Cool Thermal Energy Storage Research Articles

Role of aloe vera based nanofluids for cool thermal energy storage system: A comparative study

The present experimental investigation incorporates the preparation of aloe vera gel-based phase change nanofluid (NFPCM) for a cool thermal energy storage (CTES) system. Two sets of NFPCMs were produced by adding graphene nanoplatelets (GNP) in deionized water and aloe vera gel (0.20 wt%, 0.40 wt%, and 0.60 wt%). The zeta potential analysis shows that the NFPCM with aloe vera gel is more stable even after 60 days from the preparation (−44 mV). The thermal conductivity of NFPCMs was analyzed through the transient hot wire method and the enhancement of 42 %, and 37.5 % were measured in the ice phase for NFPCMs with aloe vera gel and DI water (0.60 wt%) respectively at the heat transfer fluid temperature of −15 °C. The NFPCMs with aloe vera gel show that the addition of GNP prepended the peak melting temperature from −16 °C to −10.5 °C, which is due to the quick formation of nuclei as compared to NFPCMs with DI water. Additionally, a slight reduction in the latent heat of only 7 % was observed. The charging characteristics of NFPCMs were studied in a single spherical capsule at −8 °C. The maximum reduction in total charging time of 25 % was recorded for the aloe vera gel-based NFPCM with a maximum concentration of GNP (0.60 wt%). The green synthesis of aloe vera gel-based NFPCM exhibited noteworthy enhancements in thermophysical properties. Additionally, it was observed that the long-term stability of the NFPCM was achieved by excluding surfactants during the preparation process. The incorporation of graphene nanoplatelets (GNP) into aloe vera gel as the foundational phase change material (PCM) facilitates the partial charging of the CTES system with a reduced energy input.

Optimizing mixed cool thermal storage systems across a connected community

A high level of electric demand flexibility must be integrated into our building infrastructure to enable greater renewable energy penetration in the grid. In the U.S., 9 % of electricity generated is used to cool buildings in a periodic manner, making this end-use an ideal target for active management through cool thermal energy storage (CTES) technologies. Historic uses for CTES are designed around central chilled water plants, but these systems cool less than 25 % of U.S. commercial floorspace. Emerging technologies are under development to serve the many smaller distributed cooling systems, such as rooftop units (RTUs), and have the potential to add CTES to an additional 66 % of cooled commercial floorspace. However, these unitary thermal storage systems (UTSS) lack the modeling and analysis tools to evaluate them in the future interactive grid context. This study develops the modeling and optimization tools necessary to simultaneously examine central and distributed ice storage systems within the multi-building, connected community context. An integrated simulation-optimization workflow is created to allow for rapid customized analysis. Results demonstrate the energy and flexibility tradeoffs of various implementations.

Influence of encapsulate material thickness and its thermal conductivity on solidification time of phase change material in spherical capsule for cool thermal storage - A novel correlation

Buildings account for 39% of global GHG emissions. In any building, space cooling/heating consumes the maximum electricity. Recently, encapsulated phase change materials (PCMs)-based cool thermal energy storage (CTES) systems have gained huge attention due to its numerous advantages in meeting building space cooling demand. Energy is stored inside these capsules in the form of latent heat. Considering the relevance of PCM solidification in capsules, two novel correlations are proposed to determine the inward and outward solidification time of phase change material (PCM) inside/around a spherical capsule based on its thermal conductivity and thickness. Further, an experimental investigation is also performed to validate the correlation. The correlation agrees closely to the experiment with a maximum inaccuracy of around 6.6%. Thereafter, a parametric analysis is also carried out to analyse the impact of both the parameters on inward solidification time of PCM. The results showed a significant reduction in solidification time up to a capsule thermal conductivity value of 0.3 W/mK. Beyond 10 W/mK thermal conductivity, capsule thickness did not affect solidification. The incorporation of these correlations into software will benefit engineers working in the fields of CTES, refrigeration, food processing, and plastics industries.

