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Energy and Buildings 47 (2012) 525–532

Contents lists available at SciVerse ScienceDirect

Energy and Buildings

j ourna l ho me p age: www.elsev ier .com/ locate /enbui ld

erformance analysis of integrated earth–air-tunnel-evaporative cooling systemn hot and dry climate

ikas Bansal, Rohit Mishra, Ghanshyam Das Agarwal, Jyotirmay Mathur ∗

echanical Engineering Department, Malaviya National Institute of Technology, Jaipur 302017, India

r t i c l e i n f o

rticle history:eceived 12 July 2011eceived in revised form3 December 2011ccepted 18 December 2011

eywords:arth–air-tunnel heat exchanger

a b s t r a c t

Performance of simple earth–air-tunnel heat exchanger (EATHE) is enhanced by integrating an evap-orative cooler at the outlet. Year round hourly analysis of the integrated system has been carried outfor predominantly hot and dry climatic conditions using multiphase computational fluid dynamics (CFD)modeling with FLUENT software (version 6.3). The analysis has been carried out individually for all 8760 hof the year for the city of Ajmer (India), considering the temperature and humidity of ambient air as con-dition of inlet air. Results show that a simple EATHE system provides 4500 MJ of cooling effect duringsummer months, whereas 3109 MJ of additional cooling effect can be achieved by integrating evaporative

vaporative coolingassive coolingomputational fluid dynamics

cooler with the EATHE. Although the winter season in most of the cities in hot and dry climatic zones isvery short, analysis of the 8760 h show that the EATHE system is capable of providing 4856 MJ equivalentof heating effect at such locations. For every hour, the condition of the outlet air has also been matchedwith the thermal comfort zone specified ay ASHRAE-55. Results show significant improvement in use-fulness of the EATHE system when integrated with evaporative cooler in hot and dry climatic conditions.

. Introduction

Passive heating and cooling systems are known for their advan-age of consuming no or very less energy as compared to activeeating and cooling systems. Out of various passive heating andooling systems, earth–air-tunnel heat exchanger (EATHE) sys-em has the relative advantage over most passive systems dueo its ability to provide both the effects: heating in cold monthsnd cooling during warm months. It uses underground soil as aeat sink or source. Hot/cold outdoor air is passed through theipes laid at 3–4 m depth in the earth called earth–air-pipes orarth–air-tunnels. When air flows through the earth–air-pipes,eat is transferred from the air to the earth or from earth-to-airepending upon the temperature of air relative to temperature ofarth that remains nearly constant at the annual mean temperaturef that place. In some cases, the thermal condition of air comingut from the earth–air-pipes is such that it can be directly sup-lied to the space connected to it for cooling or heating; whereas inxtreme weather conditions, it needs another stage of processing

efore becoming acceptable for supplying to the connected space.

The potential of earth tube air heat exchanger for space heat-ng is well accepted in cold countries. Mihalakakau et al. [1,2]

∗ Corresponding author. Tel.: +91 9982378283.E-mail address: jyotirmay.mathur@gmail.com (J. Mathur).

378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.enbuild.2011.12.024

© 2011 Elsevier B.V. All rights reserved.

and Santamouris et al. [3] evaluated the thermal performance ofEATHE system experimentally and using mathematical modeling.As reported by Ahmed et al. [4] not much research has been car-ried out in hot climates (such as in western India) because of thebelief that the cooling potential of EATHE system is low due tohigher soil temperature in summer. Investigations by Givoni [5]have shown that the potential of the system in hot climates mayhowever be improved using various soil cooling strategies to lowerthe natural subsurface soil temperature such as shading, surfaceirrigation, surface treatment using plants and pebbles. Ajmi et al.[6] studied the cooling capacity of earth–air heat exchangers fordomestic buildings in a desert climate. Some researchers like Santa-mouris et al. [7] investigated the impact of different ground surfaceboundary conditions on the efficiency of a single and a multipleparallel earth-to-air heat exchanger system and found that groundsurface covered with short grass gives better cooling performancethan bared soil condition. Several investigations on EATHE systemhave also been carried out in India. Bansal et al. [8,9] evaluatedthe performance of EATHE system for summer and winter climaticconditions and observed that air velocity in the pipe is the mostimportant parameter affecting the thermal performance of EATHEsystem and pipe material does not affect the performance of EATHE

system. Bansal et al. [10] evaluated a large earth–air-tunnel systemmeant to provide thermal comfort inside a building complex at onehospital in India. Sawhney et al. [11] and many others evaluated thethermal performance of the EATHE system experimentally. Tiwari

