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A nancial feasibility evaluation of using evaporative cooling with air-conditioning
(in hybrid mode) in commercial buildings in India
Varun Jain, S.C. Mullick, Tara C. Kandpal
Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
a b s t r a c ta r t i c l e i n f o
Article history:
Received 22 March 2012
Revised 2 November 2012Accepted 4 November 2012
Available online 19 December 2012
Keywords:
Hybrid system
Direct evaporative cooling
Payback period
Life cycle cost
Net present value
Results of a preliminaryanalysisto study thenancial feasibility of a hybrid mode operation of a direct evaporative
cooler(DEC) with an airconditioning (AC) unit to reduce theannual expenditureon electricityusage(as against a
standalone AC unit to provide almost similar level of comfort) are presented. Four different building applications
located in four different cities of India have been considered in the study. The hybrid mode operation is found
nancially attractive for movie theater and waiting hall building applications for all the climatic conditions consid-
ered in the present study.
2012 International Energy Initiative. Published by Elsevier Inc. All rights reserved.
Introduction
The need and use of air-conditioning are rapidly increasing in
urban India and normally vapor compression systems are beingused for this purpose. As a consequence the electrical consumption
for air-conditioning is also increasing at a rapid rate. It is therefore
imperative to develop and implement practically feasible alternative
options that can provide acceptable levels of comfort with relatively
lower electricity consumption. For commercial buildings, use of direct
evaporative cooling based systems in a hybrid mode with conven-
tional vapor compression based air-conditioning systems during hot
and dry months of the year is one such possibility. Besides the opera-
tional issues of a hybrid system, the primary consideration in making
a choice for the hybrid system as against a standard vapor compres-
sion based air-conditioning system would concern the nancial
viability of increased capital investment (higher cost of a hybrid sys-
tem consisting of both the vapor compression air-conditioning (AC)
system as well the direct evaporative cooler (DEC) as against its
lower overall cost of operation due to lower electricity consumption
of the hybrid system as against that of a standalone AC unit for
satisfaction of the same demand). The approach and the results of
an attempt to study the nancial feasibility of an investment in a
hybrid (AC+DEC) system as compared to a standalone AC system
are presented in this paper for four Indian cities.
Four cities in India namely Akola (hot and dry climate), Bangalore 1
(temperate climate), Delhi (composite climate) and Indore (composite
climate) were considered for the study. Though the sites of Delhi and
Indore are in the same climatic zone, but being in different regions
their ambient conditions differ considerably and hence also the room
conditions (Hindoliya, 2005). Building application congurations con-sidered include (i) high density ofce (with high internal loads due to
occupancy, lights, computers etc.), (ii) low density ofce, (iii) movie
theater and (iv) waiting hall. The external and internal input parame-
ters toTRNSYS (2005)for these buildings are presented inTable A1of
the Appendix (Jain, 2010). In the case of the standalone AC unit the
room temperature is set at 26 C and RH70%. Since with the use of a
direct evaporative cooler (DEC) the attained room conditions change
with ambient conditions, a range of room temperatures and relative
humidity values are considered as set points (27.1 C, 70%; 27.6 C,
60%; and 28.1 C, 50%) (Jain, 2010). A systematic procedure (Fig. 1)
was followed for estimating the electricity requirement for maintaining
the desired comfort level in the chosen building congurations at the
four selected locations. TRNSYS (2005) was used to simulate the
rooms/buildings. The fractions of time during the year when cooling is
needed and a DEC can provide the acceptable comfort were estimated.
The results obtained are summarized inTable 1.
Analysis
The hybrid system considered in the system consists of a DEC unit
along with the AC unit arranged in a manner that whenever the
required comfort is not achieved with the DEC unit, the AC unit is
switched on and DEC unit is switched off. The AC unit considered in
the study is a split air cooled system with indoor and outdoor units
interconnected with refrigerant piping and its cost includes the cost of
refrigerant piping, cost of air distribution system and standard control
Energy for Sustainable Development 17 (2013) 4753
Corresponding author. Tel.: +91 11 26591262.
E-mail address:[email protected](T.C. Kandpal).1 New name for city of Bangalore is Bengaluru.
