Reducing cooling energy by system innovation

Yi Jiang

Operating agency of EBC Annex 59

Building energy Research center

Tsinghua University

IEA Annex 59 Low temperature heating & high temperature cooling

Where is the energy lost through cooling?

Indoor→ chilled water → chiller → cooling water → cooling tower → outdoor

2

0

5

10

15

20

25

30

35

40

-0.25 0 0.25 0.5 0.75 1 1.25 1.5

Tem

pera

ture

/o C

Heat q /W

Evaporation Temperature

Indoor temperature

Outdoor wet bulb temperature

Air in FCU

Chilled water

Condensing Temperature

Cooling water

ΔT1

ΔT2

ΔT3

ΔT7

ΔT5

ΔT

ΔT6

Q0.5Q

ΔT4

Tin, ωin Outdoor air

AHU

Evap

Cond

Com Thro

Te

Tc Cooling tower

Where is the energy lost through cooling?

The real demand for space cooling is just raising the heat Q for 3K from 25℃ indoor to 28 ℃ outdoor, the required work is 3Q [WK]

However the chiller does lift up the heat Q from 5 ℃ at the evaporator to 40 ℃ at the condenser, the actual work is 35Q [WK], as many as 11 times!

The additional 32Q have been paid for completing the heat transfer process as well as heat flux mixed with different temperature during the heat transportation process from indoor to outdoor

The other reason is that dehumidification required. To make moisture condensation, low temperature below dew point as the cooling source is needed

3

An Innovation of space cooling system Separate humidity control from temperature control: THIC

An independent air system added to remove latent heat for humidity control

Temperature can then be controlled by a high temperature cooling source (eg. 15℃ to 20℃) to remove sensible heat only

As sensible heat normally takes more than 70% of the total heat load, high efficiency cooling source can be used to remove sensible heat Underground water or underground heat exchanger if ground temperature is

below 15℃ Evaporate cooling can also provide cooling source if the dew point outdoor is

below 15℃ COP for compression chiller can be achieved at 9 ~ 10 comparing with 5~6 at

normal state

Reduce the temperature difference between indoor space and cooling source so to raise required cooling source temperatures as high as possible

Reduce the power of fans and pumps by improvement of the heat delivering system

4

Separate humidity control from temperature control (THIC) • Humidity control as well as indoor air quality: Dried

outdoor air • Temperature control: High temperature cooling source (or

low temperature heating source in winter)

5

Outdoor air processor

Summer: Cooling source Winter: Heat resource

Displacement vent

Personalized vent.

Radiant panel

Dry FCU

Air-conditioning devices Terminal

Control indoor humidity and CO2

……

Control indoor temperature

Dry air

……

Humidity control subsystem

Temperature control subsystem

Indoor environment

16~19°C

Operating principle of the THIC air-conditioning system

* Liu XH, Jiang Y, et al. Temperature and Humidity independent Control (THIC) of Air-conditioning System. Berlin: Springer Press, 2014

16℃

An Innovation of space cooling system

Sensible heat removal for Temp. control

In more than 40% of cooling applications in the world the outdoor dew point is below 15℃. Moisture can be removed by air exchange with outdoor. Space cooling is just to remove sensible heat

To raise the cooling source temperature for high efficiency cooling, the key approach is to reduce the Δt during heat delivering process Avoid the mixing loss of heat collection process at

indoor terminals Avoid Δt loss of heat exchange process Avoid the mixing loss of heat fluxes with different

temperature

6

Terminal handling process

Task: collecting heat and moisture from sources

7

Avoid mixing loss of heat collection process at indoor terminals!

