Enhancing Comfort in Tropical Institutional Buildings: Integrating Thermal, Acoustic and Visual Performance with a Unified Index

This study explores the relationship between a country's level of development and its educational standards, emphasizing the significance of well-equipped universities in ensuring high-quality education. While research on comfort in educational buildings has often focused on individual parameters, such as thermal, acoustic, and visual elements, this paper proposes a new metric that integrates these factors to assess environmental comfort. The research was conducted in six hostel rooms at the National Institute of Technology Warangal (NITW) campus in India, utilizing both objective measurements and subjective surveys. Three single measures were introduced: a thermo-hygrometric index, an audio comfort index, and a visual illumination index, each normalized within a 0-1 range denoting comfort and discomfort conditions. A final total comfort index for each room was established by assigning appropriate weights to the three factors. The findings were compared to the questionnaire responses, evaluating the effectiveness of the proposed methodology. The results indicate a comprehensive assessment of indoor environmental comfort, with acoustic factors showing the least impact on overall comfort conditions. The study recommends equal weighting for thermal, acoustic, and lighting parameters when computing the combined comfort index. The building achieved an overall comfort rating of 0.64 out of 1, indicating a comfortable environment. The study also shows that there is a strong correlation between the new combined comfort index and the results from the questionnaire. This research contributes a straightforward and integrated approach to gauge comfort levels in educational buildings and lays the groundwork for further assessments of institutional building performance.


INTRODUCTION
There are over one million five hundred sixty-nine thousand educational institutions in India, including several public and a significant number of privately held structures [1].Government structures significantly contribute to greenhouse gas emissions (GHG).As a result, it is critical to assess the actual performance of university facilities.It has been discovered that the utilization phase of the created environment consumes a significant amount of energy [2,3].Nistratov et al. [4] innovated a method employing composite waste as environmentally-friendly building materials, cutting landfill waste costs and reducing production expenses by substituting primary materials.Significant energy savings and CO2 emission reductions can be realized during the use phase of buildings [5][6][7].Occupants spend a large portion of their lives indoors, in built-up environments.Throughout their undergraduate or graduate studies, students in the age range of 18-26 spend the majority of their time (87%) inside buildings.Hence, interior spaces should include the elements that provide a stimulating atmosphere to advance students' learning and analytical thinking [8,9].
The building sector in India consumes around 35% of the total energy, with an annual increase of 8%.Various techniques and methods are being developed to address this issue [10][11][12].The structure's use phase, which includes all amenities for the users' maximum comfort, accounts for approximately 73% of total building energy [13][14][15][16].In order to maintain thermal comfort, educational buildings consume a sizable quantity of energy.The overall energy consumption in the Indian educational building stock reaches 4,832 GWh, according to the Energy use in COmmercial buildings (ECO-III) study [17].Thermal comfort can have a significant impact on the learning process and on the motivation to engage in academic pursuits [18][19][20][21][22] .Haverinen-Shaughnessy et al. [19] discovered strong correlations between good math and reading, exam results and interior temperature, ventilation rate, and cleanliness of high contact surfaces.Lee et al. [21] reported similar findings in four university classes in Hong Kong, demonstrating high correlations between votes and total indoor environmental quality, particularly for auditory components.Toyinbo et al. [22] discovered a link between poorer mathematics exam scores in school buildings and non-recommended ventilation rates.Yang et al. [18] attempted to assess the influence of classroom characteristics on student happiness and performance.According to Wargocki and Wyon [20], poor indoor environmental quality affects learning performance by 30%.Doi [23] and Musa et al. [24] examined how passive cooling technologies can regulate urban development's impact on thermal comfort.
A recent review conducted by Zomorodian et al. [25] identified 48 studies on thermal comfort in educational buildings published in past decades.Among these studies, 25% focused on elementary and middle schools, 34% on secondary and high schools, and the remaining 41% on universities.Recent field investigations in primary and secondary schools have highlighted that children, due to their higher metabolism, experience thermal comfort differently than adults [26][27][28][29][30]. Notably, the neutral comfort temperature was found to be 23.1 °C in primary schools, 23.8 °C in secondary and high schools, and 25.1 °C in universities [25].These findings emphasize the importance of considering different age groups' thermal comfort requirements in educational buildings.Furthermore, the acoustical characteristics of primary, secondary, and tertiary-level classrooms as well as their impact on pupil success were studied.Yang and Bradley [31] conducted speech tests on elementary school pupils and adults and discovered that the intelligibility of speech for young children is influenced by reverberation time (RT), which is lower than the signal-to-noise ratio.According to Klatte et al. [32] background noise has a greater negative impact on children's speech perception and listening comprehension than it does on adults.Hodgson [33] demonstrated that the British Columbia University's classrooms had severe reverberation, low speech volumes, particularly at the rear of the rooms, and extremely noisy ventilation systems.They also created a questionnaire to assess perception of the listening environment.likewise Zannin and Marcon [34] learned that a Brazilian public school had inadequate acoustics [35].
Finally yet importantly, it is understood that having comfortable visual environments in classrooms is essential for learning and benefits the educational process.Michael and Heracleous [36] looked into how well a typical educational institution in Cyprus utilized natural lighting and suggested improvements to enhance visual comfort in classes.For the purpose of meeting the needs of the students in Athens' south-facing classrooms, Meresi [37] developed a particular light shelf for shade and light redirection as well as semitransparent, adjustable exterior shutters.Through the use of simulations and questionnaires, Korsavi et al. [38] examined a typical high school in Kashan, Iran.The results of the questionnaire revealed a wider range of sunlight acceptability, and the simulation results revealed a more upbeat approach [39].
The previous studies primarily focus on examining the effects of individual factors on environmental comfort, with limited attempts to comprehensively assess the cumulative impact of various perspectives.In order to gauge students' perceptions of acoustic and lighting comfort, tailored questionnaires were developed.By analyzing the mean responses to questions closely aligned with measured data, six acoustic indices and four visual indicators were formulated.These recommended indices are amalgamated in this study into a unified index that encompasses three distinct attributes: thermalhygrometric, auditory, and lighting comfort conditions.For each attribute, three specific single indices are initially proposed: the Predicted Mean Vote (PMV) Index for thermal-hygrometric settings, the Sound Index for acoustic comfort, and the Visual Index for lighting conditions.These indices are dimensionless and normalized within the 0 to 1 range, where values nearing 1 indicate favorable comfort conditions, while those nearing 0 signify unfavorable ones.Based on the correlation between questionnaire responses and collected data, each index was computed.Following prior research, equal importance was assigned to lighting, acoustics, and thermos-hygrometry comfort.Consequently, a composite comfort index is recommended and calculated for each classroom using these weighted factors.
The aim of this study by the authors is to investigate how the environment influences occupant comfort, considering aspects of thermal, acoustic, and lighting conditions.These fundamental factors play a vital role in shaping overall comfort conditions and can be managed through a combination of active measures such as utilizing plants and passive strategies like enhancing the building envelope [40].

