mnogu vazno - 2006-combined%20cooling,%20heating%20and%20power-%20a%20review.pdf

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Progress in Energy and Combustion Science 32 (2006) 459–495

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Combined cooling, heating and power: A review

D.W. Wu, R.Z. Wang�

Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai 200240, China

Received 25 July 2005; accepted 28 February 2006

Available online 21 August 2006

Abstract

Combined cooling, heating and power (CCHP) systems, including various technologies, provide an alternative

for the world to meet and solve energy-related problems, such as energy shortages, energy supply security,

emission control, the economy and conservation of energy, etc. In the first part of this paper, the definition and

benefits of CCHP systems are clarified; then the characteristics of CCHP technologies—especially technical

performances—are presented, as well as the status of utilization and developments. In the third part, diverse

CCHP configurations of existing technologies are presented, particularly four typical systems of various size ranges.

The worldwide status quo of CCHP development is briefly introduced by dividing the world into four main

sections: the US, Europe, Asia and the Pacific and rest of the world. It is concluded that, within decades, promising CCHP

technologies can flourish with the cooperative efforts of governments, energy-related enterprises and professional

associations.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Combined cooling, heating and power; Technologies; Developments worldwide

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460

2. Status and developments of CCHP technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464

2.1. Prime movers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464

2.1.1. Steam turbines [1,18,19] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464

2.1.2. Reciprocating internal combustion engines [1,6,7,18,20–22]. . . . . . . . . . . . . . . . . . . . . . . . . . . 464

2.1.3. Combustion turbines [1,6,18,21–24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464

2.1.4. Micro-turbines [1,6,7,15,18,20,24,25]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465

2.1.5. Stirling engines [1,6,18,20] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465

2.1.6. Fuel cells [1,6,7,15,18,20,22,24,26,27] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465

2.2. Thermally activated technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467

2.2.1. Absorption chillers [13,22,28–31] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467

2.2.2. Adsorption chillers [32–38] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469

2.2.3. Desiccant dehumidifiers [3,13,31] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

2.2.4. Other options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

e front matter r 2006 Elsevier Ltd. All rights reserved.

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ing author. Tel.: +8621 34206776; fax: +86 21 34206056.

ess: [email protected] (R.Z. Wang).

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ARTICLE IN PRESSD.W. Wu, R.Z. Wang / Progress in Energy and Combustion Science 32 (2006) 459–495460

3. Typical CCHP systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473

3.1. Diverse configurations of CCHP systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473

3.2. Representative CCHP systems in use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

1Most liter

CCHP. In fac

count these s

only take a sm

these system

CCHP in mo

3.2.1. Micro systems (under 20 kW). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

3.2.2. Small-scale systems (20 kW–1MW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478

3.2.3. Medium systems (1–10MW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478

3.2.4. Large-scale systems (above 10MW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

4. Development of CCHP around the world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481

4.1. United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481

4.2. Europe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483

4.2.1. Austria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

4.2.2. Denmark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

4.2.3. Finland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

4.2.4. The Netherlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

4.2.5. France . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

4.2.6. Germany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

4.2.7. Hungary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

4.2.8. Italy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

4.2.9. Poland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

4.2.10. Spain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

4.2.11. Sweden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

4.2.12. UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486

4.3. Asia and the Pacific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486

4.3.1. China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486

4.3.2. Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

4.3.3. India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

4.3.4. Association of South East Asian Nations (ASEAN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490

4.4. Other countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491

5. Discussions and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493

1. Introduction

Combined cooling, heating and power (CCHP), isderived from combined heat and power (CHP, alsocalled cogeneration1)—a proven and reliable technol-ogy with a history of more than 100 years, which wasutilized mainly in large-scale centralized power plantsand industrial applications. The conventional way toprovide electricity and heat is to purchase electricityfrom the local grid and generate heat by burning fuel ina boiler. But in a CHP system, by-product heat, whichcan be as much as 60–80% of total primary energy incombustion-based electricity generation, is recycled fordifferent uses. Typically, CHP is defined as thecombined production of electrical (or mechanical),

ature lists statistics of CHP/cogeneration instead of

t, data of CHP/cogeneration with cooling options

tatistics in most cases, though these applications

all fraction of the gross. For a better description of

s, the term CHP/cogeneration is substituted by

st part of this article.

and useful thermal energy from the same primaryenergy source [1]. A slight difference between CCHPand CHP is that thermal or electrical/mechanicalenergy is further utilized to provide space or processcooling capacity in a CCHP application. In someliterature, CCHP systems are also referred to as tri-generation and building cooling heating and power(BCHP) systems [2–4]. CCHP can be defined as a moreextensive concept than CHP is. In winter, many CCHPsystems can be seen as CHP units, when there is nocooling demand of building air-conditioning. In otherwords, CHP system is CCHP without any thermallyactivated equipments for generating cooling power,though this difference will change the structure ofsystems to some extent.

In general, recent development of CCHP systemsis related to the emergence of DER2 (distributed/

2Other similar abbreviations in the literature are DP (dis-

tributed/decentralized power) and DG (distributed generation/

decentralized generation), which is slightly different from DER.

ARTICLE IN PRESS

Fig. 1. Categories of CCHP and DER.

Nomenclature

Tri-generation

CCHP combined cooling heating and power

Cogeneration

CHP combined heating and power

BCHP building cooling heating and powerDER distributed/decentralized energy

resourcesDP distributed/decentralized powerDG distributed generation/ decentralized

generation

D.W. Wu, R.Z. Wang / Progress in Energy and Combustion Science 32 (2006) 459–495 461

decentralized energy resources)—a novel technicalconcept in energy supply. DER is defined as anelectricity-generation system located in or near userfacilities, which provides electrical and thermal energysimultaneously to meet local users in top-priority.Certain factors, such as various rated capacities,ownership of systems, technologies employed and typesof connection with utility grids, are not critical in aconsensus definition of DER. According to somereports, DER can be divided into two major sections[5,6]. The first section is high-efficiency CHP or CCHPsystems in industry and buildings throughout theworld, using prime mover technologies as reciprocatingengines, gas turbines, micro-turbines, steam turbines,Stirling engines and fuel cells. The second major area ofDER is on-site renewable energy systems with energyrecycling technologies, including photovoltaic andbiomass systems, on-site wind and water turbine gene-rators, plus systems powered by gas pressure reduction,exhaust heat from industrial processes, and other low-energy content combustibles from various processes.

Due to the relationship between traditional CHPand novel DER (Fig. 1), CCHP systems areclassified into two categories:

1.

3

use

con

suc

deh

Traditional large-scale CCHP applications (pre-dominantly CHP systems without cooling op-tions) in centralized power plants or largeindustries;

2.
Relatively small capacity distributed CCHP unitswith advanced prime mover and thermallyactivated technologies3 to meet multiple energydemands in commercial, institutional, residentialand small industrial sections.
Thermally activated technologies: technologies that are able to

waste heat as a fuel and offer the chance to replace electric air

ditioning and/or dehumidification loads with thermal loads,

h as absorption chiller, adsorption chiller and desiccant

umidifiers.

There is no clear borderline between two cate-gories. CCHP systems can cover a wide range ofcapacity from 1kW to 500MW. Most centralizedpower plants and industries applying cogenerationexceed 1MW. The capacity of distributed CCHPsystems ranges from less than 1 kW in domesticdwellings to more than 10MW in hospitals oruniversity campuses, and as much as 300MW tosupply energy to a district of a city [7,8]. One reportdefines ‘‘everything under 1MW’’ as ‘‘small-scale’’.‘‘Mini’’ usage is under 500 kW and ‘‘micro’’ use isunder 20 kW’’ [9].

A typical CCHP system is showed in Fig. 2. It iscomprised of a gas engine, a generator and anabsorption chiller. The engine is driven by naturalgas and the mechanical energy is further changedinto electricity power by the generator. At the sametime, the absorption chiller to generate coolingpower in summer and heating power in winterutilizes exhaust gas and jacket water derived fromthe engine. If waste heat from engine is not enoughfor users, a combustor in absorption chiller canburn natural gas as a supplement. Thus, the energydemands of cooling, heating and electrical power ina building or a district can be met by this systemsimultaneously.

Compared with the energy supply mode of largecentralized power plant and local air-conditioning

ARTICLE IN PRESS

Fig. 2. Typical CCHP system.

Fig. 3. Energy flow of traditional supply mode.

Fig. 4. Energy flow of typical CCHP system.

D.W. Wu, R.Z. Wang / Progress in Energy and Combustion Science 32 (2006) 459–495462

system, distributed CCHP systems will receive moreattention, because—along with the developingtendency and promising prospects—they possesssome advantages, which traditional energy suppliesdo not share [1,9–13].

First, overall fuel energy utilization has dramati-cally improved, ranging from 70% to more than90% compared with 30–45% of typical centralizedpower plants. In general, less primary energy isneeded to obtain the same amount of electricity andthermal energy. In addition to the saving in primaryenergy, vast reductions in net fuel costs, transmis-sion and distribution savings can be achieved.

A theoretical calculation of prime energy utilizationbased on traditional energy supply mode and typicalCCHP system as Fig. 2 can be seen in Figs. 3 and 4. Ifend user needs 33 units of electrical power, 40 units ofcooling power and 15 units of heating power in asummer day, 148 units of prime energy are consumedin a traditional way. Centralized power plant runs atthe efficiency of 33% and 100 units of prime energyare used to generate 33 units of electrical power.Traditional boiler burns 18 units fuel to heat 15 unitsof domestic hot water at the efficiency of 85%.Electrical air-conditioner driven by 10 units ofelectrical power can generate 40 units of coolingpower at COP of 4. However, consider the efficiencyof electricity generation in power plant, 30 units ofprime energy is needed in all for space cooling.

Based on a typical CCHP system shown in Fig. 2,only 100 units of prime energy are needed for 33units of electrical power, 40 units of cooling powerand 15 units of heating power in a summer day. Theelectricity generation efficiency of CCHP system issimilar to centralized power plant, because electri-city is consumed locally without loss on distributionlines, though small-scale prime mover is less efficientthan large prime mover in power plant. Thekeystone of full energy utilization of CCHP systemlies on the recovery of waste heat from prime mover.

Thirty four units of waste heat in the form ofexhaust gas and machine coolant are used to drivean absorption chiller at COP of 1.2, thus 40 units ofcooling power can be obtained. And another 18units of waste heat can be recovered to heat 15 unitsdomestic water at the efficiency of 85% similar tothe efficiency of a boiler. Compared with traditional

ARTICLE IN PRESSD.W. Wu, R.Z. Wang / Progress in Energy and Combustion Science 32 (2006) 459–495 463

energy supply mode, CCHP system can save 48units of prime energy to meet the same demand ofcooling, heating and power.

The second benefit of distributed CCHP systemsis emission reduction; viewed from two aspects andsorted by different prime movers. Some primemovers with new technologies, like fuel cells andmicro-turbines exhaust much less emissions (includ-ing NOx, CO2), than do traditional technologiesfrom centralized power plants. Other prime movers,equipped in CCHP systems with smaller capacitythan their larger counterparts in centralized powerplants, emit somewhat more NOx and CO2 perkW electricity generated. Nevertheless, the pro-motion of energy efficiency—CCHP systems shouldbe encouraged at this time: burning significantlyless fuel to meet the same demand results insignificant emission reduction, which surely over-rides the additional emissions caused by the slightdecrease in converting efficiency in small-scaleprime movers.

Last, but of equal importance, CCHP systemsincrease the reliability of the energy supply network.Obviously, generation/distribution systems can mal-function: weather and terrorism are fatal threats tocentralized power plants. A smaller, more flexibleand dispersed system, CCHP might prevent thesethreats from becoming reality, and controlledrepercussions and fast recovery could be achievedif these situations occurred. A study following the11 September attacks suggested that a system basedmore on distributed generation plants may be fivetimes less sensitive to systematic attack than acentralized power system [14].

