research article human thermal comfort and heat stress in...

Hindawi Publishing CorporationAdvances in MeteorologyVolume 2013 Article ID 693541 7 pageshttpdxdoiorg1011552013693541

Research ArticleHuman Thermal Comfort and Heat Stress in an Outdoor UrbanArid Environment A Case Study

A M Abdel-Ghany12 I M Al-Helal1 and M R Shady1

1 Department of Agricultural Engineering College of Food and Agricultural Sciences King Saud University PO Box 2460Riyadh 11451 Saudi Arabia

2Mechanical Power Engineering Deptartment Faculty of Energy Engineering Aswan University Aswan 81528 Egypt

Correspondence should be addressed to A M Abdel-Ghany aghanyksuedusa

Received 15 November 2012 Revised 19 January 2013 Accepted 19 January 2013

Academic Editor Harry D Kambezidis

Copyright copy 2013 A M Abdel-Ghany et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

To protect humans from heat stress risks thermal comfort and heat stress potential were evaluated under arid environment whichhad never been made for such climate The thermal indices THI WBGT PET and UTCI were used to evaluate thermal comfortand heat stress RayMan software model was used to estimate the PET and the UTCI calculator was used for UTCI Dry and wetbulb temperatures (119879d 119879w) natural wet bulb temperature (119879nw) and globe temperature (119879g) were measured in a summer day tobe used in the calculation The results showed the following (i) The thermal sensation and heat stress levels can be evaluated byeither the PET or UTCI scales and both are valid for extremely high temperature in the arid environment (ii) In the comfort zonearound 75 of individuals would be satisfied with the surrounding environment and feel comfortable during the whole day (iii)Persons are exposed to strong heat stress andwould feel uncomfortablemost of the daytime in summer (iv) Heat fatigue is expectedwith prolonged exposure to sun light and activity (v) During the daytime humans should schedule their activities according to thehighest permissible values of the WBGT to avoid thermal shock

1 Introduction

Human thermal comfort is defined as a condition of mindwhich expresses satisfaction with the surrounding environ-ment High temperatures and humidity provide discomfortsensations and sometimes heat stress (ie reducing the bodyrsquosability to cool itself) Moreover discomfort and heat stressreduce productivity of workers and may lead to more serioushealth problems especially for aged persons In hot summerseasons of arid regions high outdoor air temperatures dueto intensive solar radiation and low relative humidity arepresent Consequently discomfort sensations and heat stressare expected Therefore persons should take care when theygo outside in hot summer to protect their health from heatandor sunstroke

Since the 1950s human thermal comfort under indoorconditions (ie in residential industrial commercial andinstitutional buildings) and outdoor conditions have been

discussed exhaustively in several reports for example [1ndash15] These studies concerned the thermal comfort andorheat stress for worldwide regions other than arid regionsDifferent scales for thermal comfort and heat stress havebeen established in the form of numerical relations orgraphs Among these scales the temperature-humidity index(THI) and the wet bulb-globe temperature index (WBGT)are used for heat stress for long time ago Recently thephysiological effective temperature (PET) and the universalthermal climatic index (UTCI) are used for thermal comfortand heat stress as well both are in temperature scale PETis a thermal index that gives an estimation of the thermalsensation and the corresponding heat stress level PET isbased on the Munich Energy balance Model for Individuals(MEMI) and a two-node model not being constrained by asteady-state approach PET is applicable for both the indoorand outdoor environment studies [14] Several advantages ofusing PET as reported by [14] include the following (i) it is

2 Advances in Meteorology

a universal index irrespective of clothing (clo values) andmetabolic activity (met values) (ii) it gives the real effect ofthe sensation of climate by human beings (iii) it is measuredin ∘C and so can be easily related to common experience and(iv) it is useful in both hot and cold climates so it can beapplied successfully in arid environment (high temperatureand low relative humidity) PET can be calculated simplyby RayMan software which is made freely available by itsauthors RayMan model avoids all the complications of thetwo-node model and takes simple inputs that is the air drybulb temperature (119879d) relative humidity (RH) wind velocity(119881) and mean radiant temperature (119879mrt) or global solarradiation flux (119878o) [16] RayMan model is valid for hot andsunny climate in which values of 119879mrt exceed 60∘C at aroundnoon Ranges of PET in ∘C for different grades of thermalperception by human beings are reported in [17]

