Opportunities for Combined Heating and Cooling Using Data Centres

Opportunities for Combined Heating

and Cooling Using Data Centres

Gareth Davies

School of the Built Environment and Architecture, London South Bank University

103 Borough Road, London SE1 0AA Email: [email protected]

Co-authors: Graeme Maidment, LSBU

Robert Tozer, Operational Intelligence

Presented at CIBSE Technical Symposium, UCL London, 16-17th _{April 2015}

Topics to be addressed

• Approaches to data centre cooling

• Waste heat sources from data centres • Use of heat pumps

• Energy, carbon and cost savings from data centre waste heat • District heat networks

• Data centre locations in London

• Mapping of data centre heat sources • Summary

Background

• Data centres range in size from a few tens of kW to more than 100 MW

• Data centres consume 2-3% of the UK’s electricity, producing 3 x 106 _{tonnes of CO}

2 pa

• 4 fold increase projected by 2020

• Data centres generate large quantities of heat requiring active cooling

• DECC have cited data centres as a possible waste heat source for district heating

Main approaches to data centre cooling

(a) Remote air cooling – conventional cooling using CRACs or CRAH/chilled water; also air and water economisation

(b) Local air cooling – close-coupled cooling. Air cooling of servers, heat absorbed by e.g. rear door air-water heat exchanger

(c) Direct liquid on-chip cooling – cold plate water or dielectric heat exchanger contacting chips. Air cooling of other components (d) Liquid immersion cooling – server boards immersed in

Waste heat recovery

Requirements for reuse:

• For the majority of waste heat reuse applications, temperatures of 70°C and above are needed

• Many waste heat sources are produced at lower temperatures, and this is generally the case for data centres

• However, can upgrade temperature of waste heat streams by using heat pumps

Options for reuse:

• Possible applications for waste heat include: domestic and industrial space and water heating, district heating, organic Rankine cycle, absorption chillers, desalination, biomass processing

• District heating is a promising option, if suitable networks are available

Recovering waste heat from data centres

• The average temperatures/grades of the waste heat streams produced by the four different cooling methods are shown in the table below

• The highest temperature (grade) waste heat available is from the liquid cooling methods

• Waste heat recovery is possible for the air cooled methods, but at low temperatures, limiting its reuse value

Cooling system Cooling medium Waste heat source Temperature range (°C) Recovery Possible?

Remote air cooling Air Air 25-35 Yes

Chilled water 10-20 Yes

Local air cooling Air Air 25-35 No

Chilled water 10-20 Yes Hybrid liquid/air

cooling

30/40% Air Air 25-35 Possibly

60/70% Liquid Liquid 50-60 Yes All liquid cooling Liquid Liquid 50-60 Yes

Heat and temperature distribution in

IT servers

Component

For standard server For HPC Server Proportion of total heat Temperature (°C) Proportion of total heat Temperature (°C) Microprocessors 30% 85°C 63% 85°C DC/DC conversion 10% 50°C 13% 115°C I/O processor 3% 40°C 10% 100°C AC/DC conversion 25% 55°C

}

• Highest quantities of heat and highest temperatures are generally found in microprocessors, memory chips and some transformer and connection components

Upgrading of waste heat using heat pumps

• Heat pumps can be used to boost the temperature of waste heat, increasing the range of options for reuse. Both single and multistage cycles can be used

• The effectiveness and economic viability of raising the temperature in this way depend on the initial and final temperatures for the heat, and the heat pump COP

• For reuse, a minimum temperature of 70°C is generally needed. For economic viability need to deliver heat at a COP of > 3

COPs for a range of heat pump cycles

• Evaporation temperatures T_evap assumed to be 10°C lower than expected waste heat temperatures

• 2 stage cycles used where waste heat streams at two different temperatures generated (1)/(2)

• COPs are all above breakeven value of 3. Liquid cooled data centre waste heat gives significantly higher COP

Heat source No. of cycle stages Waste heat (1)/(2) % Tevap (1)/(2) (°C) Tcond (°C) COP Chilled Water 1 100 10 70 3.1 Air 1 100 25 70 4.1 Liquid/Air 2 60/40 40/25 70 5.5 Liquid 1 100 40 70 6.3

Energy, carbon and cost savings available

from reusing data centre waste heat

• Cost savings of £876,000 and 4,102 tonnes of carbon savings per annum predicted for 3.5 MW (IT load) for 1 year, for liquid cooled data centre

• Savings are compared with costs and carbon emissions assuming a heating requirement of 3.5 MW years, generated using gas

Heat Source

Energy saving

(MW years)

Carbon

Savings

(tonnes)

Cost

Savings (£)

Chilled water

2.76

1,864

£373,634

Air

3.04

2,938

£614,862

Liquid/Air

3.25

3,786

£805,212

Liquid

3.33

4,102

£876,000

District heating networks

• London plans to build a low temperature heat network – supply temperature 70°C (London Mayor reports, 2012; 2013)

• Data centre waste heat could be upgraded via heat pumps to

contribute heat at this temperature. A heat pump COP of above 3 is needed for viability

• Currently supply only 2% of heat demand in UK by district heating

• UK government plans to substantially expand district heating networks making use of waste heat sources e.g. data centres

Distribution of Data Centres across UK

• Distribution of colocation data centres in UK

• Largest concentration of data centres is in London

Locations and Sizes of Data Centres

in London

• Approx. 75 colocation data centres identified in Greater London

• Majority are concentrated in

central London, along the Thames

• Sizes range from 1 to 28 MW

• (For those shown as zero on the map, their capacity was not

London Heat Map (Heat Use)

• Greatest requirement for heat is for commercial use and public buildings in central London. Residential heat requirement is fairly evenly spread across the Greater London area

Matching of DC Heat Sources with Heat

Loads (for London districts)

• It is seen from the above table that Tower Hamlets, Ealing,

Hounslow, Islington, Havering, Newham and Hillingdon could have a significant proportion of their heat requirements met by data centre waste heat

Existing and Proposed District Heating

Networks

• Yellow lines indicate existing heat networks, red lines indicate proposed heat networks

Summary

• Data centres use significant quantities of electrical energy and demand is growing

• Almost all of the energy input to data centres is converted to heat, and needs to be removed by cooling

• If this heat could be recovered, it would provide a sizable resource for reuse

• Conventional, remote air cooling generates heat at relatively low temperatures, but newer methods e.g. liquid cooling produce higher grade heat

• Low temperature district heating networks, such as that planned for London appear to be a promising use for the waste heat

• Benefits of waste heat reuse for a 3.5 MW data centre suggest savings of over 4,000 tonnes CO₂e and nearly £1 million pa

Project supported by i-STUTE (interdisciplinary centre for

Storage Transformation and Upgrade of Thermal Energy),

one of six EUED (End User Energy Demand) research centres funded by the UK Research Councils UK Energy Programme