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Challenges and Opportunities forDistrict Cooling
Vanguards Network, BathJuly 23rd 2014
Paul WoodsTechnical Director, AECOM
July 2014
Options for Supply of Cooling
Page 2
BuildingCoolingDemand
ElectricitySource
Vapourcompression
chiller
District Cooling Network
Electric chiller
Absorption chiller(e.g.heat from
CHP)
Ground orriver water
Challenges for District Cooling in UK
Climate – periods when mechanical cooling needed formost buildings is limited (depends on building type)
Smaller flow and return temperature difference than forheating so larger water volumes and larger pipes
No tradition for district energy – DH is becomingaccepted but DC faces barriers
Peak power prices in UK are in winter not summer
Customers need to consider avoided capital costs,maintenance costs and management costs not just energyif a business case is to be made
Lack of fiscal incentives for DCPage 3
Opportunities – what will reduce cost of cooling energyproduction – to finance the DC network?
Economies of scale – higher efficiencies and lower capital cost ofchillers – of limited benefit especially if a new Energy Centre is needed
CCHP or tri-generation – but benefit is reducing
Alternative refrigerants – ammonia
Alternative condenser cooling – cooling towers, river water, waste water– more efficient than air-cooled
Storage of cooling energy
Heat recovery from condenser water (chiller heat rejection)
Free cooling from heat pump using river water
Page 4
Electricity supply from major power stations (DECC,September 2013)
Page 5
Future marginal electricity emission factor
Page 6
Assumes coal-fired generation will be phased out
CHP production will result in older gas CCGT stations reducing output
Current electrical efficiency is a good guide as currently CCGT used forload following more than base load
DUKES 2012 Table 5.6 provides data on CCGT major power stations as:
Gas used: 182,409 GWh
Electricity supplied to grid: 84,755 GWh
Hence efficiency = 46.5%
Also DUKES gives system losses at 8%
Hence electrical emissions factor of 202/0.465/0.92 = 472g/kWh
Comparisons Using CO2 Content of Cooling
Page 7
-150
-100
-50
0
50
100
150
200
250
300
300 350 400 450 500 550 600 650 700
CO2
emis
sion
sper
kWh
cool
th(g
/kW
h)
CO2 emissions per kWh electricity (g/kWh)
Variation of cooling emissions factors
Tri-gen at 35% -Abs CoP=0.7
Chiller CoP = 6
Trigen at 35% -Abs CoP=1.2
Storage of cooling energy
Capacity of chillers can be reduced – peaks met fromstore
Operating chillers at night:
• Use of night-time electricity
• Lower air temperatures gives improved efficiency
Free cooling with night-time air (in winter)
Chilled water preferred to ice for energy efficiency but willrequire large volumes
Electricity CO2 emission factor is lower at night –especially windy summer nights
Page 8
Current situation – May 2014 – from gridwatch.templar.co.uk
Page 9
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 500 1000 1500 2000 2500
Elec
trici
tyde
man
dan
dan
dsu
pply
(MW
)
5 minute periods
Electricity data for 19th May 2014 to 25th May 2014
demand
wind
nuclear
wind+nuc
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 500 1000 1500 2000 2500
Elec
trici
tyde
man
dan
dan
dsu
pply
(MW
)
5 minute periods
Electricity data for 19th May 2014 to 25th May 2014
demand
wind
nuclear
wind+nuc
Future situation – multiplier of 4 on wind, 2 on nuclear
Page 10
High CO2
Low CO2
Heathrow Terminal 5
Page 11
Heathrow Terminal 5
Page 12
Designed for 30m passengers p.a. (Gatwick was 27m at the time)
Harsh airport environment so sealed building essential
Centralised Energy Centre to maximise space in terminal with chilled waternetwork at 5C flow 14C return, direct connection to buildings
4 No 6.6MWc chillers, ammonia refrigerant and evaporative cooling towers, HVvariable speed motors - 30% reduction in energy use over distributed chillers
3,600m3 chilled water store – concrete construction
Benefits of store:Reduction in installed chiller capacity (this paid for the store)Operation at night on lower electricity rateFree cooling at nightImproved chiller performance at night
Heathrow Terminal 5 – Cooling demand profile
Page 13
Cooling Demand Phase 1 - T5A (April - Sep)
0
5000
10000
15000
20000
250001
132
263
394
525
656
787
918
1049
1180
1311
1442
1573
1704
1835
1966
2097
2228
2359
2490
2621
2752
2883
3014
3145
3276
3407
3538
3669
3800
3931
4062
4193
4324
Hours
Coo
ling
dem
and
(kW
)
Heathrow Terminal 5
Page 14
Opportunities – heating and cooling in same district
Page 15
Requires coincidentheating and coolingwithin a daily cycle
Heat pump
ChillerElectricity
District Heating(no RHI) Buildings
with heatingdemand
Buildingswith coolingdemand
District Cooling
Electricity Thermalstore
British Library, St Pancras
Page 16
Very deep plan building with multiplebasements for book storage
Heat pump uses condenser water as itsheat source to produce 60C water
Heat is stored in a tank with 60C/40Ctemperatures
Excess heat rejected from internalspaces is used to heat perimeter spaces(with heat pump electricity needed toboost temperature)
Also heat recovery used with run-aroundcoils
Page 17
Options for District Cooling and District Heating
Heat pump
HEx
River waterRequires coincidentheating and coolingwithin a daily cycle
District Heating(with RHI) Buildings
with heatingdemand
Buildingswith coolingdemand
District Cooling
Thermalstore
Electricity
Additionalchiller heatrejectionavailable
CHPAdditionalheat recovery
‘Free’cooling
Conclusions
Page 18
District Cooling possible in the right circumstances but there are significanteconomic and cultural challenges
Benefits of absorption chillers driven by gas-engine CHP will reduce in future
Storage of ‘coolth’ in the form of chilled water can bring economic benefits and, inthe future, major CO2 benefits on windy summer nights
District Cooling linked to District Heating supplied by heat pumps will offeradditional energy benefits compared to separate solutions
Thank you
paul.woods@aecom.com
www.aecom.com
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