Expermental determination of indoor conditions for human thermal comfort in Nigeria a case study of Ilorin.
Adegun, I.K. ; Popoola, O.T. ; Faniyan, T. 等
[FIGURE 1 OMITTED]
Introduction
Buildings are to provide a safe and comfortable internal
environment despite variations in external conditions. Experience has
shown that, to the occupants, the most important consideration is the
thermal comfort. This is the condition of thermal balance between man
and the indoor under given conditions. Architect and environmental
engineers always aim at creating comfort in buildings. Air-conditioning
system designers also seek for ways of creating thermal comfort and
improve the performance of the people when at work. The author aims at
improving the effectiveness of the workers at university of Ilorin so as
to bring out their best when at work. Therefore, it is essential to
build a system capable of controlling the important variables that
influence human thermal comfort. To achieve this, the heat balance
equation developed by Fanger [1] was adopted for the study. The four
activities considered in this work are:
(i) teacher that stands when delivering lecture, (ii) typists in
their offices (iii) security man standing relax and expecting the
visitors of his boss and (iv) the boss, who sits relaxing and thinking
on how to make things work well. Edward et al [2] experimentally
investigated partial and whole body thermal sensation and comfort. Zhang
et al [3] also modeled comfort in stratified environment. The model
developed predicts local sensation and thermal comfort. They obtained
that near comfort zone, acceptable stratification is up to 7[degrees]C
the result that is larger than the 3[degrees]C limit imposed by
standards. Ishii Masahisa[4] studied human thermal comfort and plant
productivity in protected horticulture. The paper investigates the
improvement of human thermal comfort while working in protected
horticulture. Passmore et al. [5] asserted that thermal comfort occurs
when there is thermal equilibrium in the absence of regulatory sweating
heat exchange between the human body and the environment.
It is stated that before a zone or a place could be said to be
comfortable, at least 80% of the occupants must experience body
sensation comfort. Eastop and McConkey [6] in their book emphasized on
the relationship between the quality of heat produces and degree of
activity. Fanger et al[7] also investigated
Man's preferred ambient temperature during the day, while
Langkilde et al [8] studied mental performance during slight cool or
thermal comfort warm discomfort. McGraw-hill Encyclopedia of science and
technology [9] pointed out that there is no condition that would satisfy
all persons within the same space at a given geographical region and
therefore, there is need to conduct experiments for different
geographical locations to be able to achieve accurate result. Among
these experiments and researches are those published by Zamba [10],
Ayoade [11] and Fanger [1]. Their conclusion, in summary, was that the
mental as well as physical performance of an individual is highest when
he is thermally comfortable. Another conclusion made by Fanger [12],
Adebayo [13] and Zamba [10] says "someone under thermal discomfort
or oppression over a long period of time will directly experience
negative effect in his health".
Moreover, much work had been done to obtain suitable mathematical
model for human thermal comfort at different locations. Larger number of
these works was done in temperate region of Europe and America. These
include Fanger [1], Gagge et al [14] and Gagge et al [15]. Fanger [1]
came up with a comfort equation on which most present works were based.
In tropic environment, no serious work has been done. Few related works
include Zamba [10], Adebayo [13] and Critchfield [16]. Many of these
investigations failed to take into consideration some of the
environmental variables and activity level. The effect of clothing was
also left out.
Mathematical Model
Fanger, P. O. [1] derived a general comfort equation from extensive
survey of literatures on experiments on thermal comfort. The equation is
complex, cumbersome and peculiar to determination of thermal comfort
condition in an enclosed space. This equation is a function of air
temperature, the temperature of the surrounding surface, relative
humidity, air movement/velocity in the vicinity of the body and thermal
insulation of the clothing. It also a function of metabolic heat
production and metabolic free energy production (i.e. external work)
Heat Balance Equation
For thermal comfort to be experienced by any occupant of a
building, the heat production by the body must be equal to heat
dissipation, and there shall be no significant heat storage within the
body. The above condition can be expressed mathematically using Fanger
[1] general comfort equation that follows:
H - [E.sub.d] - [E.sub.L] - [E.sub.SK] - [E.sub.s] = R + C (1)
Where,
C = Rate of heat exchange through convection, W/[m.sup.2] C=
[f.sub.cl] h ([T.sub.a] - [T.sub.cl]).