Influence of functionalized carbon flake on phase change characteristics of deionized (DI) water for cool thermal storage system

The current work aims to study the influence of thermal-resistance (R) and the time constant (τ) in phase change properties of carbon flake-based phase change materials (CPCM) experimentally. The CPCMs were prepared using chemically functionalized graphene flake (f-GP) in three various mass fractions (0.25%, 0.50%, and 0.75%) suspended in deionized (DI) water. The phase transition characteristics were recorded using DSC214-polyma with a heat-flow rate of 1 K/min. The remarkable variation in the peak crystallization and melting during charging and discharging processes were recorded with the combined τ -R correction method. The true peak during charging (−12.21 °C) and discharging (3.91 °C) processes is recorded through the correction of time constant for CPCM with 0.75% of f-GP. In addition, the CPCM with 0.75% f-GP has a maximum reduction in melting and freezing time of 36.01% and 27.75%, respectively. The prediction of phase change properties (peak crystallization and melting temperatures) is very important to design a cool thermal energy storage (CTES) system with maximum storage density. The selection of correct operating temperature of the CTES system reduces the energy input to the chiller plant.

Influence of functionalized graphene nanoplatelets on the phase transition performance of DI water-based NEPCMs for cool thermal storage systems

ABSTRACT This research paper describes the experimental investigation of the phase change characteristics of deionized (DI) water with the addition of functionalized graphene nanoplatelets (FGNP) in a spherical container used in cool thermal energy storage (CTES) systems. The nano-enhanced phase change materials (NEPCMs) are developed by the dissolution of FGNP in the mass concentrations of 0.25%, 0.50%, and 0.75% with DI water. The thermal conductivity (TC) and phase change enthalpy (H) of the NEPCMs were measured experimentally using the transient hot-wire method and DSC 214 polymer, respectively. At heat transfer fluid (HTF) temperatures of −10°C and 15°C, the mass fraction of 0.75 improves thermal conductivity by 48.2% and 33.2% in the solid and liquid phases, respectively. At a heating rate of 1K min-1, the addition of FGNP significantly reduces the H of the base PCM in both crystallization and melting processes. The maximum reduction in crystallization and melting time was recorded to be 32.4% and 52.4% in a spherical container with the addition of maximum concentration of FGNP at the HTF temperatures of −8°C and 25°C, respectively.

Influence of surfactants on the performance enhancement of water-based gamma Al2O3 phase change material for cool thermal energy storage system

The current work investigates the effect of various surfactants on the performance enhancement of water-based gamma Al2O3 PCM (Phase change material) during the solidification process suitable CTES (cool thermal energy storage) system. Two surfactants, one from cationic group (CTAB – cetyl trimethyl ammonium bromide) and other from anionic group (SDBS – sodium dodecylbenzene sulfonate) are selected for this study. Both the nanoparticles and surfactants with 0.1 wt% are dispersed in the base fluid. The freezing experiments were conducted at various surrounding bath temperatures of −6 ℃, −9 ℃ and −12 ℃. The outcomes reveal a reduction in subcooling, advanced onset of solidification and increased heat transfer performance by use of nanofluids. Further it is noted that the performance is also influenced due to the surfactant. The anionic surfactant NFPCM (nanofluid phase change material) displace better performance than cationic surfactant NFPCM during the solidification process. The enhanced performance of NFPCM will pave the way to design an energy efficient CTES system.

Design and dispatch optimization of packaged ice storage systems within a connected community

The traditional implementation of cool thermal energy storage (CTES) must be reimagined within the context of a dynamic grid and smart buildings operating as connected communities. As most buildings do not operate central chillers or connect to district cooling loops, this necessitates a broader use of packaged CTES. Our objective is to begin answering the question of how such packaged CTES should be implemented within a connected community. We do so by presenting a simulation–optimization workflow employing building energy modeling software and a mixed-integer linear program to design and dispatch a packaged CTES technology to achieve minimum total annual cost. We demonstrate this methodology on a seven-building case study using current utility rates and find that total annual cooling energy costs can be reduced by 17.8% compared to baseline, after accounting for the cost of storage. We perform three parametric sensitivity studies to evaluate modeling assumptions and obtain the prioritization of storage procurement as a function of annualized life-cycle cost of storage. We find that a community optimization approach provides significantly different results than individual building optimizations and provides greater savings compared to baseline.

Role of graphitized mesoporous carbon on solidification and melting characteristics of water for cool thermal storage

Cool thermal energy storage systems (CTES) using phase change materials (PCM) are paramount in the energy management of buildings. This work aims to investigate the role of graphitized mesoporous carbon (GMC) on the thermal storage behavior of water based nanofluid PCM (NFPCM) in a spherical capsule. The NFPCMs exhibit a lower contact angle, indicating a reduction in the nucleation energy barrier. Thermal conductivity of NFPCM shows an enhancement of 36% with the presence of graphitized walls and isotropic nature of GMC. Temperature–time history method is used to evaluate the latent heat of fusion for the NFPCMs and the results are compared with differential scanning calorimetry measurements. Addition of GMC shortens the solidification duration by 6% and reduces the subcooling of NFPCM compared to base PCM. The charging results of NFPCMs demonstrate a cool energy storage of 96% in accelerated mode. The melting rate of NFPCM is expedited at a minimal GMC concentration and melting duration prolongs with further GMC addition. In conclusion, the proposed NFPCMs exhibiting a lower subcooling, improved nucleation behavior and accelerated mode of charging shows great potential for CTES applications.

