Approaches to assessment of hot environment.
Kralikova, R. ; Sokolova, H. ; Wessely, E. 等
1. Introduction
Reliable assessment of thermo-hygric microclimate should take into
consideration all six primary factors affecting thermal comfort i.e. air
temperature, radiation, relative humidity, air velocity, thermo-physical
properties of clothing and metabolic rate. One way of how to evaluate
thermal environment is the use of thermal comfort indices, which
combines two or more parameters of thermo-hygric microclimate in one
variable. There are several thermal comfort indices for evaluation of
different thermal environments (ASHRAE, 2009).
2. View of Indices for Assessment of Different Thermal Environments
One way of how to evaluate thermal environment is to use thermal
comfort indices, which combines two or more parameters of thermal
microclimate into one variable. Indices can be divided into (Auliciems,
2007):
* Analytical indices--based on theoretical concepts,
* Empirical indices--based on object measurements or on simplified
relationships that do not necessarily follow a theory.
Indicators can be also divided according to class into which the
thermal environment is addressed to: moderate, hot and cold environment
(Fig.1).
[FIGURE 1 OMITTED]
ISO organization has created a number of important standards which
are dealing with categories used by thermal environment indices:
* IREQ--refers to minimum clothing insulation required by workers.
The index is used for calculation of clothing ensemble and was applied
as an initial attempt at providing thermal comfort. This index
represents a method to calculate the thermal stress associated with the
exposure to cold environments.
* WCI--Wind Chill Index is the equivalent to perceived temperature
that measures the additional loss of thermal comfort of the human body
due to the wind (especially) in winter outdoor conditions.
* PMV--Predicted Mean Vote Index. The index predicts the mean
response of a larger group of people according to the ASHRAE thermal
sensation scale where: +3 hot, +2 warm, +1 slightly warm, 0 neutral, -1
slightly cool, -2 cool, -3 cold (Fig. 2). The PMV index was expressed by
P.O. Fanger as:
PMV = (0.303[e.sup.-0,0036M] + 0.028) L (1)
where: M--metabolic rate, L--thermal load--defined as the
difference between the internal heat production and the heat loss to the
actual environment--for a person at comfort skin temperature and
evaporative heat loss by sweating at the actual activity level.
Fig. 2. Assessment Predicted Mean Vote
* PPD index (Predicted Percentage Dissatisfied) is a quantitative
measure of the thermal comfort of a group of people at a particular
thermal environment. At least approx. 5% of people in a group will be
dissatisfied with the thermal climate--even with PMV = 0, see Fig. 3.
* The Wet Bulb Globe Temperature (WBGT) is a composite temperature
used to estimate the effect of temperature, humidity and solar radiation
on humans. The three elements Tw, Tg, and Ta are combined into a
weighted average to produce the WBGT (EN 27243, 1998). The temperatures
may be in either Celsius or Fahrenheit.
WBGT = (0.7 x Tw) + (0.2 x Tg) + (0.1 x Ta) (2)
[FIGURE 2 OMITTED]
Indoors, or when solar radiation is negligible, the following
formula is used:
W BGT = (0.7 x Tw) + (0.3 x Tg) (3)
* PHS (Predicted Heat Strain) index is a rational index, based on
the thermal balance equation which uses measured environmental
parameters in a series of equations to predict the body response to the
heat stress as a raise in core temperature.
[FIGURE 3 OMITTED]
3. Practical Measurement of Thermal Microclimate
Monitoring of thermo-hygric microclimate was carried out using the
Testo 400, to which tri-functional probe was attached, three-level globe
Vernon-Jokl thermometer, and WBGT set. Used equipment meets ISO 7726
requirements for accuracy. Based on the movement of workers during their
work shift, two measuring points were selected. These most frequent
places were then monitored for 6 hours. Along with measuring points,
activities of workers were also analyzed and later served in overall
evaluation of the measurement. Because there are two major sources of
radiant heat in operation, variable air speed and people moving freely,
environment was evaluated as a heterogeneous and non-stationary.
