Retrofit of lower GWP alternative R449A into an existing R404A indirect supermarket refrigeration system

R404A is going to be phased out from most of the commercial refrigeration systems due to its high GWP value of 3943. R449A (GWP of 1282) has been proposed to replace R404A with only minor system modifications in supermarkets. This paper presents the measurements of a light retrofit replacement of R404A using R449A in a medium temperature indirect refrigeration system (secondary fluid temperature at the evaporator outlet between −9 and −4 °C). It has been demonstrated that with a slight expansion device adjustment and 4% increase of refrigerant charge, R449A can be used in this refrigeration system designed for R404A because of its suitable thermodynamic properties and acceptable maximum discharge temperature. At a secondary fluid temperature at condenser inlet of 30 °C, the COP of R449A nearly matches that of R404A (both were between 1.9 and 2.2), despite having approximately 13% lower cooling capacity. As a conclusion, attending to the GWP reduction and similar energy performance, it was demonstrated using the TEWI methodology that the use of the recently developed refrigerant R449A in these applications can reduce the total CO2 equivalent emissions of an indirect supermarket refrigeration system designed for R404A refrigerant.This research is funded by the Swedish Refrigeration Cooperation Foundation, KYS (project “Utvärdering av en potentiell R404A-ersättare – fältprov med R449A”) and Swedish Energy Agency (EFFSYS Expand P08) with the support of Bosch Thermoteknik AB, Danfoss Värmepumpar AB, Nibe AB, Nowab, Energi & Kylanalys AB and Svenska Kyltekniska Föreningen

Geothermal storage integration into a supermarket’s CO2 refrigeration system

This paper investigates the integration of geothermal storage into state-of-the-art CO2 trans-critical booster systems. The objective is to evaluate the impact of this integration on energy efficiency. Three scenarios of integration are studied including stand-alone and integrated supermarket building systems. The results show that for a stand-alone average size supermarket, heat recovery from the CO2 system should be prioritized over a separate ground source heat pump. Extracting heat from the ground by an extra evaporator in the CO2 system has also little impact on this supermarket annual energy use. However, in the case of supermarket integration with a neighboring building where the supermarket provides heat to the neighbor, geothermal storage integration can reduce the total annual running cost of the two non-integrated buildings by 20–30% with a payback time of less than 3.5 years. The results also show there is no need for a separate ground source heat pump

ANN Modeling to Analyze the R404A Replacement with the Low GWP Alternative R449A in an Indirect Supermarket Refrigeration System

Artificial neural networks (ANNs) have been considered for assessing the potential of low GWP refrigerants in experimental setups. In this study, the capability of using R449A as a lower GWP replacement of R404A in different temperature levels of a supermarket refrigeration system is investigated through an ANN model trained using field measurements as input. The supermarket refrigeration was composed of two indirect expansion circuits operated at low and medium temperatures and external subcooling. The results predicted that R449A provides, on average, a higher 10% and 5% COP than R404A at low and medium temperatures, respectively. Moreover, the cooling capacity was almost similar with both refrigerants in both circuits. This study also revealed that the ANN model could be employed to accurately predict the energy performance of a commercial refrigeration system and provide a reasonable judgment about the capability of the alternative refrigerant to be retrofitted in the system. This is very important, especially when the measurement data comes from field measurements, in which values are obtained under variable operating conditions. Finally, the ANN results were used to compare the carbon footprint for both refrigerants. It was confirmed that this refrigerant replacement could reduce the emissions of supermarket refrigeration systems

Analyse semi-empirique de la conversion des syst`emes frigorifiques des supermarch´es aux HFC avec des configurations avanc´ees du point de vue ´energ´etique, environnemental et ´economique

F-gas phase-down schedules will remove most of the HFCs (hydrofluorocarbons) used in refrigeration systems in the short term. Besides refrigerant substitution, configuration modifications can be considered in existing installations to increase energy efficiency. Basic cycle, direct injection, economiser, parallel compression, and cascade configurations with internal heat exchanger have been proposed to increase the energy efficiency of a supermarket refrigeration system when replacing R-404A with R-449A at low and medium temperatures. Both systems are based on indirect expansion and are equipped with a subcooler. Their regular operation was recorded using R-404A and R-449A during a representative period. Then, a semi-empirical approach is followed to determine R-449A energy performance with each proposed configuration. Only parallel compression (PC) and basic cycle with internal heat exchanger (IHX) benefit energy performance, highlighting the medium temperature (MT) system. However, this benefit is not extended to the environmental analysis because the R-449A charge in PC significantly increases. Moreover, additional PC components extend the expected payback period, and a drop-in replacement is financially more interesting. Therefore, using R-449A with minor modifications in the MT and LT R-404A refrigeration system decreases 52% and 60% carbon footprint, respectively. The payback period of this action is below one year in both circuits. This study provides a semi-empirical methodology for existing systems to predict alternative refrigerants’ energy performanceFunding for open access charge: CRUE-Universitat Jaume

Identification of fragments binding to SARS-CoV-2 nsp10 reveals ligand-binding sites in conserved interfaces between nsp10 and nsp14/nsp16

