P1.14 heating and insulating buildings

P1.1.4 Heating and insulating buildings

evaluate the effectiveness of different types of material used for insulation,

including U-values and economic factors including payback time

KEY WORDSEnergyWorkTransferU-valuesPayback timeSpecific heat capacity

One way to reduce the amount of heat that escapes from a house is to insulate it so that the heat energy escaping is reducedWhere is the most heat lost?What can be done to reduce the heat loss?

Important ways of reducing heat loss in a home are:

• Loft insulation – this is a thick layer of fibre glass laid across the loft space. It reduces conduction and convection.

Important ways of reducing heat loss in a home are:

Cavity wall insulation – this is foam squirted between the gaps between bricks. It reduces conduction and convection.

Important ways of reducing heat loss in a home are:

A jacket for the hot water tank this reduces conduction and radiation.

Air is an insulator/ poor conductor

Convection stopped foam is an insulator/ poor conductor

Heat is conducted through the glassHeat passes through the glass and air by radiationHeat crosses the gap by convection

LightX-raysSoundRadio

Cuts down convection currents

Air pockets trap air (from moving)

Foam is a poor conductor/ good insulator

Evaporation of water

takes energy from the house

convection

conduction

100 – (15+15+10+25) = 35%

Cavity wall insulation and roof insulation

Payback time – the time taken to recoup the initial payment - for these is calculated by:Initial cost ÷ annual saving

ExampleIt costs £250 to install and fit loft insulation in a house. It saves £50 a year.How long is the payback time?

Solution

Using: Payback time = Initial cost ÷ annual saving

Then £250 ÷ £50 = 5 years.

U-valuesa) U-values measure how effective a material is as an insulator.

The U-value shows how fast heat can transfer through a material.The higher the U-value the faster the heat transfer.

b) The lower the U-value, the better the material is as an insulator.Good insulators have a low U-value.

1 – it has the highest U-value

3 and 4 OR 1 and 2

U-values for the 20 mm windows are the same or higher than those for the 16 mm windows

therefore the 20 mm windows are no more energy efficient than 16 mm windows

c) Solar panels may contain water that is heated by radiation from the Sun. This water may then be used to heat buildings or provide domestic hot water.

The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius.

E is energy transferred in joules, Jm is mass in kilograms, kg𝛳 is temperature change in degrees Celsius, °Cc is specific heat capacity in J / kg °C

It indicates how much energy a substance can store.E = m x c x 𝛳

ExampleHow much energy is required to heat 3 kg of water from 20 °C to 100 °C. The specific heat capacityof water is 4200 J/ kg°C.

SolutionUsing E = m x c x 𝛳Substitutingm = 3 kgc = 4200 J/ kg°CT = 100-20 = 80 °CGives E = 3 x 4200 x 80 = 1008000 J

ExampleHow much energy is required to heat 2 kg of water from 10 °C to 110 °C. The specific heat capacityof water is 4200 J/ kg°C.

SolutionUsing E = m x c x 𝛳Substitutingm = 2 kgc = 4200 J/ kg°CT = 110-10 = 100 °CGives E = 2 x 4200 x 100 = 840000 J

Other ways of reducing energy loss includereplacing filament bulbs with low energy light bulbs and LED lighting

Replacing old appliances with energy efficient onesNewer appliances have an energy label. More efficient appliances are rated A.

Other ways of reducing energy loss include

An advertisement in a shop claims that:‘Replacing an old freezer with a new ‘A’ rated freezer will benefit the environment.’Do you agree that replacing the freezer will benefit the environment?

YES

Less electricity used / energy neededLess fossil fuels burnedLess polluting gases emitted

NO

Old freezer must be disposed ofHazardous chemicals inside freezer eg CFCsLot of Energy used in producing new freezer