526 V. Bansal et al. / Energy and Buil

Nomenclature

m mass flow rate of air through the tunnelcp specific heat capacity of aird diameter of the tunnelv mean velocity of air through the tunnelQc total hourly cooling from the EATHE systemTinlet temperature at the inlet of the system usedTexit temperature at the exit of system usedEATHE earth–air-tunnel heat exchanger

eif

idtitla

iCssobe

2s

puGtamfl

sbtwftwimteaT1h

6oa

PVC poly vinyl chlorideCOP co-efficient of performance

t al. [12] developed a thermal model for the greenhouse locatedn the premises of IIT, Delhi, India to investigate the use of EATHEor heating and cooling of a greenhouse.

Most of the research has been carried out through mathemat-cal modeling or experimental investigations. Huijun et al. [13]eveloped a transient and implicit model based on numerical heatransfer and computational fluid dynamics and then implementedt on the CFD (computational fluid dynamics) platform, PHOENICS,o evaluate the effects of the operating parameters (i.e., the pipeength, radius, depth and air flow rate) on the thermal performancend cooling capacity of earth–air-pipe systems.

This study presents, year round hourly performance analysis ofntegrated EATHE- evaporative cooling system using multiphaseFD modeling for investigating performance enhancement overimple EATHE system. The model was developed using the FLUENTimulation program and validated using the experimental resultsn a set-up installed in Ajmer (Western India). Investigations haveeen carried out to find the performance of integrated EATHE-vaporative system for every hour of a year.

. Description of integrated EATHE- evaporative coolingystem

The EATHE as shown in Fig. 1 comprises of horizontal cylindricalipe of 0.15 m inner diameter with buried length of 23.42 m, madep of PVC and buried at a depth of 2.7 m in a flat land with dry soil.lobe valves are fitted for pipe assembly for flow control of air. At

he inlet, the open end of this single pipe was connected through vertical pipe to a 0.75 kW (1 H.P.), single phase variable speedotorized blower having maximum speed 2800 rpm, maximum

ow 0.0945 m3/s.The air from the ambient was forced through the earth–air-pipe

ystem with the help of blower. Velocity of air through the pipe cane varied by changing the rpm of the blower with the help of an autoransformer whose range is 0–270 V, 2 A max., type: 2D-1PHASEith a least count of 1Volt. The energy consumption of the blower

or blowing the air at 5 m s−1 is 0.3 kW. In addition to blowing air,he energy consumed by the blower is also transferred to the air,hich increases the temperature of the air. This effect of increase

n temperature of the air due to blower has been considered inodeling of thermal performance of the EATHE system. Six K-type

hermocouples were inserted at fixed distance along the length ofach pipe at T1, T2, T3, T4, T5 and T6, to measure temperature of their along the length of pipe. Thermocouples T1, T2, T3, T4, T5 and6 are situated at a horizontal distance of 3.34 m, 6.68 m, 10.04 m,3.38 m, 16.73 m and 20.07 m from the upstream end of the buriedorizontal pipe.

A box type of evaporative cooler of size50 mm × 650 mm × 890 mm with a cellulose honeycomb padf thickness 38 mm and cross section of 650 mm × 650 mm is usedt the end of tunnel in such a way that the air after passing through

dings 47 (2012) 525–532

the pipe falls on the cellulose pad of evaporative cooler. Waterwas trickled from the top edge of the honeycomb pad using asmall submersible pump (10 W, 0.05 m3/min). While water flowsover the honeycomb pad due to gravity and air crosses the pad,it makes a cross flow direct contact type heat exchanger. Flowof air through evaporative cooler is maintained with the help ofblower, which is fitted at the inlet of EATHE. All the air comingfrom EATHE was fed to the evaporative cooler using a divergingduct having inlet cross sectional area equal to that of EATHE pipeand outlet cross sectional area matching with the cross sectionarea of the honeycomb pad. Before connecting the larger end ofdiverging duct with the evaporative cooler, portion of uniformsection duct is provided that is six times long as compared to thehydraulic diameter of the inlet cross section of evaporative cooler.This uniform cross section length was provided for stabilizing theflow coming out of the diverging duct. Observations were taken forair velocity of 5 m s−1. Air flow velocity are measured with the helpof a vane probe type anemometer having range of 0.4–30.0 m s−1

with a least count of 0.1 m s−1.

