Thermal Energy Storage Tank Research Articles

Investigation on a Solar Thermal Power Plant With a Packed Bed Heat Storage Unit

Abstract The objective of the present work is to research the dynamic thermal performance of the solar power plant during the phase change material (PCM) capsule heat storage tank discharging process. Therefore, a transient, one-dimensional two-phase model for a packed bed latent heat storage unit and a comprehensive concentrating solar power generation system that combines a CO2 Brayton cycle and organic Rankine cycle were integrated. The influences of the key parameters of the packed bed PCM capsule heat storage tank on the overall power output and thermal efficiency of the system during discharge have been investigated, including the heat transfer fluid (HTF) velocity, the diameter of the PCM capsule, and the height of heat storage tank. The orthogonal analysis method is selected in this article, and the results showed that the maximal transient power output and overall power output of the actual combined cycle mode are decreased about 22% and 25%, respectively, in this research, compared with the idea Carnot cycle mode. That the HTF velocity in the thermal energy storage tank can be used to control the transient power output of the solar thermal power system. Using the small-sized filler capsule is an effective method to increase the thermal performance of the concentrated solar power (CSP) combined cycle system. Moreover, the corresponding discharging time is increased obviously, and the CSP with a high packed bed height can generate a more stable power output value during thermal energy discharging.

Transient energy storage in phase change materials, development and simulation of a new TRNSYS component

In this paper, a mathematical model is developed for the simulation of encapsulated phase change material as a thermal energy storage tank. The model is modified for the TRNSYS software to enable researchers for investigating the performance of a latent heat energy store system integrated with solar energy systems and buildings. The model is validated against experimental and numerical studies and the error is found to be less than 2% and 10% for 1-D and 2-D models, respectively. The new component is applied for solar energy storage and it is concluded that it effectively follows the variation of solar irradiation. The application of a PCM tank for daily energy storage reduces the cooling and heating loads by 22.5% and 18%, respectively. The energy-saving with seasonal cooling storage using a PCM tank is about 7% of the total energy consumption.

Computational Approach of Charging and Discharging Phases in a Novel Compact Solar Collector with Integrated Thermal Energy Storage Tank: Study of Different Phase Change Materials

A numerical study was carried out to investigate charging and discharging processes of different phase change materials (PCMs) used for thermal storage in an innovative solar collector, targeting domestic hot water (DHW) requirements. The aim was to study PCMs that meet all application requirements, considering their thermal performance in terms of stored and retrieved energy, outlet temperatures, and water flow rate. Work was carried out for three flat-plate solar panels of different sizes. For each panel, a PCM tank with a heat exchanger was attached on the back plate. Simulations were conducted on a 2D domain using the enthalpy–porosity technique. Three paraffin-based PCMs were studied, two (A53, P53) with phase-change temperatures of approximately 53 °C and one of approximately 58 °C (A58H). Results showed that, during charging, A58H can store the most energy and A53 the least (12.30 kWh and 10.54 kWh, respectively, for the biggest unit). However, the biggest unit, A58H, takes the most time to be fully charged, i.e., 6.43 h for the fastest feed rate, while the A53 unit charges the fastest, at 4.25 h. The behavior of P53 lies in between A53 and A58H, considering stored energy and charging time. During discharging, all PCMs could provide an adequate DHW amount, even in the worst case, that is, a small unit with a high hot water consumption rate. The A58H unit provides hot water above 40 °C for 10 min, P53 for 11 min, and A53 for 12 min. The DHW production duration increased if a bigger unit was used or if the consumption rate was lower.

