Micro-combined cooling,heating and power systems hybrid electric-thermal load following operation

Micro-combined cooling, heating and power (mCCHP), typically designated as less than 30 kW electric, is a technology that generates electricity at or near the place where it is used. The waste heat from the electricity generation can be used for space cooling, space heating, or water heating. The operation of mCCHP systems, while obviously dependent upon the seasonal atmospheric conditions, which determine the building thermal and power demand, is ultimately controlled by the operation strategy. Two of the most common operation strategies are to run the prime mover in accordance to either electrical or thermal demand. In this study, a mCCHP system operating following a hybrid electric-thermal load (FHL) is proposed and investigated. This operation strategy is evaluated and compared with mCCHP systems operating following the electric load (FEL) and operating following the thermal load (FTL). This evaluation and comparison is based on site energy consumption (SEC), primary energy consumption (PEC), operational cost, and carbon dioxide emission reduction (CDE). Results show that mCCHP systems operated following the hybrid electric-thermal load have better performance than mCCHP-FEL and mCCHP-FTL. mCCHP-FHL showed higher reductions of PEC, operational cost, and carbon dioxide emissions than the ones obtained for the other two operation strategies for the evaluated case.     

Statistical analysis of residential building energy consumption in Tianjin

To analyze the effect of energy conservation policies on energy consumption of residential buildings, the characteristics of energy consumption and indoor thermal comfort were investigated in detail in Tianjin, China, based on official statistical yearbook and field survey data. A comprehensive survey of 305 households indicates that the mean electricity consumption per household is 3215 kWh/a, in which annual cooling electricity consumption is 344 kWh/a, and the mean natural gas consumption for cooking is 103.2 m³/a. Analysis of 3966 households data shows that space heating average intensity of residential buildings designed before 1996 is 133.7 kWh/(m²·a), that of buildings designed between 1996 and 2004 is 117.2 kWh/(m²·a), and that of buildings designed after 2004 is 105.0 kWh/(m²·a). Apparently, enhancing the performance of envelops is effective in reducing space heating intensity. Furthermore, the results of questionnaires show that 18% of the residents feel slightly warm and hot respectively, while 3% feel slightly cold in winter. Therefore, the electricity consumption in summer will rise for meeting indoor thermal comfort.     

Multi carrier energy systems and energy hubs: Comprehensive review,survey and recommendations

In this paper, the multi carrier energy (MCE) systems are reviewed from different point of views including mathematical models, integrated components and technologies, uncertainty management, planning objectives, environmental pollution, resilience, and robustness. The basic of MCE systems is formed by combination of cooling, heating and power (CCHP). The natural gas and electricity are the main inputs to MCE systems and the cooling, heating, and electricity are the common outputs. The regular energy converters in the MCE systems are combined heat and power (CHP), gas boiler, absorption-electrical chillers, power to gas (P2G) and fuel-cell. The generic energy storages are electrical, heating, cooling, hydrogen, carbon dioxide (CO₂) and hydro systems.     

Electricity and natural gas use for residential space heating: U.S. experience, 1976–1980

Energy consumption for residential space heating has been studied for households using electricity and natural gas, based on aggregate sales data for 1976–1980. The ratio of average end-use energy consumption with electricity to that with natural gas was found to be 0.44 ± 0.06, despite little use of electric heat pumps. Together with the results of other studies, this estimate suggests that electric space heating can be used in future construction without requiring more primary input energy (including generation losses) than the average input energy used for gas space heating in existing residences, assuming modest conservation measures. While these results do not establish the relative fuel consumption in future gas-heated and electrically-heated households, they do provide a rough ceiling on the amount of energy required if electricity is used.     

Characteristics of residential energy consumption in China: Findings from a household survey

A comprehensive survey of 1450 households in 26 Chinese provinces was undertaken in 2012 to identify the characteristics and potential driving forces of residential energy consumption in China. The survey covers six areas: household characteristics, dwelling characteristics, kitchen and home appliances, space heating and cooling, residential transportation, and electricity billing, metering, and pricing options. The results show that a typical Chinese household in 2012 consumed 1426 kilograms standard coal equivalent, which is approximately 44 percent of the 2009 level in the United States and 38 percent of the 2008 level in the EU-27. District heating, natural gas, and electricity are three major residential energy sources, while space heating, cooking, and water heating are three major end-use activities. Moreover, the results suggest a large urban–rural gap in terms of energy sources and purpose of usage. Commercial energy is used mainly for space heating in urban areas, while biomass dominates mainly for cooking purpose in rural areas. The survey results can help decision makers and scholars identify energy conservation opportunities, and evaluate the effectiveness of energy policies.     

