Hot Water Generation Research Articles

Energetic and exergetic assessments of a novel solar power tower based multigeneration system with hydrogen production and liquefaction

Abstract In this article, a thermodynamic investigation of solar power tower assisted multigeneration system with hydrogen production and liquefaction is presented for more environmentally-benign multigenerational outputs. The proposed multigeneration system is consisted of mainly eight sub-systems, such as a solar power tower, a high temperature solid oxide steam electrolyzer, a steam Rankine cycle with two turbines, a hydrogen generation and liquefaction cycle, a quadruple effect absorption cooling process, a drying process, a membrane distillation unit and a domestic hot water tank to supply hydrogen, electrical power, heating, cooling, dry products, fresh and hot water generation for a community. The energetic and exergetic efficiencies for the performance of the present multigeneration system are found as 65.17% and 62.35%, respectively. Also, numerous operating conditions and parameters of the systems and their effects on the respective energy and exergy efficiencies are investigated, evaluated and discussed in this study. A parametric study is carried out to analyze the impact of various system design indicators on the sub-systems, exergy destruction rates and exergetic efficiencies and COPs. In addition, the impacts of varying the ambient temperature and solar radiation intensity on the irreversibility and exergetic performance for the present multigeneration system and its components are investigated and evaluated comparatively. According to the modeling results, the solar irradiation intensity is found to be the most influential parameter among other conditions and factors on system performance.

Performance evaluation of nanofluid on parabolic trough solar collector

In the present work, the performance of aluminum oxide and deionized water nanofluid used as heat transfer fluid on a parabolic trough solar collector system with hot water generation tank is evaluated. The parabolic trough solar collector is developed using easily and locally accessible materials. Five different concentrations of aluminum oxide and deionized water based nanofluid from 0.5-2.5% is prepared by the magnetic stirrer initially and then the mixture is subjected to ultrasonication process to break aggregates with the absence of surfactant. The prepared nanofluids are allowed to flow through the absorber which is located at a focal point of the solar collector. The performance of nanofluid is compared with pure deionized water. The test is conducted from 8.00 a. m. to 16.00 p. m. daily in the whole length of the test span. The heat transfer fluid is allowed to flow at a mass-flow rate of 0.020 kg/s and 0.09246 m/s velocities. The maximum solar radiation is 821 W/m2, and maximum efficiency is observed at noon time 60.41% for deionized water and 60.49% for 2.5% volumetric fraction of alumina nanofluid. The efficiency enhancement was 3.90% than deionized water. The influence of the critical parameter on the performance is also examined.

Energy and exergy analyses of an integrated system using waste material gasification for hydrogen production and liquefaction

In this study, a new combined gasification process using various waste materials for multigenerational operation, containing the hydrogen, power, heating-cooling and hot water generation. In the present multigenerational plant, a waste material gasifier component is combined with the Brayton cycle, Stirling engine cycle, single effect absorption cooling cycle and proton exchange membrane electrolyzer for multiple outputs generation. To analyze and evaluate this integrated system, a comprehensive thermodynamic analysis and assessment for the multigeneration plant components is introduced, the second-law efficiency, associated with the overall system and its sub-systems are described, and the impacts of some arrangements and working statuses on the plant efficiency are investigated. The study results show that, this integrated plant has an overall energetic efficiency of 61.57% and an overall exergetic efficiency of 58.15%, when the produced net power is 94 MW, and also hydrogen generation rate is 0.077 kg/s, respectively.

Green Smart Technology for Water (GST4Water): Life Cycle Analysis of Urban Water Consumption

The increasing scarcity of water is encouraging strategies in water saving and urban water management systems devoted to reducing natural resource consumption and environmental impact. At household and urban scales, there is an increasing interest in onsite greywater and non-potable water reuse systems in order to improve water availability. In this framework, the project GST4Water funded by the European Union (EU) under the POR-FESR 2014–2020 Program of Emilia-Romagna Region, has been developed with the aim to implement water consumption monitoring systems, to define solutions for greywater reuse, and to develop tools for environmental sustainability evaluation applied to water systems. The present study focuses on this last goal, performing a life cycle assessment of the solutions optimized at a district level. In particular, six different scenarios are compared, starting from two models considering traditional water supply together with or without energy consumption related to hot water generation, and five additional models related with different assumptions in terms of greywater recovery systems, and energy and hot water production, at varying percentages of renewable and photovoltaic energy supply. Finally, an evaluation of the return time of environmental investment is carried out, based on the results obtained through the scenario analysis.