3. Description of CFD model

CFD tools are well known for their capability to carry out in-depth analysis of cases related to fluid flow, heat and mass transferand several others. They provide numerical solutions of partialdifferential equations governing airflow and heat transfer in a dis-cretized form. To examine the complicated airflow heat transferand mass transfer processes in an integrated EATHE-evaporativecooling system, CFD software, FLUENT 6.3, was used in this study.In order to provide easy access to solving power of CFD codes,FLUENT 6.3 packages include sophisticated user interfaces to inputproblem parameters and to examine the results. CFD codes in FLU-ENT contain three main elements: (i) a pre-processor, (ii) a solverand (iii) a post-processor. Pre-processing consists of the input ofa flow problem to a CFD program by means of definition of thegeometry of the region of interest: the computational domain,Grid generation-the sub-division of the domain into a number ofsmaller, non-overlapping sub-domains: a grid (or mesh) of cells(or control volumes or elements), selection of the physical andchemical phenomena that need to be modeled, definition of fluidproperties, specification of appropriate boundary conditions at cellswhich coincide with or touch the domain boundary. Solver uses thefinite control volume method for solving the governing equations offluid flow and heat transfer. Post-processor shows the results of thesimulations using vector plots, contour plots, graphs, animations,etc.

In the present analysis, multi phase CFD simulations have beenperformed using an unstructured grid. The fundamental equationsof fluid flow, flow through porous media, mass transfer and heattransfer have been used in the analysis. The geometric modelingand meshing have been prepared using GAMBIT version 2.3. In thisanalysis, the evaporative cooler has been considered to be placed atthe outlet of the EATHE. Due to limitation of computational poweravailable, the analysis has been carried out in two parts. First, thecondition of air at the outlet of EATHE system has been computedthrough CFD model for every hour of the year. This set of results hasbeen specified as inlet air condition for the second stage analysis,i.e., analysis of air flow through evaporative cooler using multi-phase CFD for every hour of the year. It has been assumed thatthe air coming from the outlet of EATHE has been directed to the

cooling pad of the evaporative cooler using a diverging duct andstabilizing the flow. The main objective of the CFD study was tocompare the performance of simple EATHE system with integratedEATHE-evaporative cooling system.

V. Bansal et al. / Energy and Buildings 47 (2012) 525–532 527

Fig. 1. Experimental set-up of integrated EATHE-evaporative cooling system.

Table 1Physical and thermal parameters used in simulation.

Material Density (kg/m3) Specific heatcapacity (J/kg K)

Thermal conductivity(W/mK)

Air 1.225 1006 0.0242

seh

m

4

stiCpcvs

bfd

he

Q

w

5

dtgtia

of the air increases as the air is blown through the tunnel. Thisincrement in temperature is faster for the initial length of the tunneland then it becomes moderate.

Soil 2050 1840 1.16Steel 7833 465 54.0PVC 1380 900 0.16

In the study it was assumed that air is incompressible andubsoil temperature remains constant. It was also assumed thatngineering materials used in the CFD model are isotropic andomogeneous.

The physical and thermal parameters of different engineeringaterials used in the simulation are listed in Table 1.

. Experimental validation and performance analysis

CFD based modeling of integrated EATHE-evaporative coolingystem has been validated for summer weather conditions byaking observations on an actual experimental set-up (as shownn Fig. 1) in the month of April, 2010 at Ajmer (Western India).omparison of simulated and experimental values of dry bulb tem-erature (DBT) and relative humidity (RH) at outlet of evaporativeooler is summarized for air velocity of 5 m s−1 in Table 2. In thisalidation exercise, inlet condition of air in CFD simulation was keptame as measured at the experimental set-up.

It is observed from Table 2 that there is a difference of 3.4–8.0%etween the experimental and simulated data for DBT and 2.5–6.4%or RH. Thus, the model was considered to be usable to carry ouretailed analysis for each hour of the year.