Therefore it was necessary to perform measurements at three levels: head
(1.7 m), abdomen (1.1 m), ankles (0.1 m). Results obtained from two
measurement points were put into table and basic statistic was implied
in calculation.
Outside climatic situation of workplace is also a part of the
monitoring of thermo-hygric microclimate. During the measurement there
was a sunny day and the outdoor air temperature was between 29 and 34
[[degrees]C]. Relative humidity was about 40 [%] and air velocity was
about 6 [m.[s.sup.-1]].
3.1 Experimental Measurements of Thermal-moisture Microclimate
Three basic physical quantities of thermo-hygic microclimate were
measured--Rh relative humidity [%], the dry air temperature [t.sub.a]
[[degrees]C] and air velocity [v.sub.a] [m.[sup.s-1]] with measuring
device Testo 400. Measurements took place in 2 measuring locations M1
and M2 during 6 hours. Measured values of thermo-hygric microclimate
were processed in MS Excel. Basic statistical functions such as: min
(the lowest value of the set of values), max (maximum value of the set
of value|, average (arithmetic mean arguments), stdev (standard
deviation), median (middle value of a group of numbers), var (variance
values), mode (most frequently occurring value in a group of numbers)
were used.
Measured values of dry air temperature, air velocity and relative
humidity at both measuring points and at all three levels were
statistically processed in MS Excel program. Graphical processing of
data obtained by measuring of Testo 400 is shown on the Figure 4 and 5.
On the horizontal axis measuring time is shown while on vertical axis
are values of dry air temperature, air flow velocity and the relative
humidity.
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
3.2 Globe Temperature
Temperature measurement obtained by globe thermometer was conducted
in order to determine the approximate amount of mean temperature
radiation [t.sub.r,m] [[degrees]C] by using the three level Vernon-Jokl
thermometer. Black ball thermometer is used to derive the approximate
value of mean temperature radiation from the observed simultaneous
temperatures readings of globe temperature ([t.sub.g]) [[degrees]C], air
temperature and air velocity surrounding the sphere (Auliciems,
Szokolay, Steven, 2007). Measurements done with this device were
conducted at 2 measuring locations during working shift. The values of
global temperature, measured by Vernon-Jokl were statistically
processed. Graphical processing of data obtained by measuring of global
temperature can be seen in Figure 6. and 7. On the horizontal axis
measuring time is shown while on vertical axis the final temperature of
the globe temperature is shown.
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
3.3 WBGT Sensor
The values of WBGT index were obtained by device with WBGT sensor.
Measurement was conducted on two measuring places (M1, M2) during 6 hour
work shift. During the whole measurement there was 30 minute time used
for setting the sensor. Variables such as: black globe temperature
[t.sub.r][[degrees]C], wet bulb temperature tw [[degrees]C] and dry bulb
temperature [t.sub.a][[degrees]C] were measured by this device. Measured
values from WBGT sensor were statistically and graphically processed in
MS Excel (see Fig. 8 and 9). On the horizontal axis measuring time is
shown while on vertical axis is temperature in [[degrees]C].
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
4. Processing of Evaluation
Evaluation was done by calculating the mean radiant temperature,
PMV index, the determination of metabolic rate and thermal insulation of
workers clothing.
4.1. Determination of the mean Radiant Temperature
Mean radiant temperature [t.sub.r,mi] was determined by calculation
of the mean radiant temperature measured of black ball for both measured
points (Table 1), taking into account that evaluated workplace is a
class Stress environment (see equation no. 4) (ISO 7726, 2003):
[t.sub.rmij] = [t.sub.r,mi,j] + 2 x [t.sub.r,mi,j] +
[t.sub.r,mi,j]/4 {[degrees]C] (4)
where:
[t.sub.rmij][[degrees]C]--mean radiant temperature,
i--horizontal measurement places,
j--vertical level (0.1m; 1.1m; 1.7m).
