Improving thermal sensa�on in classrooms with respect to dra� avoidance by op�mizing the mechanical air supply method Omar Husein Al-hebshi Supervisor: Dr-Ing. Mohannad Bayoumi
AR 600 Advanced Studio Department of Architecture Faculty of Architecture and Planning King Abdulaziz University
First Semester 2019/2020
Contents 01. Introduc�on 02. Research Framework 03. Point of departure 04. Research problem 05. Research objec�ve 06. Research ques�on 07. Research hypothesis 08. Literature review 09. Methodology 10. Results and discussion 11. Conclusion 12. Acknowledgments 13. References
1 2 3 4 5 6 7 8 9 10
1. INTRODUCTION Young students spend approximately 30% of their lives in school classrooms 1. (Giuli, Da, & Carli, 2012)
This paper aims to investigate thermal sensation inside KAU classrooms by studying air temperature and air velocity and adapting these two variables as necessary along with adopting different ventelation strategies to improve thermal sensation inside the classrooms .
This paper should provide guidelines to optimize thermal sensation inside classrooms in presence of a new plans to raise the targeted teacher to student ratio from 1:17 to 1:45 in high density areas
Keywords : Thermal sensation CFD simulation Subtropical climates Classrooms Ventilation strategies Comfort zone
3
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
2. FRAMEWORK
Fanger Comfort Equation
Breathing
The main factors that influence THERMAL COMFORT
M-W = (C+R+Esk) +(Cres+Eres) 1. Metabolic Rate 2. Clothing Insulation
Skin Natural Ventilation
3. Air Temperature
Testing Several Ventilation Strat-
4. Air Velocity 5. Air Humidity
Artificial Ventilation
M = Metabolic rate W = Work C = Heat transfer by convection from clothing surface R = Heat transfer by radiation fromclothing surface Esk = Evaporative convective heat exchange Cres = Respiratory evaporative heat exchange Eres = Respiratory evaporative heat exchange L = Thermal load on the body L = Internal heat production - Heat loss to the actual environment L = M - W - [(Csk + Rsk + Esk) + (Cres+Eres)] PMV = (0.303 exp (-0.036 M) + 0.028 ) x L
6. Radiant Temperature
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
4
2. Research Problem 3. Point of departure
4. Research problem
examine thermal sensation of the students in King Abdulaziz 2.Touniversity, Research problem Google form based question was published in variety of
Results of the questioner in of Fig.uncomfortable 1 illustrates thatthermal 17.13 and 33.30 % of the This paper investigate the issue sensation caused by have air draft generated by the mechanical students cold and cool and sensations respectively . ventilation Many students in system KIng insideAbdulaziz som of King Abdulaziz university classrooms . University and other educational institutions reported
social media groups of KAU students, 75 students participated in the questionnaire.
To examine thermal sensation of the students in King Abdulaziz university, Google form based contains question was published in varietyasking of social groupstoof The questionier only one question themedia students evaluate their sensation in inside the classroom by choosing KAU students, 75 thermal students participated the questionnaire one of the PMV scale’s values : cold, cool, cool, The questionier contains only one question askingslightly the students toneutral, evaluate their slightly warm, warm and hot, questionieer results are shown in Fig. thermal sensation inside the classroom by choosing one of the PMV scale's 1 as following values : cold, cool, slightly cool, neutral, slightly warm, warm and hot, questionieer results are shown in Fig. 1 %33.30
%35.00
No. of participants
%20.00
%18.60
%10.00
What is the optimum configuration of mechanical air supply diffusers in class-
%1.33
%0.00 slightly cool
Improving thermal sensation inside KAU classrooms by testing other ventilation 6. Research question
7. Research hypothesis rooms that help avoid draft sensation under certain conditions ?
%6.66
%5.00 cool
3. Research objective
4. Research question
%15.00
cold
Improving thermal sensation inside KAU classrooms by testing other ventilation types and controlling air temperature / air velocity without making major changes in the existing buildings and with minimum technical complexity .
What is the optimum configuration of mechanical air supply diffusers in classrooms that help avoid draft sensation under certain conditions ?
%22.60 %17.30
student ratio from 1:17 to 1:45 in some high density areas .
types and controlling air temperature / air velocity without making major changes in the existing buildings and with minimum technical complexity .
%30.00 %25.00
complaint about inadequate indoor air quality and thermal conditions inside the
5. Research objective classrooms. This conditions can be worsen with a new plans to raise teacher to
neutral
slightly warm
warm
PMV value
%0 hot
Air supply locations as well as air supply temperature play an important role in creating and avoiding draft sensation .
5. Research hypothesis
Air supply locations as well as air supply temperature play an important role in creating and avoiding draft sensation .
Fig. 1 Results of the implemented questionnaire to evaluate students' thermal sensation
2 5
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
d as “prima-
as “second-
8.2 Identifying a research gap
In a study carried out by Kumar, M., Ooka, R., Rijal, H. B., Kumar, S., & Kumar in 2019 (Kumar et al. 2019), The authors invesigated the progress in thermal comfort studies in classrooms over the last 50 years in different parts of the world to gives detail insight of the thermal comfort studies done in classrooms across the world and analyze the results.
8.2.1 Number of studies done about classrooms’ thermal comfort
The research articles are classified into three categories: 1. Kindergarten, elementary and primary school classrooms, referred as “primary school classroom” for analysis. 2. Secondary, senior secondary and high school classrooms, referred as “secondary school classroom” for analysis. 3. University classroom
6. Literature review
Figure below shows Type of documents on Scopus scientific data6.2 Identifying a research gap base when search with keywords “thermal comfort, adaptive thermal comfort and thermal comfort in classroom” (ac- cessed on 11th October 2018).
18,888
Thermal comfort articles
6.2.1 Number of studies done about classrooms’ thermal comfort Fig. 2 shows Type of documents on Scopus scientific database when search with 395 keywords comfort “thermalarticles comfort, adaptive thermal comfort and thermal comfort in Classroom Database classroom” (ac- cessed on 11th October 2018).
Scopus
1,090
Adaptive thermal comfort articles
To carry out this study Scopus database is searched with keyword “thermal comfort study in classrooms”. Total 93 research articles appeared
152
M.K. Singh, R. Ooka and H.B. Rijal et al. / Energy & Buildings 188–189 (2019) 149–174
M.K. Singh, R. Ooka and H.B. Rijal et al. / Energy & Buildings 188–189 (2019) 149–174
12000
12
10000
Number of documents publishes
14
10 8 6 4
Thermal comfort
Adaptive thermal comfort
165
Thermal comfort in classrooms
No. of Classroom comfort articles : 395 No. of Adaptive thermal comfort articles : 1090 No. of Thermal comfort articles : 395
8000 6000 4000 2000
Year
Re p Bu sin ort ess art icle
l
tte r Le
ito r ia
Ed
No te
Bo ok Sh ort sur vey Er r atu m
Re s ea r Co ch ar t nfe ren icle ce pap er Re vie w Bo ok cha pte Ar r tic le i np Co res nfe s ren ce rev iew
2018
2017
2016
2015
2014
2013
2012
2011
2010
2009
2008
2007
2006
2006
2004
2003
1988
1977
1975
1973
0
1972
2 1969
., & Kumar t studies in gives detail e world and
8.1 Progress in thermal comfort studies in classrooms
Number of research papers published
s over last
8. Literature review
Fig. publishedover overthetheyears years in classroom thermal comfort (accessed 11th October 2018). Fig.1.1.Number Number of of paper paper published in classroom thermal comfort (accessed on 11thon October 2018). Table 1 Characteristics of classrooms at different levels of education.
