Phase Change Material Storage Tank Research Articles

Experimental evaluation of a vapor compression cycle integrated with a phase change material storage tank based on two strategies

In this survey, the integration of a vapor compression cycle with a phase change material (PCM) storage tank has been evaluated experimentally during the hottest days of five cities with different weather conditions: Tehran, Ramsar Hamedan, Bushehr, and Ahvaz. The temperature conditions for outdoor (condenser, compressor, etc.) and indoor (evaporator) air conditioning units are provided with the help of two separated test chambers and a controller system. The desired system has been examined based on two scenarios. In each scenario, the system is assessed for the conventional air conditioning (AC) system (with no PCM involved) and the AC plus PCM unit. Based on scenario 1 operating strategy, the results indicate that adding the PCM tank decreases the total daily COP compared to the conventional AC unit, which varies from 32.07% for Bushehr city to 17.23% for Tehran city. Whereas the AC plus PCM system’s performance enhances during on-peak hours compared to the conventional AC system, which varies from 65.99% for Hamedan city to 12.84% for Bushehr city. Based on scenario 2 operating strategy, adding the PCM storage tank to the conventional AC unit increases total electric energy consumption over 24 h, which varies from 29.35% for Bushehr city to 5.49% for Tehran city. While it leads to shaving the electric peak load from 45.11% to 67.02% in which the highest peak load shaving belongs to Tehran and the least is related to Bushehr city.

An Experimental Study of the Heat Storage and the Discharge Performance and an Economic Performance Analysis of a Flat Plate Phase Change Material (PCM) Storage Tank

Solar heating technology has the advantages of being high efficiency, energy-saving, and environment protecting; however, the instability of solar energy and its mismatch with the variation characteristics of building heat load have caused great difficulties in the design and the efficient operation strategy of a solar system. A heat storage tank is an important part of a solar hot water system. In order to improve system efficiency, this paper proposes a flat plate PCM storage tank, establishes a mathematical model, and conducts experimental verification under different working conditions. Experiments show that in the heat storage process, the phase change material (PCM) only accounts for less than 20% of the space of the PCM storage tank, and its heat storage can reach 50% of the total heat storage of the tank. In the discharge process, the water temperature of the ordinary tank decreases by 20 °C within 1.5 h, and the phase change process lasts approximately 3 h, with the water temperature remaining at 45~50 °C during this period. In the natural cooling process, the heat discharge of the two water tanks at night was similar, while the temperature of the ordinary water tank decreased by 12 °C and that of the phase change water tank decreased by 7 °C. By simulating the dynamic simulation model of the composite solar phase change thermal storage combined with an air-cooled heat pump system, the results show that the solar heating system with a PCM storage tank (SHS-PCM) saves 34% more energy than a solar heating system with a common tank (SHS-without PCM), and the volume of the PCM storage tank is reduced to 1/5 of the ordinary tank. The investment payback period method of energy saving reconstruction is used to analyze the economy of the SHS-PCM and the SHS-without PCM, the initial investment cost of the SHS-PCM is CNY 9858 higher than the SHS-without PCM, but the annual operation cost is saved by CNY 12,100, and the project investment payback period is 0.81 years, which has energy-saving potential and economic benefits.

Designing a Solar Heat Storage System using Heat Pipe and Phase-Change Material (PCM)

Phase change material (PCM) is used as a storage medium in a thermal heating system. The PCM's ability to store heat for a long time is suitable for combining with solar energy. PCM can absorb or release large amounts of latent heat at relatively constant temperatures. However, the PCM has poor thermal conductivity. The superconductive heat pipe is suitable to enhance the heat transfer in the PCM. The study aims to prove the concept of a unique thermal storage system that combines solar Fresnel lens, heat pipe, and phase change materials technologies. This study presented a detailed design and testing of the combined system under an actual outdoor environment. Four Fresnel lenses refracted the sunlight and focused on a heat collector. The lenses can be manually adjusted according to the sun's position. The heat is transferred to the PCM storage tank via a finned heat pipe. The testing results showed that the paraffin wax (PCM) has a melting temperature between 54 -59 °C. The highest temperature recorded in the paraffin wax tank was 121 °C which is suitable for many future applications. The system could store the heat up to 730 kJ by using 2 kg of paraffin. During the solidification of PCM (discharging), the system retained 120 kJ of heat for almost 7 hours with minimal heat loss. The system was proven to function well for storing the heat after the sunset, and it can be used for a passive power generation system, such as using thermoelectric cells.

