Options For Energy Reduction In Data Centres.

BYRNE DIXON HAS BRIGHT IDEAS

Controlling the energy use in IT server rooms

BYRNE DIXON ASSOCIATES

How to reduce energy usage in the Server Room.

1 Define Data Centre Efficiency.

Energy Efficiency Metrics

2 Analysis of our current environment.
Data Centre power usage in Europe
Guidelines for future power reduction.

3 Server Room Efficiency Strategy.
Cooling System Overview
IT Server Efficiency
Server Room Efficiency
Mechanical Plant Efficiency
Free Cooling
Electrical Distribution

4 10+ Easy Steps
Measures which can easily be implemented without effecting business continuity.


1 Define Data Centre Energy Efficiency

The Green Grid, an industry based consortium dedicated to developing and promoting efficiency for data
centres and information services, has adapted the terms power usage effectiveness (PUE) and data centre
efficiency (DCE).

PUE (power usage effectiveness) = Total Facility Power (Green Grid 2007)
IT Equipment Power

The reciprocal of the PUE is the term data centre efficiency (DCE) which takes the following form:

DCE ( data centre efficiency) = IT Equipment Power (Green Grid 2007)
Total Facility Power


2 Analysis of our current environment
At the time of the Efficient Servers survey (2006). Data Centre power usage in Europe (EU15 +
Switzerland) was 39.6TWh. Server power usage was at 14.7TWh for 6.77 million installed servers. This
number increased by 37% between 2003 and 2006. (See www.efficient-server.eu)
Current PUE is = Total Facility Power = 39.6TWh = 2.69
IT Equipment Power 14.7TWh

For every 1Kw of IT equipment we require 1.6Kw of electrical power to facilitate it.



In Practice: In 2000 the average electrical load was 1kw per rack, by 2004 it had risen to 3kw and
in 2008 it has risen to 6kw per rack with an average design load of 10-12kw. We predict that this
trend will continue. By 2010 the average rack load shall rise to 8kw and the average design load
to 16kw.



The two most significant areas are HVAC and the UPS and these are the areas which we
shall consider.


3 Data Centre Efficiency Strategy.

3.1 Cooling System Overview 3.4 Mechanical Plant Efficiency
Data centre cooling process CRAH Vs CRAC units.
Target areas for increased efficiency CRAH system efficiency
Chiller efficiency (COP)
3.2 IT Server Efficiency
CRAC system efficiency
Technology refresh
Electronic expansion valves
Utilisation/Virtualisation.

3.3 Server Room Efficiency 3.5 Free Cooling
Temperature and humidity CRAH System
CRAH coefficient of performance COP Evaporative pre-cooling
Effective air distribution CRAC system
CRAH electrical efficiency Additional CRAC free cooling options
Kyoto Cooling

3.6 Electrical Distribution
UPS Systems


3.1 Cooling system overview.


3.2 IT Server Efficiency

Technology Refresh
The latest energy efficient servers have reduced power consumption and improved performance.
Upgrade of a server can reduce energy consumption by 15%

Utilisation/Virtualisation
The industry average for server utilisation is 20% (LBNI). Through the implementation of the latest
virtualisation techniques the utilisation factor can rise to 80%.


3.3 Server Room Efficiency

Efficiency Basics – Coefficiency of performance
3.3.1
3.3.2 Temperature and Humidity Requirements
3.3.3 Effective Air Distribution
Under-floor Air Balancing and Direction
Rack Air Distribution
Room Air Distribution
3.3.4 CRAH/CRAC Electrical Efficiency
3.3.5 EMBS vs Punker
3.3.6 EC Motors

3.3.7 N+1 Redundancy Operation


3.3.1 Efficiency Basics - Coefficient of Performance

Coefficient of Performance (COP) = Cooling Output = Qi
Work input Wnet
Increase COP = Reduce area Wnet = Decrease Condensing temp and increasing evaporator temp.


