| 1. |
- Abdi, Amir, et al.
(författare)
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Heat recovery investigation of a supermarket refrigeration system using carbon dioxide as refrigerant
- 2014
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Ingår i: 11th IIR Gustav Lorentzen Conference on Natural Refrigerants. - : International Institute of Refrigeration. - 9782362150043 ; , s. 277-285
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Konferensbidrag (refereegranskat)abstract
- This study investigates the heat reclaim of trans-critical CO2-booster refrigeration unit in a supermarket in Sweden. The aim is to compare the control strategy for heat recovery in real supermarket installation to the optimum control strategy.The optimum control strategy based on theoretical analysis is explained. By analyzing field measurement of a supermarket, heat recovery in the refrigeration system is studied and compared to the optimum case. To investigate the potential of higher heat recovery rate, a computer model is developed based on the optimum control strategy. The model is also used to calculate the boundary conditions at which the system should run for highest COP.The results show that heat can be recovered at heating COP of 3-4.5. The theoretical analysis shows that the amount of heat that can be recovered from the refrigeration system is about 1.3 times (130 %) the cooling demand in the system. However the analysis of the field measurements shows that only between 30-60 % of the available heat to be recovered is utilized, the rest is released to outdoors. The analysis in this study shows that there is a potential to recover much more heat from the refrigeration system at relatively high heating COP compared to heat pump.
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| 2. |
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| 3. |
- Arnaudo, Monica, et al.
(författare)
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Heat recovery and power-to-heat in district heating networks – Atechno-economic and environmental scenario analysis
- 2021
-
Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 185, s. 116388-
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Tidskriftsartikel (refereegranskat)abstract
- Heat recovery from local resources is shown to be a promising solution to reduce the carbon footprint of district heating. Supermarkets equipped with a CO2 refrigeration system and a geothermal storage offer a larger heating capacity, compared to traditional solutions. While district heat could benefit from this higher heat recovery availability, supermarkets could generate an income from a capacity that would be otherwise unused. For the first time, this study applies a detailed modelling approach considering both sides of such a synergy. The objective is to assess the techno-economic and environmental impact of a coordinated control strategy. Since the heat recovery from the supermarket consumes additional electricity, power-to-heat is implemented as a solution to reduce the overall CO2 emissions. This is demonstrated by scenarios simulated for a district in Stockholm. Hourly electricity CO2 intensity and prices are implemented as signals to prioritize either the district heating central supply or heat recovery. By boosting the use of electricity when cleaner, a CO2 intensity-driven control show the potential of reducing the carbon footprint of the district (−9.4%). A control based on prices, instead, is more convenient economically both for the district (−1.4% heat cost) and for the supermarket (−32% operational cost).
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| 4. |
- Duarte, Willian M., et al.
(författare)
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Refrigerants selection for a direct expansion solar assisted heat pump for domestic hot water
- 2019
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 184:May, s. 527-538
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Tidskriftsartikel (refereegranskat)abstract
- An important step during a project of a heat pump system is choosing a more suitable refrigerant. This paper presents a comparative study among refrigerants for a small direct expansion solar assisted heat pump (DX-SAHP). The mathematical model used in this study is presented in detail and validated from an experimental setup. The R134a is the reference and the refrigerants with low GWP are R290, R600a, R744 and R1234yf. The results show that R290 has better COP than others refrigerants for solar radiation between 300 W/m2 and 700 W/m2, as well as for environment temperature between 10 C and 35 C. On the other hand, for solar radiation less than 50 W/m2, the R134a has better COP than R290. TEWI (Total Equivalent Warming Impact) analysis indicates that the indirect emission is the most important effect, and then, the TEWI results almost followed the COP outcome. A parametric analysis was conducted to evaluate the influence of the CO2 emission factor for producing electricity. In countries with higher emission factor, the refrigerant with the best COP has the best TEWI. The influence of wind speed and ambient temperature in COP of a DX-SAHP using R290 were more relevant in low solar radiation
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| 5. |
- Giunta, Fabio, et al.
(författare)
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Techno-economic analysis of heat recovery from supermarket's CO2 refrigeration systems to district heating networks
- 2021
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the opportunity of utilizing the spare heating capacity of CO2 refrigeration systems in supermarkets to produce heat to be sold to district heating network operators. A comprehensive description and assessment of two control strategies that could be implemented to enable the heat export function are presented. To maximise the heating capacity during the coldest moments of the year, the integration of geothermal storage with the CO2 system was investigated as an additional scenario. The BIN method was used to perform annual energy calculations. Furthermore, a sensitivity analysis was carried out on the most critical parameters, namely the heating demand, price ratio and temperature levels of the district heating network. For the assumed prices and energy demands, the supermarket could make profits corresponding to up to 16% (10,000 (sic)/year) of the annual energy cost by selling part of the heat recovered to the district heating network operator. Furthermore, the heat exported could save up to 18% of the annual CO2 emissions of the supermarket compared to the baseline. Finally, the sensitivity analysis showed that the economics of this solution is the more profitable, the lower return temperature of the heating network where the installation is connected.
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| 6. |
- Karampour, Mazyar, et al.
(författare)
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Comparison of State-of-the-art CO2 and Alternative Refrigeration Systems for Supermarkets
- 2018
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Ingår i: 13th IIR Gustav Lorentzen Conference on Natural Refrigerants. - Valencia, Spain. - 9782362150265 ; , s. 1298-1306
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the state-of-the art features of CO2 trans-critical booster systems. The performance of various modified features have been compared to the standard CO2 booster system. Subsequently, the performance of the defined state-of-the-art CO2 system is compared to natural refrigerant-based cascade, HFC/HFO-based DX and indirect refrigeration solutions, and propane water-cooled plug-ins operating in cold and warm climates. The results indicate that flooded evaporation and parallel compression are the most promising features of the state-of-the-art CO2 system. This compact and environmentally friendly system is the most energy efficient solution in cold climates, and is also an efficient solution in warm climates, with comparable efficiency to cascade and HFC/HFO DX systems, but with no existing or potential limitations.
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| 7. |
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| 8. |
- Karampour, Mazyar, et al.