Latent Thermal Energy Storage Application in a Residential Building at a Mediterranean Climate

An innovative thermal energy storage system (TESSe2b) was retrofitted in a residential building in Cyprus with a typical Mediterranean climate. The system comprises flat-plate solar collectors, thermal energy storage tanks filled with organic phase change material, a geothermal installation consisting of borehole heat exchangers with and without phase change material and a ground source heat pump, an advanced self-learning control system, backup devices and several other auxiliary components. The thermal energy storage tanks cover the building’s needs at certain temperature ranges (10–17 °C for cooling, 38–45 °C for heating and 50–60 °C for domestic hot water). A performance evaluation was conducted by comparing the TESSe2b system with the existing conventional heating and cooling system. The systems were simulated using commercial software, and the performance of the systems and the building’s energy needs were calculated. Based on the energy quantities, an economic analysis followed. The equivalent annual primary energy consumption with the conventional system resulted in being 43335 kWh, while for the storage system, it was only 8398 kWh. The payback period for the storage system was calculated to be equal to 9.76 years. The operation of the installed storage system provided data for calculations of the seasonal performance factor and storage performance. The seasonal performance factor values were very high during June, July and August, since the TESSe2b system works very efficiently in cooling mode due to the very high temperatures that dominate in Cyprus. The measured stored thermal energy for cooling, heating and domestic hot water resulted in being 14.5, 21.9 and 6.2 kWh, respectively. Moreover, the total volume of the phase change material thermal energy storage tanks for heating and domestic hot water was calculated to be roughly several times smaller than the volume of a tank with water as a storage medium.

An innovative green multi-generation system centering around concentrating PVTs and biomass heaters, design and multi-objective optimization

This article introduces an innovative off-grid biomass/solar-based building cooling/power system equipped with concentrated photovoltaic thermal (CPVT) panels, a specific biomass heater design, an absorption chiller, and thermal energy storage tanks. The hourly variation of performance, economic, and environmental metrics is evaluated to investigate the proposed system's feasibility for a case study building in India. The effect of significant operational parameters on the system's performance is assessed by observing their influence on levelized cost of energy, biomass effectiveness, solar and biomass heat load ratios, and levelized carbon dioxide emission. The optimum design and operating conditions are ascertained through a genetic algorithm-based multi-objective optimization approach contemplating techno-economic-environmental facets to be satisfied simultaneously. According to the results, the highest monthly heat and electricity produced by the CPVT system are 521.8 kWh and 593.4 kWh in May. The results further reveal that sugarcane baggas is an excellent option compared to the most commonly used biomass in India because of the lowest price sensitivity. The parametric study results show that increasing the generator temperature leads to a favorable techno-environmental condition. Besides, the results reveal that the increase in solar panels is not economically suitable due to a higher levelized cost of energy. The optimization outcomes demonstrate that the optimum values of levelized cost of energy, biomass effectiveness, and levelized carbon dioxide emission are 58.1 USD/MWh, 3342.3 MWh, and 233.6 kg/MWh, respectively. Eventually, it can be observed that the chiller size and mass flow rate entering the CPVT panels are sensitive parameters and the optimum range of the generator temperature is between 91 °C and 95 °C.

Experimental investigations on a sensible heat thermal energy storage system towards the design of cascaded latent heat storage system

ABSTRACT In the present work, a system comprising cylindrical vertical type sensible-based thermal energy storage (TES) tanks integrated with external type compound parabolic concentrating (XCPC) solar collectors and heat loading device was designed, fabricated, constructed, experimented, and analyzed. The XCPC solar collector system transfers the solar energy to charge the insulated TES tanks through heat transfer fluid circulation and discharge the energy to the selected application. The primary objective of the present research is to study the performance and stratification effects during the charging and discharging cycles through various parameters to select the suitable phase change materials (PCMs) for the proposed cascaded latent heat storage (CLHS) system. Further, experiments were conducted under simultaneous and sequential modes of charging and discharging processes. The performance analysis of the overall system on a time-average basis (0.125 hr) was carried out. The results revealed that simultaneous mode would help to collect more energy from the solar collector, and it increases the cumulative energy stored in the tank and the average charging efficiency of the tank. The same was also ensured from the stratification performance parameters, such as stratification number, Richardson number, and mix number. The higher stratification achieved in both modes revealed that the CLHS system with three different PCMs of phase change temperatures of 70°C, 63°C, and 53°C, located at three different zones, will enhance the performance of the storage system. The results are highly beneficial for practicing engineers toward designing the CLHS system integrated with solar collector for any application.