A typical CCHP system consists of five basicelements: the prime mover; electricity generator;heat recovery system; thermally activated equip-ment and the management and control system.According to current technologies, options in primemovers can be steam turbines, reciprocating internalcombustion engines, combustion turbines, micro-turbines, Stirling engines and fuel cells; the last threeprime movers are relatively new technologies devel-oped in last decade. Any of these options can beselected to meet diverse demands and limitationsfrom site-to-site, especially local heat and electricityprofiles, regional emissions and noise regulationsand installation restrictions. Thermally activatedequipment is another part of CCHP systems, toprovide cooling or dehumidification. Commercia-lized thermally activated technologies include ab-sorption chillers and desiccant dehumidifiers;

moreover, novel adsorption chillers—currently al-most entirely for commercial use—can be anotherchoice for small CCHP systems. Some existingsystems also apply electric chillers, or engine-drivenchillers integrated with prime movers, to fulfillcooling demands, which, combined with thermallyactivated technologies, are the cooling or dehumi-dification options of CCHP systems in some of theliterature.

Different prime movers, connecting with differentcooling or dehumidification options, can result invarious kinds of CCHP systems in theory, but onlyseveral modes of combination are widely adopted incommercial markets; other promising possibilitiesare being investigated to overcome technological oreconomic problems.

In the next two parts of this paper, brief reviewsof prime mover technologies, cooling and dehumi-dification options and various CCHP system modes,with four typical examples are presented insequence, to present a clear picture of currentCCHP technologies.

Although governments worldwide, experts, man-ufacturers and users have acknowledged that CCHPsystems are the current development trend in energysupply, the share of decentralized power generation(including CCHP systems) in the world marketremains at around 7%—unchanged between 2001and 2003 [14]. The distributed CCHP market of theUS grew significantly until 2002, but since then ithas slowed sharply in the face of high natural gasprices and persistent regulatory barriers. TheEuropean distributed CCHP market was flat in last4 years. Although some developing country marketsare beginning to emerge, including China, Braziland India, it is presumed that the boom in theseburgeoning markets will take much more time andeffort than markets in developed countries. Theobstacles come from every direction: technologyperformance, costs, policies, regulations and marketdemands. The year 2004 can be viewed as a turningpoint of low growth in CCHP market worldwide.A WADE survey, forecasts that growth will bereinforced by the probable introduction of theEuropean Union Emissions Trading Scheme inJanuary 2005, which is expected to further increasepower prices. In the fourth chapter of this paper, thestatus of CCHP system development worldwide ispresented; the world is divided into the US, Europe,Asia and the Pacific and other countries, for areview of existing or potential markets, and topresent a forecast and analysis.


2. Status and developments of CCHP technologies

CCHP technologies include components relatingto energy conversion, recovery and management.Among these technologies, prime movers obviouslyplay a critical role; they are the keystones of CCHPsystems and, to some extent, they determinepossibilities and availability of other related tech-nologies. As for the importance of thermal activatedoptions, these alternative technologies dramaticallyshift the energy utilization of energy conversionsystems compared to conventional electrical powersystems. Therefore, the following paragraphs focuson these two major aspects of CCHP systems,especially the advantages, drawbacks and develop-ing trends of these technologies.

2.1. Prime movers

There are several ways to classify prime movertechnologies, based on fuel used, technical maturity,market shares or capacity range. Although quite afew newly emerging technologies appear to bepromising, reciprocating internal combustion en-gines, steam turbines and combustion turbines thatcan be considered conventional prime movers stillmake up most of the gross capacity being installed[9,15]. In addition, fuel cells, Stirling engines andmicro-turbines, mainly gas driven, present a pro-mising future for prime movers [9,15–17]. Briefintroductions follow and major parameters andperformance of these prime movers can be refer-enced in Table 2, at the end of this section.

2.1.1. Steam turbines [1,18,19]

Steam turbines are the most common technologyused in power plants and industries. Dependingupon the exit pressure of the steam, steam turbinesfall into two types: backpressure turbines andcondensing turbines. Backpressure turbines operatewith an exit pressure at least equal to atmosphericpressure, and are suitable for some sites with asteam demand of intermediate pressure. Condensingturbines have the advantage of changing electricaland thermal power independently and they workwith an exit pressure lower than atmosphericpressure. In theory, steam turbines equipped witha suitable boiler can be run on any kind of fuel. As amature technology, steam turbines have an extre-mely long life and, with proper operating andmaintenance, are very reliable. However, severalproblems limit their further application, which

include low electrical efficiency, slow start-up time,and poor partial load performance. As a result,steam turbines are more popular in large centralplant utilities or industrial cogenerations than indistributed energy applications, although someclaims are made that future ‘‘plug and play’’turbines will operate with fractional kW outputs,wherever steam pressure is reduced [6].

2.1.2. Reciprocating internal combustion engines

[1,6,7,18,20– 22]

Two types of internal combustion engines arecurrently in use; spark ignition engines, which areoperated mainly with natural gas (although biogasor landfill gas can also be used); and compressionignition engines, which can use diesel fuel, as well asother petroleum products, such as heavy fuel oil orbiodiesel. Reciprocating engines are a proventechnology with a range of size and the lowest firstcapital costs of all CCHP systems. In addition tofast start-up capability and good operating relia-bility, high efficiency at partial load operation giveusers a flexible power source, allowing for a range ofdifferent energy applications—especially emergencyor standby power supplies. Reciprocating enginesare by far the most commonly used power genera-tion equipment under 1MW.

Although they are a mature technology, recipro-cating engines have obvious drawbacks. Relativelyhigh vibrations require shock absorption andshielding measures to reduce acoustic noise. A largenumber of moving parts, and frequent maintenanceintervals, increase maintenance costs, strongly off-setting fuel efficiency advantages. In addition, fullutilization of the various heat sources with diversetemperature levels in CCHP applications is difficult.Moreover, high emissions—particularly nitrogenoxides—are the underlying aspect of this technol-ogy, which need improvement. Major manufac-turers around the world continuously develop newengines with lower emissions; at the same time,emissions control options, such as selective catalyticreduction (SCR), have been utilized to reduceemissions.

2.1.3. Combustion turbines [1,6,18,21– 24]

Combustion turbines are frequently used primemovers in larger-scale cogenerations due to theirhigh reliability and large range of power. Setssmaller than 1MW have so far been generallyuneconomical because of their low electrical effi-ciency and consequent high cost per kWe output.


Combustion turbines are easier to install than steamturbines and they have the added benefit of beingless area intensive, with lower capital costs; main-tenance costs are slightly lower than reciprocatingengines, but so is their electrical efficiency. Emis-sions are somewhat lower than that of reciprocatingengines, and cost-effective NOx emissions-controltechnology is commercially available.

Combustion turbine exhaust—typically around540 1C—can be used to support the combustion ofadditional fuel. This technology is called supple-mentary firing, and it can raise the temperature ofexhaust gas more than 1000 1C and increase theamount of high-pressure steam produced. Usingproduced steam to power a steam turbine is knownas a combined-cycle gas turbine (CCGT), withhigher net electrical efficiency (35–55%), which isappropriate for public utility companies and in-dustrial plants.

The major disadvantages of combustion turbineare described below. Combustion turbines requirepremium fuels, especially natural gas, which histori-cally has high price volatility. The high tempera-tures involved lead to demanding standard ofmaterials with higher production costs. Addition-ally, turbine performance is significantly reduced athigher altitudes or during periods of high ambienttemperatures.

2.1.4. Micro-turbines [1,6,7,15,18,20,24,25]

Micro-turbines extend combustion turbine tech-nology to smaller scales. They are primarily fuelledwith natural gas, but they can also operate withdiesel, gasoline or other similar high-energy fuels.Research on biogas is ongoing. Micro-turbines haveonly one moving part; they use air bearings and theydo not need lubricating oil, although they haveextremely high rotational speed, up to 120,000 rpm.A striking characteristic is their flexibility thatsmall-scale individual units can be combined readilyinto large systems of multiple units. Additionally,there are environmental advantages, such as lowercombustion temperatures assuring low NOx emis-sions levels and less noise than an engine ofcomparable size.

This technology has been commercialized onlyrecently and is offered by a small number ofsuppliers. The main disadvantages at this stage areits short track record and high first costs comparedwith reciprocating engines. Other issues includerelatively low electrical efficiency and sensitivity ofefficiency to changes in ambient conditions.

Micro-turbines can be used as a distributedenergy resource for power producers and consu-mers, including industrial, institutional, commercialand even residential users of electricity in the future.Moreover, the heat produced by a micro-turbinecan be used to produce low-pressure steam or hotwater for on-site requirements.

2.1.5. Stirling engines [1,6,18,20]

Compared to conventional internal combustionengine, Stirling engine is an external combustiondevice. The cycle medium—generally helium orhydrogen—is not exchanged during each cycle, butwithin the device, while the energy driving the cycleis applied externally. Stirling engines can operate onalmost any fuel (gasoline, alcohol, natural gas orbutane), with external combustion that facilitatesthe control of the combustion process and results inlow air emissions, low noise and more efficientprocess. In addition, best in class machines fewermoving parts compared to conventional engineslimit wear on components and reduce vibrationlevels.

Stirling engine technology is still in its develop-ment; no statistical data on availability is thereforeavailable. High cost also prevents popularization ofthis technology. Nevertheless, the promising pro-spects of Stirling engines stimulate further research,especially for CCHP applications. Small size andquiet operation mean that they will integrate wellinto residential or portable applications. Someliterature indicates the possibility of using a solardish to heat the Stirling engine, thus potentiallyeliminating the need for combustion of a fuel.

2.1.6. Fuel cells [1,6,7,15,18,20,22,24,26,27]

Fuel cells are quiet, compact power generatorswithout moving parts, which use hydrogen andoxygen to make electricity and; at the same time,can provide heat for a wide range of applications. Ingeneral, fuel cells show high electrical efficienciesunder varying load and; thus, result in lowemissions. The transportation sector is the majorpotential market for fuel cells. Power generation,however, seems to be another promising market inwhich fuel cells could be quickly commercialized.Five major fuel cell technologies listed below havethe most attractive prospects. In reality, with theexception of PAFC, no fuel cells are yet completelycommercially viable; a total capacity of over 40MWPAFC having been installed worldwide. A detail

ARTICLE IN PRESS

Table 1

Characteristics of fuel cells [6,20,18,26]

PEMFC AFC PAFC MCFC SOFC

Charge carrier H+ ions OH� ions H+ ions CO3¼ ions O ¼ ions

Type of electrolyte Polymeric membrane Aqueous

potassium

hydroxide soaked

in a matrix

Phosphoric acid

solutions

Phosphoric acid

(immobilized

liquid)

Stabilized zirconia

ceramic matrix with

free oxide ions

Typical construction Plastic, metal or

carbon

Plastic, metal Carbon, porous

ceramics

High temp

metals, porous

ceramic

Ceramic, high temp

metals

Catalyst Platinum Platinum Platinum Nickel Parasites

Oxidant Air or O2 Purified air or O2 Air or O2-

enriched air

Air Air

Fuel Hydrocarbons or

methanol

Clean hydrogen

or hydrazine

Hydrocarbons or

alcohols

Clean hydrogen,

nature gas,

propane, diesel

Natural gas or

propane

Operational

temperature

50–100 1C 60–80 1C 100–200 1C 600–700 1C 600–1000 1C

Size range 3–250 kW 10–200kW 100–200kW 250 kW–5MW 1–10MW

Electrical efficiencya 30–50% 32–70% 40–55% 55–57% 50–60%

Primary

contaminants

CO, sulfur and NH3 CO, CO2 and

sulfur

CO41%, sulfur Sulfur Sulfur

aElectrical efficiencies are based on values for hydrogen fuel and do not include electricity required for hydrogen reforming.


comparison of the characteristics of these fuel cellsappears in Table 1.

2.1.6.1. Proton exchange membrane fuel cell

(PEMFC). PEMFCs are quite simple and can bemade very small to adjust to variable powerdemands. They are easier to start up and they applysolid electrolyte that reduces corrosion. At the sametime, the low operating temperature requires the useof an expensive platinum catalyst, and limitscogeneration potential. As for the fuel sources, thisfuel cell technology is highly sensitive to fuelimpurities and hydrogen storage; delivery andreforming technology has yet to evolve. PEMFCsappear to be the choice for automotive applications.The advantage of being small allows application forlaptops, mobile phones and other portable appli-ances. With relatively low-quality waste heat, thePEMFC is unlikely to be widely used for highvoltage stationary power generation; but small-scaledomestic CCHP applications—the simplest thermalload of which is hot water—would be considerable.

