Human Comfort in the Urban Environment
The Human Response to Climate
•
Physical environment is the single most important
determination of human actions and activitiesenvironmental determinism
•
Climate is a major component of the environment,
gave rise to climate determinism
Solar loading impact on human thermal comfort
M + Qn + C – LE = 0
Physiological responses
• Human body temperature
is around 98.6F (37C)
balanced by body’s heat
loss and heat gain.
Loss: radiation, conduction,
evaporation of moisture
from the skin surface
Gain: absorption of longwave and short-wave
radiation, conduction
from the surrounding air
Metabolic Rates for various activities
The metabolic rate, or human body heat or
power production, is often measured in the unit
"Met". The metabolic rate of a relaxed seated
person is one (1) Met, where
1 Met = 58 W/m2 (356 Btu/hr)
The mean surface area, the Du-Bois area, of the
human body is approximately 1.8 m2 (19.4
ft2). The total metabolic heat for a mean body
can be calculated by multiplying with the area.
The total heat from a relaxed seated person with
mean surface area would be
58 W/m2 x 1.8 m2 = 104 W (356 Btu/hr)
Activity
W/m2
W1)
Btu
/hr Met
1)
Reclining
Sleepimng
46
83
282
0.8
Seated relaxed
58
104
356
1.0
Standing at rest
70
126
430
1.2
Sedentary activity (office,
dwelling,
school, laboratory)
70
126
430
1.2
Car driving
80
144
491
1.4
Graphic profession - Book
Binder
85
153
522
1.5
(shopping, laboratory,
light industry)
93
167
571
1.6
Teacher
95
171
583
1.6
Domestic work -shaving,
washing and dressing
100
180
614
1.7
198
675
Standing, light activity
http://www.shapesense.com/fitnessexercise/calculators/resting-metabolic-ratecalculator.aspx
Walking on the level, 2
110
km/h
Running
8-9
1.9
Activity
Human Metabolic Rate
(W/m2)
(Met)
Laying down
46
0.8
Sitting, relaxed
58
1.0
Standing, relaxed
70
1.2
Sitting activity (office work,
school etc.)
70
1.2
Standing activity (shop,
laboratory etc.)
93
1.6
Moving activity (house work,
working at machines etc.)
116
2.0
Harder activity (hard work at
machines, work shops etc. )
165
2.8
Heart rate, energy expenditure
Body
Energy
Expenditur
e
(watts)
Work
Duration
Restriction
(hours)
70 - 175
none
Effort Level
Typical Tasks
Heart Rate
Elevation
(beats per
minute)
Light
riding bicycle at 10 km/h, canning
paint, raking leaves, making
drawings, machining light objects,
sewing by hand
0 - 35
Moderate
building brick wall, cleaning boiler,
planing softwood, sheet-metal
35 - 55
working, soldering, using
screwdrivers, walking on level
175 - 260
>2
Heavy
digging trenches, using sledgehammer, stoking furnace, metal
grinding, walking up 5% gradient
55 - 75
260 - 420
< 1 to 2
Very Heavy
shoveling sand, using
jackhammer, stacking concrete
blocks, stone masonry, climbing
normal stairs
75 - 90
420 - 700
< 1 to 2
Extremely
Heavy
sawing wood, climbing vertical
ladder
> 90
> 700
< 0.25 to
0.3
Clothing and human comfort
The insulation of clothes are often measured in the unit "Clo",
where
1 Clo = 0.155 m2K/W
Clo = 0 - corresponds to a naked person
Clo = 1 - corresponds to the insulating value of clothing needed to
maintain a person in comfort sitting at rest in a room at 21 ℃ (70
℉) with air movement of 0.1 m/s and humidity less than 50% typically a person wearing a business suit
http://www.engineeringtoolbox.com/clo-clothing-thermal-insulationd_732.html
http://www.engineeringtoolbox.com/metabolism-clothing-activityd_117.html
Basic concepts
Radiation
Wavelength, frequency
Shortwave radiation: solar
radiation composed of
Ultraviolet radiation
(<0.4um), visible light
(0.4-0.7um), and
infrared (>0.7um)
Longwave radiation:
earth’s radiation.
Relationship between air temperature and wavelength
Wien’s law: 2897/T (in Kelvin); the higher the air
temperature the shorter the wave length
radiated
Impact of radiation on people
• UV-C: most damage, absorbed by ozone in stratosphere
• UV-B and UV-A arrives the earth’s surface
Radiation determines the effects of thermoregulation and photochemical
responses that occur in the skin
(1) Production of vitamin D, necessary for the prevention of bone disease
(2) Sunburn, red and blistering (dilating chemical), may lead to aging and skin
cancer Table 7.4;7.5)
(3) Seasonal affective disorder (SAD):
mood disturbances related to season (related to too much or
too little solar radiation). Example: winter depression.
