Numerical study of air temperature distribution and refrigeration systems coupling for chilled food processing facilities

This paper presents an air temperature distribution and refrigeration system dynamic coupling model to assess the performance of air distribution systems used in chilled food processing areas and its energy consumption impact. The coupling consists of a CFD air flow/temperature distribution system model and a compression refrigeration system model developed in EES integrated in the TRNSYS platform. The model was tested and validated using experimental data collected from a scaled air distribution test rig in an environmental chamber showing a good agreement with the measured data (an hourly energy consumption error up to 5.3 %). The CFD/EES coupling model can be used to design energy efficient cooled air distribution systems capable to maintain the required thermal environment in chilled food processing facilities

Crossing CO₂ equator with the aid of multi-ejector concept:A comprehensive energy and environmental comparative study

The ever-stricter regulations put into effect worldwide to significantly decrease the considerable carbon footprint of commercial refrigeration sector have forced the transition to eco-friendlier working fluids (e.g. CO2, R290, R1234ze(E), R450A, R513A). However, the identification of the most suitable long-term refrigerant is still today's major challenge for supermarkets located in high ambient temperature countries, especially as their air conditioning (AC) need is considered. The results of this theoretical study revealed that multi-ejector “CO2 only” systems can outperform R404A-, R290-, R1234ze(E)-, R134a-, R450A- and R513A-based solutions in an average-size supermarket located in various cities below the so-called “CO2 equator”. In fact, energy savings as well as reductions in environmental impact respectively up to 26.9% and 90.9% were estimated over conventional hydrofluorocarbon (HFC)-based solutions for the scenario including the AC demand. Also, the solution using multi-ejector block (in non-optimized operating conditions) enabled reducing the power input up to 50.3% over HFC-based units at outdoor temperatures from −10 °C to 5 °C. Finally, the study demonstrated that transcritical CO2 multi-ejector systems integrated with the AC unit allow potentially pushing the “CO2 equator” further South than Northern Africa. © 2018 Elsevier Ltd. All rights reserved.Crossing CO2 equator with the aid of multi-ejector concept: A comprehensive energy and environmental comparative studyacceptedVersio

Comparative analysis on the energy use and environmental impact of different refrigeration systems for frozen food supermarket application

In this paper the impact on the store’s energy use by different refrigeration systems, remote and centralised, is investigated as well as their environmental impact. The study is performed using the energy simulation program EnergyPlus in a reference baseline model which has been verified against measured energy and environmental conditions data. The refrigeration system of the case study includes plugged-in display cabinets to serve both medium temperature (MT) and low temperature (LT) refrigeration loads. Centralised systems are compared with the remote plugged-in refrigeration cabinets. The different refrigeration systems studied are, a) two parallel centralised systems for MT and LT loads, b) two parallel cascade systems (R134a/CO2) for MT and LT loads and c) a transcritical CO2 booster. The study is performed for DSY London weather file to capture the risk of warmer than a typical year consequences in centralised refrigeration systems operation. Besides these refrigeration systems, the CO2 transcritical appears as the one of the most promising replacement in terms not only of energy use reduction due to its high efficiency in London climate but on its low contribution to global warming as well

Investigations into air and refrigerant side heat transfer coefficients of finned-tube CO2 gas coolers

Gas coolers are heat rejection heat exchangers in vapour compression refrigeration systems that use carbon dioxide (CO2) as refrigerant. The design of gas coolers has a significant influence on the performance of CO2 refrigeration systems as it determines to a large extent the gas cooler/condenser pressure and the power consumption of the system. This paper investigates local refrigerant and air heat transfer coefficients in plain fin-and-tube gas cooler coils using Computational Fluid Dynamics (CFD) modelling. The aims were to provide insights into the variation of the local heat transfer rates in the coil and determine the influence of a) design enhancements such as the use of slit fins and b) to develop correlations for overall refrigerant and air heat transfer coefficients to be used in CO2 refrigeration component and system modelling. The results from the model which was validated against experimental measurements showed that a horizontal slit on the fin between the first and second row of tubes can lead to an increase in the heat rejection rate of the gas cooler by between 6% and 8%. This in turn can lead to smaller heat exchanger heat transfer area for a given heat rejection capacity or lower high side pressure and higher efficiency for the refrigeration system. The results and heat transfer correlations developed are a valuable resource for researchers and manufacturers of CO2 and other heat exchanger coils that experience a wide variation in refrigerant temperature during the gas cooling process.This study was supported by the RCUK National Centre for Sustainable Energy use in Food chains (CSEF) of the Research CouncilsUK Energy programme, Grant No: EP/K011820/1, GEA Searle, now Kevlion, and Directorate General for Higher Education-DIKTI–Indonesian Government for a PhD scholarship