Fig. 7. Type of documents on Scopus scientific database when search with keywords “thermal comfort, adaptive thermal comfort and thermal comfort in classroom” (acFig. 2 Type cessed on 11th October 2018).of documents on Scopus scientific database when search with keywords “thermal comfort, adaptive thermal comfort and
Classrooms at different levels of education
thermal comfort in classroom” (ac- cessed on 11th October 2018).(4) 1. Naturally Ventilated (NV): A Classroom is constructed to operate under free aggravate the unacceptability of existing thermal environrunning (FR) condition 12 months a year and same is considered under thewhich ment [39,40,83,84].
Parameters
Kindergarten
Elementary/Primary
Secondary/Sr. Secondary
University
3-6
7-11
12-18
19-26
High
Depending on class and
Depending on class and
Depending on class and
Improving thermal sensation in classrooms with Children respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi Occupants Children Children Adults Age group (Approximately) Density
6
class. So they are in transient condition for about 20–30% of the time (if a class is of 1-hour duration). So the memory of the pre-
18). 8). 8. Literature review
Buildings 188–189 (2019) 149–174 && Buildings 188–189 (2019) 149–174
malcomfort comfort
165 165
8.2 Identifying Thermal comfortainresearch classrooms gap
canbebeseen seenininFig. Fig.44that thatthe thedistribution distributionofofstudies studiesisisquite quiteskewed. skewed.The Thehih ItItcan numberofofstudies studiesisisdone doneininsub-tropical sub-tropicalcountries countriesfollowed followedbybycountries countrie estestnumber temperateclimate. climate.Mediterranean Mediterraneanand andhot hotand anddry dryclimate climatecountries countrieshave havequq aatemperate fewstudies studiesespecially especiallyabout aboutuniversity universityclassrooms classrooms(4). (4). aafew M.K. Singh, R. Ooka and H.B. Rijal et al. / Energy & Buildings 188–189 (2019) 149–174 M.K. Singh, R. Ooka and H.B. Rijal et al. / Energy & Buildings 188–189 (2019) 149–174
Thermal comfort in classrooms 8.2.2 Number of studies done in the classrooms of each climatic zone o.ofofClassroom Classroomcomfort comfort articles: 395 : 395 articles o.ofofAdaptive Adaptivethermal thermalcomfort comfortarticles articles: 1090 : 1090 Figs. 3 and 4 show the Koppen–Geiger world climatic classification o.ofofThermal Thermalcomfort comfortarticles articles: 395 : 395 and the number of studies done about thermal comfort in classrooms for each climatic zone. From Figs. 3,4 and 5, we notice the following : 1. The number of reasearch articles published about thermal comfort in classrooms is very few compared to the number research articles about thermal comfort in general . 2. Among the studies done about thermal comfort in classrooms, there is almost no studies published about thermal comfort in university classroom within hot and dry zones as shown in Fig.5.
Tropical Arid Arid Temperate Temperate Tropical
keywords “thermalcomfort, comfort,adaptive adaptivethermal thermalcomfort comfortandand ywords “thermal
70 8080 60 7070 50 6060
ResearchNumber of articles studies in % Research studies in %
hot s rtusr uvrevy Er r e y Erartu atmu m No Ntoe Ed te Eidto itroia rila l Le Lteter tte Re r Rpo Bu Bsuin eprotr t sienss essar taric tilce le
rmal comfort, adaptive thermal comfort and thermal comfort classroom” (acmal comfort, adaptive thermal comfort and thermal comfort in in classroom” (ac-
163
Polar Polar
3 Worldmap mapofofKoppen–Geiger Koppen–Geigerclimate climateclassification classification(4).(4). Fig.Fig.3 World Fig. 3. World map of Koppen–Geiger climate classification. Fig. 3. World map of Koppen–Geiger climate classification.
80
This lack of studies about thermal comfort in university classrooms within hot and dry climatic conditions represents a research gap and needs more progress in studies to povide more information and help enhance thermal sensation in classrooms in these regions which we hope this research will help to accomplish this .
Cold Cold
163
Primary Primary Secondary Secondary University University
40 5050 30 4040 20 3030 10 2020 0 1010
ass.SoSothey theyare areinintransient transientcondition conditionfor forabout about20–30% 20–30%ofofthe the Temperate Tropical and Mediterranean Hot and Dry ss. 00 Subtropical me (if a class is of 1-hour duration). So the memory of the preTemperate Tropical Tropical Mediterian HotHot e (if a class is of 1-hour duration). So the memory of the preTemperate && SubSub Mediterian && DryDry ious environment greatly affects the thermal comfort and preftropical Primary Secondary University us environment greatly affects the thermal comfort and prefFig. 4. Summary of thermal comforttropical studies conducted in different climates at various education level (total 89 articles). Fig. 4. Summary of thermal comfort studies conducted in different climates at various education level (total 89 articles). rence studentininuniversity universityclassrooms. classrooms.This Thishappens happensseveral several 4 Summaryofofthermal thermalcomfort comfortstudies studiesconducted conductedinindifferent differentclimates climatesat atvarious various nce ofofa astudent Fig.Fig.4 Summary the publication followed by conference papers. It is a healthy sign 7.2. Thermal comfort and preferences in primary school classrooms mes in a day, during their stay in the university. In classroom stueducation level (total the publication followed by conference papers. It articles)(4). is a healthy sign 7.2. Thermal comfort and preferences in primary school classrooms es in a day, during their stay in the university. In classroom stulevel (total 8989articles)(4). because it education is enriching the database which is required to develop because it is enriching the database which is required to develop entsexperience experiencea atransient transientthermal thermalcondition conditionfor forfirst first15–20 15–20min min a robust thermal comfort model for classroom. It is also showing All 93 research articles are classified into primary, secondary nts a robust thermal comfort model for classroom. It is also showing All 93 research articles are classified into primary, secondary the increasing awareness and concern among the researchers and and university classrooms based studies. 34 out of 93 studies are the increasing awareness and concern among the researchers and and university classrooms based studies. 34 out of 93 studies are na aclass classand andwhen whenignoring ignoringthis thisfact factISO ISO7730, 7730,ASHRAE ASHRAE5555and and scientists about the IEQ and its role in the human well-being in on primary school’s classrooms. Tables 2 and 3 present the imscientists about the IEQ and its role in the human well-being in on primary school’s classrooms. Tables 2 and 3 present the imdifferent kind of built environments including classrooms. A small portant set of data related to location, time of the survey, the opEN15251 15251standard standardwhich whichgenerally generallydeals dealswith withsteady-state steady-statecondicondidifferent kind of built environments including classrooms. A small portant set of data related to location, time of the survey, the opN number of classroom centric studies are a matter of concern deeration of classrooms, sample size, comfortable temperature, neunumber of classroom centric studies are a matter of concern deeration of classrooms, sample size, comfortable temperature, neuons, applied to evaluate classrooms thermal environment, the despite knowing the impact of inadeadequate IEQ on the learning tral temperature and air velocity etc. Some rows in Tables 2 and ns, applied to evaluate classrooms thermal environment, the despite knowing the impact of inadeadequate IEQ on the learning tral temperature and air velocity etc. Some rows in Tables 2 and ability and well-being of students. It demands more studies to be 3 are highlighted showing significant information is missing in ability and well-being of students. It demands more studies to be 3 are highlighted showing significant information is missing in 7 Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi iation reportedbybymany manystudies studiesseems seemsobvious obvious[25–27,121–124] [25–27,121–124] done across the globe so that a grand database can be built and it the published article. It may be possible that for particular study tion reported . . done across the globe so that a grand database can be built and it the published article. It may be possible that for particular study can be taken forward to the formulation of a new set of IEQ stanthose data were not necessary but for this study comfort survey erealso alsoit itisisthe thecase casewhere wherestandards standardsare areapplied appliedtotodesign designanan can be taken forward to the formulation of a new set of IEQ stanthose data were not necessary but for this study comfort survey re dards/guidelines for designing future classrooms. indicators and statistics are important to the data with a specific
(Kumar,Ooka, Ooka,Rijal, Rijal,Kumar, Kumar,&&Kumar, Kumar,2019) 2019) 4.4.(Kumar,
8. Literature review
8.3 Summaryreview 6. Literature 6. Literature review
6.3 Summary 6.3 Summary tween 1.1-1.4 met ( sedentary metabolic rate ) and temperatures According to Toftum who demonstrated that in metablic rates be-
from 22.5-23.5 °C, with air velocities less than 0.25 m/s at 1.1 m above the floor, only few occuoants complained of air draft and preffered lower air velocities, while most of occupants preffered no change at the same temperature range and air velocity range of 0 to 0.28m/s (3. Toftumm 2004) . Table. conclude air velocity and temperature values from researches on univer-
In order to comply with ASHRAE 55, the recommended thermal limit on the 7-point scale of PMV is between -0.5 and 0.5. ISO 7730 expands on this limit, giving different indoor environments ranges. ISO defines the hard limit as ranging between -2 and +2, for existing buildings between -0.7 and +0.7, and new buildings ranging between -0.5 and +0.5 (4. Guenther, Sebastian, 2019) .