0973-0826/$ see front matter 2012 International Energy Initiative. Published by Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.esd.2012.11.002
Contents lists available at SciVerse ScienceDirect
Energy for Sustainable Development
http://-/?-http://dx.doi.org/10.1016/j.esd.2012.11.002http://dx.doi.org/10.1016/j.esd.2012.11.002http://dx.doi.org/10.1016/j.esd.2012.11.002mailto:[email protected]://dx.doi.org/10.1016/j.esd.2012.11.002http://www.sciencedirect.com/science/journal/00000000http://www.sciencedirect.com/science/journal/00000000http://dx.doi.org/10.1016/j.esd.2012.11.002mailto:[email protected]://dx.doi.org/10.1016/j.esd.2012.11.002http://-/?-http://-/?-8/10/2019 A financial feasibility evaluation of using evaporative cooling with air-conditioning.pdf
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components (suppliedwith the AC unit). The annual costof maintenance
of the AC unit is essentially denedby thecost of its annual maintenance
contract that includes all required spares, consumables, refrigerant gas
and oil etc. as well as all scheduled and unscheduled maintenance visits.
The cost of the hybrid system includes the cost of the DEC unit,
variable frequency drive, and cost of air distribution system and control
unit as well as the cost of the AC unit. Consequently, the annual cost of
maintenance of hybrid system comprises the cost of annual mainte-
nance contract for the AC unit, the DEC unit, variable frequency drive
and the control unit.
The annual cost of operation of an AC unit is essentially de ned by
the cost of electricity consumed in its operation, while for the hybrid
system it should include both the cost of electricity consumed as well
that of water used in the DEC unit.The annual operating cost of a standalone AC unit during its rst
year of operation can be estimated as the product of annual electricity
consumption (in kWh) for standalone AC unit (AECac) and the unit
price of electricity (Upe) for the user during the rst year. If the unit
cost of electricity is expected to escalate at annual rate (in fraction)
resc, the annual operating cost of the AC unit (AOC-ACj) in jth year
of its useful life can be estimated as
AOCACj AECac Upe
1 resc
j1: 1
Cumulative present value of the life cycle operating cost of thestandalone AC unit (PVLCCac) with a useful life of n years can be
estimated as
PVLCCacAECac Upe
dresc
11 resc
1 d
n 2
where d represents the discount rate.
Similarly, the cumulative present value of the operating cost of the
hybrid system (PVLCChybrid) can be expressed as
PVLCChybrid AEChyb
Upe
dresc
11 resc
1 d
n
3
where, AEChybrepresents the annual energy consumption (in kWh) of
the hybrid system. As mentioned earlier, the annual maintenance cost
of the hybrid (DEC+AC) system (AMChyb) essentially comprises of the
annual maintenance costs of the vapor compression air-conditioning
(AC) system (AMCac), of the direct evaporative cooler unit (AMCdec), of
the VFD (AMCvfd) and that of the control (AMCcontrol). Thus
AMChyb AMCac AMCdec AMCvfd AMCcontrol: 4
If it is assumed that the overall annual cost of maintenance of
the hybrid system escalates at an annual rate (in fraction) jesc, the
cumulative present value of its annual costs of maintenance during
its useful life (PVCOMhybrid) can be expressed as
PVCOMhybrid AMChyb
djesc 1 1 jesc
1 d
n
: 5
In order to facilitate a comparison of the nancial attractiveness
of a hybrid system with a standalone vapor compression type AC
system, the values of life cycle and levelized annual costs, as well as
simplepayback period and net present value of incremental investment
on the hybrid system have been calculated, for all the four building
applications in the cities of Akola, Bangalore, Delhi and Indore.
