Performance improvement of a 70 kWe natural gas combined heat and power (CHP) system

Combined heat and power is the simultaneous production of electricity and heat. CHP plants produce energy in an efficient way. A natural gas CHP system based on an internal combustion engine (ICE) is described, which has been set up at the Building Energy Research Center in Beijing, China. The system is composed of an ICE, a flue gas heat exchanger, a jacket water heat exchanger and other assistant facilities. The ICE generates power on-site, and the exhaust of the ICE is recovered by the flue gas heat exchanger, and the heat of the engine jacket is recovered by the jacket water heat exchanger to district heating system. In order to improve the performance of the system, an absorption heat pump (AHP) is adopted. The exhaust of the ICE drives the AHP to recover the sensible and latent heat step by step, and the temperature of the exhaust could be lowered to below 30 °C. In this paper, the performance of the new system were tested and compared with conventional cogeneration systems. The results show that the new CHP system could increase the heat utilization efficiency 10% compared to conventional systems in winter. All the results could be valuable references for the improvement of the CHP system.     

Economic potential of energy-efficient retrofitting in the Swiss residential building sector: The effects of policy instruments and energy price expectations

The aim of this paper is to analyse the profitability of energy-efficient retrofit investments in the Swiss residential building sector from the house owner's perspective. Different energy price expectations, policy instruments such as subsidies, income tax deduction and a carbon tax, as well as potential future cost degression of energy efficiency measures were taken into account. The discounted cash flow method was used for the investment analysis of different retrofit packages applied to a model building scheduled for renovation, i.e. a single-family house constructed between 1948 and 1975. The results show that present Swiss policy instruments push investments for energy-efficient retrofitting to profitability. Cost degression has a minor significance for investment profitability. However, the most relevant factor for the investment analysis is the expected energy price. Expecting a future fuel oil price at the level of 2005, efficiency investments are close to profitability even without policy support. If higher energy prices were expected, energy-efficient retrofitting would be an attractive investment opportunity.     

Optimum generation capacities of micro combined heat and power systems in apartment complexes with varying numbers of apartment units

A dynamic simulation of micro combined heat and power (micro-CHP) systems that includes the transient behavior of the system was developed by modeling the generation of electricity and recovery of heat separately. Residential load profiles were calculated based on statistical reports from a Korean government agency, and were used as input data to select the optimum capacities of micro-CHP systems based on the number of apartment units being served, focusing on both economic and energetic criteria. The capacity of internal combustion engine (ICE) based micro-CHP was assumed to be in the range 1–500 kW, and the dependence of the efficiency of the generator unit on the capacity was included. It was found that the configuration (i.e., the capacity and number of generator units) that maximized the annual savings also had favorable energetic performance. Additionally, the statistical mode calculated from the annual electrical load distribution was verified as a suitable indicator when deciding the optimum capacity of a micro-CHP system.     

Exergetic comparison of efficiency indicators for combined heat and power (CHP)

Legislative regulations in favor of combined heat and power (CHP) production have been implemented in many countries. Although these regulations put different emphasis on power production vs. process heat production, they are based on energy quantities and not on exergy. In order to analyze and compare the exergetic consequences of the various legislations, a relative avoided irreversibility (RAI) is defined. This can be regarded as the exergy loss that is avoided when reference plants with separate production are replaced by an actual CHP plant. Some series of industrial and district heating CHP plants, under varying operational conditions, are used as test cases. It is seen that some, but not all, CHP cases are exergetically beneficial to separate generation. Comparison with the RAI allows a quantitative assessment of the various performance indicators. It is seen that exergetic improvements were only captured to a limited degree by the various energy-based efficiency indicators. Some legislatively defined indicators even appear to discourage thermodynamic improvements.     

Solid oxide fuel cell micro combined heat and power system operating strategy: Options for provision of residential space and water heating

Solid oxide fuel cell (SOFC) based micro combined heat and power (micro-CHP) systems exhibit fundamentally different characteristics from other common micro-CHP technologies. Of particular relevance to this article is that they have a low heat-to-power ratio and may benefit from avoidance of thermal cycling. Existing patterns of residential heat demand in the UK, often characterised by morning and evening heating periods, do not necessarily complement the characteristics of SOFC based micro-CHP in an economic and technical sense because of difficulties in responding to large rapid heat demands (low heat-to-power ratio) and preference for continuous operation (avoidance of thermal cycling). In order to investigate modes of heat delivery that complement SOFC based micro-CHP a number of different heat demand profiles for a typical UK residential dwelling are considered along with a detailed model of SOFC based micro-CHP technical characteristics. Economic and environmental outcomes are modelled for each heat demand profile. A thermal energy store is then added to the analysis and comment is made on changes in economic and environmental parameters, and on the constraints of this option. We find that SOFC-based micro-CHP is best suited to slow space heating demands, where the heating system is on constantly during virtually all of the winter period. Thermal energy storage is less useful where heat demands are slow, but is better suited to cases where decoupling of heat demand and heat supply can result in efficiencies.     

