CHAPTER on two different time of the day; morning

CHAPTER 4.0    


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The field measurements of indoor and outdoor spaces were done on two different time of the day; morning and evening from eight o’clock in the morning to six o’clock in the evening, for each set of data. Since the field measurements were conducte within two study areas (indoor and outdoor), the relative humidity level of each area was examined separately.  Hence, the components of relative humidity level in indoor spaces and outdoor spaces are represented in the following sections.  Evaluation of relative humidity with its corresponding air temperature will highlights the significant effect of the two-studied element to thermal comfort of humans at two different time of the day.


The result obtained from the study is used in establishing the relationship between the observed humidity level of the observed space at different period of time. The studied data is discussed and compared with the provided standard guidelines by DOSH for indoor rooms and standard guidelines from DOE for outdoor spaces for comparison of the optimum value of humidity and temperature level for indoor and outdoor areas, respectively. Then, suggestions of improvements are provided, wherever necessary, for the betterment of the indoor and outdoor environment for the comfort of users.





Since all the indoor studied sites are mechanically ventilated with air-conditioning system to maintain the contented temperature, thus the observed temperature can be kept constant. In Table 2, the observed temperature of all the indoor rooms in this study is observed to be within 24.6 °C to 33.0 °C. Based on the guidelines released by the Department of Occupational Safety and Health Malaysia (DOSH) under the Industry Code of Practice on Indoor Air Quality 2010, it stated that the temperature between 23 to 26 °Celsius is where most people work comfortably at. The highest observed temperature of 33.0 °C which is on the higher end of the said acceptable range, as shown in Figure 5.


The guidelines also mentioned that the optimum range for indoor relative humidity is to be kept between 40 to 70 per cent (%). From Figure 9, we can also see that the observed humidity levels for all the indoor rooms ranges between 61.0 % to 77.1 %, which are significantly higher than the provided optimum humidity level in the DOSH guidelines.


The relationship between air temperature as the independent variable and relative humidity as the dependent variable was first observed, for indoor rooms based on the quadratic model study done by Harimi et. al. (2014) to show the relationship between indoor air temperature (Ta) and relative humidity (RHin) during field study, as mentioned in Chapter 2. While the outdoor spaces data set was examined based on another study done by Shanmugavelu who developed a non-linear regression for outdoor air temperatures and relative humidity dataset.



The calculated humidity value based on the two quadratic models provided an opportunity for assessment of results between the two data models within the range of the studied data associated with the indoor air temperature. The plotted values with their corresponding observed data intervals are shown in Figure 6.

A glimpse at the scattered graph shows that the variance in the relative humidity between the two data is between 4%, when using mean values. Overall, the current studied data model is consistent with the theoretical estimate, made in the previous studies, within the indoor temperature range of 27?C to 35?C. Therefore, the results obtained from this study can be used in the prediction of future indoor relative humidity against indoor air temperature and also to approximately predicts the outdoor relative humidity against outdoor air temperature, when needed.


Figure 5: Relationship between air temperature and humidity with the corresponding studied data set.



It is observed that the relative humidity is gradually decreasing against the air temperature, as shown in Figure 5. It shows that there is a collinearity between the two datasets. This was further confirmed from the developed equations (1) and (2). The high correlation coefficient between mean air temperature and mean relative humidity suggests that statistically the combination of these two parameters for the use of the analysis for indoor thermal comfort prediction may not be valid. From the analysed results, it can be said that the effect of the individual influence of relative humidity and air temperature to an occupant thermal comfort is not possible. For further analysis of IAQ analysis, the comfort temperature needs to be predicted first, for the effect of relative humidity on occupants’ thermal comfort.


ASHRAE 55-1992 set the maximum air relative humidity at 60%. This is because mold and mildew start to grow beyond this limit, whereas no lower humidity level was recommended in ASHRAE 55-2004. However, humidity levels which are not optimum might have a health impacts to the occupants. For instance, at low relative humidity, the increase in evaporation rate may cause skin drying and irritation (Ibrahim et. al.). However, Bauman et al. observed that the humidity affects occupant thermal sensation under increased metabolic rate. This was agreed with an earlier study carried out by McNall et al.