Evaluation and analysis of water-based photovoltaic/thermal (PV/T) system

Water-based PV/T collectors are useful for simultaneous hot water and electricity generation. This paper presents the design of a grid-connected water-based PV/T and performance evaluation from outdoor experiments in weather conditions of Oman. The paper focuses on the electrical performance of the system under three days of testing and draws conclusions onto the effect of ambient conditions and solar irradiance on conventional PV panels and PV/T collectors. The proposed PV/T shows superior electrical performance during the examination period, with consistent rise in electrical efficiency over conventional PV. The peak electrical power and voltage achieved by the system are around 67 Wp and 18.9V, respectively. The average power of the PV/T panel is 6% higher than average power of conventional PV panel.

Heat Exchangers Technology and Applications in Heat Exchanger Engineering

Over the years, all parts of a commercial refrigerator, such as the compressor, heat exchangers, refrigerant, and packaging, have been improved considerably due to the extensive research and development efforts carried out by academia and industry. However, the achieved and anticipated improvement in conventional refrigeration technology are incremental since this technology is already nearing its fundamentals limit of energy efficiency is described is ‘magnetic refrigeration’ which is an evolving cooling technology. The word ‘green’ designates more than a colour. It is a way of life, one that is becoming more and more common throughout the world. An interesting topic on ‘sustainable technologies for a greener world’ details about what each technology is and how it achieves green goals. Recently, conventional chillers using absorption technology consume energy for hot water generator but absorption chillers carry no energy saving. With the aim of providing a single point solution for this dual purpose application, a product is launched but can provide simultaneous chilling and heating using its vapour absorption technology with 40% saving in heating energy. Using energy efficiency and managing customer energy use has become an integral and valuable exercise. The reason for this is green technology helps to sustain life on earth. This not only applies to humans but to plants, animals and the rest of the ecosystem. Energy prices and consumption will always be on an upward trajectory. In fact, energy costs have steadily risen over last decade and are expected to carry on doing so as consumption grows. Refrigerants such as hydrochloroflurocarbons (HCFCs) are present in the ground source heat pump (GSHP) systems and can pose a threat to the environment through being toxic, flammable or having a high global warming potential. However, new types and blends of refrigerant with minimal negative impacts are being developed. A correctly fitted system will also greatly reduce the potential for leakage, which is why using a professional installer is highly recommended. Significant CO2 savings can be gained by displacing fossil fuels. Even compared to the most efficient gas or oil condensing boilers, a well-designed heat pump with COP of 3-4 will reduce emissions by 30-35%. Further carbon savings can be made if the electricity used to power the pump comes from a renewable energy source such as photovoltaic or a renewable electricity tariff. Also, measures can be taken to reduce the impact of pollution from using grid electricity generated through fossil fuel. For example, one can purchase dual tariff green electricity from a number of suppliers. However, even if ordinary grid electricity is used to run the compressor, the system will still produce less CO2 emissions than even the most efficient condensing gas or oil boiler with the same output. The term “vapour compression refrigeration” is somewhat of a misnomer, it would be more accurately described as ‘vapour suction refrigeration’. Vapour compression is used to reclaim the refrigerant and is more aptly applied to heat pumps. Vapour compression refrigeration exploits the fact that the boiling temperature of a liquid is intimately tied to its pressure. Generally, when the pressure on a liquid is raised its boiling (and condensing) temperature rises, and vice-versa. This is known as the saturation pressure-temperature relationship.

Design methodology for combined production and distribution for domestic hot water and space heating

As local heat demand is reducing due to an increased insulation rate, investing in sustainable heat production becomes less interesting. Nevertheless a substantial demand of heat remains in which the thermal energy needed for the generation of domestic hot water grows relatively in importance. In the last two years standards to size production and distribution systems were revised and methods based on tap patterns were elaborated. Nevertheless, some aspects were not covered yet, e.g. how to deal with decentralized storage and how to use these results and new insights in combined heating systems, taking into account that modifications in standards for both space heating and domestic hot water installations are reducing the oversizing. In this paper, first some critical points of attention due to this evolution are illustrated with a case example. Next it is shown how different rules of thumb often developed by different manufacturers deal with these aspects, but lacking however compatibility with existing standards and/or new insights. Finally, a methodology is proposed and illustrated how to size distribution and production systems for combined heating systems taking into account central and decentralized storage and different kind of end users. The method can be used to size heating systems in collective housing or in district heating networks.

