Validation of a Modelica numerical model for pillow plate heat exchangers using phase change material

Refrigeration systems are often installed in industrial facilities where the difference between the peak and average thermal loads can be considerable due to the throughput of products and changes in the ambient conditions throughout the year. Cold Thermal Energy Storage (CTES) technologies can be introduced to increase the flexibility of such installations by decoupling the supply and demand of refrigeration. CTES systems based on the latent heat storage principle using Phase Change Materials (PCM) are preferred over sensible heat storage due to higher compactness, operation over a narrow temperature range and ability to tailor the storage temperature to each specific application. The current study presents a numerical model of a CTES unit using PCM as the storage medium and CO2 as refrigerant. The heat exchanger in the CTES unit consists of a stack of pillow plates immersed into a stainless-steel container filled with PCM. The charging and discharging processes of the PCM-CTES unit are carried out through evaporation and condensation of the CO2 circulating inside the plates, respectively. The dynamic model of the PCM-CTES unit is developed in the object-oriented programming language Modelica using the component library TIL-Suite. The model of the PCM-CTES unit is validated by using previously published experimental data from a test facility with an identical setup. Various heat exchanger configurations, storage medium and refrigerant parameters are tested, and the model demonstrates good agreement with the experimental data.Validation of a Modelica numerical model for pillow plate heat exchangers using phase change materialacceptedVersio

Cold thermal energy storage in solid-liquid transition of carbon dioxide: Investigating the possibility

Industrial freezing is an energy-intensive process which is growing due to the increasing demand. This is exerting stress on electrical grids, especially at peak hours. To tackle this issue, thermal energy storage has received attention; however, there is a gap in terms of suitable materials for thermal energy storage with temperatures below -40 °C commonly needed in these applications. In this paper, the solid-liquid phase change of carbon dioxide has been conceptually considered for thermal energy storage in a special type of heat exchangers known as pillow plate heat exchangers. Characteristically, these heat exchangers can withstand very high pressures which is a technical requirement for carbon dioxide thermal energy storage. This paper discusses the potential system layout and challenges ahead of this technology, along with the proposal for further investigation to verify the concept.Cold thermal energy storage in solid-liquid transition of carbon dioxide: Investigating the possibilityacceptedVersio

Innovative refrigeration concept for passenger ships - combining CO2 refrigerant, cold recovery and cold storage

More stringent international regulations on ship's emissions require a shift towards more climate friendly fuels, such as liquefied natural gas (LNG). On LNG-driven ships, the fuel is stored onboard at cryogenic temperature. The fuel must be vaporised before injected into the engine, implying a potential for cold recovery. Today, concepts are commercially available for utilising this surplus cold in conventional AC chiller system. This paper proposes an innovative concept where the LNG cold recovery system is integrated with a provision refrigeration system based on a CO2 booster unit and a cold thermal storage (CTES) due to the dynamic nature of loads and cold-recovery availability. The CTES is based on phase change materials (PCM) which, together with the choice of CO2 as refrigerant, ensures a compact system. The results show a potential for significant reduction in power consumption of the refrigeration systems and thereby contributing to reduced GHG emissions.Innovative refrigeration concept for passenger ships - combining CO2 refrigerant, cold recovery and cold storageacceptedVersio

Cold thermal energy storage for industrial CO refrigeration systems using phase change material: An experimental study

Refrigeration systems in industrial food processing plants are large users of electric energy and often show high peak power consumption. Cold thermal energy storage (CTES) technology integrated into refrigeration systems can reduce the peak power requirement and achieve peak shifting by decoupling the supply and demand of the refrigeration load. This paper presents the design and performance of a CTES unit consisting of a pillow plate heat exchanger (PP-HEX) immersed into a low-temperature phase change material (PCM) as the storage medium. It is one of the first experimental investigations featuring a large-scale technical solution that allows for coupling the evaporation and condensation processes of the refrigeration system with the melting and solidification of a low-temperature PCM in the same heat exchanger. The charging and discharging performance of the plates-in-tank CTES unit was extensively tested using CO as the refrigerant and a commercial PCM with phase change temperature of -9.6 °C. The charging time was found to be mainly affected by the refrigerant evaporation temperature, while the discharging rate and discharged energy over the cycle was higher when increasing the refrigerant condensing temperature. Using a plate pitch of 30 mm resulted in the highest mean discharge rate and total discharged energy over the cycle with 9.79 kW and 17.04 kWh, respectively. The flexible CTES-PCM unit can be adapted to fit several refrigeration load characteristics and temperature levels by changing the PP-HEX geometry and type of PCM used as the storage medium.publishedVersio

Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climates

The novel configuration presented in this work simplifies the layout of ejector-supported booster systems while maintaining all the benefits of an ejector implementation. The basic version of the solution is based on: i) MT and LT compressor suction groups, ii) flooded MT evaporation with increased evaporation temperature, and iii) ejector utilization throughout the year. The ejector is actively operated as a high-pressure-control device at elevated ambient temperatures ('summer mode'). With lower ambient temperatures the ejector is operated passively, and the high-pressure control is performed by individual metering devices upstream of the different evaporators ('winter mode'). The feasibility tests performed in the laboratory proved that energy-wise this novel system configuration outperforms traditional and parallel compression supported booster systems under any condition. The pressure lift measured with active ejector is sufficient for liquid refrigerant distribution to the evaporators, while the pressure drop recorded in passive mode is negligible for practical applications.Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climatesacceptedVersio

Integrated CO2 refrigeration and heat pump systems for dairies

Production facilities in the food industry are large consumers of electricity and thermal energy due to energyintensive processes such as steam production, cleaning, sanitising, refrigeration and drying. Furthermore, there is often a considerable thermal demand for heating the building and for air‐conditioning purposes. Dairy plants require both heating and cooling at various temperature levels to process the different dairy products. The thermal demands in these plants have traditionally been covered by separate systems, such as fossil fuel burners or electric boilers for the heating processes and various refrigeration systems for the cooling processes. In recent years, there has been an increased focus on integrated energy systems for dairies as a measure to reduce the overall energy consumption of the plant. This strategy involves integrating all functions to serve the thermal demands into one centralised energy system. This paper describes the energy system for a dairy plant in central Norway. A CO2 refrigeration system serves the various cooling loads in the production process. The energy system in the dairy is mapped and the thermal loads have been identified. Based on the current configuration of the cold side of the CO2 refrigeration units, proposals for improvements are made. Using thermodynamic calculations, the modifications are evaluated in terms of COP improvement and the annual reduction in energy consumption. The calculations show that the energy consumption can be reduced by 12 % to 21.2 % depending on the alteration of the system.Integrated CO2 refrigeration and heat pump systems for dairiesacceptedVersio

Energy flow analysis of an industrial ammonia refrigeration system and potential for a cold thermal energy storage

There is an increasing effort to reduce energy demand at food processing plants, mainly to reduce the total carbon footprint. The energy demand of a fish processing plant (using ammonia as refrigerant) has been evaluated in this study. Results show that production follows a seasonal cycle throughout the year, with no (or very low) production in the spring (Mar-May), and peak production in the autumn (Sep-Nov). By investigating data from the plant's energy management system, it was revealed that the refrigeration systems are responsible for about 75% of the total electric power demand and the compressors for 90-95% of that. Because of the large discrepancy in energy demand over the year, and also daily variation within production periods, there is a good potential for installing a cold thermal energy storage. An initial evaluation on how a CTES system can be implemented at the plant is included, discussing type of storage, choice of PCM (e.g. solid CO2) and effect on heat production, but this evaluation will be developed further.Energy flow analysis of an industrial ammonia refrigeration system and potential for a cold thermal energy storageacceptedVersio

Advanced R744 solution for supermarkets, hotel chillers and maritime applications in India

R744 integrated systems can meet oscillating heating and cooling demands efficiently and become a game changer in countries such as India. The present work aims to develop and present R744 system designs and disseminate the knowledge under the framework of the INDEE+ project in India, with the focus on three vital sectors: supermarkets, hotels, and seafood industries. Ejector-supported R744 systems are observed to be an ideal solution to increase the R744 system efficiency at high ambient temperature operations as in tropical regions. The strategy is also to evaluate the system operations to deal with an individually proposed R744 system performances to fulfil the thermal load handling demand on both heating and cooling side. Furthermore, students, vendors and end-users are planned to train by utilizing the upcoming demonstration sites with R744 technology. Support is being provided to communicate and finalize the R744 system design specification for the various system configurations. Each development aspect will be evaluated critically to make the proposed R744 technology demo units a success and to become flagship developments supporting India to transfer towards clean cooling and heating technologies.Advanced R744 solution for supermarkets, hotel chillers and maritime applications in IndiaacceptedVersio

