The basic factors that effect human comfort

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THE BASIC FACTORS THAT EFFECT HUMAN COMFORT

As a species, we human beings are warm-blooded creatures; that is we are biologically able to maintain a constant body temperature of 37° centigrade, regardless of the temperature of the air around us (within reason).  However, for us to be truly comfortable in our environment, it is desirable that the temperature of the air around us is maintained at around 10° - 20° centigrade, depending upon whether we are active or at rest.  When planning and constructing buildings for human habitation, it is very important that we bear this fact in mind; a satisfactory thermal environment is an essential purpose of good building design.

Summary of comfort measurements – temperature.

                                

100ºC

BOILING POINT OF WATER

25ºC

FINE SUMMERS’ DAY

COMFORT POINT

10ºC

WINTERS’ DAY

0ºC

FREEZING POINT OF WATER

To achieve an acceptable thermal environment we need to consider the comfort of people using the building as well as the requirements of objects stored in them.  Humans and buildings interact with the heat that surrounds them; the amount of excess heat generated by a human body is directly proportional to the level of activity in which the body is engaged.  Consequently; the temperature of a room may limit the level of human activity that occurs within.  For example, a room temperature of 19C may be comfortable for a person who is quietly reading a book, but somebody using an exercise machine in that room would soon become overheated.

Typical heat output of human body

Activity                Example                Typical heat emission of adult male

Immobile                Sleeping                                 70 Watts

Seated                        Watching TV                           115 Watts

Light work                Office                                   140 Watts

Medium work                Factory, dancing                   265 Watts

Heavy work                Lifting                                   440 Watts

Sound

Sound is a sensation produced in the ear and brain by variations in the pressure of air.  These pressure variations transfer energy from a source of vibration.  Suitable vibrations in the air can be caused by a variety of methods:

  • Moving objects.  Examples include loudspeakers, guitar strings, vibrating walls, human vocal-chords.
  • Moving air.  Examples include horns, organ pipes, mechanical fans and jet engines.

On the next page is a diagram of the human ear.

A vibrating object compresses adjacent particles of air as it moves in one direction and leaves the particles of air ‘spread out’ as it moves in the other direction.  The displaced particles pass on their extra energy and a pattern of compressions and rarefactions travels out from the source, while the individual particles return to their original positions.

While the particles return to their original positions, the energy they pass on to neighbouring particles does not; this energy travels forward in a wave.  It is this wave, which, upon striking the ear, produces the sensation of sound in the brain.

The strength or loudness of a sound depends upon the energy content of each sound ‘wave’.  The maximum displacement of each air particle is greater in stronger sounds.

We measure this scale of sound level in decibels, where 0 decibels describes the sound level at the threshold of human hearing and the threshold of pain is around 140 decibels.

                Sound level in dB                        Typical environment

                         140…………………………….Threshold of pain

                         130…………………………….Aircraft take-off

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                         120

                         110…………………………….Loud disco

                         100…………………………….Noisy factory

                          90……………………………..Heavy lorry

                          80……………………………..High street corner

                          70……………………………..Vacuum cleaner

                          60……………………………..Normal conversation

                          50

                          40…………………………….Suburban living room

                          30

                          20…………………………….Quiet countryside

                          10

                            0…………………………….Threshold of hearing

The level of sound that we are able to tolerate ...

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