Commercial Refrigeration Research Articles

Performance Improvement of The Domestic Refrigerator Using Phase Change Materials

A growing environmental Impact of global warming and rapidly increasing cost of the electrical energy cause researchers in the field of refrigeration and air conditioning to develop the sustainable cooling technologies. This study investigated the influence of latent heat storage materials on the power consumption and the temperature distribution of a commercial domestic refrigerator. The 2 kg PCMs (Phase change materials) slab of thickness 5 mm, which consisted of a 2:1 by weight mixture of refined paraffin wax and kerosene oil, were located on the back side of the roll-bond evaporator and the copper coated steel tubing coils of the hot-wall condenser, in order to improve the higher performance of refrigerator and to decrease the operating cycle time of the compressor. The experimental and CFD (Computation fluid dynamics) simulation results indicated that the refrigerator equipped with the PCMs storage unit showed a significant enhancement of the system performance and a reduction of the temperature fluctuations in the refrigerator compartment compared to a conventional system. In this investigation, the electric power consumption and the compressor on-time ratio were reduced by 15.69% and 12.13%, respectively. Moreover, the COP (Coefficient of performance) of the refrigeration system was increased by 9.53%.

Model predictive control for demand flexibility: Real-world operation of a commercial building with photovoltaic and battery systems

Hundreds of studies have investigated Model Predictive Control (MPC) for the optimal operation of building energy systems in the past two decades. However, MPC field tests are still uncommon, especially for small- and medium-sized commercial buildings and for buildings integrated with onsite renewables. This paper describes the implementation and the long-term performance evaluation of an MPC controller in a small commercial building equipped with behind-the-meter photovoltaics and electrochemical batteries. MPC controls space conditioning, commercial refrigeration, and the battery system. We tested two types of demand flexibility applications in the field: electricity bill minimization under time-of-use tariffs and responses to grid flexibility events. Results show that the proposed controller achieves 12% of annual electricity cost savings and 34% peak demand reduction against the baseline, while respecting thermal comfort and food safety. The field tests also demonstrate the ability of the MPC controller to provide a multitude of grid services including real-time pricing, demand limiting, load shedding, load shifting, and load tracking, using the same optimization framework.

A LN2-based cryogenic system prototype for future PandaX experiment

This paper describes results on R&D of an economical and efficient cryogenic system prototype for future liquid xenon detector. The test module of the prototype has a “coldhead” attached to a copper rod, which is specially designed to transport heat loads to a free-boiling liquid nitrogen bath. The performance of the test module and commercial refrigerators is compared. The module with an optimized copper rod has demonstrated more than 1500 W cooling power at 178 K. The temperature of the “cold head” can be kept stable with an error of 0.02 K, its fluctuation is within 0.1 K.

A Survey on the Sanitary Condition and Prevalence of Listeria monocytogenes in Commercial Refrigerators in Khuzestan Province, Iran

Background: Listeria monocytogenes can grow in a variety of foods that are stored in refrigerators. This bacterium can adhere to various surfaces and form biofilms. Given that refrigerator temperature can support bacterial growth and proliferation, increasing the number of bacteria in refrigerator spaces endangers the consumer’s health. Objective: The purpose of this study was to investigate the prevalence of L. monocytogenes and the sanitary conditions of commercial refrigerators used in food supply centers in Khuzestan province, southwest Iran. Materials and Methods: Overall, 204 swap samples were collected from the inner surfaces of various industrial refrigerators in five different zones. The samples were enriched in Listeria enrichment broth and cultured on PALCAM agar plates. Suspected colonies were identified by biochemical tests and the polymerase chain reaction. Additionally, the sanitary condition of the refrigerator, method and duration of refrigerator cleaning, last washing date, and type of the applied detergent were recorded, and the antibacterial susceptibility of the isolates was tested as well. Results: The results demonstrated that four refrigerators (1.96%) located in Ahvaz (center) and Ramhormoz (east) were contaminated with L. monocytogenes. The internal temperatures of 67% of the refrigerators were above 5 °C, and most operators used a mixture of water and a dishwasher or water alone to clean their refrigerators. In addition, 31.9% of the refrigerators were in an unfavorable cleaning condition, and 32.8% of the refrigerators were not sealed properly. The isolates were resistant to streptomycin and represented intermediate resistance to tetracycline and penicillin. Conclusion: The contamination of industrial refrigerators with antibiotic-resistant L. monocytogenes may pose a threat to public health. Authorities should increase the monitoring of industrial refrigerators and provide the necessary training for refrigerator users.

