Integration of heating and air conditioning into a CO2 trans-critical booster system with parallel compression Part I: evaluation of key operating parameters using field measurements.

This paper investigates key operating parameters of a supermarket in Sweden where heating and air conditioning are integrated into the CO2 trans-critical refrigeration system. The Supermarket has applied several features of a state-of-theart system including space and tap water heating, air conditioning, and parallel compression. Using field measurements data, the key operating parameters in the CO2 system are studied in a warm summer month and a cold winter month. The warm month study shows that the CO2 system provides the required temperatures for air conditioning demands; the pressure in the receiver is regulated to provide 7-8°C forward secondary fluid. Parallel compression is used to control the receiver pressure for ambient temperatures higher than 15°C. The high pressure side of integrated CO2 system is controlled mainly for heat recovery in winter. The pressure is fixed to 80-85 [bar] and the gas cooler is by-passed to recover the entire rejected heat when ambient temperature is very low. The heat recovery function of the system is analysed for both tap water and space heating circuits. The measurements show that the system is able to provide the high tap water temperature of 55-60°C throughout the year. The system is also able to provide the space heating forward temperature of up to 45°C. Analysis of the key operating parameters of the integrated CO2 system shows that it fulfils the temperature requirements of refrigeration, air conditioning, hot water, and space heating. The loads and energy efficiency of these functions of the systems have been studied in part II of this paper.