Analysis of cooling,heating, and power systems based on site energy consumption

Feasibility of cooling, heating, and power systems frequently is based on economic considerations such as energy prices. However, a most adequate feasibility of CHP systems must be based on energy consumption followed by economic considerations. CHP systems designs must yield economical savings, but more importantly must yield real energy savings based on the best energy performance. For CHP systems, energy savings is related to primary energy and not to site energy. This paper presents a mathematical analysis demonstrating that CHP systems increase the site energy consumption (SEC). Increasing the SEC could yield misleading results in the economic feasibility of CHP systems. Three different operation modes are evaluated: (a) cooling, heating, and power; (b) heating and power; and (c) cooling and power, to represent the operation of the system throughout the year. Results show that CHP systems increase site energy consumption; therefore primary energy consumption (PEC) should be used instead of SEC when designing CHP systems.     

A novel method for the design of CHCP (combined heat,cooling and power) systems for buildings

The design of capacity and operation of CHCP (combined heat, cooling and power) plants applied to HVAC (heating, ventilation and air conditioning) in buildings entails a considerable difficulty, because efficiency and economic aspects frequently interact in a complex way. Due to the strong fluctuations in thermal demands, the evaluation of a given design usually requires detailed simulations and a significant amount of input data. This paper proposes simplified approaches to estimate the main parameters characterising the thermal performance of the plant (ATD_e method) as well as to identify optimal designs for a given application under certain encouragement policies (annual PES (primary energy savings) strategy). In the ATD_e method, the duration curve of ATD (aggregated thermal demand) is used to estimate, among others, the amount of heat and cooling effectively supplied to the final user for a given design of the plant. This procedure serves to achieve a quick, global evaluation of the thermal performance of CHP (combined heat and power) or CHCP plants with little computational effort. The annual PES strategy searches the optimal values for the engine capacity, the OP (operation period) or both for CHP and CHCP plants in a particular application, defined by its energy demands. Both methods have demonstrated a notably good performance in several test cases with different patterns of the thermal demands.     

Design,testing and mathematical modelling of a small-scale CHP and cooling system (small CHP-ejector trigeneration)

Trigeneration is the production of heat, cooling and power from one system. It can improve the financial and environmental benefits of combined heat and power (CHP) by using the heat output from the CHP unit to drive a cooling cycle, as demonstrated in existing large-scale installations. However, small-scale systems of a few kW_e output present technological challenges. This paper presents the design and analysis of possible trigeneration systems based on a gas engine mini-CHP unit (5.5 kW_e) and an ejector cooling cycle. Analysis shows that an overall efficiency around 50% could be achieved with systems designed for applications with simultaneous requirements for heat and cool. While using part of the CHP electrical output into the cooling cycle boosts the cooling capacity, it does not improve the overall efficiency and increases the CO₂ emissions of the system. Emissions savings compared to traditional systems could be achieved with improvements of the heat transfer from CHP to cooling cycle.     

Performance assessment of a Stirling engine plant for local micro‐cogeneration

In this paper, we evaluate the viability of a 9.5‐kW_e wooden pellet‐fueled Stirling engine‐based micro‐cogeneration plant as a substitute for small‐scale district heating. The district heating systems against which the micro‐cogeneration plant is compared are based either on a pellet‐fueled boiler or a ground‐source heat pump. The micro‐cogeneration and district heating plants are compared in terms of primary energy consumption, CO₂ emissions, and feasibility of the investment. The comparison also considers an optimally operated individual 0.7‐kW_e pellet‐fueled Stirling engine micro‐cogeneration system with exhaust gas heat recovery. The study is conducted in two different climates and contributes to the knowledge base by addressing: (i) hourly changes in the Finnish electricity generation mix; and (ii) uncertainty related to what systems are used as reference and the treatment of displaced grid electricity. Our computational results suggest that when operated at constant power, the 9.5‐kW_e Stirling engine plant results in reduced annual primary energy use compared with any of the alternative systems. The results are not sensitive to climate or the energy efficiency or number of buildings. In comparison with the pellet‐fueled district heating plant, the annual use of primary energy and CO₂ emissions are reduced by a minimum of 25 and 19%, respectively. Owing to a significant displacement of grid electricity, the system's net primary energy consumption appears negative when the total built area served by the plant is less than 1200 m². On the economic side, the maximum investment cost threshold of a CHP‐based district heating system serving 10 houses or more can typically be positive when compared with oil and pellet systems, but negative when compared with a corresponding heat pump system. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling of biomass gasifier and microturbine for the olive oil industry

