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.     

超市热电联供系统余热利用及热电冷联供系统研究

通过建立数学模型对热电冷联供系统在超市中应用的可行性进行了分析。利用该模型对系统的节能效果、投资回收期、发动机组容量、等效满负荷运行时间等特性参数进行了研究，并对不同控制方式对系统性能的影响进行了讨论，为超市热电冷联供系统的方案优化提供了依据。     

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.     

从燃煤热电联产到天然气冷热电联供——中国工业和建筑物从一次能源到终端利用模式的战略转型

燃煤热电联产(CHP)与天然气冷热电联供(DES/CCHP)是非常重要的能源系统技术。CHP着眼于一次能源转换效率的提高,但能采用CHP的工业有限,而建筑物用能中也只有冷季节的供暖,加之碳减排的压力,进一步压缩了燃煤CHP的发展空间。天然气的快速发展和科技进步催生了DES/CCHP技术,它以"高能高用、低能低用,温度对口、梯级利用"理论指导能源领域全过程的系统优化、能效提高,目标是高能效、经济性和碳减排。中国发展燃煤CHP和天然气CCHP都比世界迟了几十年,燃煤CHP仍将继续发挥作用,而加快发展天然气CCHP无疑更为重要。"十二五"期间新增GDP的相当大一部分是在新开发的工业园区和新城区,如果新区新增1200×108m3/a天然气用量,把发电和供冷、热、汽集成在一起,建设几百个百兆瓦级的区域型DES/CCHP,就能替代3×108t标煤/a,可比传统利用途径多替代约1×108t标煤/a。如何付诸实现,首先必须转变观念,要从能源全局和战略高度规划天然气CCHP;其次有关部门应尽快把提高能效、碳减排和碳排放份额指标分解落实到位;还要制定各种政策、法规给予支持。     

某热电厂实施冷热电联产的节能分析

通过对热电联产冷分产及冷热电联产能源消耗的计算分析比较,进一步论述在热电厂热电联产基础上发展冷热电联产的可行性和合理性,结合实例说明发展冷热电联产所产生的经济性、节能性和环保性,并为其他热电厂的节能改造提出建议,     

Assessment of the greenhouse gas emissions from cogeneration and trigeneration systems. Part I: Models and indicators

The diffusion of cogeneration and trigeneration plants as local generation sources could bring significant energy saving and emission reduction of various types of pollutants with respect to the separate production of electricity, heat and cooling power. The advantages in terms of primary energy saving are well established. However, the potential of combined heat and power (CHP) and combined cooling heat and power (CCHP) systems for reducing the emission of hazardous greenhouse gases (GHG) needs to be further investigated. This paper presents and discusses a novel approach, based upon an original indicator called trigeneration CO₂emission reduction (TCO₂ER), to assess the emission reduction of CO₂ and other GHGs from CHP and CCHP systems with respect to the separate production. The indicator is defined in function of the performance characteristics of the CHP and CCHP systems, represented with black-box models, and of the GHG emission characteristics from conventional sources. The effectiveness of the proposed approach is shown in the companion paper (Part II: Analysis techniques and application cases) with application to various cogeneration and trigeneration solutions.     

A linear programming optimization model for optimal operation strategy design and sizing of the CCHP systems

Combined cooling, heat, and power (CCHP) system offers numerous potential advantages for the supply of energy to residential buildings in the sense of improved energy efficiency and reduced environmental burdens. To realize the potential for being more beneficial, however, such systems must reduce total costs relative to conventional systems. In this study, a linear programming optimization model was presented for optimum planning and sizing of CCHP systems. The purpose of the model is to give the design of the CCHP system by considering electrical chiller and absorption chiller simultaneously in economic viewpoint. A numerical study was conducted in Tehran to evaluate the CCHP system model. The linear programming (LP) model determines the optimal sizes of the CCHP equipment by considering capital cost of the system. It showed that by considering electricity buyback, the optimum size of the electrical chiller decrease and the optimum size of the combined heat and power (CHP) unit and the absorption chiller increase dramatically with respect to without electricity buyback. Also, the LP model determines the optimal operation strategy of the system by neglecting capital cost. The optimally operated CCHP system encompassing electrical and absorption chiller could result in an 18% decrease in operating cost when compared to a CHP system encompassing electrical chiller only. Without electricity buyback, the profitability of CCHP was 23%, while with electricity buyback, profitability became 39%. Furthermore, a sensitivity analysis was conducted to show how the important parameters affect the entire system performance.     

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.     