(författare)
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Energy Efficiency Evaluation of Integrated CO2 Trans-critical System in Supermarkets : A Field Measurements and Modelling Analysis
- 2017
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Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 82, s. 470-486
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates energy efficiency of an integrated CO2 trans-critical booster system installed in a supermarket in Sweden. The supermarket has applied several features to improve energy efficiency including space and tap water heating, air conditioning (AC), and parallel compression. Using field measurements data, the system performance is evaluated in a warm and a cold month. Furthermore, this integrated energy system concept is modelled and compared with stand-alone HFC-based energy systems. The results show that the system provides the entire AC demands and recovers a great share of the available heat, both with high COP values. The comparative analysis shows that integrated CO2 system uses about 11% less electricity than stand-alone HFC solutions for refrigeration (i.e. indirect HFC), heating and AC in North of Europe.Energy efficiency analysis of the integrated CO2 system proves that this system is an environmentally friendly all-in-one energy efficient solution suitable for cold climate supermarkets.
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| 9. |
- Karampour, Mazyar, et al.
(författare)
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Field Measurements and Performance Evaluation of CO2 Supermarket Refrigeration Systems
- 2013
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Ingår i: 2nd IIR International Conference on Sustainability and the Cold Chain. Proceedings. - 9782913149977
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Konferensbidrag (refereegranskat)abstract
- This paper studies field measurements and performance analysis of eight supermarkets in Sweden amongwhich five supermarkets use CO2 and three use HFC as the refrigerant. The differences in system design arediscussed and detailed performance evaluation of one of the systems is presented. The performances of allthe supermarkets are compared and the reasons for higher or lower energy efficiency are discussed. Somekey components of CO2 systems are evaluated, as well.According to the results, the older CO2 systems have lower COP than the reference systems. High vapourfraction in low temperature cabinets inlet, relatively high amount of internal and external superheating and10-15% lower overall efficiency of low temperature compressors compared to the other systems are some ofthe main reasons for this lower COP. But, the newer CO2 systems proved to have higher efficiency, or atleast, as energy-efficient as the conventional systems. This originates from the modification in the systemdesign and more efficient components. System design modification includes two-stage expansion by receiverand flash gas by-pass. The newer CO2 components have higher efficiency; medium temperature levelcompressors have 5-10% higher overall efficiency compared to HFC and older CO2 compressors and thecabinets run with lower superheating so the system can be controlled to run at higher evaporationtemperatures.This study shows that CO2 systems have comparable COP to advanced conventional systems applied in Sweden.
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| 10. |
- Karampour, Mazyar, et al.
(författare)
-
Geothermal Storage Integration into a Supermarket’s CO2 Refrigeration System
- 2019
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Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 106, s. 492-505
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the integration of geothermal storage into state-of-the-art CO2 trans-critical boostersystems. 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 neighbouring building where the supermarket provides heat to the neighbour, 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.
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| 11. |
- Karampour, Mazyar, et al.
(författare)
-
Geothermal Storage Integration into Supermarket’s CO2 Refrigeration System
- 2018
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Ingår i: Proceedings of the IGSHPA Research Track 2018. - : International Ground Source Heat Pump Association.
-
Konferensbidrag (refereegranskat)abstract
- This paper investigates the integration of geothermal storage into the state-of-the-art CO2 trans-critical booster systems. The objective is to evaluate the impact on energy efficiency of this integration. Three scenarios of integration are studied including stand-alone and integrated supermarket building systems. The results show that for a stand-alone supermarket, heat recovery from the CO2 system should be prioritized over extracting heat from the ground, which can be done either by an extra evaporator in the CO2 system or by a separate ground source heat pump. In the case of supermarket integration with a nearby district heating consumer, geothermal storage integration with extra evaporator in the CO2 refrigeration system can reduce the total annual running cost of the two buildings by 20-30%. The determining factors on profitability of geothermal storage integration are the heating demand of the supermarket and possibilities of coupling its heating system to another nearby consumer. This integration is beneficial if the full efficient heat recovery capacity of the CO2 system is not sufficient to provide the entire demands.
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| 12. |
- Karampour, Mazyar, et al.
(författare)
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Integration of Heating and Air Conditioning into a CO2 Trans-Critical Booster System with Parallel Compression-Part I : Evaluation of key operating parameters using field measurements
- 2016
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Ingår i: 12th IIR Gustav Lorentzen Natural Working Fluids Conference, Edinburgh, Scotland, 2016. - : IIR.
-
Konferensbidrag (refereegranskat)abstract
- This paper investigates key operating parameters of a supermarket in Sweden where heating and air conditioning are integrated into the CO2 trans-critical refrigeration system. The Supermarket has applied several features of a state-of-the-art system including space and tap water heating, air conditioning, and parallel compression. Using field measurements data, the key operating parameters in the CO2 system are studied in a warm summer month and a cold winter month. The warm month study shows that the CO2 system provides the required temperatures for air conditioning demands; the pressure in the receiver is regulated to provide 7-8°C forward secondary fluid. Parallel compression is used to control the receiver pressure for ambient temperatures higher than 15°C. The high pressure side of integrated CO2 system is controlled mainly for heat recovery in winter. The pressure is fixed to 80-85 [bar] and the gas cooler is by-passed to recover the entire rejected heat when ambient temperature is very low. The heat recovery function of the system is analysed for both tap water and space heating circuits. The measurements show that the system is able to provide the high tap water temperature of 55-60°C throughout the year. The system is also able to provide the space heating forward temperature of up to 45°C. Analysis of the key operating parameters of the integrated CO2 system shows that it fulfils the temperature requirements of refrigeration, air conditioning, hot water, and space heating. The loads and energy efficiency of these functions of the systems have been studied in part II of this paper.
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| 13. |
- Karampour, Mazyar, et al.
(författare)
-
Integration of heating and air conditioning into a CO2 trans-critical booster system with parallel compression part II : Performance analysis based on field measurements
- 2016
-
Ingår i: Refrigeration Science and Technology. - : International Institute of Refrigeration. - 9782362150180 ; , s. 332-340
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the energy efficiency performance of an integrated CO2 trans-critical booster system providing refrigeration, heating and air conditioning demands of a small-medium size supermarket in Sweden. Using a computer model and input data from field measurements (data presented in part-I of this paper), the system loads and energy efficiencies are evaluated for a warm summer month and a cold winter month. Having analysed the loads hourly and daily, the results show that the system is able to provide the entire air conditioning (AC) demands and a great share of the available heat is recovered for tap water and space heating. It is seen that the refrigeration energy efficiency hasn't been affected providing the heating and AC demands. Focusing on air conditioning (AC) function of the system, it is shown that the system has high COP values for Tamb<25°C, confirming that it is a suitable solution for northern Europe. On the use of parallel compression (PC) during AC delivery, it is found that COPAC and COPtot of the system are 25% and 8% higher using "AC with PC" comparing with "AC without PC", respectively. Heat recovery (HR) study indicates that CO2 system provides the heating demands with high COPHR values, usually within the 4-6 range and comparable to majority of commercial heat pumps in the market. To conclude, the energy efficiency study of the integrated CO2 system functions confirm that it can be used as an environmentally friendly all-in-one supermarket energy solution suitable for mild-cold climates.