Another scale was developed (ie the universal thermalclimatic index (UTCI)) as an equivalent temperature fora given combination of wind radiation humidity and airdry bulb temperature The associated assessment scale forthe UTCI was developed from the simulated physiologi-cal responses and comprises 10 categories that range fromextreme cold stress to very strong cold stress strong coldstress moderate cold stress slight cold stress no thermalstress moderate heat stress strong heat stress very strongheat stress and extreme heat stress [18] The UTCI canbe calculated simply by using the UTCI calculator whichis made freely available by its authors in [19] The inputparameters to this calculator are the air dry bulb temperature(119879d) relative humidity (RH) and the temperature differenceΔ119879 (Δ119879 = 119879mrt minus 119879d)

Survey of previous studies revealed that most of thesestudies focused on the environmental conditions for humanoccupancy either indoor or outdoor to evaluate the humanthermal comfort and heat stress potential in different areasworldwide However the comfort conditions under aridclimate (eg in the Arabian Peninsula) had never beenevaluated Accordingly evaluation of heat stress and humanthermal comfort in an urban setting under arid environmentsuch as in the Arabian Peninsula is urgently needed Thisstudy aims to evaluate human sensations and heat stress levelsin hot summer by (i) describing the mean sensations ofpersons in the outdoor arid environment and (ii) evaluatingthe level of risks due to heat stress potential One entire day(daytime and nighttime) was considered (May 8-9 2012) thatday represents to some extent the weather conditions insummer season Several indices (ie THI WBGT PET andUTCI) were evaluated to examine the applicability of usingthese scales in the arid environment

2 Theoretical Background

Factors affecting human thermal comfort can be classified asfollows

(i) Environmental factors such as the dry bulb temper-ature of air and its relative humidity (119879d and RH) aircurrent speed (119881) and the mean radiant temperature of thesurroundings (119879mrt) The latter is defined as that uniform

temperature of an imaginary black enclosure in which aperson would have the same radiation exchange with theactual environment Value of 119879mrt (

∘C) can be calculated bymeasuring 119879d (∘C) and the globe temperature 119879g (∘C) andusing the relation reported in [6 7] as

119879mrt =4radic(119879g + 273)

4

+

ℎcg

120576g120590(119879g minus 119879d) minus 273 (1)

where 120576g is the emissivity of the black globe (ie 120576g = 095)120590 is the Stefan-Boltzmann constant and ℎcg (Wmminus2 ∘Cminus1)is the convective heat transfer coefficient between the blackglobe surface and the surrounding air This coefficient can beestimated as in [6 15] by

ℎcg = max of

63(119881)06

11986304 forced convection

14(

119879g minus 119879d

119863)

025

free convection

(2)

where119863 is the diameter of the black globe sensor (015m) Inthe present study the free convection was considered becausethe wind speed was low (lt05m sminus1) during the experiment

(ii) Physiological factors such as the body metabolicheat generation rate (119872 in met 1met = 5815Wmminus2)which depends on different factors such as personal activitygender age nationality and type of clothing Thereforethese factors vary between individuals Accordingly manystatistical studies have been performed on large numbersof persons of all ages gender nationalities and activitiesto examine the human body responses to environmentalconditions and to arrive at a quantitative description ofhuman thermal comfort Thermal scales for human meansensation to the environment were developed based onhuman body energy balance under comfort conditions inwhich the rate of energy generated by a humanrsquos body (119872)should equal the rate of energy needed for the externalmechanical work (119882) plus the rate of energy release fromthe body through respiration evaporation convection andradiation The thermal efficiency (120578) of individual humanbodies as an engine (120578 = 119882119872) was estimated to be le20on average [8] Therefore a person should lose heat at a rateof (119872minus119882) in order to be comfortable

Thermal loss from the clothing surface of the body tothe surroundings is by radiation convection evaporation dueto sweating skin diffusion respiratory evaporative heat andrespiratory convective heat loss Humans in the outdoor orindoor are exposed to a heating load that depends mainly onthe difference between the surface temperature of clothing(119879cl) in

∘C and the mean radiant temperature (119879mrt) in (1)Value of the 119879cl is affected by the body and the surroundingconditions and it is impossible to be measured directly

Advances in Meteorology 3

Therefore value of 119879cl is usually computed iteratively usingthe following equation [4 9]

119879cl = 357 minus 0028 (119872 minus119882)

minus 369 times 10minus8

119868cl119865cl [(119879cl + 273)4

minus (119879mrt + 273)4

]

minus 119868cl119865clℎ119888 (119879cl minus 119879d)

(3)

where 119868cl is the insulation resistance of the entire clothing(eg 119868cl = 0093

∘Cm2Wminus1 for outdoor clothes) 119865cl is theratio of the clothed body area to the naked body area (119865cl =12 on average) and ℎ

119888is the convective coefficient between

the clothing surface and the surrounding air (Wmminus2 ∘Cminus1)and is given by [4 7 8] as

