Mechanisms of Heat Gain and Loss in Human Body

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.