Human Comfort in the Urban Environment

The Human Response to Climate• Physical environment is the single most important

determination of human actions and activities-environmental 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 long-wave and short-wave radiation, conduction from the surrounding air

http://www.shapesense.com/fitness-exercise/calculators/resting-metabolic-rate-calculator.aspx

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, where1 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 be58 W/m2 x 1.8 m2 = 104 W (356 Btu/hr)

Activity W/m2 W1) Btu/hr1)

Met

RecliningSleepimng

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

Standing, light activity (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

Walking on the level, 2 km/h

110 198 6751.9

Running 8-9

ActivityHuman 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

Effort Level Typical Tasks

Heart Rate Elevation(beats per minute)

Body Energy Expenditure(watts)

Work Duration Restriction(hours)

Light

riding bicycle at 10 km/h, canning paint, raking leaves, making drawings, machining light objects, sewing by hand

0 - 35 70 - 175 none

Moderate

building brick wall, cleaning boiler, planing softwood, sheet-metal working, soldering, using screwdrivers, walking on level

35 - 55 175 - 260 > 2

Heavydigging trenches, using sledge-hammer, 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

Heart rate, energy expenditure

The insulation of clothes are often measured in the unit "Clo", where1 Clo = 0.155 m2K/WClo = 0 - corresponds to a naked personClo = 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-insulation-d_732.htmlhttp://www.engineeringtoolbox.com/metabolism-clothing-activity-d_117.html

Clothing and human comfort

Basic concepts

RadiationWavelength, frequencyShortwave radiation:

solar radiation composed of Ultraviolet radiation (<0.4um), visible light (0.4-0.7um), and infrared (>0.7um)

Longwave radiation: earth’s radiation.

Wien’s law: 2897/T (in Kelvin); the higher the air temperature the shorter the wave length radiated

Relationship between air temperature and wavelength

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

EvaporationLatent heat (LE): energy stored in water by changes

in phaseSensible heat (H): energy transfer is measured

(reflected) in temperature change.Net radiation (Q)=LE+H

Human responses to extreme temperatures

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

100 38 Heavy Moderate LightNot recommended

110 43 Moderate LightNot recommended

Not recommended

120 49 LightNot recommended

Not recommended

Not recommended

Heat Discomfort Zone

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: (vapor-pressure-in-air/saturation-vapor-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 FahrenheitThe heat index can be calculated astHI = -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         (1)where tHI = heat index (oF)t = air temperature (oF) (t > 57oF)φ = relative humidity (%)

Caution - Fatigue is possible with prolonged exposure and/or physical activity2) Extreme Caution - Sunstroke, heat cramps and heat exhaustion are possible with prolonged exposure and/or physical activity3) Danger - Sunstroke, heat cramps and heat exhaustion are likely. Heat stroke is possible with prolonged exposure and/or physical activity4) Extreme Danger - Heatstroke/sunstroke is highly likely with continued exposure

Heat Index Table

Figure 2

"Chilled" Air Temperature (oF)

Ambient Air Temperature (oF)

Wind Velocity (mph)

5 10 15 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 mph and degrees Fahrenheit The "Chilled" air temperature can also be expressed as a function of wind velocity and ambient air temperature astwF = 35.74 + 0.6215 ta - 35.75 v0.16 + 0.4275 ta v0.16 (2)

"Chilled" Air Temperature (oC)

Ambient Air Temperature (oC)

Wind Velocity (km/h)

5 10 15 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

Wind Chill Index - Wind Velocity km/h and degrees CelsiusThe "Chilled" air temperature can also be expressed as a function of wind velocity and ambient air temperature astwC = 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)

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 speedThen 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 clothingWindchill advisories are based on the sensation of cold felt by the majority of people

Windchill index

Wind Chill Table

Figure 1

How We Lose Heat to the Environment

Hypothermia1. 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 HypothermiaCold 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

problemsDiseases 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, etcSecondary 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