Hourly cooling/heating effect obtained from the EATHE systemas been calculated for flow velocity 5.0 m s−1 by the followingquation:

c = mcp(Tinlet − Texit) (1)

here m = �/4d2v

. Performance of simple EATHE system

Temperature gradient between ambient air and soil is the mainriving force for the design of EATHE, therefore the most impor-ant parameter in the evaluation of ground cooling systems is the

round temperature. Thermal performance of simple EATHE sys-em significantly depends on the temperature of subsoil of the placen which it is installed. As reported by Bansal et al. [10] the temper-ture of earth varies widely up to 1 m deep, and remains relatively

Fig. 2. Temperature variation along the length of the tunnel in winter conditionsfor air velocity of 5 m s−1.

constant beyond that. This subsoil temperature is equal to annualmean temperature of the place in which EATHE is installed. Thesubsoil temperature in the present case is equal to about 26.7 ◦C.

The temperature progress of the air in the tunnel along thelength of the tunnel is shown in Figs. 2 and 3 for winter and sum-mer climatic conditions respectively. In Figs. 2 and 3, points Tinletand Texit represent the inlet and outlet of the buried pipe of theearth–pipe–air heat exchanger system respectively.

Experimental observations for temperature variation along thelength of the tunnel for December 12, 2009 and January 01, 2010have been shown in Fig. 2. It was observed that the temperature

Fig. 3. Temperature variation along the length of the tunnel in summer conditionsfor air velocity of 5 m s−1.

528 V. Bansal et al. / Energy and Buildings 47 (2012) 525–532

Table 2Comparison of simulated and experimental results (for DBT and relative humidity).

S. no. At inlet of EATHE At exit of evaporative cooler

DBT (◦C) Relative Humidity (%) DBT (◦C) Relative Humidity (%)

(Both experimental and simulated) (Both experimental and simulated) Experimental Simulated % Diff. Experimental Simulated % Difference

1 31.9 26 23.2 22.5 8.0 60.2 62.4 6.42 34.1 22 24.1 23.5 6.0 56.2 58.4 6.43 35.9 20 25.2 24.5 6.5 56.4 57.3 2.54 37.3 18 25.8 25.3 4.3 53.3 54.5 3.45 38.3 18 26.3 25.7 5.0 55.3 56.9 4.36 38.7 18 27 38.7 18 28 37.9 19 2

F

lsdtb

6

aeh

FE

ig. 4. Condition of ambient air for 4 days (96 h) spread over the month of January.

Experimental observations for temperature variation along theength of the tunnel for May 07, 2010 and May 21, 2010 have beenhown in Fig. 3. It was observed that the temperature of the airecreases as the air is blown through the tunnel. This decrement inemperature is faster for the initial length of the tunnel and then itecomes moderate.

. Approach for hourly performance analysis of EATHE

For evaluating the performance of simple EATHE system

nd then to compare its performance with integrated EATHE-vaporative cooler system, hourly analysis of both types of systemsas been carried out. For this purpose, ambient air conditions have

ig. 5. Change in state of air with respect to thermal comfort zone using simpleATHE in January.

6.4 25.9 4.1 55.6 57.1 4.06.4 25.9 4.1 55.7 57.1 3.76.0 25.6 3.4 55.3 57.1 5.0

been taken from the hourly weather file of Ajmer [14]. Conditionof air at the outlet of the EATHE system has been examined withrespect to the thermal comfort requirements as per ASHRAE 55-2004 [15]. In order to ensure readability of results, the present studypresents hourly analysis for four days of every month separated by7 days thus covering the change in weather conditions within thesame month. Hence the data sets got reduced from that of 8760 to1152 h to cover the whole year. In the analysis, with use of blower,air velocity of 5 m s−1 is considered to exist through the EATHEpipe. This velocity has been selected as a trade-off between cool-ing effect and practical limitations. At lower velocities, net coolingeffect obtained from EATHE is less as found by Bansal et al. [8,9],whereas at velocities more than 5 m s−1 other issues related to dis-tribution of air in the connected space, blower power consumptionand noise become important.

