Research Article Effect of the Evaporative Cooling on the...

Hindawi Publishing CorporationAdvances in MeteorologyVolume 2013 Article ID 361471 9 pageshttpdxdoiorg1011552013361471

Research ArticleEffect of the Evaporative Cooling on the Human ThermalComfort and Heat Stress in a Greenhouse under Arid Conditions

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

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

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

Correspondence should be addressed to A M Abdel-Ghany aghanyksuedusa

Received 7 March 2013 Revised 24 August 2013 Accepted 30 August 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

Thermal sensation and heat stress were evaluated in a plastic greenhouse with and without evaporative cooling under arid climaticconditions in Riyadh Saudi Arabia Suitable thermal comfort and heat stress scales were selected for the evaluation Experimentswere conducted in hot sunny days to measure the required parameters (ie the dry and wet bulb temperatures globe temperaturenatural wet bulb temperature and solar radiation flux) in the greenhouse The results showed that in the uncooled greenhouseworkers are exposed to strong heat stress and would feel very hot most of the day time they are safe from heat stress risk and wouldfeel comfortable during night An efficient evaporative cooling is necessary during the day to reduce heat stress and to improve thecomfort conditions and is not necessary at night In the cooled greenhouse workers can do any activity except at around noonthey should follow a proposed working schedule in which the different types of work were scheduled along the daytimes basedon the heat stress value To avoid heat stress and to provide comfort conditions in the greenhouses the optimum ranges of relativehumidity and air temperature are 48ndash55 and 24ndash28∘C respectively

1 Introduction

11 Background Human thermal comfort is defined as acondition of mind which expresses satisfaction with thesurrounding environment In the arid regions evaporativecooling is often applied to reduce the inside greenhouse airtemperature in summer Greenhouse environment is usuallydesigned according to the crop growth requirements (119879

119889 20ndash

30∘C RH 70ndash80) which in many situations may not besuitable for humans that are working in the greenhouse [1]This is mainly because relative humidity in the evaporatively-cooled greenhouses is much higher than outside High airhumidity may provide discomfort sensations and heat stressin the greenhouse On the other hand evaporative coolingand air stream can improve the comfort conditions in thegreenhouses in hot summer [2] Discomfort and heat stressreduce productivity of the greenhouse workers and maylead to more serious health problems especially for agedworkers [2] Therefore greenhouse workers should take care

when they enter the greenhouse in hot summer to protecttheir health from heat andor sunstroke [1] Factors affectinghuman thermal comfort and heat stress level can be classifiedaccording to [3] as (i) environmental factors such as the drybulb temperature of air and its relative humidity (119879

119889and

RH) air current speed and the mean radiant temperatureof the surrounding (119879mrt) (ii) Physiological factors suchas the body metabolic heat generation rate (119872 in met1met = 5815Wmminus2) which depends on different factorssuch as personal activity gender age nationality and typeof clothing Thermal scales for determining human meansensation to the environment and heat stress were developedbased on human body energy balance under comfort condi-tions in which the rate of energy generated by a humanrsquosbody (119872) should equal the rate of energy needed for theexternalmechanical work (119882) plus the rate of energy releasedfrom the body through respiration evaporation convectionand radiation Therefore a person should lose heat at arate of (119872-119882) in order to be comfortable Heat exchange

2 Advances in Meteorology

between the clothing surface of the body and surroundingis by radiation convection evaporation due to sweatingskin diffusion respiratory evaporative heat and respiratoryconvective heat loss

Human thermal comfort and heat stress in the indoorand outdoor have been discussed exhaustively in severalstudies such as [4ndash15] Most of these studies focused on theenvironmental conditions for human occupancy to evalu-ate the human thermal comfort and heat stress potentialHowever in greenhouses the wet bulb globe temperature(WBGT) was measured under mild climatic conditions [12] Both [1 2] considered the WBGT as an indication ofhuman thermal comfort However the comfort condition ofworkers is usually measured by the comfort scales not by theWBGTwhich is a scale of heat stressThese studies concludedthat the workers should take care to enter the greenhousesat around noon to avoid the heat stress risks In fact thegreenhouse environment should be evaluated by heat stresslevels together with the thermal sensation of workers

12 Heat Stress and Thermal Comfort Scales The WBGT(∘C) can be calculated in the greenhouse using a correlationproposed by ISO-7234 standard for the outdoor conditions(in the presence of solar radiation) and is given by [3 16] as

WBGT = 07 (119879nw) + 02 (119879119892) + 01 (119879119889) (1)

where 119879nw (∘C) is the natural wet bulb temperature (iecommonly measured with a thermometer that is coveredwith a moist white muslin wick and exposed to the atmo-sphere without ventilation or shading) 119879

119892(∘C) is the globe

temperature (ie commonly measured with a temperatureprobe placed in the center of a blackened hollow coppersphere) Both119879nw and119879119892 are passively exposed to the ambientenvironment To provide a schedule useful for greenhouseworkers a classification of different types of activities in thegreenhouse according to the highest permissible value of theWBGT was adapted from [2 16 17] and illustrated in Table 1

