In the humid tropics, the teaching-learning environment is often faced with the problem of reducing heat gain in the building space. This is as a result of the fact that the building space is always warm due to high temperature, relative humidity and low air movement. The inability of the building space to keep out heat usually leads to occupants’ feeling of thermal discomfort. Thermal discomfort can also induce various stress behaviours that can affect the learning of occupants in any teaching-learning indoor space.
Though there are various definitions of thermal comfort, ASHRAE, ANSI/ASHRAE Standard 55 [1
] defined thermal comfort as being that condition of mind that expresses satisfaction with the thermal environment. It is a state in which a person will judge the environment to be neither too warm nor too cold or thermally neutral, and in this condition, the strain on the body’s thermoregulatory mechanism is minimal. That is, a neutral point defined by the absence of any feeling of discomfort [3
]. Givoni [5
] defined thermal comfort as the absence of irritations and discomfort due to heat or cold, or in a positive sense, as a state involving pleasantness. Further, Dagostino [6
] defined thermal comfort as being able to carry on any desired activity without being either chilly or too hot. Though these definitions are universally agreed upon by researchers, they are also not easily converted into a physical parameter [7
] because human perceptions about the environment differ between individuals.
Various models, such as the predictive mean votes (PMV-model), actual mean votes (AMV-model) and the adaptive thermal comfort (ATC-model), have been developed to predict thermal comfort in an environment. Fanger [8
] developed the PMV model and defined PMV as the index that predicts the mean thermal sensation vote on a standard scale for large group of persons for a given combination of the thermal environmental variables, activities and clothing levels. The model is expressed on the seven-point ASHRAE scale of thermal sensation. The central three categories of this scale are labelled “slightly cool”, “neutral” and “slightly warm”, which is within the acceptable sensation level [9
]. The upper two categories of cool and cold and the lower categories of warm and hot are discomfort indications of cold and hot sensation, respectively. The PMV model includes all of the major variables influencing thermal sensation and quantifies the absolute and relative impact of six factors, of which air temperature, mean radiant temperature, air velocity and relative humidity are measured and activity level and clothing insulation are estimated with the use of tables [9
However, other researchers have compared the outcome of the PMV model to AMV, which indicates the actual thermal sensation of subjects. The results of the AMV have shown some differences as much as 1.3 ASHRAE-scale for climate chamber studies [10
]. The ATC-model predicts that contextual factors and past thermal history modifies the occupant’s thermal expectations and preferences. Thus, people in warm climate zone would prefer higher indoor temperatures than people living in cold climate zones, which contrast with the assumptions underlying comfort standards based on the PMV-model [11
]. Adaptation thermal comfort is therefore defined as the gradual lessening of human response to repeated environmental stimulations and can be both behavioural (clothing, windows, ventilators), physiological (acclimatization), as well as psychological (expectations) [11
]. These models are all developed in order to evaluate the thermal comfort or heat sensation levels of individual in an environmental space. They can also be applied in the humid tropics, as well.
Learning according to the Merriam-Webster Dictionary [14
] is an activity or process of gaining knowledge or skill by studying, practicing, being taught or experiencing something. Most activities of learning in a school environment take place within building enclosures. These learning activities can take place better when the environmental conditions are favourable. Inside a building, people are affected either positively or negatively because of the physiological reactions and psychological responses to the thermal environment [15
].In the same vein, the activities in a lecture theatre are primarily to accommodate small and large groups of learners and the teacher for the purpose of the teaching and learning. Therefore, such room spaces are also expected to provide an environment with relative thermal comfort for the learners to benefit from the lecture room activities. In this regard, Hussein and Rahman [16
] opined that, since the learning environment is a place where learners and educators congregate for extended periods of time to participate in the activity of learning, the environment created during this activity is regarded as an important component in the teaching and learning process. Thus, the sole reason a building is constructed for human habitation is to provide a comfortable and healthy place for people to work [17
]. The learning lecture theatre should also be seen to provide such an environment.