Thermoeconomic analysis method for optimization of combined heat and power systems—part II

In this paper, a thermoeconomic functional analysis method based on the Second Law of Thermodynamics and applied to analyze four cogeneration systems is presented. The objective of the developed technique is to minimize the operating costs of the cogeneration plant, namely exergetic production cost (EPC), assuming fixed rates of electricity production and process steam in exergy base. In this study a comparison is made between the same four configurations of part I. The cogeneration system consisting of a gas turbine with a heat recovery steam generator, without supplementary firing, has the lowest EPC.     

The capacity credit of micro-combined heat and power

This article is concerned with development of a methodology to determine the capacity credit of micro-combined heat and power (micro-CHP), and application of the method for the UK. Capacity credit is an important parameter in electricity system planning because it measures the amount of conventional generation that would be displaced by an alternative technology. Firstly, a mathematical formulation is presented. Capacity credit is then calculated for three types of micro-CHP units—Stirling engine, internal combustion engine, and fuel cell systems—operating under various control strategies. It is found that low heat-to-power ratio fuel cell technologies achieve the highest capacity credit of approximately 85% for a 1.1 GW penetration when a heat-led control strategy is applied. Higher heat-to-power ratio Stirling engine technology achieves approximately 33% capacity credit for heat-led operation. Low heat-to-power ratio technologies achieve higher capacity credit because they are able to continue operating even when heat demand is relatively low. Capacity credit diminishes as penetration of the technology increases. Overall, the high capacity credit of micro-CHP contributes to the viewpoint that the technology can help meet a number of economic and environmental energy policy aims.     

Theory-based policy evaluation of 20 energy efficiency instruments

Realizing a 20% energy efficiency improvement in Europe by 2020 requires the introduction of good new energy efficiency policies as well as strengthening and enforcing the existing policies. This raises the question: what characterizes good and effective energy efficiency policies and their implementation? Systematic ex post evaluation of energy efficiency policies can reveal factors determining not only what works and what does not but also explain why. Ex post evaluation of 20 energy efficiency policy instruments applied across different sectors and countries in Europe among others showed that ex post evaluation does not yet have a high priority among policy makers: Often, quantitative targets and clear timeframes are lacking, and monitoring information is not collected on a regular basis. Our analysis, however, did reveal some general factors in the process of design and implementation of policy instruments that appear as important including (1) existence of clear goals and a mandate for the implementing organization, (2) the ability to balance and combine flexibility and continuity, (3) the involvement of stakeholders, and (4) the ability to adapt to and integrate adjacent policies or develop consistent policy packages. The analysis was performed using a uniform methodology called “theory-based policy evaluation”. The general principle behind this approach is that a likely theory is drawn up on the program’s various steps of logic of intervention to achieve its targeted impact in terms of energy efficiency improvement. The approach has several benefits over other ex post evaluation methods because (1) the whole policy implementation process is evaluated and the focus is not just on the final impacts, (2) through the development of indicators for each step in the implementation process, the “successes and failures” can be determined to the greatest extent possible, and (3) by applying this approach, we not only learn whether policies are successful or not but also why they succeeded or failed and how they can be improved.     

A micro tri-generation system based on direct flame fuel cells for residential applications

A novel micro tri-generation system which combines a direct flame fuel cell, a boiler and a double-effect absorption chiller is proposed and analyzed for residential applications. Parametric analyses are conducted to investigate the effects of operating parameters (i.e. the equivalence ratio and the fuel utilization factor of the fuel cell) on the system efficiency and the thermal-to-electric ratio. Then optimum operating parameters are determined based on the typical energy demand of Hong Kong in the summer and the typical energy demand of Beijing in the winter, respectively. It is found that very high efficiency (over 90%) can be achieved by this novel tri-generation system for both Hong Kong and Beijing. Besides, the system is modified for combined heat and power cogeneration, combined cooling and power cogeneration and their efficiencies are compared with the tri-generation system to evaluate the effect of each single unit on the whole system.     