Experimental study on thermal performance of a novel medium-high temperature packed-bed latent heat storage system containing binary nitrate

The packed-bed latent heat storage (PBLHS) system has received extensive attention due to its low investment cost and good application prospects. In the past, the research on this system mainly focused on the establishment of mathematical models and the structural optimization of the thermal energy storage (TES) tank. There are few experimental studies on the thermal performance of PBLHS systems under medium-high temperature conditions. In this work, a novel medium-high temperature PBLHS experimental system is designed and constructed. Based on binary nitrate NaNO3–KNO3 (55-45 wt%) as the phase change materials (PCM), a spherical encapsulated PCM suitable for the packed bed TES is prepared. The heat transfer characteristics of the charging process, the static heat preservation process, and the discharging process are experimentally studied, respectively. In addition, the influence of the temperature and flow rate of the heat transfer fluid on the pressure drop of the PBLHS system is also investigated. The results indicate that with the continuous increase of the average air temperature inside the TES tank, the temperature difference inside the tank shows a trend of first increasing and then decreasing. When the average air temperature is around 225–272 ℃, the temperature difference is almost at a stable stage, and the temperature difference is about 84 ℃ (±1 ℃). The temperature difference decreases slowly in the initial stage of the discharging process. The overall efficiency of the current PBLHS system based on binary nitrate is 79.3%. The results also indicate that the air temperature and flow rate have a significant effect on the pressure loss of the packed-bed system. The experimental results of this work can provide experimental data support for the structural optimization design and industrial application of the packed-bed TES system.

Investigation and evaluation of building energy flexibility with energy storage system in hot summer and cold winter zones

The dramatically increasing energy demand of building air-conditioning in hot summer and cold winter zones fluctuates greatly, especially during the period of cooling and heating in summer and winter, which exerts strict operation burden and challenge on power-grid system stability. In order to realize building energy flexibility, this paper proposes a type of energy utilization system including electricity chiller, gas-boiler, electricity heater, cold and thermal energy storage tank (case II), on the basis of electricity chiller and gas-boiler for cooling and heating demand (case I), which is commonly used as cold and heat source in hot summer and cold winter zones. The total cost of the whole life period and annual carbon emission of energy systems are served as objective function is optimized. Furthermore, the system capacity confirmation and load demand management control are analyzed and discussed, the characteristics of energy-flexibility with and without energy storage are presented, the load coefficient is introduced to evaluate the impact of case II on building energy flexibility. Compared with case I, with the deployment of cold and thermal energy storage, the cost-effectiveness of case II is 16.5% and carbon emission is reduced by 30.9% compared with case I .In case II, the load coefficient of electricity chiller and electricity heater is 83.34% and 30.65% respectively, which means that energy storage system enables to promote building energy flexibility improvement and grid-friendliness enhancement. This paper provides methods and theoretical guidance for the planning-operation of building energy system and building energy flexibility in hot summer and cold winter zones.

Development and transient performance analysis of a decentralized grid-connected smart energy system based on hybrid solar-geothermal resources; Techno-economic evaluation

The world energy sector is going to change over from its present state of centralized energy generation to a future state with a larger share of distributed generation. In this respect, an innovative smart energy system based on hybrid solar-geothermal energies is proposed in this work, and transient performance assessment and techno-economic analysis are presented to evaluate its dynamic performance applying TRNSYS software. The proposed system is developed to provide power, heating, and cooling demands for a small urban community as the case study. The system consists of PVT panels, thermal energy storage tanks, a turbine, an absorption chiller, and a heat pump as the main components. Also, other subsidiary components like controllers and diverters are incorporated to guarantee the proposed system performance in a smart manner in various ambient conditions of the year. The results show that the system not only provides the annual electrical demand for the considered case study but also a considerable amount of excess power is produced, which can be sold to the power grid to compensate for some expenses of the system. The highest and the lowest exergy efficiency for the proposed system is attained in July and December with the values of 55.9% and 22.8%, respectively. Also, the highest and the lowest values of system unit product cost are obtained for January and July, respectively, as 8.38 and 32.77 $/GJ.

