Post on 10-Apr-2022
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.