Interactions of white certificates with other policy instruments in Europe

In a tradable white certificate (TWC) scheme, each certificate issued represents a certain amount of energy saved. Used in conjunction with an energy-saving obligation on certain parties in the energy supply chain and with rules for trading, monitoring and verification established, an efficient market for energy savings in sectors not covered by the European Union (EU) Emissions Trading Scheme can be established. However, a plethora of other mechanisms are already in place to promote a more sustainable use of energy in Europe. This paper analyses the interactions (both potential and realised in existing schemes) between TWCs and other policy instruments including tradable green certificates, the European Union Emissions Trading Scheme, the European Union Energy Performance in Buildings Directive as well as taxes, subsidies and loans. Measures implemented through a TWC scheme that reduce the consumption of electricity can make targets under a tradable green certificate scheme easier to attain. Where a tradable green certificate scheme contains relative targets, the target should be increased to achieve the same absolute amount of renewable power. A TWC scheme can also reduce the number of allowances electricity generators will need to surrender under the EU Emissions Trading Scheme. By reducing the available emission rights in the National Allocation Plans, this effect is possible to counteract.

Compact fluorescent lighting and residential natural gas consumption: Testing for interactive effects

Replacing incandescent light bulbs with compact fluorescents (CFLs) has traditionally been seen as a cost effective means of promoting energy conservation. Recently, however, the magnitude of energy savings associated with CFLs has been called into question. Specifically, recent findings suggest an “interactive effect” associated with the replacement of incandescent light bulbs with CFLs in the residential sector. In this scenario, the reduced wattage of CFLs, relative to incandescent bulbs, generates less heat, which in turn, requires additional natural gas usage during the heating season. Engineering studies suggest the magnitude of the effect is significant in energy terms, which implies that the energy savings associated with CFLs may be significantly overstated. In this paper, we use billing analysis to test for the presence of interactive effects. Our analysis is based on a comprehensive dataset that includes monthly household electricity and natural gas usage, the number of CFL bulbs installed, the installation date, and a set of household characteristics. Our results suggest that CFLs do indeed save electricity. However, we do not find any support for the hypothesis that CFLs cause increased usage of natural gas.     

Industrial combined heat and power (CHP) planning: Development of a methodology and application in Greece

This paper establishes a methodology for the estimation of the primary energy savings of an industrial (sub)-sector and the primary energy savings of the total energy system due to CHP. A primary energy savings indicator within a (sub)-sector and a total primary energy savings indicator are developed which are related with the actual energy use of a (sub)-sector and the way of disposal of the excess CHP energy produced. The methodology is applied in an industrial sub-sector in Greece according to the ‘power match’ and the ‘thermal match’ CHP sizing scenarios; subsequently results are presented and the developed indicators are fully explained. It was found that the primary energy savings indicator of a sub-sector is determined by the efficiencies of the relevant technologies, and the interrelation of the ‘power to heat’ ratio of the CHP technology used and the ‘power to heat’ ratio of the sub-sector examined; the total primary energy savings indicator is determined by the efficiencies of the relevant technologies and the percentage of the CHP energy exported from the sub-sector. The methodology can be utilized for optimum CHP planning.     

Assessment of potential for natural gas-based cogeneration in Thailand

Using the results of a comprehensive data analysis of final energy consumption in industry and commercial buildings, the assessment has been made of the potential for gradual implementation of cogeneration plants in these facilities. In doing so, plans for the expansion of the natural gas pipeline distribution network in Thailand are taken into consideration. The sample comprises of 2540 factories and 1651 commercial buildings from which it was found that 817 factories and 966 commercial buildings were suitable for the implementation of natural gas-based cogeneration technologies until 2020. By the implementation of cogeneration in these facilities, it is possible to save 3.2% of the total primary energy consumption in Thailand in 2003.     

Performance of residential fuel-cell-combined heat and power systems for various household types in Japan

A residential fuel-cell-combined heat and power (FC-CHP) system is considered a promising low-carbon technology that can reduce residential energy consumption and thus, achieve Japan's greenhouse gas (GHG) emissions reduction targets. However, to consider future directions for the systems' research and development, it is critical to understand the relationships between the performances of FC-CHP systems and residential energy demand profiles, which vary by household characteristic. This study evaluates the effects of applying city gas-fueled FC-CHP systems to Japanese households with different attributes. We compare total costs and GHG emissions for residential energy use between the FC-CHP systems and a conventional system. The economic performance results suggest that the basic PEMFC-CHP systems have an economic advantage only for four-person families with teenage children and further development efforts for low-output FC-CHP systems are required to enable various households save energy costs. The environmental evaluation results show that SOFC-CHP systems can drastically reduce GHG emissions from particularly small-sized households.     