The life cycle cost (LCC) is estimated as the total sum of the capital
cost, and the cumulative present value costof operation andmaintenance
during the life cycle of theproject. The levelized annual cost is the sum of
theannualized capital cost andthe levelized annualcost of operation and
maintenance. The levelized annual values of the cost of operation and
maintenance have been estimated by rst calculating the equivalentpresent value life cycle costs and then redistributing the same over the
useful life by using the capital recovery factor. Such a procedure allows
Selection of building application
Use of TRNSYS for calculation of cooling load for each
building application, for the city considered
Estimating the supply conditions and air change rate of
DEC to achieve best possible room conditions,using a
computer program developed for this purpose
Supply conditions and airchange rate calculated in the
previous step are used as inputs in TRNSYS for
respective building applications to determinethe room
conditions
DEC can provide comfort, if the room conditions is
acceptable for that particular hour, otherwise the AC is
needed
Total energy consumed in the hybrid mode operation (AC
and DEC)is compared with the energy consumed if
standalone AC is operating for all hours that require cooling
during the year
Fig. 1.Schematic diagram of the procedure for estimation of energy savings with the
use of hybrid system.
Table 1
Potential of using direct evaporative cooler unit and corresponding annual electricity savings.
Building Application Fraction of time DEC can be used for demand satisfaction Annualamount of electricity savedwith theuse ofhybrid system(kWh)
Akola Bangalore Delhi Indore Akola Bangalore Delhi Indore
High density ofce 0.56 0.88 0.37 0.65 5600 6100 1900 4500
Low density ofce 0.57 0.83 0.37 0.65 3000 4000 1300 3100
Movie theater 0.53 0.79 0.35 0.61 13,600 7100 3800 8800
Waiting hall 0.43 0.55 0.31 0.55 11,700 6700 3700 8500
Notes: (i) hours of operations of AC unit and DEC unit in a hybrid system are presented in Table A2of the Appendix.
(ii) Capacities of AC unit and DEC unit are indicated inTable A3of the Appendix.
48 V. Jain et al. / Energy for Sustainable Development 17 (2013) 4753
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internalization of any annual escalation in the cost of operation and
maintenance.
The NPV of incremental investment required for the hybrid sys-
tem essentially takes into account, the incremental costs of hybrid
unit (both capital as well maintenance costs) as well as the monetary
savings due to reduced electricity consumption. The simple payback
period is determined as the length of time required to recover
the incremental investment on DEC, VFD and controls through the
net monetary savings due to reduced electricity consumption while
using a hybrid system.
Assumptions and input parameters
Effective value of unit price of electricity to the user
Since most of the commercial buildings use diesel generating
(DG) set(s) to meet the electricity requirements during periods of
unavailability of grid electricity, the weighted average of the cost of
grid electricity and the cost of electricity from the DG set(s) has been
used as the unit cost of electricity to the user. In this study, it assumed
that, on an annual average basis, the grid electricity is available for
60% time of the year at a price of Rs 6.00 per kWh 2 and the remaining
40% of the time DG Set based electricity is used at an estimated price
of Rs 11.00 per kWh. Thus a weighted average value of Rs 8.00 per
kWh (=6(0.6)+11(0.4)) is obtained. An annual increase of 5% in the
weighted average value of the unit price of electricity for the user is
also internalized in the calculations.
Useful life
The expected useful life of the AC unit as well as that of the
DEC unit is assumed to be 15 years with the provision of an annual
maintenance contract.
Cost of annual maintenance contract for AC and DEC units
Based on detailed discussions with the manufacturers and suppliers
of both the AC and DEC units inthe country,the cost of AMC isestimated
at 10% of the total capital cost with an annual increase of 5% from the
base year value.
Cost of air distribution system
Air distribution system includes sheet metal duct, exible connec-
tion, volume control dampers, supply/return air diffusers, exhaust air
grilles etc. Using the cost estimates received from the manufacturers
and suppliers (Table 2) the following cost function is obtained for the
cost of air distribution system (Cads) in Indian Rupees as a function of
the air ow rate (AFR) in cubic meter per minute.
Cads 2752:6 AFR 0:6861
6
Capital cost of AC unit
The cost estimates as obtained from manufacturers for different
capacity split air cooled type AC units are presented inTable 3.
Capital cost of direct evaporative cooling unit
An air washer type direct evaporative cooling (DEC) unit used in
commercial buildingsis considered in the present study. It typically con-
sists of a centrifugal fan and motor assembly, isolators, lters, humidi-
cation media (cellulose pad), GI water tank, FRP header for the water
distribution, and an appropriate sized pump to re-circulate the water.
