Date post: | 13-Apr-2017 |
Category: |
Documents |
Upload: | neha-shigrekar |
View: | 154 times |
Download: | 5 times |
Quantifying air flow rate through a server in an operational data center and assessing the impact
of using theoretical fan curve
Graduate Student: Neha Shigrekar
Committee members:Dr. Dereje Agonafer (Committee Chair)Dr. Abdolhossein Haji-SheikhDr. Ratan Kumar
Thesis defenseDate: 07.28.2015
2
Agenda
• Motivation
• Objective
• Methodology
• Experimental work and Results
3
Data center• A facility that centralizes an organization’s IT
operations and equipment
• Data is stored , managed and disseminated
• Servers are used as a medium of storage for the information on the internet
4
Air movement in data center
Server inlet Server inlet
Server exhaust
5
Current data center practices
• Maintaining lower temperatures to avoid hot spots
• More than one air handler to increase air velocity
• Neglecting the actual air flow rate across the server
• Air flow rate assumptions based on manufacturer’s data
Ref:- Datacenter 'Last Mile' Challenges- A Rack Perspective : S.Venkatraman, 10th September’09
6
Why QUANTIFY the air flow rate?
Provision the servers with the right amount of air flow rate.
Utilize the conditioned air to efficiently cool the servers and in turn the racks.
Reduce power consumption caused by over provisioning the cold aisles with high velocity , low
temperature air.
7
MOTIVATION
• Fans and servers are characterized in ideal data center conditions
• Operational set points are fixed based on the data derived
• Actual air flow across the server in an operating server is not quantified
8
OBJECTIVE
• To study the impact of the operational data center conditions on the air flow rate across the servers
• To quantify the differences in the air flow rate in ideal v/s operational data center conditions
9
Methodology
1. Characterize the fan unit for fan performance & server for server impedance per ANSI/ASHRAE Standard 51
2. Obtain the system operating points for a passive & active server per Standard 51
3. Quantify the system air flow rate at various fan duty cycles in the ideal conditions
4. Quantify the system air flow rate in an operational data center
10
Air flow bench
Inlet
Static pressure tap
Differential pressure taps
Pressure transducers
Blast gateBlower
3000-5000 CFM Chamber
11
Air Flow Bench
Nozzles Equipment attached to the inlet
12
Ideal data center setup
hot
cold
Ref:- THERMO-MECHANICAL DESIGN CONSIDERATIONS AT THE SERVER AND RACK LEVEL TO ACHIEVE MAXIMUM DATA CENTER ENERGY EFFICIENCY- Dr. RICHARD EILAND
13
Sunon Fan unit Fans in series used for system having high flow resistance
Ref:- http://www.nmbtc.com/fans/engineering/multiple-fan-use/
14
Application of Fan Laws
• Fan units are placed in parallel to increase the air flow through the system
• – : experimentally derived
flow rate of a single fan unit
– : number of units within the system
Ref:- http://www.nmbtc.com/fans/engineering/multiple-fan-use/
15
Theoretical Fan Curve
0 20 40 60 80 100 120 1400
0.5
1
1.5
2
2.5
1 FAN
Volumetric flow rate (cfm)
ΔP (i
n of
H2O
)
16
System under consideration
• 1U HPSE1102 server
Fan units in parallel
Flow direction
InletExhaust
1U=1.719”
17
0 10 20 30 40 50 60 70 80 90 1000
0.5
1
1.5
2
2.5
R² = 0.998543236143846
Volumetric flow rate (cfm)
System Impedance
18
Operating PointΔP
(in
of H
2O)
0 10 20 30 40 50 60 70 80 90 1000
0.5
1
1.5
2
2.5
3f(x) = 0R² = 0
Practical operating pointPolynomial (Practical operating point)system impedance
Volumetric flow rate (cfm)
Theoretical operating point52.92 cfm
Practical operating point26.7 cfm
19
Flow Curve
Ref:-Experimental and numerical characterization of a raised floor data center using rapid operational flow curves model, InterPACKICNMM2015-48234
20
Considerations Re: Fan Laws
• There is assumed at least 1.5 to 2 fan diameter clearance
• In servers obstructions are placed in close vicinity of the fans
• HPSE1102 has a clearance of 0.5 fan diameter
Ref:- 2008 ASHRAE HANDBOOK- HVAC SYSTEMS AND EQUIPMENT; 2005 ASHRAE HANDBOOK- FUNDAMENTALS; ANSI/ASHRAE Standard 51
20mm
21
