Kim Choon Ng,Water Desalination and Reuse Center,

King Abdullah University of Science & Technology,

Saudi Arabia

Approaches to Energy Efficiency in

Air Conditioning: Processes and

Thermodynamics

INTRODUCTION

Increasing demand for air conditioning (AC) cooling - CAGR of 4.5% over

past decades, particularly in China, South & South-East Asia:- driving

factors: (i) Population growth rate and (ii) Increasing disposable income in many developing economies

World electricity consumption for AC cooling increases by 3 folds since

2010,- In 2018, AC cooling in China exceeds that in US and whole Africa, AC units

sold annually peaked at 50+ million,

IEA projection of Energy consumption by AC Availability of AC versus Income (per month)

China

2018

2000

INTRODUCTION

Year

Electricity

consumption for

Cooling (TWh/yr)

No of folds

(BAU)

World Annual

Electricity

consumption

(TWh/yr)

Percentage of

world consumption

to cooling (%)

CO2 emission from

cooling

(Gton / year)

2000 300 1 13,200 2.25 0.173

2015 815 2.71 21,240 6.8 0.479

2050 6200 20.6 31,440 19.7 4.022

2100 53,300 177 198,600 26.834.5

8

Assumption: This is a Business-as-usual (BAU) scenario for energy consumption forecast. The efficiency

of chillers remain unchanged over the forecast period.

Total AC cooling energy consumption is 37% in non-OECD countries, 35% in the

Americas, 17% in Europe.

Energy intensive refrigerant-based MVC cycle – > 0.9 ±0.05 kW_elec/Rton and it

has stagnated at to 0.85±0.3 kW/Rton – only marginal improvements from heat

exchangers and refrigerants.

Improving Energy Efficacy requires a Paradigm Change

• Energy Efficiency (the kW/Rton) of MVCs have stagnated since,

0.85±0.05 kW/Rton,

• The “Thermal Lift” in treating the moist outdoor air (OA), i.e., operating

between dew point of air (evaporator) and ambient temperatures in a

single coil (condenser).

1970 1990 2010 2030

ARI Rating “A” (5C/29.6C,

water cooled)

ARI Rating “B”

(5C/35C, Air-cooled)

1.0

0.5

1.5

kW/Rton

Year

Asymptotic trends

in energy efficiency

0.85

0.45

Thermal Lift

KAUST’s Cooling research for AC:-Emulating nature’s evaporative cooling

De-coupling of Qlatent to Qsensible in treating the moist air (previously

performed at evaporator):

(i) moisture removal by sorption uptake of adsorbent,

(ii) cooling of warm but dry air by indirect evaporation of water films

Minimized heat & mass transfer resistances across the thin-foil

between the dry and wet channels,

Exploiting the hydrophilic coatings on wall surfaces of wet sections

and optimized the purged ratio of air to enhance COPIEC.

Scaled modularly dry & wet pairs to meet capacity design.

Proposed Innovative Low-Energy Cooling Technology:

Return air

Win_DH

= 0.023

ωout_DH_IEC =

0.010± 0.001 kg/kg

Tdb-in

= 35o C

Tout= 20 to 22o C

RH80%

RH50%

Psychrometric process paths

humidification

Evaporative effect

on wet surfaces

𝒉𝒊𝒈𝒉𝒆𝒓 ∆T

lower ∆T

Temporal traces of a single generic IEC

cell (Tin = 41 oC, Tout = 23 oC, Q = 185 W, UIEC = 100±5 W/m2 .K)

“Tests conducted on a 0.8m length IEC

0

5

10

15

20

25

30

35

40

45

0 500 1000 1500 2000 2500 3000 3500

Te

mp

era

ture

(C

)

Time (sec)

Inlet DB DC_Outlet

D

H

Humidifier

De-humidifier

2 m3/hr

1 m3/hr

1 m3/hr

Dry chanel

Wet chanel

20

23

26

29

32

35

22 25 28 31 34 37 40 43 46 49

Pro

duct air D

B (

C )

Inlet air DB (C )

30% purge 40% purge 50% purge

47 44 41 37 34 31 28 25

30% purge 145.20 129.29 112.38 89.51 72.60 55.69 45.75 25.86

40% purge 159.12 142.22 124.32 101.44 82.55 64.64 50.72 29.84

50% purge 174.04 152.16 133.27 112.38 93.48 73.59 57.68 34.81

020406080

100120140160180200

Co

oli

ng

cap

acit

y (

watt

)

30% purge 40% purge 50% purge

1517192123252729313335

22 27 32 37 42 47 52

Pro

du

ct a

ir t

em

pe

ratu

re (

oC

)

Inlet air temperature (oC)

Performance of a single generic cell of SDIEC

purge 50%[experiment]purge 50%[simulation]purge 40%[experiment]purge 40%[simulation]purge 30%[experiment]purge 30%[simulation]

Dehumidification by adsorbent and

regeneration of adsorbent

Moisture removal from air stream by two major processes:

(i) liquid adsorbent such as LiCr solution with a heat source regeneration,

CoP < 1.0 due to high energy of latent evaporation

(ii) Solid adsorbent such as SiO2.nH2O (mesoporous at 700-800 m2/g

and pore diameters from 5 to 30 μm. Water vapor molecules are

desorbed from pore surfaces by resonance of molecules at 2.45 GHz of

μ-waves. CoP > 2.0 to 3.0

Honey-come coated adsorbent

structure at 1.8 to 2 mm pitch

Base structure of polyester or

paper structure up to 250 μm

Good adhersion of adsorbent

onto substract up to 40 μm.

