| 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. |
- 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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| 4. |
- Karampour, Mazyar, et al.
(författare)
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Investigation of using Internal Heat Exchangers inCO(2) Trans-critical Booster System
- 2014
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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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| 5. |
- Karampour, Mazyar, et al.
(författare)
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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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| 6. |
- Karampour, Mazyar, et al.
(författare)
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Supermarket refrigeration and heat recovery using CO2 as refrigerant : A comprehensive evaluation based on field measurements and modelling
- 2014
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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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| 7. |
- Ohannessian, Roupen, et al.
(författare)
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Thermal energy storage potential in supermarkets
- 2014
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Ingår i: Refrigeration Science and Technology. - 9782362150036 ; , s. 452-459
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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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| 8. |
- Rogstam, J., et al.
(författare)
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Carbon dioxide in ice rink refrigeration
- 2014
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Ingår i: 11th IIR Gustav Lorentzen Conference on Natural Refrigerants. - 9782362150043 ; , s. 585-592
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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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| 9. |
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| 10. |
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| 11. |
- Sawalha, Samer, et al.
(författare)
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Forskning på KTH om livsmedelskyla-En översikt.
- 2014
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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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| 12. |
- Sawalha, Samer, 1974-
(författare)
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Investigation of heat recovery in CO2 trans-critical solution for supermarket refrigeration
- 2012
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Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 36:1, s. 145-156
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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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| 13. |
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| 14. |
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| 15. |
- Sawalha, Samer, et al.
(författare)
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Värmeåtervinning med CO2 i livsmedelsbutikers kylanläggningar. – Hur ska den styras och hur effektiv kan den bli?
- 2013
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Annan publikation (populärvet., debatt m.m.)abstract
- Kylanläggningar i livmedelsbutiker har ofta stort energibehov och antalet installationer ökar oavbrutet. I ett typiskt livsmedelsbutiks installation i Sverige går 35-50% av det totala elbehovet åt för att driva kylanläggningarna (Lundqvist, 2000). Situationen i USA är likartad (Richard Royal, 2010; Arthur D. Little Inc, 1996). Samtidigt avger kyl- och frysanläggningarna avsevärda energimängdeer i form av värme som skulle kunna utnyttjas för att täcka eller åtminstone reducera behovet för värme och varmvatten.
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