内燃机冷热电联产系统设计点性能分析

简介内燃机冷热电联产系统的发展现状,总结了发电用内燃机在设计点工况下主要参数的现有分布范围:排气温度约为450~600℃,排气流量基本上与额定功率呈线性关系,发电效率一般在33%~45%。对联产系统不同形式的能量输出、联产系统经济效率等进行分析研究,表明联产系统回收的能量主要来自排气和冷却水,排气回收能量一般高于冷却水回收能量。与热电联产系统相比,由于制冷比供热困难,冷热电联产系统的经济效率较高。     

Multiple effects of energy storage units on combined cooling,heating and power (CCHP) systems

Albeit numerous studies discussing manifold issues of combined cooling, heating and power (CCHP) systems, there is still lack of theoretical studies indicating to what extent the energy mismatch and the deviating working conditions affect the CCHP performance, absence of reports systematically summarizing the multiple effects of energy saving units (ESUs), and deficiency of research quantifying the benefits from ESUs to energy savings. The shortage of such studies will confuse some CCHP designers when a CCHP system is designed. Therefore, in this research, theoretical discussions have been undertaken about the energy mismatch issue between CCHP systems and their users as well as the multiple effects of ESUs on CCHP systems. An improved calculational method of energy storage rate (ESR) has been adopted to evaluate the energy savings performance of CCHP systems. Two general heat‐to‐electricity ratios (R_user for CCHP users and R_CCHP for CCHP systems) have been used to quantify the energy mismatch between CCHP systems and their users. In the regime of ‘priority of providing cooling’, the ESR reaches its maximum when R_user is equal to R_CCHP. Otherwise, the ESR tends to decrease rapidly, especially when the electrical demand must be supplemented from the grid. Furthermore, when the CCHP system produces more electricity than required, the payment mode of extra electricity from the CCHP system will significantly affect the ESR. Therefore, it is imperative to reach an international consensus regarding the dispose of extra CCHP products. The theoretical analyses also corroborate the advantages of incorporating an ESU into a CCHP system. The ESU enables the CCHP system components to operate at their optimal working conditions. Meanwhile, the power generation unit and the absorption refrigerator capacities can then be reduced. Moreover, the ESU also promotes the productivity of electricity and ensures an undiminished ESR regardless of what extra electricity payment mode is adopted. Copyright © 2016 John Wiley & Sons, Ltd.     

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

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

Evaluation of CCHP systems performance based on operational cost, primary energy consumption, and carbon dioxide emission by utilizing an optimal operation scheme

Optimization of combined cooling, heating, and power (CCHP) systems operation commonly focuses only on energy cost. Different algorithms have been developed to attain optimal utilization of CCHP units by minimizing the energy cost in CCHP systems operation. However, other outcomes resulting from CCHP operation such as primary energy consumption and emission of pollutants should also be considered during CCHP systems evaluation as one would expect these outcomes can be subject to regulation. This paper presents an optimization of the operation of CCHP systems for different climate conditions based on operational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE) using an optimal energy dispatch algorithm. The results for the selected cities demonstrate that in general there is not a common trend among the three optimization modes presented in this paper since optimizing one parameter may reduce or increase the other two parameters. The only cities that show reduction of PEC while also reducing the CDE are Columbus, MS; Minneapolis, MN; and Miami, FL. For these cities the operational cost always increases when compared to the reference case consisting of using a vapor/compression cycle for cooling and natural gas for heating. On the other hand, for San Francisco and Boston, CCHP systems increase the CDE. In general, if CCHP systems increase the cost of operation, as long as energy savings and reduction of emissions are guaranteed, the implementation of these systems should be considered.     

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.     

Analysis of combined cooling,heating, and power systems based on source primary energy consumption

Combined cooling, heating, and power (CCHP) is a cogeneration technology that integrates an absorption chiller to produce cooling, which is sometimes referred to as trigeneration. For building applications, CCHP systems have the advantage to maintain high overall energy efficiency throughout the year. Design and operation of CCHP systems must consider the type and quality of the energy being consumed. Type and magnitude of the on-site energy consumed by a building having separated heating and cooling systems is different than a building having CCHP. Therefore, building energy consumption must be compared using the same reference which is usually the primary energy measured at the source. Site-to-source energy conversion factors can be used to estimate the equivalent source energy from site energy consumption. However, building energy consumption depends on multiple parameters. In this study, mathematical relations are derived to define conditions a CCHP system should operate in order to guarantee primary energy savings.     

