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This study explores the capability of a supermarket to fulfill the thermal demands of neighboring buildings. The research combines field measurements analysis, obtained from a Swedish supermarket which covers the neighbors' thermal demands, with theoretical calculations, using thermodynamic models of the refrigeration system and the ground source thermal storage. In contrast to previous studies, this work is unique in its use of demonstrating a real-life built case study rather than only theoretical approach. Results demonstrate that inte-grating ground source storage in a supermarket can meet the thermal demands of neighboring buildings without requiring additional equipment. The refrigeration system accounts for 80% of the total heat demand, while the ground serves as a heat source for the rest. This approach results in 67% annual operating cost savings for the neighboring buildings. In addition, ground source subcooling provides 9% annual energy savings to supermar-ket's refrigeration system. By exporting heat to neighboring buildings, the proposed solution emits 90% less CO2 in Uppsala and 67% less in Stockholm compared to solutions in which the refrigeration system only meets the refrigeration demands. Summing up, the concept of utilizing supermarkets to meet thermal demands offers a more energy-efficient operation for both supermarkets and property owners while significantly reducing annual energy consumption and emissions., QC 20230706

This paper investigates ellipsoid-shaped macro-encapsulated phase change material (PCM) on a component scale. The selected PCM is a paraffin-based commercial material, namely ATP60; differential scanning calorimetry and transient plane source method are used to measure ATP60's thermo-physical properties. A 0.382 m(3) latent heat thermal energy storage (LHTES) component has been built and experimentally characterized. The temperature measurement results indicate that a thermocline was retained in the packed bed region during charging/discharging processes. The experimental characterization shows that increasing the temperature difference between the heat transfer fluid (HTF) inlet temperature and phase-change temperature by 20 K can shorten the completion time of discharge by 65%, and increasing HTF inlet flowrate from 0.15 m(3)/h (Re = 77) to 0.5 m(3)/h (Re = 256) can shorten the completion time of charge by 51%. Furthermore, a one-dimensional packed bed model using source-based enthalpy method was developed and validated by comparison to experimental results, showing discrepancies in the accumulated storage capacity within 6.6% between simulation and experiment when the Reynolds number of the HTF inlet flow ranges between 90 and 922. Compared with a conventional capsule shaped in 69-mm-diameter and 750-mm-long cylinders, the ellipsoidal capsule shows 60% less completion time of discharge but 23% lower storage capacity. Overall, this work demonstrates a combined experimental and numerical characterization approach for applying novel macro-encapsulated PCM geometries for heating-oriented LHTES., QC 20211021

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)., QC 20210126

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., QC 20210621

Integrating latent heat thermal energy storage (LHTES) units into building heating systems has been increasinglyinvestigated as a heat load management technology. A conventional LHTES integration method for heat pumpbased heating systems is to connect the heat pump’s condenser for charging the LHTES unit. This integratinglayout however usually leads to increased electricity input to the heating system. To underline this issue andprovide solutions, this paper presents three new LHTES integrating layouts where the LHTES unit is connectedwith the de-superheater of the main heat pump (Case 2), the condenser of a cascaded booster heat pump cycle(Case 3), or a combination of using both the de-superheater and the booster cycle (Case 4). In the context of amulti-family house in Stockholm, a quasi-steady state heating system model was developed to evaluate the newintegrating layouts, which were benchmarked against the baseline heating system without storage (Case 0) andthe conventional integrating layout using the main heat pump condenser (Case 1). Hourly electric power input tothe heating system was modelled for calculating the performance indicators including the heating performancefactor, the operational expense and justifiable capital expense, and the indirect CO2 emissions. Two load shiftingstrategies were simulated for an evaluation period of Week 1, 2019: 1) charge during off-peak hours (8 pm to 6am) and 2) charge during daytime hours (10 am to 7 pm). The simulation results of the off-peak charging strategyshow that, in Cases 2–4, the heating performance factor is 22%-26% higher than Case 1 and the operational expense can be reduced by 2%-5% as compared with Case 0. The savings in the operational expense can justifythe capital expense of 11 k-25 k Swedish Krona (SEK) for the LHTES systems in Cases 2–4 assuming a 15-yearoperation. Furthermore, the advantage of using the daytime charging strategy is principally the mitigation of CO2 emissions, which is up to 14% lower t, QC 20210521

Latent heat thermal energy storage has been receiving increasing interests in residential heating applications. In this paper, a numerical heat transfer model was built with finite element method for a cylindrically encapsulated latent heat storage prototype and used for investigating its thermal performance optimization measures. The model was validated against four sets of experimental results for both charge and discharge, as the difference in accumulated storage capacity between simulation and experiment is less than 4%. Transient storage inlet boundary conditions were set in simulation for discharge considering the thermal output from the coupled radiators. The results of the optimization analyses show that: 1) reducing the capsule diameter from 69 mm to 15 mm shortens the completion time of charge and discharge by up to 70%, however, at the expense of 23% decrease in total storage capacity; 2) using parabolic or linear time-increasing heat transfer fluid flowrate profiles than a time-constant one extends around twofold the useful discharge timespan; 3) increasing the storage vessel diameter from 0.6 m to 0.7 m and to 0.8 m prolongs the useful discharge timespan from 2 hrs to the recommended 3 hrs, though the further enlargement to 0.8 m results in a lower state of charge after 3 hrs due to increase in unexploited storage capacity. From the numerical optimization study, we proposed a storage design adjustment of using 15 mm-diameter phase change material capsules in a 0.7 m-diameter cylindrical storage vessel, coupled with a parabolic flow strategy, to improve the storage on-peak discharging performance., QC 20200818

