Short-term Thermal Storage Research Articles

Design and eco-technoeconomic analysis of a natural gas cogeneration energy management center (EMC) with short-term thermal storage

This work proposes a non-islanded cogeneration energy management center (EMC) that can be used to displace grid-level natural gas turbine systems and natural gas combustion systems for heat. The design of the proposed EMC included a weighted multi-objective optimization aimed at minimizing: i) natural gas consumption; ii) capital costs; iii) utility costs; and iv) unmet thermal demand. The decision variables consisted of the existence and capacity of the equipment comprising the EMC, including: i) a natural gas boiler; ii) an internal combustion engine that generates heat and electricity; and iii) a hot water thermal storage system. Four resulting candidates EMC designs were then compared with the status-quo (SQ) in an eco-technoeconomic analysis; The SQ draws electricity from the grid and heating for dwellings come from natural gas boilers. Emissions at grid level change which alternative is favored. The findings showed that, for a system that serves 4–5 dense urban city blocks over a 20-year lifetime, the SQ system had cumulative levelized costs of 9.6 million USD for the final consumer, while the levelized costs of the EMC designs ranged from 12.9 to 15.1 million USD. In terms of emissions, the SQ emitted 959 tonnes of CO2eq per year, while the EMC system produced around 500 tonnes of CO2eq per year depending on the year, yielding a CCA varying between 364 and 653 USD/tonneCO2eq

Numerical assessment of the effect of tube geometries on the performance of phase change material (PCM) integrated solar receiver for dish-micro gas turbine systems

The temperature distribution and melting/solidification behavior of the Phase Change Material (PCM) depends largely on the arrangement of working fluid tubes in the PCM volume. A well-designed tube arrangement in the PCM results in more effective heat transfer and thermal storage. The authors previously presented a concept of Phase Change Material (PCM) integrated solar receiver for short-term thermal storage in the dish-micro gas turbine system. This solar receiver has a cylindrical shape structure filled with PCM, twelve tubes of working fluid (air) immersed in the PCM, and a conical cavity on its front surface. For such a compact thermal storage component, energy storage in the PCM and the charging/discharging rate largely depend on the arrangement of working fluid tubes in the PCM volume. The design of tubes should allow the proper distribution and release of heat in the PCM during the charging and discharging phases, respectively. In this study, the melting behavior and heat storage capacity of the PCM integrated solar receiver were analyzed by considering three different arrangements of the working fluid tubes with two cavity structures; a solar receiver with conical shaped cavity and 172° bend tubes, solar receiver with cylindrical shaped cavity and U-shaped tubes and solar receiver with conical shaped cavity with double helical tubes. The 3D numerical analysis were conducted by using Ansys Fluent 2022R1 to evaluate the effect of tube arrangements on the temperature distribution in PCM volume, melting behavior of PCM and the total storage capacity of the component. Temperature distribution on the cavity walls and heat losses were also considered. The transient simulations were performed using k−ε turbulent model with S2S radiation model and ray-tracing model. The results showed a significant effect of tube geometries on the PCM melting behavior inside the solar receiver. It was found that, in the solar receiver with conical shaped cavity and 172° bend tubes, the tubes arrangement is more suitable throughout the PCM volume and represents a more uniform temperature and melting behavior. Moreover, the pressure drop was much higher in the double helical tubes compared to other bend tubes.

Dynamic exergy and economic assessment of the implementation of seasonal underground thermal energy storage in existing solar district heating

In this paper, an exergoeconomic approach is proposed to assess the impact of the integration of a Borehole Thermal Energy Storage (BTES) in the existing district heating of the city of Chateaubriant in France. To do so, a dynamic simulation is run over ten years of operation. The model includes a new approach for cost calculation of short-term thermal storage, which is extended to seasonal BTES. The analysis of the system operation at yearly and daily scales revealed several issues. Hence, without redesigning the existing installation, it was found that a non-comprehensive control strategy results in an increase of fossil fuel share by 1.2%. At the BTES scale, from an exergoeconomic point of view, the charging stage is found particularly sensitive to the dynamic. For example, charging the BTES at low temperature increases of the specific cost of the heat stored. Hence, it is shown that some exergoeconomic indicators, like the specific cost of stored heat, could be relevant for designing and operating heating systems with borehole thermal energy storage.