Q Q

Tin

Heat sources

Mixing process

Transfer

T

Supply air

Supply water

Indoor stateTin, ωin

Indoor heat sources and moisture sources

Solar radiation

Indoor terminal

Terminal handling process

Heat sources with different temperatures

8

Heat sources’ temp. varying in the range of 26~40ºC, or even higher

平板电视flat-panel tv

message sign

Significant mixing loss from heat sources to indoor air

9

Direct solar radiation

9

Radiant floor surface (Tr)

QsTr Inner surface (Ts) QsTs

Indoor air (Ta)

5

10

15

20

25

30

35

0 10 20 30 40 50 60 70 80 90 100

Tem

pera

ture

/oC

Heat flux W/m2

QsTr

QsTs

Indoor air

Supply air

Chilled water Chilled water

Floor surface

10

5

10

15

20

25

30

35

0 10 20 30 40 50 60 70 80 90 100

Tem

pera

ture

/oC

Heat flux W/m2

Radiant floor Jet ventilation

①

②

①

②

③

Terminal handling process

> Simplify heat transfer process from heat sources to chilled water

10

Heat sources Radiant floor surface Chilled water

Heat sources Indoor air Chilled water Supply air

① ②

① ② ③

11 11

Terminal handling process

> Reducing indoor mixing loss > Decrease temperature gradient in space > Avoid fluid mixture of high temperature with low temperature

0 1000 2000 3000 4000

SystemII

SystemI

Floor radiantion

Floor convection

Floor heat conduction

Envelope convection

Mixture

Air-water convection

Entransy dissipation EnΦ (WoC/m2)

12 12

Terminal handling process

Jet supply air ~20m

~5m

Radiant floor

Displacement supply air

~20m

~2m

5

10

15

20

25

30

35

0 20 40 60 80 100 120 140 160

Tem

pera

ture

/oC

Heat flux W/m2

EnvelopeIndoor air

Supply airChilled water

Convective Entransy Dissipation

Mixture Entransy Dissipation

Convective Entransy Dissipation

Jet ventilation Radiant floor

5

10

15

20

25

30

35

0 20 40 60 80 100 120 140 160

Tem

pera

ture

/oC

Heat flux W/m2

Envelope

Indoor airDisplacement airRadiant floorChilled water

Radiant floor Displacement ventilation

Radiant Entransy

Dissipation

Convective Entransy Dissipation

Convective Entransy Dissipation

Mixture Entransy Dissipation

ConductiveEntransy Dissipation

13

Terminal handling process

13

0 1000 2000 3000 4000

SystemII

SystemI

Floor radiantion

Floor convection

Floor heat conduction

Envelope convection

Mixture

Air-water convection

Entransy dissipation EnΦ (WoC/m2)

> Total entransy dissipation of System II (2411 (W·ºC)/m2)) is less than

that of System I (3413 (W·ºC)/m2))

> Reduced entransy dissipation (1002 (W·ºC)/m2)) by system II equals to

rising 6.3ºC of chilled water temperature.

Entransy dissipation comparison

Terminals with low mixing loss Radiant panels, radiant floor, TABs

14

高さ：3000200間隔で計測

床面

放射パネル

空調室内機

2800Ceiling height：2.8mMeasuring Point：1.5m above floor

Radiant Panel

Indoor Unit

Floor Embedded radiant systems: a) Floor, b) Ceiling, c) Wall, d) TABS

Application

15

Terminal 3 of Xi’an airport Area: 258,000m2, with a maximum height of 36.5m Coming into service since May 2012

The first terminal adopting radiant cooling/heating in China Radiant cooling, displacement ventilation, liquid desiccant …

15

AC system (summer)

Large space area Stratified air conditioning in summer

16

辐射地板

分布式送风末端

渗风

建筑开口

顶部排风(排出高温高湿空气)

2 m

~ 20m

Radiant floor with high temp water

Dry air

Natural ventilation zone

Conditioned temp., low hum. zone Infiltration

Entrance

Displacement ventilation

17

Terminal handling process

1.1m

2.8m

12m

7.4m

1.7m

21.6m

17m

23.9℃

27.6℃

30.3℃

29.0℃

24.8℃

31.4℃

31.1℃

121m

1.1m

2.8m

12m

7.4m

1.7m

17m

1.1m

2.8m

12m

7.4m

1.7m

17m

West Wall

East Wall

Air

Displacement vent. 22.5℃

Displacement vent. 22.5℃

2m

Measured temperatures

Application

18

Radiant floor for cooling (without solar)

