22 May 2008

EXERGY ANALYSIS: STALKING THE POTENTIAL FOR MORE EFFICIENT AIR/WATER HEAT PUMPS


In this study, the behavior of air/water heat pumps over a wide range of operating
conditions is investigated using the exergy method. An analytical model based on the
relevant thermophysical properties has been developed to simulate the system at steady
state and to evaluate the exergetic efficiency. The exergy losses of the main process
components and the heating delivery and distribution system are discussed with
mathematical equations demonstrating the influence of important variables. Theoretical and
experimental analysis indicate that the exergetic efficiency of common heat pumps become
smaller when the ambient air temperature increases. The reason for this is the heat pump
characteristic: the less heat is required the more it delivers. In common heat pumps this is
compensated by on/off operation. As a consequence, a substantial increase in efficiency
requests continuous operation with power control of compressor and where necessary of the
fan: The generated heat flow of the heat pump shall be continuously adapted to the required
one.