Energy distribution concepts for Urban Supermarkets including energy hubs

More and more of the earths population is living in urban areas. This indicates that using urban building plots for combined purposes will be important in the future. For this reason supermarket chains are developing new building concepts that includes supermarket sales area, apartments on the upper floors and parking lots with energy supply hubs for the new generation of hydrogen/electric vehicles. This master thesis emphasizes this concept by designing the complete energy system for such a building and taking into account demands for heating, cooling and refrigeration. A literature review of subsystems and components relevant for the different parts of the building concept was performed. This includes supermarket refrigeration systems, hydrogen refueling stations, energy systems for high performance buildings and thermal storage. Based on the findings from the literature study, a complete design for the building energy system was proposed. The purpose of the energy system is to integrate the different subsystems together to enable heat recovery to use for space heating and domestic hot water, and thereby minimizing the import of primary energy to the building plot. A key feature of the energy system is that it is organized in three circuits with different temperature levels. They include a high temperature water circuit for domestic hot water, a medium temperature water circuit for space heating and low temperature antifreeze circuit connected to boreholes for heat storage, cooling of ventilation air and as a heat source. Space heating in the building is covered by a low temperature 28/33°C return/supply floor heating system as well as heating of ventilation air. Hour-by-hour energy demand over a year for space heating and domestic hot water for the building was obtained by developing a model of the building envelope in the software SIMIEN. The data obtained was based on assuming a plausible layout and design for this type of building. The supermarket occupies the whole first floor of the building and thirty apartments the three next floors, separated into ten apartments on each floor. The building envelope is designed according to the requirements and specifications to the Norwegian passive house standard. Four weeks were picked from the yearly demand report from SIMIEN to give as input to the simulation of the energy system. The four weeks serves as boundary conditions for a performance investigation of the energy system during spring, summer, fall and winter. To evaluate the chosen design of the energy system three different variants of the system, called case 1, 2 and 3, was developed in the dynamic simulation software Dymola. The three models were simulated for all four weeks and the results compared. Case 1 involves integrating the supermarket refrigeration system to the centralized heating system in the building and delivering waste heat from the gas coolers to space heating and domestic hot water. Simulations show that by operating the system in trans-critical mode, heat recovery could cover the full demand of domestic hot water in the building for all weeks. In addition, the full space heating demand could be covered by heat recovery for the summer and spring week, and reaching a share of 75.4% and 31.4% for the fall and winter week. Remaining heat demand in the building was covered by a R290 ground source heat pump connected to the energy wells on the evaporator side. Case 2 and 3 investigate heat recovery from the hydrogen refueling station in two different ways in addition to heat recovery from the supermarket refrigeration system. The waste heat at the hydrogen station is due to the operation of an electrolyser, compression of hydrogen gas and precooling of hydrogen gas during filling of vehicles. The available waste heat/refrigeration load in case 2 and 3 was linked to the daily production level of hydrogen gas in the electrolyser. The production was assumed constant through the day, and equal for all days of the week, giving a constant waste heat availability. In case 2, an antifreeze cooling circuit from the hydrogen station brings waste heat at 45°C to the centralized heating system of the building, and the heat is recovered to space heating by a heat exchanger. In case 3, the hydrogen station is integrated entirely with the CO2 booster refrigeration system in the supermarket, and the refrigeration demand at the station is covered by it. The first comparison between case 1, 2 and 3 was based on a daily production of 50 kg of hydrogen fuel, corresponding to 25% of maximum installed capacity. Results showed that case 2 and 3 displayed similar performance for space heating heat recovery, where both could satisfy the space heating demand for summer, spring and fall week, and about 60% during a winter week. Due to high uncertainty in the demand for hydrogen fuel in the area, a parameter study of the hydrogen production level was carried out. The production level was varied from 10% to 100% and simulated for the winter week. For both case 2 and 3, a daily production level of 75% (150 kg) and higher could cover all space heating demand. In addition, case 3 showed a large potential to supply domestic hot water, up to 5.5 times the demand of the building at maximum daily production of 200 kg hydrogen. Case 1 is considered the minimum integration that should be carried out for the building concept, as large energy savings can be achieved with small modifications to a standard CO2 booster system. If the hydrogen station is to be integrated, the case 3 design is the better option. It can deliver similar performance to space heating as case 2, but can in addition deliver a large supply of domestic hot water. If case 3 design of the system is chosen, delivering domestic hot water to neighbouring buildings should be considered to use the full potential of waste heat that is available

Design of a cold thermal energy storage unit for industrial applications using CO2 as refrigerant

acceptedVersio