Renewable Thermal Energy Research Articles

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その4）シミュレーションと除湿性能試験による吸放湿ブロックの評価

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その4）シミュレーションと除湿性能試験による吸放湿ブロックの評価

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その2）調湿外気処理ユニットの概要と全熱交換モジュールの評価

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その2）調湿外気処理ユニットの概要と全熱交換モジュールの評価

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その6）小型調湿外気処理ユニット二次試作機の評価

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その6）小型調湿外気処理ユニット二次試作機の評価

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その7）実外気条件下における調湿性能の検証

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その7）実外気条件下における調湿性能の検証

Evaluation of the temperature regimes of multi-level thermal networks in urban areas through exergy analysis

The overall objective of this study is to explore the potentials of district heating systems (DHS) operating on more than two high temperature levels. This characteristic allows integrating decentralized and renewable thermal energy sources. It also enables the network to minimize inefficiencies caused by mismatches between supply and demand exergy levels. This paper studies the effects of better suited exergy levels for DHS with two, three and four supply temperature levels. It is shown that having more than two temperature levels is in many cases advantageous both exergetically and economically.

Parametric study of a novel organic Rankine cycle combined with a cascade refrigeration cycle (ORC-CRS) using natural refrigerants

This paper presents a novel design of a stand-alone refrigeration system consisting of a combined organic Rankine cycle and a cascade refrigeration system (ORC-CRS) for low-evaporation-temperature applications (from −55°C to −30°C). Natural refrigerants were used as working fluids: toluene for the organic Rankine cycle and NH3/CO2 for the cascade refrigeration system. A parametric study and a regression analysis have been performed to characterize the system and to estimate the overall system coefficient of performance (COPoval) and exergetic efficiency (ηex_oval). The highest values of COPoval and ηex_oval calculated were 0.79 and 31.6%, corresponding to ORC evaporation temperatures of 315°C and 255°C, respectively. Renewable thermal energy sources from 100 to 350°C can be used to drive the facility, thus reducing dependence on fossil fuel and CO2 emissions. This stand-alone facility seems to be a feasible option to exploit low- and medium-grade thermal energy (geothermal, solar, waste heat) in places where the electricity supply is unreliable.

Sustainability assessment of large-scale storage technologies for surplus electricity using group multi-criteria decision analysis

Power to gas (P2G)-methane, pumped hydroelectric storage (PHES) and compressed air energy storage (CAES) are three methods to store surplus electricity with high capacity and long discharge time. However, there is a few research included P2G—methane in comparing with other storage technologies in general and in terms of sustainability development. This paper explored and compared the cost, efficiency, position flexibility, storage capacity/discharge time, energy carrier vector and environmental issues of those storage technologies in terms of single criterion and group multi-criteria analysis. The single criterion data of each technology was reviewed from literature and compared with each other. The data from single criterion were normalised then used as inputs of the linear additive model. The weights of criteria were determined by sending out the weighting assessment form to 10 researchers. The comparison in terms of cost and efficiency showed that PHES is better than P2G and CAES. And P2G has many benefits such as: conversion of energy vector from electricity to gas which is available for renewable thermal and transport energy; longest storage time; and minimal impact on the environment. From sustainable development strategy perspective, the evaluation results of P2G, PHES and CAES are 4.03, 2.46 and 2.16, respectively. Which means P2G was assessed as preferable.

Performance analysis of sequential Carnot cycles with finite heat sources and heat sinks and its application in organic Rankine cycles

The sequential Carnot cycle, where a number of single Carnot cycles are connected in parallel, has been researched for renewable thermal energy utilization because the characteristics of its low grade heat source, are different from those of a conventional one. In this paper, the thermodynamic analysis is conducted on the sequential Carnot cycle which uses not only finite heat sources but also finite heat sinks. Equations for efficiency and power from the whole sequential system are derived from the general theory of thermodynamics and heat transfer. Based on the equation from theory, the performance of the sequential system is calculated in various system conditions, including the ideal situation where the system has an infinite number of Carnot cycles and infinite heat exchanger inventory. In addition, the sequential concept is applied to organic Rankine cycles, which is one of the most used thermodynamic systems that generate work from low grade heat sources. From a simple simulation with properties of real working fluids, the performance of a sequential ORC (organic Rankine cycle) is investigated and its result is compared with that of theoretical sequential Carnot cycles.

