Water Thermal Storage Tank Research Articles

Compatibility assessment of thermal energy storage integration into industrial heat supply and recovery systems

Thermal energy storage (TES) systems can be used for recovering industrial waste heat and increasing energy efficiency, especially when coupled to batch thermal processes. Stratified water thermal storage tanks are the preferred technology for low-temperature applications, while molten salts are commonly used in medium and high-temperature applications with large storage capacities. No clear consensus exists on the appropriate TES technology for different industrial demands characteristics and their respective heat supply systems for medium and high-temperature applications. The present study analyzes several industrial sectors and their thermal processes, analyzing their temperature ranges, heat demands, and available TES technologies, which are classified by their operational conditions. The study presents two novel indicators for a preliminar compatibility assessment between TES and industrial sectors: a temperature compatibility indicator and exergy efficiency for TES and thermal processes. The results show that low and medium-temperature applications such as food, chemical, or textile industries exhibit high compatibilities with water (over 64%), high-temperature PCM (over 61%), and solid-state TES (100%), whereas molten salts and chemical looping demonstrate lower compatibility (below 24%). The exergy analysis for industrial cases shows that a lower temperature operating range for a TES induces low exergy efficiency. Regarding this scenario, high-temperature cPCM reaches efficiencies of over 44% for mid and high-temperature processes. Conversely, solid-state TES emerges as the most viable option for integration in high-temperature industries, exhibiting an efficiency of 62% with minimal exergy losses. The indicators defined in this study can be used for an early evaluation of TES integration in industrial applications, thus promoting emerging technologies selection through a quantitative comparison of the compatibility metrics.

Insulated concrete form foundation wall as solar thermal energy storage for Cold-Climate building heating system

Employing green energies for building energy sector decarbonization has captured the world’s attention in the current century. However, the imbalance between energy demand and availability necessitates designing reliable and cost-effective energy storage systems. The present study aims to propose an innovative building-integrated solar thermal storage method using insulated concrete form (ICF) foundation walls for residential buildings in cold climates such as that of Canada. Surplus solar thermal energy is stored inside the ICF wall, which has a high thermal capacity and mass and is integrated into the building envelope. The ICF wall and solar thermal collectors are coupled with a water-to-water heat pump to meet building space heating load and domestic hot water demand. Different configurations integrating the ICF wall are modeled and simulated in TRNSYS software to perform a yearly transient analysis. It is shown that a system with ICF walls has an 11% higher solar fraction (SF) than a similar system with a large water thermal storage tank. By replacing the solar thermal collector with a hybrid photovoltaic/thermal collector, the overall system solar fraction can increase to 20% above that of a similar system with a large water thermal storage tank system. An ICF-based system with a 16 m2 solar collector can completely cover nine months of space heating and domestic hot water load for a single-family house in London, Ontario. A detailed sensitivity analysis shows that the proposed ICF-based systems achieve an optimum solar fraction at high tilt angles (65-70°), unlike a similar design with an extensive water thermal storage tank system. Because of their ability to achieve a high SF at high tilt angles, ICF systems are suitable for vertically mounted solar systems typically required by high-rise buildings due to limited roof area. As part of the building envelope, ICF foundation walls have no additional cost and can be considered a feasible strategy for reducing the residential sector’s carbon footprint..

Fault detection and diagnosis for heat source system using convolutional neural network with imaged faulty behavior data

Faults that impair performance can occur in a heat source system because it comprises various devices and has complex controls. This article presents a novel method for fault detection and diagnosis (FDD). This study focused on a real system with a water thermal storage tank. First, system behaviors in response to faults were determined using a detailed system simulation. Then, a fault database was generated using the simulation results with fault labels. We preprocessed the database and converted the data into images. Then, convolutional neural networks (CNNs) were trained using the database, and the trained CNNs were used for diagnosing real data. The accuracy of the CNNs was 98.7% in training, and real data were diagnosed with probabilities. We analyzed the real data, where the probability indicated the likely presence of a fault and reviewed how the real data were similar to the fault assumed in the simulation. We concluded that the proposed FDD method will help in analyzing real data, as it indicates faults emerging in the real data with probability, whereas conventional data analysis requires checking the data using expert knowledge.

Application of a heat source system using solar energy with hot water storage

To increase the adoption and value of solar heat energy, a heat source system was designed and constructed that consists of a large-capacity water thermal storage tank, water source heat pump unit, and waste heat recovery chiller. This heat source system contributes to energy savings and to maintaining the function of a building when infrastructure is unavailable at the time of a disaster. This system was installed in a high school in Tokyo, Japan, and its effectiveness was verified. Actual results indicated that it operates at high efficiency with an average COP of 6.8 and full utilization of solar heat throughout the year. The actual annual usage of solar heat was about 103% that of the simulation at design time. The annual primary energy consumption was reduced by approximately 45% compared to that of an ordinary high school in Japan.