The olive oil industry generates several solid wastes. Among these residues are olive tree leaves, prunings, and dried olive pomace (orujillo) from the extraction process. These renewable energy sources can be used for heat and power production. The aim of this paper consists of modelling and simulation of a small‐scale combined heat and power (CHP) plant (fuelled with olive industry wastes) incorporating a downdraft gasifier, gas cleaning and cooling subsystem, and a microturbine as the power generation unit. The gasifier was modelled with thermodynamic equilibrium calculations (fixed bed type, stratified and with an open top). This gasifier operates at atmospheric pressure with a reaction temperature about 800°C. Simulation results (biomass consumption, gasification efficiency, rated gas flow, calorific value, gas composition, etc.) are compared with a real gasification technology. The product gas obtained has a low heating value (4.8–5.0 MJ Nm^?3) and the CHP system provides 30 kW_e and 60 kW_th. High system overall CHP efficiencies around 50% are achievable with such a system. The proposed system has been modelled using Cycle‐Tempo software^®. Copyright © 2010 John Wiley & Sons, Ltd.     

Performance analysis of CCHP and CHP systems operating following the thermal and electric load

Heating and cooling energy requirements for buildings are usually supplied by separated systems such as furnaces or boilers for heating, and vapor compression systems for cooling. For these types of buildings, the use of combined cooling, heating, and power (CCHP) systems or combined heating and power (CHP) systems are an alternative for energy savings. Different researchers have claimed that the use of CCHP and CHP systems reduces the energy consumption related to transmission and distribution of energy. However, most of these analyses are based on reduction of operating cost without measuring the actual energy use and emissions reduction. The objective of this study is to analyze the performance of CCHP and CHP systems operating following the electric load (FEL) and operating following the thermal load (FTL), based on primary energy consumption (PEC), operation cost, and carbon dioxide emissions (CDE) for different climate conditions. Results show that CCHP and CHP systems operated FTL reduce the PEC for all the evaluated cities. On the other hand, CHP systems operated FEL always increases the PEC. The only operation mode that reduces PEC and CDE while reducing the cost is CHP‐FTL. Copyright © 2009 John Wiley & Sons, Ltd.     

Power and cogeneration technology environomic performance typification in the context of CO2 abatement part I: Power generation

In this series of two articles, the concepts and approaches of environomic (thermodynamic, economic and environmental) performance ‘Typification’ of power generation technologies (Part I) and of combined heat and power (CHP) cogeneration technologies (Part II) in the context of CO₂ abatement are introduced. A methodology is then proposed for a flexible and fast project based power or CHP cogeneration system design evaluation though post-optimization integration of the operating and capital costs. This allows to effectively deal with the uncertainty of the project specific design and operation conditions (fuel, electricity and heat selling prices, project financial conditions such as investment amortization periods, annual operating hours, etc). Furthermore, the uncertainties linked to the external cost such as the CO₂ tax level under a tax scheme or the CO₂ permit price in the emission trading market can be assessed.     

Stockholm CHP potential—An opportunity for CO2 reductions?

The potential for combined heat and power (CHP) generation in Stockholm is large and a total heat demand of about 10 TWh/year can be met in a renewed large district heating system. This model of the Stockholm district heating system shows that CHP generation can increase from 8% in 2004 to 15.5% of the total electricity generation in Sweden. Increased electricity costs in recent years have awakened an interest to invest in new electricity generation. Since renewable alternatives are favoured by green certificates, bio-fuelled CHP is most profitable at low electricity prices. Since heat demand in the district heating network sets the limit for possible electricity generation, a CHP alternative with a high electricity to heat ratio will be more profitable at when electricity prices are high. The efficient energy use in CHP has the potential to contribute to reductions in carbon dioxide emissions in Europe, when they are required and the European electricity market is working perfectly. The potential in Stockholm exceeds Sweden's undertakings under the Kyoto protocol and national reduction goals.     

