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
2
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 CO2 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
3
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
dielectric liquid, either in rack, or in a separate tank
4
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
5
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
Cooling system
Cooling
medium
Remote air cooling
Air
Local air cooling
Air
Hybrid liquid/air
cooling
All liquid cooling
30/40% Air
60/70% Liquid
Liquid
Waste heat
source
Air
Chilled water
Air
Chilled water
Air
Liquid
Liquid
Temperature
range (°C)
25-35
10-20
25-35
10-20
25-35
50-60
50-60
Recovery
Possible?
Yes
Yes
No
Yes
Possibly
Yes
Yes
• 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
6
Heat and temperature distribution in
IT servers
For standard server
Component
For HPC Server
Proportion
of total heat
Temperature
(°C)
Proportion
of total heat
Microprocessors
DC/DC
conversion
30%
85°C
63%
Temperature
(°C)
85°C
10%
50°C
13%
115°C
I/O processor
AC/DC
conversion
Memory chips
Fans
Disk drives
Motherboard
3%
40°C
10%
100°C
25%
55°C
11%
9%
6%
3%
70°C
30°C
45°C
40°C
14%
40°C
}
• Highest quantities of heat and highest temperatures are generally
found in microprocessors, memory chips and some transformer and
connection components
7
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
8
COPs for a range of heat pump cycles
Heat source
Chilled Water
Air
Liquid/Air
Liquid
No. of
cycle
stages
1
1
2
1
Waste heat
(1)/(2) %
Tevap (1)/(2)
(°C)
Tcond
(°C)
COP
100
100
60/40
100
10
25
40/25
40
70
70
70
70
3.1
4.1
5.5
6.3
• Evaporation temperatures Tevap 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
9
Energy, carbon and cost savings available
from reusing data centre waste heat
Heat Source
Energy saving
(MW years)
Chilled water
Air
Liquid/Air
Liquid
2.76
3.04
3.25
3.33
Carbon
Savings
(tonnes)
1,864
2,938
3,786
4,102
Cost
Savings (£)
£373,634
£614,862
£805,212
£876,000
• 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
10
District heating networks
• 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
• 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
11
Distribution of Data Centres across UK
• Distribution of colocation data centres
in UK
• Largest concentration of data centres
is in London
(Maps from: http://www.datacentermap.com)
12
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
determined)
13
London Heat Map (Heat Use)
(Maps from: http://tools.decc.gov.uk/nationalheatmap/)
• 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
14
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
15
Existing and Proposed District Heating
Networks
(Map from: http://www.londonheatmap.org.uk/Mapping/)
•
Yellow lines indicate existing heat networks, red lines indicate
proposed heat networks
16
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
17
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
www.i-stute.org
www.eued.ac.uk