A study of high efficiency CO2 refrigerant VRF air conditioning system adopting multi-stage compression cycle

CO2 refrigerant is expected to be use for air conditioners due to its environmental property of GWP = 1, non-flammability and low toxicity and has already been applied to hot water supply system, refrigerators and freezers. However, since cycle COP of CO2 is poorer than that of HFC in applying to air conditioner, it cannot be expected to improve the performance significantly by simply improving the efficiency of a conventional single-stage cycle and components consisting of the cycle.  Therefore, it is important to improve the cycle efficiency, especially in the performance of cooling which is a weak point of CO2. Challenges also lie in reducing weight of components such as compressor and heat exchangers resulted in weight gain to resist high pressure and to achieve high efficiency in the system. In this study, a prototype of CO2 refrigerant VRF air conditioning system is constructed and evaluates the performance. The system is adopting the four-stage compression cycle applying a new type compressor and heat exchangers and so on aimed for high efficiency cycle and reducing weight As a result of the evaluation, it is confirmed that CO2 cycle performance can be improved in similar extent to HFC refrigerant cycle. On the other hand, this high efficiency cycle consists of a lot of components and becomes more complex than HFC refrigerant cycle; therefore the size and weight of outdoor unit increases to house these components. Further technical development will be necessary to overcome these weaknesses

Evaluation and Optimization of System Performance using HFO-mix Refrigerants for VRF and Mini-split Air-Conditioner

Global demand for air conditioning is expected to increase continuously. In order to minimize the impact on the climate as a total amount of CO2 equivalent, it is essential to continue to search for better refrigerants. On the other hand, product size and cost are important factors in providing value to users. This time, while using the experiment result of the mini-split type air-conditioner reported in the past, in addition, we conducted a new experiment on multi-type VRF air-conditioner. Then, the difference in COP performance between R-410A and alternative candidate refrigerants was evaluated. In addition, we studied the product design using R-452 B, R-454 B by simulation and compare the size when the performance is made identical by changing the system specifications with alternative refrigerant candidates. As a result, common results were obtained in both systems. It was found that R-452B and R-454B have better performance than R-410A. On the other hand, it was found that these refrigerants need to increase both the indoor heat exchanger and the outdoor heat exchanger to 120% in order to obtain the same performance as R-32

Exploration of new superconductors and functional materials and fabrication of superconducting tapes and wires of iron pnictides

This paper reviews the highlights of a 4-years-long research project supported by the Japanese Government to explore new superconducting materials and relevant functional materials. The project found several tens of new superconductors by examining ~1000 materials, each of which was chosen by Japanese team member experts with a background in solid state chemistry. This review summarizes the major achievements of the project in newly found superconducting materials, and the wire and tape fabrication of iron-based superconductors. It is a unique feature of this review to incorporate a list of ~700 unsuccessful materials examined for superconductivity in the project. In addition, described are new functional materials and functionalities discovered during the project.Comment: 141 pages, 127 Figures, 14 Tables, 535 Refrence

Mechanical Properties of Abandoned and Closed Roadways in the Kushiro Coal Mine, Japan

The objective of this research is to clarify the mechanical properties and self-healing ability of Excavation Damaged Zone (EDZ) around rock caverns in clastic rock. Observations of nearly 100 closed roadways up to 50 years old, which can be regarded as very severe EDZs with no initial sealability and are up to 300 m deep in clastic rock, were made at Kushiro Coal Mine, Japan, to accomplish the objective. Most old roadways were closed, though a few remain open. Closure of old roadways was mainly due to roof deflection and/or floor heave. Large plastic deformations dominated; however, severe fractures were seldom observed in closed old roadways. Rayleigh wave velocity and hydraulic conductivity in the closed old roadways were in the range of 0.3 - 1.2 km/s and 5 x 10^[-7] - 1 x 10^[-7]m/s, respectively, and those in EDZ and EdZ (Excavation disturbed Zone) around recently excavated roadways were 1.1 - 1.8 km/s and 1 x 10^[-8] - 5 x 10^[-8] m/s, respectively. The extent of EDZ around the present tailgate was in the range of 1 m to 5 m. Mechanical excavation and prevention from water are suggested as the key points for long-term maintenance of rock repositories. Pressurization from inside the cavern to decrease the permeability of EDZ is proposed for maintenance of rock repositories in medium-hard clastic rock masses at similar depths for long periods