I-STUTE Project

- WP2.3 Data Centre Cooling

Project Review Meeting 4, Lancaster University, 2nd July 2014

Background

2

• Data centres estimated to use 2-3% of total electricity consumption in the UK and generate

3.3 million tonnes of CO2 annually.

• Data centre energy use and emissions projected to quadruple by 2020 without significant

efficiency improvement

• Typically, approx. 50% of data centre energy is used for cooling and humidification

• Extreme energy saving measures have resulted in as little of 7% of total energy being used

for purposes other than IT. These methods are not feasible in all cases, however, there is

potential for large energy savings

• Use of energy for IT load is also generally inefficient, due to: (i) resilience measures; (ii)

operating at low IT loads. There is therefore potential for large energy savings in IT power

usage

Plan for data centre project

3

• Phase 1 (July 2013 – Oct 2014) - Development of roadmap:

Tasks:

(1) Study of data centre industry – gathering information, networking/identification of key

players, current areas of research interest and review current data centre industry

(2) Identify new energy/carbon saving cooling technologies and strategies for use in data

centres, and establish methods for evaluating and scoring new technologies

(3) Review and evaluate each technology/strategy against defined criteria

(4) Identify technologies for detailed study/development in second phase of project

(5) Produce roadmap document

• Phase 2 (Oct 2014 – July 2016) – Detailed study of selected technologies

Overview of activities undertaken to date

4

• Gather information on data centres e.g. types, sizes, layout, operation, current

technologies, potential future technologies

• Networking – attending data centre industry events, identifying key players,

establishing contacts with data centre operators, manufacturers/suppliers and other

research teams

• Use of data centre modelling software (Romonet) to predict energy use, emissions

and costs for a conventional data centre, to develop baseline case

• Define criteria for evaluating current and future data centre cooling technologies

• Use of exergy analysis for rating of the energy performance of different data centre

cooling approaches and potential for energy recovery

Data centre cooling approaches

5

Air based (conventional)

Advantages – Effective. Fans, air conditioners and

chillers. New: free cooling and evaporative cooling,

higher operating temperatures

Disadvantages – Low heat carrying capacity, large

volumes, costly equipment, inefficient

Water based

Advantages – High heat capacity, pumped, small

volumes, efficient, low energy input

Disadvantages – Incompatible with electronics, only

recently used in data centres

Refrigerant based

Advantages – Electronics compatible, high heat

carrying capacity, particularly 2-phase. Pumped system –

low energy input

Disadvantages – not much experience of use in data

centres

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Data centre cooling technologies

Air:

(i) Traditional – use of CRACs,

CRAHs and chillers around

perimeter of room, random

layout of racks

Improved efficiency air cooled

systems:

(ii) raised floor + hot/cold aisle

(iii) in-row cooling

(iv) contained hot or cold aisle

(v) air side economiser

(vi) direct air free cooling,

(vii) adiabatic free cooling

(viii) direct evaporative

(ix) indirect evaporative

(x) water side economiser

Water:

(i) Direct on-chip water

cooling

(ii) Conduction cold plate

cooling of server

(iii) Rear door water cooled

rack system

Refrigerant:

(i) Immersion cooling of

server boards

(ii) Spray cooling of chips

(iii) Direct on-chip 2-phase

pumped

(iv) Direct on-chip 2-phase

VC system

Future/blue sky:

(i) Thermoelectric

(ii) Thermionic tunnelling

(iii) Thermoacoustic

(iv) Stirling coolers

(v) Air cycle

(vi) Liquid air engine

(vii) Ionic wind

(viii) Porous media

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Energy flows in data centres

• Main aim of conventional data centre cooling is

to remove heat from vicinity of microprocessors

and reject to outside ambient air

• Typical air-cooled data centre

configuration

Energy (electrical and mechanical) inputs,

heat outflows and typical temperatures

8

Sources of heat in server racks in data centres

• Heat generated in data centres is not just from microprocessors

• Typical power consumption/heat generation pattern for a data centre server rack

Source: Intel

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Potential for heat energy recovery from server components

Parameter Processors Memory PCI Drives Motherboard PSU Fans DC loss Standby

% Power

consumption 30% 11% 3% 6% 3% 25% 9% 10% 2%

Operating

temperature 70°C 70°C 30°C 45°C 40°C 50°C 30°C 40°C -

Carnot

efficiency

(Tc=20°C)