Latent heat thermal energy storage (LHTES) has been receiving increasing attention from researchers and engineers. A practical LHTES installation requires a deep understanding of phase change material’s (PCM’s) thermal behavior under thermal property testing and realistic operating conditions. To enrich this understanding, an experimental study on a commercial sodium acetate trihydrate-based PCM (Climsel C58) is presented in this article. C58 was characterized with two test methods: T-history tests and full-scale LHTES tests. The results are presented and discussed to exhibit the thermal behavior of C58 with these two test methods and the variations between them. With T-history tests, the thermal properties of C58 such as melting/solidification temperature range (57–61 °C/55–50 °C) and latent heat of fusion (216 kJ/kg) were determined. In full-scale LHTES tests, a parametric study was conducted to investigate the effects of heat transfer fluid flowrate and operating temperature range on the thermal performance of a 0.38 m3 storage prototype containing cylindrically macro-encapsulated C58. Moreover, longitudinal and radial PCM temperature distributions in full-scale tests were analyzed, suggesting the presence of phase separation. In general, C58 behaved differently between the two test methods regarding phase separation (negligible in T-history tests), supercooling effects (within 3 K in full-scale but up to 10 K in T-history tests), and thermal energy storage capacity (10% lower in full-scale tests). When using C58 or other salt hydrate-based PCMs for large-scale heat storage, these thermal behavior differences between the property-measurement and the application-oriented environments should be properly addressed in the design stage to ensure performance., QC 20200122

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., QC 20200520

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., QC 20190527. QC 20191111

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, QC 20190430

Short-term latent heat thermal energy storage (LHTES) can be integrated in building heating systems for performing load shifting from on- to off-peak hours. In this study, the coupling effects of LHTES integration in heat pump heating systems are investigated for a multi-family building in Stockholm. As the reference heat pump provides heat in two separate heat exchangers, a de-superheater for domestic hot water and a condenser for space heating, two configurations for LHTES integration with the two respective heat exchangers are compared using a quasi-stationary mathematic system model. The performances of the two integrating configurations are also compared with the basic heat pump heating scenario (no heat storage) regarding the total electricity consumption, the seasonal performance factor (SPF), and the electric bills for end-users over a selected heating-season week. The simulation results reveal that, while using the condenser for charging an LHTES unit containing phase change materials melted at 58 oC inevitably increases the total electricity consumption in the heating system relative to the basic scenario, using the desuperheater instead for LHTES charging can reduce the total electricity consumptions and bills of 24 kWh and 173 SEK (17€), respectively, during that specific week., QC 20200515

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., QC 20181019

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., QC 20181019

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., QC 20181019

Using heat pump technology to provide Space Heating (SH) and to produce Domestic Hot Water (DHW) for residential buildings has been widely applied during past decades. In this study, two scenarios adopting large-capacity propane heat pumps are defined and evaluated. These two scenarios, which are named after Scenario A and Scenario B respectively, provide SH and DHW either separately by two units or integrally by one unit. The COP1s of two scenarios are compared based on the simulation results from experimentally validated models. The results show that two scenarios have almost equal efficiency; the relative difference is within 6%. In the optimization analysis of Scenario B, varying DHW heating capacity produced by the desuperheater in the heat pump is modelled. The DHW demand ratio varies from approximately 9% to 20% with no detectable influences on the COP1. The corresponding COP1s and temperature profiles in the heat exchangers are demonstrated. The simulation results indicate that increasing DHW capacity in Scenario B can narrow down the temperature approach in the condenser and insignificantly improves the overall COP1s., QC 20181019

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., QC 20181105

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., QC 20180921, Effsys Expand

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., QC 20180110, Effsys Expand

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., QC 20161005, Effsys EXPAND

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., QC 20170815, Effsys Expand, EP04

Heat pump applications working with hydrocarbons as refrigerant have been under significant development along with the gradual phasing-out of conventional HFC systems. In this study, a large capacity air-water heat pump prototype using propane as refrigerant is tested to evaluate its heating performance under different operating conditions. The experimental set-up is briefly explained. The results of the experimental investigations of the heat pump prototype are presented in terms of the COP1, heating capacity and the compressor efficiency. At the design point, the experimental COP1 and heating capacity are 3.43 and 36.59 kW respectively. Experimental results for all test conditions are compared to simulation results generated from the model, which is created by the software IMST-ART. The model is validated through comparisons of those parameters since a good agreement between simulated and experimental data have been found. The maximum discrepancies of COP1 and heating capacity are around 5% and 10% respectively., QC 20160929, NxtHPG

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)., QC 20170629

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., QC 20181019

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)., QC 20150831

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., NQC 20151216

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., QC 20181019

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., QC 20151216, Effsys+

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., QC 20160926

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., QC 20151216

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 are the 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 simultaneous refrigeration and heat recovery for 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” is calculated. It is shown 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 de-superheating improves the efficiency 3-4% for the cases with high amount of de-superheating at 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., QC 20151216, EFFSYS+

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., QC 20150807

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., QC 20181019

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., QC 20151216

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., Titre en franÇais:Solution au CO2 transcritique pour le froid dans les supermarchés : Étude sur la récupération de chaleurQC 20121206

QC 20120221