ℎ119888= max of238(119879cl minus 119879d)

025

free convection121radic119881 forced convection

(4)

In summer of arid regions human thermal comfort may notbe attainable most of the time during the day Under suchconditions the high extremity of 119879d as well as 119879mrt requriesuniversal heat stress indices to be used for evaluating thehuman thermal sensation and the levels of heat stress Thesuitable heat stress indices are the PET and UTCI Thesescales can be calculated by using RayMan software and UTCIcalculator (free available by their authors)

However apart from the availability of software thereare two heat stress indexes that can be calculated simply byusing two simple relations (ie the temperature-humidityindex (THI) and wet bulb-globe temperature (WBGT))These scales have been used successfully for long time agoThe THI in degree ∘C is given by [20 21] as

THI = 119879d minus 055 (1 minus [RH100

]) (119879d minus 1444) (5)

in which 119879d is in∘C and RH in

The levels of risks corresponding to given heat stresswere classified according to the THI values and are reportedin [21] as follows THI lt 27

∘C (safe) 27∘C lt THI lt

32∘C (heat fatigue is possible with prolonged exposure and

activity) 32∘C lt THI lt 41∘C (sunstroke and heat exhaustion

are possible with prolonged exposure and activity) 41∘C lt

THI lt 54∘C (sunstroke and heat cramps are possible) and

THI gt 54∘C (sunstroke heat stroke and heat confusion or

delirium is possible)The WBGT (∘C) is an index of heat stress imposed

on the human body by the thermal environment It is acombination of dry bulb temperature air current speed andrelative humidity of air and radiation [20]TheWBGT can becalculated using a correlation proposed by ISO-7234 standardfor the outdoor conditions (in the presence of solar radiation)and is given by [20] as

WBGT = 07 (119879nw) + 02 (119879g) + 01 (119879d) (6)

where 119879nw (∘C) is the natural wet bulb temperature (iecommonlymeasuredwith a thermometer that is coveredwitha moist white muslin wick and exposed to the atmosphere

without ventilation or shading) and 119879g (∘C) is the globetemperature (ie commonly measured with a temperatureprobe placed in the center of a blackened hollow coppersphere) Both119879nw and119879g are passively exposed to the ambientenvironment whereas dry bulb temperature (119879d) is usuallymeasured by an aspirated psychrometer

3 Experimental Measurements

The experiments were conducted in the outdoor on theAgricultural Research and Experiment Station AgricultureEngineering Department King Saud University (the centralregion of Riyadh Saudi Arabia 46∘ 471015840 E longitude and24∘ 391015840 N latitude) An experiment was conducted on thesame location to measure the environmental parameters tobe used for other purposes it was from April 29 to July15 2010 The maximum minimum and mean values of airdry bulb temperature (119879d) were depicted in Figure 1 In thisfigure the deviation between the mean and the maximumand minimum values of 119879d was small and then choosingone day in the present experiment is acceptable to representthe conditions of summer season Accordingly the currentexperiment was carried out during a complete day (dayand nighttime) in a summer season (May 8-9 2012) tomeasure the required environmental parameters to be usedin the calculation of 119879mrt 119879cl THI WBGT PET and UTCIThe measured data were taken every 10 seconds averagedand recorded at every one minute in a data logger (CR-23X Micrologger) and then averaged at every one hourThe measured parameters were as follows (i) Dry and wetbulb temperatures (119879d and 119879w) using aspirated psychrometerThe psychrometer had two type-T thermocouples (copperconstantan of 03mm in diameter) The psychrometers werecalibrated and the error was le12∘C for a dry bulb temper-ature up to 100∘C (ii) Globe temperature (119879g) using blackglobe thermometric probe (BST131) having a globe diameterof 015m a time response of 20min surface reflectancele2 a working temperature range of minus50∘Cndash80∘C and ameasuring error of plusmn05∘C for a dry bulb temperatureup to 80∘C (iii) Natural wet bulb temperature (119879nw) usinga type-T copper constantan thermocouple of 03mm indiameter whose junction was covered with a moist whitemuslin wick and kept exposed to the ambient RH in (5)was calculated by substituting the measured values of 119879d and119879w in psychrometric relations reported in [22] The dailyaverage of air speed (119881) was estimated based on the availablemetrological data to be around 05m sminus1

4 Results and Discussion

In summer it is important to evaluate heat stress and humanthermal comfort to avoid risks that may occur to personsin the outdoor in arid regions Figure 2 illustrates the timecourse of the measured meteorological parameters (ie 119879d119879g RH and 119878o) In this figure because of the intensivesolar radiation flux (119878o) the dry bulb temperature of air (119879d)reaches 40∘C the globe temperature (119879g) exceeds 50∘C ataround noon and the relative humidity (RH) drops below

