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• Numerical modeling of thermoacoustic devices can be classified into 1-D linear and 2-D/3-D non-linear models. • Linear thermoacoustic models lose their utility, in the high amplitude and high frequency regime. • CFD modeling has proven to be an effective tool in capturing the nonlinearities associated with standing wave thermoacoustic devices. • Flow dominance in a 2-D plane inside SWTADs has allowed the performance evaluation of these devices utilizing 2-D CFD models. • CFD modeling of standing wave thermoacoustic devices primarily focus on stack and the region around it. Global environmental concerns have brought the challenge of developing renewable energy technologies to cope up with the world energy needs. Thermoacoustic devices present themselves as a viable alternative to replace conventional refrigeration and power systems due to their minimal carbon footprint. These devices involve complex flow physics encompassing transient phenomenon and conversion of acoustic and thermal energies for their efficient performance. With the rapid advancement in computational capabilities, extensive numerical work is carried out to gain detailed understanding of the thermoacoustic devices. In this paper, a detailed review of the numerical modeling techniques that have been applied in the field of Standing Wave Thermoacoustic Devices (SWTAD) is carried out. At first, a brief review of analytical method is presented and the need for numerical modeling is highlighted. Numerical modeling techniques ranging from simplified linear to detailed Computational Fluid Dynamics (CFD) models are reviewed in detail. Model configurations, capabilities and tools developed and utilized so far in the research area are summarized. Challenges associated with SWTAD and applications modeled using CFD are discussed. The paper concludes with some useful recommendations regarding the numerical modeling of thermoacoustic devices. [ABSTRACT FROM AUTHOR]

Life Cycle Climate Performance (LCCP) is a widely accepted metric to evaluate the carbon footprint of air conditioning (AC) systems "from cradle to grave." This paper: (1) reviews the invention and evolution of LCCP, including a comprehensive timeline and bibliography; (2) documents the successful application of LCCP in the replacement of HFC-410A with HFC-32 in room air conditioners; (3) compares the conceptual frameworks and the operational approaches; and 4) reflects on the drawbacks of current LCCP research and points out possible future work. The major policy-relevant findings are: 1. The indirect emissions caused by energy consumption is 70 to 80 percent of the LCCP of AC systems in most countries but will decline in importance as electric power supply shifts rapidly from fossil fuel to renewable energy sources, which have near-zero carbon intensity; 2. The embodied greenhouse gas (GHG) emissions in refrigerant manufacture are, in most cases, negligible but the physical and chemical properties are crucial for system optimization for low carbon footprint; 3. The LCCP metric can be used for multiple purposes such as refrigerant selection and AC system architecture optimization; and 4. Data limitations in material manufacturing and the carbon intensity of electric power are the most significant challenges. Finally, this paper describes a variety of methods to fill in data gaps, including the correction factor method , the data-driven method , and the database searching method. The next-generation LCCP will be an enhanced evaluation process considering local climate, heat islands, and local power supply characteristics. [ABSTRACT FROM AUTHOR]

• Vapor-compression load can provide high quality ancillary services. • Fast load balancing control causes superheat regulation issues (wet compression). • A gain-scheduled feedforward plus PI controller can better reject disturbance. • The proposed controller is effective in avoiding wet compression. Utilization of renewable energy resources, such as solar and wind, has seen rapid growth on the power grid worldwide. To mitigate the adverse impact of these volatile generation on the reliability of the power grid, fast balancing services are increasingly procured by system operators from various resources, such as flexible air-conditioning and space heating loads. Recent work of the authors has demonstrated technical feasibility and various benefits of using variable-speed vapor compression equipment for two fast load balancing services, namely frequency regulation and solar photovoltaic power smoothing. A major control issue was also identified in prior experimental tests: the drastic changes of the compressor speed for fast load balancing have caused severe superheat regulation issues including oscillations and even wet compression. To this end, a gain-scheduled feedforward and proportional integral (PI) controller is proposed and presented in this paper, which uses the real-time compressor speed in determining compensating control actuation of the expansion valve to mitigate the disturbance effect. Both simulation and experimental validations of the proposed control strategy were carried out with a 3-ton variable-speed heat pump. Test results have shown that the proposed controller is effective in improving the superheat regulation performance for three load balancing scenarios, i.e., compressor speed step changes, frequency regulation and photovoltaic smoothing. The demonstrated performance gains include fast post-disturbance recovery of the superheat with the settling time shortened by 63% to 83%, complete avoidance of wet compression and enhanced transient energy efficiency. [ABSTRACT FROM AUTHOR]

For traditional air cooling/heating process in HVAC system, only single temperature of water generated by mechanical equipment is used to handle air cooling/heating load. However, there is the potential to simultaneously use waters at different temperatures to finish air cooling/heating process, which has shown a significant energy-saving effect in previous studies. Currently, there is no theoretical method for efficiently guiding the simultaneous use of multiple energies, especially natural/waste energies, for handling air cooling/heating load. Thus, this paper proposes a construction method for air cooling/heating process based on grade match between energy and load (GMEL). Considering the air cooling/heating process of typical electronic factory in Beijing as example, new air cooling/heating systems are constructed according to load grade and local natural/waste energies. Furthermore, the energy use is compared with that of traditional air cooling/heating system. The results reveal the following: (1) The GMEL method can construct air cooling/heating process that fully uses natural/waste energies to directly handle air load as much as possible, applies water at different temperatures generated by mechanical equipment to handle the corresponding grade of load, and realizes mutual utilization of air cooling and heating loads. (2) The energy-savings rate of the constructed air cooling/heating system of typical electronic factory in summer/winter is 26.7%/52.4%. The static payback period is 0.83 year. (3) The specialized air cooling/heating processes are different for different local natural/waste energies and economic condition. The method will promote the full usage of renewable energy worldwide, and significantly improve the energy efficiency of mechanical cooling/heating source. [ABSTRACT FROM AUTHOR]