By Michael Young (Pr.Eng)
Distribution of air within the data centre.
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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 does one get all the cold air from the cooling unit to various areas within the data centre so that enough air is provided to the server racks?
One method is to utilise the raised floor type of construction method. So how does this method work? Imagine we were having a birthday party, and we wanted to inflate some ballons and include them as part of the decorations.
You take a balloon and place the inlet of the balloon onto the outlet of a pump. As we begin to pump air into the ballon, it starts to get bigger. Imagine we now remove the inlet of the balloon from the pump, and we let go of the balloon, what happens?
Would you agree that the balloon flies all over the place? So why does this happen? As we inflate the balloon, the pressure within the balloon begins to increase. When we let the balloon go, all the air rushes out of the balloon due to a pressure difference from the inside to the outside of the balloon.
So how is this related to airflow distribution within a data centre? When we operate our unit, all the air leaving the cooling unit is blown into the raised floor. Since the raised floor is sealed, all the air leaving the cooling unit is trapped under the raised floor. As time passes, the air pressure within the raised floor starts to increase.
If we now had to remove a tile from the raised floor, air would start to rush out of the floor in the same way all the air rushes out of an inflated balloon. When using the raised floor type of construction, wherever there is an opening within the floor, air will rush out of that opening. Therefore, it’s important to ensure that any unnecessary openings within the floor are sealed.
This now opens another can of worms and you may be asking, so how do we distribute the air to the inlet side of the server rack if air leaks through the raised floor when we have a opening?
To regulate and distribute the air to different parts of the data centre, we replace a floor tile with a supply air floor grille with an opposed blade dampers (OBD) at locations which are at the inlet side of the rack.
By doing this, air flows out of the floor through the grille and gets sucked into the rack. By installing an opposed blade damper, we can modulate the amount of air that flows through that floor tile.
So for racks that require a high volume of air, the OBD is opened by a higher setting than racks that require a lower volume of air. By doing this, we can distribute air to various locations within the data centre and we are also able to provide the required amount of air as needed by a specific server.
Problems arise when insufficient supply air grilles are installed in the data centre or when the OBD are not set to the correct opening value. But we will talk about this in our next publication.
Wishing you a successful month ahead.
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