Simulation study of transfer characteristics for spacer-filled membrane distillation desalination modules

Membrane distillation (MD) is an emerging and promising membrane separation process, which can directly utilize renewable thermal energy or low-grade waste heat, for applications in water or wastewater treatment and food industry. However, a major drawback of MD process is its low energy efficiency. Spacer is the most suggested and studied eddy promoter to enhance the heat and mass transfer, which further improves both the separation and the energy utilization performance, of MD processes. This paper presents the results of a 3D computational fluid dynamics (CFD) simulation of DCMD (direct contact membrane distillation) modules using channels with and without spacers for desalination application. The model employs permeable wall boundary condition to take into account the transmembrane heat and mass transfer and simulates the entire module length. The simulation reveals similar fluctuating distributions of temperature polarization coefficient, transmembrane heat and mass fluxes as well as the shear stress on the membrane surface along the entire module length. Correlations have been developed for friction factor and average Nusselt number. These correlations are useful for the analysis and design of DCMD modules. The extent of heat transfer enhancement by spacers depends on the geometry of spacers and the Reynolds number of fluid.

DESIGN AND CONSTRUCTION OF A SIMPLE THERMOELECTRIC GENERATOR HEAT EXCHANGER FOR POWER GENERATION FROM SALINITY GRADIENT SOLAR POND

Solar pond is one source of renewable thermal energy. The solar pond collects and stores thermal energy at the lower zone of the solar pond. The temperature at the lower zone can reach up to 90 °C. The solar pond is capable storing thermal energy for a long period. The stored thermal energy can be converted into electricity by using thermoelectric generators. These thermoelectric generators can be operated using the cold and hot zones from a solar pond. In this paper, the experimental investigation of power generation from the solar pond using thermoelectric generator and simple heat exchanger is discussed. A maximum of 7.02 W of electrical power output was obtained from a simple heat exchanger with 40 thermoelectric modules.

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その 5） 小型調湿外気処理ユニット一次試作機の評価

再生可能エネルギー熱を活用した調湿空調システムに関する研究 （その 5） 小型調湿外気処理ユニット一次試作機の評価

Techno-economics of integrating bioethanol production from spent sulfite liquor for reduction of greenhouse gas emissions from sulfite pulping mills.

BackgroundFlow sheet options for integrating ethanol production from spent sulfite liquor (SSL) into the acid-based sulfite pulping process at the Sappi Saiccor mill (Umkomaas, South Africa) were investigated, including options for generation of thermal and electrical energy from onsite bio-wastes, such as bark. Processes were simulated with Aspen Plus® for mass- and energy-balances, followed by an estimation of the economic viability and environmental impacts. Various concentration levels of the total dissolved solids in magnesium oxide-based SSL, which currently fuels a recovery boiler, prior to fermentation was considered, together with return of the fermentation residues (distillation bottoms) to the recovery boiler after ethanol separation. The generation of renewable thermal and electrical energy from onsite bio-wastes were also included in the energy balance of the combined pulping-ethanol process, in order to partially replace coal consumption. The bio-energy supplementations included the combustion of bark for heat and electricity generation and the bio-digestion of the calcium oxide SSL to produce methane as additional energy source.ResultsEthanol production from SSL at the highest substrate concentration was the most economically feasible when coal was used for process energy. However this solution did not provide any savings in greenhouse gas (GHG) emissions for the concentration-fermentation-distillation process. Maximizing the use of renewable energy sources to partially replace coal consumption yielded a satisfactory economic performance, with a minimum ethanol selling price of 0.83 US$/l , and a drastic reduction in the overall greenhouse gas emissions for the entire facility.ConclusionHigh substrate concentrations and conventional distillation should be used when considering integrating ethanol production at sulfite pulping mills. Bio-wastes generated onsite should be utilized at their maximum potential for energy generation in order to maximize the GHG emissions reduction.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0169-8) contains supplementary material, which is available to authorized users.

Multi-apartment residential microgrid with electrical and thermal storage devices: Experimental analysis and simulation of energy management strategies