A multiobjective programming approach to energy resource allocation problems

The optimal allocation of energy resources to various energy end uses is an important strategy for bridging the energy supply and demand gap in India. It has been recognized that the allocation should be guided by multiple criteria. A multiobjective programming model for such an allocation process is presented in the paper. The normative model has been applied for the households sector of Madras city. The model is solved using non pre-emptive goal programming. Variations in the original model have been made to build alternative scenarios. The results of the original model and the alternative scenarios indicate that the use of solar thermal energy, natural gas, LPG, fuelwood, kerosene and lignite should be promoted for cooking, and the use of grid electricity and diesel, should be promoted for meeting water pumping demands. They favour the use of electricity generated from diesel for lighting, and the use of solar photovoltaics for meeting the electricity demands of household appliances. The results also indicate that grid electricity and electricity generated from fuelwood should be promoted to meet the demands of all the four household end uses, and point to the need for more research into solar photovoltaics, which may become competitive for meeting household demands in the future.     

Assessing heating and cooling demands of closed greenhouse systems in a cold climate

Reducing greenhouse gas emissions by providing non‐fossil fuel energy sources is imminently necessary. The area of particular interest in this paper is the agricultural greenhouse industry. In these structures, significant heating demands are present, especially in cold climates, and are typically met by combusting fossil fuels. In an effort towards a sustainable energy supply, the potential of closed greenhouse systems in a cold climate is explored. In these systems, natural ventilation for cooling and dehumidification is replaced with active systems, and the thermal energy removed can be re‐used, reducing the overall heating demand. A transient greenhouse model is created using TRNSYS software and validated with natural gas usage data from a reference greenhouse. The annual heating and cooling demands, effect of varying cover materials and potential for heat recovery ventilation are explored for the most concentrated greenhouse areas in Canada. Copyright © 2017 John Wiley & Sons, Ltd.     

Meeting residential space heating demand with wind-generated electricity

Worldwide, many electricity suppliers are faced with the challenge of trying to integrate intermittent renewables, notably wind, into their energy mix to meet the needs of those services that require a continuous supply of electricity. Solutions to intermittency include the use of rapid-response backup generation and chemical or mechanical storage of electricity. Meanwhile, in many jurisdictions with lengthy heating seasons, finding secure and preferably environmentally benign supplies of energy for space heating is also becoming a significant challenge because of volatile energy markets.Most, if not all, electricity suppliers treat these twin challenges as separate issues: supply (integrating intermittent renewables) and demand (electric space heating). However, if space heating demand can be met from an intermittent supply of electricity, then both of these issues can be addressed simultaneously. One such approach is to use off-the-shelf electric thermal storage systems.This paper examines the potential of this approach by applying the output from a 5.15 MW wind farm to the residential heating demands of detached households in the Canadian province of Prince Edward Island. The paper shows that for the heating season considered, up to 500 households could have over 95 percent of their space heating demand met from the wind farm in question. The benefits as well as the limitations of the approach are discussed in detail.     

Research on improving energy efficiency and the annual distributing structure in electricity and gas consumption by extending use of GEHP

The gas engine-driven heat pump (GEHP), which has been considered as a preferable choice in the heating and air-conditioning scheme can make full use of the waste heat from the engine and achieve a higher primary energy ratio (PER) than other forms of heating/cooling systems. In this paper, the relationship between the capacity characteristic of the GEHP and the heating and cooling loads of buildings has been analyzed. Meanwhile the reasons of the imbalance of the urban electricity and natural gas consumptions between summer and winter have been studied. The running characteristic of a water-to-water GEHP has been investigated experimentally and the PER was measured. Based on the analysis and experimental results, it could be concluded that if both the gas-fired boilers and electric air conditioners are replaced by GEHPs in some percentage, we can narrow the gaps between the requirement and provision of electricity and natural gas and balance the seasonal consumption differences of electricity and natural gas between summer and winter simultaneously. In order to improve energy efficiency, environmental quality and energy consumption structure effectively, the governmental incentive policies for promoting use of GEHPs should be formulated in China and some other developing countries.     