1. Available Data & Case Study
The investigation comprised the examination of six hostel rooms situated on the premises of the National Institute of Technology Warangal (NITW) campus.The methodology's visual representation is captured by the flowchart in Figure 1.These particular rooms are located within a hostel complex boasting a total capacity of 1,800 rooms (1.8k hostel/Ultra mega hostel) and are specifically designated as A3-13, B3-50, A7-12, B7-20, and B7-48.The selection of these rooms was guided by factors such as the availability of students for active participation in the investigation and survey activities.A comprehensive consolidation of essential details concerning the hostel rooms, encompassing dimensions and occupancy particulars, is outlined in Table 1.Notably, this study maintained a dedicated focus on single sharing rooms to ensure coherence and uniformity within the analytical framework.Figure 2 depicts the arrangement of single and double sharing.Figures 3 and 4 depict a typical floor plan, ariel view, and front view of the 1.8K hostel.The hostel rooms were studied in terms of thermo-hygrometrical, lighting, and acoustical conditions.
The measurements were taken at a height of 0.75 m to represent the students' usual sitting space, as shown in Figure 5. Experimental measurements of natural ventilated illumination and acoustical conditions were measured with various instruments.Table 2 lists the instruments used to collect the data.

Analysis of Questionnaire Data
The experimentally measured data are compared to the responses from the questionnaire based on the questions shown in Table 3.To accomplish this, each question is linked to each measured value in order to assess the subjective parameters that are most closely related to the experimental data.Figure 5 depicts the experimental data collection.

3. 1. Acoustic Index IA
The acoustic index IA is calculated as follow: .
where ICN, IIN, IDN, ION, IRN and ISN are explained in Table 3.The weightage for each question is given in proportion to its correlation with the experimental data, with the question that is most correlated with the experimental data receiving the most weightage.ICN is given a 10% weight.IIN receives 10% of the weight, while IDN receives 40% of the weight.ION receives a 20% weightage, IRN receives a 10% weightage, and ISN receives a 10% weightage.It is important to note that an increase in mean votes for the indexes ICN, IDN, ION, IRN, and ISN is detrimental to acoustic comfort; therefore, a complement of 10 was considered in the average.