Sizing and control optimization of thermal energy storage in a solar district heating system

Solar district heating systems have shown significant promise to facilitate the large scale adoption of solar energy technologies and thus substantially reduce greenhouse gas emissions. Given the mismatch between solar energy and district heating demand, energy storage devices play a critical role given their capacity to stockpile solar energy in both the short-term (hours to days) and long-term (months). However, the integration, sizing and control of energy storage technologies is far from simple. This paper investigates sizing and controlling thermal energy storage from the perspective of its performance within a district heating system, highlighting the close link between design and control. A 52-house Canadian solar district heating system, the Drake Landing Solar Community (DLSC), was used as a case study. This system uses solar collectors as main energy supply, borehole thermal energy storage (BTES) for seasonal storage and two 120-m3 water tanks for short-term thermal storage (STTS).The effect of (a) storage sizing (STTS volume) and (b) storage control (rate at which energy is either injected or extracted from the BTES) was evaluated. A control-oriented model, calibrated and validated with operational data at 10-min intervals, was used along with an optimal rule-based control to gauge system primary energy use. Different scenarios were tested, with STTS volumes ranging from 120 m3 to 480 m3, and BTES loop nominal flow rates between 2.5 and 4.5 L/s. An optimization routine was developed to calculate the optimum parameters of the rule-based control strategy. Results show that, in comparison with the design and control in place, primary energy savings of 13%–30% (with BTES flow rates of 2.5–4.5 L/s) could have been obtained with the proposed rule-based control strategy. By decreasing the STTS volume to 120-m3, energy savings up to 6% could still be achieved; savings could reach 27%–36% by increasing the STTS size to 360-m3.

Effect of phase change materials on the short-term thermal storage in the solar receiver of dish-micro gas turbine systems: A numerical analysis

• Solar receiver with short-term thermal storage for Dish-Micro Gas Turbine system. • Effect of suitable PCMs on the output parameters of PCM integrated solar receiver. • Detailed numerical analysis using CFD methods. • Steady state parametric analysis for the effect of important parameters of PCM. • Detailed transient analysis for thermal storage behavior of the solar receiver. The solar dish-micro gas turbine system is a new alternative to the existing technologies for small-scale power production (<100 kW) in rural off-grid areas. In these solar-only systems, the short-term thermal energy storage in the solar receiver reduces the effect of natural fluctuations of the solar flux and ensures the stable working fluid (WF) temperature to the gas turbine. It improves the system performance and stability of the small gas turbine. In this context, a concept of Phase Change Material (PCM) integrated solar receiver was presented by authors in previous studies, where the receiver was filled with high-temperature PCM and WF (air) tubes were immersed in it. The PCM stores heat during charging phase and releases heat during the solar breakdown. The selection of PCMs for this receiver is a challenging task due to the high operating temperature ( T m > 1000 K). This study deals with the analysis of the impact of main parameters of the PCM on the performance of the solar receiver and detailed thermal analysis of the component using selected suitable PCMs. The 3D numerical analysis has been performed using Ansys Fluent R2. Moreover, the optical analysis has been carried out by ray tracing using SolTrace. The results of Soltrace are input to the Ansys Fluent and solar radiations are made to impinged on the cavity of the solar receiver. Steady-state parametric analysis has been performed considering the effect of latent heat of fusion, thermal conductivity, and the specific heat of the PCM on the outlet parameters of the receiver. The results showed a significant effect of these parameters on the heat storage of the solar receiver and the solidification/melting rate of PCM. The latent heat has major effect on the thermal storage in the PCM while thermal conductivity has high impact on the solidification/melting rate of the PCM. The transient simulations have been performed for the detailed melting/solidification behavior of the receiver using four metallic PCMs including MgSi, AlSb, NiSi, and Mg 2 Si. AlSb is characterized with comparatively lower latent heat and high thermal conductivity and showed quick solidification in discharging phase. Mg 2 Si has high melting temperature and a low thermal conductivity as compared to the other selected PCMs and thus has a comparatively slow solidification rate than AlSb and MgSi. The results show a good behavior of the component short term (15–20 min) thermal energy storage and stabilization of WF (air) temperature above 1000 K during this period.

