The application of the CO2 transcritical system in the Hawkes Bay Cool Store

Maya VisnicUncategorized

The Hawkes Bay Cool Store complex consists of the three freezer rooms and three adjoining chiller rooms. The refrigeration system is a Transcritical R744 System encompassing a Low and High 2-stage system for the Low Temperature Rooms and a Medium Temperature stage for the Medium Temperature Rooms.

The refrigeration cooling system includes 2 x GEA Bock transcritical R744 compressors for the Medium Temperature Stage of the system, 2 x GEA Bock transcritical compressors for the Low Temperature Stage of the system and 2 x GEA Bock compressors for the High Stage of the Booster System, the Low Temperature Stage will discharge into the High Stage of the Booster System.

The GEA Bock HG (Hermetic Gas-cooled) range of semi-hermetic compressors offers traditional suction gas-cooled compressor state of the art technology. These compressors of the highest quality standard excel in their running comfort, easy maintenance, efficiency and reliability. Suitable as standard for conventional or chlorine-free HFC refrigerants.

The refrigerant CO2 within refrigeration technology, carbon dioxide (CO2) is known by the name R744 and has a long history. It is a colourless gas which liquefies under pressure and has a slightly acidic smell and taste. Carbon dioxide has no ozone depletion potential (ODP = 0) and a negligible direct effect on global warming (GWP = 1) when used as a refrigerant in closed systems. It is not combustible, is chemically inactive and heavier than air. Carbon dioxide has a narcotic and asphyxiating effect on humans only at higher concentrations. Carbon dioxide is available naturally in large quantities.

Special features GEA Bock compressors are of extremely high quality and robust. Additionally, the drive, valve plates and seals of our compressors have been optimized with regard to the natural refrigerant R744. Further motor adjustments ensure broader operating limits and highest efficiency. The compressors therefore convince through their long life-time, sustainability and highest reliability.
The Medium Temperature load estimate is 27kw – providing an operating temperature of +2 degrees Celsius, while the Low Temperature load estimate is 48kw – providing an operating temperature of -22 degrees Celsius.

All compressors will be operating on variable frequency drives up to 70 Hz to the meet the cooling duty required while at the same time ensuring the plant is operating efficiently to meet the client’s operating restraints.

The refrigeration is controlled by a Carel pRack transcritical control system which features an EEVS (Electronic Expansion Valve Synchronization) and capability of direct management of 2 stepper electronic expansion valves that optimize the machine performance increasing the interaction between the refrigerating unit and the up valves and the plant safety thanks to the ultracap technology.

The new Transcritical pRack platform is ideal for CO2 booster systems due to ability to manage directly and at the same time with a single control system, the main components of a CO2-based refrigerating unit:
– Medium Temperature compressors
– Low Temperature compressors
– gas cooler
– intercooler
– high pressure valve
– flash gas valve