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| 14. |
- Karampour, Mazyar, et al.
(författare)
-
Integration of Supermarket’s CO2 Refrigeration System and Geothermal Storage
- 2019
-
Konferensbidrag (refereegranskat)abstract
- This paper investigates the energy efficiency of geothermal storage integration into the state-of-the-art CO2 trans-critical booster systems. Three scenarios of integration are studied including stand-alone and integrated supermarket building systems.The results show that for a stand-alone supermarket, heat recovery from the CO2 system should be prioritized over extracting heat from the ground, which this heat extraction can be done either by an extra evaporator in the CO2 system or by a separate ground source heat pump. In the case of supermarket integration with a nearby district heating consumer, geothermal storage integration with extra evaporator in the CO2 refrigeration system can reduce the total annual running cost of the two buildings by 19-31% and with a payback time of less than three years.This integration is beneficial if the full efficient heat recovery capacity of the CO2 system is not sufficient to provide the entire demands.
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| 15. |
- Karampour, Mazyar, et al.
(författare)
-
Investigation of using Internal Heat Exchangers inCO(2) Trans-critical Booster System
- 2014
-
Ingår i: 11th IIR gustav lorentzen conference on natural refrigerants (2014). - : INT INST REFRIGERATION. - 9782362150043 ; , s. 453-460
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Konferensbidrag (refereegranskat)abstract
- This paper theoretically investigates the performance of a CO2 trans-critical booster system using various configurations of internal heat exchangers (IHX). A reference case performance is compared with eight alternatives of using IHXs after the gas cooler and liquid receiver. Cooling COP, total COP and amount of heat recovery arethe comparison criteria. Heat recovery or heat rejection from the discharge gas of low stage compressors is another modification examined in this study. According to the results, no significant improvement is found by using internal heat exchanger (IHX) focusing only on the cooling COP. Considering simultaneousrefrigeration and heat recoveryfor a sample 65 bar discharge pressure, up to 12% efficiency improvement with IHX A-AC-AD for a system "with by-pass" and up to 11% improvement with IHX AC-AD-BC-BD for a system "without by-pass" iscalculated. It isshown that superheating has less influence on the available heat to be recovered in the trans-critical region in comparison with the sub-critical region. Furthermore, low stage level heat recovery and desuperheating improves the efficiency 3-4% for the cases with high amount of de-superheatingat low stage suction line, using IHX C or D. To conclude, using IHXs improves the performance of the CO2 booster system with heat recovery. This improvement is more significant in sub-critical region.
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| 16. |
- Karampour, Mazyar, et al.
(författare)
-
Performance and control strategies analysis of a CO2 trans-critical booster system
- 2014
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Konferensbidrag (refereegranskat)abstract
- This research paper theoretically studies the performance and control strategies of a CO2 trans-critical booster system. A computer simulation with field measurement-based inputs is used to analyse the performance of the system. Energy usage/efficiency indicators including cooling-heating loads, electricity use and COPs are presented and discussed for an entire year. Subsequently, some of the controlled parameters are varied to evaluate their significance in energy saving.According to the results, in the warm months, medium temperature cooling demand is 30-35% higher than cold months and the entire heat is rejected in the gas cooler while half of the dissipated heat is recovered in the de-superheater in cold months, following the suggested heat recovery control strategy. Considering the system as a heat pump, a high seasonal performance factor of 4 is achieved. Studying the control parameters shows that lowering the gas cooler approach temperature and increasing evaporation temperature in cabinets and freezers are the most efficient methods for energy saving.CO2 trans-critical booster system with proper control strategies can provide the entire refrigeration and heating demands with high energy efficiency in relatively cold climates.
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| 17. |
- Karampour, Mazyar, et al.
(författare)
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Review of supermarket refrigeration and heat recovery research at KTH-Sweden
- 2015
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Ingår i: 6th IIR Conference: Ammonia and CO2 Refrigeration Technologies. - Ohrid, Macedonia : International Institute of Refrigeration.
-
Konferensbidrag (refereegranskat)abstract
- This paper reviews findings of main projects at the Royal Institute of Technology (KTH), Sweden on supermarket refrigeration and heat recovery systems. A main focus of the research has been on CO2 trans-critical booster system, as the emerging solution in the Swedish market, where its performance has been often compared with the conventional HFC solutions.The field measurements project investigates several supermarket installations with CO2 and conventional HFC systems, where detailed performance comparisons have been performed.In addition to the standard methods for field data analysis of refrigeration systems, a simplified method has been proposed to monitor the real-time performance of the refrigeration systems in a supermarket. Proper control strategy for heat recovery has also been investigated by computer modeling and field measurement analysis.Another major study has been examining the improvement of energy efficiency using short- and long-term thermal storage in supermarkets. Daily and yearly storage solutions have been proposed and studied in this project.Focusing on improvement in energy efficiency in supermarkets, state-of-the-art refrigeration systems have been defined for further investigations and an existing supermarket modeling software developed at KTH (CyberMart) is being upgraded to investigate the recent solutions in the market.
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| 18. |
- Karampour, Mazyar, et al.
(författare)
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State-of-the-Art Integrated CO2 Refrigeration System for Supermarkets : a Comparative Analysis
- 2018
-
Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 86, s. 239-257
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the integrated and state-of-the art features of CO2 trans-critical booster systems. The main objective is to identify the most promising solutions in terms of energy efficiency impacts. First, the performance of modified features and integrated functions have been compared with the standard CO2 system and alternative heating and air conditioning solutions. Subsequently, the performance of the defined state-of-the-art CO2 system is compared to natural refrigerant-based cascade and HFC/HFO-based DX and indirect refrigeration solutions operating in cold and warm climates. The results indicate that two-stage heat recovery, flooded evaporation, parallel compression and integration of air conditioning are the most promising features of the state-of-the-art integrated CO2 system. This compact and environmentally friendly system is the most energy efficient solution in cold climates, and is also an efficient solution in warm climates, with comparable efficiency to cascade and HFC/HFO DX systems, but with no existing or potential limitations.