0.15 0.15 0.03 0.08 0.06 0.09 0.03 0.06 -

Recoverable

energy

(100kW

input)

4.5 kW 1.65 kW 0.09 kW 0.48 kW 0.18 kW 2.25 kW 0.27 kW 0.60 kW -

• Main components from which heat could be recovered are:

(i) Processors; (ii) PSU; (iii) Memory

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Quality of waste heat from data centres

• Data centres generate very large amounts of heat energy. This heat is generally

transferred to the surrounding environment and wasted

• This waste heat should be regarded as an energy source and exploited

• To determine the potential for re-use of waste heat dissipated from a data centre, an

exergy analysis is needed

• Different cooling methods/technologies produce different temperature heat output

streams with different exergies i.e. qualities

• It is planned to categorise a range of data centre cooling technologies in terms of both

energy saving potential and exergy maximisation of waste heat streams.

Exergy and degradation of energy

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• Exergy measures the quality of a given energy source. It is defined as the maximum

potential of that energy source for doing work

• Electricity has an exergy value close to 100%. However, heat generally has a lower

exergy value that is related to its temperature

• Each process taking place in the data centre e.g. conversion of electricity to heat,

results in a loss of exergy

• Change in exergy (for a closed system) is given by:

1212

120121122

zzmgm

SSTVVPUUX

Change in Change in Work done Exergy Change in Change in

exergy internal destroyed kinetic potential

energy energy energy

Results of preliminary exergy analysis

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Ambient temperature of 30°C (303K) assumed:

Cooling

medium

Cooling

method

Chip

temperature

Exergy remaining

after electrical

energy converted

to heat

Heat Energy transfer

from chip to coolant

(1st law efficiency)

Exergy

recovered in

coolant (2nd

law efficiency)

Net exergy

destroyed

per kW IT

Exergy

recovered

per kW

cooling

Air Fan 60°C 9.0% 93% 1.1% 1.01 0.32

Air Fan +CRAC 85°C 15.3% 93% 21.0% 0.90 0.60

Water Pump 60°C 9.0% 93% 5.0% 0.93 1.47

Water Pump 75°C 12.9% 83% 7.7% - -

Water Pump 85°C 15.3% 69% 8.4% 0.86 2.64

Refrigerant Pump 85°C 15.3% 99.7% 8.7% 0.83 12.1

Refrigerant VC 85°C 15.3% 92.5% 14.8% 0.86 0.79

Aims of heat recovery from data centres

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• Need to maximise temperature of waste heat stream to enable greatest range of

applications

• Could use heat pump to boost waste heat temperature – but is this energy efficient?

• Ideally, want to recover energy in excess of that used for cooling method

• Probably best to use waste heat directly

Data centre waste energy recovery technologies

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Waste

heat in Vapour Generator Turbine

Pump Condenser

Shaft Work

Heat out

Organic Rankine Cycle

Kyoto Wheel

Waste heat driven absorption chiller

Other waste heat uses include: domestic and

industrial space and water heating, district

heating, desalination, biomass processing,

piezoelectrics and thermoelectrics

Options for efficient heat recovery from server components

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• Use of porous media evaporator

• Refrigerant could either be pumped or used with

vapour compression system

• Key to viability of waste heat recovery from data centres is to maximise coolant

temperature. This is likely to be best achieved by liquid cooling (minimise ∆T)

• Use of microchannel evaporator

• Again refrigerant may be either pumped or

used in vapour compression system

Next steps

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• Finalise evaluation method for assessing new technologies for roadmap

• Evaluate and score energy/carbon saving technologies against defined criteria.

• Produce roadmap document, including:

- review of data centre industry

- detailed description of each of the technologies evaluated

- potential for waste heat and energy recovery

• Identify technologies for detailed study/development in second phase of project

Timescales for data centre project

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Activities

Development of roadmap

Detailed study of selected

technologies

Duration

July 2013- Oct 2014

Oct 2014 - July 2016

Milestones

Finalise evaluation method – Jun 2014

Final report/roadmap – Oct 2014

Interim report – May 2015

Interim report – November 2015

Final report - July 2016

Recommendations – July 2016

Options for dissemination of results of project

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• Present results at data centre industry conferences e.g. Uptime Institute conference in

USA, Data Centre Dynamics Conference UK, Europe or USA

• Present results at other relevant industry forums e.g. IMechE, CIBSE, IOR, SIRACH

• Journal papers e.g. ASHRAE or CIBSE journals