What Makes a Heat Pump Work

Heat pumps are an effective and efficient way to both heat up and cool down substances and spaces.Heat pumps use a fluid, called a refrigerant, that circulates within a tube to transmit heat from one location to another. A heat pump can be used to cool down a room by transferring heat from it to the outside. A heat pump can also be used to heat a room by transferring heat from outside in.

There are many types of heat pumps, and once you understand how they work, in general, it becomes possible to appreciate how each of the various types works in its specific set of conditions. Heat pumps rely on two physical properties of liquids, condensation and evaporation to accomplish the heat transfer. When a liquid evaporates to the gaseous state, it readily absorbs heat from the surroundings. On the contrary, when a gas condenses to become a liquid it gives up its heat to the environment.

Now consider how the heat pump warms a room. The pump first causes the internal fluid to evaporate, and then flow through a section of the circular tube located in a space meant to lose heat. The gaseous refrigerant readily absorbs heat from the surrounding environment and then continues to circulate in the tube. Next it passes to the compressor, which compresses the gas causing it to heat up greatly. Now the hot gas circulates to the condenser, which is located in the section of the circular tube located in the room to be heated. The gas is made to condense and in the process it gives up a lot of heat to the surrounding environment.

The same heat pump can also function in the reverse direction, and it can be made to cool the same room it previously warmed. In this mode, the evaporated liquid is first made to flow through the room being warmed. The gas readily absorbs heat from the air, lowering the temperature of the chamber. Next the heated gas flows through the compressor and then the condenser, which is located outside. The gas changes to the liquid state and gives up its heat to the outside.

The refrigerant in the gaseous state can so readily absorb warmth that it can even take heat from air that is cooled to 0 degrees Celsius. Consequently heat pumps can actually warm homes even in winter weather. Of course, as the outside temperature drops, the efficiency of the pump drops. However, newer pumps can continue to work with 60% efficiency, even at temperatures as low as -17 degrees Celsius.

The efficiency of a heat pump is measured in terms of its Coefficient of Performance (COP). The COP is the ratio between the amount of energy used to make the pump work and the amount of heat change in the room being warmed or cooled. While an electrical heater normally has a COP of 1, heat pumps generally have COPs which can range as high as 7-8 in ideal conditions. This means that in most circumstances, heat pumps are more effective at heating and cooling than electrically powered heating and cooling units. This is why they are so often used today in the HVAC industry.