Transferring Heat Energy and Reducing Energy Loss in Buildings

1. Transferring Heat Energy andReducing Energy Loss in Buildings

2. Conduction Convection Radiation 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 Kennan’s 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. Roofs – Fibreglass insulation Fibreglass roof insulation prevents heat loss through conduction and convection. It prevents conduction as air is trapped between the fibres and convection is prevented as warm air cannot rise up out of the roof Doors – Draft Excluders Draft excluders prevent heat loss through convection by keeping as much warm air as possible inside the house 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