Analysis and optimization of CCHP systems based on energy, economical, and environmental considerations

Analysis of combined cooling, heating, and power (CCHP) systems is frequently based on reduction of operating cost without measuring the actual energy use and emissions reduction. CCHP systems can be optimized based on different optimization criterion such as: energy savings, operation cost reduction or minimum environmental impact. In this study, CCHP systems operated following the electric load (FEL) and the thermal load (FTL) strategies are evaluated and optimized based on: primary energy consumption (PEC), operation cost, and carbon dioxide emissions (CDE). This study also includes the analysis and evaluation of an optimized operational strategy in which a CCHP system follows a hybrid electric-thermal load (HETS) during its operation. Results show that CCHP systems operating using any of the optimization criteria have better performance than CCHP systems operating without any optimization criteria. For the evaluated city, the optimum PEC and cost reduction are 7.5% and 4.4%, respectively, for CCHP-FTL, while the optimum CDE reduction is 14.8% for CCHP-FEL. Results also show that the HETS is a good alternative for CCHP systems operation since it gives good reduction of PEC, cost, and CDE. This optimized operation strategy provides a good balance among all the variables considered in this paper.     

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.     

Economic and environmental evaluation of micro CHP systems with different operating modes for residential buildings in Japan

The growing worldwide demand for less polluting forms of energy has led to a renewed interest in the use of micro combined heat and power (CHP) technologies in the residential sector. The operation of micro CHP system results in simultaneous production of heat and power in a single household based on small energy conversion units. The heat produced may be used for space and water heating and possibly for cooling load if combined with an absorption chiller, the electricity is used within the house.In this paper, two typical micro CHP alternatives, namely, gas engine and fuel cell for residential buildings, are analyzed. For each facility, two different operating modes including minimum-cost operation and minimum-emission operation are taken into consideration by employing a plan and evaluation model for residential micro CHP systems. The analysis results show that the fuel cell system is recognized as a better option for the examined residential building from both economic and environmental points of view. With the operation considering optimal economic benefits, annual energy cost is reduced by about 26%. On the other hand, while maximizing the environmental merits, annual CO₂ emissions are reduced by about 9%.     

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.     

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.     

Residential application of internal combustion engine based cogeneration in cold climate—Canada

The objectives of this work are to model a group of test case houses using a high-resolution building simulation program, to evaluate the efficiency of internal combustion engine (ICE) based cogeneration and to determine the economical (in terms of fuel cost) impact of using ICE based cogeneration systems for residential use. The performance in terms of electrical and CHP efficiencies of the ICE based cogeneration systems in Canada were investigated and it was determined that the performance of the ICE based cogeneration system is dependent on the thermal and electrical loads of the house, on climate, especially the severity and duration of the heating season, and on the constructional characteristics of the house. Although the annual fuel cost of the household would increase, the ICE based cogeneration systems can provide savings in various aspects regarding electricity production and distribution.     

Evaluation of a turbine driven CCHP system for large office buildings under different operating strategies

Combined cooling, heating, and power (CCHP) systems use waste heat from on-site electricity generation to meet the thermal demand of the facility. This paper models a CCHP system for a large office building and examines its primary energy consumption (PEC), operational costs, and carbon dioxide emissions (CDE) with respect to a reference building using conventional technologies. The prime mover used in this investigation is a load share turbine, and the CCHP system is evaluated under three different operation strategies: following the electric demand of the facility, following the thermal demand of the facility, and following a seasonal strategy. For the various strategies, the percentages of total carbon dioxide emissions by source are presented. This paper explores the use of carbon credits to show how the reduction in carbon dioxide emissions that is possible from the CCHP system could translate into economic benefits. In addition, the capital costs available for the CCHP system are determined using the simple payback period. Results indicate that for the evaluated office building located in Chicago the CCHP operation reduces the operational cost, PEC, and CDE from the reference building by an average of 2.6%, 12.1%, and 40.6%, respectively, for all the different operational strategies.     

Performance of a large building rainwater harvesting system

Rainwater harvesting is increasingly becoming an integral part of the sustainable water management toolkit. Despite a plethora of studies modelling the feasibility of the utilisation of rainwater harvesting (RWH) systems in particular contexts, there remains a significant gap in knowledge in relation to detailed empirical assessments of performance. Domestic systems have been investigated to a limited degree in the literature, including in the UK, but there are few recent longitudinal studies of larger non-domestic systems. Additionally, there are few studies comparing estimated and actual performance. This paper presents the results of a longitudinal empirical performance assessment of a non-domestic RWH system located in an office building in the UK. Furthermore, it compares actual performance with the estimated performance based on two methods recommended by the British Standards Institute - the Intermediate (simple calculations) and Detailed (simulation-based) Approaches. Results highlight that the average measured water saving efficiency (amount of mains water saved) of the office-based RWH system was 87% across an 8-month period, due to the system being over-sized for the actual occupancy level. Consequently, a similar level of performance could have been achieved using a smaller-sized tank. Estimated cost savings resulted in capital payback periods of 11 and 6 years for the actual over-sized tank and the smaller optimised tank, respectively. However, more detailed cost data on maintenance and operation is required to perform whole life cost analyses. These findings indicate that office-scale RWH systems potentially offer significant water and cost savings. They also emphasise the importance of monitoring data and that a transition to the use of Detailed Approaches (particularly in the UK) is required to (a) minimise over-sizing of storage tanks and (b) build confidence in RWH system performance.     