Study of Thermal Transport Properties of Carbon Based NFPCM (Graphene) For Space Cooling Applications

This examination is planned to research the hardening conduct of water scattered with Graphene nano particles in a circular holder during cementing. The examinations were directed with unadulterated water and nanofluid stage change materials (NFPCMs) with GNP mass grouping of 0.35 %, 0.7 % and 1.05 %. The NFPCM was set up by scattering graphene nanoparticles and a nucleating specialist in the base PCM (stage change material). Nanoparticle’s (GNP) go about as a nucleating specialist to help the quick development of precious stones in cementing processes. The expansion of GNPs came about with an apparent decrease in the sub cooling of water from - 12 °C to - 2.5 °C alongside decrease of 25 % in cementing time attributable to its high warm conductivity and bigger explicit surface region. The expansion of the Nucleating operator lessens the serious situation of sub-cooling in the PCM, all things considered, which improves the exhibition of evaporator in a refrigeration framework. In addition, NFPCM with upgraded heat move rate and without sub-cooling can be valuable in numerous CTES (Cool Thermal Energy Storage) applications. The beginning of hardening progressed on account of NFPCM because of higher cooling rate in the sub cooling district for some random driving potential. The quickened method of vitality charging happened during 78 % of all out cementing time.

Solidification characteristics of deionized water in a spherical capsule using bio-additives: An experimental study

The present work investigates the solidification activity of deionized water as phase change material dispersed with various bio-additives such as gelatin and corn starch in a spherical capsule immersed in a constant temperature bath. Tests are carried out at two different bath temperatures (-6°C and -9°C) and it was noted that deionized water undergoes a subcooling of -3.8°C at a bath temperature of -6°C. However, no subcooling is reported for the deionized water with a concentration of 0.1wt.% for both the additives. A maximum reduction of 51% and 45% in total solidification time is observed for gelatin solution at bath temperatures of -6°C and -9°C respectively. A significant reduction of 82% is observed while considering 50% of phase change material(PCM) mass at a bath temperature of -6°C. Hence, it is concluded that reducing subcooling and partial charging of water-based PCMs would help to increase the Cool Thermal Energy Storage (CTES) system’s energy efficiency.

The Effect of Nucleation on DI-Water Based Phase Change Material for Cool Thermal Energy Storage

This report addresses the study on nucleating effects of DI – water based phase change material by adding salt hydrate like a Sodium chloride, Magnesium chloride and Calcium chloride. DI-water is selected as base PCM in which nucleating agents are added in concentration of 0.3, 0.6 and 0.9 Wt.% to study the solidification characteristics of the PCM. The samples are prepared with the help of magnetic stirring and ultra-sonification process which ensures that the nucleating agents are completely dissolved in the base PCM. An experimental trail is carried out with surrounding heat transfer fluid temperature of -7°C and the solidification history is generated for all PCM samples. From the observation it can be concluded that NaCl 0.9 Wt.%, MgCl2 0.6 Wt.% and CaCl2 0.6 Wt.% shows a significant reduction of supercooling degree. Only NaCl of 0.9 Wt.% shows a reduction of 91.32% in supercooling degree with least increase of 6.73% in solidification time. Thus, Phase change materials proves to be effective in eliminating the discrepancy between demand and supply during peak hour by storing energy during non-peak hours and retrieving when demanded. Thus, it can be used to reduce power consumption during peak hour’s demand and reduce the effects on environment.

Experimental investigation on reducing the solidification time of NFPCM by reducing sub cooling for different heat transfer fluid temperature for cooling applications

This study aims to investigate the solidification characteristics of water based nanofluid NFPCM (Nanofluid phase change material) with an aim to form an efficient CTES (Cool Thermal Energy Storage) system. Here we have taken base PCM as deionized water and Graphene is taken as nanoparticle because of its property of high thermal conductivity. The PCM was prepared by adding surfactant (0.2wt%) which is used to reduce the surface tension of the solution and then various concentration of graphene nanoparticle are added i.e. 0.2wt% and 0.4wt%, and the effect in solidification time and reduction of sub cooling is seen and studied. The enhanced heat transfer rate of NFPCM without sub cooling is advantageous for many CTES applications. So, finally it is constructed from experimental results that by embedding this technology with chiller systems which is used to cool large spaces can help us to conquer our motive to save energy and provide effective and efficient cooling.

