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Professionals who care
MICHAEL YOUNG
Michael Young is a trainer , coach and a pre-sales engineer in the HVAC industry . He graduated from the University of the Witwatersrand in the field of Mechanical Engineering ( B . Sc Mech Eng ) in 2008 and qualified as a Professional Engineer ( Pr . Eng ) in 2013 . Michael is passionate about promoting knowledge and helping other young engineers grow within the industry through his training workshops and coaching sessions .
HOW TO COOL THE DATA CENTRE IN THE 21ST CENTURY ( PART 7 )
By Michael Young , Pr . Eng .
Part 7 : Dealing with part load operations within a data centre : Things to consider when using a DX system .
When cooling units are required to operate lower than 25 % of the design load , there is a chance that the unit may display a warning or even shut down on a critical alarm . To prevent this from occurring , two actions can be taken :
• The first action is to increase the heat load within the data centre by installing heater banks within the server rack . This option is often not viable as it can waste electrical energy while trying to prevent the cooling unit from triggering any alarms .
• The second action that can be taken is to reach out to the manufacturer of the unit and see which parameters can be adjusted .
Often the requirement is to satisfy the supply air condition and in many cooling units , this setpoint is what controls the operations of the compressor . Since the load within the data centre is much lower than the design condition , either the airflow or the return air condition of the cooling unit must be adjusted to meet the lower cooling requirement .
So , let ’ s consider the two options that are available :
• For option 1 , we can operate the fans at a higher speed , and we can lower the return air condition to the unit to satisfy the required supply air temperature . This option will result in an increase in electrical consumption of the unit as well as a higher noise generation within the white space .
• Option 2 is to reduce the airflow of the unit and increase the return air condition setpoint . This option will decrease the electrical consumption of the unit as well as noise levels . warnings . My first initial thought was to choose option 2 whereby we decrease the airflow and increase the return air condition . However , in this situation , the servers were not populated in a uniform manner and decreasing the airflow of the units created hot spots within the data centre .
I also learnt that decreasing the airflow would result in low superheat alarms as insufficient heat transfer would occur over the coil , resulting in a much ‘ cooler ’ refrigerant that leaves the coil .
I had no choice but to employ option 2 which was to increase the airflow . The tricky part was to determine how much to increase the airflow to . So , I conducted a site audit where I measured the approximate airflow over each server , and this resulted in the approximate airflow for each rack .
I then consulted with the manufacturer and asked them to perform a unit analysis to predict what the return air condition should be at my measured airflow requirements . I also asked for the supplier to confirm if the modified return air condition and airflow rates would prevent the triggering of the ‘ low super heat alarm ’.
The good news was that I was able to use the supplier ’ s unit performance rating to readjust the unit ’ s setpoints which prevents the occurrence of alarms .
So , when faced with low load operations , an analysis of the entire data centre must be performed whereby the development of hot spots must be addressed , the return air condition must be selected , and operations of the compressor and expansion valve must be understood to ensure the units still operate in the correct manner . Wishing you a successful month ahead . RACA
While option 1 seems the most viable , the final decision requires an analysis of the entire system .
This situation once happened to me where the data centre was operating at low loads and the units kept triggering alarm
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RACA Journal I August 2024 www . refrigerationandaircon . co . za