Thermo-economic analysis of a cold storage system in full and partial modes with two different scenarios: A case study

https://doi.org/10.1016/j.est.2019.100783Get rights and content

Highlights

  • The refrigeration system with and without considering a cold storage system is studied.

  • Two different types of cold storage systems are examined.

  • Two different storage scenarios of full and partial are studied.

  • The possibility of reducing the consumption of energy is studied.

  • Both thermodynamical and economical investigations are considered.

Abstract

In this paper, to provide the cold water required in a factory, a refrigeration system with a storage tank is designed with two different storage modes i.e. full and partial in comparison with the non-storage system. Two different storage scenarios including cold water and ice are examined. The thermo-economic analysis is performed to study the performance of the system comprehensively. It is shown that, the volume of the storage tank in ice storage-full mode, cold water storage-partial mode and cold water storage-full mode cases are 410%, 510% and 2300% respectively, higher than volume of the storage tank in ice storage-partial mode. For full cold water storage, the current energy consumption is reduced by 72% compared to the direct cooling mode without the storage tank. The results show that a system with the partial storage of cold water has a lower initial cost than a non-storage system. Furthermore, less energy and current costs will be achieved by the partial cold water storage system. Full storage of cold water can be considered as an option, with the 14-year payback.

Introduction

The refrigeration system of each plant should be designed in such a way that provides a maximum refrigeration requirement; however, the maximum load occurs in a few hours of the year and then the refrigeration system operates at lower capacities [1]. The designing of refrigeration equipment based on maximum load increases the cost of the initial investment of the cooling systems. One of the available solutions is to increase the load factor by storing the cooling load. Therefore, in low-load hours that the plant do not need to be refrigerated, the energy cooling produced by refrigeration system is stored in ice or cold water and then the stored cold is used in the peak-load hours [2]. In this way, instead of designing based on the maximum charge load, fewer capacity chiller is required to provide the plant refrigeration demand and consequently, lower investment cost is required [3]. In other words, the demand energy is effectively managed. The capacity of refrigeration system equipped with a cold storage system can be reduced by up to 50% compared to the conventional system without any cold storage [4].

Energy storage is an essential part of energy management systems that provides a balance between supply and demand for energy over a time period [5]. Cold storage systems have been used in different applications including refrigeration systems, air conditioning, and conservation and transport of temperature sensitive materials [6]. Cold storage systems mainly consist of a chiller, a cold storage tank, an operating fluid, a heat exchanger, pumps, and three-way valves [7]. These systems can store cooling energy in cold water, ice or phase-change materials [8]. Thermal energy storage is divided based on sensible or latent thermal energy. In the sensible storage method, the energy is stored with consideration of the temperature gradients created in the storage materials. Due to the higher storage capacity of latent heat storage (LHS) systems at constant temperature, LHS systems have high ability in energy storage [[9], [10], [11], [12]].

There are a few studies in the literature on different aspects of cold storage systems using ice and cold water for storage energy. Minoru et al. [13] investigated a partial ice storage system using neural network analysis for load prediction. Two different strategies of chiller i.e. priority control and load predictive control were used for optimization of system. Kousksou et al. [14] studied on the encapsulated ice storage tank due to its high latent heat of fusion, stability, low cost and no destructive environmental effect. Martin et al. [15] studied a PCM-water cold storage system. They used water as the cold carrier in direct contact with the PCM as the main cold storage material. Yan et al. [16] studied and optimized a combined seasonal ice storage and chilled water storage as a promising solution in summer. They used the melted ice as a cold water storage system and employed the proposed system in a building. They showed that the proper combination of two types of cold storage systems can reduce the life-cycle cost of a building cooling system by 40%. Enthalpy-temperature plots to compare calorimetric measurements of phase change materials at different sample scales studied by Rathgeber et al. [17]. They investigated three scales (DSC, T-History, and pilot plant) four PCM (RT58, bischofite, D-mannitol, and hydroquinone). In this work, it was demonstrated that enthalpy-temperature plots facilitate the comparison and interpretation of measurements obtained under different experimental methods at different sample scales.

Tutumulu et al. [18] investigated thermal performance of an ice rink cooling system with an underground thermal storage tank. This study deals with mathematical modeling and energy analysis of an ice rink cooling system with an underground thermal energy storage tank. The cooling system consists of an ice rink, chiller unit, and spherical thermal energy storage tank. Destructing thermal stratification of water storage tank and effect on solar collector performance was investigated experimentally by Assari et al. [19]. First experiment was performed using conventional thermosyphon flow of water. In the second experiment, without discharging the hot water storage tank of the previous day, the experiment was continued. Third and fourth experiments were started with similar condition to the first case. A solar powered refrigeration system with cold bank studied by Pinto and Madhusudhan [20]. This paper describes experimental investigation of solar powered battery-free refrigerator, with use of cold thermal bank, to provide cooling at night. The supply of electricity to run AC compressor is provided by solar panels through the inverter. In addition to this, provision is made to work at night, by use cold thermal storage bank which provides cooling effect at night and maintains temperature by preventing thermal fluctuation caused by intermittence supply of electricity by PV panel. It can be ideal solution to store vaccines or food, which requires low temperature during transportation.

