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An experimental investigation of a household size trigeneration
Applied Thermal Engineering 27 (2007) 576–585 www.elsevier.com/locate/apthermeng
An experimental investigation of a household size trigeneration Lin Lin a, Yaodong Wang b,c,*, Tarik Al-Shemmeri d, Tom Ruxton d, Stuart Turner d, Shengchuo Zeng b, Jincheng Huang b, Yunxin He b, Xiaodong Huang b a Nanning College for Vocational Technology, Nanning, Guangxi 530003, China Mechanical Engineering College, Guangxi University, Nanning, Guangxi 530004, China Northern Ireland, Centre for Energy Research and Technology, School of Built Environment, University of Ulster, Newtownabbey BT37 0QB, United Kingdom d Faculty of Computing, Engineering and Technology, Staffordshire University, Stafford ST18 0AD, United Kingdom b
c
Received 12 February 2006; accepted 31 May 2006 Available online 17 July 2006
Abstract A household size trigeneration based on a small-scale diesel engine generator set is designed and realized in laboratory. Experimental tests are carried out to evaluate the performance and emissions of the original single generation (diesel engine generator); and the performances of the whole trigeneration including the diesel generator within the trigeneration system, the heat exchangers which are used to recover heat from engine exhaust, the absorption refrigerator which is driven by the exhaust heat; and the emissions from the whole trigeneration. Comparisons of the test results of two generations are also performed. The test results show that the total thermal efficiency of trigeneration reaches to 67.3% at the engine full load, comparing to that of the original single generation 22.1% only. Within the range of engine loads tested, the total thermal efficiencies of trigeneration are from 205% to 438% higher than that of the thermal efficiency of single generation. The CO2 emission per unit (kW h) of useful energy output from trigeneration is 0.401 kg CO2/kW h at the engine full load, compared to that of 1.22 kg CO2/kW h from single generation at the same engine load. Within the range of engine loads tested, the reductions of CO2 emission per unit (kW h) of trigeneration output are from 67.2% to 81.4% compared to those of single generation. The experimental results show that the idea of realizing a household size trigeneration is feasible; the design and the set-up of the trigeneration is successful. The experimental results show that the innovative small-scale trigeneration is able to generate electricity, produce heat and drive a refrigeration system, simultaneously from a single fuel (diesel) input. 2006 Elsevier Ltd. All rights reserved. Keywords: Trigeneration; Diesel engine generator; Performance; Emissions
1. Introduction Trigeneration is a simultaneous production of power, heat and cooling/refrigeration [1], as shown in Fig. 1. Although the basic theories and technologies for the power *
Corresponding author. Address: Northern Ireland, Centre for Energy Research and Technology, School of Built Environment, University of Ulster, Newtownabbey BT37 0QB, United Kingdom. Tel.: +44 28 90366807. E-mail address: [email protected] (Y. Wang). 1359-4311/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2006.05.031
generation, heat exchange, and absorption refrigeration are not new, combining them together is a quite new idea. The concept of trigeneration comes to use is only at the mid1990s. Some investigations have been conducted by a number of researchers [2–16], which showed an encouraging effect on raising the energy efficiency and reducing greenhouse gases emissions. The results from the investigations show that trigeneration have the advantages over single electricity generations and cogenerations (Combined heat and power): the total energy efficiency is higher; the emissions of CO2 and the other waste gases are lower; and it
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Nomenclature COP F P Q g
coefficient of performance coefficient of CO2 emission per kW h of power (useful energy) output (kg CO2/kW h) power (kW) heat flow rate, extracted or supplied (kW) thermal efficiency
G h HE EB tri
generator in the absorption system heating heat exchanger engine block trigeneration
Subscripts e electrical generation, electrical power E evaporator
Fig. 1. Trigeneration and the test rig: (a) design of trigeneration and (b) the completed trigeneration test rig.
