Air source heat pump water heaters are a promising technology and use the same mechanical principles as refrigerators and air conditioners. While refrigerators remove heat from the interior and discharge it to the environment, heat pump water heater take heat from the environment and concentrate it to heat water for service needs. The heat pump water heater, based on the vapour compression cycle, absorbs heat from a renewable energy source. Heat pump is a device that provides heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and release it to a warmer one, and vice-versa. A heat pump water heater operates on an electrically driven vapor-compression cycle and pumps energy from the air in its surroundings to water in a storage tank, thus raising the temperature of the water. The hermetically seal compressor compress the refrigerant and send to the condenser. The evaporator absorbed surrounding heat and send to compressor. The condenser gives heat to the water.