国内外热电联产性能评价指标介绍与分析

介绍了各国常用的热电联产(CHP)系统性能评价指标。我国采用CHP系统综合效率作为评价指标,但综合效率以热力学第一定律为基础,不能完全反映CHP系统的实际性能水平,也没有反映出与热电分产系统的差别。应借鉴国外经验,引入相对一次能耗节约率、相对CO2排放减少率等节能减排指标,修改补充我国CHP系统性能评价指标体系。     

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.     

Incentives for Combined Heat and Power plants: How to increase societal benefits?

Investments in new combined heat-and-power (CHP) facilities have fallen short of harnessing what is believed to be CHP's full achievable economic potential and attenuate societal benefits of reducing emissions and increasing resiliency of the power system. Various reasons have been found to explain this “CHP gap,” an example of the “energy-efficiency gap.” This paper examines the effects of understated capital costs and low and volatile CHP capacity factors, which historically are demonstrated by a large number of existing US units, on the economics of CHP facilities and thereby provide a possible explanation for the CHP gap. Given the probability distribution of profitability for a CHP plant, an incentive structure that is modeled similar to insurance against risk of unfavorable outcomes, might compare favorably to the present one-time upfront capital incentive model for attracting new investments. We recommend further research on assurance-based incentives for CHP projects.     

Effect of methanol gasoline blended fuels on the performance and emissions of SI engine

This article presents experimental results of the effect of methanol gasoline blends as alternate fuels for the spark ignition (SI) engine. As the cost of the gasoline is periodically increasing the quest for the alternative fuels are evolved with which the emissions are reduced along with improved engine performance. A set of experiments have been conducted to investigate the effect of gasoline methanol blends in methanol percentages of M5, M10 and M15 on the engine performance and emissions. A significant reduction in emissions is observed with methanol blends compared to the standard gasoline with improved engine performance and emission characteristics. The fuels blends ranging from M10 to M15 have been found suitable for reduced emissions and improved engine performance.     

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.     

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.     

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.     

Two smart energy management models for the Spanish electricity system

This paper evaluates two smart energy management models for the Spanish electricity system in terms of power consumption savings, CO₂ emissions, and dependence upon primary energy from abroad. We compare a baseline scenario with two alternatives. The first model entails the reduction of the power demand through energy savings measures, smart meters, and self-supply. The second model entails the application of all measures included in first scenario, plus measures oriented to electric vehicles. For each model a sensitivity analysis was performed. Results show that both models can result in reductions of peak loads, CO₂ emissions, and energy dependence.     

Innovative method for energy management: Modelling and optimal operation of energy systems

This paper presents an optimal management control strategy for power systems in industrial plants. A dedicated code has been developed to perform system analysis and simulation. The energy/mass balances existing between building and power plant has been depicted through a mathematical model based on vector equations, taking into account the behaviour of each system component. The main result is the definition of the power plant component set points satisfying the energy load under predefined optimization criterion (i.e. system efficiency, costs, pollutant emissions). Input data are the industrial plant loads, both electric and thermal, the technical characteristic of the installations, and the cost of electricity and fuel. As a general result we show that the optimal management of a power plant is as significant as the efficiency of its components for energy saving purposes. In particular, the correlation between the component set point profiles and the energy/cost/pollution savings is highlighted. Yearly simulations are performed on an existing energy system of an industrial plant varying the frequency of energy load dataset. The considered time steps are month, half a day, 4 h and 1 h. The results demonstrate that the whole power plant management leads to a global reduction of the cost and that the availability of more detailed energy load dataset leads to better operation cost estimation. As expected, considering a large time-step, the variation of energy load is not appreciable.The energy saving potential of this method is demonstrated allowing the best plant management solution under different energy loads.     

Performance,emission and combustion characteristics of a single cylinder spark ignition engine using ethanol–petrol-blended fuels

The performance, exhaust emission and combustion analyses of a single cylinder spark ignition engine fuelled with extended range of ethanol–petrol blends were carried out successfully at full load conditions. Ethanol produced from raffia trunks was blended with petrol at different proportions by volume. In order to establish a baseline for comparison, the engine was first run on neat petrol. The engine performance parameters (engine torque, brake power, brake specific fuel consumption, brake mean effective pressure and brake thermal efficiency), exhaust emission parameters (CO, HC, CO₂ and O₂ emissions) and combustion parameters were determined for each blend of fuel at different engine speeds. The test results interestingly revealed that the addition of ethanol to petrol causes an improvement in combustion characteristics and significant reduction in exhaust emissions which in turn improved engine performance. In all, ethanol and its blends with petrol exhibited performance characteristics trends similar to that of petrol thus confirming them as suitable alternative fuels for spark ignition engines.     

Influence of spark timing on the performance and emission characteristics of gasoline–hydrogen-blended high-speed spark-ignition engine

This article experimentally investigates the effect of spark timing on performance and emission characteristics of high-speed spark-ignition (SI) engine operated with different hydrogen–gasoline fuel blends. For this purpose, the conventional carbureted SI engine is modified into an electronically controllable engine, wherein an electronically controllable unit was used to control the ignition timings and injection duration of gasoline. The tests were conducted with different spark timings at the wide open throttle position and 3000 rpm engine speed. The experimental results demonstrated that brake mean effective pressure and engine brake thermal efficiency increased first and then decreased with the increase in spark advance. Peak cylinder pressure, temperature and heat release rate were increased until 20% hydrogen addition and with increased spark timings. NO_x emissions were continuously increased with the increment in both spark timings and hydrogen addition, whereas hydrocarbon emissions were increased with spark timings but decreased with hydrogen addition. CO emissions were reduced with the increase in spark timing and hydrogen addition.     

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...