Optical Design and Performance Analysis of Linear Focusing Solar Thermal Collectors

Linear Fresnel solar collector is a focusing concentrator suitable for direct steam generation, industrial process heat, and solar space cooling system and hot water generation for different uses. The optical design and performance simulations, experimental and numerical studies on linear Fresnel solar collector were reviewed. Studies on the optical designs and ray-tracing simulations results indicated non-uniform solar flux distributions on the receiver absorber surface. The optical quality of LFC is low due to its higher incidence angle and the cosine factor. Studies on optimizing the optical errors that affects the optical performance of the LFC are lacking in the literature. Ray tracing results at 0o incidence angle indicated three different optical losses-geometric configuration, material properties and focus errors losses. Studies on the lateral drift and uncertainty of the direction of the reflected rays, which adversely affect the concentration factor of the LFC are lacking in the literature. The optical performance of a LFC system can be improved through an optimized optical design - mirrors separation, shapes, width and their orientation.

Annual performance of photovoltaic-thermal system under actual operating condition of Dire Dawa in Ethiopia

As cooling of Photovoltaic panel by water improves the electrical conversion efficiency and produces warm water as a by-product, photovoltaic thermal system is being used for cogeneration of electrical energy and hot water. In this study, the annual performance of a glazed photovoltaic thermal system (combination of PV module and solar flat plate collector) with storage tank was investigated by the dynamic computational model. The model was developed using MATLAB under actual hot water demand condition for co-generation electrical energy at Dire Dawa in Ethiopia. The computational model determines the electrical energy production and temperature of water at different points and other components of the PV-T system within a given time interval. In addition summaries of monthly and annual incident solar irradiance, electrical energy generation, thermal energy transported to storage and thermal energy supplied as hot water to end users are computed, considering the hourly hot water consumption pattern and storage size effect. The simulation, which is conducted for 20 m2 PV-T system, consists of 12 panels with each 1.64 m2 module areas resulted in generation 803 kWh/year thermal energy and 310 kWh/year electrical energy. The annual average electrical efficiency, thermal efficiency, hot water end use overall efficiency and co-generation (PV-T) efficiency of the system were 15.4%, 50.4%, 38%, and 65.8% respectively. The fraction of solar energy in meeting the heating load for hot water generation was 44.5% for 60℃ hot water supply temperature. Hence, that PV-T system can only be used for water preheating meeting at maximum half of the heating load in tropical area.

Experimental Investigation of hot Water Generation from Small CaO/Ca(OH)2 Thermochemical Energy Storage System

Thermochemical energy storage (TCS) is a very promising method for energy applications, storage, transport and thermal generation because of its high energy density and negligible heat loss. Several storage materials are being explored, in which CaO/Ca(OH)2 is among the most attractive systems for further investigations. In this work, a small Ca based TCS system was developed, built and tested for hot water generation. Hydration and dehydration reactions involving CaO and Ca(OH)2 powders were performed. Performance in terms of temperature rise in heat transfer fluid and its efficiency during successive discharging/charging cycles was evaluated and discussed.

Effect of Additional Air Supply for Combustion of Straight Vegetable Oil Blends on Performance of Mini Hot Water Generator

This paper presents the results of an experimental investigation on the efficient combustion of blends of Straight Vegetable Oil (SVO) with diesel, fired in a non-commercial hot water generator. The high viscosity and poor atomization characteristics of straight vegetable oil lower the combustion and thermal efficiency of the system. An additional air supply system has been used to provide sufficient amount of air into the furnace to improve the mixing of fuel droplets and oxygen in the air. Thermal efficiency and emission characteristics of 25% and 50% blends of straight sunflower oil and rice bran oil with diesel have been studied with and without additional air supply. Thermal efficiency of the hot water generator has been found to be increased when the quantity of additional air supply is increased. Moreover, the emissions of CO and HC have been reduced by the additional air supply.DOI: http://dx.doi.org/10.5755/j01.mech.24.2.19783

Experimental investigation on the performance of transcritical CO2 ejector–expansion heat pump water heater system

The effects of hot-water outlet temperature, compressor discharge pressure, compressor rotation speed, and expansion valve opening on the ejector and overall system performance were investigated for tap water outlet temperatures ranging from 50 to 90 °C. The coefficient of performance (COP) of the ejector–expansion heat pump system reaches 4.6 when the tap water outlet temperature is 70 °C, which is 10.3% higher than the corresponding basic cycle. Compared to the basic system, adding an ejector is more effective for the generation of high-temperature hot water. The COP of the ejector–expansion heat pump system increases; however, the COP improvement ratio ΔCOP decreases with the increase in the discharge pressure because of lower pressure lift ratio and ejector efficiency. The COP and ΔCOP increase when the compressor rotation speed decreases under our test conditions; simultaneously, the heat capacity decreases.

