Heat Pump

The purpose of this page is to cover the basic concepts and principle of heat pump.

The heat pump technology

In recent years, the air source heat pump technology is the focus of new energy technology in the world. People is familiar with the "pump" is a kind of can increase the potential of mechanical equipment, such as pumps are mainly water from low to high
pumping. And air source heat pumps is a kind of energy from the nature of the air, water or soil to obtain the low grade heat energy power, after work, to provide people with high grade heat energy device.

Heat must flow from a system at high temperature to one at a lower temperature. As a natural phenomenon, as the water flow from a low height, the heat is always from a high temperature zone to low temperature zone. But people can create machines, like the water from low to high and the water pump, using the heat pump can take the heat from low temperature to high temperature and suction.
It is possible to reverse the direction of spontaneous energy flow by the use of a thermodynamic system known as a heat pump. A low temperature waste heat flow can be upgraded to useful high temperature heat with the use of a heat pump. 

The operating principle of a heat pump is based on the physical property that the boiling point of a fluid increases with pressure. By lowering pressure, a medium can be evaporated at low temperatures while an increase of pressure will lead to a high boiling point.

 This device consists of two heat exchangers, a compressor and an expansion device. A liquid or a mixture of liquid and vapor of a pure chemical species flows through an evaporator, where it absorbs heat at low temperature and, in doing so, is completely vaporized. The low temperature vapor is compressed by a compressor, which requires external work. The work done on the vapor raises its pressure and temperature to a level where its energy becomes available for use. The vapor flows through a condenser where it gives up its energy as it condenses to a liquid. The liquid is then expanded through an expansion valve back to the evaporator where the cycle repeats. The heat pump was developed as a space heating system where low temperature energy from the ambient air, water, or earth is raised to heating system temperatures by doing compression work with an electric motor-driven compressor.

Among the different types of heat pumps that have been developed, the mechanical heat pump is the most widely used. Its operating principle is based on compression and expansion of a working fluid, or so called 'refrigerant'. The refrigerant is the working fluid that passes through all these components. In the evaporator heat is extracted from a waste heat source. In the condenser this heat is delivered to the consumer at a higher temperature level. Electric energy is required to drive the compressor and this energy is added to the heat that is available in the condenser. The efficiency of the heat pump is denoted by its COP-Coefficient of performance, defined as the ratio of total heat delivered by the heat pump to the amount of electricity needed to drive the heat pump.

The heat pumps have the ability to upgrade heat to a value more than twice that of the energy consumed by the device. The potential for application of heat pump is growing and number of industries have been benefited by recovering low grade waste heat by upgrading it and using it in the main process stream.

Different types of heat pumps

Mechanical heat pump:

The mechanical heat pump is the most commonly used and commercially feasible heat pump. It's principle of operation: The pressure of a refrigerant is increased with a compressor causing a rise in boiling temperature. There are two varieties of mechanical heat pumps: a system with direct expansion (DX system) and a system in which a vessel is used to separate gaseous and fluid refrigerant.

Adsorption heat pump:

Although based on the same principles as the absorption heat pump, the adsorption heat pump uses a solid instead of a fluid as absorption medium.

Gas engine heat pump:

 The gas engine heat pump consists of a mechanical heat pump and a gas engine. Different to a conventional heat pump, where the compressor is driven with an electric motor, the compressor of a gas engine heat pump is driven by a gas engine. The heat from the motor cooling and flue gases of the gas engine can be utilized. Therefore the heat pump capacity can be lower.

Absorption heat pump:

The principle of operation of an absorption heat pump is based on evaporation of a refrigerant and its absorption into an absorbing medium. Well known combinations of refrigerant and absorbing medium are Lithium-Bromide and Water and Ammonia and Water. Driving force in this type of heat pump is thermal energy. Absorption heat pumps can be very useful when both heating and cooling are necessary.

Heat pump applications are most promising when both the heating and cooling capabilities can be used in combination. A heat pump can be used as a heater instead of a cooler/refrigerator. This is basically taking an air conditioner and flipping it around; so that the outside part is facing indoors and the inside part is facing outdoors. With this set up you will have a heater instead of an air conditioner.

If you use a heat pump as a cooler (air conditioner) during the summer, you cannot have an outdoor temperature that is excessively warm; otherwise your COP will go down.