human thermal perception and outdoor thermal comfort under shaded conditions in summer - a field...
TRANSCRIPT
28-Nov-2016
Human thermal perception
and outdoor thermal comfort
under shaded conditions
in summer : A field study
in an institutional campus
The 6th International Conference on Sustainable Energy and Environment
Manat Srivanit1,* and Daranee Jareemit2
1, 2 Faculty of Architecture and Planning, Thammasat University
* Corresponding author, E-mail address: [email protected]
Special Session: Urban Climate & Urban Air Pollution (UCUA)
CONTENTS
1. Background2. Objectives3. Methods in Outdoor Thermal
Comfort Study Micrometeorological
measurements and questionnaires Experimental design Thermal comfort index assessment
4. Results and Discussion5. Conclusions6. Recommendations
2
1.BACKGROUND
An institutional campus can be regarded as a small city due to its large educational buildings coverage, population size, and various complex activities, which may have serious direct and indirect impacts on the environment.
Outdoor thermal conditions might affect occupant’s thermal perception, who live in these spaces. Therefore, one must consider long-term thermal comfort based on the thermal requirements and characteristics of residents.
(Photo: Author, 2016)
3
(c) The monthly mean urban climatic variations during a 5-year period (from 2006 to 2010)
Source: Srivanit M. et al., 2013
Climatic conditions in the hot and humid tropical climate of University campus
During the summer, the highest mean monthly of solar radiation was exceeded in April. These large values of the average solar radiation and its could affect a university campus’s environment and quality of life.
4Source: http://solarchvision.com/?page_id=601
(d) Bangkok’s hourly solar direct radiation
(b) Sun path in northern hemisphere
(a) Components contributing to thermal comfort
Source: UC Berkeley Center for the Built Environment
5
How does the outdoor thermal environment affect human thermal comfort perception in university campus?, And
How do shading environments influence on human thermal comfort?
Understanding the characteristics of outdoor microclimate environment and the comfort implications for the people using them opens up new possibilities for the development of campus spaces.
Research questions:
5
The area of study:
The study was conducted to analyze the outdoor thermal conditions on university campus in Thammasat University’s RangsitCampus, which is located in the suburb of Bangkok Metropolitan Region (BMR). The campus occupies 2.8 sq.km.
2.OBJECTIVES
(1) To determine whether their thermal comfort requirements varied with two different environments (Outdoor and Semi-outdoor conditions), and
(2) To examine the thermal effects of shading on outdoor and semi-outdoor thermal comfort.
(Source: Jirawan Klaylee, 2016)
Geographical location: Lat. 14° 4.239´N, Long. 100°36.332´E 6
7
(a) Micro-Climate Measurements
(b) survey questionnaires
Air temperature
Air velocity
Humidity
Radiant temperature Thermal perception
Activity and clothing insulation*
Psychological mechanisms
Experience
Expectation
Preferences
Thermal history
Socio-cultural
Transversal Method(or True-experiments)
Human physiologyState of health
Step II. Input Conditions
& Field Survey
Calculation of thermal comfort index
Contributing factors
RayMan Model
Physiologicallyequivalent
temperature(PET)
Determination of neutral and thermal
acceptable range
Recommendations
Examine the thermal effects of shading on
outdoor and semi-outdoor thermal
comfort
Food and drink
Body shapeAge and gender
Step III. Assessment of the thermal environment
Methods to determine mean radiant temperature
(Using a globe thermometer)
Questionnaire design(Structured interviews)
Time periods of field survey
(Summer season)
* ASHRAE 55, 2010. Thermal Environmental Conditions for Human Occupancy
Instrumentation set-up (Including type of
equipment and accuracy)
Step I. Experimental design and Micrometeorological measurements
3. A general framework for a field study of outdoor thermal comfort
7
Time of day of surveyGeographic locationFisheye-photo
Experimental design and Micrometeorological measurements
What is human thermal comfort?
