Transcript Lesson

Heat loss and
insulation
Heat loss from houses
A thermogram shows the distribution of heat over the
surface of a house. It highlights where heat is being lost.
The white, yellow and
red areas are the warmest so
these are the worst insulated
parts of the house.
The blue and green areas are
the coolest so these are the
best insulated parts of the
house.
A poorly insulated house loses more energy and so costs
more to heat. It also means that more pollution particularly
carbon dioxide is created in order to heat the house.
Heat loss from houses
roof 20%
windows 12%
walls 36%
doors 4%
floor 28%
Can heat loss through windows be reduced?
A lot of heat energy can be lost through windows.
Double glazing adds an
extra pane of glass. The
air trapped between the
two panes acts as an
insulator and reduces
heat loss by conduction.
The insulating effect of
the gap can be improved
by removing the air and
creating a vacuum.
insulating
layer
of air
side-view
of double
glazing
The problems with double glazing are that it can be
expensive and that it is difficult to break in emergencies
without a special hammer.
How can heat loss through walls be reduced?
Most outside walls have an
empty space between the two
layers of bricks called a
cavity.
The air trapped in the cavity
acts as an insulator and
reduces any heat loss due to
conduction through the
bricks.
Heat loss can also occur due to
convection within the cavity.
Plastic foam insulation can be
pumped into the cavity to
prevent this.
convection
currents
in the
cavity
foam
insulation
prevents
convection
currents
How can heat loss through a roof be reduced?
The air warmed by radiators (and
other heaters) is carried around a
house by convection currents.
heat
loss
The house becomes heated but if
there is no roof insulation the warm
air continues to rise.
The heat eventually escapes through
the roof and is lost due to
conduction through the roof tiles.
Loft insulation contains trapped air
and so forms an insulating layer
between the loft and the rest of the
house. This helps to reduce loss
through the roof.
loft insulation
How can heat loss from radiators be reduced?
A radiator produces infrared radiation.
Some of this heat energy is absorbed by the wall that the
radiator is attached to and so the wall heats up.
This can be a real problem on outside walls where the heat
energy absorbed by the wall can escape from the house.
Heat loss from a radiator can be
reduced by placing shiny foil
between the wall and radiator.
The foil prevents heat radiation
from reaching the wall by
reflecting it back into the room.
This method of insulation is very
cheap to install.
How can heat loss through doors be reduced?
A draught is the movement of air due to a convection current.
A lot of heat energy can be lost from
a house due to draughts escaping
through gaps under doors and around
windows. This is one of the easiest
types of heat loss to prevent.
Draught excluders are hairy or
spongy strips that can be used to
close the gaps around doors and
windows. They prevent draughts
escaping and so reduce heat loss.
How can curtains reduce heat loss?
A draught is the movement of air due to a convection current.
Warm air rises and is carried up
towards the windows in a house
by convection currents.
This heat energy can escape
through gaps around windows
that are uncovered.
Fitting curtains and closing them
can prevent draughts leaving a
house and so reduce heat loss.
In addition, curtains are opaque
and so radiated heat does not
pass through them.
How does double glazing work?
How does double glazing keep a house warmer?
Double glazing keeps a house
warmer because there is a
layer of a__
ir between the
panes of glass.
Air is a poor c________
onductor
nsulator
so it acts as an i_______.
The trapped air r_______
educes
onduction
heat loss by c_________
from a house.
side-view
of double
glazing