Phase change behaviour study of PCM tanks partially filled with graphite foam

• The phase change behaviour of graphite foam partially inserted in PCM was studied. • For constant foam material, a full filling strategy with higher porosity is preferred. • Pertinent scale analysis was performed for PCM melting with fully-filled foams. The aim of this paper is to shorten the melting/solidification time of a high-temperature phase change material (PCM) using graphite foam inserts. Specifically, the phase change behaviour of a two-dimensional rectangular thermal storage tank, containing PCM with graphite foam insert, fully or partially filling the tank, was studied. The composite enclosure was designed assuming it was heated or cooled from the left side wall for charging or discharging, respectively, while the other three walls were perfectly insulated. First, the effect of foam porosity (0.8, 0.85, 0.9, and 0.95), under fully-filled scenarios, was numerically investigated. Then the phase change behaviour of four partially-filled scenarios, with averaged 0.9 porosity, was carried out. The 0.9 porosity foam case showed an excellent cycle performance. With this case, it only takes 68.2 and 65.1 min for entire melting and solidification, respectively. For a tank with no insert, it will take 164/856 min, respectively, to entirely melt/solidify the same mass of PCM as that of the 0.9-porosity-case. As expected, lower porosity values lead to higher heat transfer through conduction. However, our results show that with a fixed mass of foam, it is preferred to increase the foam porosity to fully fill the tank as opposed to a design with a lower porosity foam that only partly fills the tank. Finally, given the high graphite to PCM thermal conductivity ratio, the heat transfer through the foam is mainly due to conduction. Based on this assumption, a theoretical model is presented in parallel to numerical results. Our analysis for a foam-saturated PCM storage tank shows that the dimensionless time taken for completely melting the PCM, expressed as Fourier number, scales with Fo ρ PCM , s ρ PCM , l k eff k PCM , l ε Ste .

Optimization of Design Variables of a Phase Change Material Storage Tank and Comparison of a 2D Implicit vs. 2D Explicit Model

In this study, a thermal energy storage tank filled with commercial phase change material flat slabs is investigated. The tank provides heat at around 15 °C to the evaporator of a seasonal thermal energy storage system developed under the EU-funded project SWS-Heating. A 2D numerical model of the phase changed material storage tank based on the finite control volume approach was developed and validated with experimental data. Based on the validated model, an optimization was performed to identify the number, type and configuration of slabs. The final goal of the phase change material tank model is to be implemented into the whole generic heating system model. A trade-off between results’ accuracy and computational time of the phase change material model is needed. Therefore, a comparison between a 2D implicit and 2D explicit scheme of the model was performed. The results showed that using an explicit scheme instead of an implicit scheme with a reasonable number of nodes (15 to 25) in the heat transfer fluid direction allowed a considerable decrease in the computational time (7 times for the best case) with only a slight reduction in the accuracy in terms on mean average percentage error (0.44%).

Experimental study of the solar water heater integrated with shell and finned tube latent heat storage system

Abstract In this work, a new design of shell and finned tube latent heat storage system was designed, constructed and tested when it was integrated with the flat plate solar water heater. This design not only provides large heat transfer area between the storage material and the heat transfer fluid, but also it overcomes the problem of low thermal conductivity of paraffin wax (PW) by dividing it into tens of thin slices. Three configurations of storage techniques were proposed; where water, PW as phase change material (PCM) and both water and PW were used as thermal storage materials. The proposed systems were tested at different mass flow rates of heat transfer fluid (0.08–0.16 kg/s). The experimental results showed that the highest daily efficiency of 65% was achieved when the configuration that combines the PCM and water storage tank was used. Moreover, this configuration was capable of providing hot water of temperature ranging from 50 to 60.4 °C through 24 h/day. The results of this configuration showed also that the released energy from PW constitutes 52% of the total stored energy; while the remaining energy of 48% was considered backup stored energy that may help in any sudden thermal loads during night.