has more choices for useful energy outputs, i.e., electricity, heat and cooling/refrigeration. The results show that trigeneration has both of the economic and environmental merits. Most of these researches are theoretical/computational simulation [5–14]. Only a few of them are the experimental/ practical studies on trigeneration systems [4,15,16]. The systems they studied are all on quite big scales. The household size trigeneration system, which are suitable for the independent households in remote or isolated areas where no central power supplies are available, has not been studied. The objective of this study is to investigate the feasibility to realize a household trigeneration system and to carry out experimental tests to investigate the performance and the exhaust emission characters of the system, comparing to those of the original single power generation system. The trigeneration, a small-scale combination of power generation with a heat recovery unit and a small-scale absorption refrigerator is designed and has been realized in laboratory. This trigeneration is based on a diesel engine generator set, coupling with a heat recovery system which makes use of the waste heat from the exhaust gas and the cooling system of the engine to supply heating, and an absorption refrigerator which utilizes the exhaust heat from the engine to generate refrigeration effect. This com-
bination may provide three kinds of energy supply for the demands of a family uses. The following sections will present the character of the realized trigeneration; the experimental results from the investigation, including the energy efficiency and the CO2 emission of the trigeneration system, and a comparison with the original single power generation system. 2. Experimental set-up and test plan Fig. 1(a) shows the simplified schematic diagram of the experimental study of the trigeneration system and the test rig set-up. It consists of a test-bed, a diesel engine and a generator, a heat exchanger, an absorption refrigerator, a fuel tank, an air box, a data acquisition system, a computer, an operation panel, four exhaust emission analyzers, and various sensors to measure the oil pressure, the exhaust temperature at the manifold, etc. Fig. 1(b) shows the photo of the realized trigeneration system in the laboratory. 2.1. The engine and generator A Lister–Petter T series diesel engine, which is shown in Fig. 2(a), is selected for the study and is mounted on a test
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Fig. 2. Experimental equipments: (a) diesel engine and generator, (b) heat exchangers, (c) absorption refrigerator and (d) emission analyzers.
bed. The engine is type TS2, two cylinders, swept volume 1270 ml, normal aspiration, 9.5 kW capacity, 238 g/kW h brake specific fuel consumption, fixed speed (1500 rpm). It is a generator engine equipped for Lister–Petter series diesel generator. It is an air-cooled, direct injection diesel engine. The Leroy Somer LSA410 type generator, which is also shown in Fig. 2(a), 415 V, synchronous, 10 A full load current, prime power output for three phases is 8.4 kW (10 kV A) at 1500 rpm, single bearing, was connected to the engine by a prop shaft. 2.2. Heat exchangers Two heat exchangers, which are shown in Fig. 2(b), are selected for the experimental tests to recover heat from the engine exhaust gas according to the maximum heat output from the exhaust gas and the availability in the laboratory. The heat exchangers are cross flow, multi-flattened tubeand-finned, compact, and made of aluminium. The sizes of the two heat exchangers are respectively: Heat exchanger 1: height 550 mm, width 610 mm, thickness 50 mm. Heat exchanger 2: height 750 mm, width 710 mm, thickness 65 mm.
2.3. Absorption refrigerator An Electrolux absorption refrigerator is used in the experiment, which is shown in Fig. 2(c). It is a commercially
available refrigerator. It can be powered by electricity, or liquefied petroleum gas (LPG). When it is run by alternating current power (230 V), the power input is 105 W; when it is run by direct current supply (12 V), the input is 100 W; when it runs by LPG gas, the input is 186 W. The capacity of the refrigerator is 60 l; the capacity of the freezer is 6 l. 2.4. Emission analyzers Four exhaust gas analyzers, which are shown in Fig. 2(d), made by the Analytical Development Company Ltd (Hoddesdon, Hertfordshire, EN11 0DB, England), are used to analyze the exhaust emissions from the engine, i.e., carbon monoxide, carbon dioxide, hydrocarbon and oxides of nitrogen. Prior to testing, the analyzers were calibrated separately by using the special sample gases supplied by BOC Ltd. 2.5. Experimental plan A plan is designed for the experimental investigation of the performance of the trigeneration system. 2.5.1. The plan for the performance of engine generator running on a single generation scheme A series of tests are designed to evaluate the engine generator performance when it runs on a single generation scheme. In the tests, the engine load varies between idle to full loads; relevant data is to be recorded such as the engine generator power output; fuel consumption, engine exhaust temperature and emissions. The tests are to be
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conducted and repeated three times, in order to increase the reliability of the test results.
during the whole experiment process. The test results are shown in the following figures and tables.
