7. Energy performance of heat transfer fluids: comparison and choice

The heat-transfer and heat-cooling capacities, as well as the energy coefficient of performance of heat-transfer fluids, are an essential criterion in the choice of these fluids, since, as we have already seen, they determine the investment and operating costs of the system.

Prior to evaluating these parameters, the minimum temperature encountered in the refrigerant circuit must be defined: this determines the concentration of salt or alcohol in aqueous solutions required to prevent frost forming on the wall of the refrigeration unit's evaporator. Once the concentration of these solutions is known, the main properties (density, kinematic viscosity, thermal conductivity, thermal mass capacity) are evaluated at an average operating temperature.

• The comparison procedure begins with an evaluation of the three energy criteria...