Search

To clarify main factors that affect the discharge pressure and compressor frequency on air-source transcritical CO2 heat pump water heater, an experimental research is designed in which the discharge pressure is controlled by varying the expansion valve opening and the plant is tested at three different compressor frequencies (25, 30 and 35 Hz). The results show that both the gas-cooler outlet status of CO2 and the water-inlet temperature have significant effects on Q and COP. Qmax (the maximum heating capacity) and COPopt (the optimal COP) exist in the system. With the compressor frequency increasing from 25 Hz to 35 Hz, Qmax shows a rise of 30.0% and COPopt is decreased by 25.1%. Compared to COPopt, the COP corresponding to Qmax drops in a mild way. Thus, the system should be operated in a suitable situation between COPopt and Qmax under the precondition to satisfy the actual heating needs. This paper not only provides reference for designing and further study on transcritical CO2 cycle, but also an operational strategy of air-source transcritical CO2 heat pump.

In order to investigate the factors that affect the hot water outlet temperature on air-source transcritical CO2 heat pump water heater, an experimental research is designed where the expansion valve opening is controlled to adjust the discharge pressure. The experiments are conducted at different compressor speeds, water-inlet flowrates and water-inlet temperatures. Then, a new indicator named unit temperature-lift cost (UTC) is proposed to evaluate the lifting effects of hot water temperature. The results show that the rise of hot water temperature leads to the decrease of the maximum coefficient of performance (COP) but the increase in both the gas-cooler outlet temperature at the optimal status and the optimal discharge pressure, which are mainly caused by the variations of gas-cooler outlet status. At ranges of compressor speeds, water-inlet flowrates and water-inlet temperatures, the UTCs always show a drop with a higher required hot water temperature, and the corresponding average UTCs are 0.054 °C−1, 0.042 °C−1 and 0.099 °C−1, respectively. According to the results, the method of controlling the water inlet flowrate should be taken as a priority to lift the hot water temperature of the system. The compressor speed is suitable to meet the needs of increasing hot water temperature and heating capacity simultaneously. It is not advisable to increase the hot water temperature by adjusting the water inlet temperature.

In the current globalized supply chains, firms are more likely to suffer from supply risks caused by various sources, including internal production default and external disasters. This chapter focuses on the operational management problem related to the supply risk within the supply chain scope. We introduce a number of recent and important research developments, including problems in vertical supply chain interaction, horizontal supply chain competition, and supply chain network with both horizontal and vertical competitions. Analytical models are presented for each problem, and the main results are elucidated. Moreover, further research directions along with big data trends are emphasized as well.