The thermal comfort condition of a teaching-learning environment therefore depends on the perception of individuals on whether the indoors has relative thermal comfort or not for the type of classroom activities. Previous studies have also corroborated the fact that the classroom environment is a determinant of students’ outcomes [18
]. Thus, thermal comfort affects productivity and learning. Students’ achievement is also higher in those environments that students find to be relatively comfortable [19
]. Tom [17
] also reported that studies on school classrooms show similar links between thermal comfort and student learning, although perhaps at temperatures somewhat lower than those that are optimal for office workers. Many studies have also analysed the elements of comfortable environments to improve educational environments under the expectation that comfortable learning classrooms would enhance the performance of the students studying in those environments [20
]. However, it is not in all cases that individuals perform better in a thermally-comfortable indoor environment. That is, even when students perceived that the indoor thermal comfort level has increased, their learning task performance may still decrease. This finding is inconsistent with previous results that showed that a comfortable learning environment had a positive impact on students’ task performance [17
]. The answer given was that the arousal level of each participant was higher than the arousal level for optimal performance [4
Further, in the teaching-learning environment, students’ perception of thermal comfort is affected by air temperature, air movement or velocity and humidity in the classroom, as well as the clothing they wore to the lecture, the amount of physical work activity done, the mean radiant temperature, the radiant temperature of the walls, floor, windows, etc.
Adunola and Ajibola [25
] also reported that, in an indoor space, the thermal environment is constituted by the interaction of different factors of the climatic conditions, and the interaction of these conditions within the building spaces provides an indication of the level of indoor thermal comfort. Many researchers according to Hussein and Rahman [16
] and Wafi and Ismail [26
] also indicated that thermal comfort does affect its occupancy.
Further, environmental factors, such as climatic conditions, crowding and inadequate and inappropriate location of openings can affect thermal comfort. Three main climatic conditions, namely temperature, relative humidity and air movement, as well as heat production and regulation in the human body, cold and hot surfaces and air stratification [3
] can cause thermal or cold sensation in the individual’s body when the organ of touch is stimulated as the body is exposed to the medium that causes heat or cold. Temperatures at high levels beyond an individual’s tolerable limit can aggravate body heat, which may lead to muscular weakness, dizziness, as well as mental and physical fatigue [28
]. In addition, high relative humidity combined with high temperature may also reduce the frequency of evaporation of vapour liberated through perspiring occupants carrying out various human activities. Discomfort is therefore experienced because of the inability of the occupants to dissipate metabolic moisture [30
]. At high humidity, the undesirable side effects are dampness or wettedness sensation and sometimes difficulty in breathing [3
]. Further, air movement causes the feeling of freshness and the comfort of individuals, but low wind movement causes inadequate ventilation. Air movement plays an important role in increasing the rate of evaporation, especially at high humidity, where evaporative cooling is the main source of heat loss from the body [3
]. Wind therefore reduces the adverse effects of thermal discomfort resulting from high temperature and humidity. If the air is calm, the air layer close to the body becomes saturated, and little evaporation will take place. However, where there is considerable air flow, the constant replenishment of air around the body ensures that the evaporation process is maintained [31
]. Therefore, the availability of fresh air in a room space will help to supply an adequate level of oxygen for breathing, to dilute odours arising from bodies and to dilute air vitiated with bacteria [3
]. Where the three purposes of air are not met, people will feel thermal discomfort.
Crowding refers to the way we feel when there are too many people or not having enough space [32
]. Crowding occurs in a space for teaching-learning when it accommodates far more students than the requisite capacity. In a crowded room space without adequate ventilation, people give off carbon-dioxide, water vapour, dead skin cells and unpleasant odours. The observable thermal discomfort stresses in a crowded space are restlessness, inattentiveness and sometimes respiratory irritation, such as coughing and sneezing. In this regard, overcrowding can cause arousal conditions that can stimulate skin conductance, leading to palmar sweat [32
Inadequate and inappropriate location of openings in the external walls of buildings is another source of thermal discomfort. Window and door openings when adequate and appropriately located along the external walls of buildings provide ventilation into the room space. Ventilation is a determinant of thermal comfort and generally gives satisfaction within the indoor environment. The main purpose of ventilation is to provide fresh air to cool the body, to remove accumulated noxious gases and contaminants and to remove heat generated in a working area by convection. The benefits of windows are also to allow the passage of air through the envelope as ventilation and exhaust for removing the polluted air. Therefore, airflow through a building should not be hindered as much as possible [34
]. In the humid tropics characterized by high temperature and relative humidity with low wind velocity, one strategy for buildings in providing relatively satisfactory indoor space is the use of natural ventilation to enhance evaporative and convective cooling of occupants. However, there are no absolute standards of thermal comfort, as people have adjusted to live in various environments with varying conditions.
