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Indirect Evaporative Cooling Xiaoyun Xie Building Energy Research Center, Tsinghua University
Indirect Evaporative Cooling
Xiaoyun Xie
Building Energy Research Center, Tsinghua University
Background• Buildings account for nearly 1/3 of the total energy consumption, 20-30% of building energy is used for air
conditioning and maintaining indoor thermal comfort in hot seasons.
• As predicted, many regions are going to change from non-air conditioning temperate zones to air
conditioning zones, when there is a 2 °C lift of the average global temperature due to climate change.
Especially for Europe, Southeast Asia, the Middle East, and South America, as UNEP predicted.
• Changing the mode of air conditioning is one of the important solutions to meet the cooling demand without
increasing electricity consumption and carbon emission.
2
Background• Although over 85% of cooling around the world is achieved by mechanical
refrigeration, more than 40% buildings of the regions where cooling is needed can
be cooled by evaporative cooling instead mechanic, due to the dry climates.
Countries in Europe:
North France,
Germany, Holland,
most part in Russia
North of Africa
Australia
West of the U.S.,
South west of
Canada
Asia: North west of
China, Mongolia, Saudi
Arabia, Kazakhstan,
middle of india
3
Using Indirect Evaporative cooling to substitute mechanical refrigeration in
dry regions, with no refrigerants and no CFCs, to save energy significantly.
Direct Evaporative
Cooling (DEC)
Limit is inlet wet bulb
temperature
Indirect Evaporative
Cooling (IEC)
Limit is inlet dew point
temperature
To
produce
cooling
air
To
produce
cooling
water
Evaporative cooling technologies
• Evaporative cooling is to make water directly or indirectly contact with air of low relative humidity, thus water evaporated to realize cooling effect.
进风
, ,o db ot d , ,,sf dec sf dect d
水泵
填料
喷淋装置
出风 Inlet air Outlet air
Water cycle
排风 排风
进风 送风
Inlet
air
Exhaust air
Supply air
进风
排风
冷水回水
,w dect
,w ret
冷水出水
风机
水泵
Inlet air
Inlet water
outlet water
Exhaust air
outlet water
• Using IEC technology, the output
temperature of water or air can be 6-
10K lower than using DEC technology,
and 3-5K lower than the inlet wet bulb
temperature, reaching around 14-
18℃ at ambient temperature of 35℃-
38℃ and relative humidity of 20%-
25%.
• Using IEC technology, electricity
consumption can be reduced by
40%~70% compared with common
mechanical chiller system, and no
CFCs used.
4
Current situations of IEC technology: IEC air coolers
• Various kinds of processes:
• Different second air conditions
• Different heat and mass transfer process: Internal three-
stream heat and mass transfer and external two-stream heat
and mass transfer; countercurrent or crosscurrent;
• Different process structure: single stage or multi stage;
Inlet air
air
Supply air
Exhaust air
0 0.005 0.01 0.015 0.02 0.025 0.030
10
20
30
40
50
t(°C
)
d(kg/kg.air)
100%
O
P0=101.325 kPa
60%(to,do)
(tdp,o,do)
(tsf,dsf)
(twb,o,dwb,o)
E
Internal IEC air coolers with inlet air as secondary air Internal IEC coolers with one part of outlet air as secondary air
External IEC coolers with inlet air
as secondary air
0 0.005 0.01 0.015 0.02 0.025 0.030
10
20
30
40
50
t(°C
)
d(kg/kg.air)
100%
O
P0=101.325 kPa
60%(to,do)
(tdp,o,do)
(tsf,dsf)
(twb,o,dwb,o)
E
0 0.005 0.01 0.015 0.02 0.025 0.030
10
20
30
40
50
t(°C
)
d(kg/kg.air)
100%
O
P0=101.325 kPa
60%(to,do)
(tdp,o,do)
(tsf,dsf) (twb,o,dwb,o)
E
External IEC coolers with one part of
supply air as secondary airM-Cycle IEC air coolers
Different processes, with different
cooling performance and different
outlet cooling air temperature;
Multi-stage processes
Current situations of IEC technology: IEC air coolers
• Different technical structures with:
• different heat and mass transfer forms
• different heat and mass transfer coefficients
• different cost of heat transfer area;
• different size, including the volume and specific surface area
1
4
1
5
987
1
3
1
71
6
1
1
1
2
1
0
1
2 3 4 5 6
Plate type
Heat pipe type Pipe type IEC air cooler Plate type M-Cycle core Plate type, internal IEC core