Experimental investigations on the thermal performance of an ice storage system using twin concentric helical coil

The cool thermal energy storage (CTES) offers a big advantage for peak shift of high electrical power consumed by air conditioning systems. An experimental analysis for studying the thermal performance of ice storage system with twin concentric helical coil (TCHC) is conducted in the present work. Effects of operating conditions such as the heat transfer fluid (HTF) inlet temperature and flow rate on the solidified/melted mass fraction, percentage energy stored/regained, and average charging/discharging rate during charging and discharging processes are investigated. An experimental setup composed of TCHC immersed in distilled water as a phase change material (PCM) in an insulated tank is used in the present study. Three different HTF inlet temperatures of (−8, −10, and −12 °C) and (10, 12, and 14 °C) for charging and discharging processes, respectively and HTF volume flow rates (5.0, 7.5, and 10 l/min) are investigated. The results show that, about 90% of the energy stored is achieved at 59–74% of the complete charging time according to the tested parameter range in the current study. Moreover, the HTF volume flow rates have a relatively small effect on the percentage energy stored and seems to be less effective compared to the inlet HTF temperature during charging process.

Aquifer Thermal Energy Storage (ATES) for District Heating and Cooling: A Novel Modeling Approach Applied in a Case Study of a Finnish Urban District

Aquifer thermal energy storage (ATES) combined with ground-source heat pumps (GSHP) offer an attractive technology to match supply and demand by efficiently recycling heating and cooling loads. This study analyses the integration of the ATES–GSHP system in both district heating and cooling networks of an urban district in southwestern Finland, in terms of technoeconomic feasibility, efficiency, and impact on the aquifer area. A novel mathematical modeling for GSHP operation and energy system management is proposed and demonstrated, using hourly data for heating and cooling demand. Hydrogeological and geographic data from different Finnish data sources is retrieved in order to calibrate and validate a groundwater model. Two different scenarios for ATES operation are investigated, limited by the maximum pumping flow rate of the groundwater area. The additional precooling exchanger in the second scenario resulted in an important advantage, since it increased the heating and cooling demand covered by ATES by 13% and 15%, respectively, and decreased the energy production cost by 5.2%. It is concluded that dispatching heating and cooling loads in a single operation, with annually balanced ATES management in terms of energy and pumping flows resulted in a low long-term environmental impact and is economically feasible (energy production cost below 30 €/MWh).

Experimental studies on solidification and subcooling characteristics of water-based phase change material (PCM) in a spherical encapsulation for cool thermal energy storage applications

This work aims to investigate the solidification behavior of de-ionized (DI) water as the base phase change material (PCM) dispersed with various mass fractions of sodium chloride and D-sorbitol in a spherical encapsulation. The DSC analysis of water illustrated that subcooling of DI water increases with respect to cooling rate due to inadequate time to complete the crystallization. The solidification experiments were carried out at a bath temperature of −7 °C and DI water undergoes a subcooling of −5.4 °C. However, the subcooling substantially reduced to −2.8 °C for DI water with 0.5 wt. % sodium chloride and 1 wt. % of D-sorbitol. Accelerated mode of charging prevails in all the PCM samples and the innermost 6% of volume got solidified in decelerated mode. The cooling rate is found to decrease with respect to increase in concentration of the dispersants in subcooling region, but at a particular concentration both dispersants provide the enhanced cooling rate for a given driving potential than DI water. It is concluded that reduction of subcooling and partial charging of water based PCMs would be helpful to enhance the energy efficiency of the cool thermal energy storage (CTES) system.

The Use of the Photovoltaic System in Combination With a Thermal Energy Storage for Heating and Thermoelectric Cooling

The article is focused on the research of the usage of modern accumulation technology. The proposed system is able to improve the thermal comfort of building interiors. That text depicts the technology, which uses a photovoltaics and other renewable energy sources for active heating and cooling. The bases of the presented technology are the phase change material and thermal energy storages. So, it passively improves the thermal capacity of the constructions of the buildings. Moreover, there is a possibility to use it for active heating and cooling. The technology contains thermoelectric assemblies, so, there is a very interesting possibility to store thermal energy with use of renewable energy sources (such as photovoltaic system) and thermoelectric coolers side by side. In the manuscript, there are shown measurements and results of the active operating modes of proposed technology. It was found the technology is able to work in active heating and cooling modes. It works quite well in active heating mode. On the other hand, thermoelectric cooling mode had a problem with overheating. In the end, the problem was solved and the cooling mode works. The measurements and results are described in the text.

