In order to heat and cool the same area a four-way valve is required to
reverse the flow of refrigerant through the heat exchangers.
Any technology that moves heat from a warmer area to a cooler area is
referred to as a heat exchanger. (Think of water flowing downhill, no
energy is required to flow water down hill, just a tube to contain the
water) Heat exchangers create
larger surfaces areas to minimize the resistance to heat flow.
(Just like water flowing in a pipe, the larger the pipe the better
the water flows, smaller pipes require higher pressure and smaller heat
exchangers require higher temperature)
Heat exchangers use air, water, and other fluids to transport the
heat from one area to another or as an efficient means of spreading the
heat over larger surface areas for dissipation.
A car engine is a good example, it uses water/glycol to remove heat
from the cylinder block then transport the heat to the radiator.
The radiator uses the water/glycol to spread the heat over a large
surface area so the air flowing through the radiator can efficiently pick
up the heat and carry it away. Even
though a lot of energy is used on the engines water pump and fan to
move both the water/glycol and air, there is no heat pump or refrigeration
effect; heat is flowing from warm to cold.
A heat pipe is also a heat exchanger.
Heat sink and heat exchanger describe the same process, transferring
heat from a warmer area to a cooler area.
The term heat sink is more popular describing an all-metal heat
exchanger used to absorb and conduct heat without the use of fluids. Fans
are sometimes used to convect (disburse) heat off the heat exchanger.
Heat is a form of energy just like electricity,
solar (light), and wind (pressure). Heat
can be converted into electricity, light, and pressure (force).
Heat describes the amount of energy and is popularly expressed in
BTU or Calories. Temperature
describes the quality or level of the heat.
One Btu is defined as the energy required to raise one pound of
water one degree Fahrenheit. Consider this analogy, heat is analogous to a
volume of water, temperature is analogous to the water pressure, and water
flow rate, gallons per hour is analogous to heat flow rate, BTUs per hour.
In effect a water pump is similar to a heat pump. To pump a larger
volume of heat or water, more energy is required, pumping water against
higher pressures and pumping heat against higher temperatures require more
Cooling and heating can also be accomplished by absorbing heat through a
chemical process. Ice is use
to cool a beverage or food by absorbing heat as it melts (a solid absorbs
heat to become a liquid). A
liquid also absorbs heat to become a gas.
The reverse is also true; to convert gas to liquid will release
heat, and liquid to solid releases heat.
Changing the phases from liquid to vapor and from vapor to liquid
is how your typical heat pumps operate (vapor/compression