14

16

18

20

22

24

10:00

11:00

12:00

13:00

14:00

15:00

16:00

Time

Tem

pera

ture

℃) floor surface (no seat)

floor surface (under seat)

dew point

0

10

20

30

40

50

10:00

11:00

12:00

13:00

14:00

15:00

16:00

Time

Coo

ling

capa

city

(W/m

2 )

Temperatures Cooling capacity

(20~40W/m2)

Application Radiant floor for cooling (with solar) Solar radiation on floor: High intensity, transient process

19

0

40

80

120

160

200

Sola

r rad

iatio

n de

nsity

(W

/m2 )

Time (p.m.)

Point A11min

Point B24min

Point C31min

ABC

0

40

80

120

160

200

Coo

ling

capa

city

(W/m

2 )

Time

Point A Point BPoint C Point D (under chair)

18

20

22

24

26

28

Floo

r sur

face

tem

pera

ture

(°C

)

Time

Point A Point BPoint C Point D (under chair)

Cooling capacity could be higher than 100W/m2 with direct solar radiation

Application

20

T2:

Power consumption Significant energy conservation benefits

T2

T3

Application Radiant terminal in a solar house (Denmark)

21

Embedded pipes

Application Radiant terminal in a solar house (Denmark)

22

Operative temperature and external air temperature during the cooling season

0

5

10

15

20

25

30

35

Hea

t fl

ux

[W/m

2]

Floor cooling

Cooling capacity

Avoid Δt loss of heat exchange process

Direct connection of the cooling source with indoor terminals

Enlarge the heat transfer ability and adjust the flow rates at both sides so to ensure the Δt uniformed along the heat exchange process

23

Tc,out Tc,in

Th,in Th,out

Th,out

Tc,in

Th,in

Tc,out

T

Tc,in

Tc,out

Th,out

Th,in

x

T

Q

Th,in

Th,out

Tc,in

Tc,out

Unmatched flow rates

Avoid Δt loss of heat exchange process

4~5 K temperature difference for water circulation On-off control for each indoor terminal (radiative)

to obtain near linear control performance Careful design of the water piping system to avoid

large pump power consumed Remove most of control valves and other resistance device

in water loops except on-off control valve Pressure drop: 10~15 m H2O for total water loop circulation

24

× × On-off control

Case study

Evaporative cooling as cooling source Outlet water temperature 15~19℃ to remove sensible heat

25

M

Inlet air O

User heat exchanger 3

1

2

4

1

Exhaust air C

A

Cold water

Inlet air O

A

Tsp

T

• Key parts: countercurrent air cooler/packing tower • Design idea: matched flow rates and parameters

Case study

Evaporative cooling as cooling source

26

Installed in Shihezi Kai Rui Building, now four years well-running.

Shihezi outdoor design air state: dry bulb 32.8℃, wet bulb 21.5 ℃. Designed water out temperature 18.5 ℃, cooling Energy output 120kW.

Case study

Evaporative cooling as cooling source

27

0

5

10

15

20

25

30

35

4019:40

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

pera

ture

(℃)

Inlet dry bulb tempeature(℃)Inlet wet bulb temperautre(℃)Out water temperature (℃)Inlet dew point temperature(℃)

Out water Temperature lower than inlet Wet Bulb Temperature.

Tested COP (sensible heat removed/power of fan and pump) higher than 10.

Case study

Evaporative cooling as cooling source Applications in the dry region (Xinjiang province, China)

28

Shihezi Kai Rui Building

Aksu People’s Hospital Xinjiang Chinese Medicine Hospital

Xinjiang Medical University Hospital

Xinjiang air force hospital

Office building of Xinjiang medicine hospital

Changji medicine hospital

Xinjiang international exhibition center

Suitable region for evaporative cooling

Climate condition: dew point ≤15℃ System requirement: Low Δt loss terminals with on-off control Large water circulation with minimal pressure drop

29

Division: Outdoor Humidity

Ratio: 12g/kg

West China West U.S.