Experimental and Numerical Study of Heat Transfer Process of Chilled Water Storage Tank

Cool thermal energy storage using thermal stratification becomes one of the widespread applications because of the ability to shift the electrical cooling loads from on-peak to off-peak periods and significantly contributes to reducing the capacity of the refrigeration system and operating costs. Seven flow rate tests varying from 1.5 to 7.5 l/min for charging cycle were performed on small-scale vertical cylindrical storage tank equipped with three primary inlet diffusers, an elbow, two-ring linear and radial circular diffusers. The storage tank with inlet diffusers was assessed using temperature distributions and performance measures including thermocline thickness(ht), the half-cycle figure of merit ( ) and equivalent lost tank height (ELH). Commercial finite volume code was used to predict temperature distributions in a stratified water tank model, temperature data acquired from experimental tests and simulation models were compared for validation purpose. The results suggested that the storage tank with two-ring linear circular diffuser produced better performance and higher stratification than two-ring radial circular diffuser for various flow rates by 1.4% , 20.6% ELH and 10.6% ht, and much better than an elbow diffuser by 1.7% , 24% ELH and 31.1% ht, furthermore, the degree of mixing was affected essentially the flow velocity which in turn causes an increase or decrease in thermocline thickness. Temperature distributions obtained from finite volume model are found to be in very close agreement with those obtained experimentally.

Design Aspects for Large-scale Pit and Aquifer Thermal Energy Storage for District Heating and Cooling

Large-scale seasonal thermal energy storage (TES) can help maximize renewable energy integration into district heating and cooling (DHC) systems. However, expertise and concrete projects in the field is limited and there is currently a lack of reliable and adequate analysis tools and cost data to assess the technical-economic potential of aquifer thermal energy storage (ATES) or pit thermal energy storage (PTES). This paper provides a review summary for current ATES and PTES systems, including design concepts, application criteria, specific cost comparisons of various storage systems, as well as a summary of applicable modelling and design tools currently available.

Thermal performance analysis and optimization of a cascaded packed bed cool thermal energy storage unit using multiple phase change materials

This paper proposes a cascaded packed bed cool thermal energy storage (CTES) unit using multiple phase change materials (PCM). In terms of the solidification processes, the basic heat transfer characteristics were analyzed based on an experimentally validated simulation model. Thermal performances, including cold charging rate, the quantity of cold and exergy charged, as well as the exergy efficiency of the cascaded CTES unit were compared with those of a single-stage CTES unit. In order to further achieve better thermal performance, the materials, stages and thickness of each stage were optimized. According to the results, the 24-stage CTES unit with a phase change temperature difference between the highest and lowest stage (denoted as Td) of 6 °C has the best thermal performance, because it shows a 15.1% reduction in charging time compared with a single-stage unit, while its quality and quantity of cold charged remains almost equivalent to the single-stage unit. Moreover, 3–5 stages are recommended for an evenly distributed cascaded CTES as their thermal performances are quite close to the optimal 24-stage unit.

Policy recommendations for using cool thermal energy storage to increase grid penetration of renewable power sources (1607-RP)

The majority of U.S. states have adopted policies intended to increase renewable energy generation. Because of the intermittent nature of wind and solar resources, in particular, several states have also adopted energy storage policies. Energy storage serves to bridge mismatches between intermittent electricity production and demands from end-use electricity consumers. Because building air-conditioning loads commonly drive peak electric grid demands, storage in the form of thermal energy is an attractive alternative to electric storage technologies. Cool thermal energy storage systems have been used successfully for decades by building owners seeking to shift air-conditioning system electric consumption to off-peak time periods when electricity rates are low. In the current article, the authors present a strategy for controlling cool thermal energy storage systems to enable an increased penetration of intermittent wind and solar generation. It was found that cool thermal energy storage systems operated using this strategy have not only reduced life-cycle costs compared to air-conditioning systems without cool thermal energy storage, but they more effectively utilize the renewable resource. Because cool thermal energy storage is a mature technology and the results show that cool thermal energy storage is more cost-effective than electric energy storage technologies currently in widespread use, policies that aim to increase renewable energy generation should also support increased deployment of cool thermal energy storage as an enabling technology.