Using both PMV and PPD indices, ASHRAE 55 dictates that thermal Cate- Thermal state of the body as a Operative temperature Max. mean air velocity oC gory whole m/s sity classrooms mentioned previously, within subtropical and hot-humid climatcomfort can be achieved based on 80% occupant satisfaction rate or more. The PPD Summer (0,5 clo) Winter(1 clo) Summer(0,5 clo) Winter(1 clo) PMV ic percentage zones because they arecan similar in climatic conditions to our based investigated remainingTable people experience dissatisfaction on from % Cooling Heating Cooling Heating belowof conclude air velocity10% and temperature values samples. A < 6 0.2< PMV < + 0.2 25,5 – 23,5 23,0 – 21,0 0,18 0,15 whole-body discomforton (alluniversity listed influencing factors ofmentioned PMV) and 10% dissatis- within researches classrooms previously, B < 10 0.5- < PMV < + 0.5 26,0 – 23,0 24,0 – 20,0 0,22 0,18 subtropical hot-humid climatic zones because theyfewer are similar faction based on localand discomfort/partial body discomfort (includes C < 15 0.7 < PMV < + 0.7 27,0 – 22,0 25,0 – 19,0 0,25 0,21 in climatic conditions investigated samples. factors than whole-body). In ordertotoour comply with ASHRAE 55, the recomTable. 9 Recommended levels of acceptance for operative temperature and air velocity (ISO EN 7730, 2005, CR 1752, 1998 ) (14). mended thermal limit on the 7-point scale of PMV is between -0.5 and 0.5. ISO 7730 expands on this limit, giving different indoor environments ranges. ISO Location Climate Time of survey Proposed air velocity Proposed comfort temperature defines the Researchers hard limit as ranging between -2 and +2, for existing buildings between -0.75. P.F. andHu,+0.7, andZ.N. newJiang buildingsWuhan, ranging between -0.5 and +0.5 (13) . W. Liu, China Sub-tropical Jun to Sept and Dec to Feb 0.12 m/s 18.4-26.1 C° Zhang, C. Zhengalevels of acceptance Hunan University, China temperature Sub-tropical and Mar to Apr 2005 0.11 m/s 21.5-24.8 C° Table 9 gives6. G.recommended for operative Chongqing, China Sub-tropical Mar 2005 to May 2006 0.5 m/s 16-30 C° 7. R. Yao, J. Liu, B. Li air velocity for three classes of environment. 8. B. Cao, Y. Zhu Beijing, China Sub-tropical 9. Z. Wang, A. Li, J. Ren Harbin, China Sub-tropical Based on data tablesH. 9Ning, andX.10, we can Harbin, use temperature range from 23.5-25.5 10. Z.inWang, Zhang China Sub-tropical P. Baruah, M.K. Singh Tezpur, India as a comfort11.zone to evaluate your experimental values in the nextWarm ste and . humid 12. R. Vittal, S. Gnanasam Tamilnadu, India Warm and humid
Jun-Aug 2009; Nov-Dec 2007 Dec 2015-Jan 2015, Oct 2013 to Apr 2014 Feb and May 2013 Feb and May 2013
Average values
0.17 0.12 0.04 0.1 0.2
m/s m/s m/s m/s m/s
0.17 m/s
23-26 C° 22-25 C° 16-22.4 C° 22-23.5 C° 21.6-29.8 C°
23 C°
Table. 8 Summary and averages of air temperature and velocity values in university classrooms
15
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
13. (Guenther, Sebastian, 2019)
14. (Olesen, 2004)
8
7. Methodologyofofthe the study 9. Methodology study Measurement Phase 1 Selection of the study sample
Analysing results
Data Collection
Detecting best and worst places
Measurement Phase 2 CFD simulation for current status
Mixing ventilation system (MV)
Determining the ideal scenario
16
9
Evaluating scenarios based on thermal comfort parameters and energy consumption
Displacement ventilation system
CFD simulation for Proposed solving scenarios
Stratum ventilation system (DV)
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
9. Methodology of the study
sellected, teachers umber of t samples
7.39.1Objective measurements Selection of study sample 7.3.1 Phase TwoMeasurement classrooms in 1building 535 on the preparatory year faculty Field testsellected, parametersThe included air of temperature and air velocity. were choice the classrooms due to the avaliability of the students and teachers during the day; Furthermore, the the two Air temperature and air velocity were measured at the height of 1.1 m from classrooms have different area,the number of students, floor in each measurment point within classrooms as shown inwindows Fig. 7 . surfaces and orientation in order have a1 significant samples . some The measurment process took a placeto between and 4 PM when classrooms in pictures of the sellected classrooms are shown in Fig. 5 the preparatory year are almost full of students in October 9th 2019 . Measurment process lasted 10 minutes at each measurment point with time Classroom sample of 1A minute . Measurement equipment used in the experiment is REED Thermo-Anemometer model SD-4214 as shown in Fig. 9 . Table 11 shows details of the experimental equipment used .
g system, o on are hows the Classroom B
measurdifferent
measur-
A
B
Width [m] Length [m] Ceiling height [m] Volume [m³] Floor area [m²] Ceiling material Floor material Surface walls material Surface color
7.5 9.1 3 204.75 69 Metal panels Granite tiles Smooth paint White
5.9 7.8 3.07 141.28 46 Metal panels Granite tiles Smooth paint White
Air conditioning system Number of ceiling diffusers Type of ceiling diffusers
Central AC 6 Square diffusers
Central AC 4 Square diffusers
Number of sitting places Number of windows Number of doors Door type
60 2 1 Double Swing Door
45 3 1 Double Swing Door
Table. 10 Characteristics of the investigated classrooms
on of air ded basd
gate how . 7 shows nt points
Classroom
Fig. 8 REED Thermo-Anemometer model SD-4214
17 Fig. 5 Pictures from the selected classrooms
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
10
7.79
Classroom B plan
0.60
11 1.24
1.95
0.88
5.93
1.79 1.24 1.06
1.75
North direction
17
1.69
1.11
Air conditioning system Number of ceiling diffusers Type of ceiling diffusers
Width [m] Length [m] Ceiling height [m] Volume [m³] Floor area [m²] Ceiling material Floor material Surface walls material Surface color
Classroom
9.1 Selection of study sample
7. Methodology of the study
Fig. 8 REED Thermo-Anemometer model SD-4214
1.07
9.14
7.3 Objective measurements 7.3.1 Measurement Phase 1 Field test parameters included air temperature and air velocity. Air temperature and air velocity were measured at the height of 1.1 m from the floor in each measurment point within the classrooms as shown in Fig. 7 . The measurment process took a place between 1 and 4 PM when classrooms in the preparatory year are almost full of students in October 9th 2019 . Measurment process lasted 10 minutes at each measurment point with time sample of 1 minute . Measurement equipment used in the experiment is REED Thermo-Anemometer model SD-4214 as shown in Fig. 9 . Table 11 shows details of the experimental equipment used .