Hourly performance analysis of the EATHE system is carried outto observe winter heating as well as summer cooling. Followinghierarchy of operation is assumed in the operation of integratedEATHE-evaporative cooling system:

- It is assumed that if the condition of air coming from the simpleEATHE system will lie inside the thermal comfort zone for sum-mer on psychometric chart, evaporative cooler is not operated.

- In case, the condition of air coming out of EATHE system alone,does not lies within the thermal comfort zone for summer, sim-ple evaporative cooler alone will be considered (directly takingambient air from a separate inlet) for supplying the air in place ofEATHE system.

- When none of the two independent systems is able to producecondition of air as per the thermal comfort zone, then EATHEsystem integrated with evaporative cooler will be operated.

Fig. 6. Condition of ambient air for 4 days (96 h) spread over the month of May.

V. Bansal et al. / Energy and Buildings 47 (2012) 525–532 529

Table 3Hours of May in which air become suitable to thermal comfort due to simple EATHE.

Date HH:MM At inlet of EATHE At outlet of EATHE

Temperature (◦C) Relative humidity (%) Temperature (◦C) Relative humidity (%)

5/7/2005 4:00 29.0 40.0 27.2 45.75/7/2005 5:00 28.5 40.0 27.2 45.15/7/2005 6:00 28.5 37.0 27.2 42.25/7/2005 7:00 29.1 36.0 27.3 42.75/14/2005 10:00 28.6 35.0 27.2 38.45/14/2005 20:00 28.7 43.0 27.2 46.95/14/2005 21:00 28.2 48.0 27.2 51.95/14/2005 22:00 27.7 53.0 27.2 49.8

Table 4Hours of May in which air become suitable to thermal comfort due to evaporative cooler alone.

Date HH:MM At inlet of evaporative cooler At outlet of evaporative cooler

Temperature (◦C) Relative humidity (%) Temperature (◦C) Relative humidity (%)

5/7/2005 2:00 30.2 35.0 24.5 49.95/7/2005 3:00 29.6 39.0 24.5 51.5

.0

.0

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d

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daweTne

TH

5/7/2005 8:00 30.5 315/7/2005 24:00:00 29.7 375/14/2005 11:00 30.1 31

Practically, such arrangement can be realized through automaticampers that are actuated by temperature and humidity sensors.

In order to present a clear comparison of integrated EATHE-vaporative cooling system with other alternatives, i.e., simpleATHE system and simple evaporative cooler (widely used in hotnd dry climatic conditions), hourly analysis has been carried outeparately for (i) simple EATHE system, (ii) for evaporative coolerlone and (iii) integrated EATHE-evaporative cooling system.

Scope of this study has been restricted to examining the con-ition of air that can be supplied to the room/space. It has beenssumed that due to high number of air changes per hour, thereould not be much difference between the condition of air at the

xit of the analyzed systems and condition of air inside the room.his assumption hold good only for spaces having very low inter-al heat gain as well as low heat gain/loss through the buildingnvelope.

able 5ours of May in which air become suitable to thermal comfort due to EATHE integrated w

