heat pump Brief:
A heat pump is a device that transfers the heat from a cool area to a warmer one, without doing any work (in contrast with a conventional heating system). The core mechanism of the heat pump is based on thermodynamics: "heat always flows from hot to cold".
Heat pumps are often utilized as space conditioning units for homes and businesses. They have two important advantages over conventional heating systems: less operating cost, and they provide cooling as well as heating.
Heat pumps generally offer greater potential efficiency than does any other form of energy-efficient space conditioning. This is due to their ability to draw heat from and exhaust it into different parts of the building. At the same time, in most existing configurations, heat pump systems do not create any conditioned air with outdoor air, as long as the supply air temperature is below a certain point. Most heat pumps in these configurations exhaust heat (which they transfer from the supply air) directly outdoors.
Heat pumps have been used in commercial space conditioning applications since about 1990 (for example in office buildings and manufacturing facilities). Levelized costs of electric heat pumps, as of early 2009, range from about US$0.06 to US$0.08 per kWh (higher if heating or cooling is needed, lower if only cooling is required). These are significantly higher than the levelized cost of electricity in many areas, though areas with particularly low-cost electricity may be an exception.
Heat pumps can also be used in conjunction with a traditional fossil fuel or nuclear power plant for district heating. In this application they act as a large thermal battery storing summer heat for winter distribution.
The most common type of heat pump is the refrigerant-based (air-cooled) heat pump, which uses a refrigerant that cycles between a liquid (such as ammonia or R-134a) vapor phase and a gas phase (such as ammonia gas) to transfer heat. Air-cooled heat pumps are very efficient, transferring up to 70% of their input power into thermal energy; however, they are inefficient at cooling and must be designed with enough capacity to meet the heating needs of the building. These devices are also prone to damage from icing during cold weather. They can be used only if the outdoor temperature is above 30 °C or they will fail.
In the search for renewable and more sustainable sources of energy, many people are turning to heat pump systems. Heat pumps are electrical appliances that transfer heat from one place to another using refrigerants and compressors. They can be used on both heating and cooling systems, but they don’t work well in high temperatures. A challenge for these types of setups is maintaining a low air temperature without lowering the temperature inside by too much. Fortunately, increased efficiency has helped this issue get solved more often than not.
 The growing demand for energy-efficient products and increased investment in research and development are major factors driving the growth of this market. The demand for air conditioners and heat pumps is expected to rise considerably due to increasing demand for air conditioners in developing countries, in addition, use of heat pumps for heating purposes is also expected to increase by 2021 due to rising need for efficient energy recovery systems.
