International Journal of Air-Conditioning and Refrigeration

The impact of the refrigeration sector on climate change is important and growing, with four main issues: refrigerants used, energy consumption, food losses and the life cycle of materials. It is increasingly recognized at international level, but these environmental issues are complex, and most solutions are found at national and local levels. The issue of refrigerants is now well known; solutions have already been put in place, both for the stratospheric ozone layer and for climate change, even if these solutions are currently determined in a long-term perspective (mid-century). However, these timeframes may be shortened in the future. Conversely, energy issues (energy efficiency, use of renewable energies), which have so far been insufficiently addressed in most countries, have become an urgent challenge. The same applies to the implementation of cold chains in developing countries in order to reduce food losses and their carbon impact. The dramatic increase in the use of refrigeration, including air conditioning and the cold chain, makes truly sustainable development of this sector particularly important.

This paper presents an experimental study that evaluated the effects of three different non-uniform types of clothing ensembles (Type A: short-sleeve shirt, T-shirt underwear, men’s briefs, straight trousers, socks, shoes; Type B: long-sleeve shirt, T-shirt underwear, men’s briefs, straight trousers; and Type C: long-sleeve shirt, men’s briefs, straight trousers, thick socks, shoes) with almost the same thermal insulation (about 0.52 clo) on the subjects’ local and overall thermal sensation and air movement preference under a desktop local ventilation system. The experiment was conducted in a test chamber with the mean air temperature of $24\pm 0.5^{\circ }$C and under three supply air temperatures of $16^{\circ }$C, $24^{\circ }$C, and $32^{\circ }$C from a desktop ventilation system. The results revealed that the body segments with the most critical thermal sensation were (i) forearms, hands and arms for the subjects with “A type” clothing ensemble, (ii) feet, hands and forearms for the subjects with “B type” clothing ensemble, and (iii) hands, arms, forearms and chest for the subjects that wore “C type” clothing ensemble. For the three clothing types of “A”, “B” and “C”, the values of overall thermal sensation changed from $-$0.63, $-$1.25, and $-$1.13 at $16^{\circ }$C to $-$0.31, $-$0.31, and $-$0.38 at $32^{\circ }$C inlet temperature, respectively. Also, the results indicated that upon elevation of the inlet air temperature from $16^{\circ }$C to $32^{\circ }$C, the percentages of the subjects who preferred less air movement dropped from 63%, 63%, and 50% to 38%, 25%, and 38%, respectively, for wearing “A”, “B” and “C” clothing ensembles.

Ammonia is a natural compound, used more and more in refrigeration installations of absorption and vapor compression, component sizing and more particularly evaporators pass by the mastery and prediction of heat transfer. Our study aims to retrieve experimental data from the literature and verify them with known author correlations, and the differences were observed with margins of error; a new correlation has been developed giving convincing results.

In this paper, the performance characteristics of an ejector-expansion refrigeration cycle (EERC) using R410A are investigated in comparison with that using R22 based on first- and second-law perspectives. For this purpose, a numerical model of constant mixing pressure is developed and a parametric study of the effective design parameters is implemented. The results show that at evaporation temperature ($T_e$) and condensing temperature ($T_c$) equal to $5^{\circ }$C and $40^{\circ }$C, respectively, the coefficient of performance (COP), exergy efficiency and volumetric cooling capacity (VCC) of the R410A EERC is improved by 12.91%, 12.89%, and 10.8%, respectively. Compared with the conventional refrigeration cycle, the EERC is more beneficial at lower evaporation temperature and higher condensing temperature. The COP of R410A EERC, exergy efficiency and VCC improvements over the regular refrigeration cycle are also greater than that of R22 by about 34.7%, 32.3% and 31%, respectively. Exergy analysis shows that applying an ejector in lieu of a throttle valve improved the energetic efficiency by 7.793–15.42% and by 10.59–22.79% for R22 and R410A, respectively, for the given range of evaporating and condensing temperature. In addition, the effects of the suction nozzle pressure drop, area ratio and the component efficiencies of the ejector on the EERC performance are analyzed.