Fuzzy control of a cold storage refrigeration system with dynamic coupling compensation method, investigated by Xiliang et al. [21]. To reduce the adverse effects of the coupling and improve the overall control performance of cold storage refrigeration systems, a control strategy with dynamic coupling compensation was studied. Yang et al. [22] studied integrating latent heat cold storage (LHCS) system with refrigerated warehouses benefits both energy and operation cost savings, especially under a peak-valley price mechanism. This paper presented a feasible scheme with an operation strategy. Besides, a detailed three-dimensional CFD model was developed in ANSYS to test the temperature distribution in the refrigerated warehouse with phase change material (PCM) plates in order to validate the feasibility of the system. In addition, an economic analysis was also carried out to calculate the operation benefit and the payback period of the new scheme. Khatra et al. [23] investigated the process of solidification of a PCM in an internally finned rectangular cold storage unit. A parametric study was conducted in order to highlight the impact of operating parameters such as air inlet temperature and flow rate on the thermal behavior and thermal performance of the cold storage unit. Xueqiang et al. [24] investigated energy storage systems for refrigerated warehouses. Refrigerated warehouses consume a large amount of energy, most of which happens during the daytime due to the higher ambient temperature. This work evaluated the potential benefits of integrating energy storage in the refrigerated warehouses. Two types of energy storage systems have been considered, including a cold energy storage system and an electrical energy storage system. A dynamic model has been developed in TRNSYS to study the performance of those two energy storage systems and assess the benefits. Based on mass and energy balance equations and data collected in specialized bibliographies, Rodrigo et al. [25] investigated a methodology for modeling of an ice bank for thermal storage of energy at low temperature to be used in milk cooling. The data obtained in terms of prediction of ice formation, temperature of the ice bank, water and capacity of the selected refrigeration system prove the adequacy of the equations arrangement, showing that it can be used as a tool for sizing solid ice bank in smooth pipe coils, with good approximation.

The analysis here employs thermo-economic comparison of a refrigeration system in specified conditions with and without considering a cold storage system. Also, at the present work two different scenarios of cold storage systems including ice and cold water storage tanks are examined. With this type of comparison, designers and employers will be able that select the best option for cold energy storage based on the thermo-economic aspects. On the other hand, it is clear from the literature review that less attention has been made in analyzing of different scenarios for cold storage systems with a view of thermo-economic comparison. Furthermore, two different storage modes of full and partial are studied in order to study the possibility of reducing the energy consumption in comparison with the conventional system without the storage tank. In the full storage mode, the purpose is to transfer the electrical demand to the low-load hours and in the partial storage system is to reduce the energy consumption and electrical demand.

Section snippets

Problem description

In the current work, to provide the cold water required in a factory, different scenarios for storing of cooling energy are discussed and then compared thermodynamically and economically. The plant is located in Bushehr city, Iran. Fig. 1 shows a schematic of the refrigeration system with a storage tank in two scenarios i.e. cold water and ice storage systems.

In the refrigeration system of factory, the hot source temperature is considered Th=61.66C and the cold source temperatures are

Determination of the chiller capacity

Calculation of chiller capacity and specification of storage tank dimensions are different in various storage scenarios. In the ice storage system, the selected chiller should be able to provide a temperature below zero. The chillers have different nominal and practical capacities and the practical capacity is about 70–90 % of the nominal capacity. The chiller capacity is determined as a function of the hourly refrigerating load, charging and discharge hours, operating strategy (partial and

Results and discussion

In this paper, to provide the cold water required in a factory, a refrigeration system with a storage tank is designed with two different storage modes i.e. full and partial in comparison with the non-storage system. Two different storage scenarios including cold water and ice are examined. The thermo-economic analysis is performed to study the performance of the system comprehensively. All relative information about thermodynamic and economic characteristics of the system has been described by

Conclusion

To provide the cold water needed for a factory, possible scenarios are studied thermodynamically and economically in this paper for storing cold including full and partial cold storage using cold water and ice scenarios. The total daily cooling load required by the plant is 24,639.6 kWhr or 7005.83 RT of refrigeration used to water cooling. The following results have been obtained from the analysis of this case study:

  • 1

    It can be seen that in the partial storage mode, the maximum reduction in the

References (32)

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