## 3 Results and Discussion
### Temperature Monitoring of Prototype Equipment
tions inside the chambers was possible with a properly functioning system for controlling cooling units. The heat exchange process (the condenser fan operation) was regulated by a high pressure switch. When the value of 16 \(\pm\) 4 bar was exceeded, the fan was turned on; otherwise, it was turned off. In the modules, the controller also protected the chiller. If the evaporator return air temperature dropped by more than 2 \({}^{\circ}\)C from the set point, the low temperature alarm was triggered after 20 min. A protection system against too high temperatures has also been developed and installed in the modules. If the value increased by more than 5 \({}^{\circ}\)C (compared to the proper value), the alarm was also triggered after 20 min. Moreover, the refrigeration unit was protected against too low or too high pressure of the refrigerant by appropriate pressure switches. They were plugged in series into the compressor power supply electric circuit and, in the event of overpressure, they switched off the compressor power supply. It was restored when the pressure returned to the recommended value plus or minus the differential. To protect the products stored in the boxes of the cooling module against freezing when the external temperature dropped below 0 \({}^{\circ}\)C, all boxes were heated with an additional heater. The analysis of the influence of negative ambient temperature on the operation of cooling and freezing modules was performed. It was not possible to verify their operation in real winter weather conditions, due to the duration of the research. However, when analyzing the lowest temperatures in Poland in the last five years [31], it was concluded that they did not reach \(-\)30 \({}^{\circ}\)C over longer periods. Figure 8: Thermograms for the filled chamber 2 of the cooling module immediately after storage. Figure 9: Thermograms for the filled chamber 2 of the freezing module immediately after storage. For products stored in the freezing module chambers, the minus outside temperature poses no risk of damage. In the developed solution, the cooling system was turned off (there was no need for it to operate), and the storage temperature in the chambers was maintained at the level required for frozen products (approximately \(-18\)\({}^{\circ}\)C). However, when the temperature in the chamber increased, the refrigeration unit was restarted. This was possible with the installation of an appropriate compressor oil sum heater. On the other hand, products stored in the refrigeration module chambers, when exposed to negative ambient temperature, may be damaged. In order to prevent the temperature inside the boxes of the refrigerated cabinet from lowering (to negative values), heaters with a power of 500 W were used. This value was sufficient, even at the outside temperature of \(-30\)\({}^{\circ}\)C (which, as can be seen from the charts, was not achieved in Poland even in the coldest months). Even if such a temperature occurred, these are short-term periods and will not cause undesirable effects. The device had a cooling power of 410 W, and ensured trouble-free achievement of a sufficiently low temperature with a difference of \(\Delta\)T = 30 \({}^{\circ}\)C. The heaters had a power of 500 W; thus, by analogy, they ensured a temperature increase of even \(\Delta\)T = 35 \({}^{\circ}\)C. The applied solutions allowed to guarantee the proper operation of the cooling and freezing modules in the analyzed environmental conditions.