Moné et al., 2001

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Economic feasibility of combined heat and power and

absorption refrigeration with commercially available gas

turbines

C.D. Mone, D.S. Chau, P.E. Phelan *

Department of Mechanical and Aerospace Engineering, Arizona State University, P.O. Box 876106, Tempe, AZ 85287-6106, USA

Received 6 June 2000; accepted 15 November 2000

Abstract

Combined heat and power (CHP) systems often use absorption technology to supply heating and cooling

to a facility. With the availability of gas turbines spanning an increasingly wide range of capacities, it is

becoming more and more attractive to utilize CHP via a combination of gas turbines and absorption

chillers. The present study investigates the economic feasibility of implementing such CHP systems with

existing, commercially available gas turbines and single, double, and triple eect absorption chillers. Themaximum amount of thermal energy available for the chiller is calculated based on the size of turbine,

exhaust ow rate and exhaust temperature, yielding approximately 300,000 kW of cooling (85,379 tons) for

a large power turbine. The annual demand and usage avoided costs for varying turbine and absorption

system sizes are discussed as well, showing that a CHP system is capable of saving millions of dollars

annually on electricity. 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Combined heat and power; Gas turbines; Absorption refrigeration; Economic analysis

1. Introduction

Cogeneration is dened by the American Society of Heating, Refrigerating and Air Condi-tioning Engineers (ASHRAE) as the sequential generation of electrical and thermal power using

one energy source [1]. The primary objective of a combined heat and power (CHP) system, alsoknown as a cogeneration system, is to convert fuel into shaft horse power. Typically, natural gas is

Energy Conversion and Management 42 (2001) 15591573

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* Corresponding author. Tel.: +1-480-965-1625; fax: +1-480-965-1384.

E-mail address: [email protected] (P.E. Phelan).

0196-8904/01/$ - see front matter

2001 Elsevier Science Ltd. All rights reserved.P I I : S0196- 8904( 00) 00157- 6

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used, but there are installations in operation that use wood, agricultural waste, peat moss and a

wide variety of other fuels, depending on local availability. Most engines convert only 35% of the

Nomenclature

COP coecient of performanceh enthalpy (kJ kg1)

_m mass ow rate (kg s1)W work (kW)Q thermal energy (kW)DS demand savings ($year1)DC demand cost ($ kW1)

US usage savings ($year1)UC usage cost ($ kW h1)cp specic heat (kJ kg

1C1)

T temperature (C)

hfg latent heat (kJ kg1)DGC natural gas demand ($ kW1)GC natural gas cost ($ MMBtu1)kgc conversion constant (3412 Btu kW

1)g eciency factore eectiveness

Subscripts

des desorber

evap evaporatoro o peak

shld shoulder peakon on peakshaft electrical output from generatorg gas

in entering turbineout exiting turbineact actual power output

max maximum power outputmin minimum

hot,in exhaust gas

cold,in exiting desorbercold,out entering desorbersteam steamgen power generationab absorption system

1560 C.D. Mone et al. / Energy Conversion and Management 42 (2001) 15591573

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fuels available energy into shaft power. The remaining chemical energy becomes heat [2]. A more

ecient approach is to utilize CHP systems, which recover the majority of the rejected heat so thatit is suitable for space heating in buildings or for industrial processes. Typically, an overall e-

ciency of 80% is achievable with CHP [3].Combined heat and power systems require that a power generation turbine be installed on site

to produce the majority of the energy required for the company. The CHP system allows acompany to generate its own electric power and takes advantage of the rejected heat from the

turbine to run an absorption chiller for the cooling loads. These systems have an advantage overother types of cooling equipment in that they use waste heat as a source of power and do not relyon primary energy, except for small auxiliary equipment [4]. Until recently, this option has been

limited to companies requiring large amounts of energy, 1 MWe or greater. The US Departmentof Energy has been sponsoring studies of small scale CHP systems to reduce the energy re-

quirements of supermarkets, schools and restaurants [3]. This option not only saves money on thecooling load, but also saves on the overall energy requirement for the company, which greatly

decreases electrical bills.A CHP facility consists of equipment that uses energy to produce both electric energy and

forms of useful thermal energy (such as heat or steam) for industrial, commercial, heating or