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| 19. |
- Karampour, Mazyar, 1980-
(författare)
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State-of-the-art Integrated Refrigeration Systems in Supermarkets : An Energy Efficiency Evaluation Based on Field Measurements Analysis and Computer Simulations
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Supermarkets have become a vital feature of modern society. However, they have significant impact on the environment due to the large amount of refrigerants needed in the refrigeration system, and due to the large energy use in the supermarket, they are the commercial buildings with highest energy intensity. The largest energy-user in the supermarket is typically refrigeration systems; these systems consume and emit a large amount of high global warming potential (GWP) refrigerants. The impacts of the supermarket refrigeration systems on the environment has been under investigation, mainly in the recent decades. The solution to mitigate these two major impacts of high GWP refrigerant emissions, and high energy use is by building more energy efficient refrigeration systems that use environmentally friendly refrigerants. Refrigeration systems using CO2 as a refrigerant has been emerged and applied as a solution in the recent two decades.This PhD thesis explores methods to increase the energy efficiency of CO2 refrigeration systems in supermarkets. The objective is to present and evaluate technical solutions that make the system competitive with conventional systems in terms of energy, environment, and economics. This thesis focuses on design modifications and energy systems’ integration. This is based on computer simulations and field measurement analysis of a number of CO2 systems installed in Sweden. The conventional HFC solutions, as reference, and alternative cooling and heating systems are included in the comparative performance studies. As the starting point of this PhD thesis, the first study was to benchmark and compare the performance of emerging CO2 systems with conventional HFC systems, which was a completion of results from a previous project. To fulfil this objective, the field performance of five CO2 systems are compared with three HFC-based systems, all installed in Swedish supermarkets. The results show that the newer generation of CO2 systems are more, or as efficient as advanced HFC system solutions. Key system parameters that have the highest impact on CO2 system’s energy efficiency are studied by computer simulations, and a CO2 baseline system is defined as the basis for this thesis. This baseline system is used in later studies to examine design and efficiency improvements and, eventually, to define the state-of-the-art CO2 system. The second study evaluates modifications in the design and integration of heating and air conditioning into the CO2 baseline system. This integration concept is investigated primarily by analysis of the field performance of a CO2 integrated system. The system is installed in a Swedish supermarket and applied several features to increase the energy efficiency and functionality of the CO2 baseline system. These include space and tap water heating, air conditioning, and parallel compression. This integrated system is also modelled and compared to stand-alone HFC-based cooling and heating systems. The results show that the integrated solution can provide heating, with heating COP values ranging from 4 to 6, comparable to commercial heat pumps. The system can also provide the entire air conditioning demands of the supermarkets. The efficiency of the system AC performance, while assisted by parallel compression, is comparable to or higher than the HFC solutions. Considering all the thermal functions of the system (refrigeration, heating, AC), the results prove that while the integrated solution is an efficient all-in-one unit in cold to moderate climates, it requires efficiency improvements to be a potent candidate in warm climates.Energy efficiency improvement of the integrated CO2 system, both in cold and warm climates, is the subject of the third study. Design features, and integration with heating and air conditioning systems are evaluated to identify the most promising solutions in terms of energy efficiency. The outcomes of the parametric study led to defining the state-of-the-art (SotA) CO2 system. State-of-the-art integrated CO2 system is defined as an energy efficient, environmentally friendly, and all-in-one compact solution able to meet all the thermal demands of supermarkets in cold and warm climates. This system includes flooded evaporation, parallel compression, and heat recovery at two temperature levels. This system is compared to conventional and alternative refrigeration systems in supermarkets. The comparison shows that the SotA CO2 system offers at least 15% annual energy savings compared to the standard CO2 system, and at least 25% compared to conventional systems with HFC’s in Stockholm, Sweden, making the system the most efficient that can be installed in Sweden today. SotA CO2 system is also one of the most efficient system in warm climates. Integration of geothermal storage into SotA CO2 system is the subject of the fourth study. This integration gained interest in the recent years in Northern Europe. The ground thermal storage can be used as a heat sink in summer, and a heat source in winter, to improve the overall performance of the CO2 system. Three scenarios of integration, including stand-alone, integrated, and hybrid energy systems in the supermarket building are evaluated. The results of the study shows that annual operating cost of a separate supermarket and district heating consumer for space heating can be decreased by 20-30% if the systems are coupled, geothermal storage is applied, and the supermarket provides heating for the consumer. This integration is advantageous for supermarket with very high heating demands, or supermarkets that share heating systems with a neighbouring building.Some major contributions are made in this PhD thesis. First, detailed field measurements analysis of the modern CO2 system is presented. This has been missing in the literature to a great extent. Second, a comprehensive screening of the most promising solutions is carried out by computer simulations, which guarantees the CO2 system operates at the highest efficiency possible. This improves and accelerates the decision-making process of supermarket stakeholders on choosing the most energy efficient solutions. Last but not least, this thesis highlights the availability and competitiveness of environmentally friendly refrigeration technologies for supermarkets.
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| 20. |
- Karampour, Mazyar, et al.
(författare)
-
Supermarket refrigeration and heat recovery using CO2 as refrigerant : A comprehensive evaluation based on field measurements and modelling
- 2014
-
Rapport (refereegranskat)abstract
- This project investigates the potentials, challenges and opportunities of using CO2 as refrigerant in the supermarket refrigeration and heat recovery systems. The focus is on CO2 trans-critical booster system, as the emerging state-of-the-art system in supermarket refrigeration field. The CO2 booster system performance is studied using computer modeling and field measurement analysis to find the most energy efficient ways for providing simultaneous cooling and heating demands in supermarkets. Through this research work, the solutions available on the market are investigated, suggestions on system modifications and optimization are made, and new system solutions are suggested.
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| 21. |
- Karampour, Mazyar, et al.
