How Do Heat Pumps Works?

Heat pumps are devices which actively transfer heat from one area to another. Normally, heat diffuses out into the environment, spreading from hotter to cooler objects. For example, if you put a pie out to cool on the windowsill, the heat will leave it and spread through the air outside. A heat pump reverses this process, actually concentrating heat. Heat pumps are used for refrigeration, air conditioning and heating.

The Compressor

Heat pumps are driven by the compressor, a special pump able to generate a tremendous amount of pressure. The compressor compresses a liquid called the refrigerant and sends it into the condenser tube. Compressing the refrigerant heats it up quite a bit, and the condenser is very hot. The tube is cooled, either by air blown past it by a fan or simply moved around with air currents. When the refrigerant in the compressor has cooled, it is shot out through a narrow nozzle into the evaporator.

The pressure in the evaporator is very low, and the refrigerant expands quickly, cooling down rapidly. Because of this, the evaporator tube is very cold. It is warmed up either by a fan or by air drifting by. Once the refrigerant has been warmed enough, it is pumped back through the compressor to start the process all over again.

Because they are hot at the condenser tube and cold at the evaporator tube, heat pumps can be used to heat, cool, or do both. In refrigerators, the evaporator is inside. A fan blows on it, spreading cool air through the whole fridge. Meanwhile, the hot condenser is stowed in back, where it radiates waste heat out into the room. Sometimes heat pumps are used as heaters instead. The evaporator can be outside or underground, where the temperature is warm enough to heat up the cold tube. Some reversible heat pumps can actually both heat and cool a building, working as a heater in the winter and an air conditioner in the summer.