Method for evaluating the energy efficiency of a refrigeration machine (1; 2) and/or a heat pump (3; 4), in which a working fluid of the refrigeration machine (1; 2) and/or heat pump (3; 4) is running through an expansion valve (40; 40A, 40B, 40C) at one point of a thermodynamic cycle, wherein: - an entrance pressure p entrance of the working fluid is detected at a position of the thermodynamic cycle where the working fluid enters the expansion valve (40; 40A, 40B, 40C); - an exit pressure p exit of the working fluid is detected at a position of the thermodynamic cycle where the working fluid exits the expansion valve (40; 40A, 40B, 40C); - a flow factor k v is established as a function of the opening of the expansion valve (40; 40A, 40B, 40C); - a volume flow V̇ F of the working fluid through the thermodynamic cycle is calculated according to the formula: V ̇ F = k v ⋅ Δ p ⋅ ρ 0 Δ p 0 ⋅ ρ entrance, wherein: - Δp is defined as difference between the detected exit pressure p exit and the detected entrance pressure p entrance; - Δp 0 is defined as a reference difference between the exit pressure and the entrance pressure; - ρ entrance is defined as entrance density at the entrance of the expansion valve (40; 40A, 40B, 40C); and - ρ 0 is defined as the reference density of the working fluid; - using the calculated volume flow V̇ F, the mass flow ṁ F is calculated by the formula: m ̇ F = V ̇ F ⋅ ρ entrance; - a cooling power and/or a heating power ( Q̇) of the refrigeration machine (1; 2) and/or heat pump (3; 4) is determined as a function of the mass flow ( ṁ F) of the working fluid; and - the energy efficiency of the refrigeration machine (1; 2) and/or heat pump (3; 4) is evaluated by comparing the cooling power and/or heating power ( Q̇) to an electrical power ( P el) used to power the refrigeration machine and/or heat pump. - an entrance pressure p entrance of the working fluid is detected at a position of the thermodynamic cycle where the working fluid enters the expansion valve (40; 40A, 40B, 40C); - an exit pressure p exit of the working fluid is detected at a position of the thermodynamic cycle where the working fluid exits the expansion valve (40; 40A, 40B, 40C); - a flow factor k v is established as a function of the opening of the expansion valve (40; 40A, 40B, 40C); - a volume flow V̇ F of the working fluid through the thermodynamic cycle is calculated according to the formula: V ̇ F = k v ⋅ Δ p ⋅ ρ 0 Δ p 0 ⋅ ρ entrance, wherein: - Δp is defined as difference between the detected exit pressure p exit and the detected entrance pressure p entrance; - Δp 0 is defined as a reference difference between the exit pressure and the entrance pressure; - ρ entrance is defined as entrance density at the entrance of the expansion valve (40; 40A, 40B, 40C); and - ρ 0 is defined as the reference density of the working fluid; - Δp is defined as difference between the detected exit pressure p exit and the detected entrance pressure p entrance; - Δp 0 is defined as a reference difference between the exit pressure and the entrance pressure; - ρ entrance is defined as entrance density at the entrance of the expansion valve (40; 40A, 40B, 40C); and - ρ 0 is defined as the reference density of the working fluid; - using the calculated volume flow V̇ F, the mass flow ṁ F is calculated by the formula: m ̇ F = V ̇ F ⋅ ρ entrance; - a cooling power and/or a heating power ( Q̇) of the refrigeration machine (1; 2) and/or heat pump (3; 4) is determined as a function of the mass flow ( ṁ F) of the working fluid; and - the energy efficiency of the refrigeration machine (1; 2) and/or heat pump (3; 4) is evaluated by comparing the cooling power and/or heating power ( Q̇) to an electrical power ( P el) used to power the refrigeration machine and/or heat pump.