[E.sub.d] = Evaporative heat loss by diffusion, W/[m.sup.2] given
as [E.sub.d] = 0.305 x [10.sup.-4] (5765 - 7.04 M (1 - e) - [P.sub.v])
[E.sub.L] = Latent Respiration heat loss, W/[m.sup.2] given as
[E.sub.l]=1.72 x [10.sup.-5] M (5866 - [P.sub.v])
[E.sub.s] = Sensible respiratory heat loss, W/[m.sup.2] given as
[E.sub.s] = 0.0014 M (34 - Ta)
[E.sub.SK] = Heat loss due to regulatory sweating. W/[m.sup.2], it
is usually a function of activity level. h= Convective Heat Transfer
coefficient
H = Internal heat production in the human body, W/[m.sup.2]. H =
M(1-e)
R = Rate of heat exchange through radiation, W/[m.sup.2] and it is
given as
R = 3.96 * [10.sup.-8] [f.sub.cl] [[([T.sub.a] + 273).sup.4] -
[([T.sub.mrt] + 273).sup.4]
Where,
e = mechanical efficiency. See Table 2.
[f.sub.cl] = The ratio of the surface of the clothed body to the
surface area of the nude body (clothing area factor)
M = Activity level, W/[m.sup.2] given for various activities in
Table (2).
[P.sub.v] = vapour pressure
[T.sub.a] = ambient temperature
[T.sub.cl] = is the temperature of the cloth surface.
[T.sub.mrt]= Mean radiant temperature
[FIGURE 1 OMITTED]
Fig.1 gives the pictorial explanation of the equations (1).
Where,
A1 = Heat loss by convection and evaporation
A2 = convection heat loss (warm air next to skin carries heat
away).
A3 = Conduction to or from the surrounding air depending on which
is warmer
Substituting all the heat loss terms given above into equation (1)
to have the model equation (2) given below,
M(1-e)- [B.sub.0]-[B.sub.1]-[B.sub.2]-[E.sub.SK]-K= [B.sub.3] +
[B.sub.4] (2)
Where,
[B.sub.0] =0.0215 M(1-e) + [B.sub.00] (5765 - [P.sub.V])
[B.sub.00]= 3.05 x [10.sup.-3] (m/s)
[B.sub.1] = [B.sub.11] (5866- [P.sub.V]), W/[m.sup.2]
[B.sub.2] = [B.sub.22] M(34-[T.sub.a]), W/[m.sup.2]
[B.sub.3] = [B.sub.33] [f.sub.cl] [[([T.sub.a] + 273).sup.4] -
[([T.sub.mrt] + 273).sup.4]], W/[m.sup.2]
[B.sub.4] = [f.sub.cl] h ([T.sub.a] - [T.sub.cl])., W/[m.sup.2]
B11 = 1.7x[10.sup.-5] (m/s)
B22=0.0014 (1/[degrees]C)
B33 = 3.96 * [10.sup.-8] (W/[m.sup.2][K.sup.4])
K = The heat transfer from the skin to the outer surface of the
clothed body, W/[m.sup.2] (i.e. conduction through the clothing) given
as
K = [T.sub.S] - [T.sub.cl]/[0.18I.sub.cl]
[I.sub.cl] = Thermal resistance of the clothing, given in Table3
for different clothing ensembles.
K is a new term introduced to Fanger[1] general comfort equation to
compensate for resistance to heat transfer due to clothing.
Equation (2) is the heat balance equation for human body and it is
the first condition for optimum thermal comfort. The second and third
conditions for thermal comfort are the heat loss per unit body area by
evaporation of sweat secretion, [E.sub.SK] and the temperature of the
skin surface [T.sub.s]. They are functions of activity level. The
relationship between these variables can only be obtained through
experiments.
The heat loss per unit body area by evaporation of sweat secretion,
[E.sub.SK] was obtained from equation (2) as
[E.sub.SK] = H - [B.sub.0] - [B.sub.1] - [B.sub.2] - K (3)
The thermal resistance of clothing, which is an improvement on
Fanger comfort equation, can be derived from equation (3) as
[I.sub.cl] = ([T.sub.S] - [T.sub.cl])(H - [B.sub.0] - [B.sub.1] -
[E.sub.SK] - [B.sub.2])/ / 0.18 (4)
[T.sub.s] = is the temperature of the skin surface.
