if the recirculated air was not present.
The chiller plant must do more work to achieve the cooling effect the load demands of it. In a multi staged designed system this might result in premature calling of the next stage.
The premature calling for the second stage increases the wear and tear on the components called in, as well as increases the electrical consumption of the chiller having a negative impact on the PUE. Thus higher energy bills as well as possible increases in peak demand which impacts the entire monthly energy bill.
The Chiller fans run hotter, decreasing the Mean Time Between Failures (MBTF), which increases the maintenance and OPEX to replace the failed units. Shutting systems down to make repairs reduces the available redundancy while the repairs are taking place.
The Compressors are working more, and perhaps for longer periods of time, having the negative impact with regard to power consumption, MTBF, and Maintenance and OPEX.
With failures in the chilling plant there may be an inability to achieve the target temperature at the delivery end - the Air Handling Units (AHU).
Compressors shutting down due to high head pressure negatively impacts performance as extra load is placed on the working systems, maintenance cost to respond and resolve the issue.
Conclusion
It is recommended that the rooftop chillers have a thermal survey performed to verify that there is no recirculated air being drawn into the chiller inlets. As stated above there are any number of impacts that can be attributed to recirculated air, but go undetected due to a lack of monitoring.
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.