IEC Technology: Applications of IEC air coolers
Country City
type of IEC
process Size(m2) Application buildings air flow rate(m3/h)
wetbulb
temperature
efficiency
India Delhi
IEC＋DEC，3 stages public buildings
13600~68000, total
4730000( 52
projects) 1.15
India Maharashtra IEC+DEC 650 exhibition hall 70560
India IEC+DEC 650300 plants 67200000
India IEC 371.6 plants 23520
India Nagpur IEC+DEC plants 53760
India Pimpri IEC+DEC 65030 large public building
Australia Adelaide M-cycle IEC commercial building 19.7kW 1.06
Australia Adelaide IEC 4225
Australia Roxby, downs M-cycle IEC 140 resential buildings 10.5kW 1.24
Australia
New South
wales M-cycle IEC
China Urumqi
Multi stage
IEC 2,000,000
hospital building, high-
speed railway station,
office building,
exhibition centers 20,000,000 1.0~1.2
China Gansu
Multi stage
IEC+DEC 1,700 office building 0.927
China Xian
Multi stage
IEC+DEC 300 plants 30,000 1.29
Country City
type of IEC
process
Application
buildings
wetbulb
temperatur
e efficiency
The United
States Colorado M-cycle IEC
single
house 1.2
The United
States Arizona M-cycle IEC
single
house 1.2
The United
States California M-cycle IEC
single
house 1.2
The United
States Utah M-cycle IEC hosipital 1.2
The United
States California M-cycle IEC hosipital 1.2
The United
States
Watchingt
on M-cycle IEC hosipital 1.2
Mexico Mexicali M-cycle IEC food plant 1.2
South Africa
Bloemfont
ein M-cycle IEC restarant 1.2
Kuwait IEC+DEC 0.9~1.2
Iran Teheran IEC+DEC 1.1
Current situations of IEC technology: IEC water chiller
• Introduced by Prof. Yi Jiang in 2002, China, to produce the cooling water by near reversible process, with limit out water temperature to be outdoor dew point temperature.
0 0.005 0.01 0.015 0.02 0.025 0.030
10
20
30
40
50
t(°C
)d(kg/kg.air)
100%
O
P0=101.325 kPa
(to,do)
tw,r
tw
tw,1tw,sp
(tdp,o,do)
A
E
• Key processes: • to cool the inlet air to make it near the saturation line through a countercurrent air cooler by part of
the produced cooling water;
• to produce cold water by a counter current padding tower;
• flow rate ratio matching design for each of the heat transfer or heat and mass transfer process.
0
5
10
15
20
25
30
35
40
19:40
19:40
12:50
18:40
12:10
20:10
13:00
17:40
12:20
17:00
21:40
19:00
23:40
16:50
22:00
22:40
15:20
10:10
14:50
9:50
14:30
19:10
10:40
15:20
20:00
10:10
14:50
19:30
13:00
20:40
15:20
20:00
10:30
15:10
19:50
14:10
18:50
23:30
Tem
per
ature
(℃)
Inlet dry bulb tempeature(℃)
Inlet wet bulb temperautre(℃)
Out water temperature (℃)
Inlet dew point temperature(℃)
Date and time for testing (2005.8.4~8.9, 2006.7.31~8.2, 2007.7.16~7.28 )
Current situations of IEC technology: IEC water chiller
• Different process structure of
IEC chiller
• IEC chiller I:
• The limit outlet water temperature
is outdoor dew point temperature
• The total cooling energy produced
by the padding tower is higher
than the output cooling energy;
• IEC chiller II:
• The limit outlet water temperature
is higher than outdoor dew point
temperature
• The total cooling energy produced
by the padding tower is equal to
the output cooling energy;
0 0.005 0.01 0.015 0.02 0.025 0.030
10
20
30
40
50
t(°C
)
d(kg/kg.air)
100%
O
P0=101.325 kPa
(to,do)
tw,r
tw
tw,1tw,sp
(tdp,o,do)
A
E
0.005 0.01 0.015 0.02 0.025 0.03
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
humidity ratio (kg/kg.air)
Te
mp
era
ture
(oC
)
100%
40% 60%
A
D
80%F
O
E
20%
tw,in
tw,O
IEC chiller I
IEC chiller II
• For the IEC cooling system to remove indoor sensible heat, choose the IEC cooling air system or IEC water chiller system, which one is better?
Theoretical research of the process:
Indirect
evaporative
chiller
Air coolerOutdoor air
Exhaust air
Supply air
Outdoor air
M
Inlet air O
User heat exchanger 3
1
2
4
1
Exhaust air C
A
Cold water
Inlet air O
A
Tsp
T
Indirect
evaporative
chiller
Air cooler
Exhaust air
Outdoor air
Indoor air
Supply air
processes
transformation IEC air cooler
IEC water chiller
To remove the same quantity of indoor heat:
• The process produced cooling energy IEC
air cooler is larger than IEC water chiller,
when outdoor air is hotter than indoor air,
the difference is the outdoor air heat load of
IEC air cooler.