“Human thermal comfort as the state of mind that expresses satisfaction with the surrounding environment.”
Defined by ASHRAE (The American Society of Heating, Refrigerating and Air Conditioning Engineers)
(i) Measurement scale for the subjective perception of thermal environments
Thermal sensation surveys were conducted between April and May 2015, over 20 days of sampling in summer season. The data collection was conducted on the dates with clear sky condition.
(a) (b) (c)
(ii) The field survey procedures included both physical measurements and questionnaire surveys.
(a) The mobile microclimatic measurements setup, (b) research assistants conducting surveys, and (c) the sample of fisheye photograph taken from the survey location can be calculated the sky view factor (SVF) by the RayMan model. (Source: Author, 2016) 8
4. RESULTS AND DISCUSSION
Table 4-1 Summary of the respondents
A total of 600 questionnaires were collected both in the outdoor (28.83%) and semi-outdoor (71.17%) spaces during the survey.
Most of the responses (74.67%) were clustered on the warm side of the scale (TSV > 0).
The majority of the respondents (100%) stayed under trees or buildings shaded and cloudy shade conditions
0
20
40
60
80
100
120
140
160
180
-3 (Cold) -2 (Cool) -1 (Slightlycool)
0 (Neutral) +1 (Slightlywarm)
+2 (Warm) +3 (Hot)
Frequency
Outdoor
Semi-outdoor
0
50
100
150
200
250
Comfortable Slightuncomfortable
Uncomfortable Veryuncomfortable
Extremelyuncomfortable
Frequency
Outdoor
Semi-outdoor
(a) Distribution of thermal sensation votes
(b) Overall comfort votes in the both spaces
Physiological FactorsAll
(n=600)Outdoor (n=173)
Semi-outdoor (n=427)
Age (year) Avg. 34.07 34.62 33.84
Std.D. 3.52 2.24 3.90
Weight (kg.) Avg. 57.92 58.77 57.58
Std.D. 11.91 12.65 11.58
Height (cm.) Avg. 165.32 166.35 164.90
Std.D. 7.93 8.54 7.63
Body mass index (BMI) (kg m-2)
Avg. 21.08 21.09 21.08
Std.D. 3.38 3.38 3.38
Clothing (Clo)Avg. 0.54 0.43 0.59
Std.D. 0.32 0.23 0.339
(4.1) Questionnaire data
(4.2) Thermal acceptability and thermal sensation vote
The large percentage of “hot” votes made the summer season, the most uncomfortable with a rate of 81.50% and 79.63% for outdoor and semi-outdoor environments respectively.
0%10%20%30%40%50%60%70%80%90%
100%
-3 (Cold) -2 (Cool) -1 (Slightlycool)
0 (Neutral) +1 (Slightlywarm)
+2 (Warm) +3 (Hot)
Perc
enta
ge o
f the
rmal
perc
eptio
n vo
te (%
)
(a) Outdoor
Comfortable Slight uncomfortableUncomfortable Very uncomfortableExtremely uncomfortable
0%10%20%30%40%50%60%70%80%90%
100%
-3 (Cold) -2 (Cool) -1 (Slightlycool)
0 (Neutral) +1 (Slightlywarm)
+2 (Warm) +3 (Hot)Pe
rcen
tage
of t
herm
al pe
rcep
tion
vote
(%)
(b)Semi-outdoor
Comfortable Slight uncomfortableUncomfortable Very uncomfortableExtremely uncomfortable
10
y = 0.1508x - 3.7797
R² = 0.8043
y = 0.1263x - 3.3368
R² = 0.739
-3
-2
-1
0
1
2
3
15 20 25 30 35 40 45 50MT
SV
s
PET (Celsius)
Outdoor (n=173)
Semi-outdoor (n=427)
The neutral temperature of outdoor environments is slightly lower than semi-outdoor environments with a difference of 1.36 °C.