Examination of energy price policies in Iran for optimal configuration of CHP and CCHP systems based on particle swarm optimization algorithm

The current subsidized energy prices in Iran are proposed to be gradually eliminated over the next few years. The objective of this study is to examine the effects of current and future energy price policies on optimal configuration of combined heat and power (CHP) and combined cooling, heating, and power (CCHP) systems in Iran, under the conditions of selling and not-selling electricity to utility. The particle swarm optimization algorithm is used for minimizing the cost function for owning and operating various CHP and CCHP systems in an industrial dairy unit. The results show that with the estimated future unsubsidized utility prices, CHP and CCHP systems operating with reciprocating engine prime mover have total costs of 5.6 and $2.9×10⁶ over useful life of 20 years, respectively, while both systems have the same capital recovery periods of 1.3 years. However, for the same prime mover and with current subsidized prices, CHP and CCHP systems require 4.9 and 5.2 years for capital recovery, respectively. It is concluded that the current energy price policies hinder the promotion of installing CHP and CCHP systems and, the policy of selling electricity to utility as well as eliminating subsidies are prerequisites to successful widespread utilization of such systems.     

A review on energy,economical, and environmental benefits of the use of CHP systems for small commercial buildings for the North American climate

The use of combined heating and power (CHP) systems to produce both electricity and heat is increasing rapidly due to their high potential of reducing primary energy consumption (PEC), cost, and emissions in domestic, commercial, and industrial applications. In addition to producing both electricity and heat, CHP systems can be coupled with vapor compression systems to provide cooling. This paper analyzes a natural gas engine CHP system together with a vapor compression system for different American climate zones. Performance is measured in terms of operational costs, PEC, and carbon dioxide emissions as a percent of a reference building. The objective of this paper is to compare the performance of a CHP system operating 24 h a day with a system that only operates during typical office hours. Furthermore, the system is optimized based on reducing PEC, minimizing costs, and reducing emissions. In addition, the benefits of CHP systems based on the Energy Star program and the Leadership in Energy and Environmental Design (LEED) program are presented. Results show that, in general, it is more beneficial to operate the CHP system during typical office hours than to operate the system 24 h a day. Also, the CHP system performance strongly depends on the location where it is installed. In addition to reductions in cost, primary energy, and emissions, CHP systems can help achieve the Energy Star label for commercial office buildings and help obtain LEED points that go toward achieving LEED certification status. Copyright © 2009 John Wiley & Sons, Ltd.     

Power and cogeneration technology environomic performance typification in the context of CO2 abatement part II: Combined heat and power cogeneration

This is the second of a series of two articles, dealing with a new approach of environomic (thermodynamic, economic and environmental) performance ‘Typification’ and optimization of power generation technologies. This part treats specifically of combined heat and power (CHP) cogeneration technologies in the context of CO₂ abatement and provides a methodology for a flexible and fast project based CHP system design evaluation. One of the aspect of the approach is the post-optimization integration of the operating and capital costs, in order to effectively deal with the uncertainty of the project specific design and operation conditions (fuel, electricity and heat selling prices, project financial conditions such as investment amortization periods, annual operating hours, etc). In addition the approach also allows to efficiently evaluate the influence of the external cost such as the CO₂ tax level under a tax scheme or the CO₂ permit price in the emission trading market.     

分布式冷热电联供能源系统与经济发展的关系

“十二五”期间中国15.7万亿元的增量经济大部分将在新规划的新区实现,但从各地正在规划和建设的新区情况来看,缺少从一次能源到终端需求的冷、热、电、汽全过程高效联供的分布式供能规划.据推算,若“十二五”期间新区能效不变,工业和建筑物燃料需求将增加3×108t标煤/a,而这显然是不可能的.新规划区域能源模式创新、提高能效是“十二五”中国经济发展的关键,采用天然气分布式冷热电联供能源系统(DES/CCHP),可使能源终端供应能效成倍提高.“十二五”期间中国必须从区域经济发展的能源保障高度来规划分布式冷热电联供,规划决策中要按照具体情况,以经济性、能效和碳排放指标是否最优为判据.CCHP可以调峰换取电价,实现互利双赢.制订区域DES/CCHP规划时应注意区域能源规划先行,摆脱热电联产的思维定势,树立冷热电联供的科学理念,不可忽视向居民供应生活热水起到的提高能效的作用,以及如何确定电力负荷、装机容量和节能减排指标等问题.     