Besides the WBGT the temperature-humidity index(THI) is sometime used for evaluating heat stress and thepredictive mean vote (PMV) is used for human thermalcomfort [3] However the THI cannot precisely describe theheat stress in arid environment [18] Moreover the range ofthe PMV scale is limited (ie from minus3 representing very coldto +3 representing very hot) [3] it can not be applied fora greenhouse without cooling under arid conditions (119879

119889gt

45∘C RH lt 15) PMV may be useful for cooled green-

houses However under extreme arid conditions universalscales are needed to be used for evaluating the human thermalsensation and heat stressesThe suitable scales to be applied inthe arid environment could be summarized in the following

(1) The physiological effective temperature (PET) and theuniversal thermal climatic index (UTCI) are used forevaluating thermal comfort and heat stress as wellboth are in temperature scale PET gives an estima-tion of the thermal sensation and the correspondingheat stress PET is based on the Munich Energy-Balance Model for Individuals (MEMI) and a two-node model not being constrained by a steady state

Table 1 Various types of greenhouse work and the correspondinghighest permissible WBGT values

Type of greenhouse work 119872 (met) PermissibleWBGT (∘C)

No work is recommended mdash gt325Preparation of spinach defoliationof strawberry leaves swingstanding relaxed and so forth

07ndash1 lt325

Disbudding training pinchingplanting chemical spraying and soforth

1-2 lt305

Weeding fruit thinning fertilizingstanding poles extending screensand so forth

2-3 lt290

Mowing preparation of nurserybeds and so forth 3-4 lt275

Soil mounding row creationremoval of crop wastes and so forth 4-5 lt265

Digging with a spade working withan axe and so forth 5ndash7 lt25

approach PET is applicable for both the indoor andoutdoor environment studies [14] Several advantagesof using PET as reported by [14] include that (i) it isa universal index clothing (clo values) and metabolicactivity (met values) do not lead to significantly differ-ent PET values (ii) it gives the real effect of the sensa-tion of climate by human beings (iii) it is measured in∘C and so can be easily related to common experienceand (iv) it is useful in both hot and cold climates so itcan be applied successfully in the arid environmentIn the greenhouses PET can be calculated simply byRayMan software (ie freely available by its authors)RayMan model takes simple inputs that is the airdry bulb temperature (119879

119889) relative humidity (RH)

wind velocity and either mean radiant temperature(119879mrt) or the transmitted global solar radiation flux(119878119894) [19] In addition value of 119879mrt can be calculated

using theoretical models reported in [15] RayManmodel is valid for hot and sunny climate in whichvalues of 119879mrt exceed 60∘C at around noon Rangesof PET for different grades of thermal perception byhuman beings are reported in [20]

(2) The UTCI was developed for characterizing thermalstress It is an equivalent temperature for a givencombination of wind radiation humidity and air drybulb temperature The associated assessment scalefor the UTCI was developed from the simulatedphysiological responses and comprises 10 categoriesthat range from extreme cold stress to extremehot stress [21] The UTCI was designed for wideranges of activities clothing resistance and climaticconditions UTCI can be calculated simply by usingthe UTCI calculator which is made freely available byits authors on the website [22] The input parametersto this calculator are 119879

119889 RH and the temperature

difference Δ119879(Δ119879 = 119879mrt minus 119879119889)

Advances in Meteorology 3

(3) The standard effective temperature (SETlowast) indexdescribes the relationship between thermal sensation(TSENS) and discomfort (DISC) SETlowast is the mostappropriate way for comparing thermal sensationdiscomfort and physiological effect of a wide range ofenvironmental situations clothing and activity levelsunder extremeweather conditions [23]The SETlowast and119879mrt in the greenhouses can be calculated using Ray-Man software model if the transmitted global solarradiation flux (119878

119894) is available as an input parameter

Workers in the greenhouse are exposed to heating loadthat depends mainly on the difference between the surfacetemperature of clothing (119879cl) and the mean radiant temper-ature (119879mrt) Value of the 119879cl is affected by the body and thesurrounding conditions and it is impossible to be measureddirectlyTherefore value of119879cl is usually computed iterativelyaccording to [3 9] using the following equation

119879cl = 357 minus 0028 (119872 minus119882) minus 369 times 10minus8

119868cl119865cl

times [(119879cl + 273)4

minus (119879mrt + 273)4

] minus 119868cl119865clℎ119888 (119879cl minus 119879119889)

(2)

where 119868cl is the insulation resistance of the entire clothing(eg 119868cl = 011∘Cm2Wminus1 for greenhouse worker clothes) 119865clis the ratio of the clothed to the naked body area (119865cl = 12on average) and ℎ

119888is the convective coefficient between the

clothing surface and the surrounding air (Wmminus2 ∘Cminus1) and isgiven by [3 7 8] as

ℎ119888= max of238(119879cl minus 119879119889)

025

free convection121radic119881 forced convection

(3)