The paper presents the operational results of a real life residential microgrid which includes six apartments, a 20kWp photovoltaic plant, a solar based thermal energy plant, a geothermal heat pump, a thermal energy storage, in the form of a 1300l water tank and two 5.8kWh batteries supplying, each, a couple of apartments. Thanks to the thermal energy storage, the solar based thermal energy plant is able to satisfy the 100% of the hot water summer demand. Therefore the thermal energy storage represents a fundamental element in the management of the residential demand of thermal energy. It collects renewable thermal energy during day-time to release it during night-time, effectively shaving the peak of the thermal energy demand. The two electric storages, on the other hand, provide the hosted electrical subsystems with the ability to effectively increase the self-consumption of the local energy production, thus lowering the amount of energy surplus to be sold back to the grid, and increasing the self-sufficiency of the microgrid. For instance, the storage has supported self-consumption up to the 58.1% of local energy production with regard to the first battery, and up to the 63.5% with regard to the second one. Also, 3165 and 3365 yearly hours of fully autonomous activity have been recorded thanks to the first, and the second battery respectively. On the other hand, the yearly average efficiency amounts to 63.7%, and 65.3% respectively, for the first and second battery. In the second part of the paper we propose a computational framework to evaluate the overall performance of the microgrid system, while accounting different operating conditions and energy management policies. From this perspective, the framework acts as a useful modeling and design tool, to assess the opportunity of employing alternative energy management system topologies and strategies. Eight different configurations, with growing complexity, have been derived from the original system on purpose. The simulations, carried out based on real data related to one-year time period, have provided results showing that, the higher the integration level of electrical and thermal storage is, the higher degree of self-sufficiency can be achieved by the microgrid, and, in turn, the more consistent the yearly energy saving become. Nevertheless, despite the energy cost reduction achievable with the availability of storage systems in the Leaf House, their high investment cost made them not really profitable at the current price conditions for devices and energy purchase.

Efficient Heat Generation for Resorts

This study compares the energy efficiency of two processes covering the thermal energy demand of a swimming pool: a combined heat and power (CHP) unit on the one hand, and a heat pump with internal combustion engine on the other hand. The thermal energy demand of the swimming pool was 1438 kWh per day (78% heating the pool and 22% providing hot water for showers), owing to temperate climate in the city of Toluca in central Mexico; a mean annual temperature of 13.5°C (10.5°C in January and 15.7°C in June) offers a large potential of renewable thermal energy stored in the atmosphere. Its utilization in heat pumps driven by thermal combustion engines can provide energy below 60°C; this temperature level provides hot water for showers while a lower temperature level of about 40°C heats up the pool water and swimming hall. Depending on outdoor temperature, which defines the load for the units, the efficiency in terms of total primary energy consumption is better for the CHP solution (100% and 80% load) and is better for the heat pump in the case of a 57% load. The energy losses for the CHP unit on-site are equivalent to half the losses caused by extraction and distribution of natural gas under current circumstances in Mexico. The results provide a decision tool.

Thermodynamic and Economic Assessment of Integrated Desalination and Power Generation

There have been a number of studies regarding the efficiency of state-of-the-art thermal (Multi-Effect Distillation, MED), power driven (sea water reverse osmosis, SWRO) and hybrid (MED/SWRO) desalination systems. The comparisons between desalination technologies can be made on a number of critical parameters such as (i) cost of produced water, (ii) energy efficiency, (iii) environmental impact, (iv) reliability and (v) footprint. Whilst the reported relative advantages with respect to parameters (iii) through (v) are conclusive, there remain conflicting recommendations with respect to parameters (i) and (ii), partly due to energy pricing assumptions. Furthermore, existing studies work on the implicit assumption that there is demand for surplus power from integrated power generation and desalination systems. The presented assessments compare the different thermal, power driven and hybrid desalination systems for output (water/power) achieved from identical energy inputs into thermal power and co-generation cycles for different ratios of desired water and power outputs. This eliminates energy and water pricing issues from the analysis and makes the findings applicable to a range of conventional (e.g. natural gas) and renewable (e.g solar) thermal energy sources. A number of simulations studies have been performed to identify the most energy efficient and cost effective desalination technologies for different water and power generation needs. The key parameters such as power and heat requirements and capital expenditures used in the thermodynamic and economic assessments are in line with ranges reported in the literature and existing plant data. Trade-offs between capital intensity and energy efficiency, which are particularly pronounced in thermal technologies, have also been studied. The paper makes clear recommendations as to the preferred desalination technology for a given seawater quality and water and power demand situation. The paper further explores the impact of technological advances in the form of lower capital costs and higher energy efficiency in the two broad classes of (i) power driven, and (ii) thermal desalination technology. All studies have been performed for seawater qualities observed in the Arabian Gulf.