2.5.2. The plan for the performance of trigeneration A series of tests are also designed to evaluate the performances of trigeneration. In these tests, the engine load varies between idle to full load, the same as that of single generation; and the required parameters are to be recorded in order to evaluate the total output of power, heat and refrigeration effect, which including
3.1. Test results of engine generator performance and the comparison
• engine generator power output; • heat recovered from heat exchangers and the engine cooling system; • heat input to the generator in the absorption refrigerator; • refrigeration effect generated in the absorption refrigerator; • evaluation of coefficient of performance (COP) of the absorption refrigerator; • emissions from the trigeneration system. The tests are also to be conducted and repeated three times, in order to increase the reliability of the test results. 3. Test results and discussion
800
6
700
5
600 BSFC (kW)
7
4 3 2
500 400 300 200
1
100 0
0 0
25
50
75
SG
TG
0
100
25
50
Engine Load (%)
SG
35.0 30.0 25.0 η e ( %)
Pe (kW)
The diesel engine generator system runs well on the single generation scheme and the trigeneration scheme mentioned above. There are no engine faults happening
The test results of the performances of engine generator on the conventional single generation scheme (SG) from the three tests on average are shown in Fig. 3. The test results of the performances of engine generator on the trigeneration scheme (TG) from the three tests on average are also shown in the figure. Table 1 presents the comparison of the performances of engine generator on SG and on TG. The results show that the electrical power outputs are nearly the same; the differences are very small; the maximum difference is 2.0%. The test results of brake specific fuel consumption (BSFC) of engine generator on SG and TG are also shown in Fig. 3. A comparison of SG with TG is also shown in Table 1. The results show that the BSFCs of SG and TG are nearly equal each other, the differences are small; the largest is only 3.5%. The test results of thermal efficiencies of engine generator on SG and TG are also showed in Fig. 3. A comparison of SG with TG is also showed in Table 1. The test results show that the thermal efficiencies of engine generator on SG and TG are nearly the same. The maximum difference is 3.1% in absolute value, as shown in Table 1. From the test results and the comparisons above, it can be seen that when the engine generator runs on
20.0 15.0 10.0 5.0 0.0 0
25
50 SG
75 TG
100
Engine Load (%)
Fig. 3. Variation of Pe, BSFC and ge with engine load and comparison of SG with TG.
75 TG
100
Engine Load (%)
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Table 1 Comparison of electrical power output, brake specific fuel consumption and thermal efficiency of the diesel engine generator run on SG and TG Engine load (%)
SG
TG
SG
TG
SG
TG
Pe (kW) differences between SG and TG
Relative Pe differences (%)
Differences of BSFC (g/kW h)
Relative of BSFC differences (%)
Differences of ge
Relative difference of ge (%)
0 25 50 75 100
0.00 0.01 0.00 0.09 0.01
0.0 0.7 0.0 2.0 0.2
–
–
4 14 5 13
0.6 3.1 1.4 3.5
0.0 0.1 0.5 0.3 0.7
0.0 0.8 2.6 1.4 3.1
trigeneration scheme, the engine and generator performances are still the same as those of single generation. The results show that the design and the implement of the addition of the heat recovery system and the absorption refrigerator to the engine generator does not influence the performance of the engine generator. This gives a good base for the following comparison of the performances of TG system with that of SG system. 3.2. Engine emissions The emissions from the diesel engine on SG and TG are shown in Fig. 4 and a comparison of the emissions from the two systems are showed in Table 2. The results show that the differences of emissions for the two generations are for CO2 emission, the differences are between 0.4% and 2.9%; for CO emission, the differences are from 0.0% to 8.3%; for HC emission, the error are between 4.2%
and 42.9%; for NOx emission, the differences are from 0.0% to 3.7%. The results show that the differences are mostly very small and are negligible. 3.3. Test results of heat recovered from engine exhaust and engine cooling system Experiments of trigeneration are performed and the data of the heat collected from engine exhaust and engine cooling system (engine block) are recorded to evaluate the amount of heat energy obtained from the TG system. The test results are presented in Fig. 5. The results show that the heat recovered from engine exhaust with two heat exchangers is from 1.70 kW at the engine no load to 4.91 kW at the engine full load; the heat obtained from the engine cooling system (engine block) is from 3.84 kW at the engine 0% load to 6.43 kW at the engine full load; the total amount of heat obtained from TG is from
9
0.06
7
0.05
6
0.04
CO (%)
CO2 (%)
8
5 4
0.03 0.02
3 2
0.01
1
0 0
0 0
25
50 SG
TG
50 SG
75 100 Engine Load (%)
75 TG
100
Engine Load (%)
1 200
40 35
1 000 NOx (ppm)
30 HC (ppm)
25
25 20 15
800 600 400
10 200
5
0
0 0
25
50 SG
75 TG
100
Engine Load (%)
0
25
50 SG
75 TG
100
Engine Load (%)
Fig. 4. Variation of CO2, CO, HC and NOx content in exhaust with engine load and comparison of SG with TG.
