Sustainability

The use of an internal heat exchanger in vapor compression refrigeration systems of one stage is a common practice because it helps to increase the cooling capacity in the evaporator. Furthermore, the use of refrigerants with low global warming potential is becoming more frequent due to environmental regulations worldwide. Thus, this paper presents an evaluation of the improvement produced by the inclusion of an internal heat exchanger cycle (IHXC) in an experimental installation from the viewpoint of exergy, economic and environmental through to exergy, exergoeconomics, and Specific Life Cycle Climate Performance (SLCCP) studies. The tests were conducted using R1234ze(E) as a replacement alternative to R134a in three evaporating temperature conditions: 4 °C, 9 °C, and 14 °C. Comparisons were made considering R134a in BRC mode versus R1234ze(E) in BRC and IHXC modes. Results show that a lower environmental impact is produced by an evaporating temperature of 14 °C with a reduction in SLCCP of 13.3% using IHXC and R1234ze(E). Moreover, the highest increase in exergy efficiency was observed for an evaporating temperature of 4 °C, with this increase being 9%, while the lowest increase in the total cost rate was observed for the same evaporating temperature, being 12.3% and 21.2% for BRC and IHXC modes using R1234ze(E), respectivelyMDPI Academic Open Access Publishinghttps://www.mdpi.com/2071-1050/14/10/600

Screening of energy efficient technologies for industrial buildings' retrofit

This chapter discusses screening of energy efficient technologies for industrial buildings' retrofit

Influence of operational modes of the internal heat exchanger in an experimental installation using R-450A and R-513A as replacement alternatives for R-134a

This paper presents a first and second law of thermodynamics study using experimental data from a medium capacity refrigeration system using R-450A, R-513A and R-134a as working fluids and an internal heat exchanger (IHX) operating in three different modes: disabled (Off), activated at 38% thermal effectiveness (Middle), and activated at 78% thermal effectiveness, which is the maximum value by design (ON). When the IHX is in the Middle mode, R-513A showed to be the best option and its coefficient of performance (COP) overcomes that of R-450A and R-134a. On the other hand, for temperatures above of −7.5 °C, both R-450A and R-134a reached the highest COP when the ON and Off modes were set, respectively.Regarding the second law study, for the Off and Middle mode, the largest exergy destruction happens in the compressor for the three refrigerants. The influence of the IHX can be observed directly in the increase of the global exergetic efficiency which passes from being 8.7% in Middle mode to 18.3% for the ON mode. Additionally, a reduction of exergy destruction ratio is seen from the Middle mode, 10.6%–22.2% in the ON mode

A Novel Direct-Expansion Radiant Floor System Utilizing Water (R-718) for Cooling and Heating

While forced-air convective systems remain the predominant method for heating and cooling worldwide, radiant cooling and heating systems are emerging as a more efficient alternative. Current radiant cooling systems primarily rely on hydronic chilled water systems. This study introduces direct-expansion radiant cooling as a novel technique that could enhance the efficiency of radiant cooling and reduce its environmental impact. Water (R-718) has been tested as a refrigerant due to its favorable thermodynamic properties and environmental advantages; however, to the author’s knowledge, it has yet to be tested in direct-expansion radiant cooling. This research investigated several refrigerants, including water (R-718), ammonia (R-717), R-410a, R-32, R-134a, and R-1234yf, for this application. The findings indicate that water demonstrates efficiency comparable to other non-natural refrigerants, making it a promising candidate, given its favorable thermodynamic properties and substantial environmental benefits. Despite challenges such as a high compression ratio necessitating multi-stage compression, a high compressor discharge temperature exceeding 300 °C and requiring specialized blade materials, and a high suction volume flow rate, direct-expansion radiant cooling operates within a different temperature range. Consequently, the compressor discharge temperature can be reduced to 176 °C, and the compression ratio can be lowered to approximately 3.5, making water a more viable refrigerant option for this application