4 Advances in Meteorologyd119879

(∘C

)

0

5

10

15

20

25

30

35

40

45

50Outdoor environment

Max

Min

Mean

Time (hmin)

60

80

100

120

140

160

180

200

220

240 20

40

60

April 29ndashJuly 152010

Figure 1 Time course of theminimummaximum andmean valuesfor the dry bulb temperature (119879d) of air measured in the outdoorfrom April 29 to July 15 2010 in the central region of Riyadh

Tem

pera

ture

s (∘C

) and

RH

()

0

10

20

30

40

50

60

0

200

400

600

800

1000

1200

RH119878119900

Time of the day (hmin)530530 930 1330 1730 2130 130

Outdoor environment8-952012

(Wmminus2)

Sola

r rad

iatio

n flu

x119878119900

119879g

119879d

Figure 2 Time course of the environmental parameters measuredin the outdoor in a hot sunny summer day (May 8-9 2012) in thecentral region of Riyadh

30 During the nighttime values of 119879g drop below 119879d dueto the effect of the night cooling of the globe surface (ieemission to sky)

The main source of discomfort and heat stress is theheat load exchanges between the persons and their surround-ings through radiation and convection modes Radiationexchanges depend on the difference to the power fourbetween the mean radiant temperature (119879mrt) and cloth-ing surface temperature (119879cl) and the convection exchangedepends on the difference between 119879cl and the dry bulbtemperature (119879d) of air The time courses of the 119879mrt and119879cl predicted using (1) and (3) and the 119879d are illustrated inFigure 3 This figure shows that during the daytime 119879mrt wasmuch higher than 119879cl except for short periods around sunriseand sunset Therefore the human body always experiencesa positive heat radiation load (ie they have a net heatgain) During the nighttime 119879mrt was relatively lower than119879cl causing a negative radiation heat load (released from the

Tem

pera

ture

s (∘C

)

0

10

20

30

40

50

60

70

119879mrt119879cl (119872 = 2)

119879cl (119872 = 5)



119879d

Figure 3 Time course of the mean radiant temperature (119879mrt)clothing temperature (119879cl) estimated at different activities and drybulb temperature of air (119879d) in the outdoor in a hot sunny summerday in the central region of Riyadh

body) On the other hand 119879cl was relatively higher than119879d during the daytime causing a negative convective heatreleased from the body However the convection exchangeis minor during the nighttime Radiation heat load has thedominant effect because the temperature difference (119879mrt minus119879cl) is much higher than (119879d minus 119879cl) In addition variationof personrsquos activities showed no significant effects on theclothing surface temperature

Figure 4 illustrates the time course of the simply calcu-lated index (THI) and 119879d in that day (May 8-9 2012) Eventhough the air temperature level (119879d) is high and could reachabout 40∘C around noon this index indicated that personsare safe from heat stress risks before noon (up to 1130) andduring the nighttime This is because the relative humidity(RH) is low (see Figure 2) and the combination between 119879dand RH (1) produces the safe conditions to humans From1130 up to sunset heat stress is expected with activitiesHowever this index gives only an expectation of heat stress asa whole without details that show the different levels of riskduring this time (from 1130 to sunset)

Figure 5 illustrates the time course of the WBGT indexduring the whole day in the outdoor According to thepredicted values of the WBGT in this figure several typesof activities can be done safely during summer because thehigh temperature in this region is allocated with low relativehumidity However the level of activity (light medium orheavy) and the work-rest time should be distributed alongwith the daytime according to the permissible value of theWBGT to avoid risks of thermal stresses and discomfortsensation A classification of different levels of activity thatcan be done and the corresponding highest permissible valueof the WBGT was reported in [7 23 24] A person whofollows these instructions will be safe in the outdoor insummer


Heat fatigue is possible withprolonged exposure and

activities

0

5

10

15

20

25

30

35

40

45

Safe


THI

119879119889

THI

(∘C

)


119879d

Figure 4 Time course of the temperature-humidity index (THI)estimated in the outdoor in a hot sunny summer day in the centralregion of Riyadh

WBG

T (∘

C)

0

5

10

15

20

25

30

35

40


No activity is recommended

All types of activities can be done without risks

Risk is expected accordingto the level of activity


Figure 5 Time course of the wet bulb-globe temperature index(WBGT) estimated in the outdoor in a hot sunny summer day inthe central region of Riyadh