• Thus, larger heat transfer area and larger
cost when using IEC air cooler to remove
indoor sensible heat.
To remove indoor sensible heat: IEC water chiller OR IEC air cooler?
• Comparison based on real applications of IEC water chillers and IEC air coolers
To remove indoor sensible heat: IEC water chiller OR IEC air cooler?
Sensible heat removed by cold water (kW)
Electricity consumption of Fan of IEC chiller（kW)
Electricity consumption of water pump (kW)
Electricity consumption of Fan-coils(kW)
Water system COP to remove indoor sensible heat
219 13.8 14.9 19.2 4.6
Fresh air supply (m3/h)
Sensible heat removed by cooling air (kW)
Electricity consumption of IEC air cooler(kW)
Electricity consumption of supply air fan (kW)
Air system COP to remove indoor sensible heat
88000 169 13.5 28.3 4.05
Sensible heat removed by cold water (kW)
Electricity consumption of Fan of IEC chiller（kW)
Electricity consumption of water pump (kW)
Electricity consumption of radiant floor (kW)
Water system COP to remove indoor sensible heat
29.3 1.4 2.16 0 8.23
Fresh air supply (m3/h)
Sensible heat
removed by cooling air
(kW)
Electricity consumption of IEC air cooler(kW)
Electricity consumption of supply air fan (kW)
Air system COP to remove indoor sensible heat
8400 10.8 2.0 1.76 2.9
FCU
Building
FCU
FCU
FCU
Cold water
Indirect evaporative air cooler
air
outlet
Cooling fresh air
Indirect evaporative chiller
Indirect evaporative
chiller combined air
cooler
cooling fresh air
cold water
radiant floor
Building
Development of IEC water chillers• Present the innovative indirect evaporative cooling concept and the technology to produce cold water,
developed the first indirect evaporative chiller in 2005. Produces cold water with temperature lower than
outdoor wet bulb temperature and limit to outdoor dew point temperature.
0
5
10
15
20
25
30
35
40
19:4
0
19:4
0
12:5
0
18:4
0
12:1
0
20:1
0
13:0
0
17:4
0
12:2
0
17:0
0
21:4
0
19:0
0
23:4
0
16:5
0
22:0
0
22:4
0
15:2
0
10:1
0
14:5
0
9:50
14:3
0
19:1
0
10:4
0
15:2
0
20:0
0
10:1
0
14:5
0
19:3
0
13:0
0
20:4
0
15:2
0
20:0
0
10:3
0
15:1
0
19:5
0
14:1
0
18:5
0
23:3
0
Tem
per
atu
re(℃
)
Inlet dry bulb tempeature(℃)
Inlet wet bulb temperautre(℃)
Out water temperature (℃)
Inlet dew point temperature(℃)
Date and time for testing (2005.8.4~8.9, 2006.7.31~8.2, 2007.7.16~7.28 )
• Present the IEC water chiller combined air cooler processes, and developed the first device in 2008, produces cold
water with temperature lower than outdoor wet bulb temperature and cooling air with temperature more or less at wet
bulb temperature.
0
5
10
15
20
25
30
35
40
45
16:30
17:30
18:30
19:30
20:30
21:30
11:55
12:55
13:55
14:55
15:55
16:55
17:55
18:55
19:55
20:55
21:55
22:55
23:55
13:50
14:50
15:50
16:50
17:50
18:50
11:05
12:05
13:05
14:05
15:05
16:05
17:10
18:10
19:10
20:10
13:35
14:35
15:35
16:35
17:35
18:35
19:35
12:20
13:20
14:20
15:20
16:20
17:20
18:20
15:45
16:45
17:45
18:45
20:10
21:10
22:10
23:10
0:10
1:10
2:10
3:10
4:10
5:10
6:10
7:10
8:10
9:10
10:10
11:10
12:10
13:10
14:10
15:10
16:10
17:10
18:10
19:10
20:10
21:10
22:10
23:10
0:10
1:10
2:10
3:10
4:10
5:10
6:10
7:10
8:10
9:10
10:10
11:10
12:10
13:10
14:10
15:10
16:10
17:10
18:10
19:10
2 0 0 8 - 7-2 5 2 0 0 8 - 7-2 6 2 0 0 8 - 7-2 8 2 0 0 8 - 8-1 2 0 0 8 - 8-2
Tem
pera
ture
(℃)
7.21 7.22 7.23 7.25 7.26 7.27 7.28 7.31 8.1 8.2
outdoor dry bulb temperature
supply air temperature
outdoor wet bulb temperature
cold water temperature
outdoor dew point temperature
Testing date and time (2008)
• Different kinds of IEC systems design and optimization and final realized in real applications.