For this model to be adopted for location of interest,
[T.sub.a],[T.sub.s], [T.sub.cl] and Pv must be obtained
experimentally.
Experimental Set Up and Procedure
Some psychological triggers such as reactions to certain colours,
state of mind, hunger, sleepless night, sickness like fevers etc, that
can affect general comfort of the specimen were catered for by
eliminating specimen with negative answers that might affect the final
outcome of the experiment before conducting the experiment.
Experimental Set- Up
The set-up of the experiment is composed of,
(i) Experimental chamber
The place where the experiment was conducted is the postgraduates
computer laboratory of the Faculty of Engineering and Technology,
University of Ilorin.
(ii) Measuring Device
Sling psychrometer was used to measure ambient wet- and dry-bulb
temperatures from which the relative humidity and air partial pressure
were estimated. Clinical thermometer, a digital-type, was used to
measure [T.sub.s] and [T.sub.Cl].
(iii) Specimen
Undergraduate students (both male and female) of University of
Ilorin were used for the experiments. There were ten students for each
activity.
Experimental Procedure
Students were given brief lecture on the experiments and the
importance of the research work. They were taught on how to respond to
the question "how do you feel?" during the course of the
conduct of the experiment. They were to say "no" if the place
is too cold and to say "no, no" if the place is hot. They were
to say "yes" when they were comfortable with the ruling indoor
conditions. When student responded "no" or "no, no"
the answer was assumed negative and the air conditioning systems were
adjusted accordingly until the specimen responded otherwise. Before
students were admitted into the experimental chamber the air
conditioning systems were turned on and left for about 4 hours, usually
from 8:00 a.m. to 12:00 noon to allow the room to attain the desire
temperature. The room temperature was measured at different points to
verify the temperature uniformity. After an approximately uniform
temperature has been achieved, each specimen at a time was admitted into
the experimental chamber. The student was asked to perform a given
activity for some time. After a period of about 15mins, the student was
asked "how he/she was feeling?" For a negative answer the room
temperature was varied using the air-conditioning systems until a
comfortable condition was attained. When the answer was otherwise, the
room temperature was measured using sling psychrometer. At the
comfortable condition the skin temperature was measured by putting the
digital clinical thermometer under the specimen's armpit. The
temperature of the surface of the cloth was also measured with the same
instrument. The readings for [T.sub.s], [T.sub.db] (Ta), [T.sub.cl] and
[T.sub.wb] were recorded against the activity being performed. These
steps were repeated for all other specimens. The mean value of
[T.sub.db], [T.sub.cl], [T.sub.s] and [T.sub.a] were calculated and
recorded for each activity level as shown in Table 1. The rate of heat
loss ([E.sub.SK]) by sweat was calculated for each activity level (M)
using thermal comfort equation (3). A computer programme written in
quick basic was used to generate the results.
Precautions
* The investigators made sure the students were psychologically
comfortable before being used. This was achieved by making them feel
relax, comfortable and at times entertain them.
* Experiment was performed when the uniformity of the room
temperature had been examined and found okay. This was done by measuring
the temperature at different locations of the lab.
* To eliminate error due to parallax, a digital clinical
thermometer was used. Each student was allowed to perform the activity
for sometime before enquiring about his/her comfort.
* Data were only recorded when the student was thermally
comfortable.
Results and Discussion
At the end of the experiments, the data obtained for each activity
per specimen were recorded and the average values of the main variables
are given in Table 1.
Metabolic rate (M) for different activities was obtained from
Ayoade(1983) Fig2. shows that for a human body to be at comfort and to
avoid internal storage of energy, the rate at which heat is lost through
perspiration must increase with increasing activity level. Otherwise the
actor of the activity becomes uncomfortable and it performance at work
deteriorates.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Fig3 is the representation of the variation of activity level with
average skin temperature at comfort condition. The curve is of a
negative slope, which denotes the simple fact that at comfort condition,
an elevated metabolic rate causes temperature depression of the skin
surface. This is because an increase in metabolic rate necessitates an
increase in heat loss and invariably lowers the skin surface
temperature.