cooling purposes. CHP facilities are designed as either bottoming cycle or topping cycle facilities.In bottoming cycle facilities, energy is rst used to satisfy the thermal demands of a high tem-perature process, and the rejected heat is then later used to produce electric power. In contrast,

topping cycle facilities rst transform the fuel into useful electric power output. The rejected heatfrom power production is then used to provide useful thermal energy. Either of these cycles canapply thermal energy to meet process heating, ventilation and air conditioning (HVAC) or

comfort requirements for steam or for hot or chilled water. Topping cycle units, though, oer

more opportunity than bottoming cycles for energy savings because of the availability of ap-propriate technologies and because low temperature processes account for the majority of totalthermal demands. The thermal (heat) output of this type of CHP unit is, therefore, around 1.7

times the electrical rating [5].There are four key factors that renew interest in cogeneration systems in general, and speci-

cally with CHP systems. The rst has been rising electrical costs. Initially, this was a major driving

force in the 1970s and 80s with rising fuel costs, the energy crisis, and the increased cost toconstruct a large power plant. The second key factor was the Public Utilities Regulatory PoliciesAct of 1978 (PURPA). PURPA was enacted to encourage and regulate the construction and

operation of cogeneration systems in the United States as a means for conservation of non-renewable fuel resources [6]. In defense of PURPA, the NOx emissions of delivered grid electricitywere compared to a CHP system with a new gas boiler. This study showed that the CHP system

can generate the same amount of steam and electricity as a conventional system, but at a vastenvironmental improvement [7]. The third factor has been the developments made in more e-

cient heat retrieval technology. The nal factor has been, and continues to be, the uncertainties inthe electric utility industry and its future. The increased costs of building a centralized powerplant, transmission lines, payback of the investment, and now deregulation of the industry all

contribute to the utility industries dilemma.Alefeld and Ziegler [8] discussed that steam can be eectively fed into an absorption system as

the heat of generation. They proved this for single eect and double eect absorption systems,

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showing that the latter with two desorbers is more eective. Perez-Blanco [9] and Grossman [4]

investigated the use of waste heat in industrial applications. They both demonstrated the feasi-bility on a large scale of using the waste heat in conjunction with an absorption system.

2. Background for combined heat and power systems

The major components of a typical combined heat and power system, either packaged or asindividual components, can be seen in Fig. 1. It consists of the turbine generating shaft power, a

heat recovery system for exhaust gas and the absorption refrigeration system.The combustion turbine that generates the shaft power is a Brayton cycle engine and attains

maximum eciency at high operating temperatures. The amount of power (Wshaft) produced by asimple Brayton cycle engine is represented by

Wshaft _mghin hout 1

where _mg is the mass ow rate of the hot exhaust gas from the turbine, and hin and hout are the inlet

and outlet enthalpies, respectively.A typical turbine operates at temperatures above 815C (1500F) and exhausts combustion

products between 427538C (8001000F) [3]. Passing the exhaust gas through a heat recovery

boiler produces steam and saves much of the thermal energy that would otherwise be lost.Combustion turbine CHP systems are particularly attractive in their ability to satisfy a wide range

of operating conditions. Industrial rated gas turbine-generator sets are commercially available insizes from approximately 100 kW up to more than 50,000 kW [10].

Fig. 1. CHP system.


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Heat recovery from the heat recovery steam generator (HRSG) is based on the enthalpy dif-

ference between the H2O/LiBr ow entering and leaving the desorber and on the total turbineexhaust ow [11]. The calculations take into account both the products of combustion and water

vapor. In a standard large electric power plant, much of the energy in the form of waste heat islost. In a large CHP system, the high grade heat is used in a combined cycle with a steam gen-erator (Rankine cycle) while the low grade heat from both cycles is used for the process or aHVAC system.

