A financial feasibility evaluation of using evaporative cooling with air-conditioning.pdf

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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
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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

49V. Jain et al. / Energy for Sustainable Development 17 (2013) 4753
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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





Years 14.5 6.1 Not feasible 12.2


(C) Movie theater





Years 1.1 4 8.7 2.9


(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



Years 0.6 2.5 4.1 1.7


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

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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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References

Hindoliya DA. Evaporative Cooling for Thermal comfort in Buildings, Ph. D. Thesis.Delhi: Indian Institute of Technology Delhi, 2005.

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.


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A financial feasibility evaluation of using evaporative cooling with air-conditioning.pdf