Sadness, decreased physical activity, weight gain,
decreases libido, interpersonal conflict. (light therapy or
drug)
Basic concepts (continue)
Conduction: energy transfer directly from molecule
to molecule by contact one another
Convection: energy transfer by mixing of molecules
with different temperature
Evaporation
Latent heat (LE): energy stored in water by changes
in phase
Sensible heat (H): energy transfer is measured
(reflected) in temperature change.
Net radiation (Q)=LE+H
Human responses to extreme temperatures
Heat Discomfort Zone
Maximum recommended work load
Temperature
Relative Humidity (%)
oF
oC
30
40
60
80
80
27
Very Heavy
Very Heavy
Very Heavy
Heavy
90
32
Very Heavy
Heavy
Moderate
Light
Moderate
Light
Not
recommen
ded
Moderate
Light
Not
recommen
ded
Not
recommen
ded
Light
Not
recommen
ded
Not
recommen
ded
Not
recommen
ded
100
110
120
38
43
49
Heavy
Water vapor
Dew point temperature:
temperature to which a parcel
of air cools to condensation
Saturation: air is holding the
maximum moisture at the
give air temperature (Fig 4.6)
Holding capacity increases
dramatically at higher air
temperature
Vapor pressure: the weight of
vapor over a unit surface
Relative humidity: (vaporpressure-in-air/saturationvapor-pressure)*100%
How close the air to saturation
Biometeorological
Indices
Serve to predict various
responses to the
sensation of warmth
and to assess the
physiological strain
imposed by
combined
atmospheric
variables
2 most common indexes for
heat are:
(1)
Apparent
temperature (AT)
(2)
Heat stress Index (HI)
Signs of heat stroke:
(a)Cessation of perspiration
cooling mechanisms
(b)Raising body T near 110F
(c)Skin becomes dry and hot
pulse become rapid and
irregular
Heat Index in degrees Fahrenheit
The heat index can be calculated as
tHI = -42.379 + 2.04901523 t + 10.14333127 φ
- 0.22475541 t φ - 0.00683783 t2 - 0.05481717 φ2
+ 0.00122874 t2 φ + 0.00085282 t φ2 - 0.00000199 (T φ)2
where
tHI = heat index (oF)
t = air temperature (oF) (t > 57oF)
φ = relative humidity (%)
(1)
Caution - Fatigue is possible with prolonged exposure and/or physical activity
2) Extreme Caution - Sunstroke, heat cramps and heat exhaustion are possible with prolonged exposure and/or
physical activity
3) Danger - Sunstroke, heat cramps and heat exhaustion are likely. Heat stroke is possible with prolonged
exposure and/or physical activity
4) Extreme Danger - Heatstroke/sunstroke is highly likely with continued exposure
Heat Index
Table
Figure 2
Wind Chill Index - Wind Velocity mph and degrees
Fahrenheit
The "Chilled" air temperature can also be expressed as a
function of wind velocity and ambient air temperature as
twF = 35.74
+ 0.6215 t - 35.75 v0.16 + 0.4275 ta v0.16 (2)
"Chilled" Air Temperature a( F)
o
Ambient Wind Velocity (mph)
Air
Temper
5
10
15
ature
o
( F)
20
25
30
35
40
40
36
34
32
30
29
28
28
27
35
31
27
25
24
23
21
21
20
30
25
21
19
17
16
14
14
13
25
19
15
13
11
9
7
7
6
20
13
9
6
4
3
0
0
-1
15
7
3
0
-2
-4
-7
-7
-8
10
1
-4
-7
-9
-11
-14
-14
-15
5
-5
-10
-13
-15
-17
-21
-21
-22
0
-11
-16
-19
-22
-24
-27
-27
-29
-5
-16
-22
-26
-29
-31
-37
-34
-36
-10
-22
-28
-32
-35
-37
-41
-41
-43
-15
-28
-35
-39
-42
-44
-48
-48
-50
-20
-34
-41
-45
-48
-51
-55
-55
-57
-25
-40
-47
-51
-55
-58
-62
-62
-64
-30
-46
-53
-58
-61
-64
-69
-69
-71
-35
-52
-59
-64
-68
-71
-76
-76
-78
-40
-57
-66
-71
-74
-78
-82
-82
-84
Wind Chill Index - Wind Velocity km/h and degrees Celsius
The "Chilled" air temperature can also be expressed as a function of wind velocity
and ambient air temperature as
twC = 13.12 + 0.6215 ta - 11.37 v0.16 + 0.3965 ta v0.16 (1)
where twC = effective "wind" temperature (oC)
ta = air temperature (oC); v = wind velocity (km/h)
"Chilled" Air Temperature (oC)
Ambient Wind Velocity (km/h)
Air
Tempera 5
10
15
o
ture ( C)
20
30
40
50
60
10
10
9
8
7
7
6
5
5
5
4
3
2
1
0
-1
-1
-2
0
-2
-3
-4
-5
-6
-7
-8
-9
-5
-7
-9
-11
-12
-13
-14
-15
-16
-10
-13
-15
-17
-18
-20
-21
-22
-23
-15
-19
-21
-23
-24
-26
-27
-29
-30
-20
-24
-27
-29
-30
-33
-34
-35
-36
-25
-30
-33
-35
-37
-39
-41
-42
-43
-30
-36
-39
-41
-43
-46
-48
-49
-50
-35
-41
-45
-48
-49
-52
-54
-56
-57
-40
-47
-51
-54
-56
-59
-61
-63
-64
Low Temperature impact: Windchill index
(To predict frost bite)
Windchill: coined by Antarctic explorer Paul A Siple to describe the cooling power
of wind for various combinations of temperatures and wind speed
Measurement:
First in Antarctic to measure the rate of freezing of water at various temperature
and wind speed
Then modified windchill formula to include the effect of clothing variables of