Heat exchangers recover the heat from the generators for the CHP units. In this way, 8085%of the heat rejected by the engine can be recovered. Generally, heat recovery is done in a fullyclosed system with an interfacing heat exchanger between the generator and the refrigeration

system. Typical equations for analyzing a heat exchanger use the eectiveness (e) to dene theperformance. The eectiveness is dened as the ratio of the actual heat transfer (Qact) to the

maximum possible heat transfer (Qmax) for the given inlet conditions:

e QactQmax

2

The maximum possible heat transfer is taken to be the product of the minimum heat capacityrate, _mcpmin, which is the specic heat (cp) multiplied by the mass ow rate ( _m), multiplied by thetemperature dierence between the two inlet streams, (Thot;in Tcold;in):

Qmax _mcpminThot;in Tcold;in 3

Within the HRSG, the minimum heat capacity rate is that of the natural gas. Our calculationsshow that after a few cycles of the CHP system, the heat capacity of the natural gas becomes the

minimum heat capacity rate: _mcpgas _mcpmin. Substituting into Eq. (3) and algebraically

combining with the denition of eectiveness (e) in Eq. (2), yields

Qact e _mcpminThot;in Tcold;in 4

This is the amount of energy that is transferred from the exhaust gas to the steam in the heatexchanger. The water undergoes a phase transformation from saturated liquid in the heat ex-

changer to saturated vapor upon exiting the HRSG. The energy transferred to the desorber in theabsorption system is a function of the mass ow rate of the steam and the latent heat of va-porization (hfg):

Qdes e _mcpsteamTcold;out Tcold;in _mwaterhfg 5

This equation calculates the heat energy available in the form of steam produced by the HRSGfor the absorption refrigeration system. The steam is the energy input used in the desorber to boil

o the refrigerant in the working uid. This energy transfer to the solution in the desorber causes aphase transformation of the saturated steam back to a saturated liquid.

The absorption refrigeration system is a heat operated cycle because most of the operating cost

is associated with providing the heat that ``regenerates'' the vapor from the high pressure liquid.In an absorption system, low pressure vapor from the evaporator is absorbed by the liquid so-lution in the absorber. If the absorption process were executed adiabatically, the temperature of

the solution would continue to rise until eventually the absorption of the vapor ceased. To per-petuate the absorption process, the absorber is water or air cooled, and the heat is ultimately


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rejected to the atmosphere. The pump moves the low pressure liquid, from the absorber, elevates

the pressure of the liquid and delivers the solution to the desorber. In the desorber, heat from ahigh temperature source, such as waste heat from a turbine generator, drives o the vapor that the

solution absorbed. The liquid solution returns to the absorber through a throttling valve toprovide a pressure drop to maintain the pressure dierence between the desorber and absorber.

The pattern for the ow of external heat to and from the four heat exchange components in theabsorption cycle is such that the high temperature heat enters the desorber while the low tem-

perature heat (the refrigeration load) enters the evaporator. The heat rejection from the cycleoccurs at the absorber and condenser at temperatures such that the heat can be discarded to theatmosphere or a body of water. The eciency of the absorption cycle is represented by the COP

and is dened as

COP Rate of refrigeration

Heat load of desorber

Qevap

Qdes6

The steam produced from the heat exchanger is in a closed loop leading to the desorber.Manipulating Eq. (5) to solve for the steam mass ow yields

_msteam eQdes

cpsteam Tcold;out Tcold;in hfg7

This equation solves for the steam mass ow rate, which is essential for calculating Qevap, the

cooling capacity of the absorption system. Therefore, exhaust heat from the power generatorindirectly supplies the heat needed in the desorber (Qdes) to regenerate the working uid and boil

o the refrigerant. Dotiwalla [12] discussed that the energy from exothermic reactions can saveelectrical power costs by applying it in an absorption refrigeration system. He stated that a single

eect absorption system requires 8.3 kg h1 (18.3 lb h1) of saturated steam per kilowatt in thedesorber and a double eect system needs only 4.5 kg h1 (9.9 lb h1). These approximate guresare used to conrm the practicality of the present model and results.

The waste heat from the generator can be fed into dierent types of absorption systems, de-pending on the individual demands of the facility. This paper examines the three options that are

currently available single, double, and triple eect.The single eect refrigeration cycle is a two pressure heat operated cycle. The refrigerant (water)

circulates from the condenser to the evaporator, to the absorber, the desorber, and back to thecondenser. The absorbent (lithium bromide) circulates from the absorber to the desorber as adilute (weak) solution and from the desorber to the absorber as a concentrated (strong) solution.