Figure 6 shows the time course of PET indicating themean sensations of persons and the corresponding level ofheat stress along with the day of measurement A personwould feel very hot during most of the day (930 amndash500 pm) In themorning and during the nighttime themeansensations are distributed on the figure as slightly warmwarm and hot The PET is a universal index irrespective ofthe clothing and level of activityHowever increasing the levelof activity will provide more comfort sensation due to theincrease of sweating and respiration rates

The time course of the universal thermal climatic index(UTCI) is illustrated in Figure 7 this index was estimatedby using the UTCI calculator Based on the UTCI valuesin Figure 7 the distribution of the thermal sensation andthe corresponding heat stress is almost similar to that inFigure 6 Accordingly both PET and UTCI indices can beused successfully for the arid environment

Time (hmin)

PET

(∘C)

20

25

30

35

40

45

50

55Outdoor environment8-952012

Very hot (extreme heat stress)

Hot (strong heat stress)

Warm (moderate heat stress)

Slightly warm (slight heat stress)

60

80

100

120

140

160

180

200

220

240 20

40

60

Figure 6 Time course of the physiological effective temperature(PET) estimated in the outdoor in a hot summer day in the centralregion of Riyadh

Extremeheat stress

Very strongheat stress

Strongheat stress

Moderateheat stress

Time (hmin)

UTC

I (∘C)

20

25

30

35

40

45

50

60

80

100

120

140

160

180

200

220

240 20

40

60

Figure 7 Time course of the universal temperature climatic index(UTCI) estimated in the outdoor in a hot summer day in the centralregion of Riyadh

In addition to the PET the outputs of RayMan softwarealso include the predicted mean vote scale (PMV) Thusthe corresponding value of the predicted percentage ofdissatisfied (PPD) can be calculated using the well-knownexponential relation reported in [4] In general for differentlevels of activities (119872 = 1minus5) values of the PMVwere plottedagainst the values of the PPD in Figure 8 This figure showedthat even within the comfort zone that was illustrated in thefigure about 25 of the individuals would be dissatisfied anddislike the environment and about 75 of them would feelcomfortable and satisfied with the surrounding environment

5 Conclusion

Evaluation of human thermal comfort and heat stress ina summer day (May 2012) under arid climatic conditionswas presented Outdoor urban environment was selected for


PMVminus5 minus4 minus3 minus2 minus1 0 1 2 3 4 5

PPD

()

0

10

20

30

40

50

60

70

80

90


119872 = 1

119872 = 2

119872 = 5

Comfortzone

Figure 8 The predicted mean vote (PMV) against the predictedpercentage of dissatisfied (PPD) estimated at different levels ofactivities under the outdoor conditions in a hot sunny summer dayin the central region of Riyadh

the study The main conclusions from this study could besummarized as follows

(i) On hot sunny summer days individuals in the out-door environment would feel very hot and uncom-fortable most of the daytime especially around noonHeat stress is expected during most of the daytimehowever activities can be done without risks andpersons are safe from heat stress if they scheduledtheir activities according to the permissible values ofthe WBGT index

(ii) During most of the day heat fatigue is expected withprolonged exposure to solar radiation and activities

(iii) Both the PET and UTCI scales can be used success-fully for the arid environment to evaluate the thermalsensation and heat stress and their results are almostsimilar

Acknowledgment

This work was financially supported by The SustainableEnergy Technologies (SET) Deanship of Scientific ResearchKing Saud University Short track research Project no isSP12A1007

References

[1] K Van der Linden A C Boerstra A K Raue and S R KurversldquoThermal indoor climate building performance characterizedby human comfort responserdquo Energy and Buildings vol 34 no7 pp 737ndash744 2002

[2] T Stathopoulos H Wu and J Zacharias ldquoOutdoor humancomfort in an urban climaterdquo Building and Environment vol39 no 3 pp 297ndash305 2004

[3] B Givoni M Noguchi H Saaroni et al ldquoOutdoor comfortresearch issuesrdquo Energy and Buildings vol 35 no 1 pp 77ndash862003

[4] ANSIASHRAE Standard 55 Thermal Environmental Condi-tions for Human Occupancy American Society of HeatingRefrigeration and Air Conditioning Engineers Atlanta GaUSA 2004

[5] S Atthajariyakul and T Leephakpreeda ldquoNeural computingthermal comfort index for HVAC systemsrdquo Energy Conversionand Management vol 46 no 15-16 pp 2553ndash2565 2005

[6] A Forsthoff andH Neffgen ldquoThe assessment of heat radiationrdquoInternational Journal of Industrial Ergonomics vol 23 no 5-6pp 407ndash414 1999

[7] ldquoIntroduction to thermal comfort standardrdquo httpwwwutciorgcostpublicationsISO20Standards20Ken20Parsonspdf

