Mechanisms of Heat Gain and Loss in Human Body

This article explains the mechanisms of heat gain and loss in the human body through conduction, convention, radiation, and evaporation. It also describes the main paths of heat loss to the outside air in an uninsulated brick veneer house in Sydney, strategies for passive solar cooling in hot dry climates, and how angled louvre blades can be designed to manage the entry of direct sunlight into a building in a location like Sydney.

Q1. With diagrams describe the ways that the human body gains or losses heat to its
environment. Explain how these mechanisms work.
Homeostasis is a state in which body is in constant balance temperature and it is possible when
the heat loss and gain is balanced. Body usually gain heat through exercise or by applying
external sources of heat. Heat loss from body in 4 significant ways: Conduction, Convention,
radiation and evaporation.
EVAPORATION
By perspiration and respiration produce loss of heat from body. Evaporation is limited by high
humidity. By lungs and skin water vapors loses. Evaporation is when the state of liquid change
into state of gas. When anyone burns by steam its effect will be opposite. The pressure of water
vapor and significant quantity of water vapor present in air effect the comfort from thermal.
CONDUCTION
when the body touch the surface it gains or losses heat. When the body is insulated, heat is
transfer. Conduction is transfer heat but with minor source Baggs, Baggs and Baggs 1996).
CONVENTION
By air current, heat receives or degenerates from the body. Convention is mostly hotter and take
place around the body. Air and fans increase the convention. Air is heat up or change by cool air
when it contact from the body. Increase in temperature hinders the cooling.
RADIATION
When the surfaces of surrounding have different temperature so the heat from and to the body is
radiated. Cold surfaces loses heat and fire and radiator bar can help in heat gaining ( Baggs and
Baggs 1996).

Q2. For an uninsulated brick veneer house in Sydney in winter describe the main paths of heat
loss to the outside air. (Hint: Use a diagram showing a section through the building.
Comfort of thermal does not produce by insulation by itself. The interior of the houses of timber
are usually increase in temperature than the outside temperature. Insulation is placed exterior to
the mass of thermal if the is building is continuously heated. Thermal mass is isolated from the
outside if the insulation is applied but primarily it is connected with the interior. This is known as
reverse brick veneer. If the insulation is provided inside the mass of thermal, this system is not
much effective. In the north of Sydney, Brisbane water hits by the half height of tide as fort in
Sydney. As the heat flow into the structure is restricted by the construction of the passive solar,
the pattern of the movement of the Brisbane water delays in or out of the bay. Narrow neck
limited the flow rate. The level of water is change with area of bay. As Brisbane water has huge
bay and narrow neck, so it has small swing of tides. High decrease in temperature occur when
the construction is done with high capacity of heat and high resistance of thermal (Guyton and
Hall 2006).

Q3. Do a quick calculation of the thermal conductance (U value) across a cavity wall consisting
of:
Thermal conductivity of a 110m brick is 7.64 w/m2.o C.
Surface resistances
the external conductance fo = 81.20 W/m2.oC
the internal conductance fi = 8.12 W/m2.oC
Outer surface resistance Ro = 1 / fo = 1 / 81.20 = 0.0123 m2.oC/W
Inner surface resistance Ri = 1 / fi = 1 / 8.12 = 0.123 m2.0C/W
Resistance of cavity is
The resistance of a 30 mm vertical cavity = 0.153 m2.oC/W
Resistance of brickwork
If the thermal conductivity of brickwork is 7.64 W/m.oC, then its resistivity is:
kb = 1 / 7.64 = 0.131 m.oC/W
By multiplying the thickness with resistivity, the resistance of thermal of brick will be determine.
Brickwork thermal resistance Rb = 0.131 x 0.11 = 0.0144 m2.oC/W
Thermal resistance of plastic board Rp = 0.06 m2.oC
Resistance of insulation.
Insulation thermal resistance R = 2.5 m2.0C/W(supposed)
Rt is the total resistance of thermal and is the sum of all the resistance 2.86m2.0C/W
This cavity brick wall is not efficient for the Australia because heat is store in the cavities and
houses remain hot all day long.

Q4. Describe five strategies for passive solar cooling in hot dry climates. (Hint: Use diagrams)
Natural ventilation is the basic strategy to keep the building cool without any external support in
hot weather. There are many strategies for passive solar cooling and some are:
WING WALLS
Wing walls speed up the natural air because of the difference in pressure built by the wing wall.
These walls are solid perpendicular panels beside the windows vertical to walls and the house is
on the wind direction side (Koenigsberger, Ingersoll, Mayhew, Alan and Szokolay 1974).
THERMAL CHIMNEY
Thermal chimneys are use to dispersed the air out of the building. If the hot zone is created at the
external outlet, air can enter into the building by ventilate the house. For this purpose sunrooms
can be effective.
STRATEGIES OF VENTILATIONS
Openings of inlet should be larger than the opening of outlet. Inlet should be at low height so it
will easy for airflow inside the room. If the furnishing fabric are minimum in the building so the
houses with high mass will be cool with ventilation at night. During the daytime houses with
high mass should be close and open at night time.
ROOF PONDS
The thermal mass can be increase by providing ponds on the roof on the building. As water is a
material that have good thermal mass so it will be very effective. Solar radiation is collected by
the surface of the roof . ponds should be covered at night to avoid re-radiation.

ROCK BINS
Under the building the free space is used as a rock bin. On the steep slope, rock bins are used and
the space on the basement will be utilized. Two stores are use in this system. In summer season,
heat is transfer to the rock bin 1 and air is transfer from the rock bin 2 into the building. In winter
season rock bin 1 transfer the heat into the room.
Q5. Describe how angled louvre blades can be designed to manage the entry of direct sunlight
into a building in a location like Sydney. (20 marks)
In cooler winter areas angled louvers are applied to catch the sunlight directly into the building.
Horizontal angled louvers are design to the angle of sun to the mid winter and placed in such
manner to allow heat in winter and shade in summer. By the thumb rule, the angled louvers
spacing should be 75 % of their width. The louvers must be thin so that the sunlight enters
directly into the building without any blockage. Covered balconies should not be placed to the
north as they interfere the sun of winter. In winter, shading to the north faced glass should be
avoided (Bucknall 1984).

References
Baggs, Sydney A and Baggs, Joan (1996) The Healthy House; Creating a safe, healthy and
environmentally friendly home. South Wales: HarperCollins Publishers.
Baggs, Sydney A., Baggs, Joan. and Baggs, David W (1996) Australian earth-covered building.
Kensington: New South Wales University Press.
Bucknall, Graeme (1984) Flynn’s Mantle of Safety; The story of Adelaide House, The John
Flynn Memorial Book House, Alice Springs
Guyton, Arthur C and Hall, John E (2006) Textbook of Medical Physiology. 11th ed.
Philadelphia. Elsevier Saunders UWS Hawkesbury 612/1.
Koenigsberger, O.H., Ingersoll, T.G., Mayhew, Alan and Szokolay, S.V. (1974) Manual of
Tropical Housing and Building. Climatic Design, Longman, London
Lindsay, David T (1996) Functional Human Anatomy. St. Louis, UWS Hawkesbury. 6(1), pp. 8-
11.