This document discusses factors that influence human thermal comfort in buildings, including temperature, humidity, air speed and quality. It describes that an internal temperature of 19-23°C, humidity of 40-60% RH, and air speed of 0.1-0.25 m/s are typically comfortable for humans. It also examines psychrometric charts and concepts such as operative temperature, predicted mean vote and percentage dissatisfied to evaluate thermal comfort conditions. Proper ventilation is also needed to dilute contaminants and maintain adequate oxygen levels for occupant health.
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Internal Climate: Human comfort
To maintain thermal equilibrium and internal body
temperature of aprox 36.8 deg Celsius, body lose internal
heat.
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Heat is lost through:-
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Internal Climate -Human comfort
What is your ideal comfort zone (room)?
Temperature?
Speed of Fan?
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Internal Climate - Human comfort
Internal environment may be classified as follows:
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Internal Climate
Human comfort
Internal climate can be defined as ‘a band
of internal conditions’ that satisfy most of
the people, most of the time.’ for the given
function of the room/workshop.
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Internal Climate - Human comfort
Factors influencing heat loss thus feeling of comfort are as follows:
1.Dry bulb temperature of the room air – narrow band 19 to 23
Celsius acceptable
2.Humidity of the room air (%RH) – wide band of 40% to 60%
acceptable
3.Mean temperature of the surrounding surfaces (Celsius) – narrow
band 9 to 26 Celsius
4.Velocity of the air across the body (m/s) – narrow band 0.1 to 0.25
m/s
5.Extent of clothing worn by occupants – personal choice
6.Degree of physical activity of occupant (ie metabolic rate) mets or
W/m2
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Internal Climate - Human comfort
Operative temperature (previously known as resultant
temperature or dry resultant temperature, but
renamed to align with ASHRAE and ISO standards) is
‘a simplified measure of human thermal
comfort derived from air temperature, mean radiant
temperature and air speed.
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Internal Climate
Resultant Temperature (Operative Temperature)
Comfort Zone for Sedentary Occupation
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Internal
Climate
Diagram for
continuous
occupation
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Internal Climate
Mean radiant temperature (MRT) is a measure
of the average temperature of the surfaces that
surround a particular point, with which it will
exchange thermal radiation
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Internal Climate
The predicted mean vote (PMV) was developed by
Povl Ole Fanger at Kansas State University and the
Technical University of Denmark as an empirical fit to
the human sensation of thermal comfort.
It was later adopted as an ISO standard.
PMV = method to measure human
sensation of thermal comfort
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Internal Climate
It predicts the average vote of a large group of people
on the a seven-point thermal sensation scale where:
+3 = hot
+2 = warm
+1 = slightly warm
0 = neutral
-1 = slightly cool
-2 = cool
-3 = cold
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Internal Climate
The predicted percentage dissatisfied (PPD)
index provides information on thermal
discomfort or thermal dissatisfaction by
predicting the percentage of people likely to
feel too warm or too cool in a given
environment.
The PPD can be obtained from the PMV.
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Internal Climate - Air quality
Comfort building’s occupants affected by
Contaminants and
Lack of oxygen
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Internal Climate - Air quality
Atmospheric contaminants include
•Coarse dirt
•Dust – soot, mineral, organic particles
•Fumes – form by condensation vapours
•Smoke – from incomplete combustion
•Gases – carbon monoxide, sulphur dioxide etc
•Bacteria – small organisms
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Internal Climate - Air quality
•Air quality is measured using CO2 sensors.
•Solids removed by filtration
•Vapours – by cooling & washing
•Gases remain in solution in the air
•Dilution of air inside and with air outside increases
oxygen content and reduces concentrations of
pollutants.
•Bacteria – by sterilisation facility, ultra-violet light
sources
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Internal Climate - Ventilation air
Dilution air requirements may be found in
the Chartered Institute of Building Services
Engineers (CIBSE) guide,
Typical ventilation rate : 8 to 20 litres per
second per person
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Humidity of air:
Properties of humid air
Humidity of air is defined by
1.Absolute humidity or moisture content.
is the measure of water vapour(moisture) in
the air, regardless of temperature.
Measured in kg/kg or g/kg
Max AH of warm air at 30º Celsius is approx. 30gm of water
vapour (30g/m3)
Max AH of cold air at 0º Celsius is approx. 5gm of water vapour
(5g/m3)
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Humidity of air is defined by (cont’d)
2. Relative humidity
also measures water vapour but RELATIVE
to the temperature of the air.
It is expressed as the amount of water vapour in
the air as a percentage of the total amount that
could be held at its current temperature.
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Properties of humid air
Container one has a maximum volume of 30g of
water and is half full- it contains 50% of its
capacity.
Container two has a maximum volume of 5g of
water and is three quarters full- it contains 75%
of its capacity
Container one contains six times as much water
as container two, yet actually contains a lower
percentage.
Warm air can hold far more moisture than cold air
meaning that the relative humidity of cold air would
be far higher than warm air if their absolute humidity
levels were equal.
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Properties of humid air
Human body temperature is dependent on the air as it absorbs and removes
moisture from our skin to cool us down.
If the relative humidity is high, the amount of water evaporating from our skin is
limited so we feel warm and stifled.
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Humidity of air is defined by (cont’d)
Dew-point temperature – air holding
max water (saturated)
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Properties of humid air
Dry bulb temperature – is registered by an ordinary
thermometer often referred as air temperature.
Wet bulb temperature – is temperature registered by a
bulb covered by a watered- moistened wick exposed
to rapidly moving current of air
When bulb reading is the same as wet bulb reading this
indicates 100 percent relative humidity.
Dew point temperature is the temperature at which air
can no longer ‘hold’ all the water vapour which is
mixed with it and some of water vapour must condense
into liquid water
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Adverse effects of high and low levels of relative
humidity for the occupants as well as the dwelling
itself.
Hygiene,
health,
retention of value,
aesthetics and comfort
which can be affected by a failure to maintain an
optimal level of relative humidity.
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A relative humidity (RH) of 40-60% is
generally considered to be optimal for
a comfortable and healthy home.
Too much moisture can lead to mold
and overheating.
Too little causes dry eyes, chapped
lips and an environment in which
bacteria and viruses can thrive.
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Psychrometric Data
The relationship between dry bulb and
wet bulb temperature, relative humidity
and moisture content can be seen by
reference to the psychrometric chart.
It provides a measure of air state at a
variety of temperature and humidity
levels.
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Psychrometric data
Included in the chart also
Specific volume (inverse of
density – m3/kg
Specific enthalpy (heat
energy) – kJ/kg
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AC provide desirable climate for the purpose of:
Comfort to occupants
Operation of sensitive equipment (eg computers)
The storage of commodities in good condition.
Carrying out of industrial processes without
harmful effects
Occasionally the well-being of exotic plants and
animals.
