Bio-Climatic Comfort

May 22nd, 2017 Lecture 3 Ephrem M.

Man is a fool by the rule,

he wants it hot when it is cool;

When it is cool, he wants it hot,

always wanting what it is not.

Bio-Climatic Comfort

Is a term which describes the best feeling of human beings on something

depending on climate.

Comfort is a major concern of architecture, as one of Vitruvius triads

of a building, commodity.

✓ Aesthetics / beauty / Venustas

✓ Commodity / Function / Utilitas

✓ Structure / Firmitas

Thermal Comfort

is the condition of mind that expresses satisfaction with

the thermal environment and is assessed by subjective evaluation .

Comfort involves control of

• temperature,

• humidity,

• air motion, and

• radiant sources interacting with the occupants.

Odor, dusts (particular matter) noise and vibration are additional factors

that may cause one to feel uncomfortable.

Man & ClimateClimate has both Negative and positive effects on man.

The negative is expressed as stress, pain, disease and death.

The second defines the conditions in which man’s productivity, health and mental and

physical energy are at their highest efficiency.

These measurements may be combined to show coinciding and complementary

relationships, in defining desirable atmospheric and thermal conditions.

Based on the study of Ellsworth Huntington, man’s physical strength and mental

activity are at their best within a given range of climatic conditions, and that outside

this range efficiency lessens, while stresses and the possibility of disease increase.

Shelter and environment

Environment is composed of light, sound climate, space and animate. They all act

directly upon the human body, which can either absorb them or try to

counteract their effects.

Physical and psychological reactions result from this struggle for biological

equilibrium. Man strives for the point at which minimum expenditure of energy is

needed to adjust to his environment. Conditions under which he succeeds in doing

so can be defined as the “comfort zone” wherein most of his energy is freed

for productivity.

The shelter is the main instrument for fulfilling the requirements of comfort. It

modifies the natural environment to optimize livable conditions. An

environmentally balanced shelter will satisfy man’s physiological needs. Comfort

therefore is related to thermal balance.

Elements of climatic environment which

affect human comfort

The human body receives certain climatic

elements and maintains thermal stability

through air temperature, radiation, air

movement and humidity.

Factors that affect thermal comfort

Thermal comfort is determined by the body’s ability to dissipate the heat and

moisture produced continuously by metabolic action.

Thermal comfort is affected by two different conditions.

Physical conditions include air movement (draughts), relative humidity, ambient

surface temperature, air temperature, atmospheric charge, air composition and air

pressure, room occupancy, optical / acoustic influences and clothing.

Physiological conditions includes sex, age, ethnic influences, food intake, level of

activity, adaptation and acclimatization, natural body rhythms, state of health and

psycho-sociological factors

GAINS

1.heat produced by:

A. basal processes

B. Activity

C. digestive, etc. processes

D. muscle tensing and

shivering in response to cold

2. absorption of radiant energy:

A. from sun directly or reflected

B. from glowing radiators

C. from non-glowing hot objects

3. heat conduction towards the

body:

A. from air above skin

temperature

B. by contact with hotter

Objects

4. condensation of atmospheric

moisture (occasional)

LOSSES

5. outward radiation:

A. to “sky”

B. to colder surroundings

6. heat conduction away

from the body:

A. to air below skin

temperature has tended by air

movement convection

B. by contact with colder

objects

7. evaporation

A. from respiratory tract

B. from skin

Comfort Zone

Some consider sunstroke or heatstroke

as the upper temperature limit for man’s

existence, with the freezing point as the

lower limit.

Comfort Zone

The ideal air temperature may be assumed to be midway between these extremes.

Humans seeks an area where he can tolerate cold without being uncomfortable and where

it will require his circulatory and sweat secretion system to permit him to adapt to heat.

Comfort zone varies in different countries.

American scientists place comfort zone between 30 and 70% relative humidity.

However, considering the range of observations and opinions there is no precise

criterion by which comfort can be evaluated.

How to improve comfort

The indoor air temperature may be raised to decrease body heat lose or

lowered to increase body heat loss.

Humidity may be raised to decrease body heat loss and lowered to

increase body heat lose by evaporation.

Air motion may be raised to increase body heat loss and lower to

decrease body heat loss.

Occupants of the building of course have some personal control over their

own comfort for instance the amount of clothing that they wear.

Room Climate

In the same way as earth has a climate, the insides of buildings also have

a climate, with measurable values for air pressure, humidity, temperature,

velocity of air circulation and ‘internal sunshine’ in the form of radiated

heat.

Efficient control of these factors leads to optimum room comfort and

contributes to man’s overall health and ability to perform whatever tasks

he is engaged in.

Recommendations for internal climate

An air temperature of 20-24°C is comfortable both in summer and in winter. The

surrounding surface areas should not differ by more than 2-3°C from the air

temperature.

A change in the air temperature can be compensated for by changing the surface

temperature, (e.g. with decreasing air temperature, increase the surface

temperature). If there is too great a difference between the air and surface

temperatures, excessive movement of air takes place.

The main critical surfaces are those of the windows.

The surface temperature of the ceiling depends upon the height of the

room. The temperature sensed by humans is somewhere near the average

between room air temperature and that of surrounding surfaces.

It is important to control air movement and humidity as far as

possible. The movement can be sensed as breezes and this has the

effect of locally cooling the body.

For comfort, heat conduction to the floor via the feet must be avoided (i.e. the

floor temperature should be 17°C or more.).

