data center cooling efficiency: understanding the science of the 4 delta t's

Data Center Cooling Efficiency: Understanding the Science of the 4 Delta T’s

Lars Strong, P.E., Upsite Technologies

Airflow Management Awareness Month

June 22, 2016

Lars is a thought leader and recognized expert on data center optimization. He currently serves as the Senior Engineer and Company Science Officer of Upsite Technologies. Lars is a certified U.S. Department of Energy Data Center Energy Practitioner (DCEP) HVAC Specialist.

05/03/2023 © Upsite Technologies, Inc. 2

Lars Strong

Delta T PUE Bypass Airflow Commonly Known Delta T’s Less Known Delta T’s Remedial Considerations


Agenda

DELTA T (ΔT)

© Upsite Technologies, Inc.05/03/2023 4

Delta T (ΔT)= change in temperature

“The ΔT” - Facilities: across cooling unit coils (Δ between supply and return)- IT: through IT equipment

There are actually 4 ΔT’s


Delta T (ΔT)

The 4 ΔT’s

1. Through IT equipment2. IT equipment exhaust to

cooling unit3. Through cooling unit4. Cooling unit supply to IT

equipment intake


The 4 ΔT’s

PUE – RELATION TO AIRFLOW MANAGEMENT


PUE


Total Load

IT LoadPUE =

Other than IT load, cooling load is often the largest portion of total loadAirflow management is fundamental to both effective and efficient coolingMechanical plant + cooling fans: 35% of total load, 73% of non IT Load

Raised floor

area (sq ft)

# of running cooling units

Raised floor

bypass open

area (%)

Hot spots (%

of cabinets

)

Cold spots (%

of cabinets) (Data from 6 sites)

Proper perforated tile

placement (%)

Cooling Capacity Factor (CCF)

Averages 7,527 8 48% 20% 35% 77% 3.9Minimum 720 2 13% 0% 0% 7% 1.2Maximum 37,00

040 93% 86% 86% 100% 32.0

Recommended

n/a n/a <10% 0% 0% 100% 1.2Conclusion: Inefficient cooling configuration / airflow management is the problem; capacity is not the problem.

Airflow Management Research


BYPASS AIRFLOW


Bypass Airflow Clarified

© Upsite Technologies, Inc.© Upsite Technologies, Inc.05/03/2023 11

Common ratios before raised floor open area management



Common ratios after raised floor open area management



Ratios after balancing supply flow rate to IT demand flow rate

MORE COMMONLY KNOWN ΔT’S


The 4 ΔT’s



equipment intake


ΔT Through IT Equipment

Regardless of airflow management in the computer room, the IT equipment airflow temperature rise will be constant for a given work load.

Every kilowatt of electricity consumed by IT equipment becomes a kW of heat added to the flow of cooling air through the IT equipment.

There is a fixed relationship between airflow, temperature differential and heat (energy).





Heat Transfer Equation

CFM =

CFM = cubic feet per minute of airflow through the server3.16 = factor for density of air at sea level in relation to F⁰ΔT = temperature rise of air through the server in F⁰

3.16 x W Delta T



CFM/kW

IT Equipment Required Flow Rate IT

Equipment Delta T

(deg F)15° 20° 25° 30° 35° 40°

Required flow rate (CFM/kW)

211

158

126

105

90

79

“Blade” servers at 35 F ⁰ ΔT consume 90 CFM / kW

“Pizza box” servers at 20 F ⁰ ΔT consume 158 CFM / kW

UPS load (kW) x CFM/kW = Total IT CFM

UPS load (kW) x 100 CFM/kW = approximate IT cooling demand (CFM) Compare this to total cooling flowrate to determine room bypass airflow rate



Examples

The 4 ΔT’s



equipment intake


ΔT Through Cooling Unit

Ideally ΔT through cooling units would match ΔT through IT equipment, then total volumetric flow rate (CFM) of conditioned air could match the total flow rate of IT equipment

Legacy DX units ΔT was fixed at about 18˚ F

A 5˚ F increase in return air temperature might result in a 3˚ or 4˚ increase in the supply temperature



Chilled water cooling units have a much wider range of ΔT

Cooling units can be designed for much higher ΔT

Designers of high density data centers with high ΔT IT equipment are working with cooling unit manufactures to provide cooling units with a 45˚ F ΔT



LESS COMMONLY KNOWN ΔT’S


The 4 ΔT’s

1. Through IT equipment2. IT equipment exhaust

to cooling unit3. Through cooling unit4. Cooling unit supply to IT

equipment intake


ΔT IT Equipment Exhaust to Cooling Unit

In most data centers the ΔT from the servers back to the cooling source is negative, the temperature of the return air tends to decrease after it is exhausted from the IT equipment