Survey of previous studies revealed that no studies havebeen done to evaluate human thermal comfort and heat stressin greenhouses under arid climatic conditions Accordinglythe objective of this study is to evaluate human comfort andheat stress levels in a greenhouse with and without evapora-tive cooling under hot arid conditions by (i) describing themean thermal sensations of workers (ii) evaluating the levelsof heat stress theworkers are exposed to and (iii) determiningthe effects of the evaporative cooling of the greenhouse airon the heat stress and on the workers thermal sensationsTwo hot sunny days were selected for the study in one daythe greenhouse was without cooling and in the other day thegreenhouse was cooled by a wet pad and fans system Severalindices (ie WBGT PET UTCI and SETlowast) were used for theevaluation

2 Experimental Measurements

Two experiments were conducted in a greenhouse with afloor area of 48m2 coveredwith a plastic film (02mm thick)and include a wet pad and fans system for the evaporativecooling The greenhouse was oriented in a N-S direction onthe Agricultural Research and Experiment Station Agricul-ture EngineeringDepartment King SaudUniversity (RiyadhSaudi Arabia 46∘ 471015840 E longitude and 24∘ 391015840N latitude)

The measuring instruments were installed at 2m above thegreenhouse floor Layout dimensions and locations of theinstruments are illustrated in Figure 1 The greenhouse wasmechanically ventilated using three suction fans (each of130W and 458m3minminus1) The measurements were carriedout during two 24-hour periods (each period from 6 amto 6 am in the next day) in hot sunny days (May 8-9 14-15 2012) to measure the required parameters in the green-house During the first period the greenhouse was withoutcooling and during the second period evaporative coolingwas applied The measured data were taken every 10 secaveraged and recorded at every 10min in a data logger (CR-23X Micrologger) and then averaged at every one hour Themeasured parameters were (i) dry and wet bulb temperatures(119879119889and 119879

119908) using aspirated psychrometer the psychrometer

had two type-119879 thermocouples (copper constantan of 03mmin diameter) The psychrometers were calibrated and theerror was le12∘C for a dry bulb temperature up to 100∘C(ii) globe temperature (119879

119892) using black globe thermometric

probe (BST131) having a globe diameter of 015m a timeresponse of 20min surface reflectance le2 a workingtemperature range of minus50∘C to 80∘C and a measuring errorof plusmn05∘C for a dry bulb temperature up to 80∘C (iii)natural wet bulb temperature (119879nw) using a type-119879 copperconstantan thermocouple of 03mm in diameter whosejunction was covered with a moist white muslin wick andkept exposed to the greenhouse environment (iv) globalsolar radiation flux inside the greenhouse (119878

119894 Wmminus2) using

CMP3 Pyranometer (Kipp amp Zonen BV Inc USA) havinga maximum error of plusmn2 a working temperature range ofminus40∘C to +80∘C and a wavelength range of 310ndash2800 nmThe average air speed in the greenhouse was estimated basedon the greenhouse vertical cross-section area and the flowrate of air in the greenhouse to be around 03m sminus1 RH wascalculated by substituting the measured values of 119879

119889and 119879

119908

in psychrometric relations reported in [24]

3 Results and Discussion

In the arid environment existing high air temperature (119879119889)

low relative humidity (RH) and intensive solar radiation flux(119878119894) in the greenhouses (Figure 2(a)) make use of evaporative

cooling which is an essential requirement to grow cropsand to protect workers from heat stress risks At aroundnoon the evaporative cooling of the inside greenhouse airreduced the daily maximum hourly value of 119879

119889by about

7sim8∘C and enhanced the daily minimum hourly value ofRH by about 20sim25 (Figures 2(a) and 2(b)) In the presentstudy the effectiveness of the cooling systemwas low becausethe pad was old and partially blocked with salts on the padsurfaces (the cooling water used was brackish)Therefore thereduction in 119879

119889and the increase in RH were relatively low

compared to the optimum environment for crop growth to beachieved (20ndash30∘C119879

119889and 70ndash80RH) A slight reduction in

119878119894may occur due to the effect of water vapor that is attenuates

andor absorbs the transmitted solar radiation into the green-house It is worth mentioning that the current experimentswere conducted in two different days with each having its


Pyranometer to measure solar radiation flux

AirWet pad

Solarmeter

Fans Air12

3

4

1

2

3

4

820

115

320

Aspirated psychrometer to measure dry and wet bulb temperature (Td Tw)Black glob sensor to measure TgThermocouple junction to measure the natural wet bulb temperature (Tnw)

Figure 1 Layout dimensions (in cm) and locations of the instruments used to measure the required environmental parameters in thegreenhouse

70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0

60 100 140 180 220 20 60Time of the day (hmin)

Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)

Without cooling (May 8-9 2012)

(a)

70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0


Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)

With cooling (May 14-15 2012)

(b)

Figure 2 Time course of the dry bulb temperature (119879119889

) relative humidity (RH) and solar radiation flux (119878119894

) measured in the greenhouse(a) without cooling and (b) with cooling of the inside air

own 119879119889and RH distributions along with the dayTherefore it

is difficult to show the exact effects of the evaporative coolingon 119879119889 RH 119878

119894 and on the other parameters as well To show

the exact effect two identical greenhouses are needed one iswithout cooling and the other with cooling and should beoperated on time at the same location