Modeling of thermal energy sharing in integrated energy communities with micro-thermal networks

This investigation focuses on the potential of harvesting heat rejected from the cooling and refrigeration systems of buildings with high year-round cooling and refrigeration demand (e.g., ice arenas and grocery stores) and using it to heat other nearby buildings. Integrating a small group of buildings with diverse thermal demands via a low-temperature micro-thermal network effectively allows wasted thermal energy to be harvested and shared among the buildings with minimal thermal and mechanical losses. This paper presents a reduced model that shows the potential of harvesting thermal energy between buildings by calculating the amount of heat energy simultaneously shared between the connected buildings on a five-minute time resolution. The model also evaluates changes in greenhouse gas (GHG) emissions and the amount of energy that is still required from supplemental heating sources after harvesting relative to conventional stand-alone building systems. This study shows that changing the operating temperature of the micro-thermal network when primarily sharing between diverse thermal demand buildings has a minor effect on GHG emissions but can have a larger effect on electrical energy consumption. The model is applied using actual utility energy consumption at one of the potential clusters in Ontario, with results showing that approximately 48% of the cluster’s total heating requirements can be covered by instantaneous sharing between buildings, and an additional 12% can be covered by daily short-term thermal storage. This reduced heating demand results in an approximately 74% reduction in total GHG emissions.

Modeling and analysis of a solar thermal-photovoltaic-hydrogen-based hybrid power system for running a standalone cold storage

In this paper, a solar-hydrogen-based hybrid power system has been proposed to run a remotely located cold storage facility for developing countries on a sustainable basis. The proposed system includes an array of parabolic trough collectors with short-term thermal storage, an array of solar photovoltaic modules, an electrolyzer bank, compressed hydrogen storage, and a proton exchange membrane fuel cell stack to satisfy the thermal and electrical demands of a standalone multi-commodity cold storage. The cold storage is operated on a double-effect vapor absorption refrigeration system. A mathematical model of the integrated system has been developed and validated against a reference study available in the literature. The proposed system has been analyzed from the energy, economic, and environmental point-of-view. The study reveals that after meeting the in-house power requirements of the proposed cold storage facility, the designed power system can produce 2.17 MWh of surplus energy, which can be used to support the load during an exigency. The carbon dioxide mitigation potential of the proposed power system is estimated to be about 350 tons that can save an annual carbon tax of $ 5067. The estimated payback period of about seven years indicates the economic viability of the integrated system.

The effect of seasonal weather changes on the performance of databased models of the thermodynamic behaviour of buildings

Several studies have indicated that Model Predictive Control (MPC) of space heating systems can utilize the thermal mass of residential buildings as short-term thermal storage for various demand response purposes. Realization of this potential relies heavily on the accuracy of the model used to represent the thermodynamics of the building. Such models, whether they are grey box or black box, are calibrated using relevant data obtained from initial measurements, and the performance of the calibrated model is validated using data from a subsequent period. However, many studies use validation periods with weather conditions similar to those of the calibration period. Only a few studies investigate whether the calibrated model performs satisfactory when subjected to significantly different conditions. This paper presents data from a simulation-based study on the effect of seasonal weather changes on the performance of a black-box model. The study was conducted using 11 years of Danish weather data (2008-2018). The results indicate that the performance of the black-box model deteriorate as the weather data conditions become increasingly different from those used in the initial model calibration. Further, the results show that calibration in heating season leads to satisfactory model performance through the heating season, but lower performance in transitional seasons (especially spring). Results also show that calibration in February led to highest model performance through heating season, while calibration in March led to satisfactory model performance in the whole heating and fall season.

Design of high-temperature solar receiver integrated with short-term thermal storage for Dish-Micro Gas Turbine systems

Small-scale concentrated solar power plants equipped with Micro Gas Turbines (MGTs) could be an effective way for power production in the off-grid areas. One of the most relevant concerns for such no fuel-assisted systems is the solar radiation fluctuations, which reduce system performance and, in the worst cases, can damage the MGT. To overcome this issue, the solar receiver should have sufficient thermal inertia averaging the thermal power inputted in the MGT. In the present study, the design of a novel high-temperature cavity solar receiver is presented for the application in the Dish-MGT system. The receiver has been integrated with a PCM for the short-term thermal energy storage (15–30 min). The design process was based on the main parameters of the solar dish and MGT. The thermal model enables the variation of different geometrical factors and input parameters to identify the optimum receiver design. Moreover, it can be used for the evaluation of heat losses from the cavity surface and temperature distributions in the PCM. A 1D steady-state model has been developed for the heat loss calculation from the cavity and corresponding cavity surface temperature, as well as for the evaluation of number and dimensions of the MGT working fluid tubes. Furthermore, the PCM melting and the transient temperature distribution inside the PCM domain have been determined analytically with the help of a 1D thermal model. The initial design results showed that solar receiver integrated with the high-temperature PCM is a promising option for the stable outlet temperature for MGT.