Recommendations for internal climate

A relative air humidity of 40-50% is comfortable. With a lower humidity (e.g. 30%)

dust particles are liable to fly around.

To maintain the quality of the air, controlled ventilation is ideal. The CO2

content of

the air must be replaced by oxygen. A CO2

content of 0.10% by volume should not

be exceeded, and therefore in living rooms and bedrooms provide for two or three

air changes per hour.

The fresh air requirement of humans comes to about 32.0 cu. m./h so the air change

in living rooms should be 0.4-0.8 times the room volume per person/h

Recommendations for internal climate

• Air movement affects body cooling, as velocity of air movement increases, The upper

comfort limit is raised, however this rise slows as higher temperatures are raised.

• Vapor pressure is exerted by a variable quantity of water vapor contained in atmospheric

air. Depressed or “enclosed” is felt if vapor pressure surpasses the 15mm mercury

mark.

• Evaporation decreases dry-bulb temperature. Temperature decrease caused by

evaporation of added moisture will restore comfort temperatures to the outer limit of

comfort zone. Evaporative cooling can be achieved by mechanical means and with the

use of trees, vegetation, pools or fountains in hot and dry climate zones where wind

effect is of little help in lowering high temperatures.

• Radiation effect of inside surfaces can be used to higher or lower air temperatures. This

means that comfort can be achieved at low temperatures if the heat loss of the body

can be counteracted with the sun’s radiation.

Relation of climatic elements to comfort

Bio-climatic chart

The effects of the climatic elements

can now be assembled from these

separate studies into as single chart.

This chart shows the comfort zone in

the center.

The bioclimatic chart was built up with

dry-bulb temperature as ordinate(Y-

Coordinate) and relative humidity as

abscissa(X-coordinate).

Bio-climatic chartThe climatic elements around it are shown by the means of curves which indicate

the nature of corrective measures necessary to restore the feeling of comfort at

any point outside the comfort zone.

The chart provided for study is

applicable to inhabitants of moderate

climate zones, at elevations not in

excess of 1,000 feet(300mt) above

sea level, with customary indoor

clothing, doing sedentary light work.

In the middle, we can see the summer comfort zone divided into the desirable and

practical ranges. The winter comfort zone lies a little lower.

Any climatic condition determined by its DBT and relative humidity can be plotted on the

chart.

• If the plotted one falls into the

comfort zone, we feel

comfortable in shade.

• If the point falls outside the

comfort zone, corrective

measures are needed.

• If the point is higher that the

upper perimeter of the comfort

zone, winds are needed.

Bio-climatic chart

How wind effects can restore the

feeling of comfort and offset high

temperatures is charted with the nearly

parallel lines following the upper limit of

the comfort zone perimeter.

The numbers indicate the needed wind

velocities in feet per minute value

(fpm). If the temperature is high and

the relative humidity is low, we feel too

hot and dry, and winds are of little help

here.

Evaporative cooling is the tool with

which to fight high temperatures. The

dotted lines indicate the grains of

moisture per pound of air needed to

reduce temperatures to the level at

the upper comfort perimeter.

Bio-climatic chart

At the lower perimeter of the comfort

zone is the line above which shading is

needed. Conversely, radiation is

necessary below the line to counteract

lower dry-bulb temperatures.

At the left are charted the mean radiant

temperature values necessary to restore

the feeling of comfort by either radiant

heating or cooling (control of surface

temperatures of the surrounding).

Bio-climatic chart

Use of bioclimatic chart

No corrective measures are necessary for any point of known dry-bulb temperature

relative humidity which falls within the boundaries of the comfort zone. For any

point falling outside this zone, corrective measures needed to restore the feeling

of comfort can be taken directly from the chart. For example:

1. At dry-bulb temperature, 75°F(23.889 °C), relative humidity , 50%, Need is:

none, the point is already in the comfort zone.

2. At dry-bulb temperature 75°F; relative humidity, 70%, Need: 280fpm wind to

counteract vapor pressure.

3. At dry-bulb temperature 50°F; relative humidity, 56%, Need: 260Btu/hr sun

radiation.

Bioclimatic evaluation is the starting point

for any architectural design aiming at

environmental climate balance. Prevailing

climatic conditions can easily be plotted

on the chart, and will show the architect

what corrective measures are needed to

restore comfort conditions.

Natural and artificial means can be applied

as remedy. Consequently, it is most

favorable that the architect optimize the

use of natural means in order to produce a

more healthful and livable house and save

on minimizing mechanical aids for climate

control.

Bio-climatic chart

Reading exercise

Climate and ManAuthor: Robert DeC. WardSource: Bulletin of the American Geographical

Society, Vol. 39, No. 12 (1907), pp. 735-738Published by: American Geographical Society

Semester Project

Quiz I

1. List down the climatic zones in Ethiopia with their respective characteristics.

2. What are the factors that affect thermal comfort ?

3. Provide credible solution(s) for the following two conditions by reading the bioclimatic chart

given.

a) At dry-bulb temperature 87°F; relative humidity, 30%

b) At dry-bulb temperature 95°F; relative humidity, 20%,

4. Pritzker Prize Laureate Glenn Murcutt clearly shows the global tendency towards an energy and

efficient earth friendly houses. He is known for designing energy-efficient, earth-friendly homes.

He points out four methods to do so. List them all and show how it can be achieved in the

Ethiopian climatic zone Zone I – Hot Dry Lowland.