Applications of different IEC water chillers systems
Serial water cycle system using IEC water chiller, with FCUs as terminals.
FCU
Building
FCU
FCU
FCU
Cold water
Indirect evaporative air cooler
air
outlet
Cooling fresh air
Indirect evaporative chiller
Indirect evaporative
chiller combined air
cooler
cooling fresh air
cold water
radiant floor
Building
Parallel water cycle system using IEC water chiller, with FCUs as terminals.
IEC water chiller combined air cooler system All fresh air system using IEC water chiller
IEC water chiller system using radiant floor as terminals
• IEC water chillers, mainly applied in northwest of China, totally more than 2,000,000m2, as the cooling source for large public buildings, instead of mechanical chillers.
Applications of IEC water chillers
Shihezi Kairui Hotel，2005，3000m2;
International exhibition center，2008~2010, 110767㎡
Hospital ，2009, 25195.6 ㎡
Office building，2014,
7668 ㎡
Hospital，2007, 46093 ㎡
Hospital ，2012, 49200 ㎡
Sports field，2014, 75146 ㎡
Art Center，2017, 78219㎡
Theater，2015, 28654㎡
Office Building，2015, 190000㎡
Detection Building, 2018, 452000㎡
High Speed railway
station，2015, 99982 ㎡
Industry cooling system
Countries in Europe:
North France,
Germany, Holland,
most part in Russia
North of Africa
Australia
West of the U.S.,
South west of
Canada
Asia: North west of
China, Mongolia, Saudi
Arabia, Kazakhstan,
middle of india
The preliminary performance analysis of IEC technology applied in the world
The preliminary performance analysis of IEC technology applied in the world
• Take the IEC technology to produce cooling water, called IEC chiller for example, the outlet water temperature is shown as the right figure.
16
IEC Technology
Huge potential to use IEC technology to substitute mechanical cooling and
significantly reduce the energy use for cooling. 17
IEA-EBC Annex 85 : Indirect Evaporative Cooling
ANNEX 85
• IEA EBC Annex 85: Indirect Evaporative
Cooling
• Operating Agent: Xiaoyun Xie, Tsinghua
University
• Participating countries: Australia, Belgium,
China, Denmark, Egypt, France, USA.
• Project period: 2020-2025
• Main objective: study the feasibility and provide
the roadmap of using indirect evaporative cooling
technology in different dry regions of the world.
IEA-EBC Annex 85 : Indirect Evaporative Cooling
Subtask A
Subtask B
Subtask C
Subtask D
IEA-EBC
Exco meeting
Approved as
Annex 85
13th Nov 2019 20th April 2020 26th June 2020
EBC project Concept
Determine to develop a
full proposal
The first workshop
Determine the subtasks
and the participants of
each subtask
Australia, Belgium, China,
Denmark, France,
United States
Full Annex proposal
Preparation (draft Annex text)
11th June 2020
Technology Readiness
Preliminary Assessment
Online workshop
• Exchange current
study related to IEC
• Activate preparation
phase
One-year preparation
phase starting in
July 2020
11th September 2020
IEA-EBC Annex 85 Online Workshop : Indirect Evaporative Cooling
ANNEX 85
For all year industry cooling, such as data center cooling, to increase free cooling hours:
• Indirect Evaporative chillers for all year free cooling, with design of high temperature cold water;
• Indirect Evaporative Chillers combined with mechanical chillers, with design of low temperature cold
water;
• In very cold winters, using Indirect Evaporative Chillers to realize zero freezing.
0 0.005 0.01 0.015 0.02 0.025 0.030
10
20
30
40
50
t(°C
)
d(kg/kg.air)
100%
O
P0=101.325 kPa
(to,do)
tw,r
tw
tw,1tw,sp
(tdp,o,do)
A
E
Summer condition process
winter anti freezing process Real testing of no freezing process
Freezing of common cooling towers
Free cooling hours of different systems
Indirect Evaporative cooling towers
Indirect Evaporative Cooling used in Data center cooling
Conclusions
• Indirect Evaporative Cooling technologies would be one of promising
technologies to substitute common mechanical chillers, with no CFCs, to
meet the cooling demand without increasing electricity consumption and
carbon emission;
• IEC technologies have been researched, developed and applied in some
of the dry regions of the world, however not very widely, which need to be
pay more attention and finally to give solutions to promote the applications.
• IEC water chillers could be also used in industry cooling, such as data
centers, to save electricity consumption, as well as to avoid ice for
common cooling towers in cold seasons.