The flow velocity profiles in most of the central air-conditioning pipelines are, in general, not fully developed flow and difficult to obtain the accurate flow rates by flowmeters, which are used for measuring average velocity. Especially for being at the outlet of an elbow, the accuracy of flow rate by measurement is quite low. Therefore, there are some limitations for measurements of flow rate and velocity profile by the present flow measuring technologies. The objective of this study was to establish an approach on accurate predictions of velocity profiles at different measured locations of central air-conditioning pipelines for nonuniform flow measurements by simulations of computational Fluid Dynamics (CFD). All the velocity profiles will integrate as a database for predictions by neural network algorithm for smart measurement further. In the present work initially, international experiments were employed to validate the accuracy of CFD approach. The calculations were carried out by different turbulence models. The results compared with the experimental data by Realizable $k$-$\epsilon$ turbulence model with less computing resources have great agreements. Realizable $k$-$\epsilon$ turbulence model was, therefore, determined for the predictions of central air-conditioning pipeline. According to various pipings and pipe sizes, the results for three cases show that the velocity profiles in the pipelines would not be symmetrical and has strong secondary flow. Therefore, all of the flow profiles would be integrated and analyzed as a database and assist to get accurately the measured locations of ultrasonic flowmeters. Further, this database will be combined with algorithm of artificial neural network for smart predictions.

Evaporation of defrosted water in household refrigerators and condenser waste heat utilization has been reported by many researchers but limited literature is available on the study of evaporative cooling in domestic refrigerators (condenser waste heat utilization for defrost water evaporation) with helical coil heat exchangers. This paper is concerned with evaluating domestic refrigerator performance by employing an evaporative helical coil heat exchanger before hot wall condenser which is utilized for evaporation of defrost water and reducing the superheated refrigerant temperature to condensing temperature to reduce the condenser load and improve the overall performance of a domestic refrigerator. Results show that evaporative cooling increases COP of the system by 25.3%, reduces the energy consumption of the refrigerator by 7.3% and the compressor run time by 10.6%. These experimental results also revealed that using two different thermal conductivity tube materials for evaporative helical coil condenser (Copper tube and Zinc coated steel tube) provided with less wall thickness (0.2mm) PVC coating results in good agreement for the same evaporation rate of defrosted water.

The Absorption Refrigeration Cycle Turbine Inlet Conditioning (ARCTIC) system can chill the inlet air of the turbine to maintain optimum turbine performance at all ambient temperatures. However, turbine characteristics and bell-mouth icing concerns impose a minimum temperature limitation on the chilled air. Performance guarantees may also require maintaining the inlet air temperature within a narrow range throughout the year. These considerations require accurate prediction of the chilling coil performance over a wide range of operating conditions and the development of a robust controls strategy. A modified wet-surface model is used to model the chilling coil performance. The application of the model to a 2110kW (600 RT) ARCTIC providing inlet air chilling for a MARS 100 turbine is considered. A control strategy is developed to maintain the inlet air temperature at the desired set point with varying ambient temperatures and chilling loads. The TIAC controls help maintain the inlet air temperature at 7.22^∘C to maximize turbine capacity and efficiency during most of the hot/warm days and accommodates 100% turndown. Additional safety measures are incorporated to prevent bell-mouth icing.