Energy Savings Analysis for Operation of Steam Cushion System for Sensible Thermal Energy Storages

The paper presents an analytical discussion of how to improve the energy efficiency of the steam cushion system operation for a Thermal Energy Storage (TES) tank. The EU’s green deal 2050 target policy requires an increase in the energy efficiency of energy production and use, as well as an increase in the share of renewable energy in the overall energy production balance. The use of energy-efficient TES is considered as one of the most important technologies to achieve the objectives of this EU policy. The analyses presented in the paper of energy-efficient operation of steam cushion (SC) systems were carried out by using operational data received from three District Heating Systems (DHSs) that supply heat and electricity to one of the largest cities in Poland and are equipped with the TES systems. These three analyzed TESs differ in capacities from 12,800 to 30,400 m3, tank diameters from 21 to 30 m and shell height from 37 to 48.2 m. The main purpose of using a steam cushion system in the TES tank is to protect the water stored in it against the absorption of oxygen from the surrounding atmospheric air through the surge chamber and safety valves located on the roof of the tank. The technical solutions presented here for the upper orifice for charging and discharging hot water into/from the tank and the suction pipe for circulating water allow to us achieve significant energy savings in the steam cushion systems. Both the upper orifice and the end of suction pipe are movable through the use of pontoons. Thanks to the use of this technical solution, a stable insulating water layer is created above the upper orifice in the upper part of the TES tank, where convective and turbulent transport of heat from the steam cushion space to the hot water stored in the tank is significantly limited. Ultimately, this reduces the heat flux by approximately 90% when compared to the classic technical solutions of steam cushion systems in TES tanks, i.e., for the upper orifice and circulation water pipe. The simplified analysis presented in the paper and comparison of its results with experimental data for heat flow from the steam cushion space to hot water stored in the upper part of the TES tank fully confirms the usefulness of the heat-flow models used.

Development of a smart control unit for small-scale concentrated solar combined heat and power systems for residential applications

Solar energy has a significant potential for future power generation but its intermittent and variable nature results in fluctuations of the operational performance of solar power plants. Despite thermal energy storage (TES) systems improving the flexibility and the sustainability of the performance of Concentrated Solar Power (CSP) plants, smart management is required to deal with the complex dynamic variations in the behaviour and interaction of the different plant's subsystems. In this paper, the design, manufacture, and validation of a smart control unit with extended capabilities for a small-scale CSP combined heat and power (CHP) system are described. More precisely, the control unit has been designed to control and optimise the operation of a micro-scale Organic Rankine Cycle (ORC) unit coupled with Linear Fresnel Reflectors solar field and an advanced latent heat thermal energy storage tank which were developed by a consortium of universities and companies in the framework of the EU-funded project “Innova Microsolar”.In parallel to the designing and building the smart control unit, an advanced simulator has been developed in Matlab/Simulink® to investigate the performance of the plant for a wide range of varying ambient and operating conditions. The simulation framework has been connected to the real control unit according to a hardware-in-the-loop (HiL) approach to optimise the control logic of the integrated plant to overcome potential technical and reliability issues during the commissioning of the plant. The developed hardware and the proposed scientific approach can be extended to a wide range of complex solar energy systems equipped with TES and to be integrated into the built environment.

