Heat Pumps
Under normal circumstances, heat only flows from
high temperatures to low temperatures.
In order to move heat from a low temperature
environment to a high temperature environment,
work needs to be done (or energy needs to be
transferred).
This is what a heat pump does. This is why fridges
keep our food cold. They move heat from the cold
inside of the fridge to the warmer outside. This is
why the grill at the back is warm, it is the heat that
has been removed from the inside.
A simple heat pump such as a fridge has four
basic components:
1. condenser,
2. expansion valve,
3. evaporator,
4. compressor.
A→B: The electrically driven
compressor increases the temperature and
pressure of the gas and forces it into the
condenser coils [the back of the fridge].
B→C: Because the temperature of the gas
is higher than the temperature in the
room, heat transfer [QH] from the gas to the
room occurs as the gas condenses to a liquid.
C→D: The liquid then flows back through
a pressure-reducing valve to the
evaporator coils [pipes IN the fridge] cooling
rapidly.
D→A: As the liquid is now cooler than
the inside of the fridge it absorbs heat from
it.
Under normal circumstances, heat only flows from
high temperatures to low temperatures.
In order to move heat from a low temperature
environment to a high temperature environment,
work needs to be done (or energy needs to be
transferred).
This is what a heat pump does. This is why fridges
keep our food cold. They move heat from the cold
inside of the fridge to the warmer outside. This is
why the grill at the back is warm, it is the heat that
has been removed from the inside.
A simple heat pump such as a fridge has four
basic components:
1. condenser,
2. expansion valve,
3. evaporator,
4. compressor.
A→B: The electrically driven
compressor increases the temperature and
pressure of the gas and forces it into the
condenser coils [the back of the fridge].
B→C: Because the temperature of the gas
is higher than the temperature in the
room, heat transfer [QH] from the gas to the
room occurs as the gas condenses to a liquid.
C→D: The liquid then flows back through
a pressure-reducing valve to the
evaporator coils [pipes IN the fridge] cooling
rapidly.
D→A: As the liquid is now cooler than
the inside of the fridge it absorbs heat from
it.