3. Visual Comfort Index IV
The lighting index Ivc is calculated as follow:

3. 3. Thermal Comfort Index IT
The predicted mean value can be used to assess thermal comfort (PMV).The PMV value will range between -3 and +3.IPMV, with a value ranging from 0 to 1, is calculated from PMV using the following formula, taking into account the linear relationship depicted in Figure 6.
When PMV is -3 or +3, IPMV has a value of 0 and has a maximum value of 1 when PMV is 0. The intermediate values will have a linear trend ranging from 0 to 1.

3. 4. The New Overall Comfort Index INCC
The weighted average values of individual comfort indices are added to calculate the new overall comfort index.The equal weights of three individual comfort indexes, which are normalised to the 0-1 range.The formula for calculating the new combined comfort index is given below: INCC = 0.33*IA + 0.33*IV + 0.33*IT .(4)

RESULTS
During the month of October 2018, data was collected for seven days.The information gathered is related to thermal, lighting, and acoustical conditions [41].Table 4 displays the mean values of the observed data.
In the brief autumn month of October, the minimum value of mean indoor temperature reaches 30.1 o C (room B7-18), corresponding to an outdoor temperature of 31.70 o C [8]. Indoor temperatures reach a maximum of 30.56 o C. (room A7-12).As a result, there is not much of a temperature difference between the rooms; they are almost all the same temperature.Acoustic results show  PMV that sound levels in all rooms exceed 60dB.The maximum sound level was 71.91 dB (room A7-46), which could be attributed to the fact that there were more people in the room most of the time.

1. Acoustic Index IA
The acoustic survey results are tabulated in Table 5. Acoustic indices are derived using Equation ( 1) from the survey responses.Among the rooms, B7-48 exhibits the highest internal noise, while Room A3-13 attains the most favorable value (8.12 for occasional noise).A comparative assessment is presented in Table 5, confirming Room A3-13's superior performance.Upon reviewing the IA values in Table 5, it becomes evident that Room A3-13 excels with an acoustic comfort index of 0.68.Notably, almost all rooms yield an acoustic index above 0.6 (excluding B7-20 with 0.59).The consistent acoustic index values within the 0-1 scale across rooms indicate uniform behavior.Values surpassing 0.6 within the 0-1 range signify satisfactory performance, underscoring good acoustic comfort across all rooms.

2. Visual Parameter Comfort Index-IVC
Table 6 lists the illumination comfort index values.Room A7-12 is found to have a high level of visual comfort (0.75), as well as a high illumination value of 483.18 lux and low annoying glare formation from natural light.All rooms with a visual comfort index greater than 0.5 are considered visually comfortable.Because of higher glare formation due to natural lighting, rooms A3-13 and B7-48 have a lower visual comfort index (0.56).

Thermal Comfort Index IT
The thermal sensation is evaluated on a 10-point scale (0-10), which is then converted into the traditional Fanger scale (7value).Because this survey is taking place during the brief autumn month of October, and all average measured temperatures are above 30 degrees Celsius, the scale is converted to the warm side (0 to 3) of the Fahrenheit scale.If the response is 10, PMV is set to 0 and IPMV is set to 1, which is more comfortable.If the response is 0, it indicates that the occupant is more dissatisfied, resulting in a -3 on the fanger scale and an IPMV of 0. Many factors influence thermal comfort, including metabolism, clothing resistance, air velocity, mean radiant temperature, and relative humidity.Due to the lack of equipment, the only factors considered in this thermal comfort evaluation are temperature and relative humidity.Table 7 contains the PMV and IPMV.Room A has good thermal comfort (IPMV = 0.81) while Room D has IPMV = 0.74.The remaining space has an index of around 0.6.

4. The New Overall Comfort Index INCC
By substituting the individual indices in Equation ( 4), the new combined overall comfort index is calculated.The total index value of the rooms is furnished in Table 8.The new combined comfort index is measured on a scale of 0 to 1, with 0 being the worst and 1 being the best.More than 0.65 is considered comfortable shwon by smile face.Neutral is 0.45 to 0.65 shown by emotionless face, and Uncomfortable is lessthan 0.45 shown by sad face.According to this classification, rooms A3-13, A7-12, and A7-46 are comfortable, while the remaining rooms have a comfort index of less than 0.6 and fall into the neutral category.The NCC for all