4.2.1    INDOOR


Figure 6: Humidity level variations for indoor rooms during peak time and off-peak time.


Figure 6 summarizes the results of the observed relative humidity and air temperature in this study over the following two main key findings; peak time and off-peak time. From the graph, we can be say that the value of relative humidity for the same rooms in both peak time and off-peak time is almost similar.  This study also points out that the relative humidity values decrease in the rooms may have been caused by the occupants’ behaviour. As shown in Figure 12, the relative humidity is gradually increasing with an increase in the number of occupants. This may due to the water vapor that is released by people through breathings, present of sweats on skin or any other foreign water bodies that was carried by people into the room. Also, with greater number of people, greater number of heat is present in the air that was released by the body. Thus, with an increase in temperature in the area, the relative humidity will decrease accordingly.


Figure 7: Relative humidity vs. Number of occupant (Indoor)


Other than that, the occupants’ behaviour connected to the choice of the cooling set-point, where different classroom has different air-conditioned cooling point because some users in the room may prefer slightly higher temperatures. Although other measured factors such sound pressure level, particulate matters and total volatile organic compounds are needed to assess the level of comfort that affects the occupants in indoor spaces, those factors were not measured in this study. However, with the observed data set, a projection on the increasing number of occupants in a room against the relative humidity level, can be made (Figure 7). This allows us to seek the level of comparison in determination of relative humidity of a dataset.  It is known that a greater number of occupants does not only affects indoor air temperature and relative humidity but as well as concentrations of pollutants in a room.



From the result reviews, it appears that we cannot conclude that the humidity effect on thermal comfort in air-conditioned spaces might not be the main determinant factor. We also cannot conclude statistical dependence of relative humidity in indoor spaces only on the presence of occupant. This is due to the strict limitations of humidity imposed for health, indoor air quality, and other factors.


Figure 8: Level of humidity vs. No of occupants (Indoor).



4.2.2    OUTDOOR


However, thermal comfort does not only imply for indoor rooms, but it also has an implication to occupants in open spaces and outdoor areas. The results in Figure 9 shows that an acceptable range of thermal comfort (less than 35 °C) is achieved during the whole study period. The study also found that in between 11 am to 4 pm, it is measured to have high amount of sun radiation that leads to the lowest level of thermal comfort. It is important to note that the air temperature measurement of this study was based upon the daytime period (9 am to 6 pm) which is considered as the peak hours of the worst conditions.


Figure 9: The Observed Relative Humidity Against the Air Temperature (Outdoor)





Figure 9 shows the variation of the studied data for all outdoor spaces and the data is plotted against the Malaysian Meteorological Department and Department of Environment of Malaysia (DOE) guideline that stated for a temperature of between 30 °C to 35 °C, the optimum humidity shall be between 70% to 75%. The graph outlined the observed humidity levels against the maximum humidity requirement that is 75%. The studied data of humidity level is


found to be at 59.6 % and 76.5 % of humidity for temperature level that ranges between 27.6°C and 35.2°C. Most of the studied area records a lower humidity levels than the optimum, even at a high temperature reading. This suggests that the area is very dry because of the present of air movement and outdoor heat that cause water vapor to condense and evaporate at a higher state.


Figure 10: Humidity level variations for outdoor spaces during peak time and off-peak time.



It is believed that higher humidity and air temperature increases thermal feeling and reduces perspiration and evaporation of the body’s capacity, thus the body cannot be cooled by evaporation. As illustrated in Figure 10, the recorded values of air temperature showed very small differences between the selected locations (with a maximum difference value of about 0.9 °C) although there was a large change in thermal comfort conditions and their corresponding between the areas. This may be concluded that, during the measurement process, the variation of the relative humidity was typically affected by the mean radiant temperature (Tmrt) rather than the air temperature. The value of mean radiant temperature (Tmrt) was estimated from measurement of globe temperature. The Tmrt was estimated using air temperature, globe temperature and wind speed based upon ISO standard 7726. The results show that differences between observed values of the relative humidity in all five locations during peak time and off-peak time were very significant the ending hours of measurement procedure.