District heating and cooling for business buildings in Madrid

Energy needs for heating and cooling in Spain are of paramount interest in the context of the European roadmap to a decarbonized environment; because of that, it is highly desirable that more examples of district heating and cooling networks are developed. The present work evaluates the implementation of one of them into the climatic environment of Madrid. It consists on a complex of business office buildings with a total useful surface of 50,000 m², linked with heating and cooling rings of 1 km of loop length. Basic energy needs of buildings lead to the following design values: 1.7 MW of electricity, 1.3 MW of heating and 2 MW of cooling. They will be supplied by the trigeneration plant here proposed, which relies on an internal combustion engine.The high demand of cooling for air conditioning makes the dimensioning of the engine critical because of the large differences between the heat demand for summer and the one for winter. If the total amount of the cooling demand is covered with an absorption chiller, the heat demand during the summer reaches about 5 MW. In consequence, a critical decision has to be taken relative to the way the cooling demand is attended: with an absorption chiller (single or double effect) or with a conventional chiller powered by electricity. Applying the criteria developed in the present work, which are focused on maximum primary energy reduction, the fraction of the cooling demand to be met with each technology is determined as a function of the engine nominal power, on the grounds of the instantaneous demand.The high cooling demand during the summer season suggests the inclusion of a thermal solar collector field, to be used for complementing the waste heat rejection from the engine to drive the absorption chiller. During the winter, the heat provided by the solar field could be applied in attending a fraction of the heating demand. Thus a hybrid Trigeneration Plant is introduced. This way, over sizing of the engine can be avoided, as the electric demand is small.The analysis is based on the solution of energy and mass balance equations for a trigeneration plant. Monthly demands and environmental conditions (ambient temperature and solar irradiance) are introduced as input data into the model. Monthly and annual primary energy consumption and CO₂ emission reductions are obtained as outputs. Economical data, such as fuel and operating costs, electricity prices, tariffs and subsidies are considered in order to optimize the size of the plant in terms of its payback period.     

A cost-effective approach for optimal energy management of a hybrid CCHP microgrid with different hydrogen production considering load growth analysis

An optimum design and energy management of various distributed energy resources is investigated in a hybrid microgrid system with the examination of electrical, heating, and cooling demand. This paper suggested an optimal approach to design and operate a microgrid incorporating with battery energy storage, thermal energy storage, photovoltaic arrays, fuel cell, and boiler with minimization of the total operational cost of the hybrid microgrid. Two different hydrogen production methods are considered to assure the advantage of the developed proposed methodology. Furthermore, besides natural gas, residential and municipal wastes are collected and are utilized to produce electricity in fuel cell units. Load growth for different type of loads is also considered. The new number of households are added to the proposed system in different years and the proposed program is determined the optimum size of each employed resources to add each year for satisfying the total demand. To find out the optimum energy management and the optimum capacity of each employed distributed energy resources, a meta-heuristic Particle Swarm Optimization Algorithm is utilized. It is concluded from the results that by utilizing residential waste, the amount of natural gas consumption by fuel cells is reduced about 6.2%, and by utilizing residential plus municipal waste, the reduction is about 26.7%. It is also observed that the amount of CO₂ emission is reduced significantly (46.8%) in the case of utilization of produced heat by fuel cells. Finally, the results confirmed the efficacy of the suggested optimal energy management of the hybrid microgrid.     

Operational optimisation of a complex trigeneration system connected to a district heating and cooling network