Mean radiant temperature ([t.sub.r,mij]) for certain levels for
measurement places were calculated from equation (5):
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (5)
where:
[t.sub.gij][[degrees]C]--mean value of black ball temperature for
given levels of measurement,
[v.sub.aij][m.[s.sup.-1]]--speed of airflow for given levels of
measurement,
[[epsilon].sub.g][-]--black ball emissivity, [[epsilon].sub.g] =
0,95 (matte black surface),
D[m]--ball diameter.
4.2. Computer program for Calculating Predicted Mean Vote (PMV) and
Predicted Percentage of Dissatisfied (PPD)
PMV can be used to verify if the thermal environment satisfy
thermal comfort criteria. PMV is calculated from temperature, mean
radiant temperature, air velocity, humidity, energy expenditure and the
thermal resistance of clothing (ISO 7730, 2006).
Program syntax for PMV and PPD can be found in ISO 7730. Program
was rewritten in Java programming language. Thermal clothing insulation
and metabolic rate was needed for the calculation.
Thermal clothing insulation (Icl) was calculated according to the
different types of clothes stated in ISO 7730. The resulting thermal
clothing insulation of workers is 0.39 [clo].
Based on observations of work activities and movement of workers
respectively energy expenditure was obtained from the classification
table, which is included in the standard EN 27243. According to mean
energy expenditure from classification table environment is stated as
work class 2. For this class of work is determined by the size of energy
expenditure (d'AMBROSIO ALFANO, 2011):
* [q.sub.M] [W[m.sup.-2]]--per body surface area (130 <
[q.sub.M] [less than or equal to] 200) pertinently,
* M [W]--the average body surface area (234 < M [less than or
equal to] 360).
Metabolic expenditure was set at 140 [W/[m.sup.2]] which represents
2,41 [Met]. In general, the hot environment is defined as PMV > +2.0
(ASHRAE thermal sensation scale--chapter 2). From calculation done in
computer program for calculating PMV and PPD obtained results for PMV
and PPD were PMV (M1) = 3.42, PMV (M2) = 3.66. It can be seen that the
measured thermal environment was hot. For evaluating of hot environment,
WBGT index was used. The average values of WBGT obtained by statistical
processing of measured data for both measurement points were WBGT (M1) =
33.22 [[degrees]C] and WBGT (M2) = 32.84 [[degrees]C]. When compared
with a referential value (refer WBGT = 28[[degrees]C]) found in a table
in EN 27243 we can state that WBGT reference value is exceeded.
5. Discussion
Exceeding of referential values shows that it is necessary to
reduce heat load on workers. There are several ways for doing that
(ASHRAE, 2009):
* Apply more detailed analysis of thermal load by more accurate
methods,
* Reduce the heat load in a given workplace by using personal
protective equipment, adjusting the environment, reduction of time spent
in the environment.
For determination of degree of physical human body burden it is
necessary to take into account the summary of all thermo-hygric
microclimate parameters (high air temperature is worse to bear when
there is also a high humidity or air velocity affects the heat transfer
between the organism and its environment).
Generally, the more negative factors are in the work environment
the greater negative impact they will have on the health of the worker.
in this way evaluated facility was designed. is it possible that because
of these factors high values from WBGT were obtained. For a deeper
analysis of extremely hot environment, it is recommended to use the PHS
index (Predicted Heat Strain)--index of thermal strain, which was
developed for the evaluation of transition conditions in hot working
environments (EN 27243, 1998).
6. Summary
For an indoor air quality study, there are a number of empirical
equations used by some authors over the last few years. indices, such as
the predicted percentage of dissatisfied with local thermal comfort,
thermal sensation and indoor air acceptability, are determined in terms
of some measured parameter, such as dry bulb temperature, relative
humidity and speed of air (ISO 7730, 2006).
The problem of high temperatures of air inside industrial
workplaces occurs particularly during hot summer days. Assessed
workplace showed high dry air temperatures (between 32[degrees]C and
35[degrees]C), and high globe temperatures (between 31 and
40[degrees]C). This indicated high level of thermal load, occurred at
workplace. By PMV index calculation, it was proved that workers are
exposed to thermal stress. The workplace was therefore assessed by WBGT
index.