2.1.6.2. Alkaline fuel cell (AFC). AFCs were thefirst fuel cells used on spacecrafts and space shuttles.The technology has obvious merits, such as lowoperating temperature, rapid start-up time, readily

available non-precious metal electrodes, and highefficiency, up to 70%. However, the primarydisadvantage is the tendency to absorb carbondioxide, converting the alkaline electrolyte to anaqueous carbonate electrolyte that is less conduc-tive. Thus, the fuel input must be restricted to purehydrogen, which limits applications to those inwhich pure hydrogen are available. If the CO2 isremoved from fuel and oxygen streams, the operat-ing costs are much greater. Although the attractive-ness of AFC has declined substantially with thepursuit of improved PEMFC technology, recentdevelopers still believe that AFC can be used formany applications, such as stationary power gen-eration, and mobile applications including bothmarine and road vehicles.

2.1.6.3. Phosphoric acid fuel cell (PAFC). PAFCsare the most mature of the technologies incommercial production, although its costs remainuncompetitive with other non-fuel cell technologies.Hydrogen is still the ultimate fuel for the reaction inthe PAFC, but various fuels, including natural gas,LPG and methanol, can be used as raw inputconverted by a reformer. Other advantages areresistance to fuel impurities, and the ability to use aless expensive catalyst. The drawbacks of this fuel


cell include a lower efficiency than other fuel celltechnologies and corrosive liquid electrolyte. In2002, over 200 commercial units were manufac-tured, delivered and operated in the US, Europe andJapan. In the near future, with lower operatingtemperatures, PAFC would be ideal for small andmid-size power plants, replacing large electricalgenerators and other types of CCHP utilities inhospitals, hotels and airports.

2.1.6.4. Molten carbonate fuel cells (MCFC). AMCFC uses a molten carbonate salt mixture as itselectrolyte. The composition of the electrolytevaries, but usually consists of lithium carbo-nate and potassium carbonate, which is chemi-cally aggressive and puts strain on the stabilityand wear of the cell components. As a result,MCFC is more expensive than either SOFC orPEMFC in terms of capital cost. Fuel reforming ofMCFC occurs inside the stack and toleratesimpurities; therefore, this technology may use avariety of fuels. In addition, the high operatingtemperature allows for combined heat and powergeneration and high fuel-to-electricity efficiency.Nevertheless, the long start-up time to reachoperating temperatures, and poorer flexibility inoutput, make MCFC ideally suited to base loadpower generation where continuous operation isnecessary, such as heavy industries and nationalelectrical grid networks.

2.1.6.5. Solid oxide fuel cell (SOFC). Due to all-solid-state ceramic construction, SOFCs shareimportant characteristics, such as stability andreliability. A variety of hydrocarbon fuels can beused, like gasoline, methanol and natural gas. Asanother asset, the high operating temperaturemakes internal reforming possible and removesthe need for a catalyst, and also produces high-grade waste heat suited well to CCHP applications.But the high temperature also creates some diffi-culties: expensive alloys for components are re-quired, a very long time is needed for the electrolyteto heat and flexible small applications are diffi-cult. Start-up time is less of an issue for stationaryand continuous applications. SOFCs generallyachieve around 60% efficiency in an average5MW plant, compared to around 30% for atraditional gas turbine. The last critical problemthat prevents its commercialization is the compara-tively high costs of SOFC.

2.2. Thermally activated technologies

An important difference between CCHP systemsand conventional cogenerations is that CCHPsystems—including some cooling or dehumidifica-tion components—provide not only electricity andheating but also cooling capacity for space air-conditioning or process. These cooling or dehumi-dification options can employ advanced thermallyactivated technologies as well as traditional tech-nologies. But recent research indicates that ther-mally activated technologies are favored, as theoverall efficiency of CCHP systems is enhanced bytheir application. In addition to high primary fuelefficiency, other benefits such as low emissions andnet cost reduction are also achieved with thermallyactivated technologies (Table 2).

Major thermally activated technologies includeabsorption chillers, adsorption chillers and desic-cant dehumidifiers. These cooling and dehumidifi-cation systems can be driven by steam, hot water orhot exhaust gas derived from prime movers.However, waste heat from various prime moversfalls into different temperature ranges; at the sametime, cooling and dehumidification systems havetheir own suitable working temperature. As a result,best pairing of recoverable energy streams withthermally driven technologies is shown in Table 3.

2.2.1. Absorption chillers [13,22,28– 31]

Absorption chillers are one of the commercializedthermally activated technologies widely applied inexisting CCHP systems; they are similar to vaporcompression chillers, with a few key differences. Thebasic difference is that a vapor compression chilleruses a rotating device (electric motor, engine,combustion turbine or steam turbine), to raise thepressure of refrigerant vapors, while an absorptionchiller uses heat to compress the refrigerant vaporsto a high pressure. Therefore, this ‘‘thermalcompressor’’ has no moving parts.

Basic absorption cycle is illustrated in Fig. 5.After the evaporator of absorption chiller generatescooling power, vapor generated in the evaporator isabsorbed into a liquid absorbent in the absorber.The absorbent that has taken up refrigerant withspent or weak absorbent is pumped to the gen-erator. The refrigerant is released again as a vaporby waste heat from steam, hot water or hot exhaustgas, and vapor is to be condensed in the condenser.The regenerated or strong absorbent is then ledback to the absorber to pick up refrigerant vapor

ARTICLE IN PRESS

Table

2

Characteristics

andparametersofprimemoversin

CCHPsystem

s[1,6,11,15,16,18,20]

Steam

turbines

Dieselengines

Spark

ignition

engines

Combustion

turbines

Micro-turbines

Stirlingengines

Fuel

cells

Capacity

range

50kW–500MW

5kW–20MW

3kW–6MW

250kW

–50MW

15–300kW

1kW–1.5M

W5kW–2MW

Fuel

used

Any

Gas,propane,

distillate

oils,

biogas

Gas,biogas,

liquid

fuels,

propane

Gas,propane,

distillate

oils,

biogas

Gas,propane,

distillate

oils,

biogas

Any(gas,alcohol,

butane,

biogas)

Hydrogen

and

fuelscontaining

hydrocarbons

Efficiency

electrical

(%)

7–20

35–45

25–43

25–42

15–30

�40

37–60

Efficiency

overall(%

)60–80

65–90

70–92

65–87

60–85

65–85

85–90

Power

toheatratio

0.1–0.5

0.8–2.4

0.5–0.7

0.2–0.8

1.2–1.7

1.2–1.7

0.8–1.1

Outputheat

temperature

(1C)

Upto

540

aa

Upto

540

200–350b

60–200

260–370

Noise

Loud

Loud

Loud

Loud

Fair

Fair

Quiet

CO

2em

issions(kg/

MWh)

c650

500–620

580–680

720

672d

430–490

NO

xem

issions(kg/

MWh)

c10

0.2–1.0

0.3–0.5

0.1

0.23d

0.005–0.01

Availability(%

)90–95

95

95

96–98

98

N/A

90–95

Part

load

perform

ance

Poor

Good

Good

Fair

Fair

Good

Good

Lifecycle(year)

25–35

20

20

20

10

10

10–20

Averagecost

investm

ent($/kW)

1000–2000

340–1000

800–1600

450–950

900–1500

1300–2000

2500–3500

Operatingand

maintenancescosts($/

kWh)

0.004

0.0075–0.015

0.0075–0.015

0.0045–0.0105

0.01–0.02

N/A

0.007–0.05

aUpto

athirdofthefuel

energyisavailable

intheexhaust

attemperaturesfrom

370to

5401C;other

rejected

heatislow

temperature,often

toolow

formost

processes.(Jacket

coolingwaterat80–951C,lubeoilcoolingat701C

andintercoolerheatrejectionat601C,alldifficultto

use

inCHP.)

b6501C

withoutrecuperator.

cEmissionsassociatedwithasteam

turbineare

dependentonthesourceofthesteam.Steam

turbines

canbeusedwithaboiler

firinganyoneoracombinationofalargevarietyof

fuel

sources,orthey

canbeusedwithagasturbinein

acombined

cycleconfiguration.Boiler

emissionsvary

dependingonfuel

typeandenvironmentalconditions.

dStirlingengineem

issioncharacteristics

/STM

4–260.Gas-fireddistributedenergyresourcetechnologycharacterizations.


ARTICLE IN PRESS

Table 3

Recoverable energy qualities with matching technologies [28]

Power source Temp. (1C) Matching technology

Gas turbine �540 Triple-effect/ double-effect absorption

Solid oxide fuel cell �480 Triple-effect/ double-effect absorption

Micro-turbine �320 Triple-effect/ double-effect absorption

Phosphoric acid fuel cell �120 Double-effect/ single-effect absorption

Stirling engine �90 Single-effect absorption, adsorption or dehumidification

IC engine �80 Single-effect absorption, adsorption or dehumidification

PEM fuel cell �60 Single-effect absorption, adsorption or dehumidification

Fig. 5. A single-effect absorption refrigeration system [30].


anew. Heat is supplied to the generator at acomparatively high temperature and rejected fromthe absorber at a comparatively low level, analo-gously to a heat engine.

The most common working fluids for absorptionchillers are water/NH3 and LiBr/water, althoughthere are 40 refrigerant compounds and 200absorbent compounds available in the literature[30]. Lithium–bromide/water absorption chillersplay a predominant role in the absorption chillermarket in Asia-Pacific countries like China, Japan,Korea and in the US. In contrast, ammonia/waterabsorptions chillers are more popular in Europe.

Depending on how many times the heat supply isutilized within the chiller; absorption chillers can bedivided into single-effect, double-effect and triple-effect. A single-effect absorption refrigeration sys-tem is the simplest and most commonly used design.Fig. 5 shows a single-effect system using non-volatility absorbent such as LiBr/water. Whenvolatility absorbent such as water/NH3 is used, thesystem requires an extra component called ‘‘arectifier’’, which will purify the refrigerant beforeentering the condenser. The parameters and char-acteristics of different absorption chillers can beviewed in Table 4.

Absorption chillers can also be used in chilledwater storage systems to produce chilled waterduring off-peak electric load periods when the costof electricity is low and the demand for cooling islow. The stored chilled water is then drawn uponduring the peak cooling periods when electricitycosts are high, to supplement the chiller operation.The storage system helps to reduce the chillercapacity requirement and total installed cost ofchillers. The installed cost of absorption chillersvaries from 140 to 290US$/kW, with the decreaseof overall capacity. The O&M cost is in the range of4.5–9US$/kW/yr [31].

2.2.2. Adsorption chillers [32– 38]

Adsorption-cooling technology is a novel, envir-onmentally friendly and effective means of usinglow-grade heat sources. An adsorption refrigerationsystem is similar to vapor compression systemsexcept that heat—instead of work—provides theenergy needed for compression. Unlike conven-tional vapor compression systems which require amechanical compressor assembly, this new technol-ogy uses a thermally driven static sorption bed,saving as much as 90% of the required input powertypically used to drive a mechanical compressor.