Boosting the share of onsite PV-electricity utilization by optimized scheduling of a heat pump using buildings thermal inertia

Coupling electricity and heat sector is one of the most necessary actions for the successful energy transition. Efficient electrification for space heating and domestic hot water generation is needed for buildings, which are not connected to any district heating network, as distributed heating demand momentarily is largely met by fossil fuels. Hence, hybrid energy systems will play a pivotal role for the energy transition in buildings. Heat pumps running on PV-electricity is one of the most widely discussed combination for this purpose. In this paper, a heuristic optimization method for the optimal operation of a heat pump driven by the objective for maximum onsite PV-electricity utilization is presented. In this context, the thermal flexibility of the building and a thermal energy storage (TES) for generation of domestic hot water (DHW) are activated in order to shift the operation of the heat pump to times of PV-generation. Yearly simulations for a system consisting of heat pump, PV modules, building with floor heating installation and TES for DHW generation are carried out. Variation parameters for the simulation include room temperature amplitude (0.5, 1, 1.5 and 2 K) based on mean room temperature (21 °C), PV-capacity (4, 6, 8 and 10 kW) and type of heat pump (ground source and air source type). The yearly energy balances show that buildings offer significant thermal storage capacity avoiding an additional, large TES for space heating fulfillment and improving the share of onsite PV-electricity utilization. With introduction of a battery, which has been analyzed as well for different sizes (1.9, 4.8, 7.7 and 10.6 kWh), the share of onsite PV-electricity utilization can even be improved. However, thermal flexibility supplemented by the varying room temperature amplitude for a bigger battery does not improve the share of onsite PV-electricity utilization. Nevertheless, even with a battery not more than 50% of the electrical load including operation of the heat pump can be covered by PV-electricity for the specific system under investigation. This is noteworthy one the one hand, since it indicates that a hybrid heating system consisting of heat pump and PV cannot solely cover the heat demand of residential buildings. One the other hand, this emphasizes the necessity to include further renewable sources like wind power, in order to draw the complete picture. This, however, is beyond the scope of this paper, which mainly focuses on introduction and verification of the novel control method with regard to a practical building.

Modeling, Simulation, and Validation with Measurements of a Heat Recovery Hot Gas Cooling Line for Electric Arc Furnaces

Waste heat recovery has a high potential for increasing the efficiency and sustainability of electric arc furnaces. In the present work, a dynamic model of a water cooled hot gas line is presented and validated with measurements of a newly installed electric arc furnace (EAF) with a waste heat recovery system. Due to necessary reconstruction work of the EAF, the cooling pass is upgraded to a heat recovery hot gas line. With hot water from the hot gas line saturated steam can be produced and fed into the existing steam net. The heart of the system is the water cooled hot gas line which is responsible for sufficient hot gas cooling on the one hand and adequate hot water generation for the steam generators on the other hand. The water cooled hot gas line is modeled in the commercial simulation software APROS and validated with measurements of the performance test during commissioning of the heat recovery plant. The simulation results are showing an excellent agreement to the measurements. The results embody that the model is both very reliable to estimate the transient behavior of the hot gas line and able to predict the operational process conditions.

Sustainable Technologies for Greener Environment

Over the years, all parts of a commercial refrigerator, such as the compressor, heat exchangers, refrigerant, and packaging, have been improved considerably due to the extensive research and development efforts carried out by academia and industry. However, the achieved and anticipated improvement in conventional refrigeration technology are incremental since this technology is already nearing its fundamentals limit of energy efficiency is described is ‘magnetic refrigeration’ which is an evolving cooling technology. The word ‘green’ designates more than a colour. It is a way of life, one that is becoming more and more common throughout the world. An interesting topic on ‘sustainable technologies for a greener world’ details about what each technology is and how it achieves green goals. Recently, conventional chillers using absorption technology consume energy for hot water generator but absorption chillers carry no energy saving. With the aim of providing a single point solution for this dual purpose application, a product is launched but can provide simultaneous chilling and heating using its vapour absorption technology with 40% saving in heating energy. Using energy efficiency and managing customer energy use has become an integral and valuable exercise. The reason for this is green technology helps to sustain life on earth. This not only applies to humans but to plants, animals and the rest of the ecosystem. Energy prices and consumption will always be on an upward trajectory. In fact, energy costs have steadily risen over last decade and are expected to carry on doing so as consumption grows.