Determination of defrost efficiency and energy efficiency index value using different defrost methods and refrigerants: An experimental study

In this study, open-type refrigeration cabinets were designed and manufactured using hot gas and electrical resistance defrost methods and R290, R449A and R404A refrigerants. The aim of this study is to determine the temperature increase of the products during the process, CO2 emission amount, defrost efficiency, and energy efficiency index (EEI) value with different defrost methods and refrigerants for commercial refrigeration systems. The increase in package temperatures during the defrosting process was determined as 1.33 °C in the electrical method. The results showed that the hot gas method was 7.15% more efficient in terms of defrosting efficiency. The EEI value was calculated as 78.76 with the use of R290 in the hot gas method and the energy class was determined as F and the hot gas emit 5.9% less CO2 than in the resistance experiments. In the hot gas defrost method, it was seen that 20.3% less energy was consumed compared to the total consumption. It was observed that R290 refrigerant and the hot gas defrost method were the most suitable for commercial systems in terms of defrosting process losses, total energy consumption, and temperature rise of the cooled product during defrosting.

Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies

Abstract. The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past 2 decades, primarily as a result of the phaseout of ozone-depleting substances under the Montreal Protocol and the use of HFCs as their replacements. In 2015, large increases were projected in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 ∘C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries. Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2 eq. inferred HFC emissions continue to increase through 2019 (to about 0.8 GtCO2eq.yr-1) but are about 20 % lower than previously projected for 2017–2019, mainly because of the lower global emissions of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and the lower reported consumption of HFC-143a in China. Because this time period preceded the beginning of the Kigali provisions, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications in anticipation of national or global mandates. There are two new HFC scenarios developed based (1) on current trends in HFC use and Kigali-independent (K-I) control policies currently existing in several countries and (2) current HFC trends and compliance with the Kigali Amendment (KA-2022). These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2eq.yr-1 to 1.9–3.6 GtCO2eq.yr-1. The added provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 GtCO2eq.yr-1 in 2050. Without any controls, projections suggest a HFC contribution of 0.28–0.44 ∘C to global surface warming by 2100, compared to a temperature contribution of 0.14–0.31 ∘C that is projected considering the national K-I policies current in place. Warming from HFCs is additionally limited by the Kigali Amendment controls to a contribution of about 0.04 ∘C by 2100.

Flow of Neon-Nitrogen-Hydrocarbon mixture through adiabatic capillary tube at cryogenic temperatures

Capillary tubes are widely used in J-T refrigerators owing to their simplicity, easy operation, and zero maintenance. J-T refrigerators are mainly used for domestic and commercial refrigeration and air conditioning and hence the study on flow through capillary tubes is highly focused on conventional refrigerants at relatively higher temperatures. The present work is an extension of previous work done by the authors and focuses on the flow of refrigerant mixtures consisting of neon, nitrogen, and hydrocarbons at cryogenic temperatures for the capillary tube of a J-T cryocooler. The mass flow rate through the capillary tube is studied experimentally by changing refrigerant mixture composition and inlet temperature to the capillary tube. A mathematical model is developed based on a length feedback loop to predict the mass flow rate through the capillary tubes using the homogenous flow model. The model is found to predict mass flow rate through the capillary tube with an average error of 10 % for almost all the experimental values.