One drawback of the single eect absorption system is its inability to take advantage of hightemperature heat sources to achieve a higher COP. This relatively low COP causes it to be dicult

for a single eect system to compete economically with conventional vapor compression systems,except in waste heat applications. The double eect system, in which the heat input is used twice togenerate vapor, helps solve this problem. The double eect technology is much more competitive

with vapor compression, with a COP range of 1.01.2 [5].One key to the increased COP of the double eect cycle is an internal heat exchange that takes

place between the high condenser and the low rst stage desorber. The double eect cycle requires

a higher source temperature for the rst desorber than that needed in the single eect system.Vapor is generated in the high desorber, where the heat (Qdes) is input and then ows to the high


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condenser where it changes phase by rejecting heat, as in the single eect system. The second key is

that the rejected heat is at a suciently high temperature that it can be used to drive vapor out ofthe weak solution in the low desorber, taking advantage of the increased availability of the higher

temperature heat input.Single eect and double eect systems are manufactured and commercially available. The triple

eect absorption cycle is the latest development in the history of absorption systems and fewmachines have been tested outside the laboratory. In most cases, a practical COP of 1.5 is feasible

with the triple eect absorption system [13,14].The same theories apply to the triple eect system as for the double eect. A third desorber adds

a regeneration process to the cycle. Again, the key of the triple eect is the use of internal waste

heat to increase the COP. The triple eect cycle requires a higher initial temperature to the pri-mary desorber, taking advantage of the increased availability of the high temperature heat input.

3. Modeling

The equations developed in this paper can generate results for the potential cooling capacity

supplied by the evaporator for many dierent power generators. After gathering data for over 50dierent manufacturers and over 200 dierent models of natural gas turbines, it is possible tocompare the electric power output versus the evaporator cooling capacity. The detailed infor-

mation on the manufacturers and models of turbines is listed in Table 1.The modeling of the CHP systems applies the following assumptions:

Saturated water exiting the desorber to the HRSG is at 135.0C (275.0F) [15].

Saturated steam exiting the HRSG to the absorption system is at 176.7C (350.1F) [16]. The eectiveness of the counterow HRSG system is 70% [16]. Natural gas is the fuel for the turbines. All data on continuous power output, exhaust temperature from the turbine and mass ow of

gas are the latest available data [10]. All turbines have a thermodynamic eciency of 35%, which is typical of values described in

publications [3,7,17]. The cost of natural gas is $ 3 MMBtu1 [18]. The cost of electricity, rate schedule and time of day charges are those given in Table 2. The absorption system is sized per available exhaust heat from the generator. This assumes that

the absorption system supplies at least the minimum cooling and/or process load for the facility. Lithium bromide is used as the absorbent uid.

Pump is isentropic. Valves are adiabatic.

Refrigerant is pure water and at a steady state. Pressure is constant throughout except through pumps and valves. No jacket heat losses.

To provide a baseline for future work, the absorption refrigeration models were designed tocalculate a realistic COP value. Therefore, the single eect system has a COP 0:7, the doubleeect has a COP 1:2 and the triple eect cycle has a COP 1:5.


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Both the turbine and absorption systems are constantly operating at full load 8,760 h year1,

meeting the facilitys minimum power requirements.

The mass ow rate within the absorption system is the basis for calculating the potential

cooling capacity and COP. The ow rates of the lithium bromide solution between the desorberand absorber play an important role for the combined heat and power system. Within eachsystem, the ow rates are related to the potential size of the system, but between the multi-eect

absorption systems, they are dierent.All of the assumptions listed allow multiple absorption systems to be considered and compared

for power consumption and economic benet. As expected, the triple eect cycle requires less

power to regenerate the working uid than a single or double eect cycle at the same cooling

Table 1

Summary of turbine manufacturers and turbine characteristics [10]

Manufacturer Output kW continuous Exhaust mass ow

(kgs

1

)

Exhaust temperature

(

C)ABB Power Generation Ltd. 52,800265,000 179.2532.1 562612

Ansaldo Energia 62,500240,000 191.9639.6 581612

Cooper Rolls 27,21030,500 91.992.0 519540

Daihastsu Diesel Mfg. Co., Ltd. 13251326 3.09.5 512602

Dresser-Rand A/S 153041,930 15.0127.0 495655

Fiat Avio S.p.A 22,035146,915 69.0656.2 493628

GE Marine & Industrial Engines 417649,440 15.9154.0 432582

GE Power Systems 26,300255,600 122.0624.0 519659

Kawasaki Heavy Industries, Ltd. 14657,160 8.026.3 558968

Mashproekt 6700110,000 31.0357.4 205575

Mitsui Engineering & Ship building

Co., Ltd.