Date HH:MM At inlet of EATHE At outlet of

Temperature (◦C) Relative humidity (%) Temperatu

5/7/2005 1:00 31.4 33.0 28.3

5/7/2005 9:00 32.3 27.0 28.7

5/7/2005 10:00 34.0 24.0 29.4

5/7/2005 11:00 35.6 21.0 30.1

5/7/2005 12:00 37.0 20.0 30.6

5/7/2005 13:00 38.2 19.0 31.2

5/7/2005 14:00 38.9 19.0 31.3

5/7/2005 15:00 39.3 18.0 31.6

5/7/2005 16:00 39.3 18.0 31.6

5/7/2005 17:00 38.8 19.0 31.3

5/7/2005 18:00 37.9 20.0 31.1

5/7/2005 19:00 36.7 22.0 30.5

5/7/2005 20:00 35.5 26.0 30.0

5/7/2005 21:00 34.1 29.0 29.4

5/7/2005 22:00 32.6 34.0 28.9

5/7/2005 23:00 31.2 36.0 28.2

5/14/2005 12:00 31.3 30.0 28.2

5/14/2005 13:00 32.1 32.0 28.6

5/14/2005 14:00 32.6 31.0 28.9

5/14/2005 15:00 32.8 30.0 29.0

5/14/2005 16:00 32.7 31.0 28.9

5/14/2005 17:00 32.2 32.0 28.6

5/14/2005 18:00 31.2 36.0 28.2

5/14/2005 19:00 30.0 39.0 27.5

24.5 50.124.5 53.524.5 52.9

7. Results of hourly analysis

Results obtained from hourly analysis of all the systems (simpleEATHE system, evaporative cooler alone and integrated EATHE-evaporative cooling system) are represented and analyzed withrespect to the thermal comfort zone on psychometric chart. Foranalyzing the condition of treated air from thermal comfort pointof view, a thermal comfort zone has been shown on psychrometricchart as a quadrilateral marked with red boundary as depicted inFigs. 4 and 5. The thermal comfort zone is defined as per the ASHRAEStandard 55-2004. Different conditions of the air, i.e., ambient air(represented by green dot ), treated air obtained from the ana-

lyzed systems are marked by dots on the psychrometric chart. Forthe case when heating takes place in the simple EATHE system,condition of treated air is marked with red dot ( ). Similarly, inthe cases when cooling takes place in simple EATHE, condition of

ith evaporative cooler.

EATHE = at inlet of evaporative cooler At outlet of evaporative cooler

re (◦C) Relative humidity (%) Temperature (◦C) Relative humidity (%)

40.3 24.6 52.836.9 24.7 52.435.2 24.8 52.233.7 24.9 52.432.1 24.9 56.432.1 25.0 59.732.4 25.0 59.132.0 25.1 60.132.0 25.1 60.132.4 25.0 59.132.9 25.0 60.434.8 24.9 59.438.7 24.9 49.440.1 24.8 56.244.1 24.7 57.445.4 24.6 56.839.3 24.6 54.840.7 24.7 55.840.9 24.7 55.839.8 24.8 55.840.9 24.8 55.541.8 24.7 56.445.4 24.6 56.845.0 24.6 56.8

530 V. Bansal et al. / Energy and Buildings 47 (2012) 525–532

F y. (b)

M

tooced

ig. 7. (a) DBT of air at the inlet and outlet of simple EATHE for 4 days (96 h) in Maay.

reated air is marked with blue dot ( ). To differentiate the casesf simple EATHE with other two cases, condition of treated air

btained from simple evaporative cooler is represented by magentaolored dot ( ) and representation of the condition of air deliv-red by integrated EATHE-evaporative cooling system is done byark blue dot ( ).

Fig. 8. Details of comfort hours obtai

Relative humidity of air at the inlet and outlet of simple EATHE for 4 days (96 h) in

Hourly analysis results for a typical month of winter, i.e., Januaryare presented with the help of psychrometric chart in Figs. 4 and 5.

It can be noted in Fig. 4 that out of total 96 dots only 21 dotslie inside the comfort zone (i.e., ambient air is comfortable) andremaining 75 dots are outside the zone (i.e., ambient air is uncom-fortable). This analysis shows that about 78.12% time in the month

ned out of 96 h of every month.

V. Bansal et al. / Energy and Buildings 47 (2012) 525–532 531

Table 6Annual heating/cooling energy and number of comfort hour obtained by different systems.

S. No. Thermal comfort method Heating/cooling achieved Comfort hours obtained Comfort hours as %of total hours

Useful period

MJthermal kWhthermal

1 Ambient air – – 2243 25.6 All 12 months2 Simple EATHE system (Winter heating) 4856 1348.9 1587 18.1 November to February

osaCibtmteir

ii

mostztttfhstth2fftcomasm

8

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ipmttaw

3 Simple EATHE system (Summer cooling) 4500 1250.0

4 EATHE integrated with evaporative cooler 12465 3462.5

f January, ambient air requires to be treated before becominguitable for supplying into any living space. In order to treat suchmbient air, it is passed through simple EATHE system for heating.ondition of the warmer air obtained from simple EATHE system

s represented on the psychrometric chart as shown in Fig. 5. It cane noted that with use of EATHE system, during 68 h out of 96 h inhe month of January, condition of air shifts to lie within the ther-

al comfort zone (i.e., during 47 more hours air became suitable tohermal comfort due to simple EATHE system). It is observed thatven after heating through a simple system 28 dots (29.17% timen the month of January) still lie outside the comfort zone, therebyequiring further treatment.

