Heat Assignment 2: Heat Transfer in Human Body and Buildings

This assignment explores heat transfer principles in the context of both the human body and building design. It begins by detailing the mechanisms through which the human body gains and loses heat, including evaporation, radiation, conduction, and convection, supported by relevant diagrams. The assignment then examines heat loss pathways in an uninsulated brick veneer house in Sydney during winter, emphasizing the role of walls, roofs, windows, and ventilation, and includes a diagram illustrating these aspects. A key component is the calculation of the thermal conductance (U-value) for a cavity wall, using provided data, followed by a discussion on the thermal efficiency of cavity brickwork in Australia. The assignment concludes by describing passive solar cooling strategies for hot, dry climates, such as the use of louver shading devices, double glazing, green roofing, insulation, and light-colored coatings, and discusses the design of angled louver blades to manage direct sunlight entry. The assignment draws on various sources to support the analysis and recommendations.

Heat 1
ASSIGNMENT 2 – HEAT
By (Name)
Course
Professor’s name
University name
City, State
Date of submission

Heat 2
With diagrams describe the ways that the human body gains or loses heat to its
environment. Explain how these mechanisms work.
Every alive human being is continuously producing heat through the body’s metabolic processes.
The general output of this heat is 100W but it will easily fluctuate from 70W (when one is
asleep) to 700W (during an intense work out). This heat should therefor be constantly released
into the environment otherwise the body will continue increasing temperature to a point of death.
The body’s thermal-regulation in very important (Houdas & Ring, 2013).
E – Evaporation
Rd – radiation
Cd – Condensation

Heat 3
Cv - convection
The human body losses or gains heat through the following main processes; evaporation,
radiation, convention and conduction.
Heat lost through evaporation
When a person is exposed to high temperatures, for instance during the summer, or after an
energy intensive activity, he or she will sweat to reduce heat in the body (Houdas & Ring, 2013).
The cells of the skin pumps water up to the surface so that the body heat can evaporates it, and
transfers that heat into our immediate surroundings.
Heat Gained or lost through Conduction
Conduction is heat transfer when two solid bodies with different temperatures come into contact.
This means, when one touches a warm object, heat is conducted from the warm object to your
body. The inverse is also true, when one touches a cold door handle, heat is transferred from the
body to the handle.
Heat lost or gained through Radiation
Radiation heat transfer does not require a medium for heat to transfer. Heat transfer occurs
through electromagnetic waves. A good example is the warmth we feel from the heat of the sun
Heat lost through Convection
Convection is the heat transfer through fluids (liquids and gases)

Heat 4
The human body generally radiates heat that forms a protective ‘blanket’ all round our bodies.
When one wears clothes, this heat is trapped next to the skin keeping us warm (Sherwood, 2015).
In a case where the wind blows, the air next to the skin is replaced with colder air due to the
temperature differences thus heat loss through convection occurs.
This forms the basis of thermal comfort of a human being at any particular environment.
However, comfort is very subjective as it is well-defined as the state of mind which will convey
satisfaction with the surrounding thermal environment. One’s comfort level may not be the same
as the other person. Thermal Comfort is not only affected by our surroundings but by other
physical elements such as clothing. In spite of this, there is always a perfect range of comfort for
a given region or climate
2. For an uninsulated brick veneer house in Sydney in winter describe the main paths of
heat loss to the outside air

Heat 5
Buildings function in a similar way to human beings, they are thermal systems that experience
heat gains and losses from the environment. At each and every point there is flow of heat energy.
An uninsulated brick house in Sydney would experience huge heat losses because the
temperatures of the environment are very low (Law & Dewsbury, 2018). When there is a higher
temperature difference between the building and the surroundings, the quicker the rate of heat
flow would occur.
Heat is mainly lost through
● The ceiling
● The walls
● The glazing
● The floor
● ventilation
In the uninsulated brick veneer house in Sydney, about 35 % of the heat loss is via walls, 25%
via the roof and the last 40 % is via windows, ventilation and the floor (Thorpe, 2010). Insulating
the house would result in less heat loss over the winter and save costs brought about by
mechanical heating systems.
Heat loss due to Surface to Volume ratio
The surface-volume ratio is the exterior size a building would have compared to the volume
inside it. When a building is bigger, its surface area-volume ratio decreases and this means it
would be able to retain more heat. A compact building such as an Eskimo igloo has a small
surface compared to its volume, thus retains heat better. This ratio is an important concept to
keep in mind

