Heat: Mechanisms of Heat Gain and Loss in the Human Body

This article discusses the mechanisms by which the human body gains and loses heat to its environment. It covers the processes of evaporation, convection, radiation, and conduction. The article also explores the main paths of heat loss in an uninsulated brick veneer house in Sydney during winter and provides strategies for passive solar cooling in hot dry climates.

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ASSIGNMENT 2 – HEAT
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Date of submission

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With diagrams describe the ways that the human body gains or loses heat to its
environment. Explain how these mechanisms work.
Body metabolism is responsible for continuous generation of heat in human beings, with one on
average outputting 10 W but with a fluctuation that goes along with activity. Thermal regulation
is therefore important to continuously rid the body of this heat to the environment (Houdas &
Ring, 2013).
Heat in the human body is lost through the following processes;
● Evaporation
● Convection

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● Radiation
● Conduction
Heat loss by evaporation
Exposure to high temperatures especially after an intensive activity leads to sweating which is a
natural process of heat reduction in the human body (Houdas & Ring, 2013). Evaporation takes
place on the skin surface where water from body cells heats up and the energy transferred to the
external environment.
Heat loss/gain by radiation
Radiation does not need a medium to occur. Transfer of heat is by electromagnetic waves. Heat
felt by human beings from the sun is a good example of heat transfer by radiation.
Heat gain/loss by conduction
Heat transfer by conduction involves two or more solid bodies with unequal temperatures being
in contact. Heat is transferred until the two bodies achieve equilibrium temperature. So heat can
be conducted from a warm object to one’s body or vice versa.
Heat loss by convection
The medium for this mode of heat transfer is fluids. Heat from the human body is conserved by
clothing which traps the warm air around the skin (Sherwood, 2015). Wind blowing across ones
skin replaces the warm air around the skin with cold air through convection.

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2. For an uninsulated brick veneer house in Sydney in winter describe the main paths of
heat loss to the outside air
Buildings just like human beings also experience heat transfer with the environment. In Sydney
for example, a brick house without insulation would have high levels of heat losses going by
very low environmental temperatures (Law & Dewsbury, 2018). The rate of heat transfer
depends on the temperature difference between the building and its surrounding.
Heat in buildings is lost through;
 The ceiling
 The walls
 The glazing
 The floor

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 ventilation
Insulation of the house would reduce the rate of heat loss in the cold season and save costs
related to mechanical heating.
Effect of surface area to volume ratio
This ratio compares a building's exterior size to internal volume. A bigger building would
contain more heat because of a lower surface area to volume ratio.
Heat loss through walls
As earlier identified, an uninsulated brick building loses heat more to the surrounding. A brick
veneer house requires wooden frames and insulation between the studs. An inch air space
designed in the middle of sheathing and brick veneer can also attain desired insulation and offer
sufficient thermal mass.
Heat loss through ventilation
Hourly changes in air should be minimized not to exceed 0.5. Sufficient ventilation up to 0.5 ach
is necessary and including air lock at all entry doors. Heat loss can be reduced by making the
building airtight.

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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)
Retrieved from Module 5 (Szokolay, 2010)
Thermal conductivity

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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
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 good material in terms of thermal efficiency and would be appropriate for use in
energy efficient houses in Australia. It can store daytime heat and releases it slowly in the night
hence has a better performance than other lightweight materials (Aldawi, et al., 2013).

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Combination of brick with cavity improves thermal comfort in extreme conditions of
temperatures in Australia.
Sustainability in design of buildings nowadays is desirable and cavity brickwork can be applied
in achieving it. The advantage of such is reduction of energy required for forced heating and
cooling as seasons change from cold to hot (Soebarto & Bennetts, 2015). Integration with
passive design methods would culminate an optimally thermal efficient housing in Australia.
Q4. Describe five strategies for passive solar cooling in hot dry climates
Insulation
Insulation is a thermal barrier in the sense that it reduces heat gains acquired during hot seasons
therefore ensuring thermal comfort of occupants by keeping the house cool. Building sections
like roofs, ceiling and walls can be insulated with material such as a reflective bubble white poly.
Louver shading devices
Shading devices can be used as a strategic means of blocking direct sun rays experienced in
summer when aligned in SE facades. It also favors cross ventilation that aids in cooling indoor
spaces. Louvers positioned 45 degrees absorbs sun rays and simultaneously giving way to
illumination of the adjacent spaces (Chandrashekaran, 2010).
Double glazing
Windows allow the most gains and losses of heat in buildings. Insulation at the window has an
effect of reducing solar radiations. The space in the middle of two glass panes can be made to be

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a vacuum or get it occupied with gas so to decrease heat transmission (Soflaei, et al., 2016).
Solar heat gain coefficient can be well reduced with this strategy.
Green roofing
Green roofing involves covering a building roof with plants or grass from water proof substrate.
Roofs being a major source of solar heat gain as a result of their large surface area, introduction
of green roofing reduces heat conduction to building interior. Oxygen produced by the green roof
creates a heat island effect that reduces air temperature (Dabaieh, et al., 2015).
Light colour coatings
External walls that are exposed to energy from the sun by a large extent transfers solar heat to
indoor spaces. Light coating with a reflective characteristic can be applied to counter the effect.
Q5. Describe how angled louver blades can be designed to manage the entry of direct
sunlight into a building in a location like Sydney
Louvers serve the purpose of absorbing, transmitting, obstructing and reflecting solar radiations.
Its effect is subject to mounting on window, sun's position, slat angle and reflective properties.
Slats that are tilted upwards easily transmit solar light from the sun whilst those tilted
downwards transmit light coming from ground surface. Other than controlling thermal gains,
louvers can also protect against glare (Gusheh & Lassen, 2017).

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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.
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.

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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.

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