The functioning of the basic cycle of adsorptioncooling can be presented as comprising four phasesas shown in the schematic Fig. 6 and described asfollow:

1.
A heating-pressurization 1–2, during which theadsorber is isolated from both the condenser andthe evaporator. The pressure inside the adsorberthen increases until reaching the condensationpressure, thanks to the heat supplied by anexternal heat source.
2.
An isobaric condensation 2–3, during which theadsorber is connected to the condenser, allowing

ARTICLE IN PRESS

Table

4

Characteristics

ofabsorptiontechnologies[30]

System

Operatingtemp.(1C)

Workingfluid

Cooling

capacity

(ton)

COP

Currentstatus

Rem

ark

Heatsource

Cooling

Single

effect

cycle

80–110

5–10

LiBr/water

10–1500

More

than0.7

Largewater

chiller

1.Sim

plest

andwidelyused

2.Usingwaterasarefrigerant,cooling

temperature

isabove01C

3.Negativesystem

pressure

4.Watercooledabsorber

required

toprevent

crystallizationathighconcentration

Single

effect

cycle

120–150

o0

Water/NH

33–1000+

0.5

Commercial

1.Rectificationofrefrigerantrequired

2.Workingsolutionisenvironmentalfriendly

3.Operatingpressure

ashighaswithNH

3

4.Nocrystallizationproblem

5.Suitable

foruse

asheatpumpdueto

wide

operatingrange

Double

effect

(series

flow)

120–150

5–10

LiBr/water

200–1500

More

than1.2

Largewater

chiller

1.Highperform

ance

cycle,

commercially

available

2.Heatofcondensationfrom

firsteffect

used

asheatinputforsecondstage

Double

effect

(parallel

flow)

120–150

o0

Water/NH

3Upto

1000

0.8–1.2

Experim

ental

unit

1.Heatrelease

from

firststageabsorber

used

forsecondstagegenerator

Triple

effect

cycle

200–230

5–10

LiBr/water

N/A

1.4–1.5

Computer

model

and

experim

ental

unit

1.Highcomplexitycontrolsystem

2.Likelyto

bedirect-fired,asinputtempis

veryhigh

3.Requires

more

maintenance

asaresultof

highcorrosiondueto

highoperating

temperature


ARTICLE IN PRESS

Fig. 6. Standard Clapeyron’s lnp-1/T diagram of basic cycle.

Fig. 7. Schematic of two-bed adsorption refrigeration systems

[37].


the refrigerant vapor to flow the adsorber to thecondenser and condenses therein as the heating isstill continuing. This simultaneity of heating andvapor flow and condensation makes the processisobaric. The condensation heat is absorbed bythe cooling medium or could be used to provideheating if the purpose of the system is heatpumping. The condensate is then expanded anddrained into evaporator at lower pressure.

3.
A cooling-depressurisation 3–4, during which theadsorber is isolated from both the condenser andthe evaporator. The adsorber is cooled down andthe pressure decreases back to the value ofadsorption condition.
4.
An isobaric adsorption, during which the ad-sorber is connected to the evaporator andisolated from condenser. The low-pressure liquidwater contained in the evaporator is evaporatedby extracting latent heat of evaporation from thespace when being cooled down, and, simulta-neously, the evaporated vapor is adsorbed anewby the reactivated adsorbent contained in theadsorber.
The system takes advantage of the ability ofcertain adsorbent material, stored in an adsorber, tosoak up a relatively large quantity of refrigerantvapor at some low temperature and pressure. At thisstage, cooling capacity is achieved in the evaporatorbecause of the evaporation of the refrigerant. Therefrigerant is subsequently released to the condenserat a higher pressure simply by applying heat to thesorption bed. The basic cycle is the cycle withoutneither heat nor mass recovery. When operated witha single bed, the cold production of this cycle isintermittent. One step forward in the path of

improvement of this cycle has been the inventionof the two beds quasi-continuous cooling produc-tion system, shown in Fig. 7. In addition to thequasi-continuity of the cold production, the systemoffers the possibility for heat recovery and massrecuperation from one bed to anther, therebyhelping to improve cycle’s efficiency. A heatregeneration fluid also can be used to increasesystem efficiency by transferring heat from a hot toa cold bed. As a critical part of this technology, thecharacteristics of various adsorbent–adsorbateworking pairs are listed in the Table 5.

Since there are no moving parts, except for valves,the sorption system is considerably simpler, requir-ing no lubrication and thus, little maintenance.Other advantages include quiet operation andmodularity so it is readily scalable for increasedheating and cooling capacity by additional beds.Furthermore, any heat source, such as waste heat orrenewable energy resources, can be used, so energysaving can be potentially significant.

Based on these merits of the adsorption system,active research in China, Europe, Japan and the UShas resulted in the breakthrough of this technology.The adsorption refrigerators first appeared on themarket in 1986, which were produced by theNishiyodo Kuchouki, Co. Ltd. The silica gel–wateradsorption chillers produced by this company aresold in the American market by the HIJC USA Inc.This company estimated the payback of this chillerto about 2–3 years. The chiller is driven by hotwater from 50 to 90 1C, and the temperature ofchilled water is close to 3 1C. The COP can reach 0.7

ARTICLE IN PRESS

Table 5

Characteristics of adsorption working pairs [32,35,36]

Adsorbent Adsorbate Heat of

adsorption

(kJ/kg)

Toxicity Vacuum level Release

temp. ( 1C)

Heat sources Applications

Silica gel H2O 2800 No High 70–100 Solar energy, low-

temperature waste

heat

Space cooling,

refrigerationCH3OH 1000–1500 Yes High

Zeolite H2O 3300–4200 No High 4150 High-temperature

waste heat

Space cooling,

refrigerationNH3 4000–6000 Yes Low

Activated

charcoal

C2H5OH 1200–1400 No Moderate 100 Solar energy, low-

temperature waste

heat

Low temperature,

ice makingCH3OH 1800–2000 Yes High 110

Charcoal

fiber

42000 Yes High 120

CaCl2 NH3 1368 Yes Low 95 Solar energy, low-

temperature waste

heat

Low temperature,

ice makingCH3OH N/A Yes Low


when the chiller is power by hot water at 90 1C.Another company producing silica gel–water ad-sorption is Mayekawa Co. The chillers from thiscompany can be powered by hot water at 75 1C andyield chilled water at 14 1C with a reported COP of0.6. In China, a series of adsorption chillers arecommercially available with the cooperation ofShanghai Jiao Tong University and Jiangsu Shuan-gliang Air Conditioner Equipment Company. Theproducts are rated at 10, 20, 50, 100 kW, etc. and thecosts in US dollars could be $10,000, $15,000,$30,000 and $50,000, respectively.

There are two typical CCHP applications withadsorption chillers. The CCHP system installed atthe beginning of 2000, in the St. Johannes hospital iscomposed by a fuel cell, solar collectors, a heatstorage vessel, a mechanical compression chiller, anadsorption chiller, an ice-storage tank and coolingceilings. The hot water derived from solar collectorand waste heat of the fuel cell drives a 105 kWMycom ADR 30 adsorption chiller, manufacturedby the Japanese company, Mayekawa. Anotherexample is the CCHP systems set up at ShanghaiJiao Tong University, which will be specified in latersection.

2.2.3. Desiccant dehumidifiers [3,13,31]

Desiccant dehumidifiers can work in concert withsorption chillers or conventional air-conditioningsystems to significantly increase overall systemenergy efficiency by avoiding overcooling air andprecluding oversized capacity to meet dehumidifica-tion loads. The desiccant process involves exposing

the desiccant material (such as silica gel, activatedalumina, lithium chloride salt, or molecular sieves)to a moisture-laden process air stream, retaining themoisture of the air in desiccant and regeneratingdesiccant material via a heated air stream. Systemcapacity is often expressed in volume of airflow or inmoisture removal rate. Table 6 shows somespecifications and costs of desiccant dehumidifica-tion systems.

Dehumidification technology is divided into twomajor types, solid desiccant dehumidifiers andliquid desiccant dehumidifiers; both are useful forthe mitigation of indoor environmental quality andhealth problems and for humidity control inbuildings. Liquid desiccant technologies—particu-larly those with air washing and biocidal capabil-ities—are viewed as a critical path toward ensuringindoor environmental security under extraordinarycircumstances and reducing indoor air pollution ingeneral.

Dehumidification technology in the commercialsector remains a young technology with a premiumprice. To date, commercial desiccant technologieshave not been designed for integration into CCHPsystems.

2.2.4. Other options

Although thermally activated technologies indi-cate the trend in cooling and dehumidificationoptions in CCHP systems, electric vapor-compres-sion refrigeration systems still play an importantrole for their maturity and reliability. Therefore,quite a few CCHP systems in research and practical

ARTICLE IN PRESS

Table 6

Costs and performance of desiccant dehumidification systems [31]

Flux (m3/min) Cost (US$/m3/min) Thermal input (W/m3/min) Maximum latent removal (W/m3/min)

40–140 280–630 300–1000 300–600

140–280 210–390 300–1000 300–600

280+ 210–320 300–1000 300–600

Table 7

Costs and performance of engine-driven chillers [31]

Capacity (kW) Electric use (kWe/kW) Cost (US$/kW) Maintenance cost (US$/kW/yr)

35–350 0.014–0.020 230–300 12.8–28.4

350–1760 0.003–0.014 180–270 10.0–21.3

1760–7030 0.001–0.003 130–210 7.1–17.0

Table 8

Natural gas demand forecast (10millionm3) [84]

Sector Year 2005 Year 2010

Power generation 174 484

Chemicals 120 180

Industrial material 168 257

Domestic fuel 106 230

Total 568 1151


utilization still employ these conventional technol-ogies as their cooling options. Nonetheless, it isunwise for a CCHP system to drive chillers usingelectricity generated by prime movers, since smallerprime movers have lower efficiency than larger typesused in power plants.

Engine-driven chillers have emerged as a sub-stitute for electric chillers in CCHP units, avoidingthe losses in energy conversion. Engine-drivenchillers, including reciprocating, centrifugal andscrew types, are conventional chillers driven by anengine, in lieu of an electric motor. They employ thesame thermodynamic cycle and compressor tech-nology used in electric chillers, but an engine orother prime mover drives the compressor directly.In engine-driven chillers smaller than 700 kW,reciprocating compressors are typically packagedwith the engine. In applications ranging from over700 kW to less than about 4220 kW, both screw andcentrifugal compressors are used. In the largest,over 4500 kW, centrifugal compressors are the onlyoption [22]. An advantage of engine-driven chillersis better variable speed performance, which im-proves partial-load efficiency. Engine-driven chillerscan also operate in a CCHP system for hot waterloads when the waste heat produced by the engine isrecovered. Table 7 shows the costs and perfor-mances of various engine-driven chillers (Table 8).

In general, mechanical vapor compression (typi-cally by electric compression chillers and engine-driven chillers) is not a characteristic part of CCHPsystems. It can be added to increase redundancy,diversity, reliability and economics of CCHPsystems.

3. Typical CCHP systems

3.1. Diverse configurations of CCHP systems

CCHP systems, including both existing units andexperimental models in laboratories, vary from siteto site, with diverse prime movers, cooling options,connecting forms, rated size ranges, heat-to-powerrates, user demand limitations and similar char-acteristics. Based on CCHP technologies and theircharacteristics described earlier, this section willdiscuss practical and potential CCHP systems andtheir development.

Regarding the classification of CCHP systems inthe Introduction, traditional large-scale systems,predominantly CHP systems without cooling op-tions in centralized power plants or large industries,account for large portions in installed CHP capacityin many countries. The technologies used in thistype of CHP approach have developed for severaldecades and these systems are relatively mature. Forthese CHP systems, there are two common config-urations [39]: one is based on boiler and steam


turbine, shown as Fig. 8; the other system is basedon combustion turbines, shown as Fig. 9.

The steam boiler/turbine approach has alwaysbeen the most widely used CHP system. In thisapproach, a boiler produces high-pressure steamthat is fed to a turbine to produce electricity.However, the turbine is designed so that there issteam left over to feed an industrial process. Thus,one fuel input to the boiler supplies electrical andthermal energy by recovering waste heat from thesteam turbine electric generator. Typically, twothirds of the energy in a conventional power plantis lost when waste steam is condensed in the coolingtower. This type of system typically generates aboutfive times as much thermal energy as electricalenergy [39]. Thus, this kind of system is suit for heatplants in which electricity power is generated asbyproduct.

In newer, large, centralized CHP systems, acombustion turbine (a diesel reciprocating enginecan also be used) is used to generate electricity, andthermal energy is recovered from the exhaust streamto make steam for other thermal uses. In these

Fig. 8. CHP system with backpressure steam turbine [1].

Fig. 9. CHP system with combustion turbine [1].

systems (Fig. 9), the thermal energy is typically oneto two times the electric energy generated [39].