STEP—A Solar Chemical Process to End Anthropogenic Global Warming. II: Experimental Results

Alternative chemical processes are needed to decrease the level of atmospheric greenhouse gases. Experimental support is presented of our STEP theory, which predicted a path to recycle and remove CO2 at high (∼50%) solar efficiency. In STEP (solar thermal electrochemical production) of energetic molecules, electrolysis occurs, heated by excess and renewable thermal energy at high-temperature potentials below that of the room-temperature energy stored in the products. STEP is demonstrated in the efficient formation of metals, fuels, chlorine, and carbon capture. As one example, CO2 is converted to solid carbon, or CO, by distinguishing sunlight that is energy sufficient to drive photovoltaic charge transfer and applying all excess energy to heat and decrease the free energy of the enodothermic CO2 splitting electrolysis. The energy efficiency, based on chemical flow out to solar flow in, is high, at least 34%, and may reach over 50% but will depend on the extent of the solar thermal energy captured for the molten electrolysis. As another example, in an alternative to carbothermal iron production, which is responsible for 25% of worldwide industrial CO2 emissions, iron is produced without CO2 in solar thermal heated molten carbonate. Fe(III) (14 m) (as in the iron ore, hematite) is soluble in molten Li2O and Li2CO3, providing a facile path for STEP iron electrolysis. Also, water is efficiently STEP electrolyzed in molten salts to hydrogen. Finally, of relevance to bleach production and desalinization, chlorine, sodium, and magnesium are formed from the chlorides. STEP provides a different pathway for solar energy conversion, at high efficiency, and is capable of proactively removing carbon dioxide and also generating a range of useful chemicals without greenhouse gas emission.

A theoretical study of a direct contact membrane distillation system coupled to a salt-gradient solar pond for terminal lakes reclamation

Terminal lakes are water bodies that are located in closed watersheds with the only output of water occurring through evaporation or infiltration. The majority of these lakes, which are commonly located in the desert and influenced by human activities, are increasing in salinity. Treatment options are limited, due to energy costs, and many of these lakes provide an excellent opportunity to test solar-powered desalination systems. This paper theoretically investigates utilization of direct contact membrane distillation (DCMD) coupled to a salt-gradient solar pond (SGSP) for sustainable freshwater production at terminal lakes. A model for heat and mass transport in the DCMD module and a thermal model for an SGSP were developed and coupled to evaluate the feasibility of freshwater production. The construction of an SGSP outside and inside of a terminal lake was studied. As results showed that freshwater flows are on the same order of magnitude as evaporation, these systems will only be successful if the SGSP is constructed inside the terminal lake so that there is little or no net increase in surface area. For the study site of this investigation, water production on the order of 2.7 × 10 −3 m 3 d −1 per m 2 of SGSP is possible. The major advantages of this system are that renewable thermal energy is used so that little electrical energy is required, the coupled system requires low maintenance, and the terminal lake provides a source of salts to create the stratification in the SGSP.

Heat pumping technologies, applications and markets

Strategies to cope with the economic, security and environmental implications of growing energy use must include the development of renewable energy resources, and the improvement of end-use energy efficiency. Heat pumps have a role in both. They effectively utilize renewable thermal energy resources, such as natural or waste heat, and they allow a high efficiency in the provision of a number of key energy-consuming services. These include space heating and cooling, water heating, and industrial process heating. This article first of all discusses heat pumping technology in general. It highlights the fundamental features of heat pumping compared to heating alternatives, and homes in on the two most commonly applied techniques: compression and absorption. Subsequently, the applicability of heat pumps in buildings and industries is addressed. The current use of heat pumps is illustrated in an appendix, with application examples from a cross-section of countries. The article closes with a heat pump market analysis, reviewing the heat pump market size and significance, and highlighting some of the major factors affecting market development.

Measurement of rock pile heat transfer coefficients

Several authors have established single-tank packed-bed storage as a promising alternative that can be coupled with renewable thermal energy sources. The use of such systems can ensure a cost reduction of approximately 33%, compared to two-tank systems, which represents the dominating solution for high-temperature storage. Herein, an overview of the modeling approaches for assessing the yield and efficiency of packed-bed energy storage systems is presented. Additionally, the validation approaches used as well as the conventional materials and structures employed in such systems are described. One of the critical issues that affect the simulation models’ performance in packed-bed energy storage systems is the treatment of the radiation exchange among particles. The impacts of the radiation phenomena on the overall performance and internal temperature distribution of the tank, which facilitate the identification of the operating conditions within the influence of radiation and are significant for analytical purposes are discussed herein. Through parametric analysis, it is demonstrated that the radiation heat transfer coefficient could be as high as 32% of the magnitude of the convection coefficient; thus, it should not be underestimated when analyzing operation temperatures above 750 °C.