The values of119879mrt (Figures 3(a) and 3(b)) PE and SETlowast in

degree ∘C were calculated by using RayMan software modelThe input parameters were the values of 119879

119889 RH and 119878

119894in

addition to the body input parameters (ie human activity119872 value clothing factor 06 clo gender man height 175 cmand weight 75 kg) The main source of discomfort and heat

stress in the greenhouses is the heat load exchanges betweenthe workers and their surroundings through radiation andconvection modes Radiation exchange depends on thedifference to the power four between the mean radianttemperature (119879mrt) and clothing surface temperature (119879cl)the convection exchange depends on the difference between119879cl and 119879119889 The time courses of the 119879mrt 119879cl (predicted byusing (2)) and 119879

119889are illustrated in Figures 3(a) and 3(b) in

the greenhouse without and with cooling respectively Evap-orative cooling reduces 119879mrt 119879cl and 119879119889 and consequentlymodifies the environment in the greenhouse This figureshows that during the day time 119879mrt was much higher than


70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(a)

70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(b)

Figure 3 Time course of the mean riant temperature (119879mrt) clothing temperature (119879cl) and dry bulb temperature (119879119889

) estimated in thegreenhouse (a) without cooling and (b) with cooling of the inside air


WBG

T (∘

C)

45

40

35

30

25

20

15

10

5

0

No activity is recommended

Risk is expected accordingto the level of activity

All types of activities can bedone without risks

Without cooling (May 8-9 2012)With cooling (May 14-15 2012)

Figure 4 Time course of the wet bulb globe temperature index(WBGT) estimated in the greenhouse with and without cooling ofthe inside air

119879cl Therefore workerrsquos body always experiences a positiveheat radiation load (ie heat gain) During the night time119879mrt was lower than 119879cl causing a negative radiation heat load(released from the body) The convection exchange is minorduring the day and night times However radiation heat loadhas the dominant effect because the temperature difference(119879mrt-119879cl) is much higher than (119879

119889-119879cl)

With coolingWithout cooling

PET

(∘C)

60

50

40

30

20

10

0

Comfortable (no heat stress)

Slightly warm (slight heat stress)

Warm (moderate heat stress)

Hot (strong heat stress)

Very hot (extreme heat stress)

60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20

Figure 5 Time course of the physiological effective temperature(PET) estimated in the greenhouse with and without cooling of theinside air

Equation (1) is used to estimate the WBGT based onthe measured values of 119879

119889 119879119892 and 119879nw Figure 4 illustrates

the time course of the WBGT during 24-hour period inthe greenhouse with and without cooling The evaporativecooling significantly reduces the WBGT and the heat stressas well and consequently improves the comfort conditionsof workers According to the predicted values of the WBGT


60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable

Slightly uncomfortable


Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

Without coolingSE

Tlowast(∘

C)

(a)

60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

With cooling

SETlowast

(∘C)

(b)

Figure 6 Time course of the standard effective temperature (SETlowast) estimated in the greenhouse (a) without cooling and (b) with cooling ofthe inside air

in the cooled greenhouse several types of activities can bedone safely along the day and night times However thelevel of activity (light medium or heavy) and the work-resttime should be scheduled along the daytime according tothe permissible value of the WBGT to avoid risks of thermalstresses and discomfort sensation A classification of differentlevels of activity that can be done and the correspondinghighest permissible value of the WBGT is illustrated inTable 1 Workers following these instructions (Table 1) willbe safe in the greenhouse in hot arid climate

Figure 5 illustrates the time course of the PET (∘C)indicating the mean sensations of workers and the cor-responding level of heat stress during 24-hour period inthe greenhouse with and without cooling of the inside airEfficient evaporative cooling is expected to reduce the heatstress level and improve the comfort conditions of workersHowever in this study workers would feel very hot andexposed to very strong heat stress during most of the day(10 amndash330 pm) because the cooling system operated at lowefficiency During the rest of the day the mean sensations aredistributed on the figure as slightly warm warm and hotWorkers would feel comfortable during the night time andslightly warm in the morning and in the afternoon

The SETlowast index was calculated by RayMan softwaremodel based on the hourly estimated values of 119879

119889 RH and

119878119894in the greenhouse without and with cooling of the inside

air and as illustrated in Figures 6(a) and 6(b) respectivelyUnlike the PET and UTCI indices the SETlowast depends of thelevel of activity (met value) Accordingly the time course ofthe SETlowast is estimated in the greenhouse for two levels ofactivities (119872 = 1 and 2met)The thermal sensation (TSENS)

UTC

I (∘C)

Extreme heat stressVery strongheat stressStrongheat stressModerateheat stress

No

heat

stre

ss


50

45

40

35

30

25

20

15

10

5

0

60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20

Figure 7 Time course of the universal thermal climatic index(UTCI) estimated in the greenhouse with and without cooling ofthe inside air

and the discomfort conditions (DISC) were also illustratedin Figures 6(a) and 6(b) Values of SETlowast give more detailsfor the distribution of thermal sensation and discomfortconditions along the day and night times Apart from thecooling effect slight increase in the level of activity (from 1 to2met) improves the comfort conditions during the daytimeIn the cooled greenhouse workers would feel uncomfortableat around noon and during the night times The evaporative