The literature has established that thermal discomfort affects learning. However, for thermal discomfort to affect learning, students must exhibit some stress behaviours that are physiological in nature. Stress is the reaction of individuals to any external stimulus that impinges and threatens their well-being. When individuals are unable to withstand the effect of thermal discomfort, they exhibit stress behaviours [32
]. Physiological stress according to Markus and Morris [3
] is caused when the organs of the body, its chemical processes and the functions of its physiological mechanisms, such as the nervous, muscular, circulatory and breathing systems, are affected when there is a deviation from the narrow optimal temperature range where the organs of the body are expected to operate optimally. When the effects of environmental conditions on an individual’s body are beyond the acceptable threshold of either too high or too low, it creates environmental discomfort. Prolonged exposure to environmental discomfort conditions where the zone of optimum is exceeded creates physiological stress. The evidence of physiological stress is fatigue, restlessness, boredom, inattentiveness and a decreased level of vigilance, and that physiological stress depresses arousal [3
]. A depressed arousal level also depresses performance. These stress behaviours to a large extent affect learning in a school environment.
However, the judgement of whether an individual feels thermally comfortable or not varies from one individual to another just as the effect of climatic indicators on individual’s thermal comfort varies. Furthermore, no two individuals in the same teaching-learning space will have the same feeling of thermal comfort, even when they are exposed to the same indoor environmental conditions. This is due to variations in age, state of health, physical activities, type and amount of clothing, the physique of the individual and the degree of acclimatization [33
]. The degree to which thermal discomfort affects the individuals’ stress behaviours also varies according to the intensity and ability of the individual to withstand such stresses. Thus, it is difficult to establish a condition that will satisfy everyone because of human physiological variance. Rather, the internal environment should create conditions that can satisfy the largest number in the group of probable occupants. That is, the building should modify the natural or external environment to produce a satisfactory internal environment for human activities for the majority of the users [36
]. Where the thermal comfort of an individual is affected, the health, energy and comfort, as well as the physical and mental vigour of the individual is also affected [30
The likely effect of indoor thermal environment on students’ thermal comfort and stress behaviours of students that affect learning in lecture theatres in the humid tropical climate are very important because a thermal discomfort environment will not actively stimulate human development socially, intellectually, physically and emotionally. Thus, it is expected that the learning-teaching environment should be able to actively and attractively suit the functions of the education it serves, which will not only accommodate, but contribute to a very special environment for teaching and learning [37
The PMV, AMV and ATC models are the basis for determining whether an individual perceives thermal comfort or discomfort in any indoor environment. However, this study is based on the fact that in the humid tropics characterized by high temperature, relative humidity and low wind velocity, the perception of the majority of people is that there is always thermal discomfort in the indoor environment [38
]. From the foregoing, the objective of this study is therefore to establish whether the perceived reactions of individuals to strains on their body’s thermoregulatory mechanism in any indoor thermal environment will lead to the feeling of heat sensation, sweat liberation, slow sweat evaporation, wettedness, low indoor air-movement and the slow cooling effect of indoor breeze vis-à-vis thermal discomfort. In addition, the study is also concerned with whether the perceived thermal discomfort in any indoor space will lead to stress behaviours, such as concentration (mental fatigue), tiredness (physical fatigue), vigilance, restlessness, attentive and irritation levels that will affect learning.
The findings of the study revealed that the lecture theatres were overcrowded at full capacity; the door and window openings where inadequate; the heat and vapour input, average indoor temperature and relative humidity were high, while the indoor wind velocity was low. Overcrowding occurred because the space accommodated more than the required seating capacity. The implication was that the occupants will give off carbon dioxide, water vapour, dead skin cells, as well as unpleasant odours if the space was not adequately ventilated [33
]. Overcrowding can cause arousal conditions that will stimulate skin conductance, leading to palmar sweat, restlessness, inattentiveness and sometimes respiratory irritation, such as coughing and sneezing [32
]. This will invariably create thermal comfort problems in the lecture theatres. Ventilation determines thermal comfort and provides satisfaction in the indoor environment. Ventilation also helps to remove heat generated in a working area by convection and cools the body, provides fresh air and removes accumulated noxious gases and contaminants [33
]. Thus, when door and window openings on the external walls were inadequate for ventilation, a given room space will be hot and uncomfortable. This was because the occupants generate heat and liberate sweat (vapour) into the indoor environment, which was already characterized by high external and internal temperature and relative humidity. For a building to provide ventilation, it should not impose as much resistance as possible to airflow through it [34
The average minimum and maximum temperatures and relative humidity readings of 29–32 °C and 78%, respectively, were above the thermal comfort limits of 22–27 °C for relative humidities between 70%–100% [1
