Technological innovations in heat pump systems

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Technological innovations in heat pump systems Renato M. Lazzarin Dipartimento di Tecnica e Gestione dei Sistemi industriali – DTG Università di Padova (Italy) E-mail: renato@gest.unipd.it Abstract It is estimated that about 140 million heat pumps are working in the world. This evidences that the equipment conceived by Lord Kelvin back in 1852 has finally penetrated into the market. In the last 20 years the heat pump has improved both regarding the thermal exchange surfaces, the compressor, and the control and defrosting systems. Thus not only was the COP strongly improved but also seasonal performances. Further equipment improvements are aimed to better exploit the properties of new refrigerants, utilising even the pressure drop between condenser and evaporator, usually dissipated by throttling. Gas driven heat pumps were also improved with higher efficiency i.c. motors and much longer maintenance intervals. Absorption heat pumps are now available in many different models suitable to different applications. Probably most improvements took place with lower heating temperatures and the use of cold sources more suitable than the outside air, above all surface and underground water, the ground and the recovery in mechanical ventilation systems. Keywords heat pump; innovation 1. A survey of the actual heat pump market During the last ten years the heat pump market has spread greatly in the world. After developing in the US and Japan, it has spread towards new and unexpected markets, particularly in China. A recent evaluation gives an estimate of 130–140 millions of heat pumps in the world with an annual thermal production estimated at 1300 TWh for 2001. This energy is used for 57% in residential heating, 27% in commercial applications and 16% in industry. The first promoting element of thermodynamic heating, as heat pump heating is sometimes called, was the reversible operation. An inversion valve on a summer air conditioner allows switching from summer operation with an evaporator inside to winter operation with a condenser inside (Fig. 1). This promoted firstly the selling of heat pumps in the US during the 1970s (more than 100,000 units were already installed in 1972). Then, secondly, it favoured the spreading of heat pumps in Japan where at the beginning of the 1990s more than one million units were sold every year. Even nowadays most heat pumps are installed in residential buildings in tem- perate and mild climates where summer cooling is requested and during winter outside air can be a very suitable heat source. Other applications are, however, increasing from surface or ground water heat pumps to ground heat pumps. The latter can be favourably used even in cold climates and they are used increasingly in Northern countries such as Canada and Sweden. Other heat pump developing fields are in heat recovery in building mechanical ventilation and in sanitary water heating. Yet one sector of the market which should Downloaded from https://academic.oup.com/ijlct/article/2/3/262/758006 by guest on 21 June 2022 International Journal of Low Carbon Technologies 2/3

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