1. BASIC FACTORS THAT
AFFECT HUMAN
COMFORT IN THE
INTERNAL ENVIRONMENT
UNIT 4 - Science and Materials in construction
LEVEL 3 – BTEC Construction & Built Environment
By Kenneth Bowazi – MSc BE, BSc Hons QS, BSc CE

2. Thermal and air quality
 What affects the surroundings you live in?
 Air quality is affected by how hot it is outside or inside your
environment
 What is humidity and what affects humidity?
 The amount of moisture that is present within the air will have
an effect on humidity, which is linked to the amount of
ventilation entering
 What is the normal temperature of a human being?
 Human temperature maintain an average core temperature
of 37º depending on the metabolic rate

3. Nature of heat
• What is the measure of temperature
• Temperature is measured in degrees celsius
• The lower is 0 fixed at a melting point of ice at a stand at
atmospheric pressure of 101.32kN/m2
• The upper point is 100 degrees – temperature of steam
above the boiling point
• What is the acceptable value of temperature taken at normal
design?
• Normal design temperature are taken at 21 degrees inside
and -1 degrees outside on average

4. Thermodynamic temperature
scale
•
•
•
•
This is another measure of temperature in degrees Kelvin
0 degree celsius= 273.16 Kelvin (K)
100 degree celsius = 317.16 Kelvin
The unit of thermodynamic temperature is the fraction of the
thermodynamic temperature at the triple point water
• (equilibrium point of the temperature and pressure at which
three known phases of substance can exist i.e. liquid, water
vapour and pure ice)

5. Quantity of heat
 How do we measure the quantity of heat?
 Heat is measured in joules (J) which is a measure of work
done
 The rate of expenditure of energy or doing work or of heat
loss is measured in watts (W)
 1 watt is = 1 Joule per second
 1 W =1 J/s

6. Heat transfer
 Name three ways heat is transferred from one mass to
another, for instance a person sitting next to a radiator.
 Conduction
 Convection
 Radiation

7. Thermal comfort
 In high activity the temperature rises and the more heat you
will give off. Several factors influences the level heat is
generated (metabolic rate) including:
 Your surface area
 Age
 Gender
 Level of activity
 e.g.
 Sleeping heat output 70W. Lifting 440W.

8. Typical heat output of an adult
male
Activity
Example
Heat output
Immobile
Sleeping
70W
Seated
Watching TV
115W
Light work
Office
140W
Medium work
Factory Work
265W
Heavy work
Lifting
440W

9. Clothing
 The amount of clothing that we wear generally depends on
the season and affects our thermal comfort
 Clothing is measured in a scale called clo value
 1 clo= 0.155m2 K/W of insulation to the body
 Typical values vary from 1-4 clo

10. Typical clothing values
Clo value
Clothing
Typical comfort
temperature when
sitting
0 clo
Swimwear
29ºC
0.5 clo
Light clothing
25ºC
1 clo
Suit , jumper
22ºC
2 clo
Coat, gloves, hat
14ºC

11. Heat losses from buildings
 Comfortable temperature for humans is provided by
balancing the heat lost through conduction and ventilation
through the fabric with similar heat
 Optimum temperature will depend on material used , type of
construction, orientation of the building and degree of
exposure to the rain and wind

12. Room temperatures
 What would you consider in design to maintain temperature
in buildings?
 The resistance of a material to the passage of heat and the
thermal conductivity of the material in passing the heat along
are the basics of understanding of maintaining a steady
temperature and a comfortable thermal indoor environment
 In order to maintain a comfortable room temperature the
building must be provided with as much heat as is lost
through ventilation

13. What will the loss of heat in
buildings depend on?
 Materials used
 Type of construction
 Orientation of the building in relation to the sun
 Degree of exposure to rain and wind

14. Thermal conductivity (k)
 The amount of heat loss in one second through 1m2 of
material, whose thickness is 1 metre
 The units are W/mK (watts per metre Kelvin)

15. K-Values
Material
K Value (W/mK)
Brickwork (internal/exposed) (1700kg/m3)
0.84
Concrete, dense (2100kg/m3)
1.40
Concrete, lightweight (1200kg/m3)
0.38
Plaster, dense
0.50
Rendering
0.50
Concrete block, medium, weight (1400kg/m3)
0.51
Concrete block, lightweight (600kg/m3)
0.19

16. Thermal resistivity (r)
 Thermal resistivity is the reciprocal of thermal conductivity:
 R=1/K

17. Air movement
 Properties are tested for airtightness
 Draught seals are fitted to all openings to restrict thermal
losses
 If warmer air enter a room is not mixed with cooler air the
room becomes hotter near the ceiling and colder at floor level

18. Humidity & Ventilation
Humidity- the amount of water or moisture in the air measured
in grams per cubic metre(g/m3)
 Relative Humidity or percentage saturation
 This the percentage saturation
 Actual amount of water vapour/maximum amount of water
vapour that can be held X 100% of the temperature

19. RELATIVE HUMIDITY
 Humans are used to a relative humidity of between 40 and
60%. Greater than this we start to describe air as being
‘Humid’.