Heat 6
Heat loss through Windows
Heat can be easily lost to the environment through the windows as they have a very low thermal
mass. Because of this, the surface area occupied by windows kept to a minimum. Heat loss due
to Surface to Volume ratio the glazing should also be either double glazed or triple glazed with
low-e treatment and have partly evacuated with inert gas fill. Windows should be kept small
oriented to face the winter sunshine and placed low altitude sun for maximum solar heat gain.
Heat loss through walls
The uninsulated brick veneer house in Sydney would loss most of its heat through the walls due
to the lack of insulation. Though this might be the case, a brick veneer home is made of a
wooden frame and insulation can be put in the cavities in between the studs.
In addition, wall should have at least an inch air space should be in between the sheathing and
brick veneer to achieve insulation and enough thermal mass from the brick.
Heat loss through ventilation
The air hourly changes should be kept at a minimum and should not exceed 0.5. Adequate
ventilation should be provided up to 0.5 ach and all entry doors should have an air lock. The
building should be generally airtight to prevent heat loss.

Heat 7
Q3. Do a quick calculation of the thermal conductance (U value) across a cavity wall
consisting of:
X Outer skin 110mm brickwork (South facing, exposed aspect)
X 30mm cavity
X Inner skin of 90mm studwork with 10mm plasterboard
U value = 1/ Thermal resistance (R)
Thermal conductivity
Outer skin = 0.6
Inner skin = 0.6
Plaster = 0.5
R= Thermal conductivity/Thickness of material
110/0.6 = 183
90/0.6 = 150
10 / 0.2 = 50
1/1.83 = 0.546
1/1.50 = 0.667
1/0.50 = 2

Heat 8
U = 1/R1 + 1/R2 ….
0.546 + 0.667 + 2 = 3.213Wm2K
Discuss whether or not cavity brickwork is a thermally efficient wall for housing in
Australia.
Brick is a thermally efficient wall for Australia for it has the capabilities of creating energy
efficient houses. Brick has an excellent ability to store heat during the day when it is warmed up
by the sun and slowly release it into the night making it perform better than most lightweight
materials (Aldawi, et al., 2013). When it is combined with a cavity it forms the excellent solution
to the thermal comfort of the people living in extreme temperature changes of Australia
Cavity brickwork as a material will perform well enough in all seasons to ensure that mechanical
heating and cooling needs are kept to a minimum. This intern, saves money and proves to be an
excellent environmentally friendly solution for housing.
Achieving the Sustainability of today’s buildings is very important. Cavity brickwork can be
used to design energy efficient houses that ensures less energy is used when heating or cooling
houses during winter and summer respectively (Soebarto & Bennetts, 2015). When its properties
are combined with passive design methods, then the optimum thermally efficient housing can be
achieved in Australia.

Heat 9
Q4. Describe five strategies for passive solar cooling in hot dry climates
Louver shading devices
Shading devices should be positioned in the SE facades as a strategy to block the direct sun rays
during summer and allow cross ventilation to cool the indoor spaces. The louvers are placed in
45 degrees. The sun rays heating the louvers will absorbed while at the same time allowing light
to illuminate the adjacent spaces.
Double glazing
The heat gains and losses in buildings mainly occur through the windows. It is then clear that
windows play a big role when it comes to solar heat transfer between the external environment
and the building spaces. Window insulation can used as a strategy to minimize the effects of
solar radiations. Space is created between two glass panes can either be filled by a vacuum or gas
to reduce the transmission of heat (Soflaei, et al., 2016). This strategy will essentially reduce the
solar heat gain coefficient (SHGC).
Green roofing
A review of a number of literatures suggests that a green roof is a building roof covered with
plants or grass that grown on a water proof membrane. Roofs are the main source of solar heat
gain in building interiors due to their large surface ratio, therefore, introducing green roof as an
insulation will greatly reduce heat conducted into the interiors of the building. Production of
oxygen by the green roof also helps in creating a heat island effect in the urban environment thus
reducing air temperature (Dabaieh, et al., 2015).