1.07
Classroom A plan
7. Methodology of the study
1.27
7.50
60 2 1 Double Swing Door
Central AC 6 Square diffusers
5 7. 3 1 4
7.5 9.1 3 204.75 69 Metal panels Granite tiles Smooth paint White
4 3 1
C 4 S
G S
B
A
Table. 10 Characteristics of the investigated classrooms
8.2 Data collection
The device used to collect data from classrooms is REED Thermo-Anemometer model SD-4214 as shown in Fig. 9 . Table 11 shows parameters, range, resolution and accuracy details of the same device . To facilitate the data collection in the classrooms and get more accurate information, the data collection process carried out in two phases as following :
Number of sitting places Number of windows Number of doors Door type
9. Methodology of the study
Equipment Parameters
REED SD-4214 Hot Wire ThermoAnemometer/Data Logger Air velocity
Air temperature
Range Resolutions
0.2 - 5.0 m/s 0.01 m/s
5.1 - 25.0 m/s 0.1 m/s
-50 - 1300 C°
-50.1 - 100 C°
0.1 C°
Accuracy
± ( 1% + 0.1 m/s )
± ( 0.4% + 0.5 C° )
± ( 0.4% + 1 C° )
Fig. 6 Plans of the selected classrooms
Table. 11 Details of the experimental equipment
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
Comparing Figs 9-14 ( Class A readings ) and 15-18 ( Class B readngs ) indicated that in class A Values of air temperature and air velocity is much closer to the
9. Methodology of the study 9.2 Data collection
7. Methodology of the study
Measurement Phase 1
Classroom A plan Classroom A
Classroom B plan
Classroom B 9.14
1.24
1.79
1.24
1.06
Section A 1
Section A 3
Section A 5
Section A 2
Section A 4
Section A 6
Section B 2
Section B 1
Section B 3
Section B 4
1.27
1.07
7.79
1.95
7.50
0.88
1.07
1.69
1.11
0.60
5.93
Section boundary
Measurement point
North direction
1.75
19
Fig. 7 Division of the classrooms and measurement points
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
12
7. Methodology of the study
9. Methodology of the study 9.2 Data collection
23.4
0.15
23.3 23.2
0.1
23 °C
23.1
0
1
2
3
4
5
6
7
8
9
10
11
23.7
0.25
23.65
0.2
23.6 0.15
23.55 23.5
23.4 °C
23.45
0.05
23
0.3
23.75
Air temperature °C
Air temperature °C
0.2
23.5
0
23.35
0 0
Air velocity
0.35
7
8
9
10
0.25
23.65
0.2
23.6
0.15
23.55 23.5
0.1
23.4 °C 3
4
5
6
7
8
9
10
Time ( in minutes ) Air temperature Air velocity Fig. 9 Air velocity and air temperature measurements in section A1 Average air velocity : 0.044 Average air temperature : 24.91
11
Air temperature °C
23.7
2
11
0.3
24
Air velocity m/s
Air temperature °C
6
24 °C
24.1
0.3
23.4
13
5
Fig. 12 Air velocity vs air temperature in section A4
23.45
20
4
Fig. 10 Air velocity vs air temperature in section A2
23.75
1
3
Air temperature Air velocity Average air velocity : 0.215 Average air temperature : 23.56
23.8 °C
0
2
Average air temperature : 23.32
23.8
23.35
1
Time ( in minutes )
Air temperature
Average air velocity : 0.211
0.1 0.05
23.4
Time ( in minutes )
23.85
0.35
23.8
0.25
23.6
22.9
23.85
Air velocity m/s
0.3
23.7
23.8 °C
0.25
23.9
0.2
23.8 0.15 23.7 23.6
0.05
23.5
0
23.4
23.5 °C
0.1
Air velocity m/s
23.7 °C
Fig. 11 Air velocity vs air temperature in section A3
Air velocity m/s
23.8
Fig. 9 Air velocity vs air temperature in section A1
0.05 0
0
1
2
3
4
5
6
7
8
9
10
11
Time ( in minutes ) Series2
Average air velocity : 0.172
Series1
Average air temperature : 23.74
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study
9. Methodology of the study 9.2 Data collection Fig. 13 Air velocity vs air temperature in section A5
0.18
24.3
0.16
24.2
0.14
23.4
0.12
23.2
0.1 0.08
23
0.06
22.8
22.6 °C
22.4
0
1
2
3
4
5
6
7
8
9
10
0.25 0.2
24.1
0.15
24 23.9
0.1
23.8
0.04
23.7
0.02
23.6
0
23.5
0.05
23.6 °C 0
11
1
2
3
4
Air temperature
Average air velocity : 0.123
Average air temperature : 23.33
0.25
24.3 0.1
24.2
23.9 °C
0.05
23.9 23.8
0 2
3
4
5
6
7
8
9
10
11
Air temperature °C
0.15
24.4
Air velocity m/s
Air temperature °C
24.5
1
10
0
11
Average air temperature : 23.98
0.18 0.16 0.14
24.5
0.12
24.4
0.1
24.3
0.08
24.2
0.06
24.1 °C
0.04
24.1
0.02
24
0
0
Time ( in minutes )
Air velocity
24.6
0.2
24.6
0
9
24.6 °C
24.7
24.7
24
8
Fig. 16 Air velocity vs air temperature in section B2
24.7 °C
24.1
7
Air temperature
Air velocity
Fig. 14 Air velocity vs air temperature in section A6 24.8
6
Time ( in minutes )
Time ( in minutes )
Average air velocity : 0.078
5
Air velocity m/s
22.6
24.3 °C
Air velocity m/s
23.6
24.4
Air temperature °C
Air temperature °C
23.8
Fig. 15 Air velocity vs air temperature in section B1 0.2
Air velocity m/s
23.9 °C
24
1
2
3
4
5
6
7
8
9
10
11
Time ( in minutes ) Air temperature
Air velocity
Air temperature
21
Average air velocity : 0.108
Average air temperature : 24.45
Average air velocity : 0.073
Air velocity
Average air temperature : 24.39
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
14
7. Methodology of the study
9. Methodology of the study 9.2 Data collection Fig. 17 Air velocity vs air temperature in section B3
Fig. 19 Average air temperature and velocity in class A sections
25.00
0.05
24.50
0.04
24.3
0.03
24.25
0.02
24.2 °C
24.15 0
1
2
3
4
5
6
7
8
9
10
24.91
0.21
24.00 23.50
Average air velocity : 0.03
22.00
0
0
11
1
2
3
Average air velocity
24.1 24
24.50
0.03
23.9
0.02
23.6 °C
0.01
23.5
0 2
3
4
5
6
7
8
9
10
Time ( in minutes ) Air temperature
15
0.05 0.04
23.6
22
25.00
Average air velocity : 0.034
11
Air temperature °C
24.2
0.06
Air velocity m/s
Air temperature °C
24.3
1
6
0.00 7
Average air temperature : 23.89 Standard deviation : 0.65 Standard air temperature : 23.00
Fig. 20 Average air temperature and velocity in class B sections
24.3 °C
0
5
Average air temperature
Average air velocity : 0.14 Standard deviation : 0.07
Average air temperature : 24.31
Fig. 18 Air velocity vs air temperature in section B4
23.7
4
Class section
Standard air velocity : 0.17
23.8
0.10 0.05
0.04
Air velocity
24.4
0.11
23.33 0.08
23.00
Time ( in minutes ) Air temperature
0.15
23.74
23.56
23.36
22.50
0.01
0.20 24.45
0.17
24.39
24.00
24.31 24.02
23.98 0.12
23.50 0.07
23.00 22.50
0.03
0.03
3
4
22.00 0
1
2
0.20 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 5
Air velocity m/s
24.2
0.25 0.22
Air velocity m/s
24.35
25.50
0.06
Air temperature °C
Air temperature °C
24.4
0.07
Air velocity m/s
24.4 °C
24.45
Class section
Air velocity
Average air temperature : 24.02
Average air velocity
Average air velocity : 0.07 Standard deviation : 0.04 Standard air velocity : 0.17
Average air temperature
Average air temperature : 24.18 Standard deviation : 0.21 Standard air temperature : 23.00
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study 9. Methodology of the study 9.2 Data collection Section No.
