Data Centre Cooling and its CFD Modeling

Why Data Centre Cooling is Important?

 

Introduction to Data Centre

  • Data Centre is similar CPU of our PC or laptop. But its size is very big and huge data is saved in thousands of servers or memory units. Google data Centre is spread over large land. Fans are placed outside the plant.
  • They operate all 24 x7 hours and consume a lot of electricity for maintenance
  • Cooling of the Data Centre is necessary, otherwise, the whole data Centre would shut down.
  • The cooling system conjures a large portion of power.

Google Data center Unit in Nnetherlands

Google Data center Unit in Nnetherlands

 

Working Principle of Data Centre

  • Data center cooling is carried out air conditioning unit in the server room. Cold air is allowed to flow through the heated data Centre. The heated air is sucked in by the AC unit
  • Using a heat exchanger, the coolant absorbs heat from hot air in AC units. After that air temperature comes down
  • The cold air forced through from the bottom cold passage to middle chamber between server racks. Air again recirculates through the server chamber

 

In this article, we will learn the following hallmarks

  • Introduction of Data Centre Cooling
  • Component of Data Centre Cooling
  • Room Air Conditioning Units (RAC) for Data Centre
  • Scope of CFD Modelling
  • How to create a 3D Model of Data Centre
  • CFD Input for Data Centre
  • Case study with CFD Results

Server room of  Data Centre 

  • Data center cooling is exactly what it sounds like: controlling the temperature inside data centers to reduce heat
  • Failing to manage the heat and airflow within a data center can have disastrous effects on a business
  • Not only is energy efficiency seriously diminished—with lots of resources spent on keeping the temperature down—but the risk of servers overheating rises rapidly
  • The cooling system in a modern data center governs several parameters for better convective cooling with maximum efficiency. The following parameters are key:
    • Temperatures (T)
    • Heat Removal rate in watts (Q1)
    • Power consumption by AC units in watt (E)
    • Cooling Efficiency (Q1/E)
    • Cooling fluid flow characteristics
    • Design of Servers racks
  • All s components of the data center cooling system are interconnected to keep higher heat removal
  • Irrespective of the type of data center, continuous cooling is necessary for smooth functioning  without shutting down operations

 

  • Perforated tiles are kept between two rows of racks for better cooling efficiency

Importance of Data Centre Cooling

  • The entire AC room is kept around 20 degrees Celsius. If the cooling system fails, there the rack temperature may increase more than 50°C
  • Raised the temperature of their data centers can be around 27°C (80° Fahrenheit)
  • A poorly designed cooling system could deliver the wrong type of server cooling to your center This, again, would lead to serious overheating, a risk that no business should accept willingly
    • Irregular shut down of server
    • Overheating of electronics items due to hot spots during high load
    • Melting of insulation and disconnection of data cables
    • Burning and damage of rooms
    • Fire propagation of control room
    • Overview of data cooling

Parts of Data Centre Cooling

  • UPS/ Data server racks
  • Cold Aisle containment
  • Monitoring sensors
    • Smoke Detector
    • Temperature sensor:
  • Temperature sensors
  • IP camera
  • Control Panel

 Types of Data Centre Cooling 

Chiller water Cooling of  Data Centre

  • Chilled water is commonly used for medium and large-sized data centers. There is an exchange of heat energy between hot and cold water in the chiller unit. In the cooling tower, the warm water is further cooled via natural circulation.
  • The room Air conditioning (RAC) unit is used to cool down the heated air from the server
  • Air is cooled by blowing over a cooling coil which is connected to a chiller
  • Heat absorbed air is transferred to water coolant in the

  • Schematic of Data Centre cooling system

Computer Room Air Conditioner (CRAC)

  • This is one of the popular and low-cost  cooling techniques for small and medium data centers
  • CRAC units are quite similar to conventional room air conditioners. These are powered by a sealed compressor which draws ht air across a refrigerant-filled cooling unit. Cold air is thrown into the room.
  • They are quite inefficient concerning energy usage, however, the equipment itself is comparatively inexpensive

  • The flow pattern in the Data Centre room with Computerized Refrigeration and Air conditioning (CRAC) is shown below

The Latest Innovations in Data Center Cooling Technology

Alternate Cold and Hot Aisle Containment

  • Alternate cold and hot aisle containment are widely used for rack deployment. A cold aisle means a cold chamber of cold inlet air passage is formed and heated air exhausted from the rear of the rack flows into the hot aisle containment
  • Hot aisles push hot air into the air conditioning (CRAC) intakes to be cooled and then it is vented into cold aisles. Empty racks are covered with full of blanking panels to avoid overheating or wasted cold air.
  • Data Centre is placed at a certain height above the floor to keep the smooth circulation of air

Data Center Cooling Trends: Room, Row and Rack Cooling

 

  • The bottom portion of the cold aisle is consist of perforated tile for uniform entry of cold air

A review on airflow management in data centers - ScienceDirect

 

Liquid Cooling Technologies

  • Liquid cooling provides faster and high cooling compared to air cooling systems. However, the system should be leak proof to avoid liquid flow over the data center
  • . Two common liquid cooling methods are full immersion cooling and direct-to-chip cooling.