Water desalination unit powered by renewable energy sources is sometimes needed at places far from the energy grid lines. Consequently, even countries with rich energy resources, such as the Arabian Gulf countries, have shown strong interest in desalination processes that often use renewable energy sources. This work aims to conduct an exergy analysis of solar-powered humidification–dehumidification (HDH) unit. The exergy analysis input data are extracted from a previous work conducted in August 2020 under Baghdad conditions, 33.3^∘N latitude and 44.14^∘E longitude. The previous work’s HDH unit consisted of six parabolic trough solar collectors (PTSCs), with a total aperture area of 8.76m². Meteonorm v7.3 software was used to obtain the weather data for Baghdad City, Iraq. The HDH unit results had revealed low exergy efficiency, where the maximum overall exergy efficiency was 0.305% at 12.00noon, August 17, 2020, when the salty water flow rate was 1 L/min. The unit’s overall exergy efficiencies were 0.09%, 0.16%, 0.31%, and 0.085% when the salty water flow rates were 0.8, 0.9, 1, and 1.2 L/min, respectively. Maximum exergy destructions for the HDH unit components were 0.513, 0.156, 0.332, and 0.304kW for solar radiation, dehumidifier, humidifier, and PTSC, for a salty water flow rate of 1L/min. In contrast, the overall exergy destruction of the HDH unit was 1.3kW.

This paper presents a computational study on the inter-phase heat transfer inside a conical fluidized bed reactor when hot air is introduced through the bottom inlet. Two different diameters, 2.0mm and 4.0mm glass particles are used as the first and second solid phase and hot air is used as the third phase. A gas–particle heat transfer and particle–particle heat transfer are investigated by using computational fluid dynamics. Euler–Euler two-fluid model is used to describe dynamics of particles and fluid flow in the reactor. We observe that gas–particle heat transfer coefficient is large when solid particle is small. This is the same tendency as the gas–particle heat transfer coefficient when cold air is introduced among hot particles. Particle-to-particle heat transfer depends much on the superficial velocity at the inlet.

Ambient conditions greatly affect the combustion turbine performance. The Absorption Refrigeration Cycle Turbine Inlet Chilling (ARCTIC) system can chill the inlet air of the turbine to maintain optimum performance at all ambient temperatures. However, turbine characteristics, bell-mouth icing concerns, economics and performance guarantees require maintaining the inlet air temperature within a narrow range throughout the year. These considerations require strict control of the Turbine Inlet Air Chilling (TIAC) coil performance over a wide range of operating conditions. This paper describes the field performance and control of the chilling coil for a Mars 100 turbine. The controls logic had been developed from previously published empirical model of the chilling coil and model of the chilling loop performance at the various ambient conditions. Since commissioning at the end of summer 2020, the ARCTIC has provided inlet air chilling over a range of ambient conditions. Typically, the inlet air is maintained at 7.2^∘C (45^∘F) by controlling the TIAC chilled water flow rate and temperature. On cooler days, if the inlet air temperature drops to 5.6^∘C (42^∘F) the chilled water pump turns OFF automatically to prevent bell-mouth icing. Thus, the chiller accommodates chilling load variations down to zero load. On colder days, the ARCTIC continues operating till the ambient temperature drops below 1.7^∘C (35^∘F) and then turns OFF. The chiller turns back ON when the 8 h average inlet air temperature exceeds 10^∘C (50^∘F). These parameters can be adjusted remotely by the operator and help maintain performance guarantees while minimizing chiller cycling. Quasi-steady state data were analyzed to quantify the chilling load and coil performance over a range of operating conditions.

In this paper, the window air conditioner performance with commercial LPG as a replacement of HFC134a is assessed with modified capillary lengths for charge optimization. Global Warming Potential (GWP) of commercial LPG is only three, which is neglected compared to HFC134a (1300). Flammability issues will also be reduced in charge optimization and adopting safety standards. Initially, baseline tests are conducted with HFC134a and commercial LPG in the existing system, and optimum refrigerant charge is determined. The simulation study is conducted with modified capillary lengths for charge reduction of commercial LPG. Experimental assessment is conducted for the charge optimization as per IS 1349 (Part 1) for low ambient test conditions (Domestic Test-DT and Export Test A-ETA) and high ambient test conditions (Export Test B-ETB). With the optimized capillary length and optimum charge quantity, 0.4–2.03% higher cooling capacity, 0.62–8.9% lesser power consumption, and 10.49–16.4% higher COP are achieved with commercial LPG than that of HFC134a baseline at low and high ambient test conditions, respectively.