Life cycle cost analysis of an electric centrifugal chiller integrated with a district cooling plant

ABSTRACT Electric Centrifugal Chillers (ECC) are mostly incorporated into District Cooling (DC) systems for charging the Thermal Energy Storage (TES) tank or/and to supply Chilled Water (CW) directly to the DC network for Air Conditioning (AC). ECC accounts for the highest percentage of the total electrical energy consumption, making it the most energy-intensive system in the DC setup. The high positive correlation between energy consumption and cost, and its influence on the decision-making process, necessitate the requirement to conduct an economic performance evaluation of the ECC plants. To achieve this objective, a Life Cycle Cost (LCC) analysis is performed to quantify the economic implication resulting from the ECC system's acquisition, operation, and maintenance. In this analysis, four (4) ECC systems installed in a large DC plant in Malaysia are considered the case study. The result obtained from the analysis of the study year revealed that April and June accounted for the maximum and minimum cost implication per outcome, respectively. It is also observed from the results that the climatic temperature conditions had a significant influence on the monthly cooling demand, energy consumed, and cost incurred. The operational phase of the system's life cycle accounted for the highest cost implication from the overall LCC result. A significant reduction in the operating cost is recorded as the indirect energy source used for driving the chiller plant is switched from the electricity supplied from the National Electricity Grid (NEG) and supplied from the Natural Gas Plant (NGP). The LCC per refrigeration ton of the ECC system is estimated to be MYR 1.44/RTh. The impact of system degradation (i.e. decrease in Coefficient of Performance (COP) value) over time on the overall cost per output refrigeration was also investigated. The study also revealed that operating an actual ECC system on electricity from NGP led to a 31% cost savings compared to an ideal system running on electricity from NEG. A sensitivity analysis is also conducted at the end of the study to determine the influence of the input variable on the output result.

Cyclic and standby behavior evaluations of liquid lead-bismuth eutectic thermal energy storage tank for concentrated solar power

This paper presents a simulation study on the sensible thermal energy storage (STES) tank using liquid lead-bismuth eutectic and packed medium. The cyclic, charging, discharging and mechanical performances of the STES tank are investigated. The results reveal that the stable operation process of the STES tank can be achieved after five cycles are completed. When the STES tank operates stably, the discharging efficiency is 91.9%, the discharging duration is 5.3 h, and the peak maximum mechanical stress of the steel wall is 138 MPa. With the standby time increased from 0 h to 9 h, the thermocline expands and thus the thermocline thickness increases from 2.7 m to 5.8 m. But after about 9 h, the thermocline thickness variation is relatively small. As the standby time increases from 0 h to 24 h, the heat loss power of the tank decreases from 313.1 kW to 263.1 kW, and the total heat loss of the tank increases linearly. When the standby time is 24 h, the total heat loss is 2.38 × 1010 J. It can be concluded that the STES tank using lead-bismuth eutectic can operate stably, and thus has relatively good potential for the application in concentrated solar power plants.

Forecasting solar-thermal systems performance under transient operation using a data-driven machine learning approach based on the deep operator network architecture

Modeling and prediction of the dynamic behavior of thermal systems operating under intermittent energy input and variable load requirements represent one of the greatest challenges in the development of efficient and reliable renewable-based power generation technologies. In this work, a data-driven machine learning modeling framework was developed based on a modified version of the Deep Operator Network architecture where the time coordinate in the trunk net is replaced with historical data of the predicting quantity. The modeling framework can be used to accurately predict the performance of renewable-based energy conversion technologies including wind- and solar-based power plants. This novel framework was applied on a solar-thermal system that consists of a solar collection loop using a flat plate collector, a power generation loop comprising an Organic Rankine Cycle, and a thermal energy storage tank connecting both loops. Variable solar irradiance, air temperature, and power load profiles were used by the Deep Operator Network to predict the State-of-Charge and the efficiency of the thermal system for several days. The results were compared with the State-of-Charge and efficiency functions calculated using a physics-based model. For a simple operation scenario, characterized by a clear sky solar irradiance profile and constant load, the standard deviation in the State-of-Charge prediction by Deep Operator Network is below 0.9% during a seven-day prediction time horizon. For the most realistic operation scenario that considers real solar irradiance and a rough load profile, the maximum standard deviation in the predictions for the State-of-Charge and efficiency are below 6.8% and 2.5%, respectively. A comparison between Deep Operator Network and Long Short Term Memory network was also performed. In general, both networks predict very well the State-of-Charge for different data density conditions; however, a higher accuracy, with a standard deviation below 2.0%, is obtained by the Deep Operator Network during three and half days using sparser training data of 20-minute points. The same accuracy for the State-of-Charge prediction with the Long Short Term Memory network is achieved only for 14 h. Average standard deviations for the State-of-Charge prediction of 1.1% with the Deep Operator Network and 1.5% with the Long Short Term Memory network are obtained for a four-day prediction time using a denser training data of 5-minute points.