(författare)
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Theoretical analysis of CO2 trans-critical system with parallel compression for heat recovery and air conditioning in supermarkets
- 2015
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Ingår i: Refrigeration Science and Technology. - Yokohama, Japan : International Institute of Refrigeration. - 9782362150128 ; , s. 2321-2328
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Konferensbidrag (refereegranskat)abstract
- This paper theoretically analyses a CO2 trans-critical booster system in which parallel compression, heat recovery and air conditioning are integrated. The performance of the system is studied in various running modes using flash gas by-pass (FGBP) or parallel compression (PC). These running modes include summer cases with/without air conditioning and winter case with heat recovery. The results show that parallel compression is more efficient than flash gas by-pass in summer cases; the increase in COPtot is up to 14% comparing the best cases for PC and FGBP. The increase in COPtot in winter heat recovery mode is marginal, less than 4-6% and hardly-feasible in practice. Comparing the AC function of the CO2 system with a conventional HFC air conditioning system, it has been found that CO2 system is more efficient in moderate ambient temperatures lower than 20-25°C. The CO2 system's AC performance is less efficient than HFC solution in ambient temperatures higher than 25°C. To conclude, an integrated CO2 trans-critical booster system can to provide the entire supermarket's refrigeration and air conditioning demands for cold-mild climates with comparable or higher energy efficiency than the HFC solutions.
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| 22. |
- Mateu-Royo, Carlos, et al.
(författare)
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High temperature heat pump integration into district heating network
- 2020
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Ingår i: Energy Conversion and Management. - : Elsevier. - 0196-8904 .- 1879-2227. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- This study illustrates the potential of high temperature heat pumps (HTHPs) integration into district heating network (DHN) through a twofold approach, using DHN as a heat sink and source. It is used as a heat sink of HTHP that uses waste heat from the supermarket's refrigeration system as a heat source whereas it is used as a heat source to HTHP that provides heat to industrial applications. When the DHN acts as the heat sink, the integrated system provides a coefficient of performance (COP) of the waste heat recovery (WHR) system between 3.2 and 5.4, reducing the operating costs between 50% and 100% with an average price ratio of 2.25 compared with the standard CO2 refrigeration system. If the DHN is the heat source, the integrated system provides a COP from 2.8 to 5.7 for a heat sink of 110 degrees C. The alternative low-GWP refrigerants assessment illustrates that HC-290, HFO-1234ze(E) and HFO-1234yf were considered the ideal candidates to replace the HFC-134a, whereas HCFO-1233zd(E) and HCFO-1224yd(Z) were the most promising low-GWP refrigerants to replace HFC-245fa. Finally, the environmental results showed that the utilisation of the DHN as the heat sink in the integrated system solution produces about 60% lower equivalent CO2 emissions than the DHN generation mix. Moreover, using DHN as the heat source, the equivalent CO2 emissions can be reduced up to 98% in Sweden compared to conventional natural gas boilers. Hence, the combination of HTHPs and the DHN represents a step forward in the mitigation of climate change through the utilisation of sustainable energy conversion technologies.
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| 23. |
- Mateu-Royo, Carlos, et al.
(författare)
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Integration of geothermal storage in CO2 refrigeration systems of supermarkets
- 2018
-
Ingår i: Refrigeration Science and Technology. - : International Institute of Refrigeration. - 9782362150265 ; , s. 1265-1272
-
Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to study the benefits of integrating CO2 trans-critical booster refrigeration system with geothermal storage. The ground is used as a heat sink for sub-cooling during the summer period and as a heat source for extracting heat in the winter season. Using field measurements from medium size supermarkets in Sweden, proposed and the existing system solutions for integrating geothermal storage in CO2 refrigeration systems are modelled and compared with standard CO2 trans-critical booster system. The techno-economical comparative analysis shows that hybrid CO2 trans-critical booster system with ground source heat pump (GSHP) as an integrated geothermal solution has 6% lower annual energy use compared to a stand-alone CO2 system with heat recovery.
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| 24. |
- Nilsson, Per-Olof, et al.
(författare)
-
Ice Rink Refrigeration System with Carbon Dioxide as Secondary Fluid in Copper Tubes
- 2006
-
Konferensbidrag (refereegranskat)abstract
- This investigation presents the development of a refrigeration system for ice rinks based on carbon dioxide as phase changing secondary fluid in copper tubes with aim at optimising heat transfer, pressure drop and costs. A miniature ice rink was built and designed with copper tubes imbedded in a concrete slab. The tubes were developed for this purpose to have best possible conduction, protection and manufacturability at low cost.Experimental tests were conducted with CO2 circulated in the tubes of two different lengths and diameters by a hermetic pump. Correlations for heat transfer and pressure drop were compared with the experimental results to find the most suitable ones for this application.Based on the found correlations a theoretical model was developed for numerical optimisation of the geometry. Good agreement was found between the model and the experimental results.The numerical optimisation shows that the circulation rate (CR) has little influence on the overall temperature difference across the tubes when super imposing the influence of pressure drop and heat transfer. Consequently the CR should be chosen as low as possible to ensure no superheat. An economical optimisation illustrates the influence of the tube pitch on the cost of operational and the investment. The higher the annual average heat load is, the tighter the pitch should be chosen. For moderate average loads, up to 100 W/m2, the standard 100 mm pitch is found to be sufficient for 1/2” tubes.
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| 25. |
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| 26. |
- Ohannessian, Roupen, et al.
(författare)
-
Thermal energy storage potential in supermarkets
- 2014
-
Ingår i: Refrigeration Science and Technology. - 9782362150036 ; , s. 452-459
-
Konferensbidrag (refereegranskat)abstract
- The objective of this research is to evaluate the potential of thermal energy storage in supermarkets with CO2 refrigeration systems. Suitable energy storage techniques are investigated and the seasonal storage technology of boreholes is chosen to be the focus of the study. The calculations are done for four supermarket refrigeration systems with different combinations of heating systems. The two heating systems analyzed are the ground source heat pump and the heat recovery from the supermarket's refrigeration system. The simulation results show that the introduction of thermal energy storage in the scenarios with ground source heat pump can reduce the annual total energy by about 6%. Moreover, it is established that a supermarket system with heat recovery consumes 8% less energy than the one using ground source heat pump.
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| 27. |
- Piscopiello, Salvatore, et al.
(författare)
-
Guidelines of How to Instrument and Measure and Evaluate Refrigeration Systems in Supermarkets; with Focus on CO2 Trans-Critical Booster Systems
- 2018
-
Ingår i: 13th IIR Gustav Lorentzen Conference on Natural Refrigerants. - : International Institute of Refrigeration. - 9782362150265 ; , s. 1289-1297
-
Konferensbidrag (refereegranskat)abstract
- This paper reviews the guidelines of how to instrument, measure, monitor and evaluate refrigeration systems in supermarkets. The guidelines principles are firstly illustrated for a simple, single stage, refrigeration system: measurements requirements are analysed and the methodology to estimate refrigeration quantities are defined. Estimation for refrigerant mass flow rate and compressor power are more extensively described and their application on real field measurement data presented and discussed. The extension of the guidelines for a more complex refrigeration system is finally presented with focus on centralized systems providing cooling a multiple temperature levels: a HFC system with LT subcooler and a simple CO2 booster system.
