www . refrigerationandaircon . co . za RACA Journal I March 2024 43
Professionals who care
HOW TO COOL THE DATA CENTRE IN THE 21ST CENTURY
By Michael Young , Pr . Eng .
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 .
Part four – Increasing operating conditions within a data centre : is it a good or bad thing ?
In the pursuit to reduce electrical consumption and expand on the number of hours of ‘ free cooling ’, there has been an ongoing effort to raise the operating IT temperatures within the data centre .
While it may seem trivial to pay so much attention to operating IT temperatures ; performance , noise levels and operating costs of the cooling unit are greatly impacted by this one design parameter .
ASHRAE provided guidance on the operating air conditions of the IT equipment by publishing the ‘ Thermal Guidelines for Data Processing Environments ’. This document recommended the inlet air condition of dry bulb temperatures and relative humidity ( RH ) for different types of IT equipment .
According to this guideline , the objective is to raise the operating temperature of the data centre while still ensuring reliability of the IT equipment . Now before the operating temperature of a data centre is raised , it is important to look at a data centre holistically as the system dynamics are complex in that the energy consumption of some systems decrease while
others increase . If a chilled water type of system is used to cool the data centre , raising the IT temperature set point can cause designers to also raise the operating water temperatures of the chiller . This decreases the energy consumed by the chiller as the data centre can operate in ‘ free-cooling ’ mode for a larger portion of the year and the chiller efficiency increases .
However this isn ’ t the entire picture , as even though the chiller energy decreases , server energy increases as the server fans operate at higher speeds due to the increase in operating temperature .
This in turn causes the computer room air handler ( CRAH ) fans to also increase in speed to support the higher server airflow requirements . This means greater CRAH energy consumption .
CRAH units have to increase in size due to a loss of heat transfer between the return air condition and the higher inlet water temperature .
Where space is a constraint , the CRAH unit design is often modified and taller coils are installed within the unit , and supply air fans are required to operate at higher speeds to deliver the increased airflow rates which increases noise levels within the white space .
Therefore , it is important to not only consider the performance of the chiller but also consider the operations of the CRAH unit . Simply increasing the operating temperature of the data centre can sometimes not yield the desired result . Moving forward , the entire system must be analysed to confirm if a higher operating condition has a positive or negative effect for the construction of a data centre at a specific location .
Join us in our next publication where we will discuss how operating conditions influence the performance and operations of a DX system .
Wishing you a successful month ahead . RACA
“ If a chilled water type of system is used to cool the data centre , raising the IT temperature set point can cause designers to also raise the operating water temperatures of the chiller .”
www . refrigerationandaircon . co . za RACA Journal I March 2024 43