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Table 2 Comparison of engine emissions of CO2 (%), CO (%), HC (ppm) and NOx (ppm) in exhaust Engine load (%)
SG
TG
SG
TG
SG
TG
SG
TG
Differences of CO2
Relative differences of CO2 (%)
Differences of CO
Relative differences of CO (%)
Difference of HC (ppm)
Relative difference of HC (%)
Difference of NOx (ppm)
Relative difference of NOx (%)
0 25 50 75 100
0.05 0.08 0.12 0.12 0.03
2.6 2.7 2.9 2.1 0.4
0.002 0.000 0.001 0.001 0.002
8.3 0.0 5.6 5.3 3.6
6 3 2 1 4
42.9 16.7 10.0 4.2 13.3
3 0 7 6 39
1.3 0.0 1.3 0.8 3.7
12.00 10.00 Q (kW)
8.00 6.00 4.00 2.00 0.00 0
25
50
75
100
Engine Load (%) Heat from enigne exhaust
Heat from Engine Block
Total heat
Fig. 5. Variation of heat from exhaust and engine block with engine load in trigeneration.
5.54 kW at the engine 0% load to 11.34 kW at the engine full load. 3.4. Test results of refrigerator performance driven by the heat from engine exhaust in trigeneration The parameters of the performance of refrigerator were recorded and evaluated when the trigeneration were running on five engine loads (0%, 25%, 50%, 75% and 100%), according to the test plan. The test results presented and discussed below are mainly concerned about the most important parameters for the refrigerator as following: • heat input into the generator in the absorption refrigerator QG; • refrigeration effect generated QE; • coefficient of performance (COP) of the absorption refrigerator; • Generator (boiler) temperature in the refrigerator tG; • Evaporator temperatures in the refrigerator tE1 (in freezer) and tE2 (in food compartment). The generator temperature is the indicator of the heat energy input to the refrigeration system; the evaporator temperature is the indicator of the refrigeration effect generated in the refrigerator. The following table present the test results of QG, QE, and COP; and the following figures present the following temperatures: refrigerator boiler tem-
perature tG; refrigerator evaporator temperature 1 (at the point in freezer) tE1; refrigerator evaporator temperature 2 (at the point in refrigerator food compartment) tE2. The test results for temperatures in the refrigerator are showed in Fig. 6 and Table 3. Table 3 also includes the test results for the original power supplies as reference cases (AC power, DC power and liquid petroleum gas). From Fig. 6 and Table 3, it can be seen that: At the engine load of 0%, the generator temperature is between 126 C and 132 C (see Fig. 6(a)). The final evaporator temperatures at freezer point and at food compartment point do not change; these indicate that there is no refrigeration effect generated in the refrigerator. At the engine load of 25%, as showed in Fig. 6(b), the generator temperature is between 169 C and 178 C. The final evaporator temperatures at freezer point and at food compartment point keep the same value as that the value at the starting points; these also indicate that there is no refrigeration effect generated in the refrigerator. At the engine load of 50%, it can be seen that the generator temperature is between 202 C and 205 C (see Fig. 6(c) and Table 3). The final evaporator temperature at freezer point is 17.5 C; the temperature at food compartment point is 0.8 C, when the environment air temperature is 25.0 C; these indicate that there is refrigeration effect generated in the refrigerator. In this case, the heat input to the refrigerator QG is 184 W on average for the three tests; the refrigeration effect QE is 6.1 W; and the coefficient of performance of the refrigeration system is 0.033. At the engine load of 75%, as shown in Fig. 6(d) and Table 3, the generator temperature is between 209 C and 218 C. The final evaporator temperature at freezer point is 24.9 C; at food compartment point is 8.2 C, when the environment air temperature is 24.0 C. The heat input to the refrigerator QG is 210 W on average for the three tests; the refrigeration effect QE is 7.2 W; and the coefficient of performance of the refrigeration system is 0.035. At the engine load of 100%, as showed in Fig. 6(e) and Table 3, the generator temperature is between 227 C and 245 C. The final evaporator temperature at freezer point is 20.1 C; at food compartment point is 1.9 C, when the environment air temperature is 24.5 C.
