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Abstract
A performance comparison of experimental results for CO2 trans-critical cycle is presented for an overview of the current level of technology. The published performance data were collected as research objects through comprehensive literature review on experimental research. The methods for data processing, error analysis, and performance evaluation are introduced in the research methodology section. Through the proposed research method, 28 groups of performance results from developed prototypes or test rigs are compared and analyzed using the coefficient of performance and the second law efficiency of thermodynamics. A discussion of the performance comparison between developed CO2 devices and commercial products of synthetic working fluid is also presented based on China's national standards (General Administration of Quality Supervision, Insection and Quarantine of the People's Republic of China 2001, 2003). Based on the comparison results, the state-of-art and possible research directions for CO2 trans-critical cycle technology are summarized and presented.
Nomenclature
| AC | = | air conditioning |
| AAC | = | automotive air conditioning |
| AT | = | approach temperature, °C |
| A | = | air source or air sink |
| B | = | brine water source |
| C | = | cooling |
| COP | = | coefficient of performance |
| DB | = | dry bulb temperature, °C |
| DC | = | direct calculation |
| DHW | = | domestic hot water |
| EC | = | estimated calculation |
| ECU | = | environment control unit |
| G | = | ground source |
| GHP | = | ground source heat pump |
| H | = | heating |
| HP | = | heat pump |
| HPWH | = | heat pump water heater |
| IHX | = | internal heat exchanger |
| R | = | refrigeration |
| R&HP | = | refrigeration and heat pump |
| RAC | = | residential air conditioning |
| Recip | = | reciprocate |
| T or t | = | temperature, °C |
| TCC | = | trans-critical CO2 cycle |
| TD | = | temperature difference, °C |
| TH | = | temperature-enthalpy |
| TST | = | two stage |
| W | = | water source or water sink |
Subscripts
| a | = | air |
| amb | = | ambient |
| C | = | reverse carnot cycle |
| ex | = | exergy |
| ex_c | = | exergy for cooling |
| ex_h | = | exergy for heating |
| evap | = | evaporating |
| gc | = | gas cooler |
| h | = | high temperature side of cycle |
| hw | = | hot water or setpoint for water heating |
| in | = | inlet |
| ind | = | indoor |
| l | = | low temperature side of cycle |
| LZ | = | Lorentz cycle |
| m | = | mean value (average value) |
| mh | = | mean value for high temperature side of cycle |
| ml | = | mean value for low temperature side of cycle |
| o | = | outlet |
| out | = | outlet |
| p | = | practical results from experiments |
| r | = | refrigerant |
| w | = | water |
| sf | = | secondary fluid side (coolant side) |
| 1, 2, 3, 4 | = | state points in cycle |
Greek
| η | = | Efficiency |
| Δ | = | Difference |