This paper presents a mathematical model of heat pump exchangers and their thermal interaction with a fan for an air dryer. The calculation algorithm developed for the finned heat exchangers is based on the ε-NTU method, allowing the determination of air side and refrigerant side heat transfer coefficients, evaporator and condenser heat capacity and air parameters at the dehumidifier outlet with known exchanger geometries, initial air parameters and mass flow rate. The model was verified on an industrial dehumidifier test bench. This enabled the heat transfer coefficients for the exchanger to be calculated as a function of the speed and, therefore, the power of the fan’s drive motor. An increase in fan performance on the one hand results in an increase in the heat transfer rate, but, on the other hand, it causes an increase in the total energy consumption of the motor. Thus, while it causes an increase in drying capacity, it also causes an increase in the energy consumption of the dehumidifier. In order to optimise the unit in terms of energy consumption, it is therefore necessary to determine a function that relates the amount of heat exchanged to the efficiency of the fan.

This paper presents the thermal calculations of an air-finned heat exchanger working at temperatures above zero degrees and their verification through testing on a real device. Then, on the basis of the calculations, the influence of evaporation temperature on the drying rate of the constant speed of air flowing through the exchanger was analysed. A quantitative analysis of the effect of the temperature difference between the air being dried and the evaporator on the acceleration of the process was performed. For the analysed case, the same water mass (condensate) can be obtained for an evaporation temperature of 0 °C almost four times faster than for 10 °C. To compare temperature cases, the SMER (specific moisture evaporation ratio) was calculated, which allowed the systems to be compared in terms of energy consumption. The theoretical analysis showed that by reducing the boiling point by 10 degrees, we could increase the SMER from 0.51 ${\mathrm{kg}}_{{\mathrm{h}}_{2}0}/\mathrm{kWh}$ to 2.18 ${\mathrm{kg}}_{{\mathrm{h}}_{2}0}/\mathrm{kWh}$. After receiving the experimental results and including the efficiency of the system, these values were, respectively, 0.44 ± 0.01 ${\mathrm{kg}}_{{\mathrm{h}}_{2}0}/\mathrm{kWh}$ and 1.91 ± 0.06 ${\mathrm{kg}}_{{\mathrm{h}}_{2}0}/\mathrm{kWh}$.

This article describes how an energy audit of equipment and the resulting design changes can have a major impact on reducing the electricity consumption of refrigeration equipment. The legal basis introduced by legislation forcing work on the improvement of refrigeration unit is provided. Eight points detail and describe the changes applied to the construction of cooling units. Additionally, a list of the refrigerants which are used is presented, along with the essential parameters of their work. The following analysis includes a description of the research performed along with the measured and calculated results for individual optimisations. The basic parameters that were used for comparison are: daily electricity consumption [kWh/24 h] and the temperature of the packages placed in the device [°C]. Finally, the percentage differences in energy consumption for each modernisation are summarised in a tabular form. The device used for the tests was the VARNA refrigerated rack, model 900, manufactured by P.P.H.U. JUKA Sp. z o.o. sp. k.