18 May 2017
In this paper the possibility of using vapor-compression heat pumps to increase the temperature of carrier of lowtemperature
waste energy is assessed. We have studied thermodynamic cycles of heat pumps that use high
temperature refrigerant (HTR) and operate within extreme range of evaporation and condensation temperatures.
Due to the limitations imposed by the Second Law of Thermodynamics, it is necessary to artificially increase the
potential of the energy absorbed from the low temperature heat source. Either mechanical work (vapor
compression) or high temperature heat has to be delivered to the cycle.
From thermodynamic point of view, the most important optimization factor would be the minimization of the work
input, that is necessary for specified output. The minimal work input is calculated from the Second Law of
Thermodynamics, under the assumption that entropy of the system never decreases. This leads to an efficiency
optimized heat pump cycle.
Analyzed systems use natural refrigerants CO2, N2O and zeotropic mixtures R124/R142b/R600a and
R32/R125/R1234yf. Feasible thermodynamic cycles were modelled, compared and discussed in terms of their