breathing and heat transfer through clothing
Model assumptions: a healthy adult (1.7m height, body surface area 1.7m2)
walking outdoors at 1.33 m/s will to generate 188wm-2 of heat
To main thermal equilibrium, amount of heat loss must not exceed the amount of
heat generated. The balance is achieved by wearing an appropriate thickness of
clothing
Windchill advisories are based on the sensation of cold felt by the majority of
people
Windchill index
Wind Chill Table
Figure 1
Hypothermia
1. Hypothermia - "a decrease in the core body temperature to a
level at which normal muscular and cerebral functions are
impaired." - Medicine for Mountaineering
2. Conditions Leading to Hypothermia
Cold temperatures
Improper clothing and equipment
Wetness
Fatigue, exhaustion
Dehydration
Poor food intake
No knowledge of hypothermia
Alcohol intake - causes vasodilation leading to increased heat loss
Climate and Health
Climatotherapy: the utilization of prevailing climate as
therapeutic
“escape weather”-travel for climate (Summer palaces,
Mediterranean yachts, Florida homes)
Intense heat stresses circulatory system;
Cold , damp weather cause depression and circulatory
problems
Diseases of respiratory system are worsened in places with
high airborne particle counts (asthma, bronchitis,
tuberculosis).
Morbidity and Mortality
Incidence of asthma increases
markedly with onset of cold
weather; respiratory
disease occur much more in
winter than in the summer
(older and very young
people are more vulnerable)
Heatwave and mortality
This graph tracks maximum
temperature (Tmax), heat index (HI),
and heat-related deaths in Chicago
each day from July 11 to 23, 1995. The
gray line shows maximum daily
temperature, the blue line shows the
heat index, and the bars indicate
number of deaths for the day.
Impact of other extreme weather events on human
health
Direct impacts: injury and death by storms, flooding, etc
Secondary impact: changes in ecosystem (bacteria, fungus etc);
in public health infrastructure (availability of safe drinking
water); mental problems (post traumatic disorder)
Stratospheric Ozone and UV radiation
• Decreases in ozone in stratosphere(5-10 miles above surface) lead to
increases in UV radiation on troposhere
• During the 1980s and 1990s at northern mid-latitudes (such as Europe),
the average year-round ozone concentration declined by around 4% per
decade: over the southern regions of Australia, New Zealand, Argentina
and South Africa, the figure approximated 6-7%. (ozone hole was detected
during southern hemispheric spring over the Antarctic)
• The groups most vulnerable to skin cancer are white Caucasians, especially
those of Celtic descent living in areas of high ambient UV.
• Culturally-based behavioral changes have led to much higher UV exposure,
through sun-bathing and skin-tanning. The marked increase in skin cancers
in western populations.
A more complete view
of UV on human health
Indirect impacts: through infectious
diseases
1. vector mosquitoes species that causes malaria, dengue and
yellow fever (tropical and subtropical).
2. rodents act as reservoirs for various disease; flooding is
associated with rodent-borne diseases. Other diseases
associated with rodents and ticks thrive in temperate climate
with wild winter.
3. Many diarrhoeal diseases vary seasonally, suggesting
sensitivity to climate. In the tropics, it peaks during the rainy
season. Both floods and droughts increase the risk of
diarrhoeal diseases. Major causes of diarrhoea linked to heavy
rainfall and contaminated water supplies.
4. food-borne infections (e.g. salmonellosis) peak in the warmer
months
5. Climate affects air-pollution related diseases
Climate and Architecture
Shelter with food is one of mainstays of human life on
earth.
The nature of shelter required largely depends on the
conditions of the environment, climate is the most
important
Primitive people used the limited resources at hand
developed shelters that were in harmony with the
climatic conditions under which they lived.
How Cities Use Parks To Improve Human Health
Parks provide people with contact with nature, known to confer
certain health benefits and enhance well-being.
Physical activity opportunities in parks help to increase fitness
and reduce obesity.
Parks resources can mitigate climate, air, and water pollution
impacts on public health.
Cities need to provide all types of parks, to provide their various
citizen groups with a range of health benefits.
Central Park, NY