Reasons
• Fan laws apply to aerodynamically similar fans running in same flow conditions
• The flow conditions for fans vary - Tested as a unit on the air flow bench with good i/o conditions -Mounted in a server with improper i/o conditions
22
0 10 20 30 400
0.2
0.4
0.6
0.8
1
26.7
Passive Server
System ImpedancePolynomial (System Im-pedance)100%90%80%70%60%50%40%30%
Operating points at various duty cycles
Volumetric flow rate (cfm)
ΔP (i
n of
H2O
)
23
Operating points at various duty cyclesΔP
(in
of H
2O)
Volumetric flow rate (cfm)
0 10 20 30 400
0.2
0.4
0.6
0.8
1
28.7
Active Server
System ImpedancePolynomial (System Im-pedance)100%90%80%70%60%50%40%30%
24
Data center
Cold aisle Hot aisle
25
Anemometers
Velocity anemometers attached in front of the servers
Anemometers plugged into Accusensor
ATM2400
26
Calculation of air flow rate
• Velocity readings at different fan duty cycles
• Effective inlet area of the server considered
• Qwhere, - Q is the air flow rate - is the velocity -A is the effective area
27
Volumetric flow rate vs Duty cycle
Volumetric flow rate (cfm)
Duty
cycl
e (%
)
2 4 6 8 10 12 140%
20%
40%
60%
80%
100%
120%
cfm vs duty cycles
13.28
28
Observations• The air flow rate measured at same fan duty cycle in ideal data
center differs from the air flow rate in a data center by ~50%
• Fan laws cannot be applied to practical air flow rates to predict the air flow rate through a server in data center due to differences in flow conditions
• Flow conditions are altered due to presence of external impedances like presence of other servers, non-uniformity in the rack and pressure variations across the rack
29
Summary of ResultsΔP
(in
of H
2O)
Volumetric flow rate (cfm)
10 15 20 25 30 35 40 45 50 55 600
0.2
0.4
0.6
0.8
1
1.2
13.28
26.7
52.92
Theoretical operating pointActive operating pointPassive operating pointOperational operating point
28.7
30
Reasons • The operating conditions in the ideal data center are controlled -No pressure variations -No leakages -No bypass air flow -Uniform flow rate
• Operating conditions in the actual data center are hindered by - Non uniformity across the rack - External impedances -Variable pressures in both the aisles - Leakages in the rack - Bypass airflow
31
Conclusions• A fan unit and server were characterized per Standard 51 and found to be in
agreement with the manufacturer’s published data
• The system performance was quantified in ideal data center conditions– The system operating point was found to be ~ 50% less than the theoretical operating
point
• The system performance was quantified in a representative data center environment– The system operating point was found to be ~ 75% less than the theoretical operating
point– The reason being the external impedances that cause pressure variations and thus affect
the air flow rate through the server
• This study has shown a significant difference in the observed air flow rate through the system as compared to the assumed operating point used by facility designers and operators to provision the cooling system
32
Future Work
• Study the effect of aisle pressure on the fan performance in operational data center
• Consider the impact of non-uniformity within the rack
• Study the effect of clearances within the cabinet on flow uniformity
33
AcknowledgmentsI am very grateful to…
Dr. Agonafer for his continuous support and encouragement Dr. Kumar and Dr. Haji-Sheikh for being a part of my committee Marianna Vallejo for mentoring me throughout my research Nirav Dodia, Ashwin Siddarth, Ruturaj Kokate and Divya Mani
for their support in experimental work Sally Thompson and Debi Barton for helping me in all the
educational matters My family and friends for all the moral support
34
QUESTIONS
35
THANK YOU
36
Appendix1.Duty Cycle v/s RPM
2. Duty cycle v/s cfm passive server
3.Duty cycle v/s cfm active server
Passive operating point 100% 26.7 0.23483
Active operating point 100% 28.7 0.266659
Theoretical operating point 100% 52.92 1.09
Operational operating point 100% 13.28239 0.013
4. Operating points in different conditions
37
Manufacturer’s Datasheet