Data Centre Best Practises Workshop
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Using Computational Fluid Dynamics
(CFD) for improving cooling system
efficiency for Data centers
Data Centre Best Practises Workshop
17th March 2009Shishir Gupta
You are Here ↓↓
Data Centre Case Study – Geometrical Details
Introduction to CFD
CFD while designing of HVAC system
CFD during installation of Data Centre
CFD for maintenance of Data Centre – Feedforward System
• Computational (having to do with mathematics & computation)
Fluid Dynamics (the dynamics of things that flow)
• CFD is built upon fundamental physics equations: equations
of motion and conservation. CFD applications range from
numerical weather prediction to vehicular aerodynamics design.
• CFD applications are linked with advances in computing
software and hardware. CFD software is characterized by the
physical models in the software.
• Fine-scale CFD applications closely match the true
geometry of the physical objects and processes being
modeled.
Introduction to CFD
Mathematics
Navier-Stokes Equations
Fluid Mechanics
Physics of Fluid
Fluid Problem
Computer Program
ProgrammingLanguage
Simulation Results
Computer
Grids
Geometry
Numerical Methods
Discretized Form
Comparison&Analysis
CFD
What is CFD?
Some Dangerous SafeSecurity
Some All Repeatable
Measured PointsAllInformation
Small/MiddleAnyScale
LongShortTime
ExpensiveCheapCost
ExperimentSimulation(CFD)
Why use CFD?
reactor vessel - prediction of flow separation and residence time effects.
Streamlines for workstation ventilation
HVAC
Chemical Processing
Hydraulics
Chemical Processing HVAC(Heat Ventilation
Air Condition) Hydraulics Aerospace Automotive Biomedical Power Generation Sports Marine
Where use CFD?
Chemical Processing
HVAC Hydraulics
Aerospace Automotive Biomedical Power Generation Sports Marine
Temperature and natural convection currents in the eye following laser heating.
Aerospace
Automotive
Biomedicine
Where use CFD?
Flow around cooling towers
Marine
Sports Power Generation
Chemical Processing HVAC Hydraulics Aerospace Automotive Biomedical Power Generation Sports Marine
Where use CFD?
You are Here ↓↓
Data Centre Case Study – Geometrical Details
Introduction to CFD
CFD while designing of HVAC system
CFD while installation of Data Centre
CFD for maintenance of Data Centre – Feedforward System
CFD Case Study for Data Centre
Introduction to the Case Study
• Case Study is taken from one of the project that we did
for a Data Centre in India
• The case study includes what we did for the client also
extends it for what could have been done for the same
project using CFD
• There were two software applications used for the
project : OpenSource CFD platform of OpenFoam and
commercial CFD package of Fluent
• Both packages produced about the same results, in this
presentation the results from OpenFoam are being
shown
Case Description
• The analyzed Data Centre is rectangular with of area
516m2 and height 3.35mt
• Cooling is to be provided using raised flooring layout
and demarcation is done for Cold Aisle and Hot Aisle
• The sources of heat gain inside the data centre are
listed below:
– Heat gain through exterior walls accounting for thermal
resistance of the wall
– Heat gain from Server Racks, 154 Server racks each
providing about 8 KW combine to about 1.26 MW
• Three fans of about 500CMH were assumed to
transport air from cool aisle to hot aisle in each rack
unit (Since detailed blade specification is not known)
HVAC System Specification
• 10 CRAC units, 1 Standby Specification: – Each CRAC unit of 30,585 CMH– Cooling capacity of Each Rack is 150 KW– Temperature of supply air is 9.4 oC– Return Air opening area (On top surface): 2.23 m2
•Supply Air Diffuser (Cold Aisle) Specifications:
–Dimension of 600mm X 600mm–70% open area–1 supply diffuser per rack (Total 154)–Supply air velocity can be controlled using under floor fan
•Return Air Diffuser (Hot Aisle) Specification:
–Dimension of 600mm X 600mm–50% open area–Total no. of diffusers: 242
Objective of the Study
• To maintain recommended temperature by
ASHRAE for Class 1data centre
• The recommended atmosphere is defined as:
– Temperature of 20oC - 25oC
– Relative humidity of 40% - 55 %
– The allowed change in temperature should be less
than 5oC/hr
Recommended Operating Conditions
Design Parameters
• Number of CRAC’s
• Location of CRAC’s
• Velocity of supply air
You are Here ↓↓
Data Centre Case Study – Geometrical Details
Introduction to CFD
CFD while designing of HVAC system
CFD while installation of Data Centre
CFD for maintenance of Data Centre – Feedforward System
Base Case Design
Isometric View of the Designed Data Centre
Server Racks
False Flooring
False Ceiling
Supply Diffusers
Return Diffusers
CRAC Units
(11 Nos.)
Case Study Cont…
COLD AISLE Diffusers HOT AISLE Diffusers
Server Racks
CRAC Units
(11 Nos.)
Top View of the Designed Data Centre
CFD Simulation of Base Case
Temperatures across Y-Z plane
Temperature Contour
Temperature Profile at vertical planes along the racks and cold aisle.