An improved system model called combined cyclegas turbine system (CCGT) combined combustionturbine with steam turbine in one configuration(Fig. 10), which is the most widely used model inlarge central power plants today. The reliability ofcombined cycle systems is 80–85%, the annualaverage availability is 77–85% and the economic lifecycle is 15–25 years. The electrical efficiency is in therange 35–45%, the total efficiency is 70–88% andthe power to heat ratio is 0.6–2.0. The electricalefficiency can be increased further.

As for other categories of CCHP systems,relatively small-capacity-distributed CCHP unitsare the trend in future applications. In this category,novel technologies such as fuel cells, micro-turbines,Stirling engines, adsorption chillers and dehumidi-fiers are emerging in some research models andpractical applications, which possess some promis-ing characteristics, including low emission, highefficiency and low-grade thermal energy recovery.Reciprocating engines, combustion turbines, elec-trical chillers and absorption chillers are predomi-nant in the recent distributed CCHP market, for thematurity and stability of these technologies.

Reciprocating engines plus absorption or elec-trical (engine driven) chillers are popular for smallutilizations. Jacket cooling fluids, lubricating oilsystems, and engine exhaust are three heat recoveryoptions which can produce hot water using ex-changers, for heat demands and other cooling anddehumidification usages. This configuration, shownin Fig. 11, represents a large percentage of CCHPsystems with reciprocating engines as prime mover.Reciprocating engines with engine driven chillershave fewer applications with low on-site electricitydemands. This small-scale engine-based CCHP(CHP) system was a research issue addressed in

Fig. 10. Combined cycle CHP system with backpressure steam

turbine [1].


much of the literature. Maidment [40,41], men-tioned energy management of an engine-basedCCHP system with the application of an absorptionchiller. Riley [42], examined the emission from thistype of small CCHP system. Talbi [43], examinedthe interfacing of the turbocharged diesel enginewith an absorption refrigeration unit in a CCHPsystem and estimated the performance enhance-ment. Miguez et al. [44,45], illustrated design andperformance of a CCHP system with engine andheat pump equipment. Smith [46], also analyzed asimilar system in his articles. Reciprocating engines,as the most mature prime mover technology used indistributed CCHP systems, made new improve-ments in some recent research. Moss et al. [47],attempted to combine the Joule-cycle used in gasturbines with an internal-combustion engine andformed a reciprocating Joule-cycle engine-basedCHP system. A project at Shanghai Jiao TongUniversity [48], experimented with novel adsorptionchillers, using heat recovered from engines, togenerate cooling capacity because of the relativelylow byproduct heat temperature of small engines inCCHP systems. Research on engine-based CCHPsystems is active and the literature is extensive.

Micro-turbines became available commercially in2001 and 2002, and they immediately became anideal prime mover for small-scale distributed CCHPsystems. Absorption chillers and desiccant dehumi-difiers driven by byproduct heat of micro-turbinesare employed to meet cooling demands of users.A number of the same micro-turbine units can beconnected to fulfill any electricity range in practice.This configuration of CCHP systems is applied inmany locations, especially in the US, where micro-

Fig. 11. Schematic of reciprocating engine heat recovery [7,22].

turbine-based units have become serious competi-tors with engine-based units in the small-scaleCCHP market. With rising awareness of micro-turbine-based systems, more research has beenfocus on this method in recent years [49,50].Fig. 12 illustrates a typical schematic diagram of amicro-turbine CHP system.

In this category of CCHP systems, the Stirlingengine is viewed as a promising prime mover insmall commercial and residential applications fortheir low emissions, fewer moving parts, low noise,small-scale availability and relatively low byproductheat. Only a few commercial Stirling engine unitscan be found on the market, but research on Stirlingengines in some companies and laboratories hasadvanced to a near-commercial stage, both in theUS and in Europe. There has also been research onthe feasibility of CCHP driven by Stirling engines[51]. Some possible cooling and dehumidificationoptions for Stirling engines are absorption chillers,dehumidifiers and adsorption chillers. Fig. 13 showsan STM 4-120 Stirling engine system [18], which isthe first commercialized Stirling engine in the world;until now it has had limited applications.

It is envisioned that fuel cell systems will serve avariety of CCHP applications in the future, butthere is limited experience to validate potentialapplications. Since most fuel cells are still in an earlystage of development and commercial use, fuel cellsCCHP systems carry high capital costs and higherproject risk due to unproven durability andreliability. Simpler CHP systems based on PAFCsystems have been deployed in commercial practice.Although difficulties remain, some fuel cell CCHPsystems have already emerged in the US; Fig. 14demonstrates a solid polymer fuel cell plant [52].Tokyo Gas Co., Ltd. will market the first domesticpolymer electrolyte fuel cell in 2005 [53]. Inaddition, Hamada et al. [54] field-tested the

Fig. 12. Schematic diagram of micro-turbine [7,22].


performance of a polymer electrolyte fuel cell for aresidential energy system. According to the fuel cellcharacteristics illustrated earlier, different fuel cellscan produce various temperature levels of bypro-duct heat to drive certain cooling and dehumidifica-tion equipment.

One major challenge of CCHP systems is the lackof integrated systems [22]. In the US, sevenindustrial teams have announced research, develop-ment and testing of ‘‘first generation’’ integratedCHP and absorption chillers with controls—somewith desiccant units as well. This program holdspromise for the building market for CHP, offeringmultiple benefits, such as lower integration costs

Fig. 13. STM 4-120 power unit packaged DG system [18].

Fig. 14. Typical configuration of a so

and risks. In addition, it is a positive step forwardfor the use of thermal cooling with CHP in theindustrial sector.

3.2. Representative CCHP systems in use

In terms of rated sizes, CCHP applications arecategorized into micro, small-scale, medium andlarge-scale systems, while the size range of thesecategories are under 20 kW, from 20 kW to 1MW,from 1 to 10MW and above 10MW, respectively.In the following sections, four typical CCHPapplications, selected to represent these four cate-gories, are discussed in detail for a close look atvarious size CCHP systems currently in use.

3.2.1. Micro systems (under 20 kW)

In this category, there are limited examples in thecurrent market for a relatively small capacity,although micro systems show great potential forcommercial, institutional and residential utilization.As regards their technological feasibility, recipro-cating engines, fuel cells and Stirling engines areregarded as prospective prime movers. At ShanghaiJiao Tong University, a micro CCHP system,comprised of a 12 kW gas-fired reciprocatingengine, a 10 kW adsorption chiller, a floor radiateheating system, a waste heat recovery, a hot watertank and a cooling water tower, has been set up

lid polymer fuel cell plant [52].


(Fig. 15), which is one of the smallest CCHPapplications currently in use [48].

Fig. 16 shows the configuration of the micro-CCHP system at SJTU. Natural gas or LPG is usedto drive the engine. Engine jacket cooling waterpasses through the heat exchanger and is reheatedby exhaust gas that is up to 580 1C. Reheated waterthen passes through an adsorption chiller toproduce chilled water for space cooling in summer;or through the heat exchanger to produce hot waterfor a floor radiate heating system in winter. Afterthat, the jacket water enters water tank to producedomestic hot water and finally returns to the enginejacket. The generator at rated power (electricityefficiency is about 21.4%) recovers 13.6 and14.4 kW heat from exhaust gas and cylinder jacketcooling water, respectively.

The highlight of this micro CCHP system is itspractical utilization of an adsorption chiller devel-oped by SJTU with the cooperation of JiangsuShuangliang Air Conditioner Equipment Company(Fig. 17), which makes possible the recovery of low-

Fig. 15. Test facility view of the micro CCHP.

Fig. 16. Schematic diagram o

grade thermal energy [55,56]. In the tests, the COPof silica/gel–water adsorption chiller reaches 0.3–0.4with a heat source of 60–95 1C. With the help of thisthermal-activated technology, the overall thermaland electrical efficiency of the micro CCHP systemis more than 70%. After an analysis was executedbased on this micro CCHP system [48,55], it wasconcluded that the payback period is between 2.1and 3.2 years for commercial buildings, or between1.7 and 2.4 years for hotels, while the natural gascosts from 0.193 to 0.230 US$/Nm3.

In recent years, many other new developmentshave been achieved to commercialize waterchillers with small cooling capacities. Examples ofthese are:

1.

f th

Water–LiBr absorption chillers� EAW in Westenfeld, Germany (lowest avail-

able cooling capacity 15 kW)� Phonix Sonnenwarme in Berlin, Germany

(10 kW)� University de Catalunya in Terrassa, Spain:

air-cooled system (10 kW)� Rotartica in Spain: air-cooled system with

rotating absorber/generator (10 kW)

e m

2.
Ammonia water systems with mechanical solu-tion pump� Joanneum Research in Graz, Austria (10 kW,
operation temperature �20–10 1C)� AOSOL in Portugal: air-cooled machine

(6 kW)
3. Ammonia water systems without mechanical
solution pump� University of Applied Research in Stuttgart,

Germany (approximately 2–5 kW)� SolarFrost in Graz, Austria

icro-CCHP [48].

ARTICLE IN PRESS

Fig. 17. Adsorption chiller prototype.


4.
Solid sorption� Sortech in Halle, Germany: adsorption heat
pump (10 kW, working pair water/silica gel)� ClimateWell AB in Hagersten, Sweden

(10 kW, working pair lithium chloride/water;includes thermo-chemical storage)� SWEAT b.v., in the Netherlands (working

pair sodium sulfide/water; includes thermo-chemical storage)

These products are not yet well established in themarket, but promise to open new market segmentsfor CCHP in small commercial buildings (e.g.,offices, small hotels, etc.) and even residentialbuildings.

3.2.2. Small-scale systems (20 kW– 1 MW)

In this group of size ranges, a large number ofapplications are constructed for different uses, suchas retail stores, supermarkets, hospitals, offices,schools, small industry, etc. This sector is the mostactive and mature market for CCHP, since almostevery prime mover and cooling/dehumidificationtechnology above can find their particular market.Micro-turbines are strong competitors of internalcombustion reciprocating engines in this stage.Following the example of small-scale CCHP sys-tems, one of the first CCHP applications withmicro-turbines is located at University of Maryland,

College Park. Fig. 18 shows the CCHP package atthe University of Maryland.

The small-scale CCHP system is located inChesapeake Building of the University of Mary-land. This 4900m2 building is representative of themedium-sized commercial buildings accounting for23% of all buildings in the US [58]. The primemover is a Capstone C60 micro-turbine thatgenerates 60 kW electricity at 90,000 rpm andexhausts flue gas at 310 1C after recuperation [59].The average efficiency of the micro-turbine is26.9%, when operating at full output capacity andan average air inlet temperature of 7 1C. However,the partial-load efficiency drops to a low of 11% at9 kW output power. Waste heat from the micro-turbine exhaust powers a Broad BD6.4NF-15 singleeffect absorption chiller, which achieves 65 kW ofcooling power at the COP of 0.65. The absorptionchiller assists the RTU (316 kW direct expansionelectric rooftop cooling units) in providing airconditioning for cooling zone two, seen in Fig. 19.Chilled water produced by the absorption chiller issupplied at 7 1C and returns at 12 1C [49]. Flue gasfrom the chiller powers the ATS solid desiccantdehumidifier. The dehumidifier dries the supply airfor the building, a function normally performed bythe roof top unit and the absorption chiller,reducing the need for grid-based electrical power.Together, these interactive components efficientlysupply air conditioning for cooling zone two andsupplement the power requirement for the entirebuilding. The overall fuel utilization of this CCHPsystem is as much as 72%. Compared with theconventional energy supply for this building, annualsavings of applying the new CCHP system areforecasted to be $25,000, with a 40% reduction inCO2 [49].

3.2.3. Medium systems (1– 10 MW)

Generally, existing applications ranging from 1 to10MW are set up for industrial sites, where nocooling demand is needed. As an example, thesystem in the Domain Plant of Austin is equippedwith a combustion turbine for electricity demandsas well as an absorption chiller for cooling andheating.

This plant is powered by a 4.6MW Solar TurbineCentaur 50 gas turbine (Fig. 20), which generates4.3MW net outputs for full-load continuous dutywith 28.6% electrical efficiency and 510 1C exhaust.The exhaust from the gas turbine is ducted into atwo-stage indirect-fired Broad Co. absorption chil-


ler (Fig. 21) via a diverter valve, which produces8918 kW of cooling power at chiller water volu-metric flow rate of 1390m3/h. The chilled water issupplied to users at 6.7 1C and returns to the chillerat 12.2 1C [60–63]. The overall schematic layout ofthe CCHP system is illustrated in Fig. 22.

