Sizing of residential μCHP systems

Combined heat and power (CHP) is a well-known technique for producing heat and power simultaneously onsite. However, the micro level of this technology has just been recently introduced around the world, and expected to widely spread. Therefore, identifying the optimal size of such systems would give them the potential for being more beneficial.In this paper, a generic deterministic linear programming model, which aims to minimize expected annual cost of the system, has been developed. This model is capable of optimally determining the optimal size (electrical rating) of a micro CHP (μCHP) unit and the optimal size (thermal rating) of a back-up heater for any given residential demand regardless of the type of μCHP technology.An investigation has been conducted to identify economically the optimal μCHP investment for three typical residential dwellings in England. The four candidate μCHP technologies that have been considered in this paper are: internal combustion engine (ICE), Stirling engine (SE), solid oxide fuel cell (SOFC), and proton exchange membrane fuel cell (PEMFC). Sensitivity analyses have been conducted to understand the influence of some important key parameters on decision making regarding the deployment of residential μCHP systems.     

MIP approach for designing heating systems in residential buildings and neighbourhoods

In this work, a mixed integer linear programming (MIP) approach for the optimal design of energy systems in residential buildings is presented. The optimization model considers the economic criteria of the guideline VDI 2067. The objective of the MIP is to minimize the annual costs which comprise the investment as well as demand- and operation-related costs. Conventional boilers, electrical heaters, combined heat and power (CHP) units, heat pumps (HPs), photovoltaic (PV) systems and thermal storages as well as local heating networks (HNs) are defined as options. The investigation on a building level shows that a boiler is the economically optimal solution for small buildings, followed by a HP unit. In multi-family buildings, both boilers and CHP units hold an economical advantage over HPs. For apartment buildings, CHP is identified as the economically optimal system. In the neighbourhood analysis of six buildings, the solver establishes a local HN which allows for both economical and CO₂-emission reductions.     

Potential use of cold thermal energy storage systems for better efficiency and cost effectiveness

The present article deals with the employment of combined heat and power (CHP) micro gas turbines using natural gas and cold thermal energy storage system (CTES) in Tehran (with mild climate), Bandarabas (with hot and humid climate) and Kerman (with semi-hot climate). A micro CHP produces electricity to meet the electrical energy needs of the building, and it is also considered to meet part of the heating, cooling and domestic hot water energy needs through a heat pump and refrigeration system. A detailed study considering the effect of CTES system on the selection of micro gas turbines of a residential building located in Tehran is performed. The results show that since the number of micro gas turbines is dependent on the maximum cooling load required in the summer using CTES system reduces the CHP micro gas turbine units from 21 to 11 and costs from US$ 1,133,221 to US$ 799,061 (29.5% economical) for the residential building which is located in Tehran. Also, using this system in Kerman and Bandarabas reduces the micro CHP gas turbine units from 21.75 to 11.40, respectively.     

长春市民用建筑采用热电联产系统的可行性分析

对长春市民用建筑四种能源供给方案在同样的负荷水平下,进行节能、环保和经济效果分析。计算四种能源供给系统的一次能源消费量、二氧化碳排放量、初期投资、运行费用和单纯回收年数。计算结果为：与空调系统相比,锅炉系统、热主电从和电主热从的热电联产系统的节能率分别为．2．1％、21．2％和6．0％;二氧化碳排放量的消减率分别为．0...     

Modeling and economic analysis of gas engine heat pumps for residential and commercial buildings in various climate regions of Iran

There is an increasing trend in using heat pumps in air conditioning (heating/cooling) systems of residential and commercial buildings. The required power to drive the compressor of vapor compression heat pump cycles may be provided by either an electrical motor or an internal combustion engine. In this paper thermal modeling and economic analysis of gas engine heat pumps (GEHPs) are presented based on energy and mass balance equations as well as the gas engine operating parameters (such as thermal efficiency, fuel consumption and fuel mass flow rate) and heat pump operating parameters (such as evaporator and condenser capacity and compressor input power). Based on the modeling results and with estimating GEHP fuel consumption, the economic analysis of using gas engine heat pumps (in comparison with the electrical heat pumps) at various climate regions of Iran, for both residential and commercial (office) buildings, and for both cooling and heating modes, was performed. Appropriate cost functions for predicting GEHP capital investment were proposed. Three approaches including equivalent uniform annual cost (EUAC), the annual cost of energy consumption, and payback period were applied in the economic analysis.     