The cause is very straightforward: excess cooling air is bypassing the IT equipment and returning to the cooling units, reducing the temperature of the return air along the way




Hot area shows air that passed through IT equipment

Cooler area shows bypass airflow


The 4 ΔT’s


cooling unit3. Through cooling unit4. Cooling unit supply to

IT equipment intake


ΔT Cooling Unit to IT Equipment Intakes

It is surprising that the ΔT between the cooling unit supply/output and the server inlet is not on many radars

Supply temperatures around 55˚ F are fairly typical, approximately 9˚ F below the recommended minimum temperature for data processing equipment per the ASHRAE environmental guidelines

Low supply temperature is often not a problem because by the time it reaches the IT equipment it has warmed dramatically




Infrared Image of Operating Data Center• Cold spots and hot

spots in every cabinet

• Trying to solve poor AFM with cold supply


REMEDIAL CONSIDERATIONS


Any server inlet temperature that is more than 5˚F above the supply temperature being produced by cooling units means that there is hot air

If the return air intake of the cooling units is more than 5˚F lower than the exhaust temperature from the IT equipment, then there is a bypass airflow problem.

These 5˚F guidelines for calibrating ΔT’s are suggestions that will help move a data center into the top 20% of efficiently and effectively performing data centers.


Remedial Considerations

Monitoring all four ΔT’s can provide valuable assistance for optimizing the data center

The goal, particularly if free cooling is available to the data center, is to get the differentials between the cooling supply and IT intake, and server exhaust and the cooling unit return as close to zero as possible, this will increase free cooling hours.

Raise control temperatures to improve cooling unit capacity and efficiency

IR Thermometer and IR cameras are very valuable tools


Remedial Considerations

A holistic approach An iterative process ‘Check in’ at the room level

after making any AFM improvements

Watch video at:upsite.com/resources/airflow-management/

Upsite’s 4 R’s of Airflow Management™


http://www.upsite.com/resources/airflow-management/

http://www.upsite.com/resources/airflow-management/

Raised Floor: Manage openings in the raised floor so that all cold air is entering the room through supply tiles located in front of IT equipment

Rack: Manage all openings through and below the rack or cabinet enclosure, so air can only pass through the IT equipment.

Row: Manage all openings between cabinets so no air can pass between them, and manage openings at the end of the aisle and above cabinets to contain cold air and prevent hot air wrapping around the ends of rows or over cabinets.

Room: Manage the conditioned airflow (flow rate and temperature) so that the maximum established IT inlet temperature is not exceeded, and there are no hotspots.


Upsite’s 4 R’s of Airflow Management™

37

Upsite’s 4 R’s of Airflow Management™Raised Floor

Integral GrommetP/N: 1010

Mini GrommetP/N: 10077

Round GrommetP/N: 40001 (4”) 40003 (6”)

Surface Mount Grommet

P/N: 2020 (Original) 2030 (Large)

2040 (Xlarge)

Extended Brush GrommetP/N: 10012 (3” x 24”) 10013 (6” x 24”) 10097 (3” x 60”) 10098 (6” x 60”)

Row

Under Rack Panel 10126 (27.5”) 10127 (31.5”) Adjustable Rack

Gap PanelP/N: 10164

Rack Top Baffles P/N: 10160/1

Bi-Directional DoorsP/N: 10163

Modular Containment

Room

Temp Sensor

Temp + Humidity

Sensor

Leak Detection Sensing

Rope

Temp Sensor w/ Digital InputTemp

Sensor

EMS 300 Wireless Network Manager

EMS 200 Wired Network Manager

Point Repeater

Rack

White Blanking PanelP/N: 10114 (1U) 10115 (2U)

1U Black Blanking PanelP/N: 10031 (19”) 10177 (23”)

2U Black Blanking Panel

P/N: 10033

Rack Airflow Management KitPass Through Blanking Panel

P/N: 10112 (1U) 10113 (2U)

Rack Mount GrommetP/N: 40002


June 1: The Science Behind Airflow ManagementPresented by Lars Strong, P.E., and Mark Seymour

June 8: Myths of Data Center ContainmentPresented by Lars Strong, P.E.

June 15: How IT Decisions Impact FacilitiesPresented by Lars Strong, P.E., and Ian Seaton

June 22: The 4 Delta T’s of Airflow ManagementPresented by Lars Strong, P.E.

Watch all recordings at upsite.com/airflow-management-awareness-month

Airflow Management Awareness Month

http://www.upsite.com/airflow-management-awareness-month/

Thank you!

@UpsiteTech

blog.upsite.com

On LinkedIn

Lars Strong, P.E.Senior Engineer, Upsite [email protected]

Follow Upsite for the latest news and information on data center AFM.

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data center cooling efficiency: understanding the science of the 4 delta t's

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