Transferring Heat Energy and Reducing Energy Loss in Buildings

1
Transferring Heat Energy andReducing
Energy Loss in Buildings
2
Transferring Heat Energy

• Energy flows from a place where the temperature
  is higher to a place where the temperature is
  lower.
• In solids, this heat is transferred through
  conduction
• In liquids and gases heat is transferred through
  convection
• Objects that are hot emit heat through infrared
  radiation
• You will learn more about the processes of
• conduction and convection in Kennans
• presentation

3
Heat through Radiation

• When we say heat is transferred through
  electromagnetic radiation it is usually through
  infrared radiation
• When an object absorbs this radiation its
  temperature increases. Energy carried by the
  radiation makes the atoms of a material vibrate
  more and so the temperature rises.

4
Absorption and Emission of Heat

• The most important factor affecting the rate of
  absorption of radiation is the surface of the
  material
• Generally, black surfaces are the best absorbers
  of radiation, while shiny silver/ white surfaces
  are the worst.
• Similarly, the emission of radiation depends on
  the surface of the material.
• Generally, dull, black surfaces are the best
  emitters, whilst shiny silver/ white surfaces are
  the worst.

This can be shown by putting hands around a bulb
as in the diagram. It can be clearly felt that
the air around the black side of the bulb grows
warmer at a faster rate than the unpainted side.
Example
5
Reducing Heat loss by Design

• There are two main examples of where heat is lost
  through conduction, convection and radiation that
  need to be known for the exam. Firstly...
• The Thermos Flask.
• There is a stopper to reduce heat loss through
  evaporation...
• A vacuum to stop heat loss through conduction...
• Glass coated with aluminium to prevent heat loss
  through conduction and radiation.

6
Reducing Heat loss by Design

• The second example that should be known is in the
  home.
• The Home
• Half the heat that we use is to heat and light
  our buildings. With fossil fuels running out, we
  need to think about how to reduce the amount of
  energy wasted in our homes.

• This infrared photograph shows the areas of the
  house that lose the most heat. The main areas
  where heat is lost is through
• The roof
• The windows
• The doors
• The walls
• These can be reduced...

7
Windows Double Glazing
Double Glazing prevents heat loss through
conduction. A thin layer of air is trapped
between two sheets of glass. Air is a very good
insulator (30x better than glass) and therefore
prevents heat loss through conduction.
Walls Cavity Insulation
Cavity wall insulation prevents heat loss through
conduction and convection. Conduction is
prevented as the air in the space is a bad
conductor and convection is prevented by foam
which traps the air, stopping it from moving.
8
The most effective of these methods is the one
which saves the most money each year. The most
cost-effective of these methods is the method
which pays for itself as quickly as possible
after a few years.
Most Effective
Most Cost-Effective