Analysis of operation performance of three indirect expansion solar assisted air source heat pumps for domestic heating

To achieve the goal set for net-zero emissions of greenhouse gases in the UK by 2050, the domestic heating must be decarbonised. Solar assisted air source heat pumps, integrating solar collector, thermal energy storage tank and heat pump, offers a promising alternative application under the UK weather conditions. Literature review shows that investigations of solar assisted air source heat pumps in the regions like the UK are still insufficient. The serial, parallel and dual-source indirect expansion solar assisted air source heat pumps are modelled and simulated under the weather conditions in London using TRNSYS to investigate the operation performance over a typical year. These three heat pumps are applied to provide space heating and hot water of 300 L per day for a typical single-family house. The simulation results show comparisons of the three systems. The serial type heat pump shows the highest seasonal performance factor of 5.5, but requiring the largest sizes of the solar collector and thermal energy storage tank. The dual-source and parallel type heat pumps show slightly lower seasonal performance factors of 4.4 and 4.5, respectively, requiring smaller sizes of solar collector and thermal energy storage tank. Furthermore, the results show that the air source part contributes to an important proportion of the heat provision and stable operation of the systems. The yearly seasonal performance factor higher than 4.4 achievable by the three heat pumps suggests that they are potentially applied in the regions with relatively lower solar irradiance. The economic analyses indicate that the parallel and dual-source type heat pumps provide good alternatives to replace the gas-boiler heating system.

Experimental Validation of a Dynamic Photovoltaic/Thermal Collector Model in Combination with a Thermal Energy Storage Tank

The primary objective of this paper is to present a dynamic photovoltaic/thermal collector model in combination with a thermal energy storage tank. The added value of the proposed model is the use and integration of existing dynamic models for describing the entire photovoltaic/thermal system. The presented model was validated using measurements on the experimental system located at the Institute of Energy Technology, Faculty of Energy Technology, University of Maribor. The validation was carried out based on three different weather conditions—sunny, cloudy, and overcast. The validation results were evaluated using the normalized root mean square error and mean absolute percentage error for the temperature and output power of the photovoltaic/thermal collector and the temperature of the thermal energy storage tank. The model results concurred with the measurements, as the average mean absolute percentage error values for the temperature and output power of the photovoltaic/thermal collector and thermal energy storage tank temperature were 5.82%, 1.51%, and 7.58% respectively.

Numerical Study to Investigate the Thickness of the PCM Layer for the Three Layers Tank for the CSP Plants

In the present study, the phase change material (PCM) layer thickness of the top and bottom PCMs change gradually with constant the middle PCM layer thickness for the three-layers thermocline thermal energy storage (TES) tank. It has been studied using spherical capsules packed with three types of PCMs with different thermophysical properties. A transient two-phase dispersion-concentric (D-C) model is used to calculate the process of phase change inside pellets to identify the temperature allocation. The method of heat transfer among molten salt and PCMs capsules is extensively discussed, with multiple numerical results shown. The results show that the thickness of the PCM layer has a high impact on the thermal performance of the TES tank. As the layer thickness of the top PCM increases, the time required to discharge the thermocline TES tank increases. The (80 % high phase change material (HPCM) -10 % intermediate phase change material (IPCM) - 10 % low phase change material (LPCM)) configuration has 14.6 %, 27.2 %, and 46.8 % higher overall efficiency than (33.3 % HPCM - 33.3 % IPCM -33.3 % LPCM) configuration, (70 % HPCM - 10 % IPCM - 20 % LPCM) configuration, and (10 % HPCM -10 % IPCM - 80 % LPCM) configuration. In contrast, the (80 % HPCM - 10 % IPCM - 10 % LPCM) configuration shows the highest capacity and utilization ratio.