SOFC热电联供系统热电性能调节方法研究

针对固体氧化物燃料电池热电联供系统提出了两种热电性能调节方法,调节方法1控制电池操作温度和燃料利用率不变,调节方法2控制电池操作电压和操作温度不变.采用参数分析法研究了不同调节方法对系统热、电综合性能的影响.两种调节方法适用于建筑物热电联供系统,在实际应用中需要根据需求侧的热、电输出特性,考虑系统的综合性能,选择最佳的调节方法.     

Performance assessment of fuel cell micro-cogeneration systems for residential buildings

The reduction of greenhouse gas emissions in the building sector to a sustainable level will require tremendous efforts to increase both energy efficiency and the share of renewable energies. Apart from the lowering of energy demand through better insulation and fenestration, small combined heat and power (micro-cogeneration) systems may help improve the situation on the supply side by cutting both the non-renewable energy demand for residential buildings and peak loads in the electric grid. Though still on the brink of market entry, fuel cells are the focus of interest as the prime technology for such systems. In this study, a methodology for assessing the performance of such systems in terms of primary energy demand and the CO₂ emissions by transient computer simulations is established, and demonstrated for a natural gas driven solid oxide fuel cell (SOFC) and, to a lesser extend, a polymer electrolyte fuel cell (PEFC) home fuel cell cogeneration system. The systems were evaluated for different grid electricity generation mix types and compared to traditional gas boiler systems. The interaction with hot water storage and solar thermal collectors, and the impact of storage size and predictive control was analyzed. Typical heat and electricity demand load profiles for different types of residential buildings and occupancy were considered, and the sizing of the fuel cell system in relation to the heat demand of the building was analyzed. Primary energy savings decline for cases with lower heat demand and for cases with solar thermal systems, and peak for fuel cell systems sized in accordance with the heat demand of the building. Future assessments of fuel cell systems will need a refined methodology, and depend on realistic performance characteristics and models that accurately consider dynamic conditions.     

Primary energy implications of end-use energy efficiency measures in district heated buildings

In this study we explore the effects of end-use energy efficiency measures on different district heat production systems with combined heat and power (CHP) plants for base load production and heat-only boilers for peak and medium load productions. We model four minimum cost district heat production systems based on four environmental taxation scenarios, plus a reference district heat system used in Östersund, Sweden. We analyze the primary energy use and the cost of district heat production for each system. We then analyze the primary energy implications of end-use energy efficiency measures applied to a case-study apartment building, taking into account the reduced district heat demand, reduced cogenerated electricity and increased electricity use due to ventilation heat recovery. We find that district heat production cost in optimally-designed production systems is not sensitive to environmental taxation. The primary energy savings of end-use energy efficiency measures depend on the characteristics of the district heat production system and the type of end-use energy efficiency measures. Energy efficiency measures that reduce more of peak load than base load production give higher primary energy savings, because the primary energy efficiency is higher for CHP plants than for boilers. This study shows the importance of analyzing both the demand and supply sides as well as their interaction in order to minimize the primary energy use of district heated buildings.     

Energy, economic and environmental (3E) analysis of a micro gas turbine employed for on-site combined heat and power production

This paper studies the optimization of micro turbine application to meet the electrical, heating and cooling loads of a building by energy, economics and environmental analysis. In this study following three cases are considered: 1: A simple micro gas turbine to meet the electrical power of the building. 2: A simple micro gas turbine to meet the electrical power of the building as well as the power required by heat pump and mechanical refrigerator needed for heating, cooling and domestic hot water (DHW) systems. 3: A CHP micro gas turbine to meet the electrical power of the building as well as part of the power required by heat pump and mechanical refrigerator needed for heating, cooling and DHW systems. The remaining part of the power for heat pump and mechanical refrigerator is provided by the exhaust gases.The research shows that the initial investment is a considerable portion of electricity cost. For an annual interest rate of 10% this portion ranges from 31 to 40% depending on system design configurations, and the lower interest rates results in the smaller portions. It is also concluded that the number of turbine units and electricity cost are highly depended on electricity consumption management.     

Primary energy implications of ventilation heat recovery in residential buildings

In this study, we analyze the impact of ventilation heat recovery (VHR) on the operation primary energy use in residential buildings. We calculate the operation primary energy use of a case-study apartment building built to conventional and passive house standard, both with and without VHR, and using different end-use heating systems including electric resistance heating, bedrock heat pump and district heating based on combined heat and power (CHP) production. VHR increases the electrical energy used for ventilation and reduces the heat energy used for space heating. Significantly greater primary energy savings is achieved when VHR is used in resistance heated buildings than in district heated buildings. For district heated buildings the primary energy savings are small. VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the amount of electricity used for VHR and the airtightness of buildings. This study shows the importance of considering the interactions between heat supply systems and VHR systems to reduce primary energy use in buildings.     