The cost estimates of DEC units as a function of airow rate as obtainedfrom the manufacturers and suppliers are presented in Table 4. The
following cost function is obtained for the capital cost of the DEC (C dec)
in Indian Rupees as a function of the air ow rate (AFR) using the data
presented inTable 4.
Cdec 466:1 x AFR 0:9792
: 7
Discount rate
A discount rate of 12% is used in the study.
Cost of variable frequency drive (VFD) and controls
Based on the inputs received from the manufacturers the cost of
VFD and cost of controls is assumed to be Rs. 25,000 each.
Results and discussion
Using the numerical values of input parameters presented in
Assumptions and input parameters section, the values of life cycle
cost (LCC), levelized annual cost, as well as the simple payback period
(SPP) and NPV of incremental investment on a hybrid system have
been calculated. The results are presented in Table 5 and a brief
discussion on the results is presented in the following paragraphs.
It is observed, that in Indore the hybrid system is nancially
attractive for high density ofce, movie theater and waiting hall and
not for the low density ofce. This may be attributed to a relativelylow value of LCC of a standalone AC unit in the low density ofce.
2
US $1=Indian Rupees (Rs) 45.50 in October, 2010.
Table 2
Dependence of cost of air distribution system on the ow rate.
Air ow rate
(in cubic feet per minute)
Air ow rate
(in cubic meter per minute)
Costa of air distribution
system (Rs)
1000 28 27,050
2000 57 44,400
3000 85 58,550
5000 142 81,450
a Values of various costs quoted in the paper pertain to year 2010 (US $1=Rs 45.50
in October, 2010).
Table 3
Costs of split air cooled AC units.
Capacity of AC unit (TR) Cost of AC unit (Rs)
3.0 48,000
5.5 78,000
8.5 110,000
11.0 145,000
17.0 210,000
22.0 280,000
Table 4
Capital cost of direct evaporative cooler (DEC) units (air washer type).
Capacity of DEC unit
(cubic feet per minute)
Capacity of DEC unit
(cubic meter per minute)
Cost of DEC unit
(Rs)
2500 71 30,000
3000 85 36,000
5000 142 60,000
10,000 283 120,000
15,000 425 172,500
20,000 567 230,000
25,000 708 287,500
30,000 850 345,000
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Table 5
Measures ofnancial attractiveness for all the four building applications in Akola, Bangalore, Delhi and Indore.
Unit Akola Bangalore Delhi Indore
AC system Hybrid system AC system Hybrid system AC system Hybrid system AC system Hybrid system
(A) High density ofce
Life cycle cost 1000 Rs 1165 1002 750 543 739 823 746 674
Levelized annual cost 1000 Rs 171 147 110 80 108 121 110 99
Simple payback period
(of incremental investment)
Years 3.6 3.3 42 6
NPV (of incremental investment) 1000 Rs 163 207 84 73
(B) Low density ofce
Life cycle cost 1000 Rs 680 710 551 489 535 658 547 565
Levelized annual cost 1000 Rs 100 104 81 72 79 97 80 83
Simple payback period
(of incremental investment)
Years 14.5 6.1 Not feasible 12.2
NPV (of incremental investment) 1000 Rs 30 62 123 18
(C) Movie theater
Life cycle cost 1000 Rs 3012 2329 1107 906 1979 1967 1625 1321
Levelized annual cost 1000 Rs 442 342 162 133 291 289 239 194
Simple payback period
(of incremental investment)
Years 1.1 4 8.7 2.9
NPV (of incremental investment) 1000 Rs 684 201 12 304
(D) Waiting hall
Life cycle cost 1000 Rs 3180 2519 1384 1124 2011 1923 1752 1371Levelized annual cost 1000 Rs 467 370 203 165 295 282 257 201
Simple payback period
(of incremental investment)
Years 0.6 2.5 4.1 1.7
NPV (of incremental investment) 1000 Rs 661 260 89 354
Fig. 2.Sensitivity of the net present value of hybrid system (DEC+AC) in high density
ofce to the values of (a) discount rate, (b) useful life, and (c) unit price of electricity.
Fig. 3. Sensitivity of net present value of hybrid system (DEC+AC) in low density
ofce to the values of (a) discount rate, (b) useful life, and (c) unit price of electricity.