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| 28. |
- Piscopiello, Salvatore, et al.
(författare)
-
Performance evaluation of a large capacity water-water heat pump using propane as refrigerant
- 2016
-
Ingår i: Refrigeration Science and Technology. - : International Institute of Refrigeration. - 9782362150180 ; , s. 803-810
-
Konferensbidrag (refereegranskat)abstract
- The use of natural refrigerants has become of increasing concern in recent years due to the high GWP and ODP of commonly used CFCs, HCFCs and HFCs. The use of hydrocarbons can be considered as potential long term solution in heat pump applications. Propane is highly flammable and potentially explosive, however; with proper safety measures in place it can be a suitable candidate for residential heat pump as it has a negligible ODP and a low GWP (3). This study presents the analysis of experimental data obtained from tests on a 45 kW heating capacity water-water heat pump. The unit is tested in heating mode, i.e. production of hot water for space heating with the possibility of simultaneous-generation of domestic hot water. The performance evaluation is carried out at system level, based on the two key parameters: heating capacity (Qh) and andehtheating COP (COP1). A map of the heat pump performance under different working conditions is developed. Simulations using the modelling software IMST-ART are performed and compared to the experimental results. The results of this study were developed in the framework of the FP7 European project 'Next Generation of Heat Pumps working with Natural fluids' (NxtHPG).
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| 29. |
- Purohit, Nilesh, et al.
(författare)
-
Integrated supermarket refrigeration for very high ambient temperature
- 2018
-
Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 165, s. 572-590
-
Tidskriftsartikel (refereegranskat)abstract
- This paper analytically investigates and compares the performance of a proposed ‘all-natural’ NH3/CO2 cascaded booster system to a conventional R404A direct expansion system as well as to an ‘all-CO2’ system with multi-ejector unit and flooded evaporator. Performance comparison is made based on the annual combined COP and Life Cycle Climate Performance (LCCP) for operation in selected cities of Middle East and India. Our results show that in extreme warm climate, the energy efficiency of the proposed configuration exceeds that of all-CO2 configuration by a maximum of about 12.23% and the total emissions are lower by up to 11.20%. However, the all-CO2 multi ejector system performs better in cold and mild warm climate. In the NH3/CO2 cascade, the high temperature NH3 system can be designed to be isolated from the accessible locations of the supermarket. The work presented is expected to help adoption of natural refrigerants such as CO2 and NH3 for commercial application in extreme warm climate conditions prevailing in many cities of Middle East and India.
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| 30. |
- Raka Adrianto, Lugas, et al.
(författare)
-
Heat Recovery from CO2 Refrigeration System in Supermarkets to District Heating Network
- 2018
-
Konferensbidrag (refereegranskat)abstract
- In the process of moving towards sustainable energy systems for future cities, the district heating system will have to be more dynamic and accessible to the different heating sources available in the society. A main potential heat source to be connected to the district heating network is the heat rejected from refrigeration systems in supermarket applications. This paper investigates the main possible scenarios for recovering heat from supermarket refrigeration system with CO2 as the refrigerant. The efficiency of the refrigeration system under the different heat recovery scenarios is studied with the aid of computer modelling. The cost of producing the recoverable heat is calculated and compared to market price from local district heating company. The total energy cost for running the system in the winter season in the different scenarios is also calculated. This study shows that the best scenario is to recover heat for space heating in the supermarket building as a priority and then recover all or part of the remaining available heat to district heating. In an average size supermarket in Sweden, all the space heating demand can be recovered from the refrigeration system with space heat recovery COP (i.e. heating COP) of about 4.5 in average. To produce 1 kW heat supplied to district heating, 2/5 to 1/8 kW of compressor power is used; i.e. district heating recovery COP is 2.5-8. This scenario results in the lowest annual energy cost of the system, about 40% lower than the reference scenario, where the refrigeration system runs at floating condensing and space heating is delivered by district heating.
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| 31. |
- Rogstam, J., et al.
(författare)
-
Carbon dioxide in ice rink refrigeration
- 2014
-
Ingår i: 11th IIR Gustav Lorentzen Conference on Natural Refrigerants. - 9782362150043 ; , s. 585-592
-
Konferensbidrag (refereegranskat)abstract
- The average energy usage of an ice rink is around 1000 MWh/year, of which approximately 70% goes to the refrigeration and heating systems. CO2 as refrigerant has favourable properties in this specific pplication due to its low-toxicity and high heat recovery potential. The use of CO2 refrigeration systems in the ice rink industry has potential to provide a paradigm shift moving from indirect systems to CO2 DX systems. This study evaluates the ice rink refrigeration system application where the overall energy performance including the heat recovery function is the main focus. A simulation model compares a conventional ice rink system with the CO2 DX alternative. The model is based on field measurements where real load profiles are generated. The results show that the CO2 DX system is the most efficient refrigeration system with the lowest total energy usage. Regarding the heat recovery function the CO2 DX system has a higher energy saving potential compared with conventional systems.
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| 32. |
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| 33. |
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| 34. |
- Sawalha, Samer, 1974-
(författare)
-
Carbon Dioxide in Supermarket Refrigeration
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis theoretically and experimentally investigates different aspects of the application of CO2 in supermarket refrigeration. Theoretical analysis has been performed using computer simulation models developed to simulate CO2 indirect, NH3/CO2 cascade, CO2 trans-critical and direct expansion (DX) R404A systems. The models supported the selection of the CO2 system solutions to be tested experimentally and facilitated the design of NH3/CO2 cascade and trans-critical systems test rigs. Performance evaluation and systems’ optimizations have also been carried out. In order to verify the findings of the theoretical analysis an experimental evaluation has been performed whereby a scaled-down medium size supermarket has been built in a laboratory environment. NH3/CO2 cascade and trans-critical systems have been tested and compared to a conventional R404A system installed in the same laboratory environment. Experimental findings have been compared to the computer simulation models. In supermarket refrigeration applications, safety is a major concern because of the large number of people that might be affected in the event of leakage. Therefore, a computer simulation model has been developed to perform calculations of the resulting concentration levels arising from different scenarios for leakage accidents in the supermarket. The model has been used to validate some of the risks associated with using CO2 in the application of supermarket refrigeration. Results of the experiments and the computer simulation models showed good agreement and suggest that the NH3/CO2 cascade system is a more efficient solution than the analyzed conventional ones for supermarket refrigeration. On the other hand, CO2 trans-critical solutions have efficiencies comparable to the conventional systems analyzed, with potential for improvements in the trans-critical systems. From a safety point of view, the analysis of the calculations’ results clearly shows that using CO2 in supermarket refrigeration does not create exceptional health risks for customers and workers in the shopping area. Studies conducted in this thesis prove that the CO2 systems investigated are efficient solutions for supermarket refrigeration.