Energy analysis and thermoeconomic assessment of the closed greenhouse – The largest commercial solar building

The closed greenhouse concept has been studied in this paper. The closed greenhouse can be considered as the largest commercial solar building. In principle, it is designed to maximize the utilization of solar energy by use of seasonal storage. In an ideal fully closed greenhouse, there is no ventilation window. Therefore, the excess heat must be removed by other means. In order to utilize the excess heat at a later time, long- and/or short-term thermal storage technology (TES) should be integrated. A theoretical model has been derived to evaluate the performance of various design scenarios. The closed greenhouse is compared with a conventional greenhouse using a case study to guide the energy analysis and verify the model. A new parameter has been defined in this paper in order to compare the performance of the closed greenhouse concept in different configurations – the Surplus Energy Ratio showing the available excess thermal energy that can be stored in the TES system and the annual heating demand of the greenhouse. From the energy analysis it can be concluded that SER is about three in the ideal fully closed greenhouse. Also, there is a large difference in heating demand between the ideal closed and conventional greenhouse configurations Finally, a preliminary thermo-economic study has been assessed in order to investigate the cost feasibility of various closed greenhouse configurations, like ideal closed; semi closed and partly closed conditions.Here, it was found that the design load has the main impact on the payback period. In the case of the base load being chosen as the design load, the payback period for the ideal closed greenhouse might be reduced by 50%. On the other hand, glazing type, ventilation ratio, and the closed area portion have a minor impact on the payback period.

Applications of Phase Change Material in highly energy-efficient houses

Thermal mass combined with other passive strategies can play an important role in buildings energy efficiency, minimizing the need of space-conditioning mechanical systems. However, the use of lightweight materials with low thermal mass is becoming increasingly common. Phase Change Materials (PCMs) can add thermal energy storage benefits to lightweight constructions. There are many studies about the use of PCM in buildings, but there are still some difficulties for effective use and practical application of these materials. The study of applications used in real buildings could help us find solutions to these difficulties. This paper analyzed different PCM applications presented in highly efficient lightweight construction houses that have participated in the American Solar Decathlon, an international competition organized by U.S. Department of Energy. These houses have been tested and monitored in Washington DC, place with suitable climate conditions for short term thermal storage systems. The study started with a classification of the PCM applications and included an analysis of the systems, materials, switching temperatures, containments and design strategies used to improve the houses energy performance. Also, it included results of numerical simulations and experimentation that the participant team had done, complemented with information available in the literature about similar materials or applications.

Influence of interfacial intermetallic compound on fracture behavior of solder joints

This paper studies the solder joints of an Sn–Ag lead-free solder system with pure copper wires. The study focuses upon the interrelationships, which exist between the adhesive strength of the joint, its shear strength, the formation of interfacial intermetallic compounds (IMC) and the fractographic morphology. Additionally, the paper determines how these characteristics, and the relationships between them, are influenced by the storage duration and the storage temperature. Experimental results show that both the adhesive strength and the shear strength of the solder joints decrease significantly following short-term thermal storage. As the storage time is increased, it is noted that both the thickness and the roughness of the interfacial IMC layers increase. Regarding the fracture of the solder joints, fractographic observation reveals that fracture morphology under adhesive loading are similar to those observed under shear loading conditions. In the as-soldered condition, the fracture surface appears to be flat, and some broken Cu 6Sn 5 and residual solder pieces are evident. When the total thickness of the IMC layer lies within the range 1–10 μm, it is observed that the fracture morphology gradually becomes a dimple-like structure. This phenomenon may be attributed to the residual stresses caused by phase transformation, and by the increasing roughness of the IMC layers which causes an increase in the stress concentration within the Cu 6Sn 5 layer, and which ultimately results in fracturing of this layer. When the total thickness of the interfacial IMC layers exceeds 10 μm, the roughness of the IMC layers and the residual stress between them and the solder both continue to increase. Eventually this results in a fracture being initiated and propagated within the Cu 6Sn 5 layer. Fractographic observation shows the fracture to have a cleavage-like morphology.