Air reversing CO2 heat pumps

CO2 is an environmentally friendly refrigerant that has a no global warming potential when used as refrigerant. The current refrigerants used for air conditioning in public transport are chemical components, and have a high global warming impact. The possibility of replacing the conventional refrigerants by CO2 is investigated for various parts of the transport sector. A possible CO2system for heating and cooling for public transport has been modeled and simulated. This system is a turntable prototype which is reversing the airflows to provide either cooling or heating. It has two gascoolers and two evaporators for separate treatment of ambient and recycled air. The plate is rotated 180˚ to switch from heating to cooling mode. CO2 has large potential for expansion work, due to the normally large throttling losses for high ambient temperatures. An ejector has therefore been implemented in the heat pump circuit. The turntable prototype is modeled by the simulation tool Modelica, and it is investigated how this ejector system adjusts to varying ambient conditions and power demand. Weather data from the climate database Meteonorm was used as a basis for calculation of heating and cooling demand for a train compartment in five different cities, covering a variety of climates. A case study was performed based on an occupancy rate profile and operative hours of the heat pump for the compartment. Simulations were performed of the air reversing heat pump based on the heating -and cooling demand calculations for the five cities. The COP values obtained are very positive, and they are in general higher for heating than cooling mode. The COP is depending on the load, and decreases with reduced occupancy rate. For cooling mode the COP ranged from 3.1 to 6. For heating mode it ranged from 8.2 to 2.8. With the occupancy rate chosen, the annual energy savings is about 80% for all the 5 cities of the study. The fan work of the heat pumps was also included for 4 different operating modes. This reduced the total COP by between 10 to 40%, depending on heating and cooling power requirement and ambient conditions. The fin and tube gas coolers that were used in the Modelica model were compared to a set of MPE gas coolers. The total mass of the heat exchangers was reduced by 50%. One would still have to weigh the reduced mass and increased LCCP performance against the increased investment cost of the MPE heat exchangers

Review of experimental research on supercritical and transcritical thermodynamic cycles designed for heat recovery application

Supercritical operation is considered a main technique to achieve higher cycle efficiency in various thermodynamic systems. The present paper is a review of experimental investigations on supercritical operation considering both heat-to-upgraded heat and heat-to-power systems. Experimental works are reported and subsequently analyzed. Main findings can be summarized as: steam Rankine cycles does not show much studies in the literature, transcritical organic Rankine cycles are intensely investigated and few plants are already online, carbon dioxide is considered as a promising fluid for closed Brayton and Rankine cycles but its unique properties call for a new thinking in designing cycle components. Transcritical heat pumps are extensively used in domestic and industrial applications, but supercritical heat pumps with a working fluid other than CO2 are scarce. To increase the adoption rate of supercritical thermodynamic systems further research is needed on the heat transfer behavior and the optimal design of compressors and expanders with special attention to the mechanical integrity

Thermodynamic evaluation of CO2 for ultra-low temperature refrigeration

Carbon dioxide (CO2, R744) is the only refrigerant in the safest class by the ASHRAE 34 Standard in the group of natural refrigerants, with zero ozone depletion potential and a global warming potential of 1. It has been recently proposed for commercial refrigeration and heat pumps. Ultra-low temperature (ULT) refrigeration considers two-stage cascades with hydrofluorocarbon synthetic refrigerants (R404A/R23 high and low-temperature stages, HTS and LTS, respectively) and, lately, hydrocarbons (R290/R170). This paper examines the potential of R744 in ULT refrigeration cascade configurations in combination with other promising refrigerants. R744 is proposed in the medium temperature stage (MTS) of a three-stage cascade and the HTS of a two-stage transcritical operation (subcritical and transcritical with and without ejector, respectively). The operational and energy performance are compared with standard two- and three-stage ULT refrigeration cascades. Also, the cycles have been optimized, changing the main parameters as cascade heat changer temperatures or gas cooler pressure to maximize COP. This optimization and all the models have been made with Python, extracting the thermodynamic properties of REFPROP. The results show that in the HTS, the coefficient of performance (COP) is 39 % lower than the same two-stage cascade cycle with R290. In the MTS of a three-stage cascade, COP is 10 % lower than the same three-stage cascade cycle with R290. The ejector increases the COP by 38 % in the transcritical HTS, but remains below the hydrocarbon two-stage cascade. The choice of alternative refrigerants in the other stages does not significantly vary the COP results. Technological advancements in single subcritical and transcritical R744 configurations should be transferred to ULT refrigeration cascades to increase competitiveness and take advantage of its environmental and safety characteristics