[8] L Banhidi and Z B Biro ldquoDesign and calculation possibilitiesfor the heat exchange conditions of the human bodyrdquo PeriodicaPolytechnica vol 44 no 2 pp 185ndash193 2002

[9] L Serres A Trombe and JMiriel ldquoSolar fluxes absorbed by thedweller of glazed premises Influence upon the thermal comfortequationrdquo International Journal ofThermal Sciences vol 40 no5 pp 478ndash488 2001

[10] M Prek ldquoThermodynamical analysis of human thermal com-fortrdquo Energy vol 31 no 5 pp 732ndash743 2006

[11] S Yilmaz S Toy and H Yilmaz ldquoHuman thermal comfortover three different land surfaces during summer in the city ofErzurum Turkeyrdquo Atmosfera vol 20 no 3 pp 289ndash297 2007

[12] H Mayer J Holst and F Imbery ldquoHuman thermal comfortwithin urban structures in a central European cityrdquo in Pro-ceedings of the 7th International Conference on Urban ClimateYokohama Japan June-July 2009

[13] Y Epstein and D S Moran ldquoThermal comfort and the heatstress indicesrdquo Industrial Health vol 44 no 3 pp 388ndash3982006

[14] C Deb and A Ramachandraiah ldquoThe significance of phys-iological equivalent temperature (PET) in outdoor thermalcomfort studiesrdquo International Journal of Engineering Scienceand Technology vol 2 no 7 pp 2825ndash2828 2010

[15] S Thorsson F Lindberg I Eliasson and B Holmer ldquoDifferentmethods for estimating the mean radiant temperature in anoutdoor urban settingrdquo International Journal of Climatologyvol 27 no 14 pp 1983ndash1993 2007

[16] A Matzarakis F Rutz and H Mayer ldquoModelling radiationfluxes in simple and complex environmentsmdashapplication of theRayManmodelrdquo International Journal of Biometeorology vol 51no 4 pp 323ndash334 2007

[17] A Matzarakis F Rutz and H Mayer ldquoModeling the thermalbioclimate in urban areas with the RayMan modelrdquo in Pro-ceedings of the 23rd Conference on Passive and Low EnergyArchitecture (PLEA rsquo06) Geneva Switzerland September 2006

[18] httpwwwutciorgutci dokuphp[19] httpwwwutciorgutcineuutcineuphp[20] ldquoTemperature-humidity index scalerdquo httpwwwengineering-

toolboxcomheat-humidity-factor-d 1505html[21] ldquoEstimating wet bulb globe temperature using standard mete-

orological measurementsrdquo WSRC-MS-99-00757 httpstisrsgovfulltextms9900757ms9900757pdfsearch=rsquowsrcms990-0757rsquo

[22] A M Abdel-Ghany E Goto and T Kozai ldquoEvaporationcharacteristics in a naturally ventilated fog-cooled greenhouserdquoRenewable Energy vol 31 no 14 pp 2207ndash2226 2006


[23] T Itagi ldquoDeployment of laborsaving and comfortable technol-ogy on cultivation Managementrdquo in Handbook of GreenhouseHorticulture Jagh Ed pp 218ndash227 Agripress Tokyo Japan2003

[24] OSHA Technical Manual (OTM)-Section III Chapter IV HeatStress httpwwwoshagovdtsostaotmotm iiiotm iii 4html

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a universal index irrespective of clothing (clo values) andmetabolic activity (met values) (ii) it gives the real effect ofthe sensation of climate by human beings (iii) it is measuredin ∘C and so can be easily related to common experience and(iv) it is useful in both hot and cold climates so it can beapplied successfully in arid environment (high temperatureand low relative humidity) PET can be calculated simplyby RayMan software which is made freely available by itsauthors RayMan model avoids all the complications of thetwo-node model and takes simple inputs that is the air drybulb temperature (119879d) relative humidity (RH) wind velocity(119881) and mean radiant temperature (119879mrt) or global solarradiation flux (119878o) [16] RayMan model is valid for hot andsunny climate in which values of 119879mrt exceed 60∘C at aroundnoon Ranges of PET in ∘C for different grades of thermalperception by human beings are reported in [17]

Another scale was developed (ie the universal thermalclimatic index (UTCI)) as an equivalent temperature fora given combination of wind radiation humidity and airdry bulb temperature The associated assessment scale forthe UTCI was developed from the simulated physiologi-cal responses and comprises 10 categories that range fromextreme cold stress to very strong cold stress strong coldstress moderate cold stress slight cold stress no thermalstress moderate heat stress strong heat stress very strongheat stress and extreme heat stress [18] The UTCI canbe calculated simply by using the UTCI calculator whichis made freely available by its authors in [19] The inputparameters to this calculator are the air dry bulb temperature(119879d) relative humidity (RH) and the temperature differenceΔ119879 (Δ119879 = 119879mrt minus 119879d)