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| 35. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
CO2 as Secondary Refrigerant in Sweden
- 2000
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The selection of an available natural alternative to replace harmful artificial refrigerants depends on the application, which defines the system boundaries and the operation range. In the last ten years, CO2 was introduced as a semi ideal refrigerant due to its environmentally friendly and good performance characteristics. In some applications the unique thermophysical and performance properties of CO2 match the boundary conditions of the system and make it very close to be the ideal working fluid for that specific application.Since the rediscovery of CO2 as a refrigerant [Lorentzen, 1990], the studies focussed on finding the possible applications of CO2 according to its properties. Commercial refrigeration accounts for almost 17% of worldwide refrigerants consumption, 11% is the percentage in cold storage applications, 28% in total (135576 tons/year) [DOE/AFEAS, 1991]. CO2 as a phase changing secondary refrigerant was studied and applied successfully in Sweden in the applications of supermarkets and cold stores. By the year 2000, 40 plants are running with capacities ranging from 10 to 280 kW; the refrigerants used in the machine room are NH3, R404, and Care50 (ethane/propane). Two and single-stage plants are used for chilling and freezing needs within the supermarkets.This study present the basics of technologies applied in these specific applications and the main results obtained compared to the old systems with artificial refrigerants.Installation and running costs, of the systems and the technical problems appearing during the installation of the CO2 systems are discussed. Another important issue discussed in this study is the possibility of converting the old plants to CO2 secondary systems.The operation and the analysis of the existing plants proved that CO2 could be successfully used as an alternative for the artificial refrigerants within the application of refrigeration in supermarkets. In addition to the obvious environmental advantages by using such systems, an extra economical achievement was observed during the installation and running of the plants.
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| 36. |
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| 37. |
- Sawalha, Samer, 1974-
(författare)
-
Commercial Refrigeration
- 2009
-
Ingår i: Natural refrigerant CO2. - : KHLim vzw. - 9789081346733 ; , s. 101-172
-
Bokkapitel (refereegranskat)
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| 38. |
- Sawalha, Samer, et al.
(författare)
-
Dagens effektivaste livsmedelsbutik är definierad; den kommer att byggas och verifieras i en verklig livsmedelsbutik
- 2018
-
Annan publikation (populärvet., debatt m.m.)abstract
- Projektet ”Morgondagens energieffektiva livsmedelsbutik” avslutades i februari 2018. Det har letts av KTH och genomförts i samarbete med en grupp industripartner, och medfinansierats av Energimyndigheten inom ramen för Effsys EXPAND-program. Projektet har utforskat en ökning av effektiviteten hos standardkoldioxidkylsystem i livsmedelsbutiker genom att undersöka ändringar av utformningen och möjligheterna att integrera systemen med andra energisystem i livsmedelsbutiken.
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| 39. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
Energy Consumption Evaluation of Indirect Systems with CO2 as Secondary Refrigerant in Supermarket Refrigeration
- 2003
-
Konferensbidrag (refereegranskat)abstract
- In this study, we investigate the influence of the pressure and temperature drops in the suction and return lines on the energy consumption of a supermarket refrigeration plant. We calculate the energy consumption of CO2indirect systems with R404A, ammonia or propane as the primary refrigerant and compare it to conventional direct expansion (DX) system with R404A or R502. CO2pressure drop and the corresponding saturation temperature drop in the indirect circuit is calculated and compared to that of R404A. The energy consumption of R404A/CO2indirect systems was found to be very close to R404A-DX system using the same pipe size in the return and suction lines. Replacing R404A by ammonia or propane in the indirect system reduced the energy consumption. This study indicates that it is more economical to use CO2indirect system with proper primary refrigerant rather than using the conventional DX systems.
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| 40. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
Experimental and Theoretical Evaluation of NH3/CO2 Cascade System for Supermarket Refrigeration in Laboratory Environment
- 2006
-
Konferensbidrag (refereegranskat)abstract
- In this paper we investigate and evaluate the performance of an NH3/CO2 cascade system forsupermarket refrigeration application in a laboratory controlled environment. The system solutionunder investigation replicates a medium size supermarket in Sweden. CO2 is used at the low andmedium temperature levels with several possibilities available for system variations and parametricanalysis. Along with the experimental rig a computer simulation model has been developed toevaluate the performance and test the influence of different parameters on the system’s efficiency.Overall system evaluation has been performed. Different circulation rates at the mediumtemperature level have been tested. Control system of the freezing cabinets has been evaluated.The results of the tests show that the experimental COP’s are in good agreement with the onescalculated by the computer model. Evaluation of different circulation rates show that it should bekept as low as possible and there is no optimum value as in the case of conventional brine. Thecontrol of the electronic expansion valve should be based on the evaporating pressure rather thanmeasuring surface temperature of the evaporator.
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| 41. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
Experimental Investigation of NH3/CO2 Cascade system and comparison to R404A system for supermarket refrigeration
- 2007
-
Konferensbidrag (refereegranskat)abstract
- This study investigates the performance of an NH3/CO2 cascade system for supermarket refrigerationapplication in a laboratory environment. The tested CO2 system is designed and scaled to fulfil therequirements of an average size supermarket in Sweden. Possibility for hot gas defrost in the freezers hasbeen investigated and compared to the conventional electric heaters defrost method. Two cascade condenserarrangements have been evaluated. The cascade system has been compared to R404A system installed in thesame laboratory.The results show that connecting the cascade condenser via thermosyphon or hot gas de-superheatarrangements yields good system stability and heat transfer performance. Hot gas defrost successfullydefrosted the freezer evaporator but with long period and higher energy consumption compared to theconventional electric defrost method. The tested cascade system had up to 60% higher total COP comparedto the R404A system installed in laboratory.