Estimating the environmental burdens of residential energy supply systems through material input and emission factors

This paper introduces a method and application for the assessment of environmental burdens due to the construction and operation of a residential energy supply system. The methodology encompasses energy and environmental impact analyses with sensitivity analysis. Here, natural resource consumption is assessed through material input factors. Global warming and acidification potentials are estimated by way of CO₂− and SO₂− equivalents. A simple optimization scheme is established to capture uncertainties related to preferential treatment between natural resource categories. A computational study on the energy supply of a group of low-energy single-family houses in Finland is presented. Specifically, the potential of micro-cogeneration is evaluated with respect to traditional options based on grid electricity, district heat and natural gas. The energy analysis suggests that the operation of a heating system causes a major part of environmental burdens and that no more than 1000 W on-site generated electrical power per one household would result in minimum thermal losses and thus environmental burdens. On the basis of environmental impact analysis, the use of state-of-the-art micro-cogeneration may decrease the annual use of abiotic resources and water to some extent, but for practical applications, further improvement of system efficiency is still required.     

Build-up and performance test of a novel solar thermal roof for heat pump operation

Global increase in energy demand and fossil fuel prices loaded ever-increasing pressure on identifying and implementing new means to utilise clean and efficient energy resources. Due to the environmental benefits, technical and economic possibilities of Solar-Assisted Heat Pump Systems, there has been a growing interest for such hybrid systems with a variety of system configurations for various climates. International Energy Agency Task 44 of the Solar Heating and Cooling Programme has recently started working on finding methods to most effectively use solar heat pump systems for residential use. In the present study, a novel solar thermal roof collector was developed by primarily exploiting components and techniques widely available on the market and coupled with a commercial heat pump unit. The proposed indirect series Solar-assisted Heat Pump system was experimentally tested and system performance was investigated. Yet, the analysis based on indoor and outdoor testing predominantly focuses on the solar thermal roof collector. A detailed thermal model was developed to describe the system operation. Also, a computer model was set up by using Engineering Equation Solver to carry out the numerical computations of the governing equations. Analyses show that the difference in water temperature could reach up to 18°C while maximum thermal efficiency found to be 26%. Data processing of the series covering the test period represents that Coefficient Performance of the heat pump (COP_HP) and overall system (COP_SYS) averages were attained as COP_HP?=?3.01 and COP_SYS?=?2.29, respectively. An economic analysis points a minimum payback period of about three years for the system.     

A modelling study for the integration of a PEMFC microCHP in domestic building services design

Fuel cell based micro-combined heat and power( CHP) units used for domestic applications can provide significant cost and environmental benefits for end users and contribute to the UK 's 2050 emissions target by reducing primary energy consumption in dwellings. Lately there has been increased interest in the development of systematic methods for the design of such systems and their smoother integration with domestic building services. Several models in the literature,whether they use a simulation or an optimisation approach,ignore the dwelling side of the system and optimise the efficiency or delivered power of the unit. However the design of the building services is linked to the choice of heating plant and its characteristics. Adding the dwelling's energy demand and temperature constraints in a model canproduce more general results that can optimise the whole system,not only the micro-CHP unit. The fuel cell has various heat streams that can be harvested to satisfy heat demand in a dwelling and the design can vary depending on the proportion of heat needed from each heat stream to serve the energy demand. A mixed integer non-linear programming model( M INLP) that can handle multiple heat sources and demands is presented in this paper.The methodology utilises a process systems engineering approach. The model can provide a design that integrates the temperature and water flowconstraints of a dwelling's heating system with the heat streams within the fuel cell processes while optimising total CO2 emissions. The model is demonstrated through different case studies that attempt to capture the variability of the housing stock. The predicted CO2 emissions reduction compared to a conventionally designed building vary from 27%to 30%and the optimum capacity of the fuel cell ranges between 1. 9 kW and3. 6 kW. This research represents a significant step towards an integrated fuel cell micro-CHP and dwelling design.     