Thermal energy storage using phase change material: Analysis of partial tank charging and discharging on system performance in a building cooling application

Thermal energy storage coupled with phase change materials is a technology that offers the potential to shift and in some case reduce building cooling loads and increase energy efficiency. This simulation study uses a TRNSYS building and HVAC system model to investigate whether partially charging and discharging a phase change material thermal energy storage tank can improve the operational characteristics required by a light-weight commercial building located in a Mediterranean climate. The results indicate that partial charging and discharging can lead to better energy performance of the phase change material thermal energy storage HVAC system. If the phase change material thermal energy storage tank is not required to operate at maximum capacity (i.e., maximum charge), energy savings are possible by only partially charging the tank. Further energy efficiency gains are also possible by control of the heat transfer fluid flow rates in the HVAC thermal energy storage system loops. Generally, higher charging loop flow rates and lower discharge loop flow rates produce better energy performance. Charging a phase change material thermal energy storage tank above 90% is not recommended, as at very high charge fractions, the energy performance decreases considerably, while the charging time increases significantly.

Life Cycle Assessment of a Vapor Compression Cooling System Integrated within a District Cooling Plant

In standard district cooling (DC) plants, central chillers produce cold energy for space cooling throughout the district network. In recent times, the integration of the vapor compression system, which includes the functionalities of vapor compression chillers (VCC), and thermal energy storage (TES) tanks in the DC setup, has gained more implementation across the globe. This is due to the possibility of load shifting by using the VCC to produce chilled water for charging the TES tanks during off peak periods. Since the environmental implications of various energy intensive systems are largely determined by the amount of material and energy consumed throughout their life cycle, it is critical to conduct a sustainability assessment of these systems in terms of environmental contributions, and suggest design options to reduce these impacts. A cradle to grave life cycle assessment (LCA) model is created in response to these issues and in order to meet the project’s objectives. The life cycle impact assessment (LCIA) results of the analysis reveal that the carbon footprint per 1 RTh of the produced chilled water is estimated at 0.72 kg CO2 eq/RTh. The operation phase of the system’s life cycle accounted for the most impact, about 98%, with other life cycle phases having negligible contributions. In substantiating the study’s investigation, the environmental performance based on several design options were discussed and compared to the case study. Among the several scenarios considered, incorporating the Sweden mix technology provided the case study with the most significant environmental savings, of about 94%.

An improved genetic algorithm for determining the optimal operation strategy of thermal energy storage tank in combined heat and power units

The TES (thermal energy storage) tank has been widely used in CHP (combined heat and power) units to consume more renewable energy. In this paper, the hourly operation model has been established to solve the operation strategy problem of TES tank. The limitations of standard genetic algorithm used in the operation strategy of TES tank have been analyzed, then an improved genetic algorithm is proposed. At last, the improved genetic algorithm is used to optimize the operation strategy of TES tank by combining the characteristic day method. The results show that the improved genetic algorithm can enhance the local search ability and calculation speed obviously, and the calculation speed will be further improved after combining the characteristic day method. In order to obtain the maximum profit, the TES tank should store thermal energy at high minimum power load and release thermal energy at low minimum power load. In addition, the optimal capacity of TES tank in different months varies greatly during the period of thermal energy supply. The optimal capacity of TES tank should be the maximum value among all the months to ensure the thermal energy supply.