[FIGURE 4 OMITTED]
Fig.4 shows the plot of air temperature against the metabolic rate.
The curve is of a negative slope. The reason is as explained in (Fig3.)
above. It could be deduced from Figs. 3 and 4 that for skin temperature
to be lowered, the ambient temperature must be lowered otherwise the
specimen becomes thermally discomfort and ineffective.
[FIGURE 5 OMITTED]
Fig. 5 is the plot of the specific humidity against the activity
level. It shows the direct proportionality of specific humidity to
metabolic rate. It is deduced from the figure that as the activity level
increases the loss via perspiration increases and thereby causes an
increase in the water vapour of the ambient.
[FIGURE 6 OMITTED]
Comparism of Figs. 5 and 6 shows the relationship between vapour
pressure and specific humidity. This is an indication that the more the
water vapour in the ambient the more the vapour pressure.
Conclusion
The micro climatic conditions for human thermal comfort in Ilorin
and its environs has been attained to cater for the geographical
location A conducive working environment can now be created for workers
in the zone using the knowledge acquired in the research work. For
example:
* If a lecturer at university of Ilorin and its environs is to
perform well and dish out his best, the indoor conditions of the lecture
room should be at a temperature of 20.19[degrees]C and a relative
humidity of 0.0112.
* For all Principal Officers, Rectors, Deans, Directors and Heads
of Department of the zone to perform effectively, their offices must be
subjected to a temperature of 23.69[degrees]C and a relative humidity of
0.0111.
Appendix
Table 2: Metabolic Rate for different activities.
S/No. Activity Metabolic Rate Mechanical
W/[m.sup.2] Efficiency,
e
1 Sleeping 40.705 0
2 Reclining 46.52 0
3 Seated quiet 58.15 0
4 Standing relaxed 69.78 0
5 Walking, 3.2km/hr 116.30 0
6 Walking, 4.0km/hr 139.56 0
7 Teaching 93.04 0
8 General lab. Work 93,04 0
9 Digging trenches 348.9 0.2
10 Basket Ball 441.94 0-0.1
11 Wrestling 505.91 0-0.1
12 Typing 69.78 0-0.1
13 Office work(banking) 69.78 0
14 House cleaning 116.3-192.71 0-0.1
15 Car driving 58.15 0
(light traffic)
16 Car driving 116.30 0
(Heavy traffic)
Table 3: Data for different clothing ensembles.
S/No. Clothing ensemble [I.sub.Cl] [f.sub.Cl]
(Clo)
1 Nude 0 1.0
2 Shorts 0.1 1.0
3 Typical tropical clothing ensemble: 0.35 1.05
short,open neck shirt with short
sleeves, light socks and sandals
4 Light clothing : Long light -weight 0.5 1.1
trousers, open neck shirt with
short sleeves
5 Light working ensemble: Athletic 0.6 1.1
shorts, woolen socks, cotton work
shirt(open neck), and work trousers
6 Military combat uniform: Army 0.8 1.1
fatigues but with shirt and
trousers of cloth, wind resistant,
poplin.
7 Light outdoor sportswear: cotton 0.9 1.15
shirt, trousers, T-shirt, shorts,
socks, shoes and single ply poplin
(cotton and Dacron) jacket
8 Typical business suit 1.0 1.15
N.B Clo = 0.155 [m.sub.2] K/W
Courtesy of Ayoade [11].
Acknowledgment
The authors appreciate the management of Faculty of Engineering and
Technology Computer laboratory, University of Ilorin, for giving us the
opportunity of using the postgraduate computer laboratory as the
experimental chamber. Also appreciated are the students that took part
in exercise.
References
[1] Fanger P.O. "Conditions for thermal comfort. Introduction
of a General Comfort Equation". Chapter 11in James D. Hardy, A.
Pharo Gagge and J.A.J. Stolwijk (eds.): Physiological and Behavioral
Temp. Regulation, Charles C. Thomas, Illinois, 1970, pp.152-176.
