Integrated Cascading Plant

Abstract

An integrated refrigeration and air conditioning plant working with environmentally friendly natural refrigerant carbon dioxide (CO2) and an ozone friendly non CO2 refrigerant. The low temperature refrigeration is provided by evaporating CO2 and the fluid is used as a secondary refrigerant, predominantly in liquid mode, for medium temperature refrigeration. The heat rejection from CO2 occurs to another upper stage cascaded refrigeration system that operates with a ozone friendly non CO2 refrigerant. Since air conditioning applications require cooling at temperatures higher than refrigeration for food sector, cooling for this range is derived from the non CO2 refrigerant.

Description

FIELD OF INVENTION[0001]The invention relates to refrigeration and air conditioning systems, including such systems when used in a supermarket setting. It specifically addresses the lacuna in integrating seemingly different, but intricately related, domains of cooling requirements at various temperature levels. The objectives are sought to be achieved in a manner that is environmentally friendly, energy efficient and operated in an intelligent way that marries the thermodynamic, fluid dynamic interface at two different refrigerants.BACKGROUND TO THE PRESENT INVENTION[0002]In this document the numbering of refrigerants is in accordance with the protocol recommended by the learned societies relevant to the profession of refrigeration and air conditioning, such as American Society of Refrigeration, Heating and Air conditioning Engineers (ASHRAE), International Institute of Refrigeration (IIR), Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH), Japan Society of...

AI Technical Summary

Benefits of technology

The patent is about a system that uses both CO2 and non-CO2 refrigerants in a cascading system. The patent explains that the preferred temperature between the CO2 circuit and the non-CO2 refrigerant circuit is -7°C or higher. This allows the non-CO2 refrigerant circuit to use smaller compressors and increase efficiency. The invention also mentions that partial evaporation of CO2 in the system can decrease the amount of liquid CO2 needed and offset the increased operating pressure. Additionally, the patent mentions the use of a compact water cooled heat exchanger and heat recovery, which can be more efficient than current state-of-the-art systems. Overall, the invention provides technical improvements in efficiency and reduced size of components in refrigeration systems.

Problems solved by technology

The current Australian refrigeration and air conditioning trade practices are unable to reduce the leakages below 10% of initial charge per year.

While this may not appear much, the amount of supermarkets Australia wide is 1500 and therefore the collective damage caused by their leveraging emissions is high.

However, CO2 has not made much of market penetration due to (i) requirements of high pressures in operating systems and (ii) problems associated with its storage in liquid form.

This gives rise to a significant safety hazard (suffocation) if there is any significant leakage of CO2 into the circulating air.

In order to limit the operating pressures, the cascading medium temperature in conventional refrigeration systems is about −10° C. The upper stage cascading with a synthetic refrigerant mandates cooling to be obtained at a maximum of −15° C. At this temperature the specific volumes of refrigerants are so large that either large reciprocating compressors need to be used or screw compressors have to be chosen, both options being economically unattractive.

As foreshadowed above, use of CO2 circulation in cooling coils of air conditioning system has the inherent danger of possible leak of the gas into the air stream that is induced in to public areas.

This necessitates large wall thicknesses for the receiver and consequent engineering and economic draw backs.

Further, independent controls do not allow fine tuning of matching interfaces resulting in high energy consumption for current refrigeration.

The cascade plant controls are somewhat ad-hoc resulting in hunting and unstable operation under dynamic conditions experienced in a supermarket environment, such as refrigerated cabinets are being opened and closed by shoppers.

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