Short nozzles design for real gas supersonic flow using the method of characteristics

Finding a supersonic nozzle minimum length is a classical application of the method of characteristics (MOC) for aerospace propulsion technology among many other applications, such as air and vapor handling processes. That methodology allows design contoured nozzle free of oblique shock waves created at sharp area changes in short nozzles. While the designing technique is well established in textbooks for ideal gas flow, the use of the MOC technique for real gas is problematic due to the highly complex fluid behavior, captured by modern real gas equations-of-state (EOS). This work presents the MOC devised for real gases using multi-parameter equations-of-state (MPEOS) for different substances and compositions. This paper also compares the MPEOS solution obtained from other classical EOS, such as Peng–Robinson, and the ideal gas equation to establish the optimal application range for each EOS and their effect on the nozzle wall construction. The study was carried out for a commercial fluid refrigerant, pure carbon dioxide, and a CO2−CH4 mixture. The methodology can be used for designing industrial pieces of equipment, such as turbo-machineries and supersonic gas separators or supersonic ejectors, to evaluate the isentropic flow expansion within those devices.

Evaporator Performance for Water Refrigerant Adsorption Cooling System

Adsorption Cooling System gives an alternative to the commercial vapor compression refrigeration cycles due to their benefits of having a very environmentally friendly and promising energy-saving system. An adsorption cooling system consists of four main components which are thecondenser, evaporator, expansion valve, and adsorption bed for the system to effectively function. One of the factors that affect the efficiency of the system is the performance of the evaporator itself as the system operates at sub-atmospheric pressure and the performance is mediocre when using conventional evaporators. Due to the low-pressure condition, hydrostatic pressure may affect the saturated temperature of the water refrigerant in a flooded type evaporator. Therefore, in this study, the performance of the evaporator was investigated based on the water height variation. The highest heat transfer coefficient and evaporation heat transfer rate are achieved when the water is set at the heat exchanger tube diameter level. Furthermore, 0.1 kg of silica gel adsorbent is used to obtain the maximum of 250 W/kg of Specific Cooling Power when the heat transfer fluid is set to 20 ºC.

Energetic, exergetic and financial evaluation of a solar-powered absorption chiller integration into a CO2 commercial refrigeration system

This study investigates the integration of a solar absorption chiller by means of subcooling to a CO2 booster system that serves the refrigeration needs of a supermarket refrigeration plant with an installed capacity of 80 kW and 20 kW for medium and low-temperature regimes, respectively. The proposed energy saving configuration is analyzed in an energetic, exergetic, and financial manner, using the climatic data for the city of Athens, Greece. The current approach constitutes the theoretical reference for the actual implementation of this novelty either in new plants or as a retrofit in existing ones. The proposed solution includes the employment of a single-stage absorption chiller operating with LiBr–H20 working pair, which is driven by heat produced in evacuated tube collectors installed in the store’s rooftop. The energy analysis is conducted with validated numerical models that are developed in MATLAB using the CoolProp library. The collecting area and the corresponding chiller capacity of the proposed configuration are selected through financial evaluation. More specifically, the collecting area is analyzed parametrically from 25 m2 to 200 m2. Finally, 100 m2 of collecting area with 60 kW of chiller capacity are proved to be the optimum solution financially with 8.4 years payback period and 44.57 k€ net present value. This optimum solution results in an annual power consumption decrease of 8.12% which leads to energy savings of 27.45 MWh/year.

Effects of the soaking-related parameters in a combined freezing-based seawater desalination process.

A combined freezing, soaking, and centrifugal desalination (FSCD) process was employed to desalt seawater taken from Bohai Bay. The seawater was frozen into two kinds of sea water ice having different texture and size using either commercial refrigerator or experimental setup. For both kinds of ice samples, the influences of soaking-related parameters on the desalination effect were studied. For most ice samples treated with FSCD process, the salt removal efficiencies are higher than 90%. The purity of ice product increases as increasing soaking time and at higher initial soaking liquid temperature, while the ice yield rate decreases. At the same ice yield rate, the salt removal efficiency for ice flakes is higher than that for crushed ice samples, whereas when the raw seawater of 27°C is used as soaking liquid, FSCD process is not feasible due to too lower ice yield rate.