Waste heat availability in the raw meal department of a cement plant

The main aim of this study was to determine the available heat in the cement kiln exhaust gas subject to different process conditions. A Norwegian cement plant producing about 1.3 million tons of cement per year was used as a case study. A mass and energy balance was made for the raw meal department, and process data available from the plant process database as well as manually measured gas flow rates were used to calculate the available heat. The available heat can be utilized by a combination of low pressure (LP) steam generation and hot water generation. It was found that waste heat is 1.5–4.2MW for LP steam generation and 2.2–5.8MW for hot water generation. The variation in available heat is due to different raw meal types being produced, requiring different gas inlet temperatures to raw meal mill. In cases when no raw meal is produced (in maintenance shutdown periods), all the gas will bypass the mill, and approximately 20MW of LP steam and 6MW of hot water can be generated. The heat loss from the system was estimated based on measurements, and the fan power inputs were calculated. Both were found to be negligible compared to the available heat. Furthermore, the total false air coming into the system was estimated as 40–50% of the total gas flow rate going out from the raw meal department.

スマートビル構築のための要素技術検証とその最適化に関する研究 （第2報）CGS併用システムの排熱投入型ガス吸収冷温水機のガス消費量に関する研究

スマートビル構築のための要素技術検証とその最適化に関する研究 （第2報）CGS併用システムの排熱投入型ガス吸収冷温水機のガス消費量に関する研究

スマートビル構築のための要素技術検証とその最適化に関する研究 （第6報）CGS併用システムの排熱投入型ガス吸収冷温水機のガス消費量に関する研究2

スマートビル構築のための要素技術検証とその最適化に関する研究 （第6報）CGS併用システムの排熱投入型ガス吸収冷温水機のガス消費量に関する研究2

Enhanced oil recovery and natural bitumen production through the use of sinusoidal wells and solar thermal method

Thermal enhanced oil recovery is known to be the most effective way of heavy oil production. This article discusses the application of sinusoidal wells to improve the efficiency of thermal enhanced oil recovery methods. As a result of numerical simulation of steam-assisted gravity drainage (SAGD) process, it has been shown that the application of sinusoidal wells allowed 8990 m3 of the incremental oil production during 10 years simulation period. However, the high cost of hot water and steam generation, as well as significant environmental impact, limit the application of thermal oil recovery methods. The article presents the concept of year-round generation of desalinated hot water and steam from sea and reservoir brine at low cost by the newly developed solar collector. The collector can be placed in the vicinity of injection wells to provide constant hot water, steam, and electrical power supply.

Research trend of cascade heat pumps

Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heating and hot water purposes. Single stage heat pumps have not been able to meet these temperature demands and have been characterized by low capacities and coefficient of performance (COP). Cascade heat pump has been developed to overcome the weaknesses of single stage heat pumps. This study reviews recent works done by researchers on cascade heat pumps for refrigeration, heating and hot water generation. Selection of suitable refrigerants to meet the pressure and temperature demands of each stage of the cascade heat pump has been discussed. Optimization of design parameters such as intermediate temperature (low stage condensing and high stage evaporating temperatures), and temperature difference in the cascade heat exchanger for optimum performance of the cascade heat pump has been reviewed. It was found that optimising each design parameter of the cascade heat pump is necessary for maximum system performance and this may improve the exergetic efficiency, especially of cascade refrigeration systems, by about 30.88%. Cascade heat pumps have wider range of application especially for artificial snow production, in the supermarkets, for natural gas liquefaction, in drying clothes and food and as heat recovery system. The performance of cascade heat pumps can be improved by 19% when coupled with other renewable energy sources for various real time applications. Also, there is the need for much research on refrigerant charge amount of cascade heat pumps, refrigerant-refrigerant heat exchangers to be used as cascade heat exchanger, cascade heat pumps for simultaneous cooling, heating and hot water generation and on the use of variable speed compressors and their control strategies in matching system capacity especially at part load conditions.