100

80

60

40

20

0

20 22 24 26 28 30 32 34 36 38

PPD

()

With cooling M = 1

Td (∘C)

(a)

100

80

60

40

20

0

PPD

()

40 45 50 55 60 65 70 75

M = 1 with cooling

RH ()

(b)

Figure 8 The dry bulb temperature (119879119889

) and relative humidity (RH) against the predicted percentage of dissatisfied (PPD) estimated at lowor no activity (119872 = 1) in the cooled greenhouse (a) for 119879

119889

and (b) for RH

cooling slightly reduces the heat stress level and improves thecomfort conditions during the day time However using theevaporative cooling during the night time is not necessary Anefficient cooling to the greenhouse air should be performedduring the day time to achieve better thermal sensation andto avoid heat stress risks

The time course of the universal thermal climatic index(UTCI) is illustrated in Figure 7 This index was estimatedin the greenhouse during 24-hour period with and withoutcooling of the inside air The UTCI calculator [21 22] wasused and the hourly estimated values of 119879

119889 RH and the

temperature difference (119879mrt-119879119889) were the input parametersto the calculator Based on the UTCI values in Figure 7 thetime period at which a certain level of heat stress occurred(periods of slight moderate strong and very strong) isalmost similar to those in Figure 5 Accordingly either PETor UTCI (ie heat stress scales) can be used to describeheat stress levels in the greenhouses along the day underarid conditions However SETlowast is a thermal comfort scaleprovides more specific information about thermal sensation(TSENS) and discomfort conditions (DISC) along the dayand night times

In the cooled greenhouse using the predictive mean voteindex (PMV) with its limited scale (minus3 to +3) is possibleto evaluate the comfort conditions Value of the PMV wascalculated by using RayMan software model as PET andSETlowast scales Thus the percent of workers who likely feeluncomfortable (ie the predicted percentage of dissatisfiedPPD) can be calculated according to [3] as PPD = 100 minus95Exp (minus003353PMV4 minus 02179PMV2) Values of the PPDwas estimated for the cooled greenhouse and plotted against119879119889in Figure 8(a) and against RH in Figure 8(b) respectively

The results of this figure showed that the lowest valueof the PPD was about 5 when 119879

119889was in the range of

24minus28∘C (Figure 8(a)) and when RH was in the range of48ndash55 (Figure 8(b)) This means that about 95 of thegreenhouse workers would be satisfied with the surrounding

environment under such conditions These results are inaccordance with the standard comfort conditions (ie PPD lt5 when 119879

119889= 25∘C and RH = 50) [3] Lowering 119879

119889to

be less than 24∘C and RH less than 48 will produce cooledfeeling and cold stress and increasing 119879

119889to be more than

28∘C and RH more than 55 will produce hot feeling andthermal stressHowever inmost cases these ranges of RHand119879119889are not exactly suitable for plant growth requirements and

this is another challenge should be taken into consideration

4 Conclusion and Recommendation

Human thermal comfort and heat stress in a greenhouse insummer under arid climatic conditionswere evaluated Effectof the evaporative cooling of the greenhouse air on the heatstress and on the comfort conditions of workers was alsoexamined The main conclusions from this study could besummarized as follows

(i) In the uncooled greenhouses workers would feel veryhot and uncomfortable most of the day time espe-cially at around noon the heat stress risk is expectedHowever workers are safe from heat stress and wouldfell comfort most of the night time

(ii) Efficient evaporative cooling of the greenhouse aircan improve the comfort conditions of workers andreduce the heat stress levels during the hot sunny daysin arid climate Cooling the greenhouse air shouldbe applied during the day time in summer Howeverduring the night times cooling is not necessary

(iii) In the cooled greenhouses the activities of workersshould be scheduled and distributed along the dayaccording to the highest permissible values of theWBGT

(iv) The PET or the UTCI scale can be used to evaluateheat stress potential in the greenhouses under arid


conditions The SETlowast is an optimum scale to specif-ically describe the thermal sensations and discomfortconditions along the day in the greenhouses at anylevel of activity

(v) A relative humidity in the range of 48ndash55 and adry bulb temperature in the range of 24ndash28∘C in thegreenhouses can provide comfort sensation to around95 of the greenhouse workers in arid climate

Nomenclatures

ℎ119888 Convective coefficient between the

clothing surface and the surrounding(Wmminus2 ∘Cminus1)

119868cl Insulation factor of the entire clothing(W ∘Cmminus2)

119872 Metabolic heat generation rate (met1met = 5815Wmminus2)

RH Relative humidity of the greenhouse air()

119879119889 Dry bulb temperature of the greenhouse

air (∘C)119879cl Clothing surface temperature (∘C)119879119892 Globe temperature (∘C)119879nw Natural wet bulb temperature of the

greenhouse air (∘C)119879119908 Wet bulb temperature of the greenhouse

air (∘C)119879mrt Mean radiant temperature in the

greenhouse (∘C)119882 External mechanical work done by the

worker (Wmminus2)