Air temperature ranking
Air velocity ranking
Total points
Final ranking
Section No.
Air temperature ranking
Air velocity ranking
Total points
Final ranking
A1
2
2
10
1 . A1
B1
1
1
8
1. B1
A2
6
6
2
2 . A4
B2
4
2
4
2. B4
A3
3
3
8
3 . A3
B3
3
4
3
3. B2
A4
4
1
9
3 . A5
B4
2
3
5
3. B3
A5
1
5
8
4 . A6
A6
5
4
5
5 . A2
Table 12 : Ranking of sections of Classroom A based on how close their air temperatures and velocities averages are to standard values
Classroom A plan
Classroom B plan
1
3
4
0.211 m/s 23.32 °C
0.215 m/s 23.56 °C
0.078 m/s 23.33 °C
2
5
0.172 m/s 23.74 °C
0.108 m/s 24.45 °C
6 0.044 m/s 24.91 °C
Table 13 : Ranking of sections of Classroom B based on how close their air temperatures and velocities averages are to standard values
Fig. 21 Ranking of sections of Classroom A based on how close their air temperatures and velocities averages are to standard values
Sections has been ranked based on how close the conditions within them to the comfort conditions. Although the results are too close, The inner sections adjacent to the window got the best results in both classrooms
3 0.073 m/s 24.39 °C
4 0.030 m/s 24.31 °C
1 0.123 m/s 23.98 °C
2
As the result of measurement phase 1 indicates that there is no thing wrong either with air temperature or air velocity in both classrooms as temperature readings are compitable with ASHRAE 55 in all measurment points and air velocities are less than 0.25 m/s which is very acceptable according to Toftumm (6. Toftumm 2004), These results contradict the questionnaire carried out at the beggining of this study what can be interpreted that the selected measurment points might not be enough to represent
0.034 m/s 24.02 °C
Fig. 22 Ranking of sections of Classroom B based on how close their air temperatures and velocities averages are to standard values
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
16
7. Methodology of the study
9. Methodology of the study 9.2 Data collection 7.3.2 Measurement Measurement PhasePhase 2 2 Classroom A plan
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
29
17
19
18
39
19
30
20
20
21
10
22
1
23
2
24
40
25
31
26
21
27
11
28
41
29
32
30
22
31
12
32
3
33
42
34
33
35
23
36
13
37
4
38
43
39
34
40
24
41
14
42
5
43
6
44
44
45
35
46
25
47
15
48
36
49
26
50
16
51
7
52
37
53
27
54
17
55
8
56
38
57
28
58
18
59
9
60
45
Classroom B plan
Fig. 22 Division of the classrooms A in measurement phase 2 Seat No.
Mean air velocity
18
0.24
22.68
37
0.24
22.70
1
0.12
21.57
19
0.13
22.79
38
0.23
22.65
2
0.25
21.61
20
0.15
22.96
39
0.20
22.60
16
0.13
22.17
33
0.08
21.75
3
0.13
22.08
21
0.13
22.95
40
0.12
22.75
17
0.10
22.17
34
0.17
21.57
23.00
23.40
22.44
0.22
0.07
0.10
22
1
4
41
0.12
22.94
2
0.08
22.50
18
0.08
22.00
35
0.09
21.67
5
0.20
22.17
23
0.23
22.59
42
0.16
23.10
3
0.15
22.40
19
0.07
22.00
36
0.08
21.73
0.08
21.79
Mean air Temperature
Seat No.
Mean air velocity
Mean air Temperature
6
0.15
22.35
24
0.13
22.79
43
0.21
22.73
4
0.06
22.37
20
0.10
21.96
37
7
0.19
22.29
25
0.15
22.73
44
0.14
23.00
5
0.06
22.25
21
0.09
21.90
38
0.06
21.90
0.14
22.89
0.09
22.33
22
0.07
21.90
39
0.12
21.86
8
0.11
22.44
26
45
0.11
22.79
6
9
0.23
22.50
27
0.23
22.85
46
0.23
22.81
7
0.08
22.40
23
0.09
21.93
40
0.13
21.87
10
0.20
22.49
28
0.26
22.74
47
0.24
22.72
8
0.10
22.27
24
0.13
21.90
41
0.14
21.43
0.20
22.59
0.09
22.37
25
0.09
21.85
42
0.15
21.54
11
0.20
22.48
29
48
0.16
22.79
9
12
0.23
22.67
30
0.13
22.77
49
0.11
22.89
10
0.08
22.37
26
0.14
21.57
43
0.10
21.60
13
0.23
22.69
31
0.29
22.70
50
0.19
22.90
11
0.12
22.13
27
0.09
21.65
44
0.16
21.59
0.25
22.71
12
0.15
22.09
28
0.08
21.69
45
0.15
21.70
13
0.08
22.17
29
0.08
21.70
Average
0.10
21.98
14
0.09
22.24
30
0.15
21.70
15
0.10
22.23
31
0.10
21.70
32
0.10
21.70
14
0.25
22.49
32
51
0.20
22.81
15
0.11
22.71
33
0.14
23.05
52
0.24
22.84
16
0.13
22.85
34
0.13
23.01
53
0.16
22.96
17
0.19
22.87
35
0.11
22.97
54
0.22
22.96
36
0.22
22.81
55
0.30
22.87
56
0.23
22.81
57
0.24
22.72
58
0.16
22.79
59
0.11
22.89
60
0.19
22.90
Average
0.18
22.70
Table 10 Reading averages for classroom A in measurement phase 2
17
Fig. 23 Division of the classrooms B in measurement phase 2
Table 11 Reading averages for classroom A in measurement phase 2
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
9. Methodology of the study 9.2 Data collection
7. Methodology of the study Classroom A plan
Fig. 24 : Air temperature vs air velocity for class A seatings
26.00
0.35
0.30 25.00
0.25
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
24.00
Air temperature Air Velocity m/s
Air Temperature C°
0.20
23.00
S60 22.90 °C
S20 22.96 °C
0.10
S1 21.57 °C 0.05
20.00
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
21.00-22.00 C° 22.01-23.00 C° 23.01-26.00 C°
0.15
22.00
21.00
Cool Slight Cool Comfort zone
Red points indicate clearly that most of the values are not included within ASHRAE 55 comfort zone, although these readings are not cmpitable with ASHRAE 55, almost all of them are located within 1 degree down the limit ( between 22 and 23 °C ) what might not be a significant issue .
0.00
Seat No.
ASHRAE 55 recommended thermal limit
Air temperature reference point
Mean air Temperature
Mean air velocity
Air velocity reference point
Inlet location
26
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
18
9. Methodology of the study 9.2 Data collection
7. Methodology of the study Classroom B plan
Fig. 25 : Air temperature vs air velocity for class B seatings 0.18
26.00
9 25.50
8
0.16
7
25.00
6
0.14 24.50
5 4
0.12
24.00
3
S1 23.40 °C
23.00
2
0.10
0.08
Air Velocity m/s
Air Temperature C°
23.50
1
18
28
38
17
27
37
16
26
36
45
15
25
35
44
14
24
34
43
13
23
33
42
12
22
32
41
11
21
31
40
10
20
30
39
19
29
22.50
Air temperature 0.06
22.00
21.50
S45 21.70 °C
21.00
0.04
0.02 20.50
0.00
20.00
1
2
3
4
5
6
7
8
9
10
11 12
13
14
15 16
17
18
19 20
21
22
23 24
25
26
27 28
29
30
31 32
33
34
35
36
37
38
39
40
41
42
43
44
45
Seat No.