108010,690 5.0102.0 469534

MTU Motoren and Turbinen-

Union

14,32044,850 46.7127.7 482555

Niigata Engineering Co., Ltd. 20010,730 2.640.0 434652

Nuovo Pignone SpA 2000255,600 24.6638.0 482659

Pratt & Whitney Canada Inc. 4651984 3.08.0 541630

Rolls-Royce 147252,550 8.1158.8 460612

Solar Turbines Incorporated 351512,611 6.548.9 400540

Thomassen International B.V. 10,000282,000 52.0613.0 402639

Turbomeca 1001230 0.96.0 512607

Westinghouse Electric Corporation 27,240236,700 91.1669.5 458646

Table 2

Assumed rate schedule, cost of electricity and peak times

On-peak rate Shoulder-peak rate O-peak rate

Demand charge ($ kW1) 7.520 2.055 0.255

Usage charge ($ kW h1) 0.0458 0.0414 0.0248

Hours/peak 1444 1812 5504


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requirement. This will greatly benet the utilization of waste heat. For the same quantity of

energy input to the desorber, a greater amount of cooling capacity is possible.Given these assumptions, each power generator is capable of producing a certain amount of

available cooling based upon its exhaust mass ow and temperatures, as shown in Figs. 2 and 3.

Because of the exhaust temperatures limited range, 427538C (8001000F), the exhaust tem-perature has a much smaller eect on the amount of cooling possible than the exhaust gas mass

Fig. 2. Calculated available cooling capacity from existing, commercially available turbines used in CHP systems.

Fig. 3. Calculated available cooling capacity from existing, commercially available turbines used in CHP systems (050

kWe only).


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ow rates, 0.88669.5 kg s1. The amount of cooling available from the absorption system is not

only a function of the turbine exhaust ow rate but also of the number of stages in the absorptionrefrigeration system. As explained previously, the mass ow within the absorption system varies,

along with the stages, and will aect the amount of energy needed for a specic cooling load. Fig.3, taking into consideration only the smallest CHP systems, shows that if the amount of heat tothe desorber is held constant, then the amount of refrigeration available from the evaporatorincreases as the number of stages increases. The slight data point variation is due to the exhaust

temperature dierences from similar power generators.

4. Economic analysis

The fuel savings and economics of CHP are grounded in the laws of thermodynamics, which

state that a heat source at an elevated temperature has a greater capability to perform work thanthe same amount of heat at a lower temperature. Thus, the high temperature heat converts to

electricity, and the lower temperature exhaust streams are used for process heat.If only process heat were needed and the electricity in a resistance heater were used to obtain

additional process heat, using electricity to create heat indirectly would produce a net loss,

compared with using an ecient single purpose boiler supplying steam for process heat. Allenergy savings which avoid purchasing grid electricity for both process electrical requirements andto power an electric chiller must be related to the alternative of independent electricity generation

for other than thermal energy for heating applications.The nancial benet that a CHP system yields may stimulate companies to invest in such sys-

tems. To evaluate the simple payback period for a CHP installation, the costs of purchasing,

maintaining and running the unit must be apparent, coupled with the value of the generated heatand power. The latter will depend on the existing facility, cost of electricity and taxes. The daily and

annual hours of operation are also critical in determining the cost eectiveness of the installation.It is possible to assume, strictly for comparison, the hours of operation and a standard rate

schedule used by the electric companies, as listed in Table 2. A single, double, or triple eect

absorption system will have dierent economic advantages. The cost of natural gas will remainconstant, as will the avoided cost of not having to purchase as much power from the utility

company, with respect to a particular natural gas power generating turbine. The annual savingsfrom the utility company will adjust according to the number of stages in the absorption cycle ofthe CHP system. This is due to the waste heat being used to meet the cooling loads in an ab-

sorption system, avoiding the cost of running conventional electric chillers.The economic equations for the demand savings, DS, and usage savings, US, all calculated

using the utility demand charges, DC, and usage charges, UC, for each peak (subscripts: on-peak,

shld-peak and o-peak) are straightforward:

DSgen QgenDCon-peak QgenDCshld-peak QgenDCoff-peak 8

USgen QgenUCon-peakton-peak QgenUCshld-peaktshld-peak QgenUCoff-peaktoff-peak 9

DSab QabDCon-peak QabDCshld-peak QabDCoff-peak 10


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USab QabUCon-peakton-peak QabUCshld-peaktshld-peak QabUCoff-peaktoff-peak 11

where Qgen and Qab represent the electricity being avoided with a CHP system for the electrical

(turbine) and thermal (absorption) requirements. Both the generator and the absorption systemassist in the electrical savings. Producing power on site and utilizing the waste heat for coolingreduces the amount of electricity purchased from the utility company and, therefore, avoids some

electric cost.The avoided cost is the savings achieved by eliminating the purchase of electricity from the

utility company by producing power and using the exhaust heat for the absorption system. Fig. 4shows the avoided cost by utilizing a CHP system as the alternative to grid electricity for doubleeect systems. Although not shown, a single eect system would appear to have the greatest

avoided cost. This is due to the eciency of the system being lower than that of the double andtriple eect systems, thus requiring more energy for the same cooling capacity.

The avoided costs in Fig. 4 are not the total annual savings. A CHP system requires that a

turbine be installed at the facility to generate electricity. Therefore, natural gas will need to bepurchased to operate the turbine. The amount of fuel needed is dependent upon the output of theturbine, Wshaft, and its eciency (ggen):

DGC Wshaft

ggen

kgcGC 12

where kgc is a conversion constant between the turbine power output (kWe) and the cost of the

natural gas ($ MMBtu1). Fig. 5 shows the cost of the natural gas (DGC), the total avoided cost,and savings for a given generator output, for a double eect absorption refrigeration system.

Fig. 4. Double eect CHP avoided costs (turbine and chiller).


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5. Discussion

Any building with accurate electrical and cooling load proles is a potential application for acombined heat and power absorption chiller [17]. These simulations were established using thegeneric cooling load prole depicted in Fig. 6. It is based on examples supplied in Refs. [19] and

[20]. The daytime and nighttime loads throughout the year are assumed to be constant. The

annual electrical cost avoided by installing a natural gas turbine at a facility can be a substantialamount. However, these results do not take into consideration the initial cost of purchasing and

installing a CHP system, which would relate to the return on the investment of the CHP system.

Fig. 5. Double eect CHP total costs and savings.

Fig. 6. Generic daily cooling load prole.


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This is on account of the tremendous dierence between manufacturers turbine costs, installation,

geographical location for shipping and the inability to collect sucient data.The annual savings due to the chiller depend upon the number of stages in the absorption

system. The triple eect system, although not in production yet, has the best chance of being

cost eective by reason of the avoided expense in purchasing electricity. In the same respect, thetriple eect has the greatest annual savings, as Fig. 7 represents. The dierences in the annual

savings come from the fact that for the same heat of generation supplied from the rejected heat,more cooling is possible with an increase in the number of stages due to the higher COP values.

This is taking into account that the triple eect is capable of achieving the same cooling ca-pacity in the evaporator with less energy required to regenerate the absorbent solution in thedesorber.

6. Conclusions

The goal of this paper was to demonstrate the economic feasibility of combined heat and power

systems using commercially available gas turbines. The scenario was the use of waste heat from aCHP system on site to satisfy the cooling and heating requirements of a facility using a single,double, or triple eect absorption refrigeration system and then compare the potential savings and

payback of such systems.The combined heat and power systems are demonstrated to be potentially benecial to con-

sumers. The amount of heating or cooling available from rejected heat is immense with the actual

amount available to the absorption system being a function of the mass ow rate of the exhaustgas, the temperature of the gas, and the turbine size. The cooling capacity of the evaporator is

Fig. 7. Comparison of annual savings with a CHP system.


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more a function of the gas exhaust ow rate than the temperature due to the small variation in

temperatures between turbine manufacturers.The possible savings achieved by installing a CHP system, in both the avoided electrical costs

due to the power produced on site and the absorption system using thermal energy from theturbine, are determined. The savings are a function of the cost of natural gas and the avoided gridelectricity purchased for the demand and usage of the facility. The triple eect system has thegreatest cooling capacity with the least amount of rejected heat required.

Acknowledgements

CDM wishes to acknowledge ASHRAE for their support provided by a Grant-In-Aid Schol-arship that made this research possible. All authors wish to acknowledge the Rebuild America

Project for its support of personnel during this project.

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