Abbreviations of Thermal Scales

PET Physiological effective temperature (∘C)PMV Predictive mean vote scale (mdash)PPD Predicted percentage of dissatisfied ()SETlowast Standard effective temperature (∘C)UTCI Universal thermal climatic index (∘C)WBGT Wet bulb globe temperature (∘C)

Acknowledgment

This work was supported by the National Plan for Sciencesand Technology (NPST) Program King Saud University as aresearch project No 09-ADV914-02

References

[1] L Okushima S Sase L In-Bok and B J Bailey ldquoThermalenvironment and stress of workers in naturally ventilatedgreenhouses under mild climaterdquo in Proceedings of the 5thInternational Symposium on Protected Cultivation in MildWinter Climates Current Trends for Suistainable TechnologiesFernandez Martinez and Castilla Eds pp 793ndash798 2001

[2] T Shimazu H Hamamoto T Okada T Ikeda and K TanakaldquoMicroclimate and human thermal comfort in pipe green-houses with insect-proof screens for vegetable cultivation withrestricted use of chemical pesticidesrdquo Journal of AgriculturalMeteorology of Japan vol 60 no 5 pp 813ndash816 2005

[3] ldquoThermal environmental conditions for human occupancyrdquoANSIASHRAE Standard 55The American Society of HeatingRefrigeration and Air Conditioning Engineers Atlanta GaUSA 2004

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

[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 PeriodicaPolytechnicaMechanical Engineering vol 44 no 2 pp 185ndash1932000

[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-ceeding of the 7th International Conference on Urban ClimateYokohama Japan June2009

[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 ldquoReview of studies on outdoorthermal comfort using physiological equivalent temperature(PET)rdquo International Journal of Engineering Science and Tech-nology vol 92 no 7 pp 2825ndash2828 2011

[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] ldquoEstimating wet bulb globe temperature using standard mete-orological Measurementsrdquo WSRC-MS-99-00757 httpstisrsgovfulltextms9900757ms9900757pdfsearch=rsquowsrcms9900757rsquo

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

[18] A M Abdel-Ghany I M Al-Helal and M R Shady ldquoHumanthermal comfort and heat stress in an outdoor urban arid envi-ronment a case studyrdquoAdvances inMeteorology vol 2013 Arti-cle ID 693541 7 pages 2013


[19] A Matzarakis F Rutz and H Mayer ldquoModelling radiation flu-xes in simple and complex environments application of theRayManmodelrdquo International Journal of Biometeorology vol 51no 4 pp 323ndash334 2007

[20] A Matzarakis F Rutz and H Mayer ldquoModeling the ther-mal bioclimate in urban areas with the RayMan modelrdquo inProceeding of the 23rd Conference on Passive and Low EnergyArchitecture (PLEA rsquo06) Geneva Switzerland September 2006

[21] httpwwwutciorgutci dokuphp[22] httpwwwutciorgutcineuutcineuphp[23] ldquoOSHA Technical Manual (OTM) Section III chapter IV heat

stressrdquo httpswwwoshagovdtsostaotmotm iiiotm iii 4html

[24] 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

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of


EarthquakesJournal of


Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining


Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics

OceanographyInternational Journal of


Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering


GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of


OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in


MineralogyInternational Journal of


MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Geological ResearchJournal of


Geology Advances in


between the clothing surface of the body and surroundingis by radiation convection evaporation due to sweatingskin diffusion respiratory evaporative heat and respiratoryconvective heat loss

Human thermal comfort and heat stress in the indoorand outdoor have been discussed exhaustively in severalstudies such as [4ndash15] Most of these studies focused on theenvironmental conditions for human occupancy to evalu-ate the human thermal comfort and heat stress potentialHowever in greenhouses the wet bulb globe temperature(WBGT) was measured under mild climatic conditions [12] Both [1 2] considered the WBGT as an indication ofhuman thermal comfort However the comfort condition ofworkers is usually measured by the comfort scales not by theWBGTwhich is a scale of heat stressThese studies concludedthat the workers should take care to enter the greenhousesat around noon to avoid the heat stress risks In fact thegreenhouse environment should be evaluated by heat stresslevels together with the thermal sensation of workers

12 Heat Stress and Thermal Comfort Scales The WBGT(∘C) can be calculated in the greenhouse using a correlationproposed by ISO-7234 standard for the outdoor conditions(in the presence of solar radiation) and is given by [3 16] as

WBGT = 07 (119879nw) + 02 (119879119892) + 01 (119879119889) (1)

where 119879nw (∘C) is the natural wet bulb temperature (iecommonly measured with a thermometer that is coveredwith a moist white muslin wick and exposed to the atmo-sphere without ventilation or shading) 119879

119892(∘C) is the globe

temperature (ie commonly measured with a temperatureprobe placed in the center of a blackened hollow coppersphere) Both119879nw and119879119892 are passively exposed to the ambientenvironment To provide a schedule useful for greenhouseworkers a classification of different types of activities in thegreenhouse according to the highest permissible value of theWBGT was adapted from [2 16 17] and illustrated in Table 1