Parametric modeling and simulation of Low temperature energy storage for cold-climate multi-family residences using a geothermal heat pump system with integrated phase change material storage tank

A novel geothermal heat pump (GHP) system with an integrated low- to moderate-temperature salt hydrate phase change material (PCM) storage tank for buildings in cold climates is proposed in this study. The purpose of the PCM storage tank is to dampen peak heating loads and to remove annual ground thermal load imbalances on the ground heat exchanger (GHX) to assist in achieving an optimally-sized GHX. As heat is extracted from the closed-loop system by heat pumps in heating mode, a significant portion of this heat is used to solidify a salt hydrate PCM. This heat of fusion is later released back into the heat transfer fluid, storing it in the PCM tank and GHX for later diurnal and seasonal use. To examine the merits of the proposed concept, electric utility meter data on 15-minute time intervals were mined from an actual apartment building and used to estimate space heating, cooling, and hot water heating loads. Those data were used in an hourly, dynamic 20-year life-cycle simulation model in TRNSYS to design an optimum combination of GHX and PCM storage, where each component was sized to balance the annual ground thermal loads. The system simulation results show significant potential for GHX size reduction with a PCM storage tank, but the system is quite sensitive to the PCM melt temperature due to significant hysteretic nature of the salt hydrate PCM heating and cooling curves. We also find that there is no unique optimum unless other factors are considered such as installation cost and physical constraints; many combinations of GHX size and PCM mass are capable of achieving the design goal with similar annual electric energy consumption. For the cases examined here, a PCM melt temperature of 27 °C yields the most favorable economic results, and a preliminary economic analysis suggests that with typical drilling cost and PCM tank cost values, the GHX size can be reduced by over 50 %.

A multi-objective optimal design method for thermal energy storage systems with PCM: A case study for outdoor swimming pool heating application

Traditional design methods for thermal energy storage systems (TES) with phase change material (PCM) are mostly based on worst-case scenario, which causes too large size of main components. Current optimal design methods for these systems mainly focus on single optimization objective, which only satisfies the unilateral requirement. A multi-objective optimal design method for these systems is urgently needed, and therefore this paper remedies this knowledge gap. The response surface methodology is adopted to develop the surrogated models of the optimization objectives to improve the computational efficiency. Then, the non-dominated sorting genetic algorithm II is used to perform the double-objective and triple-objective optimization for acquiring the Pareto optimal solutions. Finally, the final decision-making methods that includes LINMAP and TOPSIS are adopted to identify the final optimal solutions. A case study of optimizing the design for an outdoor swimming pool (OSP) heating system with PCM storage tank, is conducted to illustrate the proposed approach. Eight final optimal solutions were identified, and the s p of the system in these solutions was 1.05, 1.24, 1.04, 1.22, 1.06, 1.06, 1.07, and 0.88 years, respectively. Results indicate that the proposed approach is effective to conduct the multi-objective optimization for the OSP heating systems and guide the design optimization for the TES systems with PCM.

Techno-economic optimization of open-air swimming pool heating system with PCM storage tank for winter applications

Feasible heating systems have been designed to increase the availability of open-air swimming pools in winter in subtropical climate regions. However, the approach to optimally size the main components of the system from multiple aspects is lacking. A techno-economic optimization method for swimming pool heating systems is proposed here. Minimizing the lifecycle cost of the system while ensuring the thermal comfort of the pool are considered as the optimization objectives. The volume of phase change material storage tank and the heating capacity of air-source heat pumps are selected as design variables. To improve computational efficiency, surrogate models are developed using the response surface approach, in which the dataset is generated from the simulation platform established using MATLAB and TRNSYS. Generic algorithm and non-dominated sorting genetic algorithm II are adopted to conduct single-objective and double-objective optimizations, respectively. Case studies indicate that optimal combinations for the size of main components can be identified using the proposed optimization approach. The energy and economic performance of the heating system are enhanced after optimization. The proposed techno-economic optimization method provides an instructive guideline for the optimal design of swimming pool heating systems.