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a
b
250
250 225
200
200
175
175
Temperature (ºC)
Temperature (ºC)
225
150 125 100
150 125 100
75
75
50
50
25
25 0
0 -25
0
50
100
150 200 Time (min)
-25
0
50
100
150 200 Time (min)
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
250
d 250
225
225
200
200
175
175 Temperature (ºC)
Temperature (ºC)
c
150 125 100 75
150 125 100 75
50
50
25
25 0
0 -25
0
50
100
150
200
-25
0
50
150
200
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE
e
100
Time (min)
Time (min)
250 225 200 Temperature (ºC)
175 150 125 100 75 50 25 0 -25
0
50
100
150
200
Time (min) 1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
Fig. 6. Absorption fridge performances run by exhaust gas: (a) 0% engine load, (b) 25% engine load, (c) 50% engine load, (d) 75% engine load and (e) 100% engine load.
L. Lin et al. / Applied Thermal Engineering 27 (2007) 576–585 Table 3 Refrigerator performance comparison tE1 (C)
tE2 (C)
QG Q 0 G QE COP (W) (W) (W)
Tests
tG (C)
Run by AC power Run by DC power Run by LPG gas
200–205 18.2 3.4 105
470
8.1
0.0173
201–204 16.3
448
7.4
0.0165
201–204 26.0 1.5 186
7.3
0.0390
126–132 169–178 202–205 209–218 227–245
– – 6.1 7.2 7.4
– – 0.033 0.035 0.031
Run by engine exhaust gas (load, %)
0 25 50 75 100
– – 17.5 24.9 20.1
5.3 100
– – 0.8 8.2 1.9
– – 184 210 237
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ature of the refrigerator above 200 C; the results show that the COPs of the refrigerator driven by exhaust gas are higher than that of electrical power driven from the primary energy consumption point of view. But at the engine load of 0%, 25%, the temperature of exhaust gas is not high enough to drive the refrigerator. 3.5. Test results of the whole system performance of trigeneration compared to that of single generation The test results of the whole trigeneration system are presented as following:
The heat input to the refrigerator QG is 237 W on average for the three tests; the refrigeration effect QE is 7.4 W; and the coefficient of performance of the refrigeration system is 0.031. The test results show that at the engine load above 50%, the temperature of the exhaust gas is high enough to make the refrigerator work. The test results also show that the exhaust heat can be used as an energy resource for the absorption refrigerator if the exhaust gas is hot enough to make the boiler temper-
• power output and emissions from engine generator (as shown in 3.1 and 3.2); • heat recovered from heat exchangers and the engine cooling system (as shown in 3.3); • refrigeration effect generated in the absorption refrigerator; the coefficient of performance (COP) of the refrigerator (as shown in 3.4); • the performances of the total trigeneration. The detail test results of the whole trigeneration system from the engine load of 0–100% are shown in Fig. 7 and Table 4. From the figure and the table, it can be seen that
20 100
18 80
TG
14
60
12 ηt (%)
Useful Output (kW)
16
10 8 6
40 20
SG
4
0
2
0
0 0
25
50
75 100 Engine Load (%)
25
50
Single Generation
75 100 Engine Load (%) Trigeneration
5
1100
4
900 800
kg CO2/ kWh
SFC (g/kWh)
1000
700 600 500 SG
400
3
2 SG
300 200
1
TG
TG
100 0 0
25
50
75
100
Engine Load (%)
0 0
25
50
75
100 Engine Load (%)
Fig. 7. Variation of useful output energy, ge, SFC and CO2 emissions with engine load for TG and SG and their comparison.