Combined cooling heat and power in supermarkets

With recent initiatives from the UK government on reduced energy use, energy efficient systems such as combined heat and power (CHP) have been considered for new applications, including supermarkets. In these commercial buildings, the seasonal demand for heat results in underutilisation of the CHP equipment, limiting the primary energy savings that may be achieved. To increase the utilisation time, it has been proposed that heat generated by the CHP unit could be used to power an absorption refrigeration system providing cooling for the refrigerated cabinets. The application of an integrated CHP/absorption scheme or combined cooling heat and power (CCHP) in the supermarket is the subject of this paper.The paper initially describes the cooling/heating/power requirements of a typical supermarket and then reviews a number of CCHP options involving the use of different cooling and engine technologies. The investigation calculates and compares the energy savings/capital costs of the different options against typical conventional supermarket technology.     

Influence of supply and return water temperatures on the energy consumption of a district cooling system

In a district heating and cooling system, for example, the Beijing combined heating, cooling and power (CHCP) system studied here, high temperature water generated by cogeneration plants circulates through a network between the plants and the heating substations. In heating substations, high temperature supply water from the network drives absorption chillers for air-conditioning in the summer, satisfies space heating demands in the winter and provides domestic hot water using heat exchangers throughout the year. This paper studies the significant effect of the parameters, i.e. the supply and return water temperatures in the network, on the CHCP system energy consumption for cooling and for domestic hot water.     

Economic and environmental assessment of phosphoric acid fuel cell-based combined heat and power system for an apartment complex

Economic and environmental potential of medium-scale combined heat and power (CHP) systems in the residential sector was assessed by introducing a 400 kW_el-scale phosphoric acid fuel cell (PAFC)-based CHP system into an apartment building in New York City. Simulation-based analyses were carried out under two different CHP operation strategies; electrical-load-following (ELF) and thermal-load-following (TLF). Technical and economic analyses indicated that ELF would be the appropriate operation mode for this CHP application. Economic analysis indicated that the CHP/ELF system operation could economically benefit users within 10 years under the present grid prices in New York City. However, because the CO₂ emission factor of the NY grid is very low (300 g/kWh), the CHP/ELF system operation would increase CO₂ emission. Achieving carbon neutrality in this application thus requires improvement in the utilization ratio of recovered heat.     

Potential of biomass‐fired combined heat and power plants considering the spatial distribution of biomass supply and heat demand

Combined heat and power (CHP) plants fired by forest wood can significantly contribute to attaining the target of increasing the share of renewable energy production. However, the spatial distribution of biomass supply and of heat demand limits the potentials of CHP production. This article assesses CHP potentials using a mixed integer programming model that optimizes locations of bioenergy plants. Investment costs of district heating infrastructure are modeled as a function of heat demand densities, which can differ substantially. Gasification of biomass in a combined cycle process is assumed as production technology. Some model parameters have a broad range according to a literature review. Monte‐Carlo simulations have therefore been performed to account for model parameter uncertainty in our analysis. The model is applied to assess CHP potentials in Austria. Optimal locations of plants are clustered around big cities in the east of the country. At current power prices, biomass‐based CHP production allows producing around 3% of the total energy demand in Austria. Yet, the heat utilization decreases when CHP production increases due to limited heat demand that is suitable for district heating. Production potentials are most sensitive to biomass costs and power prices. Copyright © 2009 John Wiley & Sons, Ltd.     

Methodology to estimate the economic,emissions, and energy benefits from combined heat and power systems based on system component efficiencies