Besides the WBGT the temperature-humidity index(THI) is sometime used for evaluating heat stress and thepredictive mean vote (PMV) is used for human thermalcomfort [3] However the THI cannot precisely describe theheat stress in arid environment [18] Moreover the range ofthe PMV scale is limited (ie from minus3 representing very coldto +3 representing very hot) [3] it can not be applied fora greenhouse without cooling under arid conditions (119879

119889gt

45∘C RH lt 15) PMV may be useful for cooled green-

houses However under extreme arid conditions universalscales are needed to be used for evaluating the human thermalsensation and heat stressesThe suitable scales to be applied inthe arid environment could be summarized in the following

(1) The physiological effective temperature (PET) and theuniversal thermal climatic index (UTCI) are used forevaluating thermal comfort and heat stress as wellboth are in temperature scale PET gives an estima-tion of the thermal sensation and the correspondingheat stress PET is based on the Munich Energy-Balance Model for Individuals (MEMI) and a two-node model not being constrained by a steady state

Table 1 Various types of greenhouse work and the correspondinghighest permissible WBGT values

Type of greenhouse work 119872 (met) PermissibleWBGT (∘C)

No work is recommended mdash gt325Preparation of spinach defoliationof strawberry leaves swingstanding relaxed and so forth

07ndash1 lt325

Disbudding training pinchingplanting chemical spraying and soforth

1-2 lt305

Weeding fruit thinning fertilizingstanding poles extending screensand so forth

2-3 lt290

Mowing preparation of nurserybeds and so forth 3-4 lt275

Soil mounding row creationremoval of crop wastes and so forth 4-5 lt265

Digging with a spade working withan axe and so forth 5ndash7 lt25

approach PET is applicable for both the indoor andoutdoor environment studies [14] Several advantagesof using PET as reported by [14] include that (i) it isa universal index clothing (clo values) and metabolicactivity (met values) do not lead to significantly differ-ent PET values (ii) it gives the real effect of the sensa-tion of climate by human beings (iii) it is measured in∘C and so can be easily related to common experienceand (iv) it is useful in both hot and cold climates so itcan be applied successfully in the arid environmentIn the greenhouses PET can be calculated simply byRayMan software (ie freely available by its authors)RayMan model takes simple inputs that is the airdry bulb temperature (119879

119889) relative humidity (RH)

wind velocity and either mean radiant temperature(119879mrt) or the transmitted global solar radiation flux(119878119894) [19] In addition value of 119879mrt can be calculated

using theoretical models reported in [15] RayManmodel is valid for hot and sunny climate in whichvalues of 119879mrt exceed 60∘C at around noon Rangesof PET for different grades of thermal perception byhuman beings are reported in [20]

(2) The UTCI was developed for characterizing thermalstress It is an equivalent temperature for a givencombination of wind radiation humidity and air drybulb temperature The associated assessment scalefor the UTCI was developed from the simulatedphysiological responses and comprises 10 categoriesthat range from extreme cold stress to extremehot stress [21] The UTCI was designed for wideranges of activities clothing resistance and climaticconditions UTCI can be calculated simply by usingthe UTCI calculator which is made freely available byits authors on the website [22] The input parametersto this calculator are 119879

119889 RH and the temperature

difference Δ119879(Δ119879 = 119879mrt minus 119879119889)






119868cl119865cl

times [(119879cl + 273)4

minus (119879mrt + 273)4


(2)




ℎ119888= max of238(119879cl minus 119879119889)

025


(3)











119889and 119879

119908






119889by about









AirWet pad

Solarmeter

Fans Air12

3

4

1

2

3

4

820

115

320



70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0


Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)


(a)

70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0


Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)


(b)










119889 RH and 119878

119894in






70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(a)

70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(b)




WBG

T (∘

C)

45

40

35

30

25

20

15

10

5

0







119889-119879cl)


PET

(∘C)

60

50

40

30

20

10

0






60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20






60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

Without coolingSE

Tlowast(∘

C)

(a)

60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

With cooling

SETlowast

(∘C)

(b)





119889 RH and



UTC

I (∘C)


No

heat

stre

ss


50

45

40

35

30

25

20

15

10

5

0

60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20




100

80

60

40

20

0

20 22 24 26 28 30 32 34 36 38

PPD

()

With cooling M = 1

Td (∘C)

(a)

100

80

60

40

20

0

PPD

()

40 45 50 55 60 65 70 75

M = 1 with cooling

RH ()

(b)



119889

and (b) for RH



119889 RH and the







119889= 25∘C and RH = 50) [3] Lowering 119879

119889to














Nomenclatures











worker (Wmminus2)



Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in






119868cl119865cl

times [(119879cl + 273)4

minus (119879mrt + 273)4


(2)




ℎ119888= max of238(119879cl minus 119879119889)

025


(3)











119889and 119879

119908






119889by about









AirWet pad

Solarmeter

Fans Air12

3

4

1

2

3

4

820

115

320



70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0


Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)


(a)

70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0


Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)


(b)










119889 RH and 119878

119894in






70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(a)

70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(b)




WBG

T (∘

C)

45

40

35

30

25

20

15

10

5

0







119889-119879cl)