Model-Based Fault Detection and Diagnosis Using Convolutional Neural Networks in Heat Source System with Water Thermal Storage Tanks

Since a heat source system that produces and conveys the heat for air conditioning comprises various devices, and has complex controls, faults that impair performance occur. Heat source systems are customized, however, and are complicated to the extent that a ‘one-fits-all’ approach to fault detection and diagnosis (FDD) has not been established. Here we propose a novel method for FDD, using a fault database generated by a simulation, and using convolutional neural networks (CNNs) trained by the database. A real system, with a water thermal storage tank, was the object of this research. Firstly, system behaviors in response to faults were calculated, using a detailed simulation, and then a database was generated, using the simulation results with fault labels. There were 16 fault types in total, which included a condition without faults, four types of faults, and their combinations. The assumed four types of faults: were chiller deterioration by condenser fouling, improper sewage pump set value, heat exchanger fouling, and temperature sensor error at the supply side of the heat exchanger. Then, we preprocessed the database, and converted the data into images, with two axes of time series, and with items from one 24-hour data set as a representative image. Then, CNNs were trained by the database, and trained CNNs were tasked with the diagnosis of real data. The CNNs performed with 98.7% accuracy in training, and diagnosed the real data using probabilities. We reviewed the analysis of the real data, where the probability indicated the likely presence of a fault, and how the real data was similar to the fault severity assumed in the simulation. We concluded that this FDD method will help analyze real data, because it indicates faults emerging in the real data with probability, whereas conventional data analysis requires checking the data using expert knowledge.

Performance of a small-scale solar-powered adsorption cooling system

ABSTRACTIn this study, an experimental investigation on the performance of a small-scale residential-size solar-driven adsorption (silica gel-water) cooling system that was constructed at Assiut University campus, Egypt is carried out. As Assiut area is considered as hot, arid climate, field tests for performance assessment of the system operation during the summer season are performed under different environmental operating conditions. The system consists of an evacuated tube with a reflective concentration parabolic surface solar-collector field with a total area of 36 m2, a silica gel-water adsorption chiller of 8 kW nominal cooling capacity, and hot and cold water thermal storage tanks of 1.8 and 1.2 m3 in volume, respectively. The results of summer season field test show that under daily solar insolation varying from 21 to 27 MJ/m2, the solar collectors employed in the system had high and almost constant thermal efficiency. The daily solar-collector efficiency during the period of system operation ranged from about 50% to 78%. The adsorption chiller performance shows that the chiller average daily coefficient of performance (COP) was 0.41 with the average cooling capacity of 4.4 kW when the cooling-water and chilled-water temperatures were about 31°C and 19°C, respectively. As the chiller cooling water is cooled by the cooling tower in the hot arid area, the cooling water is at a higher temperature than the design point of the chiller. Therefore, an experiment was carried out using the city water for cooling. The results show that an enhancement in the chiller COP by 40% and the chilling power by 17% has been achieved when the city water was 27.7°C.

Performance modeling and parametric study of a stratified water thermal storage tank

Thermal energy storage (TES) can significantly increase the overall efficiency and operational flexibility of a distributed generation system. A sensible water storage tank is an attractive option for integration in building energy systems due to its low cost and high heat capacity. As such, this paper presents a model for stratified water storage that can be used in building energy simulations and distributed generation simulations. The presented model considers a pressurized water tank with two heat exchangers supplying hot and cold water respectively, where 1-D transient heat balance equations are used to determine the temperature profiles at a given vertical location. The paper computationally investigates the effect of variable flow-rates inside the heat exchangers, the effect of transient heat source, and buoyancy inside the tank induced by location and length of the heat exchangers. The model also considers variation in thermophysical properties and heat loss to the ambient. TES simulation results compare favorably with similar 1-D water storage tank simulations, and the buoyancy model presented agrees with COMSOL 3-D simulations. The analysis shows that when the inlet hot fluid temperature is time dependent, there is a phase lag between the stored water and the hot fluid temperature. Furthermore, it was observed that an increase in flow-rate inside the hot heat exchanger increases the stored water and the cold water outlet temperature; however, the increment in temperature observes diminishing returns with increasing flow-rate of hot fluid. It was also noted that for either heat exchanger, increasing the vertical height of the heat exchanger above a certain value does not significantly increase the cold fluid outlet temperature. Results from the model simulations can assist building designers to determine the size and configurations of a thermal storage tank suited for a given distributed generation system, as well as allowing them to accurately predict the fraction of heat generated by the system that could be stored in the tank at a given time when charging, or the fraction of heating load that could be met by the tank when discharging.

Experimental Study of a Thermal Storage Technique with Phase Change Material Closure for Solar-Biogas Hybrid Fermentation System

It is a key energy policy in China that developing biogas technology is to crack energy short problem in its rural areas. A pilot water thermal storage tank with phase change material insulation closure was developed to collect the daily solar energy for satisfying the heat loading required by biogas fermentation tank which should keep at about 35°C optimum efficient fermentation temperature in each winter day. The thermal performance of the water thermal storage tank was investigated under the different typical local winter air temperatures of 10°C, 5°C and 0°C. Both the numerical and experimental data demonstrate that the phase change material paraffin layer improves the thermal storage time of the tank effectively. This suggests that the proposed water thermal storage tank with phase change material insulation closure could be a promising heat storage device utilized towards solar-biogas hybrid system in rural regions of the middle and lower reaches of Yangtze river.