Liquid Cooling Solutions of data centre

 

Immersion Cooling with Dielectric liquid

  •  The hardware of the Data Centre is immersed in a tub of non-conductive, non-flammable dielectric liquid coolant
  • Both the fluid and the hardware should be contained within a leak-proof case
  • The dielectric fluid absorbs heat much faster than air cooling. This fluid turns to vapor and condenses and falls back into the fluid by a cooling tower

immersion cooling of data centre

Direct  to Chip Cooling

  • Liquid coolant directly flows  into a cold plate that sits atop a motherboard’s chips to extract heat
  • The extracted heat is subsequently transferred to some chilled-water loop to be transported back to the facility’s cooling plant and expelled into the outside atmosphere
  • Both methods provide far more efficient cooling solutions for power-hungry data center deployments.

Direct Chip Cooling method

  • The liquid pipe is placed at the top of the chips to cool faster. It reduced space and maintenance costs. This method is effective for the small data centre.

 direct liquid cooling of chips

 

Which cooling method is more effective for the data center?

  • Various cooling methods have been developed to cool data centers or chips
  • Among all techniques, jet impingement provides a higher heat removal rate from the chips
  • Liquid cooling methods are more effective than air cooling but their maintenance is not easy

High Powered Chip Cooling -- Air and Beyond | Electronics Cooling

  • Two-phase (water vapor cooling) has high transfer coefficients compared to air and oil

Heat transfer coefficients for Electronics Cooling

Design of Data Centre Cooling 

Precision Air Conditioning (PAC)

  • Precision Air Conditioning (PAC) systems are dedicatedly designed for cooling data center and server room environments instead of that designed for general buildings (homes, commercial offices, and halls)
  • Precision Air Conditioning systems  can provide superior design and reliability and have a high ratio of the sensible-to-total cooling capacity (COP)
  • Precision Air Conditioning (PAC) system controls the environment, providing the constant temperature and humidity conditions for sophisticated, expensive, and sensitive electronic equipment throughout the year

Design of Precision Air Conditioners (PAC)

  • Precise Temperature control
    • Inlet air temperature of cold air is kept between 10 to 15 °C
    • The maximum temperature should not exceed 50°C.
    • The cooling temperature can be decreased if the flow rate of air is limited
  • Precise humidity control
    • Electronic devices require a steady level of humidity for proper functioning
    • Both high or low humidity levels can affect the performance if PAC units for the long run
  • Concinnous Cooling  
    • Room air conditioners are generally designed to be used for summers (3 Star, 1800 hrs)
    • PACs are designed for 365 days
  • Manage High Levels of Sensible heat
    • Room ACs are designed to manage latent heat (heat with humidity, emanated by people
    • PAC units designed to heat without humidity generated by machines
  • Better Air Distribution
    • They handle higher mass flow rates that move more air volume at higher speeds compared to standard ACs
    •  fewer airborne particles  can be carried out due to the AC
    • Precision air conditioners handle the higher cooling load and AC load densities per each unit
    • Automatically controlling for increase or decrease is possible for efficient cooling

Computer Room Air Conditioning (CRAC) Units

  • A CRAC unit is similar to traditional air conditioning
  • It is designed to maintain the temperature, air distribution, and humidity in a data center’s computer rooms. The CRAC unit can use a direct expansion refrigeration cycle
  • It is used to pressurize the spaces below the floors
  • The parts of CRAC units are shown below

CRAC unit computer room air conditioner - The Engineering Mindset

 

Scope of CFD Modelings for Data Centre

  • Number of Racks required in a room with RAC units
  • Assess the performance of PAC/CRAC Units
  • Effect of Supply Temperature
  • Influence of Surrounding Ambient Conditions during extreme weather
  • To find out the hottest /critical server which is prone to fire
  • Design optimization of Data Centre

 

CFD Input and Steps in Modelings

  • CFD users can create geometry and mesh as per the dimensions of server rooms and racks
  • After the creation of the CFD model, Major CFD Input is the mass flow rate of air and temperature, and heat load to the server
  • The basic steps of CFD modeling are the same as any CFD problem

Case Study 1: Data Centre with two Racks

  • A simple data Centre of 12 servers was simulated using a CFD solver (ANSYS FLUENT)
  • Cold air flows entre through the Centre of racks

  • Temperature contours across the data server room are shown below. Temperature is very high in server rooms.

  • The heat removal rate can be increased by increasing the velocity of air
  • It is observed that air velocity is maximum in the Centre

Case study 2: Data Centre with four Racks

  • Temperature contours 

Temperature contours in heater server racks through which cold air gets heated by absorbing heats

  • Temperature Contours in Cold Passage through which cold air flows between two opposite racks

Summary

  • Cooling of Data Centre is necessary to avoid shut down operation due to overheating of data servers or UPS
  • Data Centre cooling is continuously carried out using cold air and comprised refrigeration and air conditioning units (CRAC)
  • Data Centre is also connected with another water cooling circuit for improved cooling efficiency
  • CFD modeling helps to determine hot spots in the data center. CFD results show high velocity in the Centre of racks and high temperature at end of racks

 

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