Conference Agenda

The design and performance modeling of a compressor relies heavily on thermodynamic and physical models, but many times compressor models are validated and calibrated empirically. Representations of compressor performance using polynomial fits such as defined by AHRI 540 as well as more complicated mid-fidelity semi-empirical models rely on the method of test defined in ASHRAE standard 23 to produce performance data. Even with an empirical representation of compressor performance, one must understand the sources of error in this process to best understand the impact of design related changes, or how this error may propagate to system level predictions. This study will compare different compressor test facility types and evaluate the pros and cons of each cycle architecture as well as sources of measurement variation and uncertainty. Compressor performance testing facility cycles generally fall into 3 categories, (fully condensing, partial condensing, and non-condensing) which use similar components and measurement devices, but each have unique characteristics which will be highlighted. Characterization of testing variation and uncertainty will be evaluated considering short term tests, long term tests, as well as testing on multiple different compressor test facilities. Variation in compressor performance metrics will be evaluated given normal variation in setpoint stability, instrument uncertainty, refrigerant composition, and other common sources of compressor testing variation.

Millions of compressors are used in refrigeration, air conditioning and heat pump systems. Their energy consumption is the most significant contributor to the efficiency of an entire HVAC system. The component specific isentropic efficiency is used for the energetic evaluation of compressors in accordance with globally standardized test procedures. The isentropic efficiency represents a relationship between the total power input and the friction-free, adiabatic power needed when compressing a refrigerant at a defined operating point. However, compared to the Carnot cycle, the isentropic efficiency seems to be imperfect in its significance. Depending on the fluid properties of the refrigerant used, a significant proportion of the ideal compression (isothermal proportion) may lie outside the liquid-vapor region. However, it would be advantageous to take this proportion into account in the energy efficiency to emphasize the refrigerant-specific influences of compression on the cycle and the system more clearly.
Presented in this work, a new proposal for the isentropic-isothermal efficiency is to be introduced and compared with typical efficiencies discussed in the literature for the energetic evaluation of compressors. The aim of the comparison is to work out the advantages and disadvantages of the isentropic-isothermal efficiency and to assess the usefulness of its future use.

This work describes the control algorithms used for automating a test stand to impose suction and discharge pressures and suction temperature on reciprocating compressors, allowing the operation to be evaluated under different conditions within the compressor envelope. Since the objective is to impose conditions on the compressor, a superheated gas cycle was considered. In addition, an auxiliary circuit was considered, which is responsible for cooling the fluid as it passes through the reservoir in the intermediate region of the main circuit. This auxiliary system is particularly important to achieve low discharge pressure conditions even after the compressor under test has been operating for a long time. To reach the entire operating envelope of several compressor models, an automatic procedure is proposed to insert and remove the refrigerant fluid from the test stand. For this purpose, a reservoir tank was connected through solenoid valves to both the discharge and service lines, making it possible to control the volume of fluid in the main circuit. The dynamics of the variables of interest were identified using experimental data and the resulting models were used to tune automatic controllers for imposing the compressor operating condition in terms of pressures and temperature. The current version of the test stand is able to automatically impose any condition inside the operating envelope of a family of compressors and keep the compressor operating around this point with tolerances of less than 1 °C.

In this paper, the differences between APF of Japanese and Chinese standards were analyzed. In the APF standard of Japanese, the intermediate condition had the greatest influence on APF. Therefore, in the process of researching compressors for the Japanese market, it was necessary to focus on improving the energy efficiency level of middle and low frequency. Some ideas for the development of high-efficiency compressor was also provided. With the improvement of energy efficiency of air conditioning, compressor design should dare to innovate and dare to break through the routine. Based on innovative technologies such as rocker blade, high-efficiency technology of eccentric part of crankshaft and breakthrough of motor, the energy efficiency of compressor was greatly improved compared with the base compressor, and the improvement rate of intermediate cooling condition was 9%, and the improvement rate of other conditions was about 5%. Equipped with Japan's high-efficiency air conditioning system, the APF was reaching a higher level in the industry.

Due to its compact design and reliable performance, the Roots pump is deemed suitable for hydrogen recirculation in fuel cell vehicles (FCVs). Nevertheless, the significant noise issue associated with this pump type poses a substantial barrier to its widespread adoption in FCVs. This study employed numerical simulation to analyze the noise radiation characteristics of the Roots pump. The hybrid computational aeroacoustics (CAA) method was utilized, coupling a computational fluid dynamics (CFD) solver with an acoustic prediction module (APM). The CFD simulation identifies noise sources, while the APM simulates the propagation of noise from sources to observers. The numerical model was validated by comparing the simulated and experimental sound pressure level distributions. A parametric study was further conducted to explore the impact of parameters such as rotational speed, pressure ratio, and clearance on noise field, using the validated numerical model. Additionally, the noise control strategy was proposed and validated. The results demonstrate that the hybrid CAA method could effectively predict the noise field of the Roots pump. Noise control measures proposed based on the numerical model are found to be viable for reducing the noise generated by Roots hydrogen-circulating pumps in FCVs.

Aerodynamic noise is one of the important sound sources of rotary compressors. The airflow velocity is about 20m/s~50m/s near the discharge port when the high pressure refrigerant is discharging , and the airflow impacts the wall, so it forms complex vortexes, which generates aerodynamic noise. Therefore it is necessary to reduce the noise source near the discharge port of main bearing in rotary compressors. The discharge slope is redesigned, VG, serration and Helmholtz resonance chamber structure are used to control the flow. The 3D unsteady turbulent simulation is performed with DES method, then the dipole noise field is simulated using Simcenter3D. The CFD simulations show that VG and serrations help to reduce the turbulent kinetic energy in the muffler, FFT of the pressure at the muffler outlets shows a significant decrease in the pressure amplitude at 400,1000 Hz frequency interval. The Helmholtz resonance chamber works in a wider range than the design point. 3 compressors are manufactured for each scheme, the pressure at discharge port and sound power are tested. The test results show that the VG scheme reduces about 2dB in 1kHz frequency interval, and the Helmholtz resonance scheme reduces the noise from 1250Hz to 3150Hz compare to original one.