Survey of previous studies revealed that most of thesestudies focused on the environmental conditions for humanoccupancy either indoor or outdoor to evaluate the humanthermal comfort and heat stress potential in different areasworldwide However the comfort conditions under aridclimate (eg in the Arabian Peninsula) had never beenevaluated Accordingly evaluation of heat stress and humanthermal comfort in an urban setting under arid environmentsuch as in the Arabian Peninsula is urgently needed Thisstudy aims to evaluate human sensations and heat stress levelsin hot summer by (i) describing the mean sensations ofpersons in the outdoor arid environment and (ii) evaluatingthe level of risks due to heat stress potential One entire day(daytime and nighttime) was considered (May 8-9 2012) thatday represents to some extent the weather conditions insummer season Several indices (ie THI WBGT PET andUTCI) were evaluated to examine the applicability of usingthese scales in the arid environment

2 Theoretical Background

Factors affecting human thermal comfort can be classified asfollows

(i) Environmental factors such as the dry bulb temper-ature of air and its relative humidity (119879d and RH) aircurrent speed (119881) and the mean radiant temperature of thesurroundings (119879mrt) The latter is defined as that uniform

temperature of an imaginary black enclosure in which aperson would have the same radiation exchange with theactual environment Value of 119879mrt (

∘C) can be calculated bymeasuring 119879d (∘C) and the globe temperature 119879g (∘C) andusing the relation reported in [6 7] as

119879mrt =4radic(119879g + 273)

4

+

ℎcg

120576g120590(119879g minus 119879d) minus 273 (1)

where 120576g is the emissivity of the black globe (ie 120576g = 095)120590 is the Stefan-Boltzmann constant and ℎcg (Wmminus2 ∘Cminus1)is the convective heat transfer coefficient between the blackglobe surface and the surrounding air This coefficient can beestimated as in [6 15] by

ℎcg = max of

63(119881)06

11986304 forced convection

14(

119879g minus 119879d

119863)

025

free convection

(2)

where119863 is the diameter of the black globe sensor (015m) Inthe present study the free convection was considered becausethe wind speed was low (lt05m sminus1) during the experiment

(ii) Physiological factors such as the body metabolicheat generation rate (119872 in met 1met = 5815Wmminus2)which depends on different factors such as personal activitygender age nationality and type of clothing Thereforethese factors vary between individuals Accordingly manystatistical studies have been performed on large numbersof persons of all ages gender nationalities and activitiesto examine the human body responses to environmentalconditions and to arrive at a quantitative description ofhuman thermal comfort Thermal scales for human meansensation to the environment were developed based onhuman body energy balance under comfort conditions inwhich the rate of energy generated by a humanrsquos body (119872)should equal the rate of energy needed for the externalmechanical work (119882) plus the rate of energy release fromthe body through respiration evaporation convection andradiation The thermal efficiency (120578) of individual humanbodies as an engine (120578 = 119882119872) was estimated to be le20on average [8] Therefore a person should lose heat at a rateof (119872minus119882) in order to be comfortable

Thermal loss from the clothing surface of the body tothe surroundings is by radiation convection evaporation dueto sweating skin diffusion respiratory evaporative heat andrespiratory convective heat loss Humans in the outdoor orindoor are exposed to a heating load that depends mainly onthe difference between the surface temperature of clothing(119879cl) in

∘C and the mean radiant temperature (119879mrt) in (1)Value of the 119879cl is affected by the body and the surroundingconditions and it is impossible to be measured directly



119879cl = 357 minus 0028 (119872 minus119882)


119868cl119865cl [(119879cl + 273)4

minus (119879mrt + 273)4

]


(3)





ℎ119888= max of238(119879cl minus 119879d)

025


(4)




]) (119879d minus 1444) (5)











WBGT = 07 (119879nw) + 02 (119879g) + 01 (119879d) (6)








(∘C

)

0

5

10

15

20

25

30

35

40

45


Max

Min

Mean

Time (hmin)

60

80

100

120

140

160

180

200

220

240 20

40

60



Tem

pera

ture

s (∘C

) and

RH

()

0

10

20

30

40

50

60

0

200

400

600

800

1000

1200

RH119878119900



(Wmminus2)

Sola

r rad

iatio

n flu

x119878119900

119879g

119879d




Tem

pera

ture

s (∘C

)

0

10

20

30

40

50

60

70

119879mrt119879cl (119872 = 2)

119879cl (119872 = 5)