This paper presents a methodology to estimate the economic, emissions, and energy benefits that could be obtained from a base loaded CHP system using screening parameters and system component efficiencies. On the basis of the location of the system and the facility power to heat ratio, the power that must be supplied by a base loaded CHP system in order to potentially achieve cost, emissions, or primary energy savings can be estimated. A base loaded CHP system is analyzed in nine US cities in different climate zones, which differ in both the local electricity generation fuel mix and local electricity prices. Its potential to produce economic, emissions, and energy savings is quantified on the basis of the minimum fraction of the useful heat to the heat recovered by the CHP system (φ_min). The values for φ_min are determined for each location in terms of cost, emissions, and energy. Results indicate that in terms of cost, four of the nine evaluated cities (Houston, San Francisco, Boulder, and Duluth) do not need to use any of the heat recovered by the CHP system to potentially generate cost savings. On the other hand, in cities such as Seattle, around 86% of the recovered heat needs to be used to potentially provide cost savings. In terms of emissions, only Chicago, Boulder, and Duluth are able to reduce emissions without using any of the recovered heat. In terms of primary energy consumption, only Chicago and Duluth do not require the use of any of the recovered heat to yield primary energy savings. For the rest of the evaluated cities, some of the recovered heat must be used in order to reduce the primary energy consumption with respect to the reference case. In addition, the effect of the efficiency of the power generation unit and the facility power to heat ratio on the potential of the CHP system to reduce cost, emissions, and primary energy is investigated, and a graphical method is presented for examining the trade‐offs between power to heat ratio, base loading fraction, percentage of recovered heat used, and minimum ratios for cost, emissions, and primary energy. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of combined heat-and-power and absorption cooling in a supermarket

In recent years, it has become standard practice to consider Combined Heat-and-Power (CHP) systems for commercial buildings. CHP schemes are used, because they are an efficient means of power generation. Unlike conventional power stations, they produce electricity locally and thus minimise the distribution losses, however, they also utilise the waste heat from the generation process. In applications where there is a combined heating and electricity requirement, a very efficient means of energy production is achieved compared to the conventional methods of providing heating and electricity. With new initiatives from the UK government on reduced energy-use, energy-efficient systems such as CHP have been considered for new applications. This paper summarises the results of an investigation into the viability of CHP systems in supermarkets. The viability of conventional CHP has been theoretically investigated using a mathematical model of a typical supermarket. This has demonstrated that a conventional CHP system may be practically applied. It has also been shown that compared to the traditional supermarket design, the proposed CHP system will use slightly less primary energy and the running costs will be significantly reduced. An attractive payback period of approximately 4 years has been calculated. Despite these advantages a considerable quantity of heat is rejected to atmosphere with this system and this is because the configuration utilises the heat mainly for space heating which is only required for part of the year. To increase the utilisation time, a novel CHP/absorption system has been investigated. This configuration provides a continuous demand for the waste heat, which is used to drive an absorption chiller that refrigerates propylene glycol to −10°C for cooling the chilled-food cabinets. The results show this concept to be theoretically practical. The system has also been shown to be extremely efficient, with primary energy savings of approximately 20%, when compared to traditional supermarket designs and this would result in significant revenue cost savings as well as environmental benefits. Based upon these savings a payback period for this system of approximately 5 years has been demonstrated.     

Comparison between externally fired gas turbine and gasifier-gas turbine system for the olive oil industry

The olive oil industry generates during the extraction process several solid wastes as olive tree leaves and prunings, exhausted pomace and olive pits. These renewable wastes could be used for power and heat applications. The aim of this paper is to compare the performance of two small-scale CHP systems: a gasification- gas turbine system and an EFGT (externally fired gas turbine system). For this reason, several parameters have been calculated: generated heat and power, electric and overall efficiencies, biomass consumption, exergy efficiency, optimum pressure ratio, etc. These systems provide 30 kW_e and about 60kW_th. Simulation results show that the electrical and overall efficiencies achieved in EFGT system (19.1% and 59.3%, respectively) are significantly higher than those obtained in the gasification plant (12.3% and 45.4%). The proposed CHP systems have been modeled using Cycle-Tempo^® software.     

Exergy analysis and optimization of a biomass gasification, solid oxide fuel cell and micro gas turbine hybrid system

A hybrid plant producing combined heat and power (CHP) from biomass by use of a two-stage gasification concept, solid oxide fuel cells (SOFC) and a micro gas turbine was considered for optimization. The hybrid plant represents a sustainable and efficient alternative to conventional decentralized CHP plants. A clean product gas was produced by the demonstrated two-stage gasifier, thus only simple gas conditioning was necessary prior to the SOFC stack. The plant was investigated by thermodynamic modeling combining zero-dimensional component models into complete system-level models. Energy and exergy analyses were applied. Focus in this optimization study was heat management, and the optimization efforts resulted in a substantial gain of approximately 6% in the electrical efficiency of the plant. The optimized hybrid plant produced approximately 290 kW_e at an electrical efficiency of 58.2% based on lower heating value (LHV).