Modeling Must Do’s:

Minimum Inputs for Ensuring Accuracy

and

Using Simulation in Capacity Management

Our Findings....The Devil is in the Detail!

3kW - Simple 3kW - Detailed

One Room, two different representations of 3kW

Completely Different Results

Modeling Must Do’s –

Minimum CFD Inputs

• Accurate Representation of IT Devices

• Differences in cabinet modeling

• Buoyancy modeling

• Cooling unit discharge

Modeling Must Do’s –

Minimum CFD Inputs

• Accurate Representation of IT Devices

• How does representation of air jets from high density servers, such as blades,

affect results?

• Differences in cabinet modeling

• Does the modeling of blanking plates matter?

• Do cabinet accessories such fans, vents, penetrations, etc. affect the results?

• Buoyancy modeling

• How much does buoyancy affect the flow field?

• Cooling unit discharge

• How do different fan types affect airflow?

• Uniform discharge

• Blower

• Plug fans

• Axial/Propeller fans

Capturing Exhaust Jets

“Simple CFD” –

•Little or no capability to model multiple

outflows – lumped outflow is best way of

modeling…

• The outflow for this model is same height

and width of the device

RoomLite -

Outflows are modeled as per

specification i.e. width and

height

Thermal Footprint

Both servers are the same power density

and same exhaust flow volume but have a

different thermal footprint

Sample Room

• 7 Racks with IBM Blade Center

Chassis

• 2’ Raised Floor

• Single ACU

• 30% Perforated Grills

Result of Modeling Details

With Accurate Thermal Footprint

of Blade Center Fans

With a Lumped Exhaust from

Blade Center

Modeling Must Do’s –

Minimum CFD Inputs

• Accurate Representation of IT Devices

• How does representation of air jets from high density servers, such as blades,

affect results?

• Differences in cabinet modeling

• Does the modeling of blanking plates matter?

• Do cabinet accessories such fans, vents, penetrations, etc. affect the results?

• Buoyancy modeling

• How much does buoyancy affect the flow field?

• Cooling unit discharge

• How do different fan types affect airflow?

• Uniform discharge

• Blower

• Plug fans

• Axial/Propeller fans

Difference in Cabinet Modeling

Unblanked Rack Blanked Rack

Empty U-Slots

Open

Side Gap

Open

Gap Below

First U-Slot

Open

Difference in Results

Temperatures are higher

in the cabinet with no

blanking

Airflow Paths in Unblanked Cabinet

Open U-Slot

Recirculation

Side Gap Open

Recirculation

Under Cabinet

Recirculation

Modeling Must Do’s –

Minimum CFD Inputs

• Accurate Representation of IT Devices

• How does representation of air jets from high density servers, such as blades,

affect results?

• Differences in cabinet modeling

• Does the modeling of blanking plates matter?

• Do cabinet accessories such fans, vents, penetrations, etc. affect the results?

• Buoyancy modeling

• How much does buoyancy affect the flow field?

• Cooling unit discharge

• How do different fan types affect airflow?

• Uniform discharge

• Blower

• Plug fans

• Axial/Propeller fans

Demonstration of Ducted Delivery and

Buoyancy

• Overhead ducted

Air delivery

system

• Return Vent in hot

aisle

• 3.5 kW per cabinet

Demonstration of Ducted Delivery and

Buoyancy

Gravity Modeled Gravity Ignored

Buoyancy driven flow not captured when Gravity Ignored.

Hot air seems to sink!

Demonstration of Ducted Delivery and

Buoyancy

Gravity ModeledGravity Ignored

Major Variation in Airflow Paths

Demonstration of Ducted Delivery and

Buoyancy

Gravity Modeled Gravity Ignored

Results in Major Variation in Cabinet Inlet Temperature

Modeling Must Do’s –

Minimum CFD Inputs

• Accurate Representation of IT Devices

• How does representation of air jets from high density servers, such as blades,

affect results?

• Differences in cabinet modeling

• Does the modeling of blanking plates matter?

• Do cabinet accessories such fans, vents, penetrations, etc. affect the results?

• Buoyancy modeling

• How much does buoyancy affect the flow field?

• Cooling unit discharge

• How do different fan types affect airflow?

• Uniform discharge

• Blower

• Plug fans

• Axial/Propeller fans

Fan Types

Centrifugal Fan

(Blower)

Radial Fan

(Plug Fan)

Axial Fan

(Propeller Fan)

Airflow Patterns

Centrifugal Fan

Radial Fan Axial Fan

Uniform Discharge

Pressure Distribution

Centrifugal Fan Radial Fan Axial FanUniform Discharge

Grill Airflow Distribution

Centrifugal Fan Radial Fan Axial FanUniform Discharge