The thermal behaviour of a special heat exchanger filled with the phase change material dedicated for low – temperature storage applications

The work deals with an experimental and theoretical analysis of a special heat exchanger filled with the PCM (Phase Change Material) mixture of paraffin wax capsuled in the melamine-formaldehyde membrane and water, dedicated to low-temperature storage applications. In the first part of the article, the PCM topic was introduced. The next part consists information about the designed and manufactured special heat exchanger with the PCM. During the experiment as a PCM is utilized mixture of paraffin wax in microcapsules within the water. The experimental results of temperature distributions and stored energy in the heat exchanger were compared with the theoretical model proposed in the literature. In the discussion section, the authors describe a new idea of the PCM storage tank application, which could be applied e.g. in nuclear facilities.

Mathematical modelling of operation modes and performance evaluation of an innovative small-scale concentrated solar organic Rankine cycle plant

In this paper an innovative small-scale concentrated solar 2 kWe organic Rankine cycle plant coupled with a phase change material storage tank equipped with reversible heat pipes is investigated using a simulation analysis. The plant, intended for residential applications, is going to be built and tested under the European funded H2020 Innova MicroSolar project executed by the consortium of several Universities and industrial organizations, led by Northumbria University. The authors of this work used the design of the integrated system, developed by the consortium, to preliminary estimate the overall performance of the system in order to provide useful information for its forthcoming real operation. In particular, according to the varying ambient conditions, the influence of different operation modes of the prototype plant are evaluated. The dynamic simulation analysis has shown an interesting performance of the system in terms of annual operating hours, power production and conversion efficiencies. More precisely, the organic Rankine cycle unit is able to operate for more than 3100 h/year, achieving the design performance when solar power is sufficiently high, producing about 5100 kWhe/year. For the considered operating set-point temperatures of the thermal energy storage, the plant is able to reach high conversion efficiency also when the organic Rankine cycle unit is supplied by discharging the energy stored in the storage tank, for about 800 h/year. Hence, the work has provided some useful insights into the best working conditions of such micro combined heat and power system to be integrated in residential buildings. Moreover, the analysis could serve as a general guide for the design and optimization of the mutual interactions of the different subsystems in small-scale concentrated solar organic Rankine cycle plants.

Energy-Saving Analysis of Solar Heating System with PCM Storage Tank

A solar heating system (SHS) with a phase change material (PCM) thermal storage tank is proposed with the view that traditional heat water storage tanks present several problems including large space requirements, significant heat loss and unstable system performance. An entire heating season (November–March) is selected as the research period on the basis of numerical models of the SHS-PCM. In addition, taking a public building in Lhasa as the object, the heating conditions, contribution rate of solar energy, and overall energy-saving capability provided by the heating system are analyzed under different PCM storage tanks and different terminal forms. The results show that an SHS with a PCM tank provides a 34% increase in energy saving capability compared to an ordinary water tank heating system. It is suggested that the design selection parameters of the PCM storage tank should specify a daily heat storage capacity that satisfies 70~80% of the entire heating season. A floor radiant system with supply/return water temperatures of 40/35 °C provides the optimal operation and the largest energy saving capability.

Seven Operation Modes and Simulation Models of Solar Heating System with PCM Storage Tank

A physical model and dynamic simulation models of a solar phase-change heat storage heating system with a plate solar collector, phase-change material (PCM) storage tank, plate heat exchanger, and auxiliary heat sources were established. A control strategy and numerical models for each of seven different operation modes that cover the entire heating season of the system were developed for the first time. The seven proposed operation modes are Mode 1: free cooling; Mode 2: reservation of heat absorbed by the solar collector in the PCM storage tank when there is no heating demand; Mode 3: direct supply of the heating demand by the solar collector; Mode 4: use of the heat absorbed by the solar collector to meet the heating demands, with the excess heat stored in the PCM storage tank; Mode 5: use of heat stored in the PCM storage tank to meet the heating demands, Mode 6: combined use of heat stored in the PCM storage tank and the auxiliary heating sources to meet the heating demands; and Mode 7: exclusive use of the auxiliary heat sources in order to meet the heating demands. Mathematical models were established for each of the above seven operation modes, taking into consideration the effects of the outdoor meteorological parameters and terminal load on the heating system. The real-time parameters for the entire heating season of the system with respect to the different operation modes can be obtained by solving the simulation models, and used as reference for the optimal design and operation of the actual system.