European perspective on absorption cooling in a combined heat and power system – A case study of energy utility and industries in Sweden

Mankind is facing an escalating threat of global warming and there is increasing evidence that this is due to human activity and increased emissions of carbon dioxide. Converting from vapour compression chillers to absorption chillers in a combined heat and power (CHP) system is a measure towards sustainability as electricity consumption is replaced with electricity generation. This electricity produced in Swedish CHP-system will substitute marginally produced electricity and as result lower global emissions of carbon dioxide. The use of absorption chillers is limited in Sweden but the conditions are in fact most favourable. Rising demand of cooling and increasing electricity prices in combination with a surplus of heat during the summer in CHP system makes heat driven cooling extremely interesting in Sweden. In this paper we analyse the most cost-effective technology for cooling by comparing vapour compression chillers with heat driven absorption cooling for a local energy utility with a district cooling network and for industries in a Swedish municipality with CHP. Whilst this case is necessarily local in scope, the results have global relevance showing that when considering higher European electricity prices, and when natural gas is introduced, absorption cooling is the most cost-effective solution for both industries and for the energy supplier. This will result in a resource effective energy system with a possibility to reduce global emissions of CO₂ with 80%, a 300% lower system cost, and a 170% reduction of the cost of producing cooling due to revenues from electricity production. The results also show that, with these prerequisites, a decrease in COP of the absorption chillers will not have a negative impact on the cost-effectiveness of the system, due to increased electricity production.     

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.     

Energy,exergy and thermoeconomic analysis of a combined cooling,heating and power (CCHP) system with gas turbine prime mover

In this paper energy, exergy and thermoeconomic analysis of a combined cooling, heating and power (CCHP) system has been performed. Applying the first and second laws of thermodynamics and economic analysis, simultaneously, has made a powerful tool for the analysis of energy systems such as CCHP systems. The system integrates air compressor, combustion chamber, gas turbine, dual pressure heat recovery steam generator (HRSG) and absorption chiller to produce cooling, heating and power. In fact, the first and second laws of thermodynamics are combined with thermoeconomic approaches. Next, computational analysis is performed to investigate the effects of below items on the fuel consumption, values of cooling, heating and net power output, the first and second laws efficiencies, exergy destruction in each of the components and total cost of the system. These items include the following: air compressor pressure ratio, turbine inlet temperature, pinch temperatures in dual pressure HRSG, pressure of steam that enters the generator of absorption chiller and process steam pressure. Decision makers may find the methodology explained in this paper very useful for comparison and selection of CCHP systems. Copyright © 2010 John Wiley & Sons, Ltd.     

冷热电三联供系统的优化研究

冷热电联供系统主要应用于大型集中性供能系统中。作为分布式能源的一种,冷热电联供系统具有节约能源、改善环境、提高电力综合效益的优势。一般情况下,三联供系统是以天然气为燃料带动燃气轮机、微燃机或内燃机发电机等燃气发电设备运行,产生的电力供应用户的电力需求,系统发电后排出的余热通过余热回收利用设备(余热锅炉或者余热直燃机等)向用户供热、供冷。通过这种方式提高整个系统的一次能源利用率,实现能源的梯级利用,还可以提供并网电力作能源互补,经济收益和效率均得以提升。研究较为常见的燃气轮机中的一种蒸汽型吸收式冷热电联产系统,对不同配置方式和运行方式进行横向与纵向交叉比较,以完成系统优化研究。     

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.     

System analysis in a European perspective of new industrial cooling supply in a CHP system

In the municipality of Södertälje two large industries use much of the electricity, district heating (DH) and chilled water in the area. The Södertälje energy system is not isolated, however, but is connected to the DH systems of southern and central Stockholm, and a change in the Södertälje energy system will also influence the connected energy systems in Stockholm. The cooling demand in Södertälje is currently covered by lake water cooling and compression chillers, but in order to reduce the use of electricity, conversion to absorption cooling or increased lake water cooling can be considered. The large combined heat and power (CHP) plant in Södertälje is not used to its full potential today, but investment in absorption cooling and/or a cold condenser unit integrated with the CHP plant could increase the plant’s operation hours. In this paper the system effects of introducing new industrial cooling supply in Södertälje has been investigated through optimizations of a model including both the industries and the district heating supply in Södertälje and Stockholm. The results show that, independently of whether condensing power production is feasible in the CHP plant or not, investments in both increased lake water cooling and absorption cooling are profitable. A sensitivity analysis of how energy market prices affect the results shows that even though the system cost will change depending on energy market prices, the optimum cooling technology mix will remain the same. However, a sensitivity analysis of the transfer DH capacity between the Södertälje and Stockholm energy systems shows that if the transfer DH capacity is increased, absorption cooling will be less profitable since more heat can be sold from Södertälje to Stockholm while at the same time reducing the use of fuel resources.