3.3.2 Temperature and Humidity Requirements

ASHRAE Recommendation
Temperature 20 – 25 degC
Humidity 40 – 50%Rh


3.3.2 Temperature and Humidity Requirement

ASHRAE Recommendation
Temperature 20 – 25 degC
Humidity 40 – 50%Rh

To raise the air output of a 60kw
CRAC unit from 30% to 40% RH
requires 7.5kw
(Approx €1k/Kw/yr)

Dry Bulb = 26 deg C
Dry Bulb = 20 deg C
RH = 30%
To reduce the air output of a RH = 40%
60kw CRAC unit from 45% to DP = 6 deg C
DP = 6 deg C
40% RH 11.5 kw
W = 5.8g/kG
W = 5.8g/kG
(Approx €1k/Kw/yr)

Same level of moisture
– different RH


3.3.2 Temperature and Humidity Requirement
ASHRAE Recommendations 20-25ºC room temperature.
Ignore room temperature because its misleading.
Think cold aisle air temperature and return air temperature
Supply enough segregated cold air at the right temperature and return temperature will be high.

Increase CRAH COP = Increase Return Air temperature = Effective Air Management

100kw of cooling at 26degC
requires 19.6kw of electricity
100kw of cooling at 21degC
requires 28.5kw of electricity
8.9kw represents a 31% reduction
in CRAC unit power consumption.
8.9kw shall cost us € 9,356.00
over the year.

COP (Coefficient or performance) = Cooling output Kw
Electrical Power Input


3.3.3 Effective Air Management = Step 1 Balance under-floor air pressure

Through CFD analysis we can analyse the layout of a room to ensure airflow balance.

Eddy Currents and Rivers below floor Creates hotspots above floor


More balanced pressure and airflow.

Sub floor partitioning can divert the
airflow and also reduce the velocity
therby balancing the pressure.


3.3.3 Effective Air Management = Step 2 Rack airflow management

Blanking Plates
Side Panels

Koldlok Airguard
Perforated Doors


3.3.3 Effective Air Management = Step 2 Rack airflow management

WWW.BYRNEDIXON .COM WWW.BYRNEDIXON .COM

With Blanking Plates Without Blanking Plates


3.3.3 Effective Air Management = Step 3 Room airflow management

Cold Aisle Containment
Hot Aisle Containment

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Project : Reinsurance Company
Location : Bermuda
Before Optimisation



Project : Reinsurance Company
Location : Bermuda
After Optimisation



3.3.4 CRAH/CRAC Unit Electrical Efficiency

CRAH Unit Electrical Efficiency

Centrifugal Fans : Forward Curved Impeller Vs Backward Curved Impeller



Centrifugal Fans : Forward Curved Impeller Vs Backward Curved Impeller

Forward Curved Fan Backward Curved Fan

Low velocity 6 m/s
High velocity 15m/s
High pressure
Low pressure
Efficiency 65-75%
Efficiency 50-60%



EC (Electronic Commutation) Fans

80% efficient Vs 40% for Ac
fans
DC driven, no pf losses
Smaller profile, reduced
resistance in flow.
Combined in CRAH unit
can reduce power by 50%
Higher efficiency at part
load



EC fan motor profile AC fan motor profile


3.3.4 N+1 Redundency Operation.
If we increase the fan speed by 33% we increase the electrical load by 180% (Third fan Law)


3.4 Mechanical Plant Efficiency

3.4.1 CRAH Vs CRAC units.
3.4.2 CRAH System
3.4.3 Chiller efficiency (COP)
3.4.4 CRAC System
3.4.5 Electronic Expansion Valves


3.3.4 CRAH Vs CRAC Units
CRAH units CRAC units
Water or Glycol cooled by chiller, water tower/dry cooler Refrigerant cooled at external Condenser
Generally used in large facilities. Hybrid water precooling
Chilled water temp may be raised to increase efficiency Generally Used in smaller facilities
(Remove latent cooling) Refrigerant temperature is set.
More opportunity for efficiency and free cooling


3.3.4 CRAH Unit operation

1 Chiller 5 Chiller Refrigerant
2 Chilled Water Loop
3 Condenser/Dry Cooler
4 Condenser water loop

CRAH Unit operation


3.3.4 Chiller Efficiency

Chiller efficiency is governed by the difference in temperature between the chilled water and the
condenser water. The lower the differential temperature the higher the efficiency. Lowering the condensor
temperature is more difficult that raising the chiller temperature which is easier to implement and predict. Each
one degree increase in chilled water temperature increases the efficiency 3-4%. But each 1 degree raised
reduces the CRAH capacity by 10% unless the return air temperature is raised as well. By raising the chilled
water temperature above the dew point we will eliminate latent cooling.