Suitable region for evaporative cooling

Climate condition: dew point ≤15℃

30 Outdoor Humidity Ratio (g/kg)

North Europe

0

10

20

30

40

50

60

0 0.005 0.01 0.015 0.02 0.025

含湿量 /(kg/kg)

温度

/o C OO

RS

转轮除湿

溶液除湿

冷凝除湿

R

S

ω

T

Efficient dehumidification process

Weak point of dehumidification by condensation: Require the cooling source below dew point Reheat, or mix with higher temperature environment

31

For moist region: humidity control is part of the task in space cooling

New approaches for dehumidification are required!

Reheating

Conventional desiccant wheel

Efficient dehumidification process

New approaches for dehumidification Liquid desiccant dehumidification

32

Fresh air Supply air

Return air Exhaust air

Throttle

Condenser

Evaporator

Compressor

Two-stage total heat recovery

Multi-stage process for dehumidification, matched parameters

Efficient dehumidification process

New approaches for dehumidification Liquid desiccant dehumidification

33

Close to the iso-relative humidity line instead of isenthalpic line

Efficient dehumidification process

New approaches for dehumidification Liquid desiccant dehumidification

34

Cooling Dehumidify

Deep Dehumidify Total Heat Recovery

Humidify

Fresh air t (°C) 36.0 22.8 22.8 35.9 6.4 4.3

Fresh air d (g/kg) 24.6 8.6 8.6 26.7 2.1 1.6

Supply air t (°C) 17.3 16.1 11.9 30.4 22.5 25.6

Supply air d (g/kg) 8.6 5.1 3.4 19.5 7.2 10.7

Return air t (°C) 26.0 33.2 26.3 26.1 20.5 22.1

Return air d (g/kg) 12.2 18.3 16.3 12.1 4.0 5.1

Exhaust air t (°C) 39.1 43.9 42.2 32.6 7.0 6.6

Exhaust air d (g/kg) 37.3 23.4 24.1 20.3 2.7 2.9

COP 5.00 2.32 1.74 62.5% 6.2 4.6

Efficient dehumidification process

New approaches for dehumidification Solid desiccant dehumidification (DESICA, Japan)

35

压缩机

排风

回风

新风

送风

compressor SA

RA

FA EA

Heat pump utilized for internal cooling in dehumidification

Efficient dehumidification process

New approaches for dehumidification Solid desiccant dehumidification (DESICA, Japan)

36

fresh air

return air

exhausted air

supplied air

Freshair

return air

exhausted air

Suppliedair

heat exchangers glued with silica-gel

heat exchangers glued with silica-gel

after a period：• Four-way valve changes direction• Air valves change direction

Return air

Supply air

Exhaust air

Supply air

Outdoor air

Return air

Outdoor air

Return air

FA

RA

SA

EA

100%

60%

20%

40%

80%

15

20

25

30

35

40

45

5 10 15 20 25ω(g/kg)

T (℃

)

A typical process

Close to the iso-relative humidity line instead of isenthalpic line

COP is as high as 4.0

37

Application——Liquid desiccant

37

Temperature and Humidity Independent control system

Cooling water pump

Outdoor air

Outdoor air processor

Supplied air

Return air Exhaust air

Cooling tower

Chiller Chilled water pump

FCU & radiant panel

1st floor

4th floor

2nd floor

3rd floor

Outdoor air processor 17ºC

37

38

Application——Liquid desiccant

Outdoor air process Chilled water process

Entire system

OAHU Fan Chiller Chilled water pump

Cooling water pump

Cooling tower

Fan Coil Unit

Cooling capacity

/kW 773.0 446.1 1219.1

Energy consump

/kW 166.9 20.0 52.5 30.6 14.6 3.7 19.4 307.7

COP 4.3

(OAHU=4.6) 3.7

(Chiller=8.5) 4.0

39

Application——Liquid desiccant

0

15,000

30,000

45,000

60,000

75,000

90,000

105,000

Apr May Jun Jul Aug Sep Oct

Annual power consumption: 32kWh/(m2 AC area) Common building in Shenzhen: ~50kWh/(m2 AC area) Energy saving: ~30%