炼油过程余热回收热电联产系统综合用能效率分析

对大连石化公司自备电厂锅炉和汽轮发电机组进行全面的测试,在此基础上进行了锅炉正、反平衡计算,汽轮机机相对内效率、汽轮机械效率和汽机发电机效率的计算,综合各项数据,得出了热电厂余热资源的综合热效率,并分析了热效率低的原因。     

Energy saving and energy efficiency concepts for policy making

Departing from the concept of rational use of energy, the paper outlines the microeconomics of end-use energy saving as a result of frugality or efficiency measures. Frugality refers to the behaviour that is aimed at energy conservation, and with efficiency we refer to the technical ratio between energy input and output services that can be modified with technical improvements (e.g. technology substitution). Changing behaviour from one side and technology from the other are key issues for public energy policy. In this paper, we attempt to identify the effects of parameters that determine energy saving behaviour with the use of the microeconomic theory. The role of these parameters is crucial and can determine the outcome of energy efficiency policies; therefore policymakers should properly address them when designing policies.     

Low temperature heat source for power generation: Exhaustive analysis of a carbon dioxide transcritical power cycle

The main results of a theoretical work on the use of a low temperature heat source for power generation through a carbon dioxide transcritical power cycle are reported in this paper. The procedure for analyzing the behaviour of the proposed cycle consisted in modifying the input pressure to the turbine from 66 bar, maintained constant each evaluated temperature (60 °C, 90 °C, 120 °C and 150 °C) until the net work was approximately zero. As a result, the maximum exergy efficiency was 50%, while the energy efficiencies obtained were 9.8%, 7.3%, 4.9% and 2.4% and the net specific work was 18.2 kJ/kg, 12.8 kJ/kg, 7.8 kJ/kg and 3.5 kJ/kg, respectively. Furthermore, the effect of the addition of an internal heat exchanger, which obviously supposed an increase in the efficiency, was analyzed. The analysis of the proposed system shows the viability of implementing this type of process as an energy alternative and/or strengthener of non-conventional energy sources in non-provided zones, or for increasing the energy efficiency in the industry.     

Planning of micro-combined heat and power systems in the Portuguese scenario

High efficiency cogeneration is seen by the European Commission as part of the solution to increase energy efficiency and improve security of supply in the internal energy markets. Portuguese residential sector has an estimated technical market potential of around 500 MW_e for cogeneration of <150 kW_e in size. Additionally, in Portugal there is a specific law for power production in low voltage, where at least 50% of the produced electric energy must be own consumed and the maximum power delivered to the power utility should be less than 150 kW_e. Therefore, generic application tools cannot be applied in this regard. In this work, we develop the MicroG model for planning micro-CHP plants in agreement with the Portuguese energy legal framework. The model is able to design, evaluate and optimize from the techno-economic point of view any micro-CHP plant. MicroG appeals to some data bases, such as micro-cogeneration technologies and power consumption profiles that are also described. In addition, a practical case on a gym is considered to show all the functionalities of the model. The developed model has proven to be extremely useful from the practical point of view. This model could help the development of the micro-CHP Portuguese market, which in turns contributes to accomplish the targets of Kyoto protocol and EU cogeneration Directive. Other improvements to MicroG model can be made in order to enlarge the range of application to other micro-cogeneration technologies and to accomplish with the CO₂ emissions trading.     

Evaluation of the effectiveness of an energy efficiency program for new home construction in eastern North Carolina

This paper reports on the evaluation of the effectiveness of an energy efficiency program in eastern North Carolina. This subject program is focused on improved construction methods for residential housing. The program incorporates proven energy saving technologies, construction procedures, onsite inspections, and design construction methodologies in new residential construction. The analysis compared the energy usage associated with the houses built in conjunction with the energy efficiency program (test group) with similar new residential construction unrelated to the program (control group). Several statistical methods were employed to establish differences between the energy efficiency program participants and the control group. The analysis provides significant support for the effectiveness of this energy efficiency program and supports the suitability of similar efforts for inclusion in plans for renewable energy offsets and energy efficiency standards.     

Medium-term energy outlook for Cyprus and its policy implications

This short paper presents results from an energy forecast model for the Republic of Cyprus. The model was used during years 2010–2011 to assist national authorities in their preparation of the National Renewable Energy Action Plan and the Energy Efficiency Action Plan of Cyprus in line with the requirements of European Union Directives. Major macroeconomic and price assumptions of the model are presented, and results from model application under different assumptions with regard to the evolution of energy efficiency are outlined and discussed. On the basis of these scenarios the paper discusses policy implications for Cyprus regarding the country's compliance with EU energy and climate legislation.