Anderson Sec Sch 2007 Sec 4 CA1 Q12
When a house is heated, energy is lost to the outside.
The figure below shows where the energy is lost from the house.
(a)
(i) Describe how the house loses energy to the surroundings by the three processes of heat transfer.
(ii) Fitting carpets on the floor reduces energy loss. Explain how a carpet reduces energy loss.
(b) The table gives information about three methods of reducing energy loss.
| | Method of reducing energy loss | Installation cost | Saving on energy costs in one year | Number of years of saving needed to cover installation costs |
| A | Fitting carpets on the floor | $600 | $10 | 60 |
| B | Insulating the roof | $300 | Y | 3 |
| C | Fitting modern windows | X | $20 | 40 |
(i) Calculate the values of X and Y.
(ii) Which one of these three methods should the house owner choose? Explain your answer.
(iii) State two other ways, not already mentioned, of reducing energy loss from the house.
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Answer:
(a)
(i) Heat is lost by conduction through the roof, windows, grounds and walls as solid is a good conductor of heat and energy is transferred from one particle to another. Heat is lost by convection through the air near the ground; hot air which is less dense rises and cold air sinks. Heat is lost be radiation as electromagnetic waves travel through the walls of the house.
(ii) Carpets trap tiny pockets of air among its fibre and air is a poor conductor of heat.
(b)
(i) Y = $300 / 3 = $100
X = 40 * $20 = $800
(ii) Method B, insulating the roof. This is because in 3 years, the cost of insulation can be recovered.
(iii) (State three ways here instead)
Paint the house with lighter colours to reduce heat loss by radiation.
Install double glazed windows to reduce heat loss through the windows by conduction.
Reflective insulation within the roof/walls of the house to reduce heat loss by radiation.
