Integrated CO2-CHP system
Brunel - a UK University - and 14 industrial partners in the commercial refrigeration sector have presented an innovative integrated energy system which has been designed to meet the needs of medium and large supermarkets and can be tailored to the use of a variety of local power generation and sorption refrigeration technologies. The system utilizes the energy released by a combined heat and power (CHP) system to drive a sorption refrigeration system which in turn is used in a cascade arrangement to condense the CO2 refrigerant of a subcritical CO2 refrigeration system. This ensures operation of the CO2 refrigeration system in the subcritical region all the time and at a constant condensing temperature which ensures high energy efficiency throughout the year. The CHP module can be based on an internal combustion engine driven by any fuel or micro gas turbines. The sorption refrigeration system can use absorption or adsorption depending on the temperature of the heat available from the CHP plant and the desired condensing temperature for the CO2 refrigeration plant. The refrigeration system uses CO2 as a secondary refrigerant for the medium temperature (MT) cabinets and direct expansion (DX) for the low-temperature (LT) cabinets. This maximizes the system efficiency as the compressor power for MT refrigeration which is the predominant load in a supermarket is replaced by a much lower pump power to pump the liquid refrigerant to the refrigerated cabinets. The system can also be employed with cascade CO2 refrigeration systems for retrofit or new applications. Tests in the laboratory have shown that the LT system delivers a steady state COP of 4.0 at an evaporating temperature of -32°C and condensing temperature of -7°C. The COP of the MT system is very high, exceeding 50, due to the low power requirement of the pump. System simulation and energy analyses of a conventional R404A system and the integrated system in a 5000 m2 sales area supermarket has shown the integrated energy system to produce energy savings of 30%.