PCM-based High-density Thermal Storage Systems for Residential and Small Commercial Retrofit Applications

Environmental cooling loads comprise 11% of overall electric usage in the United States, and during peak cooling months in hot/humid climates these cooling loads can comprise more than 50% of peak electric energy loads. Thermal storage systems can shift these environmental cooling loads to non-peak hours, making better use of baseload generation capacity as well as reducing the need for expensive and environmentally inefficient peak power plants. Residential and small commercial buildings generate much of the cooling responsible for peak electric load, but these structures may not have the space or facilities to support conventional sensible energy thermal storage systems, such a chilled water thermal storage tanks. For these applications a compact, high-density, retrofittable thermal storage system is needed. This paper investigates the development, testing, and modeling of a compact, scalable PCM (phase change material) based latent thermal storage system for these applications. The results show that a simple tube-encapsulated, tetradecane PCM-based thermal storage system can reduce the size of a thermal store by at a factor of between 2 and 4 while providing acceptable energy recovery rates.

Hydrodynamic considerations on the performance of chilled water thermal storage tanks in the discharge cycle

The paper analyzes the effect of hydrodynamic viscous boundary layer growth over the performance of a thermal storage tank during the discharge cycle. As well established in Fluid Mechanics textbooks, a viscous boundary layer modifies the velocity profile across the tank section. Consequently, in a discharge cycle the warm water flowing outside the boundary layer (i.e., in the core region) reaches the tank bottom exit faster than that if the down flow water were flowing at the mean velocity based on the discharge flow rate, which is the usual designing and tank selection assumption. Consequently, the storage tank height must be greater than that determined using the simple mean flow velocity. Two controlling parameters appear naturally in the analysis: the Reynolds number based on tank diameter, ReO, which is also associated with the hydrodynamic entry length, and f, which defines the position of a given contact surface from the tank entrance to the hydrodynamic entry length. Results show that the tank loss of capacity due to viscous effects may not be negligible and the selection of a height-to-diameter tank ratio is essential for minimizing those effects.

State of Charge Estimation of Thermal Storages for Distributed Generation Systems

The aim of this work is the development of three different models to calculate the enthalpy content of a stratified water thermal storage tank from discrete temperature measurements. The difficulty related to enthalpy value evaluation comes from the discrete temperature measurement along the storage (often only 2 to 4 temperatures along the volume height are known): the actual temperature distribution between two subsequent probes is unknown. Three different models based on three different approaches were developed and compared, basing on experimental data. A first model calculates the enthalpy value considering the measured temperatures and the thermal power difference between generation and consumption. The second model uses a mathematical pre-defined temperature shape fitted considering real-time experimental data. The latter model is based on a 1-D physical approach using a multi-nodal method. All the models were validated against the experimental data obtained from the distributed generation laboratory installed in Savona, Italy.

Investigation on a Passive Solar House Equipped with Water Thermal Storage Wall

The numerical simulation method is employed in this paper to study the indoor thermal performance of an existent passive solar house, south internal wall of which is equipped with water thermal storage tanks. The actual measured meteorological data of 2010 in Tianjin is applied in this study to obtain the hourly indoor temperature, and the indoor condition is assessed by the adaptive thermal comfort model. The results indicate that, cooling measures are not required during the summer in Tianjin weather condition when the water thermal storage wall is used combined with natural ventilation technology, thermal storage effect of the wall can reduce the indoor maximum temperature of 4 °C while increase the minimum temperature of 3°C, and make regulation of the heating system simple and feasible in the winter.

Measured and Modeled Charging of a Stratified Chilled Water Thermal Storage Tank with Slotted Pipe Diffusers

As part of ASHRAE Research Project 1185, field data from the constant flow rate charging of a stratified chilled water storage tank with double-ring octagonal slotted-pipe diffusers serving a university chilled water system were compared with results of a transient axisymmetric computational fluid dynamics (CFD) model. Charge processes at flows near design flow rate and 50% of design were modeled. Laminar and turbulent simulations were performed for a range of slot dimensions. Performance of the model was assessed by direct comparison of temperature profiles and by comparison of common thermal performance metrics, including thermocline thickness, lost capacity, and equivalent lost height. The inlet Richardson number based on slot hydraulic radius was found to have the strongest effect on model results. The model Richardson number giving best agreement with the lost height of the field data for near design flow rate was roughly an order of magnitude greater than the Richardson number of the actual diffuser. It is conjectured that this is due to inherent differences between the flow produced by multiple three-dimensional jets in the actual diffuser and the continuous slot of the axisymmetric model. The effect of turbulence varied from negligible to moderate as the Richardson number decreased.