Refrigerators and heat pumps are heat engines operated in reverse cycle. They absorb heat from the cold reservoir and release this heat to the hot reservoir while work is done on the engine's working substance. In a household refrigerator, heat is taken from the food kept inside and released into the surroundings. Here, the aim is to remove the heat from a particular area. The measure of a refrigerator's effectiveness is known as the coefficient of performance, which is the ratio of the heat removed from the cold reservoir to the amount of work done on the working substance. Unlike refrigerators, heat pumps are used in colder regions to make houses warm. They focus on releasing the heat into a specific area. Heat pumps work like a refrigerator that has been turned inside out. The coefficient of performance for a heat pump is the ratio of the heat released to the hot reservoir to the amount of work done on the working substance.