[2] Edward Arens, Hui, Zhang, Charlie Huizenga (2006),"Partial
and whole body Thermal sensation and Comfort", Journal of Thermal
Biology, Vol. 31, Pp. 53-59.
[3] Zang, H., Huizenga, C., Arens E., and Wang D.,
(2005),"Thermal Sensation and Comfort in Transient Non-Uniform
Thermal Environment", European Journal of Applied Physiology,
Vol.92, Pp. 728-733
[4] Masahisa I., Marau T,, Ito T., Sase S., Okushima
R.,(2001),"Thermal Comfort and Plant Productivity in Protected
Horticulture -Environment "Journal of Environmental Control in
Biology, vol. 39, no.1, pp.9-16.
[5] Passmore, R and Durnin, J. V. A. (1967), "Energy, Work,
and Leisure", Heinemann, London
[6] McConkey, A. and Eastop, D. (1978), "Applied
Thermodynamics for Engineering Technologist", Longman London.
[7] Fanger, P.O., Hojberre, J. and Thomsen, J.O.B.,
(1973)"Man's preferred Ambient Temperature During The
Day", Archives of science and Physiology, 27(4), pp. A393-A402.
[8] Langkilde, G., Alenxandersen, K., Wyon, D. and Fanger,
P.O.,(1973), "Mental Performance During Slight Cool or thermal
Comfort Warm Discomfort", Archives of Science and Physiology,27(4),
pp.A511-A518
[9] McGraw-Hill Encyclopedia of Science and Technology,(1992),
McGraw-Hill Inc. New York, St. Louis San Francisco, Vol. 2. 7th Edition.
[10] Zamba A.A. (2003), "The Influence of Climate on
Physiological Comfort in Jimet-Yola, Nigeria", Journal of Science
and Technology Research, Vol.2, PP. 23-29.
[11] Ayoade, J.O. (1983), "Introduction to Climatology For
Tropics", Spectrum Books Limited, Ibadan, Nigeria.
[12] Fanger P.O. (1972),"Thermal Comfort Analysis and
Applications in Environmental Engineering" McGraw-Hill Book
Company, New York.
[13] Adebayo, A.A.(2000),''Temperature variability and
Outbreak of Meningitis and Measles in Yola, Nigeria", Global
Journal of Pure and Applied Sciences, Vol. 7, No. 1, Pp 133-136.
[14] Gagge, A.P. and Stowijk, J.A. and Saltin B. (1969),
"Comfort and Thermal Sensations and Associated Physiological
Responses during Exercise at Various Ambient Temperature",
Environmental Research, Vol. 3, PP. 209-229.
[15] Gagge, A.P. and Stowijk, J.A. and Hardy, J.O. (1967),"The
Effective Radian Field and Operative Temperature Necessary for Comfort
with Radiant Heating", ASHRAE Journal, PP. 63-66.
[16] Critchfield, H.J. (1974), "General Climatology",
Prentice Hall, New Jersey.
Mechanical Engineering Department, Faculty of Engineering and
Technology University of Ilorin, P.M.B. 1515, Ilorin, Nigeria.
Email:kadegun2000@yahoo.com
Table 1: Average comfort parameter for each activity
Activity Reclining Seated Standing
quiet relax
[T.sub.S] ([degrees]C) 36.70 35.92 35.65
[T.sub.Cl] ([degrees]C) 34.63 33.21 32.75
[T.sub.a] ([degrees]C) 23.90 23.69 21.50
[omega]/(kg/kg 0.0090 0.0110 0.0115
Dry ir)
[P.sub.V] (N/[m.sup.2]) 1450 1760 1840
[E.sub.t] (W/[m.sup.2]) 7.12 12.09 22.99
M (W/[m.sup.2]) 46.52 58.15 69.78
Activity Standing Typing
talking
[T.sub.S] ([degrees]C) 34.90 35.36
[T.sub.Cl] ([degrees]C) 32.26 32.67
[T.sub.a] ([degrees]C) 20.19 20.85
[omega]/(kg/kg 0.0112 0.0119
Dry ir)
[P.sub.V] (N/[m.sup.2]) 1950 19150
[E.sub.t] (W/[m.sup.2]) 45.96 23.09
M (W/[m.sup.2]) 93.04 77.56