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As for CO2 emission, a comparison of CO2 emission for these two kinds of generations is also shown in Table 5 and Fig. 7. From the figure and the table, it can be seen that
Table 4 Performance of trigeneration Load (%)
Qtri = Pe + Qh + QEB + QE (kW)
gtri (%)
BSFC (g/kW h)
Ftri (kg CO2/kW h)
0 25 50 75 100
5.54 8.06 11.14 14.18 17.83
64.6 64.0 68.3 67.1 67.3
131 131 126 120 128
0.418 0.422 0.395 0.402 0.401
• the CO2 emission per unit (kW h) of Electrical power output are from 1.22 to 2.27 kg CO2/kW h; • the CO2 emission per unit (kW h) of trigeneration output (electrical power + heating + refrigeration effect) are from 0.395 to 0.422 kg CO2/kW h. The CO2 emission per unit (kW h) of useful energy output of trigeneration are reduced by 67.2–81.4% compared to those of single generation. The emission quantities of CO2 emission from trigeneration are much lower than those from single generation.
• the useful energy outputs (Qtri) vary from 5.54 kW at the engine no load to 17.83 kW at the engine full load; • the thermal efficiencies of trigeneration vary from 64.6% at the engine no load to 67.3% at the engine full load; • the specific fuel consumptions are from 131 g/kW h at the engine load 0% and 25%, 126 g/kW h at the engine load 50%, 120 g/kW h at the engine load 75%, to 128 g/kW h at the engine full load; • the CO2 emissions are from 0.418 (kg CO2/kW h) at the engine no load, 0.422 (kg CO2/kW h) at the engine load 25%, 0.395 (kg CO2/kW h) at the engine load 50%, 0.402 (kg CO2/kW h) at the engine load 75%, to 0.401 (kg CO2/kW h) at the engine full load.
4. Conclusions From the results above, the following conclusions can be drawn: • When the engine generator runs as a single generation or in a trigeneration, the electric power outputs and the electrical thermal efficiencies are the same; the fuel consumptions are the same. • It is feasible to utilize the waste heat from exhaust gas of a diesel engine to drive the absorption refrigerator, when the engine load is over 50% with the exhaust gas hot enough to heat the generator above 200 C.
Table 5 shows the comparisons of the useful energy output, which includes electricity, heat and refrigeration effect, between trigeneration and single generation. From the results, it can be seen that the useful energy outputs from trigeneration are much higher than that of single generation: The increase rates are from 434% at the engine 25% load to 196% at the engine full load. Table 5 also shows the comparisons of the total thermal efficiency of trigeneration with the thermal efficiency of single generation. The total thermal efficiencies of trigeneration are from 205% to 438% higher than that of single generation. Table 5 shows the comparison of the brake specific fuel consumption of trigeneration with that of single generation. The fuel consumed by trigeneration is much less than that of single generation. The saving rates of fuel consumption for trigeneration over single generation are from 81.3% at the engine 25% load, to 66.1% at the engine full load.
The lowest evaporator temperature at the point in freezer of the refrigerator is 24.9 C; the temperature at the point in food compartment is 8.2C while the refrigerator is powered by the heat from engine exhaust gas at the engine load of 75%. • The total thermal efficiencies of trigeneration are from 205% to 438% higher than that of single generation under different engine loads. • The CO2 emission per unit (kW h) of useful energy output from trigeneration are reduced by 67.2–81.4% compared to those from single generation under different engine loads.