The CCHP plant was constructed by Burns &McDonnell partnered with the municipal utilityAustin Energy, in an existing building that is theright size to house the modular package layout.A remarkable characteristic of this system is itsmodularization, which enables ease of construction.Austin Energy owns and operates the CCHP systemas part of an existing central utility station thatgenerates power for the grid and sells chilled waterto industrial tenants and a downtown districtcooling system. Overall system integration is con-trolled by Allen Bradley software, which providesprogrammable logic remote monitoring capacity for

Fig. 19. Schematic diagram of the CCHP applica

Fig. 18. The CCHP package at the University of Maryland [57].

the complete system. The system is intended to runin continuous duty operation at full base loadoutput 24 h a day [62,63].

After beginning commercial service, the CCHPsystem operated at overall fuel efficiency of 76.8%with less than 15 ppm NOx and no catalyst exhausttreatment. The system is expected to cut equipmentand installation costs by 15–30% and achieve 3million m3 in natural gas saving annually, depend-ing on the amount of infrastructure available at thesite [62,63].

3.2.4. Large-scale systems (above 10 MW)

Large-scale CCHP systems with capacity above10MW are the ideal energy supply scheme for largeindustries or institutional/commercial/residentialdistricts. Although large cogenerations can be foundeverywhere, large systems that provide vast coolingcapacity simultaneously have limited applica-tions similar to micro CCHP systems. The57.4MW CCHP plant at the University of Illinoisat Chicago is a successful model for large-scaleCCHP applications.

This CCHP system provides service to the entirecampus of about 744,000m2 and a student popula-tion of over 27,000 [64]. This application consists oftwo sections: the East Campus system and the WestCampus system, which were established from 1993to 2002. The CCHP plant on the campus is shown inFig. 23.

Equipment utilized in the East Campus systemincludes: two 6.3MW Cooper-Bessemer dual-fuelreciprocating engine generators; two 3.8MW Wart-sila 18V-28SG gas reciprocating engine generators;

tion at the University of Maryland [49,58].

ARTICLE IN PRESS

Fig. 20. Solar gas turbine package [60].

Fig. 21. Broad absorption chiller.

Fig. 22. Schematic layout of the CCHP system in Austin [62].


a 3.5MW Trane two-stage absorption chiller; two7MW York International electrical centrifugalchillers; and several remote building absorptionchillers activated by the hot water loop (4.7MWmaximum cooling capacity). The system generates20.2MW of electricity total, to cover nearly 100%of the entire electrical demand of the East Campus.The recovered heat from the CCHP system offsetsthe heating and cooling requirements of 29 eastcampus buildings, more than 353,400m2. Theconfiguration of this complex system is illustratedin Fig. 24. The overall installed cost is 25.7 millionUS dollars and estimated payback is less than 10years. It is estimated that the CCHP applicationprovides an overall source energy reduction of14.2%, an estimated 28.5% reduction in CO2, a52.8% reduction in NOx, and an 89.1% reduction inSO2, along with approximately three million USdollars in annual operating saving [65].

After the success of CCHP system in the EastCampus, a second system began operation onthe West Campus, with an additional 37.2MWelectricity power to offset the heating and cool-ing demands of the several hospitals and otherbuildings on the West Campus. At the heart ofthe West Campus CCHP system are three5.4MW Wartsila gas engine generators and three7.0MW Solar Taurus turbines. The cooling com-ponents of the system are several Carrier absorp-tion chillers, totaling 7MW cooling capacity.The schematic configuration of the West CampusCCHP system is illustrated in Fig. 25. The in-stallation cost of the system was 36 million USdollars; annual savings of 7 million US dollars areexpected, with an estimated simple payback of 5.1years [66].


4. Development of CCHP around the world

4.1. United States

The beginning of CCHP development in the USdates back to 1978, when Public Utility RegulatoryPolicy Act of 1978 (PURPA) was enacted to requireutilities to purchase electricity generated by inde-pendent suppliers and thus, stimulate the develop-ment of renewable energy and CCHP (CHP orcogeneration). In 1995, the installed capacity ofCCHP systems in the US was 45GW compared to

Fig. 24. System configuration o

Fig. 23. CCHP plant at the University of Illinois at Chicago [66].

12GW in 1980 and; in this period, the averageincreased capacity annually was about 2.2GW[67–69].

However, in the mid 1990s; a liberated marketconcept was introduced into the electricity genera-tion industry by government; during this time,intense competition and instability in the electricitymarket blocked the rapid development of CCHPapplications. The installed capacity of CCHPincreased very slightly from 45GW in 1995 to46GW in 1998. Subsequently, the US governmenttook a series of measures to promote CCHPdevelopment again. First, the US Department ofEnergy (DOE), with the cooperation of the Envir-onmental Protection Agency (EPA) and the Com-bined Heat & Power Association (CHPA), put a‘‘CHP Challenge’’ into effect in 1998. The aim ofthis ‘‘challenge’’ was to boost the installed capa-city of CCHP from 46GW in 1998 to 92GWin 2010. Then, in 1999, ‘‘Combined Cooling Heating& Power for Buildings 2020 Vision’’ was pub-lished by the DOE, which presented a timetable ofCCHP development. It was recommended thatobstacles to connect distributed CCHP applica-tions with utility grids be eliminated, and thatparameters be established to achieve change be-fore 2005. By 2010, CCHP is to be applied in 25%of new constructions and 10% of existing commer-cial and institutional buildings; CCHP will sub-stitute in 50% of CHP buildings. By 2020, 50% ofnew construction and 25% of existing commercial/institutional buildings will be equipped withCCHP [67,69].

f the East Campus [64,65].

ARTICLE IN PRESS

Fig. 25. System configuration of the West Campus [64,66].


In 2001, President George W. Bush establi-shed the National Energy Policy Development(NEPD) Group, directing it to ‘‘develop a na-tional energy policy designed to help the privatesector, and, as necessary and appropriate, State andlocal governments, promote dependable, affordable,and environmentally sound production and distri-bution of energy for the future.’’ CHP policyrecommendations contained in The NationalEnergy Policy of 2001, set forth by the NEPDGroup included [70–74]: encouraging increasedthe use of these cleaner, more efficient techno-logies CHP projects by shortening the depreciationlife for CHP projects or providing an investment taxcredit.

As mentioned in the Introduction, CCHP isdivided into traditional large-scale CCHP applica-tions (CHP non-DG) and relatively small capacitydistributed CCHP (CHP DG). These two parts ofrecent CCHP capacity additions can be seen inFig. 26. The overall electricity capacity addition(2001–2003) in the US presented on the left below,including both utility and non-utility, intercon-nected and non-interconnected, capacity additionsof all sizes. The 15.5GW change in CCHP reflectsincentives to build after the California crisis andother market changes. It should be noted that 87%of new CCHP is non-DG, which is traditional large-scale CCHP applications.

The installed capacity of CCHP in 2001 was aslarge as 56GW and about seven percent of overallinstalled capacity that year. Examined from the aspectof electricity generation, 310 billion kWh wasgenerated by CCHP systems that year—up to ninepercent of the overall electricity generated in the US.

The US CCHP market grew significantly through2002 but has since slowed sharply in the face of highnatural gas prices and persistent regulatory barriers.The major blackout of 2003 in North Americabrought about major review of options to minimizesuch disruption in future. CCHP, especially DGCCHP, can reduce vulnerability to such outages,and to the threat of terrorist attack on power systems[14,75,76]. Fig. 27 shows 35.2GW non-DG CCHPcapacity was added from 1990 to 2003, includingmany merchant plants and 7.2GW DG CCHPcapacity was added the same period, creating a totalCHP DG capacity of 22GW [69].

The overall electricity capacity of CCHP in theUS reached 80GW in 2004. There were 1540existing commercial CCHP applications, with9024MW and 1189 industrial CCHP sites with65,621MW in the US [77]. Capacities of variousapplication sectors are compared by years (1995,2000 and 2004), shown in Figs. 28 and 29.

The future of CCHP markets in the US ispromising; though there are still certain factors thatinfluence the potential outcome. Key motivatorsand barriers to CCHP development are listed asfollows [14]:

Key motivators

�
Need for higher quality power supply. � Congested transmission and distribution lines. � Concerns about system vulnerability. � State/national energy policy support for cogen-
eration and renewable energy. (States currentlyrepresent a more important policy leader thandoes national government.)

ARTICLE IN PRESS

Fig. 26. Capacity additions 2001–2003 (GW) [69].

Fig. 27. CCHP capacities in all sizes by 1st year installed [69].


Key barriers

�
High gas prices (with delayed impact on powerprices) and energy price volatility. � Non-standardized grid access and interconnec-
tion requirements across the USA.
� Continuing monopoly of energy utilities. � Emissions standards that do not reflect the
efficiency of cogeneration and other DE.
�
Fig. 28. Industrial CCHP applications [77].

Continued ban on private wires and prohibitionsagainst third party sales in 15 states.

It is estimated that the potential US CCHPmarket could be as large as 209.9GW, based on theanalysis of overall capacity data in 1999. Theindustrial CCHP potential could be another 88and 75GW of the commercial sector. Moreover, theexisting 22GW of CCHP/DG could double to42GW, even under high gas price conditions[14,77]. CCHP applications would dominate overallDG industrial and commercial market potential,comprising over two-thirds of all DG base casemarket potential and over half of the future casemarket potential. Also, CCHP is currently under-utilized in the commercial building sector, wherethere is great potential.

4.2. Europe

In the European Union, the most importantlegislative initiatives of CCHP development are theCogeneration Directive, the Emissions TradingDirective, the New Electricity and Gas Directives,and the Energy Performance of Buildings andTaxation of Energy Products Directives. EU poli-cies both recognize the importance of CCHP for

achieving climate change commitments and definepossible instruments to promote the technology atthe EU level. When the strategy was issued in 1997,the share of electricity produced from CCHP in theEU was about 9%. The strategy sets a target of 18%by 2010 [67,78,79]. However, possible measures andinstruments to achieve this target have so far notbeen defined in depth.

The development of CCHP in the EU ischaracterized by a wide diversity, both in the scaleand nature of the development. This diversityreflects differences in policy priorities, naturalresources, history, culture and climate and has itclose links to the structure and activity of electricitymarkets. Obviously, the main reason for thisdiversity has been the different political choicesmade by governments in energy matters. Fig. 30portrays, as nearly as possible, the situation ofCCHP development in EU countries and theprojected scenario in 2010 [1,9,16].

ARTICLE IN PRESS

Fig. 29. Commercial CCHP applications [77].


In the diagram, it can be concluded that Austria,Denmark, Finland and the Netherlands are the fourleading countries in the popularization of CCHPutilization.

4.2.1. Austria

Austria has strong environmental policies, andCCHP technology has always been encouraged.Industrial and district heating sectors have devel-oped relatively well; the former through the benefitsthat the technology brings to high-energy intensityusers and the latter as a response to energy pricerises in the 1970s and central state support [9].

4.2.2. Denmark

At the time of the oil crisis, in the beginning of the1970s, Denmark was 90% dependent on foreign oil.Today, Denmark is self sufficient in oil and gas, oneof several factors, which led the government topromote CHP technology. The popular use of windenergy in Denmark is also a contributing factor.The existence of district heating networks and theenvironmental concerns of the society also propelledCHP development. The success of CHP develop-ment in Denmark has been largely due to govern-ment policy resolved to ensure that the technologycan flourish, and has been achieved throughsignificant subsidy and grant provisions [1,16,78].

4.2.3. Finland

Finland has always been one of the most liberalenergy markets in Europe. The development ofCCHP in Finland has not been largely a conse-quence of specific political action, since no parti-

cular supportive policies are undertaken.Nevertheless, CCHP was recognized as the econom-ic means of generating electricity. Other reasons forthe healthy development of CCHP have been thehigh demand for heating, subsidies for new tech-nologies and an absence of barriers [9].