Microwave desorption

𝑃𝑎𝑣𝑔 = 2𝑉𝜋𝑓𝜖𝑜 𝜀"𝐸𝑟𝑚𝑠

2

V Volume of work load (m3)

𝜖𝑜 free space or vacuum permittivity (F/m)

𝜀" Permittivity loss factor (imaginary part)

𝐸𝑟𝑚𝑠2 Average Electric Field Intensity

(V/m)

f Electromagnetic frequency (GHz)

Microwaves desorption: - a challenge

Temperature and mass transients under

microwave irradiation (Silica RD)

Simulation of the electric field

by magnetron

De-coupled processes: (i) Dehumidification

and (ii) sensible cooling

1st process 2nd process

Avoided Equipment of AC Plant

Combined DH (COP=3) and IEC (COP=30)

An example to demonstract the efficacy

of DH-IEC disruptive cooling technology

We examine the cooling demand of an Island state, Singapore.

Annual AC energy demand is about 37% of total electricity production

Most AC chillers are of the MVC of assorted sizes and district cooling share is 4.5% of total cooling load

Assume a realistic improvement to COP fro, 5 to 16

Case study of Singapore

Cooling Technology Perspective

• Base line year : 2016

• Annual total cooling load : 19,698.90 x 106 RT

• Comparison studies : 3 scenarios (BAU, MVC+DC(35% to 65%%),

MVC(20%)+DG-IEC (COP =16, 20)

• Cost of electricity : 0.18 $

• COP of MVC: 3.91

• DC(District cooling) efficiency: 0.83 kW/RT

• Current annual throughput of DC in Singapore : 894,396,000 RT(4.54%)

• IPCC conversion factor : 0.54288 t/MWh

Annual Throughput of DC: 894,396,000 RT (4.54% of annual total cooling load)

Installed capacity

Marina Bay Sands 25,600 RT

Changi Business park 37,500 RT

One-North: Biopolis, Mediapolis 28,0000 RT

Woodland Wafer Fab Park 11,000 RT

Energy scenario between BAU and

DH-IEC for Singapore

32,95831,370

1,5880

6,382

01,583

4,799

11,949

6,573

1,583

3,793 4,654

01,583

3,071

10,583

6,573

1,583 2,428

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(1

6)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(1

6)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(2

0)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(2

0)

BAU 0% MVC 20% MVC 0% MVC 20% MVC

DH-IEC COP 16 DH-IEC COP 20

Scenario I Scenario III

GW

h_

SP

E/y

ea

r

Annual primary energy consumption for cooling (GWh)

BAU (COP=4.5) =32,958 GWh/y

versus

Energy cost scenario between BAU

and DH-IEC for Singapore (2)

281267.6

13.50

54

0.013.5

40.9

102

56.1

13.532.4 40

0.013.5

26.2

90

56.1

13.5 20.7

0

50

100

150

200

250

300

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(1

6)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(1

6)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(2

0)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(2

0)

BAU 0% MVC 20% MVC 0% MVC 20% MVC

DH-IEC COP 16 DH-IEC COP 20

Scenario I Scenario III

Mill

ion

$/y

ea

r

Total primary fuel (NG) cost (mn$/y)

Water scenario between BAU and

DH-IEC for Singapore (3)

212,637197,019

15,6180

60,569

015,791

44,777

112,069

41,27835,396

35,396

89,554

0

44,777 44,777

112,069

41,27835,39635,396

0

50,000

100,000

150,000

200,000

250,000

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(1

6)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(1

6)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(2

0)

To

tal

MV

C(4

.5)

DC

(4.2

4)

DH

-IE

C(2

0)

BAU 0% MVC 20% MVC 0% MVC 20% MVC

DH-IEC COP 16 DH-IEC COP 20

Scenario I Scenario III

m3/d

ay

Total water consumption (m3/day)

Conclusion

A paradigm shift in AC technology is needed for achieving sustainable cooling future (with reduced CO2 and environment friendly cycle),

DH-IEC is one of the most plausible ways to a quantum EE improvement, significant savings up to 50% of energy consumption;

Other benefits include low capital cost, avoided extensive infrastructure,

Caveat:- DH-IEC addresses only space comfort of AC not other aspects such as refrigeration or low temperature cryogenics, etc.