3.3.4 CRAC Unit operation

1 Evaporator
2 Compressor
3 Expansion valve
4 Refrigerant Loop

CRAC Unit operation


3.3.4 Electronic Expansion Valve

Electrical consumption is governed by work carried out by the Compressor.
The work at the compressor is dependent on the system pressure.
A proportional electronic expansion valve can vary the pressure in accordance with the
Cooling load required
Outside air temperature.

By varying the valve position we can minimise the condensing pressure and maximise the
evaporation pressure.
Hence reduce the amount of work performed and energy used.

May be requested as an option from suppliers.


3.5 Free Cooling

3.5.1 Free Cooling Hours
3.5.2 CRAH System
3.5.3 Evaporative precooling
3.5.4 CRAC System
3.5.5 Additional CRAC free cooling options

3.5.6 Kyoto Cooling


3.5.1 Free Cooling Hours

Number of hours below 13 deg C

Dublin Airport Shannon Airport

Mean (1977 to 2006)
Mean (1977 to 2006) Number of hours with
Number of hours with temperatures <= 13
year Month temperatures <= 13 deg. C month deg. C
2006 1 741 1 742
2006 2 674 2 674
2006 3 730 3 728
2006 4 679 4 649
2006 5 576 5 506
2006 6 352 6 278
2006 7 170 7 105
2006 8 193 8 122
2006 9 330 9 263
2006 10 577 10 534
2006 11 685 11 675
2006 12 735 12 736

6442 6012


3.5.2 CRAH System

Free cooling chiller which combines a DX condensor and a free cooling coil
Can provide full and partial free cooling
Free cooling available for 75% of the year
Available in stages for part load

Free Cooling Chiller Indirect Free Cooling


3.5.3 Evaporative Precooling

Can be installed to existing chillers
Requires additional maintenance

Evaporative Cooling Direct Free Cooling


3.5.4 CRAC System

CRAC System
Hybrid system combining water and refrigerant loops
Dry cooler provides cold condenser water to the refrigerant condensor
Also precooling the air in the CRAC unit


3.5.5 CRAC System - Additional options for incorporating free cooling to CRAC units


3.5.6 Kyoto Cooling System

Kyoto is the use of outside air to provide cooling to the server room.
< 21ºC Kyoto cooling only 95%
21-26ºC Kyoto cooling plus compression 5%
> 21ºC Compression cooling only < 1%



Contain Cold Aisles
Allow cold aisle air to raise from 16ºC up to 22ºC Increase hours of free cooling
Return temperature at 28-37ºC
No humidity transfer across wheel.


3.6 Electrical Efficiency

Specify UPS based on efficiency at full and part load
Newer UPS have quoted very high efficiency at 50% load

Passive Stand-by Topology
High efficiency, low cost
Does not condition the mains


Data centre power usage before and after optimisation.

The two most significant areas are HVAC and the UPS and these are the areas which we
shall consider.


4 10 + Easy Steps
Measures which can be implemented without effecting business continuity.

1 Implement a hot aisle - cold aisle layout.
2 Reduce air loss
3 Install blanking plates, air guards and, perforated doors.
4 Install sub floor partitioning to balance the airflow and pressure

Balance the load in the room – match the load to the airflow
5
6 Check the location of air distributing floor tiles, relocate or provide additional.
7 Replace perforated floor tiles with air grills.
8 Install containment between the hot and cold aisles
9 Widen the temperature and humidity bands
10 Bring all units CRAC units on at lower fan speed.
Ensure two free tiles between cabinets in cold aisle – Bring cabinets to edge of floor tiles
11
Maintain filters – Ensure filters with minimum pressure drop are installed.
12
13 Reset chilled water temperature incrementally after return air temperature has risen.
Check for and eliminate free cooling – Is there water coming from the condensate drain
14

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