On Refrigerators and Rage: Secrecy and Pacification in the Florida Restaurant Industry

Designed based on careful specifications and regulations, commercial refrigerators can be found in almost all restaurants across the United States. In this article I explore the multifaceted role of the commercial walk-in refrigerator as a space of mediation, secrecy, and pacification among restaurant industry workers in central Florida. I analyze two years of ethnographic research conducted from 2015 to 2017, and argue that the refrigerator acts as a liminal zone within the restaurant, which is used by management to subdue, pacify, and placate employees. To do so I draw on literature by design justice scholars on discriminatory design, to consider the ways in which the physical structure of American restaurant establishments perpetuate physical and emotional abuse of workers.

Experimental study on the operating characteristics of a display refrigerator phasing out R134a to R1234ze(E) and its binary blends

In recent years, the refrigerant drop-in replacement of R134a has been mainly motivated due to environmental issues. This study aims to experimentally compare the operating characteristics in light commercial refrigeration using a display refrigerator when R134a is substituted with pure R1234ze(E) and R1234ze(E)-R134a blends. The refrigerants R450A (R1234ze(E)-R134a 58-42wt% blend), and R1234ze(E)-R134a 90-10wt% blend with GWP of 547 and 150 respectively are evaluated. The adequate refrigerant charge is determined, and the performance evaluation is carried on under controlled ambient temperatures of 24, 32, and 40°C. The results show a slightly reduced refrigerant charge for higher operating temperatures. Pure R1234ze(E) and its mixtures with R134a are a suitable short-term solution in light commercial refrigeration, satisfying ambient regulations with the maximum electric energy input increase by 6% under ambient temperature of 40°C. Its reduced operating pressure of 36% at the condenser might result of interest for some applications.

Investigating the impact of indoor temperature on the performance of the retail commercial refrigeration system

Commercial food outlets in the UK are responsible for 3% of the UK total energy consumption, with refrigeration systems account for 29% of this total. In this paper, a validated model that simulates a commercial refrigeration system installed over 2000 sq. ft to mimic a real express store installed at the Riseholme Refrigeration Research Centre at the University of Lincoln, UK, is presented. Investigations are conducted to examine the different failures of air conditioning (AC) systems and their impacts on the indoor store temperature, and hence on the refrigeration performance and energy consumption. Three different scenarios were examined: gradual increase in store temperature caused by an AC system with reduced performance, sudden increase in store temperature caused by a drastic AC failure and fluctuations in store temperature caused by a faulty AC system. The results of the investigation for different failure scenarios of the AC system during 3 h of continual operation showed an increase in the energy consumption of the refrigeration system by 17.4% as a result of gradual AC failure, 33.6% for the sudden failure and 5.3% for the intermittent failure. It is concluded that the AC failures caused the power drawn to increase due to spending a prolonged period of time at higher temperatures than during the normal AC operation. Also, the frequency which the compressors switch on and off increases the level of wear on the compressors. Both gradual and sudden failures of the AC system show a sustained increase in temperature that leads to a greater duty cycle for the expansion valve to increase the amount of refrigerant available. It is found that the sudden failure of the AC system had the greatest impact on the system, as the temperature of the store rises quickest, the display cases are exposed to higher temperatures for a longer time; this causes the greatest demand on the system and so lead to the largest power consumption. It is notable that for all three failure types that the product temperature experiences, there are no noticeable fluctuations and they remain comfortably within the temperature boundaries between 3 and 1 °C, as the system is able to provide an adequate cooling.

Integration of a solar-powered absorption chiller for performance enhancement of a supermarket CO2 refrigeration plant