The average values of WBGT were obtained by statistical processing
of measured data for both measurement points. Results of statistical
processing shows average values of WBGT (M1) = 33.22[[degrees]C] and
WBGT (M2) = 32.84[[degrees]C]. These values were compared with a
referential value (refer WBGT = 28[[degrees]C]). From this we can state
that WBGT reference value is exceeded. That means it is necessary to
reduce the heat load in the given workplace in the future (Buchancova,
2003).
Hot summer days are increasing the temperature inside of the
building. That is why ventilation and air conditioning systems are
common. in many manufacturing plants temperature and humidity are
provided by air conditions. if hot industrial facilities are not able to
provide air condition they must provide at least natural ventilation
(Simonson, 2001).
Nowadays tropical days are more frequent and because of that it is
recommended to use air conditioning in hot industrial plants in the
future.
7. Acknowledgment
This work was supported by project KEGA 032TUKE-4/2012.
8. References
American Society of Heating, Refrigerating and Air-Conditioning
Engineers (2009). ASHRAE Handbook-Fundamentals, ASHRAE, (SI Edition),
ISBN: 978-1 933742-55-7
A. Auliciems, Y. Szokolay, V. Steven, Thermal comfort, (2007).
Passive and Low Energy Architecture International Design tools and
techniques, Brisbane--The University of Queensland--Department of
Architecture, ISBN 0-86776-729-4. F.R. d'Ambrosio Alfano, B.I.
Palalla, G.Riccio, (2011). Thermal Environment Assessment Reliability
Using Temperature-Humidity Indices, Industrial health, vol. 3, No. 4, pp
95-106. ISSN: 0019-8366
EN 27243: 1998 Hot environments. Estimation of the heat stress on
working man, based on the WBGT-index (wet bulb globe temperature)
ISO 7726:2003 Ergonomics of the thermal environmnent--Instruments
for measuring physical quantities
ISO 7730: 2006 Moderate thermal environmnent--Determination of the
PMD and PPD indicase
J. Buchancova, (2003). Occupational medicine and toxicology, Osveta
s.r.o., ISBN 80-8063-113-1, Martin, Slovaki
C.J Simonson, M. Salonvaara, and T. Ojanen, (2001). Moisture
content of indoor air and structures in buildings with vapor permeable
envelopes, Proceedings of Performance of Exterior Envelopes of Whole
Buildings VIII, Atlanta ASHRAE
Authors' data: Doc. Ing. Kralikova, R[uzena]*; Ing. Sokolova
H[ana] *; Doc. Ing. Wessely E[mil] ; Ing. Polak J[an], * Department of
environmentalistics, Faculty of Mechanical Engineering, Technical
University of Kosice, Park Komenskeho 5, 042 01 Kosice, University of
Security Management in Kosice, Faculty of Electrical Engineering and
Informatics, Technical University of Kosice, Letna 9, 042 00 Kosice,
Slovakia., ruzena.kralikova@tuke.sk, hana.sokolova@tuke.sk, polakj
ano@gmail .com
DOI: 10.2507/daaam.scibook.2013.14
Tab. 1. Statistical processing of the measured values on
workplace M1
Function [R.sub.h] [%]
Head Abdomen Ankles
min 33,1 32,7 33,6
max 43,1 42,6 42,8
average 39,07 36,75 37,70
