SPAIN: A team made up of researchers from two Spanish universities are looking for commercial licensees for a CO2 cascade refrigeration system that is said to overcome many of the current drawbacks of the technology.
In addition to an increased energy efficiency, the system developed by the Spanish research team from Jaume I University of Castellón and the Polytechnic University of Valencia is said to incorporate a number of innovative safety features which allow the system to be started and stopped safely without the need to use auxiliary cooling equipment.
While environmental concerns have led to an increase in popularity of CO2 systems, particularly amongst supermarkets, there are still a number of technical issues to be overcome surrounding the energy efficiency and safety of the systems.
Some of the problems of today’s CO2 cascade refrigeration systems revolve around overcoming the high pressures of CO2 with the system at rest, problems of overpressure as a result of failure in the feed system, difficulty in starting and stopping the systems and the need for auxiliary refrigeration equipment connected to a separate electricity generator.
This new Spanish development is said to offer a solution to these shortcomings by incorporating a high pressure CO2 storage system and a set of associated sectioning valves and different regulating pressure switches.
It is said to allow the low-temperature circuit to start up when it is at rest and the pressure in the storage tank exceeds the maximum admissible value for that circuit. In addition it is said to ensure the integrity of the system and prevents most incidents of leaking of refrigerant from the low-temperature circuit in the event of the high-temperature circuit suddenly failing or in case of failure of the circuit itself.
Although only tested experimentally in a laboratory prototype, the developers maintain proper design of the refrigeration system could increase the energy efficiency of the cycle, achieving sub-cooling of the liquid in the low-temperature circuit by cooling with the refrigerant from the high-temperature circuit.
The system incorporates a high-pressure tank (3 in diagram below), capable of withstanding pressures up to 70bar and acting as a receiver to hold all or most of the CO2 refrigerant during the stops and starts of the system or while it is undergoing maintenance. A CO2 cooling exchanger (10) is incorporated within the high-pressure tank, either as an internal coil or installed outside it. In both cases this coil or heat exchanger is used to cool the high-pressure liquid CO2 inside the storage tank. The refrigerant from the high-temperature circuit is made to flow through this heat exchanger by activating different solenoid valves. Additionally, this exchanger connects the high-temperature and the low-temperature circuits thermally, thereby allowing increases to be achieved in the overall energy efficiency.
High-pressure solenoid valves are provided at the inlet and outlet of the tank. Capable of supporting pressures up to 70bar, both valves are controlled manually or automatically by the set up regulation system.
Further information from Enterprise Europe quoting reference TOES20140513003.