Modeling of Heat Losses from a PCM Storage Tank for Solar Thermophotovoltaic Systems

This work explores the influence of lateral heat losses from a phase change material (PCM) storage tank on the performance of a storage integrated solar thermophotovoltaic (SISTPV) system by means of an analytical model. The heat losses from the lateral surface of the PCM tank are modeled using Newton’s law of cooling by prescribing a heat-loss coefficient on the lateral surfaces. The results show that at high heat losses, low thermal efficiencies are realized. Correspondingly larger solar concentrations are required to fully melt the PCM tank. At low heat losses, such as can be expected when using thermal insulation on the lateral surfaces, approximately 40% thermal efficiency can be realized. The results also demonstrate that a high absorber area:length of PCM tank squared (SR) ratio enables the system to have a high thermal efficiency. For a high-SR, low-heat-loss design case, having a high taper ratio, high area ratio between absorber area and inlet hole area, and small PCM tank length all achieve higher thermal efficiencies. It is expected that these SISTPV systems will be designed at steady-state to be fully molten in order to maximize thermal energy storage via the latent heat of the PCM. The analytical model developed here can be used to predict the design conditions under which the PCM tank will be fully molten.

Thermal Analysis of Solar Flat Plate Collector using Phase Change Material

Objective: The objective of the paper is to study the performance of solar flat plate collector using phase change material. Methods/analysis: A phase change material (PCM) was combined with the thermal energy storage system to study the performance of Integrated Collector Cum Storage Solar Water Heater (ICSSWH). The Latent Heat Storage (LHS) was preferred as it stores the excess thermal energy beyond the sunshine and releasing it when there is energy demand. There are many phase change materials that melt and solidify over a range of temperature, among that paraffin wax was selected as it is cost effective and provides better thermal efficiency for longer duration. Findings: Regardless of the daily operations, the Integrated Collector Cum Storage Solar Water Heater (ICSSWH) gives good thermal efficiency for longer duration by using paraffin wax. In contrast to the conventional solar water heater the integrated PCM storage tank with solar water heater is more efficient because of its large storage capacity, isothermal nature during the charging and discharging and smaller size. During the discharging process, the heat transfer fluid gained large amount of heat from the PCM and it withstood heat for nearly more than five hours. During the night, it was found that the Latent Heat Storage (LHS) was effective as it allows minimum energy losses and conservation of energy. The maximum water outlet temperature was achieved by using paraffin wax and so this PCM can be considered as the most beneficial for the solar application from techno-economical aspects. Application/Improvements: The mentioned thermal system is used for water heating and space heating as it is cost effective. The system can be further be modified by combining with Sensible Heat Storage (SHS) for better utilization of energy.

Experimental investigation of the dynamic behavior of a large-scale refrigeration – PCM energy storage system. Validation of a complete model

In the area of buildings refrigeration, the use of thermal energy storages coupled with heat pumps is a significant way for reducing the operating costs and optimizing the design of equipment. In this paper, a prototype of large-scale refrigeration - PCM (Phase Change Material) energy storage system is described, from which experimental results on transient behavior are obtained. A dynamic model for transient simulation of the coupled system is presented. The fluid flows through the heat exchangers and the storage tank are represented by a cascade of Continuous Stirred Tank Reactors (CSTRs). Switching procedures between different model configurations associated to phase transitions within heat exchangers and PCM storage tank are mathematically performed by matrix operations. The compressor, the expansion valve and the pressure drop across the evaporator are represented by static models based on empirical correlations. A PI controller for the expansion valve opening is integrated in the heat pump model to maintain the superheat at evaporator exit. The model is validated by a complete and detailed comparison between simulation and experimental results.