Environments Simple linear regressionNeutral temperature (°C PET) (MTSVs=0)
1. Outdoor MTSVsOutdoor= 0.1508PET – 3.7797 25.06
2. Semi-outdoor MTSVsSemi-outdoor= 0.1263PET – 3.3368 26.42
(4.3) Thermal sensation and neutral temperature
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Table 4-2 Comparing the neutral temperature in difference spaces
Where: PET = Physiological Equivalent Temperature (°C), and MTSVs = Mean thermal sensation votes
The results found that the upper boundary is obtained at 35.2 °C PET for outdoor environments and 37.3 °C PET for semi-outdoor environments.
It indicates that the respondents, who stay in outdoor environments, are psychologically intolerant against the summer conditions more than those living in semi-outdoor environments.
y = 0.2593x2 - 12.842x + 150.76
R² = 0.8144
y = 0.2084x2 - 12.407x + 192.74
R² = 0.486
0
10
20
30
40
50
60
70
80
90
100
10 15 20 25 30 35 40 45 50
Per
centa
ge
of
ther
mal
unac
cepta
ble
(%
)
PET (Celsius)
Outdoor (n=173)
Semi-outdoor (n=427)
Environments
Thermal neutrality (°C PET) Thermal
acceptable
ranges *
(°C PET)
Thermal
uncomfortable
rages
(°C PET)
Simple linear
regression
Quadratic
polynomialDifferential
1. Outdoor 25.06 24.77 -0.29 14.33-35.20
(range=20.87)
<14.33 and
>35.20
2. Semi-outdoor 26.42 29.76 +3.34 22.20-37.33
(range=15.13)
<22.20 and
>37.33
(4.4) Comparing linear regressions of thermal sensation and thermal acceptable ranges for the respondents voted in different environments
Table 4-3 Comparing linear regressions of thermal sensation and thermal acceptable ranges
Remark: * ASHRAE Standard 55 corresponded with minimum standard of 80% acceptability (or 20% unacceptability)12
20% Unacceptability Line
City/ Country Location
climate classification a Neutral
temperature
[◦C PET]
Upper limit
of neutral
temperature
[◦C PET]
Climate Group
Rome, Italy
(F. Salata et al., 2016)
41.5◦N,
12.3◦E
Mediterranean Csa 26.9 29.2 c
Cairo, Egypt
(A.H.A. Mahmoud, 2011)
31.0◦N,
31.3◦E
Hot desert BWh 27.04 30.0c
Guangzhou, southeastern China*
(K. Li et al., 2016)
23.1◦N,
113.3◦E
Humid subtropical Cfa n.a. 34.03b
Taiwan
(T.P. Lin and A. Matzarakis, 2008)
24.1◦N,
120.7◦E
Humid subtropical Cwa 25.6 35.4 b
Hong Kong, China
(V. Cheng et al., 2012)
22.3◦N,
114.2◦E
Humid subtropical Cwa 25.0 32.0
Thammasat University Rangsit
Campus** [present study]
14.1° N,
100.6° E
Tropical wet and dry Aw 25.1 35.2b
Singapore, Singapore*
(W. Yang, N.H. Wong, S.K, 2013)
1.4° N,
103.8° E
Tropical rainforest Af 26.5 31.7
Sydney, Australia
(J. Spagnolo & R. de Dear, 2013)
33.9◦S,
151.2◦E
Humid subtropical Cfa 22.9 n.a.
Remark: * whole year survey, ** under shaded conditions, a Köppen climate classificationb by assuming the ASHRAE Standard 55 corresponded with minimum standard of 80% acceptability (or 20% unacceptability)c by assuming the comfort range was the interval +0.5 of the ASHRAE 7-point scale
Table 4-4 The neutral PET and comfort ranges of summer in other studies.
