Example of Refrigeration:

let us assume travel in a car. Outside temperature is so high. This is highly uncomfortable. For a relaxing drive, today we have air-conditioned cars. Refrigeration is an integral component of air-conditioning. To enjoy a comfortable drive in the car, the temperature inside the car ought to be lowered from approximate 40^oC to 25 ^oC. It means that heat of the space inside the car and its occupants ought to be thrown outside. It is done by the refrigeration unit fitted in the car. The volume of the car is a lot less than from surroundings. With the discarded heat there is a considerable change in the temperature inside the car, but no modification in the temperature of the environment.

In various places & situations, environment temperature is lower than the temperature of the space that we want. As an instance consider car driving in the winter. Temperature outside is approximate 2-6^oC. For a relaxing drive with light clothing, temperature inside the car ought to be about 25^oC. It means that heat ought to be supplied or pumped inside the car and therefore its temperature must be increased. The machinery that does this operation is called up heat pump. But in applications such as a comfortable driving in a car that based upon the season needed temperature to be lower or higher than the surroundings, heat ought to be pumped to the car or discarded from the car. As both the operations are done by the similar unit in the car, in a much wide sense we may say that a refrigeration unit controls the temperature of a space. In the normal refrigeration system, it is done by reversing the operation.

That is a refrigeration system may also be utilized as a heat pump.

Journey in a Car is relaxing if the Temperature inside the Car is Maintained at approximate 25 ^oC. To do so, in a Summer, Heat from inside the Car ought to be Rejected to the Surroundings

Heat is pumped out from a lower temperature space to a higher environment in refrigeration. We know from our experience in today life that water flow from a higher level to lower and heat flows from a body at a higher temperature to lower temperature. The reverse that means, flow of water from a lower level to a higher and flow of heat from a body at a lower temperature to higher temperature do not occur naturally. In practice these are attained at the cost of external work (power) done on the water and heat (here the refrigerant) with help of a mechanical device.

Whether the space under consideration ought to be maintained at a temperature lower or higher than the nearby environment, to pump out or in the heat, external power is always needed.

Power is needed to Pump Water uphill; the similar is true for Pumping Heat from a Lower Temperature to a Higher Temperature Body.