Results of the hourly analysis for a typical month of summer,.e., May are presented with the help of psychometric charts shownn Fig. 6 and Tables 3–5.

Psychrometric condition of ambient air for various hours in theonth of May is shown in Figs. 6 and 7(a and b). The hourly analysis

f four typical days in the month of May (i.e., total 96 dots corre-ponding to 96 h of analysis) shows that only for 11 h (i.e., 11.46% ofotal time) the condition of ambient air is lying within the comfortone and for remaining period of 85 h (i.e., 88.54% of total time)he ambient air is uncomfortable. For making this air suitable forhermal comfort, firstly, the ambient air is considered to be passinghrough a simple EATHE system for cooling. It can be noted that onlyor 19 out of 96 h, the air becomes comfortable (i.e., during 8 moreours air became suitable to thermal comfort due to simple EATHEystem as shown in Table 3). For remaining 77 h (i.e., 80.20% of totalime) when evaporative cooler is considered to be used for treatinghe air, taking the ambient air directly, the period of comfortableours gets enhanced by from 19 h (with simple EATHE system) to4 h (i.e., during 5 more hours air became suitable to thermal com-ort due to evaporative cooler alone as shown in Table 4). Finally,or remaining hours, when ambient air is considered to be passinghrough integrated EATHE-evaporative cooler system for cooling,ondition of the treated air is thermally comfortable for 48 h outf 96 h (i.e., during 24 more hours air became suitable to ther-al comfort due to integrated EATHE-evaporative cooler system

s shown in Table 5), showing the enhancement in usefulness ofimple EATHE and/or evaporative cooler working in stand-aloneode.

. Summary of annual performance

Detailed results of hourly analysis for all 12 months of a yearave been obtained and summary of the results of hourly analysis

s shown in Fig. 8.Results of hourly analysis as shown in Fig. 8 revealed that even

n predominantly hot climatic condition, the performance of sim-le EATHE system is most effective for winter heating, i.e., in theonths of November to February. It is also observed that during

hese months for certain period none of the three analyzed sys-ems sufficiently treats ambient air, due to the fact that ambientir is too cold. In the months of March to May and in Octoberhen mostly dry summer season prevails at Ajmer, out of the three

456 5.2 March to June, October5235 59.8 All 12 months

systems, no single system can sufficiently treat the ambient air forall the hours. However, the integrated EATHE-evaporative coolersystem produces significantly better results as compared to theother two working in stand-alone mode.

Results of the benefits related to the cooling/heating effectobtained from the integrated EATHE-evaporative cooling systemare presented in Table 6.

9. Conclusion

Performance analysis of integrated EATHE-evaporative coolingsystem over complete year shows that while ambient air itselfis comfortable for 25.6% of the hours, use of integrated EATHE-evaporative cooling system provides comfortable air for 34.16%hours in one year, whereas simple EATHE system is able to pro-vide comfortable air for only 23.33% additional hours. During thepre-monsoon and monsoon period, from the month of June toSeptember, when temperature and relative humidity of ambient airboth are high, none of the three systems sufficiently treats ambientair to make it thermally comfortable. It has also been noted fromthe results that out of the remaining 42.51% duration of the year,when it appears that even the integrated EATHE-evaporative cool-ing system is not able to sufficiently treat ambient air, there aremany condition points that lie in close vicinity of the thermal com-fort zone. This shows that if thermal adaptation of occupants withambient temperature is considered, integrated EATHE-evaporativecooling system would appear to be providing acceptable air formost of the time in a year.

Further, it has been found that on annual basis, the integratedEATHE-evaporative cooling system, delivers 4856 MJ equivalent oftotal heating effect and 7609 MJ of total cooling effect. Out of total7609 MJ of cooling effect, 4500 MJ is achievable with simple EATHEsystem, and remaining 3109 MJ is achieved due to integration ofEATHE with evaporative cooling at its outlet.

It has finally been concluded that the integrated EATHE-evaporative cooling system enhances the duration for which thesystem is able to produce air at comfortable temperature and rela-tive humidity and hence is better than simple EATHE or evaporativecooler working in stand-alone mode in hot and dry climatic condi-tion like Ajmer (India).

References

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