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(4.5) Examine the thermal effects of shading on outdoor and semi-outdoor thermal comfort
PE
T (
Cel
sius)
Shaded Conditions
the upper acceptability limit of outdoor
the upper acceptability limit of semi-outdoor
the neutral temperature of outdoor
the neutral temperature of semi-outdoor
25.06
26.42
35.20
37.33
Air
Tem
per
atu
re (
Cel
siu
s)
Shaded ConditionsM
ean R
adia
nt T
emper
ature
(C
elsi
us)
Shaded Conditions
(a) (b)
Different conditions of shade categorized
The label represent: (1) tree shade(2) building shade(3) both tree and building
shade(4) cloudy shade
It is found that occupants living in semi-outdoor environments for all shade characteristics are satisfied their environment, which the PET values are within the thermal acceptable range with the upper acceptability limit of 37.3 °C.
Some of occupants living under tree shades and both tree and building shades for outdoor environment feel slightly hot.
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5. CONCLUSIONS
The neutral temperature is 25.06 °C and 26.42 °C PET for outdoor and
semi-outdoor environments, respectively. The neutral temperature of outdoor environments is slightly lower than semi-outdoor environments with a difference of 1.36 °C and the results indicated that occupants of
semi-outdoor environment was more tolerant regarding thermal comfort than occupants of outdoor environments.
The acceptable range of thermal comfort for respondents living in semi-outdoor environment is from 22.2-37.3 °C PET, which is higher than the range of 14.3-35.2 °C PET for the occupants living in outdoor environment.
The results indicates that the acceptable range of outdoor context wider than the semi-outdoor context due to different expectation and this contradiction could be due to the method of calculating the acceptable temperature range. Another reason for the contradiction could be due to the special tropical climate context of outdoor. Thus, it is reasonable to find big differences among the semi-outdoor and outdoor conditions in terms of acceptable temperature range for tropical climate.
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6. RECOMMENDATIONS
The calculated PET values for each shading environment varies, which were influenced by local air temperature and mean radiant temperature. Shading is the key strategy for promoting outdoor thermal comfort in tropics because it leads to a reduction of air temperature and mean radiant temperature and hence to a cooler thermal sensation.
Therefore, in a hot-humid tropical region such as Thailand , the configuration of buildings in relation to the sun or shadow is important, as is the strategic placement of elements that provide shade, such as planting and street and garden furniture, and applied with sunshine eliminating design strategies can effectively increase occupant thermal comfort and further increase their utilization rate of these spaces in the summer. 16
(a) Sun path of Bangkok, Thailand
Influencing sun and
shade in tropical northern
hemisphere
(b) Shadow diagram of a cubic form measuring 3x3x3m (XYZ)
17
(a) Summer solstice [20 June]
(c) Equinox [21 March and 23 September]
(b) Perpendicular position [26 April and 16 August]
(d) Winter solstice [22 December]
Note: Shadows are calculate for a location at Bangkok, Thailand in SketchUp (Latitude 13.7563° N, Longitude 100.5018° E).
(Source: Author, 2016)
Dimensions and spacing of buildings affect outdoor thermal environment by shading back into space at different hours
18
Summer solstice (20 June)
Equinox (21 March and 23 September)
Perpendicular position (26 April and 16 August)
Winter solstice(22 December)Note: Shadows are calculate for a location at Bangkok, Thailand in SketchUp (Latitude 13.7563° N, Longitude 100.5018° E).
(a) N-S axis: H/W=1.0 (b) NE-SW axis: H/W=1.0
(Source: Author, 2016)
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Shading Design Options to Improve Outdoor Thermal Comfort
Implementation of shading design such as passways, arcades, and activity spaces for the student
Trees and other plants help cool the environment by providing shade and through evapotranspiration19
20
Artificial shading facilities can also create a good shading effect
20
END
Thank you for your attention.
The 6th International Conference on Sustainable Energy and EnvironmentSpecial Session: Urban Climate & Urban Air Pollution (UCUA)
Organizers:
28-30 November 2016, Dusit Thani Bangkok Hotel, Thailand.