stdev 3,02 2,99 2,34
median 39,65 36,9 37,35
var 9,15 8,91 5,48
mode 41,4 38,7 34,9
Mean value [[PHI].sub.Rh] [%]
[PHI] 37,57
Function [t.sub.a] [[degrees]C]
Head Abdomen Ankles
min 31,1 30,4 29,7
max 36,2 34,7 33,7
average 32,98 32,82 32,07
stdev 1,38 1,2 1,29
median 33 32,4 32,5
var 1,89 1,44 1,67
mode 33,2 32,1 29,7
Mean value [[PHI].sub.ta] [[degrees]C]
[PHI] 32,67
Function [v.sub.a] [m/s]
Head Abdomen Ankles
min 0,18 0,14 0,18
max 0,46 0,41 0,36
average 0,28 0,27 0,27
stdev 0,05 0,05 0,04
median 0,28 0,27 0,27
var 0,002 0,002 0,001
mode 0,28 0,29 0,25
Mean value [[PHI].sub.va] [m/s]
[PHI] 0,27
Tab. 2. Statistical processing of the measured values on
workplace M2
Function [R.sub.h] [%]
Head Abdomen Ankles
min 33,7 32,8 33,5
max 43,6 38,5 40,4
average 38,29 36,02 36,5
stdev 2,28 1,71 1,67
median 37,95 36,45 36,9
var 5,2 2,93 2,8
mode 36,9 37,5 37,6
Mean value [[PHI].sub.Rh] [%]
[PHI] 36,71
Function [t.sub.a] [[degrees]C]
Head Abdomen Ankles
min 33,2 33 25,4
max 34,9 34,3 34,3
average 33,95 33,69 33,06
stdev 0,54 0,41 1,6
median 33,8 33,5 33,25
var 0,29 0,17 2,4
mode 33,9 33,4 33,3
Mean value [[PHI].sub.ta] [[degrees]C]
[PHI] 33,6
Function [v.sub.a] [m/s]
Head Abdomen Ankles
min 0,12 0,01 0,15
max 0,31 0,4 0,66
average 0,23 0,22 0,26
stdev 0,04 0,08 0,11
median 0,23 0,23 0,23
var 0,002 0,01 0,01
mode 0,26 0,23 0,23
Mean value [[PHI].sub.va] [m/s]
[PHI] 0,23
Tab. 3. Statistical processing of the measured values
Function [t.sub.g] head [t.sub.g] abdomen [t.sub.g] ankles
[[degrees]C] [[degrees]C] [[degrees]C]
Measuring point M1
min 34 33 31,5
max 37,5 36,5 35
average 35,65 34,69 33,39
stdev 1,25 1,23 1,33
median 35,5 34,5 33
var 1,56 1,52 1,76
mode 37 36 35
Measuring point M2
min 38 36,5 34,5
max 40,5 38,5 36
average 39,27 37,46 35,31
stdev 0,88 0,66 0,52
median 39 37,5 35,5
var 0,78 0,44 0,27
mode 39 38 35
Function Mean value
[PHI][t.sub.g]
[[degrees]C]
Measuring p M1
min
max
average
stdev 37,38
median
var
mode
Measuring p M2
min
max
average
stdev 34,61
median
var
mode
Tab. 4. Statistical processing of the measured WBGT values
Measuring point Ml
Function [t.sub.r] [t.sub.w] [t.sub.a]
[[degrees]C] [[degrees]C] [[degrees]C]
min 32 29,9 29,6
max 37 34,4 36,7
average 35,38 32,29 33,53
stdev 0,94 0,84 1,32
median 35,7 32,6 33,8
var 0,88 0,7 1,74
mode 35,8 32,7 33,9
Measuring point M2
Function [t.sub.r] [t.sub.w] [t.sub.a]
[[degrees]C] [[degrees]C] [[degrees]C]
min 34,4 31,1 33
max 35,9 32,6 34,6
average 35,07 31,89 33,76
stdev 0,34 0,33 0,36
median 35,1 31,9 33,8
var 0,12 0,11 0,13
mode 35,1 31,8 33,8
Measuring point Ml
Function WBGT
[[degrees]C]
min 30,8
max 35,1
average 33,22
stdev 0,86
median 33,5
var 0,74
mode 33,6
Measuring point M2
Function WBGT
[[degrees]C]
min 32,1
max 33,6
average 32,84
stdev 0,33
median 32,8
var 0,11
mode 32,8
Tab. 5. The mean radiant temperature values for M1 and M2
WORKPLACE M1
[t.sub.rm1,1] [t.sub.rm1.2] [t.sub.rm1.3] [t.sub.rm1]
37,88 36,80 34,90 36,60
WORKPLACE M2
[t.sub.rm2.1] [t.sub.rm2.2] [t.sub.rm2.3] [t.sub.rm2]
44,40 41,09 37,77 41,09
