Danish sensor manufacturer HB Products lowered the energy consumption of a Romanian cold storage facility’s DX (direct expansion) ammonia/NH3 (R717) system by 43% after switching it from superheat control to vapor quality control.
Although vapor quality control has been tested in Australia and the U.S. with favorable results, the Romanian installation is said to be the first of its kind in Europe.
This project was presented by Henrik Kudsk, HB Products’s Product Manager, and Adrian Balaoi, CTO of contractor AB Tehnic, during Part 2 of ATMOsphere (ATMO) Europe Summit 2022’s Refrigeration Case Studies session.
The cold storage facility, located in Halchiu, Romania, is used predominantly for storing frozen meat. It employs a 250kW (71TR) refrigeration system charged with 200kg (441lbs) of ammonia. The system’s evaporation temperature is -28°C (-18°F) with the condensation temperature at 42°C (108°F).
The system has two Sabroe compressors with economizers. All the equipment was installed inside a container for exterior mounting at the facility. Cooling is provided to two rooms via seven Thermofin DX evaporators.
Switching to vapor quality control
With the support of the cold storage operator, contractor AB Tehnic and Frigo Consult, HB Products, installed vapor quality control sensors on each evaporator. Pressure sensors and temperature sensors were also installed. The European team was supported by Stefan Jensen Managing Director of Australian system manufacturer Scantec Refrigeration, a leading expert on ammonia refrigeration systems.
A vapor quality sensor detects the small amount of liquid coming from the evaporator, providing a 4–20mA signal that can be used in the control system. The expansion valve is then controlled based on the vapor quality – instead of superheat. This can have significant benefits on boosting energy efficiency.
This sensor can be used with all refrigerants, not just ammonia. It is also suitable for use in traditional liquid overfeed ammonia systems, as well as DX models.
After installation, the sensors were put to the test. The system was switched from superheat to vapor quality control without changing anything else.
In the Romanian cold storage facility, the superheat was around 7K before the change. This was reduced to nearly 0 once the sensor was installed. As the system was running more efficiently, there was no longer a great need for superheat. The pressure loss from superheat was also eliminated, further improving the evaporator’s performance.
As a result, the energy consumption was reduced by 43% for the complete cold storage facility. Typical savings were 20% in full load and 50% during part load.