The combined production of electricity, heat and cold by polygeneration systems ensures maximum utilization of resources by reducing emissions and energy losses during distribution. Polygeneration systems are highly integrated systems characterized by the simultaneously production of different services (electricity, heating, cooling) by means of several technologies using fossil and renewable fuels that operates together to obtain a higher efficiency than that of an equivalent conventional system. The high number of distribution technologies available to produce electricity, heating and cooling and the different levels of integration make it difficult to select of the optimal configuration. Moreover, the high variability in the energy demand renders difficult the selection of the optimal operational strategy. Optimization methodologies are usually applied for the selection of the optimal configuration and operation of energy supply systems. This paper presents a scenario analysis using optimization models to perform an economic, energetic and environmental assessment of a new polygeneration system in Cerdanyola del Vallès (Spain) in the framework of the Polycity project of the European Concerto Program. This polygeneration system comprise high-efficiency natural gas cogeneration engines with thermal cooling facilities and it will provide electricity, heating and cooling for a new area in growth known as Alba park including a Synchrotron Light Facility and a Science and Technological park through a district heating and cooling network of four tubes. The results of the scenario analysis show that the polygeneration plant is an efficient way to reduce the primary energy consumption and CO₂ emissions (up to 24%).     

基于能量枢纽的综合能源系统优化规划

  [目的]  提出了基于能量枢纽的综合能源系统优化规划模型用于解决综合能源系统长期规划问题。  [方法]  能量枢纽(Energy Hub)是分析综合能源系统的重要模型,代表各种不同能源形式之间的耦合关系,例如电力,天然气,供热系统等。  [结果]  此综合能源系统优化规划模型在考虑系统可靠性,能源效率,排放指标等多种决策因素的情况下解决了不同能源形式之间的最优规划问题。  [结论]  综合能源系统算例分析用于验证该模型用于优化规划综合能源系统的有效性,并表明基于能量枢纽的综合能源系统针对系统的长期规划具有更大的灵活性,是研究综合能源系统规划的重要方向。     

Domestic LPG interventions in South Africa: Challenges and lessons

A majority of grid-connected households in South Africa use electricity for cooking and heating tasks. This thermal intensive use of electricity has a high load factor and is a contributory factor of electricity demand outstripping supply at peak demand periods. The government has promoted liquefied petroleum gas (LPG) as an alternative thermal energy source for household cooking and heating. This study evaluates the long-term successes, challenges and social impacts of an LPG intervention project that was piloted in Atteridgeville Township, a typical low-income suburb. The data was gathered through one-on-one household interviews with a sample of the beneficiaries. The results indicate that seven years after the LPG intervention, about 70% of the beneficiaries continue to use LPG and report that the intervention has improved their welfare. Fast cooking is cited as the key tangible benefit of LPG technology in households, followed by saving on electricity bills. The project would have achieved more success through better community engagement, including strict beneficiary selection criteria; a long-term LPG distribution and maintenance plan; and inclusion of recurring monthly LPG subsidies for indigent households. The study discusses the subset of factors necessary for successful rollouts of similar energy projects.     

Integrated design and evaluation of biomass energy system taking into consideration demand side characteristics

In this paper, a linear programming model has been developed for the design and evaluation of biomass energy system, while taking into consideration demand side characteristics. The objective function to be minimized is the total annual cost of the energy system for a given customer equipped with a biomass combined cooling, heating and power (CCHP) plant, as well as a backup boiler fueled by city gas. The results obtained from the implementation of the model demonstrate the optimal system capacities that customers could employ given their electrical and thermal demands. As an illustrative example, an investigation addresses the optimal biomass CCHP system for a residential area located in Kitakyushu Science and Research Park, Japan. In addition, sensitivity analyses have been elaborated in order to show how the optimal solutions would vary due to changes of some key parameters including electricity and city gas tariffs, biogas price, electricity buy-back price, as well as carbon tax rate.     

污水源热泵供热空调的技术经济分析

污水源热泵是一种以污水(包括处理的和未处理的污水)作为其冷热源的空调系统。作为一种新兴事物，技术的可靠性和经济的竞争力是其推广的关键。本文对污水源热泵的原理和形式作了详尽的介绍，并将污水源热泵和传统热泵空调进行了技术上的比较。同时使用了能源工程项目中最常用的两种方法，将污水源热泵同燃煤 空调、燃油 空调、燃气 空调及电锅炉 空调这几种传统的供暖空调形式分别进行了供暖经济性比较、制冷经济性比较和综合经济性比较分析。     

Performance investigation of a combined biomass gasifier-SOFC plant for compressed hydrogen production

