The design of a habitat
which reflects the consideration and analysis of environmental variables
like dry bulb temperature, relative humidity, air movement and radiation
as they effect human perception and response, can be called Bio-climatic Design.
Bio-climatic Analysis can
be carried out with the help of either the Bio-climatic chart or the
chart. This tutorial will work with the psychrometric chart for bio-climatic analysis. The psychrometric chart was developed for engineering calculations for the design of HVAC systems. The psychrometric chart helps to determine the comfort zone, in terms
of the four environmental variables for a person engaged in a specified
activity and wearing a specified amount of clothing. We are going to adapt its use in an architectural context.
Psychrometry (from the Greek: psukhros = cold)
is the study of moist air (which is mostly oxygen, nitrogen and water vapor) and of the changes in its condition. We are going to use the psychrometric chart to determine comfort conditions.
response to heat
Heat, or rather the thermal
state of the environment, is perceived by the skin surface of a living body. The temperature sensors on the skin are most sensitive around
34°C (93.2 °F), where quite small changes or differences in the temperature can be perceived. The
sensitivity decreases towards the limits of tolerable temperatures.
The heat produced by a resting adult is about 85.83 Kcal/h (340 Btu/h). Because most of this heat is transferred to the environment through the skin it is often convenient to characterize metabolic activity in terms of heat production per unit area of skin. For the resting adult, this is about 50 kcal/(h.m²) (18.4 Btu/h.ft²) (average person has a skin surface area of about 1.82 m² (19.6 ft²) and is called 1 met). Higher metabolic rates are often described in terms of the resting rate.
Heat from the environment
can reach the body surface by any or all of the three ways of heat transfer
(conduction, convection and radiation) and the skin perceives the total,
combined thermal effect. Thermal balance exists when the heat produced
by the body is fully dissipated to the environment. The heat produced in
deep-body tissues is continuously transported to the skin surface (and
to the lungs), whence it is emitted to the environment by convection, radiation
and evaporative heat transfer (some also by conduction).