Integration of trigeneration and CO2 based refrigeration systems for energy conservation

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.Food retail with large supermarkets consumes significant amounts of energy. The environmental impact is also significant because of the indirect effect from CO2 emissions at the power stations and due to the direct effect arising from refrigerant leakage to the atmosphere. The application of trigeneration (local combined heat, power and refrigeration) can provide substantial improvements in the overall energy efficiency over the conventional supermarket energy approach of separate provision of electrical power and thermal energy. The use of natural refrigerants such as CO2 offers the opportunity to reduce the direct impacts of refrigeration compared to conventional systems employing HFC refrigerants that possess high global warming potential. One approach through which the overall energy efficiency can be increased and the environmental impacts reduced, is through the integration of trigeneration and CO2 refrigeration systems where the cooling generated by the trigeneration system is used to condense the CO2 refrigerant in a cascade arrangement. This research project investigates experimentally and theoretically, through mathematical modelling and simulation, such a system and its potential application to supermarkets. A small size CO2 refrigeration system for low and medium food temperature applications was designed and constructed to enable it to be integrated with an existing trigeneration system in the refrigeration laboratory at Brunel University to form an integrated trigeneration and CO2 refrigeration test facility. Prior to the construction, the design of the system was investigated using mathematical models developed for this purpose. The simulations included the CO2 refrigeration system, CO2 evaporator coils and the integration of the trigeneration and CO2 refrigeration systems. The physical size of the design and component arrangement was also optimised in a 3D AutoCAD model. A series of experimental tests were carried out and the results showed that the medium temperature system could achieve a very good COP, ranging from 32 to 60 due to the low pumping power requirement of the liquid refrigerant. The low temperature system performed with average steady state COP of 4, giving an overall refrigeration system COP in the range between 5.5 and 6. Mathematical models were also developed to investigate the application of the integrated trigeneration and CO2 refrigeration system in a case study supermarket. The models were validated against test results in the laboratory and manufacturers’ data. The fuel utilisation efficiency and environmental impacts of different trigeneration and CO2 refrigeration arrangements were also evaluated. The results indicated that a system comprising of a sub-critical CO2 refrigeration system integrated with a trigeneration system consisting of a micro-turbine based Combined Heat and Power (CHP) unit and ammonia-water absorption refrigeration system could provide energy savings of the order of 15% and CO2 emission savings of the order of 30% compared to conventional supermarket energy systems. Employing a trigeneration system with a natural gas engine based CHP and Lithium Bromide-Water sorption refrigeration system, could offer energy savings of 30% and CO2 emission savings of 43% over a conventional energy system arrangement. Economic analysis of the system has shown a promising payback period of just over 3 years compared to conventional systems.Department for Environment, Food & Rural Affairs(DEFRA)-Advanced Food Manufacturing LINK Programm

Development of a fossil-free heating system for chicken barns based on heat pumps and thermal storage

