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close this book National design handbook prototype on passive solar heating and natural cooling of buildings
close this folder IV. Thermal comfort
View the document A. Variables influencing comfort
View the document B. Environmental comfort

IV. Thermal comfort

The principal reason for constructing buildings is to provide protection from the environment and security of person and property. What is sought is protection from the environment when there is inadequate thermal comfort. A building can control the environment to provide for thermal comfort by either active or passive energy mechanisms. Unfortunately, too many buildings designed today are dependent on non-renewable energy sources to provide the desired thermal comfort instead of making use of the energy from the sun and the natural capacity of the climate.

The human body is a complex mechanism that is comfortable under a relatively limited range of environmental conditions. It needs to maintain a relatively stable "deep body temperature" at approximately 37C. The body continuously produces heat at rates that depend on its level of activity and. depending on the conditions of the environment, it gives off heat at various rates. If someone feels cold, it means that the body is giving off heat too quickly. Likewise, if someone is too hot then it is because the body cannot rid itself of body heat fast enough. Under normal sedentary conditions in a comfortable environment an average person gains or looses heat in three ways in approximately the following proportions:

Evaporation 25 per cent

Convection 30 per cent

Radiation 45 per cent

Only a minimal amount of heat is dissipated by conduction. Table 5 gives some examples of the rate of heat dissipation by an average sized human in good health for various activities:

Table 5. The body's heat production

Activity

watts

Sleeping

min. 70

Sitting, moderate movement, e.g. typing

130-160

Standing. light work at machine or bench

160-190

Sitting, heavy arm and leg movements

190-230

Standing, moderate work, some walking,

220-290

Walking, moderate lifting or pushing

290-410

Intermittent heavy lifting. digging

440-580

Hardest sustained work

580-700

Maximum heavy work for30-minutes duration

max. 1100