CFD Simulation of Base Case
Temperatures across X-Y plane
Temperature Contour
Temperature Profile at Horizontal planes along the racks and cold aisle. Lets look at the mid-plane contour in more detail…..
Temperature Contour in Middle Plane
The temperature contour at the Horizontal plane at the middle portion of the rack
CFD Simulation of Base Case
Temperatures across X-Z plane
Temperature Contour
Temperature Profile at the middle plane is showing most uneven distribution. Lets analyse the middle plane in detail
Temperature Contour in Middle Plane
The temperature contour at the vertical plane at the middle portion of the rack
Velocity Vectors in Middle Plane
The Velocity Vectors at the vertical plane at the middle portion of the rack
Conclusion from the base case CFD
1. The Average temperature on the rack surface at the cold Aisle side is 15
2. The temperature at Cold Aisle is varying from 12 to 17
3. The Average temperature on the rack surface at the Hot Aisle side is 27
4. The temperature at Hot Aisle is varying from 18 to 32
5. The simulation shows that a good number of servers are experiencing temperature well above and below the ASHRAE recommended temperature levels
6. Short circuiting of cold air is clearly visible in the simulation
Optimizing number of CRAC units & Supply Air Velocity
1. Maximum heat load : 154 X 8 = 1264 KW (1.26 MW)
2. Heat capacity of each CRAC : 150 KW
3. Minimum number of CRAC required: [8.4] = 9
4. The system was designed with 9 CRAC units and
velocity of supply air was adjusted to avoid short
circuiting and temperature stratification
5. In this case the velocity of 2.2 m/s is coming out to be
higher
6. The simulation was conducted with velocity of 1.6,
1.7, 1.8, 1.9, 2.0 & 2.1 m/s
7. The results with 1.8 m/s showed best results
Temperature Distribution with 9 CRACs & 1.8 m/s
The temperature contour at the vertical plane at the middle portion of the rack
Velocity Vectors with 9 CRACs & 1.8 m/s
The Velocity Vector at the vertical plane at the middle portion of the rack
Results of improved design CFD
1. The Average temperature on the rack surface at the cold Aisle side is 16
2. The temperature at Cold Aisle is varying from 13 to 17
3. The Average temperature on the rack surface at the Hot Aisle side is 23
4. The temperature at Hot Aisle is varying from 19 to 29
5. Short circuiting of cold air is reduced to a substantial level, however still prevalent
6. The simulation shows that a most of the servers are experiencing temperature as recommended by ASHRAE
Conclusion
• Using Computational Fluid Dynamics the
system was designed to reduce to 90% of
original design, thus bringing about first cost
saving of 10% in the capital cost.
• The new system uses less energy and
produces better result than the initial design
based on thumb rules
You are Here ↓↓
Data Centre Case Study – Geometrical Details
Introduction to CFD
CFD while designing of HVAC system
CFD during installation of Data Centre
CFD for maintenance of Data Centre – Feedforward System
Case Description
• The capacity of this data centre of of 42 X 154
= 6,468 Server Blades
• 4,000 server blades are to be installed
• 1,000 servers are by Dell, 2,000 by IBM &
1000 by Sun
• The design variables are:
– Number of CRAC units
– Which CRAC unit should be operational
– Location of Server Blades in the racking system
– Velocity of supply air inlet
CFD Simulation Setup
• The power requirement of 3000 Server is
minimum 713 KW – 5 CRAC (750KW) are
minimum number of units which can provide
the required tonnage
• The CFD simulation were conducted with
various locations of Servers, CRAC’s and
Supply air velocity
• The best result was found with following
parameters:
– Top Racks are empty
– Alternative CRACs are operating
– Velocity of Supply air is 1.2 m/s
CFD Simulation Results
Server Positions in the Racks
CFD Simulation Results
Operational CRAC’s
Temperature Distribution with 5 CRACs & 1.2 m/s
The temperature contour at the vertical plane at the middle portion of the rack
Velocity Vectors in Middle Plane
The Velocity Vectors at the vertical plane at the middle portion of the rack
Calibration during Installation
Temperature Sensors
• The Result from CFD shall be compared with
average reading shown by temperature and
velocity sensors
• If there is any difference, the modeling shall
be improved to arrive at the actual values.
You are Here ↓↓
Data Centre Case Study – Geometrical Details
Introduction to CFD
CFD while designing of HVAC system
CFD during installation of Data Centre
CFD for maintenance of Data Centre – Feedforward System
Feedforward System
• Whenever capacity of the data centre is to be
increased, the design parameters like number
of CRACs and supply air velocity should be
determined using CFD
• If the capacity ramp up is not that frequent
than CFD simulation can be conducted at that
stage to arrive at design parameters
• If ramp-up/ramp-down is very frequent then a
custom made CFD code should be developed
using OpenSource Libraries. This would
enable data centre administrator to conduct
CFD’s for his data centre and analyze various
design options
Conclusion
CFD can help design and operate the data
centre HVAC system with optimum
efficiency
Thank You
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