Mens det globale forbruket av fjørfekjøtt fortsetter sin oppadgående trend, rettes det uunngåelige søkelyset mot den betydelige miljøpåvirkningen, spesielt de betydelige CO2-utslippene knyttet til konsum av kyllingkjøtt. For å forene den økende etterspørselen med behovet for bærekraft, foreslår denne studien integrasjonen av fornybare og økonomisk levedyktige oppvarmings- og kjølesystemer innen fjørfenæringen, i tråd med Den europeiske unions forpliktelse til karbonreduksjon og rimelig energi. For øyeblikket brukes pelletskjeler til å opprettholde temperaturen inne på gården. Energiforbruket ble logget for å registrere energiforbruket på fjørfegårder. Den resulterende usikkerhetsanalysen av energiforbruket viste en lav feilmargin, estimert til 0,41 %. Studien gikk deretter inn på en vurdering av alternative oppvarmings- og kjølesystemer, med fokus på ytelsen til en 120 kW CO2-varmepumpe. Blant de ulike konfigurasjonene som ble simulert, viste systemet med en Flash Gas Bypass Valve (FGBV) og parallelle fordampere den mest imponerende ytelsen, med en effektfaktor (COP) som varierte mellom 4 – 4,6 som svar på ulike belastninger. Sammenlignet med det oppsettet som brukte byvann som kilde, hadde dette oppsettet en stabil COP på 3,6 i likevekt. For å vurdere systemets effektivitet ble tørketiden for en 2 cm vannfilm på en 2000 m2 betongoverflate beregnet. Når luft med en temperatur på 50 ℃ ble jevnt fordelt med en luftfart på 1 m/s, var tørketiden 23 timer. Bemerkelsesverdig førte sakte og jevn luftstrøm til mer effektiv tørking enn høye luftstrømningshastigheter, noe som indikerer betydelig potensial for energisparing. Prosessen førte til høy relativ luftfuktighet ved utløpet på grunn av fuktighet som ble absorbert fra betongoverflaten. Årlig energiproduksjon ble beregnet for nye og gamle fjørfegårder til henholdsvis 145,1 MWh og 73,1 MWh. Den nye gården viste en topp månedlig energiproduksjon på over 20 MWh i mai, juni og juli, mens desember registrerte den laveste produksjonen. Denne forskningen understreker det transformative potensialet til fossilfrie oppvarmings- og kjølesystemer. Ved å forene miljøansvar med forbedret produktivitet og økonomisk bærekraft, kan disse nye systemene innlede en ny æra innen bærekraftig fjørfeproduksjon.As global poultry meat consumption continues its upward trajectory, it casts an inevitable spotlight on its sizable environmental footprint, particularly the considerable CO2 emissions associated with broiler consumption. To reconcile the growing demand with the need for sustainability, this study proposes the integration of renewable, economically viable heating and cooling systems within the poultry industry, consistent with the European Union’s commitment to carbon reduction and energy affordability. At present, pellets boilers are used to maintain the temperature inside the farm. Energy consumption was conducted to log energy consumption in poultry farms. The resulting uncertainty analysis of energy consumption data demonstrated a low error margin, estimated at 0.41%. The study then delved into an evaluation of alternative heating and cooling systems, focusing on the performance of a 120 kW CO2 heat pump. Among the diverse configurations simulated, the system featuring a Flash Gas Bypass Valve (FGBV) and parallel evaporators delivered the most impressive Coefficient of Performance (COP), fluctuating between 4 to 4.6 in response to various source loads. In contrast, the setup utilizing the city water as a source manifested a steady state COP of 3.6. To assess system efficiency, the calculated drying time for a 2 cm water film on a 2000 square meter concrete surface. When 50 ℃ air was uniformly distributed at an air velocity of 1 m/s is 23 hrs. Notably, slow, and steady airflow led to more effective drying than high flow rates, indicating significant potential for energy savings. The process resulted in high relative humidity at the exit, due to moisture absorption from the concrete surface. Annual energy production was calculated for new and old poultry farms at 145.1 MWh and 73.1 MWh. The new farm exhibited peak monthly energy production exceeding 20 MWh during May, June, and July, with December registering the minimum output. This research underscores the transformative potential of fossil-free heating and cooling systems. By fusing environmental stewardship with improved productivity and economic viability, these novel systems could herald a new era in sustainable poultry production