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It is noted the LCC for the standalone AC system is maximum for
waiting hall building and minimum for low density ofce, for all the
four cities considered in the present study. Also, as expected, the
hybrid system becomes attractive when there is a large difference
between LCC of standalone AC unit and that of a hybrid system.
In Delhi, the hybrid system is not attractive in two out of four build-
ing applications (i.e., hybrid system is attractive for movie theater and
waiting hall building only). For city of Delhi, in the case of low density
ofce theuse of a hybridsystem thoughreduces electricity consumption
its operating cost (cost of AMC, electricity and water cost) is much more
in than that for a standalone AC system. The attractiveness of the hybrid
system at Akola is somewhat similar to that observed for the city of In-
dore, i.e., the hybrid system is attractive for high density ofce, movie
theater and waiting hall. However, the recovery of the capital cost isfaster as compared to Indore. For the case of high density ofce the sim-
ple payback period (SPP) of incremental investment in a hybrid system
is 6.0 years in Indorewhileit is 3.6 years forAkola. Similarly, while in In-
dore the values of the SPP for movie theater and waiting hall buildings
are 2.9 years and 1.7 years respectively the corresponding values for
Akola are 1.1 year and 0.6 years respectively. In Bangalore, the hybrid
system isnancially attractive for all the four building applications.
Variation of the NPV of the incremental investment on a hybrid
system, with discount rate, useful life and unit price of electricity,
for high density ofce for all the four cities is presented in Fig. 2
(a to c). It may be noted that the NPV of incremental investment
in a hybrid system is quite sensitive to the values of these input
parameters. Results of similar sensitivity analysis for the case of low
density ofce for three locations (excluding Delhi) are presented in
Fig. 3. Results for the cases of movie theater and waiting hall are
presented inFigs. 4 and 5respectively for all the four locations consid-
ered in the study. It may be noted that except the low density ofce, all
the other three building applications in Indore and Akola can benet
from the use of a hybrid system with monetary gains for the investor.
In Delhi, only the movie theater and the waiting hall building can
benet from the use of a hybrid system. This is different from the
results obtained for Indore, although the city of Delhi is grouped in
the same climatic zone i.e. composite zone as per the National Build-
ing Code. In Bangalore, all the four building applications can benet
from the hybrid system. A summary of the feasibility of using hybrid
Fig. 4.Sensitivity of net present value of hybrid system (DEC+AC) in movie theater to
the values of (a) discount rate, (b) useful life, and (c) unit price of electricity.
Fig. 5.Sensitivity of net present value of hybrid system (DEC+AC) in waiting hall tothe values of (a) discount rate, (b) useful life, and (c) unit price of electricity.
Table 6
Feasibility of using hybrid system as against standalone vapor compression AC system
{feasible: []; not feasible: [X]}.
S. no. Cities (climatic zone
as per NBC)
High density
ofce
Low density
ofce
Movie
theater
Waiting
hall
1 Akola (ho t and dry
climatic zone)
X
2 Bangalore (temperate
climatic zone)
3 Delhi ( composit e
climatic zone)
X X
4 Indore (composite
climatic zone)
X
51V. Jain et al. / Energy for Sustainable Development 17 (2013) 4753
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Table A1
External and internal input parameters for different building applications (Jain, 2010).
Sl. no. Description High density of ce Low density ofce Mo vie the at er Waiting hall Remar ks
1 Area (m2) Unit size of,
10 m5 m
Unit size of,
10 m5 m
Unit size of,
10 m5 m
Unit size of,
10 m5 m
Same area modular unita considered for
purpose of comparison.