Heat 10
Insulation
Insulation acts as membrane barrier to the flow of heat by reducing the amount of heat gain in
summer to maintain the thermal comfort of the house, thus keeping it cool. Having air leakages
and lack of insulation in the building envelope are the main causes of heat loss (Szokolay, 2008).
Insulation can be installed on the roofs, wall, ceiling and walls. Example of insulating material is
the reflective bubble white poly insulation that can be combined the vapor and radiant barrier.
Use of Light colour coatings
According to Dabaieh et al. (2015) external walls exposed to the solar radiation largely transfer
heat into the interior spaces thus affecting the indoor temperatures which reduce thermal
comfort. Light coating with high reflective property can be used to minimize solar heat gain.

Heat 11
Q5. Describe how angled louver blades can be designed to manage the entry of direct
sunlight into a building in a location like Sydney
Window louvers have the ability to absorb, obstruct, transmit, and reflect solar radiations to the
interior spaces of the building. Their effect mainly depend on their position on windows, position
of the sun, slat angle and its reflectance properties. Upward-tilted slats have the ability of
transmitting light form the sun, while the downward tilted slats have the ability of transmitting
light from the ground surface (Chandrashekaran, 2010). Louvers can also increase the
penetration of direct light from the sun. When the sky are over cast, louvers promote the even
distribution of daylight. Operable and fixed louvers can be used to control thermal gains,
protection against glare and redirected light (Gusheh & Lassen, 2017).

Heat 12
References
Aldawi, F., Date, A., Alam, F., Khan, I. and Alghamdi, M., 2013. Energy efficient residential
house wall system. Applied Thermal Engineering, 58(1-2), pp.400-410.
Chandrashekaran, D., 2010. Air flow through louvered openings: Effect of louver slats on air
movement inside a space. University of Southern California.
Dabaieh, M., Wanas, O., Hegazy, M.A. and Johansson, E., 2015. Reducing cooling demands in a
hot dry climate: A simulation study for non-insulated passive cool roof thermal performance in
residential buildings. Energy and Buildings, 89, pp.142-152.
Gusheh, M. and Lassen, C., 2017. Marie Short House: Glenn Murcutt. Companion to the History
of Architecture, pp.1-10.
Houdas, Y. and Ring, E.F.J., 2013. Human body temperature: its measurement and regulation.
Springer Science & Business Media.
Law, T. and Dewsbury, M., 2018. The Unintended Consequence of Building Sustainably in
Australia. In Sustainable Development Research in the Asia-Pacific Region (pp. 525-547).
Springer, Cham.
Thorpe, M., 2010. Brickwork Level 3. 3rd ed. Abingdon, United Kingdom: Routledge.
Sherwood, L., 2015. Human physiology: from cells to systems. 2nd ed. Boston, United States:
Cengage learning.
Soflaei, F., Shokouhian, M. and Shemirani, S.M.M., 2016. Investigation of Iranian traditional
courtyard as passive cooling strategy (a field study on BS climate). International Journal of
Sustainable Built Environment, 5(1), pp.99-113.

Heat 13
Szokolay, S.V., 2008. Introduction to architectural science: the basis of sustainable
design/Steven V. Szokolay.
Soebarto, V. and Bennetts, H., 2014. Thermal comfort and occupant responses during summer in
a low to middle income housing development in South Australia. Building and environment, 75,
pp.19-29.