CO2 emission consequences of energy measures in buildings

This paper studies the way in which CO₂ emission levels are affected by different measures to reduce energy consumption in a building. A case study is presented which deals with a residential building in Navestad, a suburb of the Swedish city Norrköping. The building is supplied with district heating primarily delivered from a combined heat and power (CHP) plant. Three types of energy measures are studied: extra insulation, new types of window and the introduction of a heat pump. The first perspective is the city of Norrköping, with the system boundary encompassing the residential building and the CHP plants. A second worst case scenario is then presented: a Nordic perspective in which electricity produced in coal condensing power plants is assumed to cover the marginal electricity production. With the former perspective, the measures extra insulation and new windows reduce the CO₂ emissions, and with the latter both measures increase the CO₂ emissions. The measures extra insulation and new windows are ranked, with respect to cost for the first perspective, using a cost reduction curve for CO₂ emissions. In the paper, costs from the ExternE research project are also used.     

对核供热方式的探讨

本文根据热力学原理,对采用何种供热方式,选择何种堆型其核能利用率最佳这一问题进行分析。分析结果认为,采用模块式高温气冷堆实现核热电联供是核供热的最佳方式,与其它核供热方式相比,采用核热电联供不仅可以节约大量的核燃料,而且在其它方面也具有较大的优越性。     

基于热气机分布式冷热电三联供效益分析

以上海地区一幢典型五层住宅建筑热、电、冷负荷需求为计算基础,分别计算了基于热气机的冷热电三联供系统和传统冷热电分供系统的一次能耗率、全年净收益以及投资回收期,验证了三联供系统的节能性和经济性。分析表明热气机余热利用率和能源价格是影响该三联供系统节能效益和经济效益的主要因素。     

Analysis and optimization of the use of CHP-ORC systems for small commercial buildings

The use of combined heating and power (CHP) systems is increasing rapidly due to their high potential of reducing primary energy consumption (PEC), cost, and carbon dioxide emissions (CDE). These reductions are mainly due to capturing the exhaust heat to satisfy the thermal demand of a building. However, when the CHP system is operated following the electric load, the recovered exhaust heat may or may not be sufficient to satisfy the thermal demand of the facility. When the recovered exhaust heat is more than the heat required, the excess is usually discarded to the atmosphere. An organic rankine cycle (ORC) can be used to recover the surplus exhaust heat to generate extra electricity. Therefore, combining the ORC system with the CHP system (CHP-ORC) reduces the electricity that has to be produced by the CHP system, thereby reducing the total PEC, cost, and CDE. The objective of this paper is to study the energetic, economical, and environmental performance of a combined CHP-ORC system and compare its performance to a standalone CHP system and a reference building for different climate zones. A comparison of a CHP-ORC system operating 24 h with a system operating during typical office hours is also performed.     

Cost-optimized real-time operation of CHP systems

The Cooling, Heating, and Power (CHP) systems have been widely recognized as a key alternative for thermal and electric energy generation because of the outstanding energy efficiency, reduced environmental emissions, and relative independence from centralized power grids. Nevertheless, the total energy cost of CHP systems can be highly dependent on the operation of individual components. This paper presents an energy dispatch algorithm that minimizes the cost of energy (e.g., cost of electricity from the grid and cost of natural gas into the engine and boiler) based on energy efficiency constrains for each component. A deterministic network flow model of a typical CHP system is developed as part of the algorithm. The advantage of using a network flow model is that the electric and thermal energy flows through the CHP equipment can be readily visualized allowing for easier interpretation of the results. This algorithm has been used in simulations of a case study on the operation of an existing micro-CHP system. The results from the simulation are presented in the paper to demonstrate the economical advantages resulting from optimal operation.     

Exergo-economic study of a dual-pressure HRSG in gas/steam combined cycle plants

ABSTRACT

Combined power plants are among the most attractive options to optimally utilise conventional fuel energy with respect to energy conversion and the environment. In the present study, a dual-pressure heat recovery steam generator (HRSG) used in a gas/steam combined cycle power plant is investigated. This paper presents exergy and economic analysis of a dual-pressure HRSG. The parameters used for the investigation of the exergo-economic study are pinch point, fuel price, cost of exergy losses, gas turbine inlet temperature and cycle pressure ratio. A parametric study shows that the considered parameters have a huge impact on the total annual cost per unit exergy of steam produced in the HRSG. It is seen that best exergo-economic conditions are obtained at the pinch point value of 10?K to get the total annual cost per unit exergy of steam produced to be the minimum.     

天然气CHP、CCHP系统在工业企业的应用

介绍了天然气热电联供（CHP）系统、天然气冷热电联供（CCHP）系统在我国的发展现状,提出在工业企业应用天然气CHP、CCHP系统,改变采用一次能源直接供应热风、热水的现状,实现能源的梯级利用,提高能源利用效率。