Optimized design and operation of heat-pipe photovoltaic thermal system with phase change material for thermal storage

This work aims to optimize the design and operation of a heat pipe photovoltaic-thermal (HP-PV/T) panel integrated with a phase change material (PCM) thermal storage water tank to produce electricity and hot water for an office building. A transient mathematical model for the integrated HP-PV/T-PCM system was used to predict its performance for known environmental and solar conditions and PCM melting point. The validated model was applied on a typical office space in the city of Beirut to obtain an optimal design using a derivative free genetic algorithm. The incremental system cost associated with a heat pipe and PCM tank was used in the optimization to obtain a design resulting in minimum annual auxiliary heating cost to meet the hot water demand while providing the electricity needs at a lower number of PV panels due to improved efficiency. An optimal system of 4 kW (20 PV panels each at 1.6 m2) was found to meet the electric power needs all year round. The optimal PCM storage tank size per panel was 37 l at PCM total mass of 22.42 kg with melting temperature of 33 °C.

Experimental assessment of a phase change material storage tank

This paper describes the experimental study carried out to assess the performance of a Phase Change Material (PCM) storage tank in various operating conditions in a dynamic test bench. The studied horizontal PCM tank contains stacks of slab-like PCM capsules between which heat transfer fluid can circulate. The commercially available capsules were instrumented so the PCM behaviour could be measured in addition to that of the PCM tank as a whole. Numerous melting and solidification cycles were completed with different inlet fluid temperatures, flowrates and load profiles for which at least three repetitions were made. Analysis of test results shows significant variations in the PCM behaviour under the same tests conditions including varying degree of supercooling and differing phase change temperature. The outlet fluid temperature from the tank can however be predicted accurately from operating conditions and the initial state of the PCM. Interrupting phase change processes before the PCM is completely melted or solidified affects the temperature at which the PCM changes phase as well as the degree of supercooling measured. Results from this investigation will be especially useful for researchers developing and validating numerical models for use in various building energy systems as the complete experimental data set is made available as an online companion to this paper.

A comparative study on PCM and ice thermal energy storage tank for air-conditioning systems in office buildings

Significant increasing demand of air conditioning (A/C) systems has led to more power consumption during on-peak hours in recent years. In this paper, a vapor compression A/C system has been analyzed via two strategies of hybrid systems. First, an ice thermal energy storage (ITES) system is used in the a.m. hybrid system; and thereafter a phase change material (PCM) tank is used as a full storage system (in order) to shift (the load) from on-peak to off-peak mode. This A/C system is modeled and analyzed from exergetic, economic and environmental point of views for both cases; then, using non-dominated sorting genetic algorithm-II (NSGA-II), multi-objective optimization is carried out and the optimal values of decision parameters are achieved. The exergy efficiency and total cost rate are considered as objective functions, and then ITES, PCM and conventional systems are compared. The results have illustrated that the power consumption of ITES and PCM systems are 4.59% and 7.58% lower than the conventional system respectively. Moreover, CO2 emission production for ITES and PCM systems are 17.8% and 27.2% lower than conventional system respectively.

Experimental analysis of hydroquinone used as phase change material (PCM) to be applied in solar cooling refrigeration

This present paper is focused on the study of high temperature thermal energy storage (TES) using phase change materials (PCM) to be applied on cooling and refrigeration systems by solar cooling. Thus, a pilot plant with a working temperature range between 150 and 200 °C was designed and built at the University of Lleida (Spain). Hydroquinone was selected for the specific application from different PCM candidates as the most suitable material after a literature review and a differential scanning calorimetry (DSC) analysis. This PCM has a phase change temperature range between 166 °C and 173 °C and a melting enthalpy of 225 kJ kg−1. Two storage configurations were evaluated using the same PCM to have preliminary results before the final storage tank design. From the pilot plant results and experience, a 5 Tn PCM storage tank was designed and built to work in a real solar cooling installation in Seville (Spain).