Novel reactive refrigerants to make vapour compression heat pumps more efficient and suitable for industrial applications
Thermodynamic cycles represent the backbone of our current energy systems: thermal power plants, which underpin the global electricity production; and heat pumps, which are expected to triple their installed capacity within 2030 in the residential sector and be deployed in the industrial one. Thermodynamic cycles are currently known to operate with chemically inert working fluids throughout the cycle. To substantially increase the performance of thermodynamic cycles, and to allow the more feasible use of heat pumps at industrial level, the original approach, which we are investigating through different research projects, proposes the use of working fluids being the site of a reversible dimerization reaction. These chemical reactions evolve across each unit operation, as a consequence of the impact that the imposed changing of temperature and pressure has on the reaction’s chemical equilibrium. In a preliminary study based on the use of fictitious reactive fluids, we have demonstrated that using reactive rather than inert working fluids more than doubles the heat pump’s coefficient of performance. This is mainly explained by the occurrence of an exothermic reaction in the hot heat exchanger (releasing more heat in the environment), and of an endothermic reaction in the compression process (requiring less energy to compress the fluid). After introducing the concept of “reactive refrigerant”, this work validates those preliminary results, using a real reactive refrigerant. Focusing on industrial heat pump applications, we present the behaviour of dimerizing carboxylic acids (e.g., formic acid), which we have identified as a suitable working fluid for residential and industrial heat pumps.