4.2.4. The Netherlands

Success in the Netherlands has been achievedthrough strong promotional activities and a clearpositive policy framework:

�
fuel (gas) tax exemption for fuel used to generateCHP electricity; � investment in highly-efficient CHP units, partly
fiscally deductible;
� eco-tax exemption for heat supplied by CHP.
The unofficial national long-term target for CHP isto achieve CCHP capacity of 15GW by 2010.

The development in other countries in the EUfollows [1,9,14,16,80–83].

4.2.5. France

The major electricity demands of France arefulfilled by nuclear energy, which comprises morethan 70 percent of overall capacity. Thus, thecapacity of CCHP is responsible for a small fractionof electricity. As shown in Fig. 31, after the boom inCCHP installation in 1998, a sharp decline occurredthe next year, which remains unchanged in recentyears [16,80].

4.2.6. Germany

In Germany, liberalization has had negativeeffects on CCHP due to price wars between theutilities that have caused electricity to be sold belowits production cost. Although the price of electricityhas begun to rise again, about 20GW CCHPcapacity was closed down before 2001. Thus, thegovernment has taken several measures [1,14,16]listed below. First, ecological tax reform wasundertaken: cogeneration with a global efficiencyof 70% or more is exempt from electricity and gastaxes. The second measure was the Emergency Planmaking it compulsory to buy electricity fromcogeneration with an extra subsidy of 0.03DM/MWh [1]. In addition, a quota model was intro-duced, mandating that every company supplyingelectricity to a final consumer must supply a certainpercentage from cogeneration. New projects under

ARTICLE IN PRESS

Fig. 30. Percentage of CCHP in 1999 and 2010 [80].


the new CCHP law in Germany can be seen inFig. 32.

4.2.7. Hungary

As one of the European Union’s accessioncountries, the statistics for CCHP in Hungary areincomplete. However, the government and electri-city company each take measures to promote CCHPdevelopment. Cogenerated electricity of 2004 inHungary is 5600GWh, about 15.6% of totalgeneration, and cogenerated heat is 46,335TJ,about 71% of total generation. It is hopedcogenerated electricity will reach 9.0–9.5 TWh—about 20–22% of total generation—by 2010 [81].

4.2.8. Italy

The annual electricity demand supplied by CHPis about 15%. Industrial sector applications aremore important than district heating or smallerpublic or private utilization. A series of policies havebeen set forth by the government to establish lowtax rates on gas used for district heating; taxreductions on gas for industrial CHP schemesproportional to their electrical efficiency; carbontax exemptions for CHP; dispatch priorities forCHP in the transmission network and more [16,78].

4.2.9. Poland

There are over 1000 CCHP installations inPoland, but no specific legal framework is estab-lished. General provisions in the 1997 Energy Lawapply. Although there is no obligation upondistribution companies to purchase electricity fromCCHP, in general, they do purchase it. Thegenerator-producing electricity from cogenerationmust be licensed if the installed capacity of the unitexceeds 50MW. For the promotion of CCHP,KOGEN Polska, has been created, which is thenational member for COGEN Europe in Poland[1,16].

4.2.10. Spain

Approximately 12% of electricity production isfrom CHP, generated mostly in the industrial sectorand with no district heating. Natural gas fuels halfof the existing CHP installations. A special regimefor new CHP units meeting certain criteria wasintroduced in 1998; it included mutual obligationsby CHP producers and distribution companies.Some funding for small-scale CHP installations wasmade available from the Institute for Energy Savingand Diversification [16,78].

4.2.11. Sweden

CHP represents about 6% of the total electri-city production, mostly in district heating and

ARTICLE IN PRESS

Fig. 31. CCHP projects in France 1991–2002 [80].

Fig. 32. New projects under the new CCHP law in Germany

(February 2002) [80].


industrial use. The low CHP share is not theresult of regulatory obstacles, but rather of theabundance of low-priced electricity. In Sweden,more than 90% of electricity is hydro or nuclearpower [16,78].

4.2.12. UK

Since the year 2000, the government has intro-duced a wide range of measures to support thegrowth of CCHP capacity. These measures fall intoseveral categories: fiscal incentives, grant support,regulatory framework, promotion of innovationand government leadership and partnership. Themain support measures favored by the CCHPindustry in their response to the strategy consulta-tion were a CCHP obligation, and exempting

CCHP from the renewable obligation base. Duringthe 1990s, installed CHP capacity in the UK morethan doubled [83]. However, this buoyant trendhas been interrupted by recent market conditions.Fig. 33 shows the trend in installed CCHP capacityand how it relates to the 10GW target [1,16].

Attempts have been made in many EuropeanUnion countries to remove the barriers andpromote cogeneration. Various incentives have beenused, such as relatively high prices for exportedelectricity sold to the grid, and grants on invest-ments. Other measures have included spreadingrelated information, energy auditing and analysis ofdata, and support of research and development.

Most of these measures were designed at a timewhen many of the barriers to the development ofCCHP derived from the existence of monopolisticelectricity and gas markets. The most frequentlymentioned barriers to CCHP in the EU were:

�
low price paid for the surplus of electricityexported to the grid; � high fees for top-up and back-up supplies; � no possibility of third party access; � predatory pricing against possible competition.
The share of CCHP in the electricity productionin Europe is currently about 10%. This is far fromits full potential, which COGEN Europe estimatesto be at least 30%. This can be supported by the factthat three countries have achieved this share[1,9,16]. As previously mentioned, in its 1997Strategy to Promote Combined Heat and Power,the European Commission (EC), set a target of 18%by 2010. In the current situation, uncertaintiescaused by incomplete liberalization of electricitymarkets in Europe make it unlikely that this targetwill be reached without a reorientation of the policyframework. Political support for CCHP, and energysaving technologies from various national govern-ments is a proven necessity. A possible estimate offuture CCHP capacity by sectors in Europe isshown in Fig. 34.

4.3. Asia and the Pacific

4.3.1. China

In the 1980s, China became concerned aboutCCHP (CHP/cogeneration) development for thefirst time. The government emphasized that size andtype of these systems should be determined by heatdemands of users, (called as ‘‘heat-match mode’’).


During that period, many single systems with 3–12MW steam turbines were constructed. In the late1980s and early 1990s, when China experiencedelectricity supply problems, the government setforth a series of policies which included taxexemption, investment tax credit and direct subsidyfor energy saving projects—especially CCHP sys-tems. The rapid development of CCHP systemsslowed at the end of the 1990s, as preferentialpolicies were abolished with several factors, such asan abundance of temporary electricity, reform ofthe national accounting system and monopolizationin the electricity market [67,84,85].

After the National Energy Conservation Lawtook effect in 1998, China encouraged the develop-ment of general energy-saving technologies andprojects; energy grade utilization and overallefficiency was promoted. Through the end of 1999,there were as many as 1402 cogeneration units withindividual capacity over 6MW in China. Theoverall capacity of these units was 28,153MW,consisting of 12.6% fuel-combustion electricitygeneration [14,84,86]. Fig. 35 shows the capacityof different size ranges CCHP systems in 1999.However, most systems were fueled with coal andapplied boilers and steam turbines as prime movers.In 2001, the government enacted the regulation ofCHP for better management of CHP (includingCCHP) projects; it stressed the heat-match modeand prescribed the lowest efficiency limitation andheat-to-power ratio of different systems. This

Fig. 33. CCHP installed capaci

measure sparked development not only of centra-lized cogeneration plants, but also small-scaledistributed CCHP systems. In recent years, CHPunits with cooling capacity developed rapidly, andseveral cities have coal-combustion CHP plantswith cooling capacity supply. Jinan has 49.6MWcooling supply CCHP system, and in Hangzhouthere are two systems of more than 120MW coolingcapacity each. CCHP systems based on gas-com-bustion turbines or engines also emerged; typicalexamples are Shanghai Huangpu Central Hospital,Pudong International Airport, the Beijing GasCompany building and the system used in TsinghuaUniversity [67,84,85].

Current CCHP development in China has someunique characteristics. Following the heat-matchmode, users select the system size based on pra-ctical on-site heat demands; as a result, there aremany more small-scale units than large ones. Insmall and middle size cities of north China,cogeneration plants supply steam for both indu-strial processes and domestic space heating, whilethe heating connections and distributions are quitecomplex and require a large investment. In bigcities of the north, cogeneration plants consist oflarge steam turbines—more than 100MW perunit—which can supply space heating of 10 millionm2. Most CHP systems in large industries are setup solely for the power and heat demands ofthat industry. Although these systems connect withutility grids, they sell very little of the electricity

ty and targets in UK [83].

ARTICLE IN PRESS

Fig. 34. Future possible scenario for CCHP capacity [80].

Fig. 35. The capacity (GW) of different size range CCHP systems

in 1999 [84].


generated. Most CCHP systems supported by thegovernment generate cooling capacity for pro-cess utilization in textile mills, chemical indu-stries or large institutional buildings. Domesticspace cooling by CCHP systems cannot be ad-dressed, as the problem of metering and chargeremains. In general, more than 95% of CCHPor CHP systems are fueled with coal and thereare limited combined-cycle projects in China, sincethe production capacity of nature gas in China islow and the price of natural gas is relativelyexpensive [84].

To further CCHP applications in China, severalmeasures should be taken [86]:

1.
Distributed CCHP generators should be per-mitted grid access on transparent and non-discriminatory terms.
2.
Emerging industry structures should not main-tain market control in the hands of incumbentutilities.
3.
The transmission and distribution costs asso-ciated with central generation should be fullyaccounted for in any system planning.
4.
Fuel and power pricing should be determined bymarkets as much as possible.
5.
Private and foreign investors should face noundue commercial, legal or regulatory barriers incarrying out their business.
6.
The overall output efficiency (including usableheat), of utility plants should be rewarded.
7.
The clean development mechanism should beencouraged to contribute significantly to China’spower demand requirements.
Fuel diversification for future CCHP develop-ment is likely to be significant with biomass, biogasand natural gas providing new opportunities fordevelopers. Natural gas-driven combined cycleCCHP systems will play an important role in futuremarkets. Although gas-driven systems cannot com-pete with coal-driven cogenerations in the north,they can become a strong competitor with 600MWunits using coal in the south. It is believed thatabout 1GW combined cycle CCHP systems usinggas will be put into production in 2005 and evenmore in the next several years [84].

The capacity of CCHP applications in China ispredicted to grow at a high rate in coming years,with an estimated potential increase of 3.1GWannually, comprising 620MW for industries,2000MW for cities in north China and 500MWfor new industrial area in south China [84]. At thesame time, the increase in annual capacity is about4.5GW. By 2006, CCHP capacity could reach45GW. If some, or all of measures listed above,can be achieved, the scale of DER (most are CCHP)development in China could exceed that of centralpower and go beyond 100GW by 2010 [14].

4.3.2. Japan

At the end of March 2003, there were 2915 CCHP(including cogeneration) units, totaling 1429MWinstalled for commercial applications and 1600 unitstotaling 5074MW for industrial usages [87]. Theaccumulated data of installation numbers and totalcapacity are illustrated in Fig. 36. The number ofinstallations as well as the capacity has been steadilyincreasing over the last decade, which can be seen inFig. 37. After a sharp rise in 1990, the growth rate

ARTICLE IN PRESS

Fig. 36. The cumulative capacity of CCHP in each fiscal year

[87].


slowed in 1992, due to recession and decline inenergy prices. There has been a renewed interest inCCHP, proven by the fact that over 850MW wasadded between March 1996 and 1998 [88].

In recent years, development of CCHP applica-tion in Japan restarted with the emergence of newCCHP technologies. Data of commercial andindustrial cogeneration by type of activity, includingnumber of installations and generating capacities,are summarized in Table 9.

Among commercial applications, commercialstores rank first in terms of number and totalcapacity, followed by hospitals, hotels and offices.The main features of these sites include long andcontinuous operating hours, constant demand onthermal energy for hot water, steam and chilledwater. Although few in number, the district heatingand cooling network projects, with much largeraverage sizes, represent an important application inJapan. Among industrial uses, gas and oil industrieshave the largest share in terms of capacity. Othersectors having large capacities are pulp and paper,chemical pharmaceutical, iron and metals, andglass, soda and ceramics industries. In contrast,the food industry uses many smaller systems.