PET

(∘C)

60

50

40

30

20

10

0






60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20






60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

Without coolingSE

Tlowast(∘

C)

(a)

60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

With cooling

SETlowast

(∘C)

(b)





119889 RH and



UTC

I (∘C)


No

heat

stre

ss


50

45

40

35

30

25

20

15

10

5

0

60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20




100

80

60

40

20

0

20 22 24 26 28 30 32 34 36 38

PPD

()

With cooling M = 1

Td (∘C)

(a)

100

80

60

40

20

0

PPD

()

40 45 50 55 60 65 70 75

M = 1 with cooling

RH ()

(b)



119889

and (b) for RH



119889 RH and the







119889= 25∘C and RH = 50) [3] Lowering 119879

119889to














Nomenclatures











worker (Wmminus2)



Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in



AirWet pad

Solarmeter

Fans Air12

3

4

1

2

3

4

820

115

320



70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0


Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)


(a)

70

60

50

40

30

20

10

0

700

600

500

400

300

200

100

0


Td

Tg Si

RH

Tem

pera

ture

s (∘C)

and

RH (

)

Sola

r rad

iatio

n flu

xSi

(W m

minus2)


(b)










119889 RH and 119878

119894in






70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(a)

70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(b)




WBG

T (∘

C)

45

40

35

30

25

20

15

10

5

0







119889-119879cl)


PET

(∘C)

60

50

40

30

20

10

0






60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20






60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

Without coolingSE

Tlowast(∘

C)

(a)

60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

With cooling

SETlowast

(∘C)

(b)





119889 RH and



UTC

I (∘C)


No

heat

stre

ss


50

45

40

35

30

25

20

15

10

5

0

60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20




100

80

60

40

20

0

20 22 24 26 28 30 32 34 36 38

PPD

()

With cooling M = 1

Td (∘C)

(a)

100

80

60

40

20

0

PPD

()

40 45 50 55 60 65 70 75

M = 1 with cooling

RH ()

(b)



119889

and (b) for RH



119889 RH and the







119889= 25∘C and RH = 50) [3] Lowering 119879

119889to














Nomenclatures











worker (Wmminus2)



Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(a)

70

60

50

40

30

20

10

0

60 100 140 180 220 20 60Time (hmin)

Td

Tem

pera

ture

s (∘C)


Tcl

Tmrt

(b)




WBG

T (∘

C)

45

40

35

30

25

20

15

10

5

0







119889-119879cl)


PET

(∘C)

60

50

40

30

20

10

0






60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20






60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

Without coolingSE

Tlowast(∘

C)

(a)

60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

With cooling

SETlowast

(∘C)

(b)





119889 RH and



UTC

I (∘C)


No

heat

stre

ss


50

45

40

35

30

25

20

15

10

5

0

60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20




100

80

60

40

20

0

20 22 24 26 28 30 32 34 36 38

PPD

()

With cooling M = 1

Td (∘C)

(a)

100

80

60

40

20

0

PPD

()

40 45 50 55 60 65 70 75

M = 1 with cooling

RH ()

(b)



119889

and (b) for RH



119889 RH and the







119889= 25∘C and RH = 50) [3] Lowering 119879

119889to














Nomenclatures











worker (Wmminus2)



Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

Without coolingSE

Tlowast(∘

C)

(a)

60 100 140 180 220 20 60

55

50

45

40

35

30

25

20

15

10

5

0

Com

fort

able

Neutral

Very uncomfortable

Uncomfortable



Limited tolerance

Very coldCold

Cool

Slightly cool

Slightly warm

Warm

Uncomfortable

Hot

Very uncomfortable

Very hot

DISCTSENS

M = 1metM = 2met

Unacceptable hot

Time (hmin)

With cooling

SETlowast

(∘C)

(b)





119889 RH and



UTC

I (∘C)


No

heat

stre

ss


50

45

40

35

30

25

20

15

10

5

0

60 80 100 120 140 160 180 200 220 240 40 60Time (hmin)

20




100

80

60

40

20

0

20 22 24 26 28 30 32 34 36 38

PPD

()

With cooling M = 1

Td (∘C)

(a)

100

80

60

40

20

0

PPD

()

40 45 50 55 60 65 70 75

M = 1 with cooling

RH ()

(b)



119889

and (b) for RH



119889 RH and the







119889= 25∘C and RH = 50) [3] Lowering 119879

119889to














Nomenclatures











worker (Wmminus2)



Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


100

80

60

40

20

0

20 22 24 26 28 30 32 34 36 38

PPD

()

With cooling M = 1

Td (∘C)

(a)

100

80

60

40

20

0

PPD

()

40 45 50 55 60 65 70 75

M = 1 with cooling

RH ()

(b)



119889

and (b) for RH



119889 RH and the







119889= 25∘C and RH = 50) [3] Lowering 119879

119889to














Nomenclatures











worker (Wmminus2)



Acknowledgment


References


































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in




Nomenclatures











worker (Wmminus2)



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 Effect of the Evaporative Cooling on the...

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Transcript of Research Article Effect of the Evaporative Cooling on the...