2 Height (m) 3.50 m 3.50 m 6.00 m 3.50 m Same height considered for the purpose of
comparison (except theater)
3 Volume (m3) 175 m3 175 m3 300 m3 175 m3
5 Occupancy (numbers) 8 4 75 50 As per National Building Code (NBC)6 Fresh air in cubic meter per minute
(CMM)
4.8 2.4 36 24 As per NBC
7 Air changes per hour (ac/h) 1.65 0.82 7.2 8.23
8 No rt h wall area (m2) 35 35 60 35
9 South wall area (m2) 35 35 60 35
10 Ceiling Internal partition Internal partition Internal partition Internal partition
11 No rt h windo w (m2) 14 14 0 14 40% glass, as per Energy Conservation
Building Code (ECBC)
12 South windo w (m2) 14 14 0 14 40% glass, as per ECBC
13 Equipment load
(light/power density in W/m2)
24 W/m2 11.8 W/m2 12.9 W/m2 10.8 W/m2 As per ECBC
14 Wall U-factor (W/m2/K 0.39 0.39 0.39 0.39 Within the limit given in ECBC i.e., 0.4
15 Solar heat gain coefcient (SHGC) 0.75 0.75 0.75 As per ECBC 0.25b
16 Glass U-factor (W/m2/K) 2.83 2.83 0 2.83 Within the limit given in ECBC.
Notes:
All the other
oors, walls are considered as internal partitions.
Room internal capacitance is considered as 2100 kJ/K for all the buildings excluding Movie theater where it is 3600 kJ/K.a Part unit size considered from a building oriented along eastwest (facing northsouth direction).b As per information received from the architects and HVAC designers, glass available with SHGC of 0.25 are very expensive, therefore, generally glass are provided with SHGC of
0.7 to 0.75 with internal shadings (in buildings), to make up for the rest. In present study, SHGC of 0.75 with suitable internal shading accordingly is considered.
system (as against the standalone vapor compression AC system) is
presented inTable 6.
Concluding remarks
The results of the simple nancial analysis presented in the present
study suggest that a hybrid system (comprising of an AC unit as well
as a DEC unit) can be a nancially attractive option in certain cities/
region of the country for high density ofce, movie theater and
waiting hall applications as the hybrid system appears to be more
attractive for building with higher cooling loads. Efforts should
therefore be directed towards exploiting the potential of hybrid
systems for meeting high cooling loads in suitable climatic
conditions.
Table A2
Hours of operation of AC unit and DEC unit is a hybrid system for comfort conditions of 26 TSI (Jain, 2010).
Building application Operating hours of AC and DEC in a hybrid system for comfort conditions of 26 TSI
Akola Bangalore Delhi Indore
AC DEC AC DEC AC DEC AC DEC
High density ofce 3868 4887 1028 7732 3691 2187 2542 4727
Low density ofce 3623 4881 1420 7090 3605 2146 2461 4510
Movie theater 3956 4385 1774 6511 3711 1955 2643 4175Waiting hall 4854 3702 3842 4782 3998 1793 3141 3908
Table A3
Selected DEC unit capacity in m3/h for different building application and AC unit capacity for different building applications as well as for different cities (Jain, 2010).
Building applications Capacity of selected DEC unit inow rate in m3/mina Capacity of selected AC unit (in tons of refrigeration (TR) and ow rate in m3/min).
Akola Bangalore Delhi Indore
TR m3/min TR m3/min TR m3/min TR m3/min
High density ofce 87.5 5.5 62 3 34 3 34 3 34
Low density ofce 87.5 3 34 3 34 3 34 3 34
Movie theater 150 17 193 5.5 62 11 125 8.5 96
Waiting hall 87.5 17 193 5.5 62 11 125 8.5 96
a DEC unit capacity is calculated with volume of the room and air change rate. In our case, volume (10 m5 m3.5 m) and air change rate (30 ac/h) is same for all the type of
buildings except in movie theater where volume is different as height is 6.0 m (air change rate is same as 30 ac/h).
Appendix
Thebuilding applications considered are of multi-storied and with multi-zone, however, for the purpose of study, part unit size of 10 m5 m
is considered from a building oriented along east-west (facing northsouth direction). Same area modular unit* considered in all the building
application for the purpose of comparison.
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Jain Varun. Energy Conservation In Space Conditioning in India through Direct
Evaporative Cooling, Ph. D. Thesis. Centre for Energy Studies, Indian Institute ofTechnology Delhi, 2010.
TRNSYS, 16. A transient system simulation program. Solar Energy Laboratory, Universityof Wisconsin-Madison, 1500 Engineering Drive, 1303 Engineering Research Building,Madison, WI 53706 USA; 2005.
53V. Jain et al. / Energy for Sustainable Development 17 (2013) 4753