ASHRAE 55 recommended thermal limit
Air temperature reference point
Mean air Temperature
Mean air velocity
Cool Slight Cool Comfort zone
21.00-22.00 C° 22.01-23.00 C° 23.01-26.00 C°
Air temperature readings in classroom B are much farther from ASHRAE 55 comfort zone as air temperature in many locations / seating places lays between 22 and 21 °C Air velocity reference point
Inlet location
2719
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
Methodology of the studystudy 9.7.Methodology of the
Table 14 : Evaluation of classroom A's readings
Table 15 : Evaluation of classroom B's readings
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
30
29
20
19
10 1
31 21 11
2
32 22 12
3
33 23 13
4
34 24 14
5
35 25 15
6
36 26 16
39
54
40
55
41
56
42
57
43
58
44
59
45
60
7
Mean air Temperature 23.40 22.50 22.40 22.37 22.25 22.33 22.40 22.27 22.37 22.37 22.13 22.09 22.17 22.24 22.23 22.17 22.17 22.00 22.00 21.96 21.90 21.90 21.93 21.90 21.85 21.57 21.65 21.69 21.70 21.70 21.70 21.70 21.75 21.57 21.67 21.73 21.79 21.90 21.86 21.87 21.43 21.54 21.60 21.59 21.70
37
Mean air velocity 0.07 0.08 0.15 0.06 0.06 0.09 0.08 0.10 0.09 0.08 0.12 0.15 0.08 0.09 0.10 0.13 0.10 0.08 0.07 0.10 0.09 0.07 0.09 0.13 0.09 0.14 0.09 0.08 0.08 0.15 0.10 0.10 0.08 0.17 0.09 0.08 0.08 0.06 0.12 0.13 0.14 0.15 0.10 0.16 0.15
27
Seat No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
17
Classroom B plan
8
Mean air Temperature 21.57 21.61 22.08 22.44 22.17 22.35 22.29 22.44 22.50 22.49 22.48 22.67 22.69 22.49 22.71 22.85 22.87 22.68 22.79 22.96 22.95 23.00 22.59 22.79 22.73 22.89 22.85 22.74 22.59 22.77 22.70 22.71 23.05 23.01 22.97 22.81 22.70 22.65 22.60 22.75 22.94 23.10 22.73 23.00 22.79 22.81 22.72 22.79 22.89 22.90 22.81 22.84 22.96 22.96 22.87 22.81 22.72 22.79 22.89 22.90
38
Mean air velocity 0.12 0.25 0.13 0.10 0.20 0.15 0.19 0.11 0.23 0.20 0.20 0.23 0.23 0.25 0.11 0.13 0.19 0.24 0.13 0.15 0.13 0.22 0.23 0.13 0.15 0.14 0.23 0.26 0.20 0.13 0.29 0.25 0.14 0.13 0.11 0.22 0.24 0.23 0.20 0.12 0.12 0.16 0.21 0.14 0.11 0.23 0.24 0.16 0.11 0.19 0.20 0.24 0.16 0.22 0.30 0.23 0.24 0.16 0.11 0.19
28
Seat No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
18
Classroom A plan
9
9.2 Data collection
Fig. 26 : Graphical distribution for tables 14 and 15 in classrooms A and B plans respectively
According to the Cool result of measureSlight Coolphase 1, Secment tions Comfort of zoneeach classroom have been ranked and ordered based on how close the averages of air temperature and air velocity of each of them to the refference average values in Table 2 . Tables 12 and 13 illustrate the ranking of classrooms A and B sections respectively and Fig. 13 represents this thanking graphically for both classrooms . Fig. 13 indicates that the the best sections in both classrooms in general are the ones in th front and center of the classroom .
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
20
7. Methodology of the study
9. Methodology of the study
7.3 CFD simulation of the current situation
9.3 CFD simulation
9.3.1 Grid Independence Test
CFD Simulation Framework Variables
Classroom A
Classroom B
Classroom Area Classroom volume Meshing method Mesh sizing Nodes Elements Gravitational acceleration Turbulence model Inlet velocity Inlet temperature Number of occupants Human body heat generation rate Other heat sources Heat Transfer Coefficient of walls Wall thickness Number of inlets Number of outlets
69 m² 204.75 m³ Tetrahedrons Fine, medium and coarse Varies Varies 9.81 m/s2 K-epsilon (k-ε) 2 m/s 22 °C 60 55 W/m2 No 1.1 W/(m2K) 0.2 m 3 3
46 m² 141.28 m³ Tetrahedrons Fine, medium and coarse Varies Varies 9.81 m/s2 K-epsilon (k-ε) 2 m/s 21 °C 45 55 W/m2 No 1.1 W/(m2K) 0.2 m 2 2
21
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study
9. of the study CFDMethodology simulation 9.3 simulation GridCFD Independence Test
9.3.1 Grid Independence Test
Mesh sizing configuration in Ansys
Classroom and reference points
Coarse
Medium
Fine
Classroom A
1
2
3
4
5
6
7
8
9
10
Nodes = 2121 Elements = 9130
Nodes = 11905 Elements = 58431
Nodes = 53423 Elements = 280999
Nodes = 56448 Elements = 300385
Nodes = 12078 Elements = 59912
Nodes = 1993 Elements = 8863
Classroom B
1
2
3
4
5
6
7
8
9
10
Supply air temperature = 22 C° , Supply air velocity = 2 m/s
1 Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
22
9. Methodology of the study
7. Methodology of the study 9.3 CFD simulation CFD simulation Grid Independence Test
9.3.1 Grid Independence Test
Classroom A plan
Classroom B plan
Measurment values Point No. Temp °C 1 22.75 2 22.6 3 22.65 4 22.7 5 22.81 6 22.97 7 23.01 8 23.05 9 22.71 10 22.7
Fine mesh size Temp °C 22.74 22.67 22.69 22.73 22.74 22.73 22.71 22.66 22.70 22.78
Relative error % Temp 0.06 0.33 0.18 0.15 0.32 1.04 1.31 1.68 0.05 0.34
Mediun mesh size Temp °C 22.76 22.76 22.74 22.71 22.74 22.76 22.75 22.77 22.76 22.69
Relative error % Temp 0.03 0.71 0.38 0.03 0.30 0.91 1.12 1.23 0.22 0.03
C oarse mesh size Temp °C 22.96 22.86 22.81 22.72 23.10 23.08 22.98 23.01 22.64 22.81
Relative error % Temp 0.92 1.14 0.70 0.10 1.26 0.48 0.15 0.18 0.29 0.48
Measurment values Point No. Temp °C 1 21.69 2 21.65 3 21.57 4 21.85 5 21.9 6 21.93 7 21.9 8 21.9 9 21.96 10 22
Fine mesh size Temp °C 21.81 21.65 21.58 21.65 21.77 21.92 22.12 22.32 22.51 22.01
Relative error % Temp 0.56 0.01 0.06 0.93 0.60 0.02 1.00 1.94 2.50 0.05
Mediun mesh size Temp °C 21.75 21.69 21.69 21.77 21.93 22.04 22.10 22.14 22.15 22.15
Relative error % Temp 0.26 0.21 0.56 0.35 0.12 0.51 0.92 1.09 0.86 0.68
C oarse mesh size Temp °C 21.88 21.61 21.87 22.04 21.95 22.34 22.15 22.45 22.50 22.05
Relative error % Temp 0.89 0.17 1.38 0.87 0.25 1.87 1.13 2.52 2.48 0.23
Averag 22.80 Maximum 23.05
22.71 22.78
0.55 1.68
22.74 22.77
0.50 1.23
22.90 23.10
0.57 1.26
Averag 21.84 Maximum 22.00
21.94 22.51
0.77 2.50
21.94 22.15
0.56 1.09
22.09 22.50
1.18 2.52
Table 13 : Grid independent test on Classroom A, Supply air temperature = 22 °C, Supply air velocity = 2 m/s
Table 14 : Grid independent test on Classroom B, Supply air temperature = 22 °C, Supply air velocity = 2 m/s
Usually 5 % relative error is acceptable in such cases (13. Ernest Z., 2014)
Supply air temperature = 22 C°, Supply air velocity = 2 m/s 22.60 22.40 Air Temperature C°
Air Temperature C°
Supply air temperature = 22 C°, Supply air velocity = 2 m/s 23.15 23.10 23.05 23.00 22.95 22.90 22.85 22.80 22.75 22.70 22.65 22.60
22.20 22.00 21.80 21.60
0
1
2
3
4
5
6
7
8
9
10
11
21.40 0
1
2
3
4
Seat No. Fine mesh size
Fig. 21 : Three mesh sizes comparison for classroom A status quo
1
23
Medium mesh size
5
6
7
8
9
10
11
Seat No. Coarse mesh size
Fine mesh size
Medium mesh size
Coarse mesh size
Fig. 22 : Three mesh sizes comparison for classroom B status quo
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study 7.3 CFD simulation
9. Methodology of the study 9.3 CFD simulation 9.3.2 CFD simulation of the current conditions of Classroom A
7.3.1 CFD simulation of of status quo
7.3.1.1 CFD simulation of the current status of Classroom A
1
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
