Search

A novel combined cooling, heating and power (CCHP) system is proposed based on mixture consisting of CO2 and organic fluids to meet the seasonal energy demand in buildings. Thermodynamic model was constructed based on the laws of thermodynamics, and seasonal operation modes were also established. Techno-economic performance was analyzed and the performance of mixture consisting of CO2 and organic fluids compared with CO2 and pure organic fluids. Results show that the temperature of the turbine inlet in trans-critical power cycle should be 10 °C lower than the heat source temperature, with the turbine inlet pressure being approximately 1.4 times as large as critical pressure. Turbine inlet temperature is negatively correlated to the payback period and levelized energy cost while turbine inlet pressure is positively correlated to the system economic performance. The carbon dioxide content is negatively correlated to net power output, thermal efficiency and exergy efficiency, while coefficient of performance will hit the bottom with the carbon dioxide content, except CO2/Propane. For the carbon dioxide content is between 5 % and 10 %, the system overall performance is also close to optimal value. In general, CO2/R134a (0.10/0.90) and CO2/R1234ze(E) (0.10/0.90) is recommendable.

The stand-alone energy production for power generation, heating or cooling is an usual method for low-medium grade energy utilization. To enhance the energy utilization efficiency, a combined cooling, heating, and power (CCHP) system, which is based on two-stage vapor compression cycle (TSVCC) and organic Rankine cycle (ORC), is proposed with temperature and humidity independent control (THIC). The essential parameters are changed to enhance the CCHP performances based on the thermodynamic model constructed. Moreover, the cooling performance are evaluated under different energy-supply scenarios, and the coupling effects of the CCHP are demonstrated through the THIC strategies. The results display that when the return air and fresh air are treated with energy of corresponding grade respectively, the higher outdoor relative humidity and the lower fresh air ratios are beneficial for enhancing refrigeration performance. The adverse effects of condensation temperature on both the economic and environmental performance far surpasses that of sub-cooling degree. With a rise of 10 °C in condensation temperature and sub-cooling degree, the economic performance decreases by 27.89% and 3.7% respectively, while the environmental performance decreases by 24.33% and 0.35% respectively. Furthermore, the proposed system can be switched to variant models according to different strategies in seasons to improve efficiency of energy utilization, which could be used in engineering applications.

Owing to different temperature rages of power generation and refrigeration in the cogeneration system, for the sake of selecting the working fluids that are suitable for both power generation and refrigeration simultaneously, 17 commonly used working fluids are evaluated in this paper, based on an organic Rankine cycle coupled with a two-stage vapor compression cycle system in different geothermal fluid temperatures. The performances of working fluids under different working conditions, and the maximum power generation as well as cooling capacity are analyzed. Additionally, the main parameters are analyzed to optimize the system performance. The results indicate that net power output has a local maximum where it corresponds to the optimal evaporation temperature. Besides, the lower the critical temperature, the greater the thermal conductance, and the pressure ratio decreases with evaporation temperature. Hydrocarbons all have higher total heat source recovery efficiency. R1234yf, propane and R1234ze, R152a have excellent maximum net power output when the geothermal fluid temperature is low and high, respectively. R134a always has better maximum net power output and cooling capacity. The net power output is used for cooling, and the COP is closed, therefore, maximum net power output results in the maximum cooling capacity. In addition, that of propane and R1234yf are excellent until the geothermal fluid temperature are 140 °C and 120 °C separately. R1234ze and R152a are good when the geothermal fluid temperatures are 140 °C and 150 °C, respectively.

This paper aims to fill the research gap on the effect of steam quality and non-condensable gas on heat-carrying fluid productivity, system performance and optimization. First, the effect of the temperature and quality of the heat-carrying fluid and non-condensable gas (NCG) content on the production parameters was evaluated. After that, three energy conversion systems which included a single flash (SF) system, an organic Rankine cycle (ORC) system and a single flash combined ORC (SFORC) system were constructed in this paper to utilize the heat-carrying two-phase flow with non-condensable gas. Finally, based on thermodynamic modeling, the effects of the temperature and quality of the heat-carrying fluid and non-condensable gas content on the performance and optimization of the three power conversion systems were investigated. The results show that single-phase heat-carrying fluids are more productive than two-phase heat-carrying fluids. NCG is always detrimental. The heat-carrying fluid temperature and quality are positively correlated with system efficiency and negatively correlated with the net power output. In the comparison of comprehensive performances, the SFORC system is the better, and the ORC system and the SF system are the worse. The optimal net power output of the SF system, the ORC system and the SFORC system is 4883 kW, 6557 kW and 7251 kW, respectively.