Pow

er c

onsu

mpt

ion

/kW

h

40

Application——DESICA

Office building in Japan DESICA for humidity control and VRF for temp. control

41

Application——DESICA

Office building in Japan DESICA for humidity control and VRF for temp. control

42

Application——DESICA

DESICA for humidity control and VRF for temp. control

0.00 0.05 0.10 0.15 0.20 0.25

THICSystem

ConventionalSystem

Average Daily Energy Consumption（ｋWh/m2・day)

Ventilation Fan

HP Desiccant Compressor

Ventilation Standby PowerRequirement

Inner Unit of VRF

Outer Unit of VRF

VRF Standby PowerRequirement

-46.5%

0.00 0.05 0.10 0.15 0.20 0.25

THICSystem

ConventionalSystem

Average Dayly Energy Consumption（ｋWh/m2・day)

Ventilation Fan

HP Desiccant Compressor

Ventilation Standby PowerRequirement

Inner Unit of VRF

Outer Unit of VRF

VRF Standby PowerRequirement

-47.4%

Set temperature is 28℃

Set temperature is 26℃

THIC applications in China

43

Dry area: Indirect evap. cooling

Wet area: Dehumidification solution

THIC applications in China: Over 10 million m2 buildings

since 2006

How much energy can be saved? Office building in dry climate Conventional system for cooling: electricity used 50 kWh/㎡，

Total cooling: 100 kWh/㎡, COP=2, fans: 17kWh/㎡, pumps: 11kWh/㎡, chiller:22kWh/㎡

Evaporate cooling with the innovative system: electricity used 23kWh/㎡, 54% saved

Total cooling 100 kWh/㎡, COP=5, fans:8kWh/㎡, pumps: 15kWh/㎡

Office building in moist region Conventional HVAC system for cooling: electricity used 65kWh/㎡

Total cooling:130 kWh/㎡，COP=2, fans:22kWh/㎡, pumps:14kWh/㎡, chiller:29kWh/㎡

THIC system: electricity used 44kWh/㎡, 32% saved Total cooling:130kWh/㎡, dehumidifier with fan: 14kWh/㎡,

pumps:15kWh/㎡, chiller:15kWh/㎡ Latent heat:35kWh/㎡，COPL=2.5, sensible heat:95kWh/㎡，COPs=3.2

44

Conclusion Huge potential saving in space cooling technology! Dry regions, ~40% of current cooling applications

Direct/indirect evaporative cooling instead of mechanical chillers System should be well designed both for indoor terminal and heat

delivering to adapt “high temperature cooling” More than 50% energy can be saved!

Moist regions: east China and US, Japan, south India Humidity should be treated independently with temperature Desiccant humidity control techniques should be applied for

dehumidification Sensible heat should be removed with high temperature cooling

source About 30% saving can be achieved!

45

IEA EBC Annex 59

High Temperature Cooling & Low Temperature Heating In Buildings (2012-2016)

46

This presentation is the summary of EBC Annex 59: High temperature cooling & low temperature heating in buildings

47

For more information: jiangyi@mail.tsinghua.edu.cn

Reducing ΔEn in HV&AC system

2. Coupled Temp. & Humid. control Conventional system: coupled control of indoor Temp. & Humid. ~7ºC chilled water is required for cooling & dehumidification

49

0

5

10

15

20

25

30

35

40

-0.25 0 0.25 0.5 0.75 1 1.25 1.5Heat /W

Tem

pera

ture

/o C

Indoor temperature

Outdoor wet bulb temperature

Air in FCU

Chilled water

Evaporating temperature

Condensing temperature

Cooling water

ΔT 1

ΔT 2

ΔT 3

ΔT 4

ΔT 6

ΔT CH

ΔT 5

Q0.5Q

ΔTHP

0

5

10

15

20

25

30

35

40

-0.25 0 0.25 0.5 0.75 1 1.25 1.5Heat /W

Tem

pera

ture

/o C

Condensing temperature

ΔT CH, high T

Q0.5Q

Indoor temperature

Outdoor wet bulb temperature

Air in FCUChilled water

Evaporating temperature

Cooling water

Conventional system THIC system (for Temp. control) Adopting other approaches for Humid. control