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9. Methodology of the study 9.3 CFD simulation 9.3.2 CFD simulation of the current conditions of Classroom A Fig. 27 : CFD simulation for Classroom A's status quo
comfort zone
Air velocity m/s
comfort zone
comfort zone
comfort zone
Air temperature C°
Supply air temperature = 22 C° , Supply air velocity = 2 m/s
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study 9. Methodology of the study CFD simulation 9.3 CFD simulation
9.3.2 CFD simulation of the current conditions of Classroom A
Air temperature distribution Air temperature distribution
81% below 23 °C
Compatibility with ASHRAE 55 Air velocity distribution
90% below 25 m/s
PMV = -1.14
Supply air temperature = 22 C° , Supply air velocity = 2 m/s
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7. Methodology of the study 7.3 CFD simulation
9. Methodology of the study 9.3 CFD simulation 9.3.3 CFD simulation of the current conditions of Classroom B
7.3.1 CFD simulation of of status quo
7.3.1.2 CFD simulation of the current status of Classroom B
1
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
9. Methodology of the study 9.3 CFD simulation
7. simulation Methodology ofcurrent the study 9.3.3 CFD of the conditions of Classroom B CFD simulation
Fig. 27 : CFD simulation for Classroom B's status quo
1
comfort zone
Air velocity m/s
comfort zone
comfort zone
comfort zone
Air temperature C°
Supply air temperature = 22 C° , Supply air velocity = 2 m/s
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
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9. Methodology Methodology of the 7. of the studystudy 9.3 CFD simulation CFD simulation
9.3.3 CFD simulation of the current conditions of Classroom B
Air temperature distribution Air temperature distribution
96% below 23 °C
Compatibility with ASHRAE 55 Air velocity distribution
93% below 25 m/s
PMV = -1.32
Supply air temperature = 22 C° , Supply air velocity = 2 m/s
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study
9. 7.4Methodology CFD simulation of the study 9.3 CFD simulation
9.3.4 CFD simulation of proposed scenarios
7.4.2 CFD simulation of proposed scenarios Supply
Return
Return
Supply
Return Supply
Supply
Supply
Supply
1. Mixing ventilation (MV)
2. Displacement ventilation (DV)
3. Stratum ventilation (SV)
Raising supply air temperature to 24 °C and velocity to 2 m/s
Raising supply air temperature to 24 °C and velocity to 2 m/s
Raising supply air temperature to 24 °C and velocity to 2 m/s
1.1 Retain ceiling diffusers configuration
1.2 Changing ceiling diffusers configuration
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9. Methodology of the study
7.4 Proposed scenarios
9.3 CFD simulation 9.3.4 CFD simulation of proposed scenarios
CFD Simulation Framework Variables
Classroom A
Classroom B
Classroom Area Classroom volume Meshing method Mesh sizing Nodes Elements Gravitational acceleration Turbulence model Inlet velocity Inlet temperature Number of occupants Human body heat generation rate Other heat sources Heat Transfer Coefficient of walls Wall thickness Number of inlets Number of outlets
69 m² 204.75 m³ Tetrahedrons Medium 11905 58431 9.81 m/s2 K-epsilon (k-ε) 2 m/s 24 °C 60 55 W/m2 No 1.1 W/(m2K) 0.2 m 3 3
46 m² 141.28 m³ Tetrahedrons Medium 12078 59912 9.81 m/s2 K-epsilon (k-ε) 2 m/s 24 °C 45 55 W/m2 No 1.1 W/(m2K) 0.2 m 2 2
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
10. Results and discussion 10.3 CFD simulation of the study 7. Methodology
7.4 CFD simulation 10.3.4 CFD simulation of proposed scenarios 10.3.4.1 Scenario 1 : Mixing ventilation (MV 1)
Senario 1 Mixing ventilation (MV)
Classroom A
Classroom B
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7. Methodology of the study
CFD simulation Scenario 1 (MVand 1) discussion 10. Results 10.3 CFD simulation
10.3.4 CFD simulation of proposed scenarios 10.3.4.1 Scenario 1 : Mixing ventilation (MV 1)
Classroom A in Scenario 1.1
Classroom B in Scenario 1.1
Air temperature
Air temperature
Air velocity
Air velocity Comfort zone
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
10. Results and 7. Methodology of discussion the study 10.3 simulation CFDCFD simulation
10.3.4 CFD simulation of proposed scenarios 10.3.4.1 Scenario 1 : Mixing ventilation (MV 1)
Classroom A in Scenario 1.1 Compatibility with ASHRAE 55
Air temperature distribution
Classroom B in Scenario 1.1 PMV = -0.52
Air velocity distribution
Compatibility with ASHRAE 55
Air temperature distribution
PMV = -0.47
Air velocity distribution
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7. Methodology of the study
10. CFDResults simulation and discussion 10.3 CFD1.1 simulation Scenario (MV 2)
10.3.4 CFD simulation of proposed scenarios 10.3.4.2 Scenario 1.1 : Mixing ventilation (MV 2)
Classroom A in Scenario 1.2
Classroom B in Scenario 1.1
Air temperature
Air temperature
Air velocity
Air velocity
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
10. Results and 7. Methodology of discussion the study 10.3 simulation CFDCFD simulation
10.3.4 CFD simulation of proposed scenarios 10.3.4.2 Scenario 1.1 : Mixing ventilation (MV 2)
Classroom A in Scenario 1.1 Compatibility with ASHRAE 55
Air temperature distribution
Classroom B in Scenario 1.1 PMV = -0.54
Air velocity distribution
Compatibility with ASHRAE 55
Air temperature distribution
PMV = -0.16
Air velocity distribution
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10. Results and discussion 7. Methodology of the study 10.3 CFD simulation
7.4 CFD simulation
10.3.4 CFD simulation of proposed scenarios 10.3.4.3 Scenario 2 : Displacement ventilation (DV)
Senario 2 Displacement ventilation (DV)
Classroom A
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Classroom B
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study
10. CFDResults simulation and discussion 10.3 CFD2simulation Scenario (DV)
10.3.4 CFD simulation of proposed scenarios 10.3.4.3 Scenario 2 : Displacement ventilation (DV)
Classroom A in Scenario 2
Classroom B in Scenario 2
Air temperature
Air temperature
Air velocity
Air velocity
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10. Results and 7. Methodology of discussion the study 10.3 simulation CFDCFD simulation
10.3.4 CFD simulation of proposed scenarios 10.3.4.3 Scenario 2 : Displacement ventilation (DV)
Classroom A in Scenario 1.1 Compatibility with ASHRAE 55
Air temperature distribution
Classroom B in Scenario 1.1 PMV = -0.13
Air velocity distribution
Compatibility with ASHRAE 55
Air temperature distribution
PMV = -0.15
Air velocity distribution
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
10. Results and discussion 7. simulation Methodology of the study 10.3 CFD
7.4 simulation CFD simulation 10.3.4 CFD of proposed scenarios 10.3.4.4 Scenario 3 : Stratum ventilation (SV)
Senario 3 Stratum ventilation (SV)
Classroom A
Classroom B
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7. Methodology of the study
CFDResults simulation and discussion 10. 10.3 CFD3simulation Scenario (SV)