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| 42. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
Field measurements of supermarket refrigeration systems : Part I: Analysis of CO2 trans-critical refrigeration systems
- 2015
-
Ingår i: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 87, s. 633-647
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the refrigeration performance of three CO2 trans-critical solutions based on field measurements. The measurements are carried out in five supermarkets in Sweden. Using the field measurements, low and medium temperature level cooling capacities and COP's are calculated for ten-minute intervals, filtered and averaged to monthly values. The results indicate that the systems using trans-critical booster system with gas removal from the intermediate vessel have relatively the highest total COP. The reasons are higher evaporation temperatures, lower internal and external superheat and higher total efficiency of booster compressors. Another important factor is gas removal from the intermediate vessel which leads to higher COP of low temperature level. Comparing the older and newer installed systems, a trend in energy efficiency improvement has been seen. The study shows this improvement originates from both changes in the system design (e.g. two stage expansion) and components efficiency improvement (e.g. higher total efficiency of compressors - lower internal superheat and higher evaporation temperatures of cabinets).
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| 43. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
Field measurements of supermarket refrigeration systems. Part II: Analysis of HFC refrigeration systems and comparison to CO2 trans-critical
- 2017
-
Ingår i: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 111:1, s. 170-182
-
Tidskriftsartikel (refereegranskat)abstract
- This part of the study investigates the performance of HFC refrigeration systems for supermarkets and compares the performance with alternative CO2 trans-critical solutions. The investigated HFC system solutions are typical in supermarkets in Sweden. The analysis in this study is based on field measurements which were carried out in three supermarkets in Sweden. The results are compared to the findings from Part I of this study where five CO2 trans-critical systems were analyzed. Using the field measurements, low and medium temperature level cooling demands and COP’s are calculated for five-minute intervals, filtered and averaged to monthly values. The different refrigeration systems are made comparable by looking at the different COP’s versus condensing temperatures. The field measurement analysis is combined with theoretical modelling where the annual energy use of the HFC and CO2 trans-critical refrigeration systems is calculated. Comparing the field measurement and modelling results of COP’s for HFC and CO2 systems, the new CO2 systems have higher total COP than HFC systems for outdoor temperatures lower than about 24 C. The modelling is used to calculate the annual energy use of HFC and new CO2 system in an average size supermarket in Stockholm, new CO2 systems use about 20% less energy than a typical HFC system. The detailed analysis done in this study (Part I and Part II) proves that new CO2 trans-critical refrigeration systems are more energy efficient solutions for supermarkets than typical HFC systems in Sweden.
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| 44. |
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| 45. |
- Sawalha, Samer, et al.
(författare)
-
Forskning på KTH om livsmedelskyla-En översikt.
- 2014
-
Annan publikation (populärvet., debatt m.m.)abstract
- På avdelningen för Tillämpad Termodynamik och kylteknik, Institutionen för Energiteknik på KTH har vi arbetat med livsmedelskyla för butiker och stormarkander sedan mer än 15 år. Detta har skett inom ramen för olika projekt och med olika inriktning, innefattande datorsimuleringar, experimentella arbeten och fältmätningar. Vi har därigenom byggt upp en gedigen kompetens inom området och vi har också tillgång till värdefulla vetenskapliga verktyg för att belysa olika fundamentala frågeställningar inom området som på senare år undergått en mycket dynamisk utveckling.
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| 46. |
- Sawalha, Samer, 1974-
(författare)
-
Investigation of heat recovery in CO2 trans-critical solution for supermarket refrigeration
- 2012
-
Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 36:1, s. 145-156
-
Tidskriftsartikel (refereegranskat)abstract
- Using computer simulation modeling this study investigates the performance of a CO2 trans-critical system with heat recovery from the de-superheater. The influence of sub-cooling (or further cooling) in the condenser/gas cooler on system performance is investigated. Following the suggested control strategy in this study, the extra operating energy demand required to recover the needed heating energy from the analyzed CO2 system is smaller than what a typical heat pump would require for the same load. This is the case for almost all ambient temperatures over a full season. When taking the simultaneous heating and cooling loads into account, the CO2 trans-critical system has lower annual energy usage in an average size supermarket in Sweden when compared to a conventional R404A refrigeration system with separate heat pump for heating needs. CO2 trans-critical systems are efficient solutions for simultaneous cooling and heating needs in supermarkets in relatively cold climates.
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| 47. |
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| 48. |
- Sawalha, Samer
(författare)
-
Korttidslagring av energi med fasändringmaterial för effektiv integrering med värme- och kylsystem i byggnader-Effsys Expand projekt på KTH
- 2016
-
Annan publikation (populärvet., debatt m.m.)abstract
- International Energy Agency (IEA) presenterade nyligen sin plan för energieffektiva byggnader där termisk energilagring lyfts som en av fyra nyckelkomponenter i byggnaders värme- och kylsystem. PCM-baserad (Phase Change Materials – fasändringsmaterial) termisk energilagring (PCM-TES) har några fördela jämfört sensibla lager: kompakta system (hög energidensitet), samt lagring i ett litet temperaturintervall. Sådana egenskaper gör det lättare att integrera och nyttja förnybar energi (t ex solvärme och frikyla), realisera byggnadskoncept för lågenergi/passivhus, samt ökar effektiviteten i utrustning såsom värmepumpar och kylmaskiner.
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| 49. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
Laboratory Tests of NH3/CO2 Cascade System for Supermarket Refrigeration
- 2005
-
Konferensbidrag (refereegranskat)abstract
- The development of a laboratory test rig of an NH3/CO2 cascade system is presented in this paper along with a theoretical model that simulates the performance of the system. The system solution under investigation replicates a medium size supermarket in Sweden, it is designed to fulfil the general requirements of the supermarket and operate within its temperature boundaries. Several possibilities to modify the system and test the influence of different parameters were implemented; this will facilitate the optimization of the system for the best of its performance. A theoretical model was used to design the system and size its components. Based on the input system requirements the performance of the system can be simulated.
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| 50. |
- Sawalha, Samer, 1974-, et al.
(författare)
-
Safety Analysis of CO2 as a Refrigerant in Supermarket Refrigeration
- 2002
-
Konferensbidrag (refereegranskat)abstract
- In this study we analyse some safety aspects related to the usage of CO2 in supermarket refrigeration. The concentration levels in the supermarket’s shopping area and machine room that result from different accident scenarios are calculated for a selected practical example. The ventilation requirements in the supermarket under normal conditions and during a leakage accident are taken into consideration. For the selected case, the analysis of the calculations’ results showed that CO2 does not enclose a heath hazard for the customers and workers within the shopping area, whereas safety requirements expressed by efficient ventilation and proper alarm system must be installed in the machine room
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