ΔEn is significantly reduced for Temp. control in the improved system

49

50

Application in buildings——Data center

50

Conventional system 测试机架Racks

Return air

Rack

HEX

Q Q

Q

Tchip

Q Tcoldsource

Tout

Tin Treturn

Tsupply

Tex

Air flow

Outdoor Environment

Temperature

Heat

Entransy dissipation of rack cooling process

Entransy dissipation of air mixing process

Entransy dissipation of heat exchanging process

Entransy dissipation of heat

flow into outdoor environment

50

Application in buildings——Data center

Internal cooled new system

Server 1

Server 2

Server N

LHP2

LHP 1

Rack intake air(Room temperature)

Rack exhaust air(Room temperature)

Server intake air Server exhaust air

Liquid pipe 2 Steam pipe 2

Liquid pipe 1

Steam pipe 1

LHP 1LHP 2Chilledwater in

Chilledwater out

Room temp Rack temp distribution

Tem

p

℃

51

Compressor power

kW

Fan power

kW

Server power

kW

EER

Indoor air temp ℃

Evaporative temp℃

Supply/ Return air

temp℃

Rack inlet/exhaust air temp ℃

Outdoor air dry/wet bulb

temp ℃

January 2nd

16.8 4.5 58 2.7 23.5 8.7 14/24 24/33 6 / 0.2℃

May 7th 18.0 4.2 56 2.5 24.6 8.5 15/25 24/33 22 /13℃

August 10th

21.0 4.6 58 2.3 25.0 8.2 14/25

25/34

29 /19℃

Cooling tower kW

Chiller 1 power

kW

Chiller 2 power

kW

Pump power

kW

Rack fan kW

Server power

kW

EER

Indoor air temp ℃

Supply/Return water temp ℃

Rack inlet/exhaust air temp℃

January 2nd

2.2 0 0 2 2.9 58 8.2 23.5 9.5/18 23.8/24.2

May 7th 2.2 7.6 0 2 3.1 58 4.0 24.6 12.5/21 24.9/25.3

August 10th

0 6.4 6.8 2 3.1 59 3.2 23.0 9.2/19 23.2/23.8

Former CRAC

Current distributed cooling Former：rack exhaust T=indoor T +9℃ Current：rack exhaust T≈indoor T

52

Compressor power

kW

Fan power

kW

Server power

kW

EER

Indoor air temp ℃

Evaporative temp℃

Supply/ Return air

temp℃

Rack inlet/exhaust air temp ℃

Outdoor air dry/wet bulb

temp ℃

January 2nd

16.8 4.5 58 2.7 23.5 8.7 14/24 24/33 6 / 0.2℃

May 7th 18.0 4.2 56 2.5 24.6 8.5 15/25 24/33 22 /13℃

August 10th

21.0 4.6 58 2.3 25.0 8.2 14/25

25/34

29 /19℃

Cooling tower kW

Chiller 1 power

kW

Chiller 2 power

kW

Pump power

kW

Rack fan kW

Server power

kW

EER

Indoor air temp ℃

Supply/Return water temp ℃

Rack inlet/exhaust air temp℃

January 2nd

2.2 0 0 2 2.9 58 8.2 23.5 9.5/18 23.8/24.2

May 7th 2.2 7.6 0 2 3.1 58 4.0 24.6 12.5/21 24.9/25.3

August 10th

0 6.4 6.8 2 3.1 59 3.2 23.0 9.2/19 23.2/23.8

Former CRAC

Current distributed cooling EER：Increased from 2.6 to 5.7 PUE: Decreased from 1.6 to 1.35

53