10.3.4 CFD simulation of proposed scenarios 10.3.4.4 Scenario 3 : Stratum ventilation (SV)
Classroom A in Scenario 1.2
Classroom B in Scenario 1.1
Air temperature
Air temperature
Air velocity
Air velocity
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
10. Results and 7. Methodology of discussion the study 10.3 simulation CFDCFD simulation
10.3.4 CFD simulation of proposed scenarios 10.3.4.4 Scenario 3 : Stratum ventilation (SV)
Classroom A in Scenario 1.1 Compatibility with ASHRAE 55
Air temperature distribution
Classroom B in Scenario 1.1 PMV = -0.10
Air velocity distribution
Compatibility with ASHRAE 55
Air temperature distribution
PMV = -0.14
Air velocity distribution
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7. Methodology of the study
10. CFDResults simulationand discussion 10.3 CFD simulation
Evaluating scenarios
10.3.5 Evaluating scenarios
Fig. 34 : Comparing scenarios based on PMV values according to ASHRAE Standard 55-2017 Classroom
Status quo
MV 1 scenario
MV 2 scenario
DV scenario
Classroom A
PMV value = -1.14
PMV value = -0.52
PMV value = -0.54
PMV value = -0.13
SV scenario
PMV value = -0.10
Average air temperature = 22.57 °C Average air temperature = 25.21 °C Average air temperature = 25.21 °C Average air temperature = 25.30 °C Average air temperature = 25.32 °C Average air velocity = 0.15 m/s Average air velocity = 0.25 m/s Average air velocity = 0.26 m/s Average air velocity = 0.11 m/s Average air velocity = 0.11 m/s Complies with ASHRAE 55 : No Complies with ASHRAE 55 : No Complies with ASHRAE 55 : No Complies with ASHRAE 55 : Yes Complies with ASHRAE 55 : Yes
Classroom B
PMV value = -1.32
PMV value = -0.47
PMV value = -0.16
PMV value = -0.15
PMV value = -0.14
Average air temperature = 21.91 °C Average air temperature = 25.21 °C Average air temperature = 25.39 °C Average air temperature = 25.25 °C Average air temperature = 25.28 °C Average air velocity = 0.10 m/s Average air velocity = 0.23 m/s Average air velocity = 0.15 m/s Average air velocity = 0.12 m/s Average air velocity = 0.12 m/s Complies with ASHRAE 55 : No Complies with ASHRAE 55 : Yes Complies with ASHRAE 55 : Yes Complies with ASHRAE 55 : Yes Complies with ASHRAE 55 : Yes
Test conditions : 1. Operative temperature = Varies as above, 2. Air speed = Varies as above, 3. Relative humidity = recommended value ( 40-60%), 4. Metabolic rate = 1 met (sitting quietly condition), Clothing level = 0.57 clo ( Trousers, short-sleeve shirt, socks, shoes and underwear ) 1 43
Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi
7. Methodology of the study
CFD simulation 10. Results and discussion 10.3 CFD simulation Evaluating scenarios 10.3.5 Evaluating scenarios 1.5
1
0.5
Status Quo 0
A
B
-0.5
MV1 A
-0.52
MV2 B
-0.47
A
DV
SV
B
A
B
A
B
-0.16
-0.13
-0.15
-0.10
-0.14
-0.54
-1 -1.14
-1.5
-1.32
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11. Conclusion
12. Acknowledgments
This study was conducted to enhance thermal sensation in KAU classrooms by testing and comparing several mechanical ventilation strategies using CFD simulation, the main conclusion of the present work can be summarized in the following points :
The author would like to express gratitude to Dr-Ing. Mohannad Bayoumi, Course Instructor, for giving me a numerous consultations and guidelines throughout the semester .
1. The distribution of air temperature and air velocity varies in different places within the classrooms, while the best places include the middle section and the front one adjacent to the window, the worst sections generally are the ones at the back of the classroom opposite to the windows, where air temperature and air velocity are much further from the comfort limits .
In addition, a thank you to Dr. Salah Hafiz from Aerospace Engineering Department , Faculty of Engineering who introduced a valuable consultations in aerodynamics related issues.
2. The current conditions of the classrooms don’t fit within ASHRAE 55’s comfort zone, whereas air temperature is lower than 23 °C in most cases ( it should be between 23-26 °C to match ASHRAE 55 ), air velocities tend to be lowe than 0.25 m/s usually which seems good . 3. Testing different ventilation methods with reducing supply air temperature to 22 °C and retaining supply air velcity at 2 m/s showed that the currently installed displacement ventilation method don’t give the recommended PMV value by ASHRAE 55, although the PMV value of this mehod can be enhanced by using linear ceiling diffucers as tested in scenario 1.1 . The two best ventilation strategies in the two classrooms are the strstum and displacement ventilation in order, as both resulted in more consistence distribution of air temperature and air velocity in addition to PMV values which are more close to neutral condition .
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13. References [1] Giuli, V. De, Da, O., & Carli, M. De. (2012). Indoor environmental quality and pupil perception in Italian primary schools. Building and Environment, 56, 335–345.
[8] B. Cao, Y. Zhu, Q. Ouyang, X. Zhou, L. Huang, Field study of human thermal comfort and thermal adaptability during the summer and winter in Beijing, Energy Build. 43 (2011) 1051–1056.
[2] Kumar, M., Ooka, R., Rijal, H. B., Kumar, S., & Kumar, A. (2019). Energy & Buildings Progress in thermal comfort studies in classrooms over last 50 years and way forward. Energy & Buildings, 188– 189, 149–174. https://doi.org/10.1016/j.enbuild.2019.01.051
[9] Z. Wang, A. Li, J. Ren, Y. He, Thermal adaptation and thermal environment in university classrooms and offices in Harbin, Energy Build. 77 (2014) 192–196.
[3] Toftum, Jorn. (2004). Air movement - Good or bad?. Indoor air. 14 Suppl 7. 40-5. 10.1111/j.1600-0668.2004.00271.x. [4] Guenther, Sebastian. “What Is PMV? What Is PPD? The Basics of Thermal Comfort.” www.simscale.com. Last modified September 18, 2019. https://www.simscale.com/blog/2019/09/what-is-pmvppd/. [5] P.F. Hu, W. Liu, Z.N. Jiang, Study on the indoor thermal sensation of young college students in the area which is hot in summer and cold in winter, Int.J. Arch. Sci. 7 (2006) 47–52.
[10] Z. Wang, H. Ning, X. Zhang, Y. Ji, Human thermal adaptation based on university students in China’s severe cold area, Sci. Technol. Built Environ. (2016),doi: 10.1080/23744731.2016.1255495. [11] P. Baruah, M.K. Singh, S. Mahapatra, Thermal comfort in naturally ventilated classrooms, PLEA -2014 Conference, December 16–18, 2014. [12] R. Vittal, S. Gnanasambandam, Perceived thermal environment of naturally ventilated classrooms in India, Creat. Space 3 (2016) 149–165.
[6] G. Zhang, C. Zhenga, W. Yanga, Q. Zhanga, D.J. Moschandreasa, Thermal comfort investigation of naturally ventilated classrooms in a subtropical region,Indoor Built Environ. 16 (2007) 148–158. [7] R. Yao, J. Liu, B. Li, Occupants’ adaptive responses and perception of thermal environment in naturally conditioned university classrooms, Appl. Energy 87 (2010) 1015–1022.
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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method - Omar Hussein Al-hebshi