CO2 refrigeration configurations are the most viable solution for commercial refrigeration plants, which are however accompanied with energy challenges due to their low energy efficiency when operating under high ambient temperatures. This study examines the coupling of a CO2 booster system with a solar absorption chiller, used to sub-cool the CO2 of the main cycle. The refrigeration system under study is projected to cover the cooling requirements of a supermarket refrigeration plant with an installed capacity of 80 kWR for the medium and 20 kWR for the low-temperature circuit, in the region of Athens, Greece. The investigated process involves utilization of an absorption chiller module with 60 kWR of cooling capacity working with a LiBr-H20 pair powered by heat produced in fifty evacuated-tube solar collectors with a total collecting area of 115 m2. The energy performance analysis was based on validated numerical models developed in MATLAB using the CoolProp library. Through parametric analysis the coefficient of performance (COP) of the proposed topology was compared to the COP of a conventional booster system under constant low (450 W/m2) and high (800 W/m2) incident solar radiation for the temperature range 1–40 °C, resulting in maximum COP increments of 26.44% and 47.34% respectively. Performance simulation on an annualized basis was also conducted, by using the average hourly values of ambient temperature and solar radiation for every month of the year. The results showed that in comparison to the conventional booster system, the sub-cooling rates achieved a maximum increment of COP of 47.48% hourly and 16.36% monthly for August which is the warmest month of the year. Annual electricity consumption decreased by 8.93%, resulting in an energy savings of 30.19 MWh/year.

Airflow to disperse refrigerant leaks from hydrocarbon refrigeration systems✰

Whilst R290 is currently used to a limited extent in room air conditioners there is a desire for wider application due to its excellent performance and negligible global warming potential. The product standard IEC 60335–2–40 specifies requirements to limit the allowable refrigerant charge in such a way that it obstructs the wider use of R290. Airflow of an indoor unit can be used to dilute a refrigerant leak, enabling substantially greater charge quantities to be used. A numerical model based on entrainment theory was developed and supported by analysing the behaviour of experimentally simulated releases under various conditions with indoor unit airflow. The work determines the minimum airflow rate necessary to prevent formation of a flammable concentration within the room. Further, the work includes determination of appropriate response time and leak rate to initiate airflow once a leak has begun. The developed methodology can equally be applied to commercial refrigeration units and other flammable refrigerants.

The Shoemaker and the Gibson Girl

The Shoemaker and the Gibson Girl

Colossal and reversible barocaloric effect in liquid-solid-transition materials n-alkanes

Emerging caloric cooling technology provides a green alternative to conventional vapor-compression technology which brings about serious environmental problems. However, the reported caloric materials are much inferior to their traditional counterparts in cooling capability. Here we report the barocaloric (BC) effect associated with the liquid-solid-transition (L-S-T) in n-alkanes. A low-pressure of ~50 MPa reversibly triggers an entropy change of ~700 J kg−1 K−1, comparable to those of the commercial refrigerants in vapor-based compression systems. The Raman study and theoretical calculations reveal that applying pressure to the liquid state suppresses the twisting and random thermal motions of molecular chains, resulting in a lower configurational entropy. When the pressure is strong enough to drive the L-S-T, the configurational entropy will be fully suppressed and induce the colossal BC effect. This work could open a new avenue for exploring the colossal BC effect by evoking L-S-T materials.

Natural technologies for sustainability: accelerating implementation

Natural technologies for sustainability: accelerating implementation The Life-C4R project is an international marketing project that, thanks to Epta’s Full Transcritical Efficiency (FTE) and Extreme Temperature Efficiency (ETE) systems, will substantially contribute to replacing HCFC and HFC greenhouse refrigerants with CO2 in commercial refrigeration in a very simple, efficient and reliable way in any country, with any external temperature, allowing 10 per cent energy and 30 per cent installation and maintenance savings.

Solid-state cooling by elastocaloric polymer with uniform chain-lengths

Although the elastocaloric effect was found in natural rubber as early as 160 years ago, commercial elastocaloric refrigeration based on polymer elastomers has stagnated owing to their deficient elastocaloric effects and large extension ratios. Herein, we demonstrate that polymer elastomers with uniform molecular chain-lengths exhibit enormous elastocaloric effects through reversible conformational changes. An adiabatic temperature change of −15.3 K and an isothermal entropy change of 145 J kg−1 K−1, obtained from poly(styrene-b-ethylene-co-butylene-b-styrene) near room temperature, exceed those of previously reported elastocaloric polymers. A rotary-motion cooling device is tailored to high-strains characteristics of rubbers, which effectively discharges the cooling energy of polymer elastomers. Our work provides a strategy for the enhancement of elastocaloric effects and could promote the commercialization of solid-state cooling devices based on polymer elastomers.