].High temperature and relative humidity beyond individual’s tolerable limit can generate heat and activate the sweat glands that produce moisture in the body of individuals. The feeling of the increase in sweat production creates body heat and a wettedness sensation and sometimes breathing difficulties at high relative humidity when vapour liberated through perspiring occupants carrying out various human activities was not evaporated as frequently as possible [3
]. Thus, when the air is humid, evaporation of perspiration from the body will be limited; and a feeling of oppression so common in the humid tropic is created. Therefore, extreme conditions of humidity should be avoided [31
In addition, the measured average indoor wind velocity of 0.32 m/s was also below the required wind velocity of 0.5–1.0 m/s required for a feeling of a pleasant cooling effect [39
]. The available air in the room space will be utilized quickly without any corresponding replenishment as a result of the low wind velocity. Therefore, high temperature and relative humidity combined with low wind velocity in room space indicated that the ventilation of that space can never be assured, except with the use of artificial ventilation; that is, the lecture theatre space did not provide the required thermal comfort. The effect is a stuffy room environment with body odour from the sweat of the occupants, which will lead to a contaminated room space. Since the common denomination of lecture theatres was for a large number of people to be assembled in an enclosed space for an appreciable period of time, the primary problem was to furnish sufficient air and to distribute it properly [50
In addition, it was the perception of the students that there was thermal discomfort in the two lecture theatres due to the indoor environmental conditions. A significant difference did not exist between the students in LTH-2 and LTH-3, respectively, in their perception of thermal discomfort due to the indoor environmental conditions. This was because the students in the two lecture theatres perceived that the feeling of heat sensation, liberation of sweat, slow evaporation of sweat, wettedness, a slow rate of indoor air movement and a slow cooling effect of the indoor breeze were the cause of thermal discomfort. This perception can be explained by the climate in Bayelsa State in Niger Delta region being hot and humid. The average outdoor relative humidity is between 78% and 89%, with monthly minimum and maximum temperatures of 21–23 °C and 28–33 °C, respectively, wind velocity between 1.5 and 3.3 m/s [43
], while the observed average minimum and maximum indoor air temperature was 29–32 °C, relative humidity, 78% and wind velocity, 0.32 m/s, making it inevitable that there was thermal discomfort in the indoor space. This finding is consistent with Puteha, Ibrahimb, Adnana, Che’Ahmada and Noh [27
], who reported that outdoor average temperatures of 23.7–36.9 °C and relative humidity of 67%–95% have an adverse impact on occupant’s comfort indoors. In this regard, Tom [17
] opined that a reasonable indication of comfort, even if it is not perfect, is better than having no indicator at all.
The findings further revealed that the thermal discomfort in the indoor space had an effect on stress behaviours affecting learning, as perceived by the students. There was no significant difference in the mean students’ perceived stress behaviours affecting learning for the two groups of students in LTH-2 and LTH-3; that is, the thermal discomfort conditions in the lecture theatres affected the stress behaviours of students’ vis-à-vis their learning. The stress behaviours exhibited as perceived by the students were mental fatigue (lack of concentration), physical fatigue (tiredness), restlessness, inattention, non-vigilance and irritation. These stress behaviours were common indicators of thermal discomfort that affected learning. With a temperature range of between 22 and 32 °C, average relative humidity between 62% and 87% and an overcrowded indoor space, which decreases thermal comfort, it is therefore expected that the indoor thermal comfort conditions in the lecture theatre will affect learning. Tom [17
] observed that a range of temperatures exist between roughly 22 and 25 °C at which people are most productive. However, their productivity decreases rapidly when the temperatures are above or below this range. In agreement, Choi and Chun [53
] while examining attention level at 20 and 23 °C, found that, in general, an indoor temperature of 23 °C provides an environment more conducive for concentration. Further, the knowledge that a reasonable and constant temperature can positively impact students’ health and learning is still relatively firm [54
Furthermore, there was no correlation between the students’ perceived indoor thermal discomfort and the students’ perceived stress behaviours affecting their learning in LTH-2. This meant that the indoor thermal environment created thermal discomfort for the students’, as well as the stress behaviours affecting learning; the effect was not significant enough to have a correlation. Markus and Morris [3
], therefore, opined that although the perception of stress behaviours in a thermal environment can coincide with effective learning-teaching, there were some evidence that such perceptions may not necessarily coincide with those for comfort, but due in part to the arousal level of the students in the thermal environment. Another reason is that the arousal level of the students was higher than the arousal level for optimal performance [24
]. However, there was a correlation between the students’ perceived indoor thermal discomfort and the students’ perceived stress behaviours affecting learning in LTH-3. This finding was not unexpected, but only confirmed that stress behaviours exhibited in a learning environment can have a profound effect on learning. From case studies in actual workplaces, Romm and Browning [55
] also confirmed that there was a link between comfort and productivity, especially at temperatures between 20 and 25 °C.