SophiA project: HKA Lab test progress

SophiA HKA (Karlsruhe University of Applied Sciences) Lab test is intended to provide a better understanding of the cooling system in in different climate zones.

SophiA HKA Lab test is intended to provide a better understanding of the cooling system in the field.


Picture of the cold room
Small refrigeration cell and its components, placed outside

It is built inside a small cooling chamber where the three different temperature levels are created with the same components as in the containers. In addition, thyristor-controlled resistance heaters are installed to simulate the higher heat fluxes at the four different demo locations.


Initially, it was planned to have a plate HX as a cascade heat exchanger since the cost would be much lower and the space needed would be less compared to a tubes-in-shell HX.

However, the lab tests showed that a height difference is required in order to push the liquid out of the plate, thus reducing the heat exchanging area. The tests also showed a sufficient and homogeneous ice growth in 8 hours and that the thermal energy storage could hold the ice for over 50 hours with no additional heat input into the chamber.


The design of the CO2 cycle then changed after discussions with many experts. The fear was that the oil of the CO2 compressor could be trapped at the lowest point of the cycle, which is the bottom of the thermosiphon. The flow velocity of the two-phase refrigerant is not sufficient at this point to entrain the oil and return it to the compressor.


The CO2 system was therefore modified, and results of the -30°C room will be shown soon.


Sources :

SophiA project (Sustainable Off-grid solutions for Pharmacies and Hospitals In Africa) - Newsletter n°3 (october 2023)

Présentation of the cold room :