2. The document outlines various factors that influence human thermal comfort, including physical conditions like temperature, humidity, air movement, and radiant sources, as well as physiological conditions like sex, age, health, and activity level. It provides recommendations for

1. 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.

2. 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 .

4. 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.

5. Man & Climate
Climate 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.

6. 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.

7. 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.

8. 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

9. 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

10. Comfort Zone
Some consider sunstroke or heatstroke
as the upper temperature limit for man’s
existence, with the freezing point as the
lower limit.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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

16. 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

17. • 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

18. 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).

19. Bio-climatic chart
The 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.

20. 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

21. 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

22. 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

23. 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.

24. 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

25. Reading exercise
Climate and Man
Author: Robert DeC. Ward
Source: Bulletin of the American Geographical
Society, Vol. 39, No. 12 (1907), pp. 735-738
Published by: American Geographical Society

26. Semester Project

27. 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.