Simulated performance of thermal storage in a solar cooker

An explicit finite-difference method is used to simulate the thermal performance of short-term thermal storage for a focusing, indoor, institutional, solar cooker. The cooker storage unit consists of a cylindrical solid block. The block is enclosed in a uniform layer of insulation except where there are cavities on the top and bottom surfaces to alllow heating of a pot from storage and heating of the storage by solar radiation. A paraboloidal concentrator focuses solar radiation through a secondary reflector onto a central circular zone of the storage block through the cavity in the insulation. The storage is charged for a set period of time and heat is subsequently discharged to a pot of water. In these simulations a pot of cold water is placed on the hot storage block and the time then estimated until the water either boils or the temprature of the water reaches a maximum value. Simulations are made for a given pot capacity with the storage block made from either cast iron or granite (rock). The effects on cooker performance are compared for a variety of height to diameter ratios of the storage block and size of the area of solar input zone.

Energy efficiency in new houses. Heat demand reduction versus cogeneration?

Heat demand reduction and cogeneration are two main options to reduce fuel consumption for space heating and warm tapwater in buildings. This article compares fuel saving and costs of these two options for the case of new Dutch houses. In the calculations, simulation techniques are used to account for diurnal and seasonal variations of both the heat demand level and the operational conditions of cogeneration. The use of a short term thermal storage is considered in order to match heat supply and demand. Heat demand reduction and cogeneration appear to have a considerable fuel saving potential in new Dutch houses. At present Dutch natural gas prices both options are not cost-effective. However, expected investment cost reductions and energy taxes that are under consideration may eliminate this hindrance. These developments would also open possibilities towards combinations of heat demand reduction and cogeneration. Such combinations could make a large contribution to fuel consumption reduction goals in The Netherlands.

Solar Thermal Power Towers

The solar thermal central receiver technology, known as solar power towers, is rapidly evolving to a state of near-term energy availability for electrical power generation and industrial process heat applications. The systems consist of field arrays of heliostat reflectors, a central receiver boiler, short term thermal storage devices, and either turbine-generators or heat exchangers. Fluid temperatures up to 550°C are currently achievable, and technology developments are underway to reach 1100°C. Six solar power towers are now under construction or in test operation in five countries around the world.

Short-term storage and wind power availability

IN a discussion on the economics of alternative energy sources, Ryle1 suggested that wind power in conjunction with short-term thermal storage can provide a viable and attractive source of energy in the UK. Leicester, Newman and Wright2 have recently analysed wind data and empirically derived heating demand over a six-month period. On the basis of these data they suggest that short-term (∼150 h) storage is inadequate to provide a reasonably reliable supply from wind generators for heating purposes. This conclusion has been criticised by Diesendorf and Westcott3 and, in view of the limited data sample used it is clear that a more extensive analysis is required. Here we use hourly wind and temperature measurements over a 17-yr period (data obtained from the Meteorological Office, Bracknell) to investigate the performance of a simple system in which wind power is used in conjunction with 150-h thermal storage to provide domestic space heating. The results are promising, even for this basic system, and confirm that, with some modifications, such a system can provide adequate reliability. A significant result of this analysis has been to indicate the importance of selecting an appropriate value for the wind speed at which the wind turbine is to produce its peak output (the ‘rated’ wind speed). It is shown that the use of too high a rated speed not only greatly exaggerates the fluctuations in available power but could also result in a more expensive design of turbine for a given annual energy output.

THE INFLUENCE OF SNOW COVER ON LOCAL CLIMATE IN GREENLAND

Abstract Study of thermal storage in the local environment (landscape and climatologic air) provides an approach to an understanding of surface-created local climates, such as those in snow-covered regions. Such a local climate, dominated by the snow surface, occurs 40 to 45 per cent of the time on the Greenland icecap, in spite of convexity of ferrain. In winter, the local climate is distinguished by long-term thermal storage of 100 to 1.50 calories per square centimeter in a three-layer environment. This heat, conserved from periods of advection of maritime air into interstorm periods, supplies two-thirds of the heat lost from the local climate. In summer, short-term thermal storage conserves approximately 30 cal/cm2 from the high-sun to the low-sun part of the day. During the daily cycle, the range in radiation balance is 17 cal cm−2 hr−1: but because the regional specific heat is small, range in snow and air temperature is relatively large. In addition to its value in applying meteorology to problems ...