Since the 1980s, the support extended by govern-ment for promoting CCHP may be classified intofour categories: special taxation, low interest loans,investment subsidies, and subsidies for new technol-ogy development. The ‘‘Law Concerning Promotionof the Use of New Energies’’ was enacted in June1997, as a framework for encouraging the introduc-tion of renewable and non-conventional fuels(including CCHP/cogeneration). The budget in1998 allocated 74.8 billion JPf (up from 56 billionJPf in 1997) for new energy promotion [89].

Other detailed measures taken by the governmentare listed as follows: CCHP system investors maychoose either 30% depreciation on the installationcost or 7% of tax exemption in the 1st year ofacquisition of cogeneration plant; low interest loans(2.3% per year) can be obtained for 40–70% of thetotal investment cost.

Additionally, electricity market reform also hasan obvious effect on CCHP development. Underthe former Electricity Supply Law, nine regionalelectric utilities had the monopoly to supplyelectricity in the whole country. This law wasrevised in 1995, which now helps in furtherpropagation of cogeneration. The law allows theprivate sector to sell self-generated electricity to theelectric utilities or supply self-generated electricity

to third parties. Such action, or even the crediblepossibility of such action, would put competitivepressure on the utility to change its prices andreduce its costs to those customers who can crediblyself-generate.

In addition to this encouragement for CCHPdevelopment, the obligation of environmental pro-tection also plays a critical role. Following the ThirdConference of Parties held at Kyoto in December1997, Japan set itself a target of reducing green-house gas emission by 6% by the year 2010, taking1990 as the base year. An Environmental WhiteBook was released in June 1998 wherein CCHPappears as one of the important measures to reduceCO2 emission [89,93].

In the ‘‘Energy Policies of IEA Countries: Japan1999 Review’’ [89], the target of cogeneration set bythe Japanese government concludes that totalinstalled cogeneration capacity is expected toincrease from 3.85GW in 1996 to 10GW in 2010(cogeneration is regarded as a demand side newenergy in Japan).

4.3.3. India

With continuing economic growth, the Indianelectricity system is in need of urgent investmentand development. DER (mainly CCHP systems)capacity is only 4.1GW—about 3.6% of totalelectricity capacity in India. High priced andunreliable electricity supply, government capitalgrants and soft loans are the key drivers for CCHPdevelopment. At the same time, some barriers exist,such as lack of adequate policy framework, lack oftechnical knowledge and support services, shortage

ARTICLE IN PRESS

Fig. 37. The number and generating capacity of CCHP in each fiscal year [87].

Table 9

CCHP commercial and industrial applications at the end of March 2003 [87,93]

Commercial sectors Number of

sites

Generation

capacity (MW)

Industrial sectors Number of

sites

Generation

capacity (MW)

Store 497 264 Food 294 1333

Hospital 460 213 Chemical pharmaceutical 279 4344

Hotel 440 219

Office 289 193 Machinery 223 2865

Sports facility 236 94 Electric equipment 158 2981

Welfare facility 214 11

Public bath 169 23 Iron and metal 141 4078

Training center/ sanatorium 124 43 Textile 90 2433

Pulp and paper 73 4657

Gasoline station 86 5 Gas, oil and other energy 66 9500

School 77 42

District heating and cooling 21 81 Glass, soda and ceramics 44 4091

Other 302 242 Other 232 1806

Total 2915 1429 Total 1600 3171


of investment finance and limited natural gasnetwork for cogeneration [14].

In the CCHP market, there is tremendouspotential in industrial sugar cane. Bagasse-basedcogenerations in sugar mills are the main formof CCHP development in India [90,91]. A dis-tributed generation revolution began in India with87 new local power projects, producing 710MWfrom sugar cane waste. In September 2001, theMinistry of Power estimated that there was a

total potential for some 15GW of cogenerationcapacity, of which 2GW had been implementedto date.

4.3.4. Association of South East Asian Nations

(ASEAN)

There is huge potential for CCHP systems inASEAN but market conditions differ from onecountry to another. The driving force for industryto invest in CCHP is lower energy cost, which is


independent of overcapacity present in some coun-tries. Financing is the largest obstacle to investment,despite market liquidity. Most countries have anindirect biomass cogeneration policy through bio-mass power and energy efficiency policy, legislationand support programs. However, none of theASEAN countries have any particular policy,legislation or support program for coal and naturalgas cogeneration presently [92,93].

The huge difference between developments inthe electricity supply industry in ASEAN Coun-tries is illustrated in Table 10. Typically, CCHP(cogeneration) policy is part of national energypolicy, which is often scattered between differentagencies.

The EC-ASEAN COGEN Program is an eco-nomic cooperation program between the EC andASEAN; about 15 million EURO is funded by theEC. The program lasted for 3 years from January2002 to December 2004. As a result, 24 full-scaledemonstration projects (FSDP) candidates selectedranges from 0.3 to 41MW, and the total capacity is174MW. With assistance from developed countriesand organizations, the potential will become arealistic market of CCHP applications in ASEAN[92,94,95].

4.4. Other countries

In addition to the above three sections of theworld, many other countries develop their ownCCHP applications by different means.

Russia leads in the development of CCHP (mostare cogeneration) around world. About 30% ofelectricity generation is from cogeneration, mostlyin association with municipal use, which generates65GW annually. The very cold temperature holdsgreat potential for district heating as a whole.Widespread supply of natural gas and its low costcompared to Europe are additional drivers fordevelopment of cogeneration applications. How-ever, lack of financial support and a strongmonopoly-based market structure block furtherincrease in cogeneration. Once this situationchanges, there could be rapid market growthbased on growing demand and abundant naturalresources [14].

In the Middle East, profuse crude oil resourcesseem to offer no need for developing an efficientpower supply, such as CCHP systems. But environ-ment and economy make CCHP applicationsvaluable. Jaber [96] proposed a commercial-sized

oil shale integrated tri-generation system (OSITGS)in his article. The proposed plant will probably belocated close to the vast naturally occurring oil-shale deposits, which will be financially attractivecompared with conventional utilization methods, aswell as an environmentally acceptable technique forproducing synthetic (liquid and gaseous) fuels andelectricity from oil-shale. Other literature indicatesthat countries with abundant energy resources arewell aware of CCHP [97].

Large-scale hydropower plays an important rolein Brazil’s electricity structure, and the overall DERcapacity of this big country is 2.8GW—about 3.8%of electricity capacity [14]. Several articles revealthat Brazil hopes to join the trend of CCHPdevelopment around the world. In his article, Szklo[98,99] applied a COGEN model to two cases inBrazil—a chemical plant and a shopping mall—showing the highest economic potential for gas-firedcogeneration in Brazil. Another article, by Silveiraand Gomes [100], presents a study of technical andeconomic feasibility for the installation of cogenera-tion systems utilizing fuel cells, connected to anabsorption refrigeration system for a building of thetertiary sector, subject to conditions in Brazil.Furthermore, a recent discovery of natural gas nearthe State of San Paulo has at least tripled Brazil’sreserves, although it will take a few years to develop.Brazilian gas companies have announced a majormove towards increasing distribution—the CCHPmarket being their main target [14].

The potential CCHP market is also significant inMexico, where petrochemical refinery sites canoperate with onsite power generation. Althoughstate-owned companies dominate the power market,changes are being made to electricity regulations,opening areas of the market to the private sector.The government is promoting investment in DER/cogeneration. In January 2004, the Energy Secretaryannounced possible additional investments of1000MW by 2010. DER is expected to accountfor 20% of growth in the power market from 2004to 2010, according to a survey of WADE [14].

In Africa, CCHP development remains in aprimary stage. The foremost problem of manycountries is the promotion of electricity supplyinfrastructures nation-wide. To some extent, small-scale distributed CCHP systems provide anotherpower supply method to remote areas, rather thanlarge centralized power plants. Joseph and Roy-Aikins [101] investigated the potential economicbenefits that can be accrued by installing gas turbine

ARTICLE IN PRESS

Table 10

Present differences in ASEAN electricity supply [94]

Country Present situation Installed capacity

(MW)

Forecasted annual

growth of power

demand (%)

Policy on

cogeneration

Cambodia No national grid 160 �10 Preparing phase

Indonesia Govt.—56% IPP—4% 23,425 IPPa, conservation

Captive power —40% captive power

Malaysia Govt.—85% 13,760 6–10 SREPb,

Private—15% cogeneration

Philippines Govt.—55% 14,700 �9 Renewable energy

Private—45%

Singapore Power pool 8140

Thailand Govt.—60% 24,500 �10 SPPc, VSPPd,

Private—40% renewable

Vietnam Govt.—90% 3296 �13 Preparing phase

Private—10%

aIPP—independent power producers.bSREP—small renewable energy power.cSPP—small power producers.dVSPP—very small renewable power.


cogeneration sets along an oil pipeline in a ruralarea of one sub-Saharan country. South Africapredominantly fueled by coal (93% of overallelectricity capacity) and the capacity of DER isonly 0.5GW—about 1.4% of total capacity [14]. Insummary, prospects for CCHP and renewable DERin Africa are hopeful, inspite of many barriers.

5. Discussions and conclusions

1.
Combined cooling, heating and power systemsare derived from the CHP category, which sharessome merits with CHP—especially energy con-servation. Small-scale distributed CCHP applica-tions, an important part of novel DERtechnologies, are the issue of CCHP recently.Generally, CCHP indicates large-scale technolo-gies and applications that appear complicated tosome government officials, investors and endusers. Thus, the definition, benefits and classi-fication of CCHP systems should be madeknown universally, since the lack of educationand awareness about CCHP remains the fore-most barrier to progress. Lack of understandingabout CCHP concepts, benefits and techno-logies have halted its further popularization;‘‘wait and see’’ is the attitude of both investorsand users.
2.
Existing and potential technologies of CCHP areavailable. These technologies contain both im-proved conventional approaches, like steamturbines, reciprocating engines, combustion tur-bines and electric chillers, as well as relativelynew technologies such as fuel cells, micro-turbines, Stirling engines, sorption chillers anddehumidifiers. Most prime mover technologiesare still based on fossil fuel combustion, sincerenewable energy technologies cannot totally andeconomically replace traditional technologies inthe near future. Therefore, CCHP technologiesprovide the world with a transitional system ofreliable and stable energy supply. There may begrounds for the argument that there are toomany alternative technologies and modes ofconfigurations existing, confusing potential usersabout a particular CCHP unit. However, it isbelieved that the more choices available, themore possibilities—exist for CCHP utilization indiverse circumstances. Better understanding ofuser demands, careful selection of technologiesand full consideration of revenue are the key-stones to a successful CCHP application.
3.
The CCHP world market has grown rapidly in thelast decade, despite the fact that development levelsdiffer from country to country. CCHP developmentin the US and Europe restarted recently, after a


short period of slow growth. Nonetheless, barriersto development still exist in these countries, such aslimited liberated electricity market, gas price vola-tility, high initial cost, etc. Development in Japanseems to be steady; the number of sites and the totalcapacity are gradually increasing. The two newlyemerging markets, China and India still are a longway from a boom in CCHP applications. Otherdeveloping countries have begun to encouragedevelopment of CCHP in their domestic energysupply market, and the governments of thesecountries follow various strategies according to theunique characteristics of their countries. Fromanalysis of the world market, section by section, itis apparent that government policies, liberation ofthe electricity market and price of electricity andfuels are critical in the development of CCHP.Many countries have set a short-term target forCCHP applications, so the capacity share of DER isplanned to double from 7% currently to 14% in2012, with the combined efforts of governments,entrepreneurs, energy professionals and end users.

Acknowledgements

This work was supported by the Research Fundfor the Doctoral Program of Higher Educationunder contract no. 20040248055 and the NationalScience Fund for Distinguished Young Scholars ofChina under contract no. 50225621. The supportfrom the Key Research Program of MOE Chinaregarding Distributed Energy Systems is alsoappreciated.

The authors thank Elsevier for the kind permis-sion to use the Figs. 5, 7 and the Tables 1, 2, 4, and5, from the references [20,30,35,37].

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