DISCUSSION
This study has examined a novel composite comfort index that integrates thermal, acoustic, and lighting aspects within an educational building.A comprehensive analysis was conducted by crossreferencing the responses obtained from Table 3's questionnaire with empirical measurements.Each question was matched with corresponding measurements, facilitating an assessment of the questionnaire's key subjective elements in relation to real-world data.The subsequent section delves into the correlation between the combined comfort index (INCC) and the average occupant ratings for heat, noise, and lighting factors (Figure 8).This investigation aims to establish whether the newly proposed INCC indicators effectively characterize the collective comfort conditions within the room.The findings in Table 9 underscore that rooms A3-13, A7-12, and A7-46 exhibit notably improved comfort conditions in comparison to other spaces.Room A3-13 demonstrates a heightened thermal comfort index (IT = 0.81) but a relatively lower visual comfort index (IV = 0.56), contrasting with room B3-50's lower thermal comfort (IT = 0.53) and elevated visual comfort (IV = 0.66).The compromised state of the thermo-hygrometric dimension is likely to additionally, Table 10 presents the relative weights assigned to acoustic, thermal, and lighting parameters for overall indoor environmental comfort, as gleaned from prior field studies.This facilitates parameter-level comparisons to provide comprehensive insights.While study data from various geographical regions can't be directly correlated, it's noteworthy that acoustics had the least influence on the overall indoor environmental comfort conditions among the three parameters examined.Field studies did not yield conclusive trends in comfort parameter weighting.Buratti [50] suggests that acoustic, thermal, and illumination factors hold nearly equal importance, which aligns with the findings of this study.The INCC indicators exhibit a notable alignment with the three distinct comfort conditions, as observed through Mean S.Q and Mean O.Q measurements (refer Table 9).Classrooms B7-20 and B7-40 are assessed as neutral with an INCC value of 0.59, which resonates with occupants' average votes of 5.13 and 5.49 (Mean O.Q).The potential influence of poor thermohygrometric conditions on these rooms is plausible.For room A7-46, the INCC value does not closely mirror the occupants' mean vote (neutral for acoustic and visual comfort).It is conceivable that students attributed more significance to the thermal aspect.A noteworthy correlation was identified between the mean votes assigned to the rooms and the INCC, established for both S.Q and O.Q metrics.The obtained R 2 values from this analysis are substantial, registering 0.67 and 0.79, respectively.This consistency aligns with the efficacy of the composite thermal, acoustic, and visual comfort indicator formulation.Conducting a broader experimental campaign with the new questionnaire could provide valuable validation of the newly proposed index.This approach involves calculating the index using data distinct from those used to develop the methodology, thereby augmenting its robustness.

CONCLUSION
This study introduces a pioneering approach to comprehensively assess the comfort levels within institutional buildings, unveiling a newly devised combined comfort index.Through an intricate analysis of thermal, acoustic, and visual comfort factors in six university hostel rooms, this research formulates a comprehensive model for evaluating comfort that goes beyond conventional parameters.The distinctive aspect lies in its ability to holistically measure comfort through a user-friendly questionnaire.The significance of each question aligns with its correlation to real-world data, leading to higher weighting for questions closely connected to actual experiences.
Building upon this framework, distinct equations are crafted for each comfort parameter (thermal, acoustic, and lighting).These parameters are subsequently normalized within a 0-1 range, where enhancements in comfort elevate dimensionless values from 0 to 1. Drawing from preceding research, equal importance is assigned to the three comfort-related indexes -IT (Thermal Index), IA (Acoustic Index), and IV (Illumination Index) -to establish the equation for the New Combined Comfort Index.By amalgamating individual indexes with uniform weights, a consolidated index emerges as the ultimate metric.The building's overall comfort achieves a rating of 0.64 out of 1, characterizing it as a comfortably conducive environment.Notably, a robust correlation emerges between room-specific mean votes and the INCC, substantiated through both S.Q and O.Q metrics.The ensuing R 2 values, 0.67 and 0.79 respectively, underscore the statistical robustness of this association.
This study not only introduces a fresh paradigm for evaluating comprehensive comfort but also demonstrates its practicality by devising the New Combined Comfort Index.Such insights open avenues for advanced strategies in designing and enhancing comfort conditions in built spaces.

Figure 4 .
Figure 4. Front view of the 1.8K hostel

Figure 5 .
Figure 5. Illustrates the aggregation of factual data

Figure 7 .
Figure 7.Comparison of indices of rooms

Figure 8 .
Figure 8. Correlation of INCC with Mean Vote

TABLE 2 .
Comfort parameters range, accuracy and resolution

TABLE 3 .
Acoustic, Lighting and Thermal questionnaires: selected questions and correspondent indexes

Table 3
defines the terms INL, INR, IAG, and IAL.INL receives 46% of the weightage, INR receives 1%, IAG receives 3%, and IAL receives 50% of the weightage.We used a negative value in the calculations by subtracting the votes from 10.Because an increase in mean votes for the indices IAG and IAL reduces visual comfort.

TABLE 4 .
Mean values of observed data of one week

TABLE 5 .
Acoustic Index (IA) based on questionnaire

TABLE 6 .
Visual comfort index IV based on questionnaire

TABLE 8 .
New combined comfort index value of rooms

TABLE 9 .
Comparison between INCC and mean votes

TABLE 10 .
Summarization of previous studies based on indoor environmental comfort