119879d







activities

0

5

10

15

20

25

30

35

40

45

Safe


THI

119879119889

THI

(∘C

)


119879d


WBG

T (∘

C)

0

5

10

15

20

25

30

35

40









Time (hmin)

PET

(∘C)

20

25

30

35

40

45

50






60

80

100

120

140

160

180

200

220

240 20

40

60


Extremeheat stress


Strongheat stress

Moderateheat stress

Time (hmin)

UTC

I (∘C)

20

25

30

35

40

45

50

60

80

100

120

140

160

180

200

220

240 20

40

60



5 Conclusion




PPD

()

0

10

20

30

40

50

60

70

80

90


119872 = 1

119872 = 2

119872 = 5

Comfortzone






Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in



119879cl = 357 minus 0028 (119872 minus119882)


119868cl119865cl [(119879cl + 273)4

minus (119879mrt + 273)4

]


(3)





ℎ119888= max of238(119879cl minus 119879d)

025


(4)




]) (119879d minus 1444) (5)











WBGT = 07 (119879nw) + 02 (119879g) + 01 (119879d) (6)








(∘C

)

0

5

10

15

20

25

30

35

40

45


Max

Min

Mean

Time (hmin)

60

80

100

120

140

160

180

200

220

240 20

40

60



Tem

pera

ture

s (∘C

) and

RH

()

0

10

20

30

40

50

60

0

200

400

600

800

1000

1200

RH119878119900



(Wmminus2)

Sola

r rad

iatio

n flu

x119878119900

119879g

119879d




Tem

pera

ture

s (∘C

)

0

10

20

30

40

50

60

70

119879mrt119879cl (119872 = 2)

119879cl (119872 = 5)



119879d







activities

0

5

10

15

20

25

30

35

40

45

Safe


THI

119879119889

THI

(∘C

)


119879d


WBG

T (∘

C)

0

5

10

15

20

25

30

35

40









Time (hmin)

PET

(∘C)

20

25

30

35

40

45

50






60

80

100

120

140

160

180

200

220

240 20

40

60


Extremeheat stress


Strongheat stress

Moderateheat stress

Time (hmin)

UTC

I (∘C)

20

25

30

35

40

45

50

60

80

100

120

140

160

180

200

220

240 20

40

60



5 Conclusion




PPD

()

0

10

20

30

40

50

60

70

80

90


119872 = 1

119872 = 2

119872 = 5

Comfortzone






Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


(∘C

)

0

5

10

15

20

25

30

35

40

45


Max

Min

Mean

Time (hmin)

60

80

100

120

140

160

180

200

220

240 20

40

60



Tem

pera

ture

s (∘C

) and

RH

()

0

10

20

30

40

50

60

0

200

400

600

800

1000

1200

RH119878119900



(Wmminus2)

Sola

r rad

iatio

n flu

x119878119900

119879g

119879d




Tem

pera

ture

s (∘C

)

0

10

20

30

40

50

60

70

119879mrt119879cl (119872 = 2)

119879cl (119872 = 5)



119879d







activities

0

5

10

15

20

25

30

35

40

45

Safe


THI

119879119889

THI

(∘C

)


119879d


WBG

T (∘

C)

0

5

10

15

20

25

30

35

40









Time (hmin)

PET

(∘C)

20

25

30

35

40

45

50






60

80

100

120

140

160

180

200

220

240 20

40

60


Extremeheat stress


Strongheat stress

Moderateheat stress

Time (hmin)

UTC

I (∘C)

20

25

30

35

40

45

50

60

80

100

120

140

160

180

200

220

240 20

40

60



5 Conclusion




PPD

()

0

10

20

30

40

50

60

70

80

90


119872 = 1

119872 = 2

119872 = 5

Comfortzone






Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in



activities

0

5

10

15

20

25

30

35

40

45

Safe


THI

119879119889

THI

(∘C

)


119879d


WBG

T (∘

C)

0

5

10

15

20

25

30

35

40









Time (hmin)

PET

(∘C)

20

25

30

35

40

45

50






60

80

100

120

140

160

180

200

220

240 20

40

60


Extremeheat stress


Strongheat stress

Moderateheat stress

Time (hmin)

UTC

I (∘C)

20

25

30

35

40

45

50

60

80

100

120

140

160

180

200

220

240 20

40

60



5 Conclusion




PPD

()

0

10

20

30

40

50

60

70

80

90


119872 = 1

119872 = 2

119872 = 5

Comfortzone






Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in



PPD

()

0

10

20

30

40

50

60

70

80

90


119872 = 1

119872 = 2

119872 = 5

Comfortzone






Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in













Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in

research article human thermal comfort and heat stress in...

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