Since the emergence of SARS-CoV-2 in 2019, Covid-19 has developed into a serious threat to our health, social and economic systems. Although vaccines have been developed in a tour-de-force and are now increasingly available, repurposing of existing drugs has been less successful. There is a clear need to develop new drugs against SARS-CoV-2 that can also be used against future coronavirus infections. Non-structural protein 10 (nsp10) is a conserved stimulator of two enzymes crucial for viral replication, nsp14 and nsp16, exhibiting exoribonuclease and methyltransferase activities. Interfering with RNA proofreading or RNA cap formation represents intervention strategies to inhibit replication. We applied fragment-based screening using nano differential scanning fluorometry and X-ray crystallography to identify ligands targeting SARS-CoV-2 nsp10. We identified four fragments located in two distinct sites: one can be modelled to where it would be located in the nsp14–nsp10 complex interface and the other in the nsp16–nsp10 complex interface. Microscale thermophoresis (MST) experiments were used to quantify fragment affinities for nsp10. Additionally, we showed by MST that the interaction by nsp14 and 10 is weak and thereby that complex formation could be disrupted by small molecules. The fragments will serve as starting points for the development of more potent analogues using fragment growing techniques and structure-based drug design

Gene Expression Profiling in Gastric Mucosa from Helicobacter pylori-Infected and Uninfected Patients Undergoing Chronic Superficial Gastritis

Helicobacter pylori infection reprograms host gene expression and influences various cellular processes, which have been investigated by cDNA microarray using in vitro culture cells and in vivo gastric biopsies from patients of the Chronic Abdominal Complaint. To further explore the effects of H. pylori infection on host gene expression, we have collected the gastric antral mucosa samples from 6 untreated patients with gastroscopic and pathologic confirmation of chronic superficial gastritis. Among them three patients were infected by H. pylori and the other three patients were not. These samples were analyzed by a microarray chip which contains 14,112 cloned cDNAs, and microarray data were analyzed via BRB ArrayTools software and Ingenuity Pathways Analysis (IPA) website. The results showed 34 genes of 38 differentially expressed genes regulated by H. pylori infection had been annotated. The annotated genes were involved in protein metabolism, inflammatory and immunological reaction, signal transduction, gene transcription, trace element metabolism, and so on. The 82% of these genes (28/34) were categorized in three molecular interaction networks involved in gene expression, cancer progress, antigen presentation and inflammatory response. The expression data of the array hybridization was confirmed by quantitative real-time PCR assays. Taken together, these data indicated that H. pylori infection could alter cellular gene expression processes, escape host defense mechanism, increase inflammatory and immune responses, activate NF-κB and Wnt/β-catenin signaling pathway, disturb metal ion homeostasis, and induce carcinogenesis. All of these might help to explain H. pylori pathogenic mechanism and the gastroduodenal pathogenesis induced by H. pylori infection

Bacterial Adaptive Responses - Coping with Oxygen Limitation, Reactive Nitrogen Species and Disulfide Stress

Bacteria have a remarkable ability to adapt to different environments. When bacteria encounter stress that causes macromolecular damage in the cell, leading to a suboptimal performance of cell metabolism, they can elicit an adaptive response. In this thesis Bacillus subtilis is used as the primary model organism to study bacterial adaptation to oxygen limitation, reactive nitrogen species and disulfide stress. Sudden changes in the oxygen availability leads to changes in the intracellular NAD:NADH ratio. In this work, the B. subtilis Rex protein is characterized. Rex acts as a transcriptional repressor that can sense the intracellular NADH concentration. When the concentration of NADH is low, Rex represses genes needed for growth under conditions of low oxygen availability. Reactive nitrogen species (RNS) are present in many environments inhabited by bacteria, and may cause severe damage to bacterial cells. Here, we show that the major enzyme required for protection against RNS in B. subtilis is the Hmp flavohemoglobin. The hmp gene is regulated by the ResDE two-component system and the NsrR transcriptional repressor. Under normal conditions, the bacterial cell cytoplasm is a reducing environment where protein cysteines are kept in their reduced form. However, if the cytoplasm becomes oxidizing, unwanted disulfide bonds may form, a phenomenon known as disulfide stress. Spx is a global regulator governing the disulfide stress response in B. subtilis. Under non-stress conditions, Spx is rapidly degraded by the ClpXP protease. In this work, YjbH is identified as a negative effector of Spx, that is required for the efficient degradation of Spx by ClpXP

Experimental cooling load analysis of ice rinks

Ice rinks for ice hockey use approximately 1000 MWh per year. These figures are based on statistics from over 100 Swedish ice rinks. The refrigeration system accounts for in the range of 35 to 75% of the total energy usage in the ice rinks, with an average value of 43%. This study evaluated a method to field measure the refrigeration system to establish the cooling capacity, which with minor corrections is equal to the ice surface heat load. The performance of the distribution system and at the main components of the heat load is in focus in this study. To analyze the performance of the ice rinks refrigeration system an "internal method" was used. In this method the compressor is used as a mass flow meter and therefore there is no need installing an external mass flow meter. The refrigerant mass flow rate is calculated by an energy balance over the compressor. By knowing the mass flow, enthalpy of the refrigerant, etc. the cooling capacity and COP of the system can be calculated. During the evaluation period the average cooling capacity corrected for the ground heat gain and the brine pump power was 98.5 kW and the corresponding heat load based on the surface ice sheet conditions was estimated to 92.5 kW. This represents a deviation of 7% which is a measure of the modelling accuracy compared to the measurements.QC 20140114</p