20. HEAT LOSS DUE TO
VENTILATION
 Natural ventilation leads to the complete volume of air in a
room changing a certain number of times in one hour
 Type of room
 Halls
 Bedrooms /lounges
 WCs and bathrooms
Air changes in hr
1.0
1.5
2.0

21. HEAT LOSS DUE TO
VENTILATION
 The fresh air entering the room will need to be heated to the
internal temperature of the room. This is calculated with the
formula:
 Volume of room x air change rate x volumetric specific heat
for air x temperature difference
 The volumetric specific heat for air is approximately
1300j/m3K and is considered a constant in this formula which
will give an answer in joules per hour.
 This then has to be converted into watts in order to find the
rate of heat loss which is achieved by dividing the number of
joules by the number of seconds in one hour

22. Heat loss to ventilation
 This then has to be converted into watts in order to find the
rate of heat loss which is achieved by dividing the number of
joules by the number of seconds in one hour
 Volume of room/building x air changes hr x 1300J x
Temperature difference / 3600s = Watts
 It is convenient when carrying out heat loss calculations to
assume an average internal temperature of 19°C minus
average of -1°C in winter which gives 20°C difference
between inside and outside temperatures

23. Theory into practice
 Calculate the rate of heat loss due to ventilation for the
building measuring 4.5m x 3.25 in plan and has a ceiling
height of 2.6m. The number of air changes in one hour is
1.35. The outside temperature is 6°C and the inside
temperature is 19°C.

24. Calculation
 {(4.5x3.25x2.6)m3 x 1.35 x 1300J x (19-6)°}/ 3600s
 240.983 Watts

25. Theory into practice
 A domestic semi-detached dwelling is subject to 1.5
changes per hour. Calculate the total heat loss due to
ventilation. In this example we have removed the circulation
space which is uninhabited.
 Room Dimensions
 Lounge is 3.5m x 3.5m
 Kitchen/diner is 4.0m x 2.5m
 Bedroom 1 is 3.0m x 3.0m
 Bedroom 2 is 2.75m x 2.75m
 Bathroom 3 is 2.5m x 2m
 Storey height is 2.4m
 Air changes for all rooms 1.5 per hour
 Temperature difference -1°C outside, 19°C inside.

26. Calculation
 Lounge
3.5 x 3.5 x 2.4 =29.4
 Kitchen
4.0 x 2.5 x 2.4 =24.0
 Bedroom One3.0 x 3.0 x 2.4 =21.6
 Bedroom Two2.75 x 2.75 x 2.4
=18.15
 Bathroom Three
2.5 x 2.0 x 2.4 =12.0
 Total volume = 105.91m3

27. Calculation

28. condensation
 This is formed when hot , humid air meets a cold surface, it
condenses onto this surface forming droplets of water
vapour.
 What are the effects of condensation in the internal
environment?
 Cause timber rot
 Encourage mould growth
 Produce cold spots
 Produce high humidity
 Cause corrosion to steelwork
 Dampen insulation, reducung its effectiveness

29. Heat flow through a structure

30. Acceptable values
 The acceptable values of heat loss or U-values is a
complicated topic and you will need to refer to the Building
regulations Part L Conservation of fuel and power for
guidance on the acceptable U- values.
 Ventilation is linked to the Building Regulation Part L that it
restricts air tightness of modern structure. Forced ventilation
has to be provided in form of fans in bathrooms and cooking
areas

31. Thermal conductivity (k)
 The amount of heat loss in one second through 1m2 of
material, whose thickness is 1 metre
 The units are W/mK (watts per metre Kelvin)
 P= kA (T1-T2)/ x
 A= Area
 X= thickness in m² and m respectively
 T1-T2= temperature difference in °C or K
 Which can be written as follows
 W=k x m² x °C/m
W/mK
; k = W x m/(m² x °C) = W/m°C or

32. U-Values
 A measurement of the rate of heat loss through a structure
 Thermal resistivity is the reciprocal of thermal conductivity:
 R=1/K