As an alternative, clean and sustainable solution, a biomass-based integrated power plant is designed and studied both thermodynamically and parametrically. Due to the environmental, economic and performance related advantages, the design of multigeneration energy plants is now increasing and becoming widespread technology. Biomass, which is one of the renewable power sources, is selected for the plant to be more sustainable and environmentally friendly. The proposed system using biomass as an energy source consists of several sub-plants integrated to utilize the waste thermal energy and to generate useful products which are electricity, hydrogen, fresh and hot water, heating, and cooling. In this paper, comprehensive work is carried out for plant modeling and simulation. The thermodynamic assessment results reveal that both energetic and exergetic effectiveness of the whole plant are 56.17% and 52.83%, which are affected positively by varying the reference state conditions, combustor temperature, biomass gasifier temperature, SOFC temperature and pressure, and biomass mass flow rate. In addition, the lowest energy and exergy efficiencies occur in the ORC combined ejector refrigeration cycle with 21.87% and 18.26%, respectively.     

A highly-advanced solar house with solar thermal and sky radiation cooling

A unique energy-independent house (‘HARBEMAN house’; HARmony BEtween Man And Nature) incorporating solar thermal, underground coolers, sky radiation cooling, photovoltaic electricity generation and rain-water collection was built in Sendai (latitude; 38° 17′00″ north and longitude; 140° 50′14″ east), Japan during July, 1996. The average solar energy received on a horizontal surface there in January is 7900 kJ/m²/day. This paper reports the experimental results since September 1996 to date. The annual variations of water temperature in the underground main tank, heating /cooling/domestic hot water demands, collected and emitted heats by solar collector and sky radiator, were measured. The paper also clarifies the method of computer simulation results for the HARBEMAN house and its results compared with the annual experimental data. The proposed HARBEMAN house, which meets almost all its energy demands, including space heating and cooling, domestic hot water, electricity generated by photovoltaic cell and rainwater for standard Japanese homes. The proposed system has two operational modes: (i) a long-term thermal energy storage mode extending from September to March and (ii) a long-term cool storage mode extending from April to August. The system is intended to utilize as little energy as possible to collect and emit the heat. This paper also clarifies the primary energy consumption, the external costs (externalities) and the means for the reduction of carbon-dioxide (CO₂) emissions. The primary-energy consumption and carbon-dioxide emissions of the proposed house are only one-tenth of those of the conventional standard house. Moreover, the thermal performance of this house will be compared with the results of the IEA solar low-energy house TASK 13. Finally, this paper validates the external costs of this house, which have been intensively discussed in recent years in European countries. The present energy-sufficient house will be attempting in 21st century to reduce carbon dioxide emissions, which will be one of the key factors for mitigating global warming.     

Thermoelectric Module Integrated Fuel Cell in a Liquid Desiccant-Assisted Air-Conditioning System

Abstract

This study aims to estimate the energy performance of a liquid desiccant and evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) combined with a thermoelectric module integrated proton exchange membrane fuel cell (TEM-PEMFC). During the cooling season, recovered heat from the PEMFC was reclaimed to heat a weak desiccant solution and the generated electricity was used to operate the LD-IDECOAS. The TEM was operated as an auxiliary heater for heating the weak desiccant solution. In the off-cooling season, the PEMFC was operated to generate electricity and the recovered heat was also used to generate electricity using TEMs. In this study, a detailed energy simulation model was developed to estimate the energy savings potentials of the proposed system compared with the conventional LD-IDECOAS that uses a gas boiler and grid power without TEM-PEMFC. The result shows that TEMs can operate with a mean coefficient of performance of 2.0 when utilized for auxiliary heater in the cooling season. In addition, TEMs generate additional electricity with a mean power generation efficiency of 0.9%. Finally, the proposed system can save the 10.6% of annual primary energy compared with the conventional LD-IDECOAS. Therefore, the advantages of using TEM-PEMFC as heating and energy harvesting components were verified.     

Integration of trigeneration system and thermal storage under demand uncertainties

In a commercial building, a large portion of electricity is usually consumed in air conditioning to control indoor-air temperature and humidity. Energy savings or efficient production in air conditioning system is, therefore, crucial. In recent years, trigeneration systems, which provide electricity, heating and cooling, and thermal storage systems, which temporarily store cooling energy to smooth its production pattern, are attracting more attentions. These systems with different operating principles are usually designed based on nominal or peak loadings. With altering seasonal or day/night cooling demands, the performance and overall economics of the design may deprive.