Humidity control is to add or remove water vapor from atmospheric air, so that the humidity will stay within proper ranges. Low humidity can cause dryness of the eyes, nose and throat and may also increase the frequency of static electricity shocks. High humidity, above 80% can be associated with fatigue and report of “stuffiness” (DOSH,1996). Several strategies can be implemented to regulate the humidity control for both indoor and outdoor as well as the temperature control for outdoor spaces. Based on the study that has been conducted, few suggestions on improvements need to be done. Thus, this section will discuss and suggest methods of improvement for the improvement of indoor and outdoor relative humidity.


4.3.1 (a)           INDOOR


Good indoor air quality is crucial and can be achieved through appropriate room ventilation.  Some ways to keep people in indoor rooms comfortable is to use the ceiling or wall fans to move air when it’s too warm and keeping surrounding surfaces with good insulation. Installation of HVAC equipment like boilers, fans, and heat exchangers can temper the air temperature and humidity too. Other practical recommendations include daily breathing exercises and outdoor leisure activities for occupants to gain fresh air.

Other than that, the layout of the spaces can be changed to improve the air condition. A desk situated in direct sunlight will be much warmer than the average temperature in the room and a desk situated directly under an air-conditioning vent can be cooler than average. So, additional windows, skylights or glass partitions in rooms should not allow excessive temperatures during hot weather thus improves the humidity control.


4.3.1 (b)          OUTDOOR



This study verifies and approves that air temperature alone is an unsuitable indicator for the assessment of relative humidity and the overall thermal comfort in outdoor spaces. It should be noted that, air flow can decrease the values of air temperature as well, although, solar radiation plays more important role than wind speed when measuring the relative humidity. The findings also show that the use of trees and shadings lead to a decrease in the air temperature values of area by protection from direct solar radiation. Accordingly, the locations which are protected by the shade of surrounding buildings and plants show tendency to be slightly cooler than the others due to their lower exposure to direct solar radiation. Hence, high shading level is required in outdoor environments to increase thermal comfort and extend the continuity of the acceptable thermal conditions during the day.

The conditions of location that was provided with shade of surrounding objects and suitable shade structures are greatly affect the creation of a comfortable outdoor spaces. It is recommended to architects, planners and urban designers to consider the respective facts in the design process of shaded outdoor spaces in order to achieve the thermal comfort level specifically in hot and humid climate countries.  Other than that, an Economizer Control of outdoor air can also be used for free cooling through the use of an economizer cycle, under the right conditions.


CHAPTER 5.0    



In a nutshell, all the common indoor rooms and common outdoor spaces used by the students of FKA has been observed in regard of the respective humidity and air temperature level. The data for both study sites is interpreted according to the observation time, as outlined in Table 2 and 3.

Based on the study that has been conducted, it is found that most of the studied areas in indoor rooms shows a slightly lower humidity levels than the humidity level requirement outlined by the standard guidelines by DOSH of 70.0 % relative humidity, with an average recorded humidity level of 67.2%. In contrast, for outdoor spaces, the relative humidity levels observed shows that none of the spaces are at the optimum relative humidity level of 70%, as stated by the DOE. In average, most spaces recorded a very low humidity level of average 64%. Humidity level which are too high or too low poses a great impact to the overall comfort of building occupants. Thus, this issue needs to be address by providing some relevant recommendations for the required areas.

Based on the study as well, few suggestions on improvements need to be done. The improvement of indoor humidity level can be achieved through appropriate room ventilation.  Some ways to keep people in indoor rooms comfortable is to use the ceiling or wall fans to move air when it’s too warm and keeping surrounding surfaces with good insulation or by installing HVAC equipment. The findings also found that the use of trees and shadings lead to a reduction in the air temperature values of area by protection from direct solar radiation. Thus, high shading level is required in outdoor environments to increase thermal comfort and extend the continuity of the acceptable thermal conditions during the day.



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