Table 5 Comparison of useful energy output, thermal efficiency, BSFC and CO2 emission of single generation to trigeneration Engine load (%)
Increase of output (kW) (Qtri Pe)
Increase rate (%) (Qtri Pe)/Pe (%)
Increase of efficiency (gtri ge)
Increase rate (%) (gtri ge)/ge (%)
Savings of BSFC (g/kW h) (BSFCSG BSFCTG)
Savings rate (%) (BSFCSG BSFCTG)/ BSFCSG
Savings of CO2 emission Fe Ftri (kg CO2/kW h)
Savings rate (%) (Fe Ftri)/ Fe
0 25 50 75 100
5.54 6.55 8.10 9.77 11.80
– 434 266 222 196
64.6 52.1 49.6 45.9 45.2
– 438 265 217 205
– 568 335 267 250
– 81.3 72.7 69.0 66.1
– 1.85 1.05 0.87 0.82
– 81.4 72.6 68.4 67.2
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• The experimental results show that the idea of realizing a household size trigeneration is feasible and the design of the trigeneration is successful. The experimental results show that the innovative small-scale trigeneration is able to generate electricity, to produce heat and to drive a refrigeration system simultaneously from a single fuel (diesel) input. Acknowledgements The support of the Faculty of Computing, Engineering and Technology of Staffordshire University of UK and the support of the Mechanical Engineering College of Guangxi University of China are all greatly appreciated. References [1] Cogen Europe, The European Association for the Promotion of Cogeneration, The Future of CHP in the European Market – The European Cogeneration Study, May 2001. Available from:. [2] F. Ziegler, P. Riesch, Absorption cycles: a review with regard to energetic efficiency, Heat Recovery Systems and CHP 13 (1993) 147– 159. [3] T.R. Casten, District energy with trigenerated ammonia cooling, ASHRAE Transactions, 0001-2505 100 (1) (1994) 1136–1143. [4] D. Li, S. Zhang, Shanghai Power Equipment Research Inst (SPERI), Shanghai, China, Tri-generation (electrical power, heated and chilled water) system and their application in Shanghai, American Society of Mechanical Engineers, Power Division (Publication) PWR, vol. 34 (2), 1999, pp. 265–270.
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[5] P. Rosen, T. Torisson, Wet cycles for generation of power, heat and refrigeration, in: International Conference Proceedings (ENSUS 2000) on Marine Science and Technology for Environmental Sustainability, September 2000, ISBN 0701700939. [6] Piero Colonna, Sandro Gabrielli, Industrial trigeneration using ammonia–water absorption refrigeration systems (AAR), Applied Thermal Engineering 23 (4) (2003) 381–396. [7] E. Cardona, A. Piacentino, A methodology for sizing a trigeneration plant in Mediterranean areas, Applied Thermal Engineering 23 (13) (2003) 1665–1680. [8] J. Herna´ndez-Santoyo, A. Sa´nchez-Cifuentes, Trigeneration: an alternative for energy savings, Applied Energy 76 (1–3) (2003) 219– 227. [9] E. Cardona, A. Piacentino, A measurement methodology for monitoring a CHCP pilot plant for an office building, Energy and Buildings 35 (9) (2003) 919–925. [10] X.Q. Kong, R.Z. Wang, X.H. Huang, Energy efficiency and economic feasibility of CCHP driven by sterling engine, Energy Conversion and Management 45 (9–10) (2004) 1433–1442. [11] Galip Temir, Durriye Bilge, Thermoeconomic analysis of a trigeneration system, Applied Thermal Engineering 24 (17–18) (2004) 2689– 2699. [12] E. Teopa Calva, M. Pico´n Nu´n˜ez, M.A. Rodrı´guez Toral, Thermal integration of trigeneration systems, Applied Thermal Engineering 25 (7) (2005) 973–984. [13] A. Rong, R. Lahdelma, An efficient linear programming model and optimization algorithm for trigeneration, Applied Energy 82 (1) (2005) 40–63. [14] D. Ziher, A. Poredos, Economics of a trigeneration system in a hospital, Applied Thermal Engineering 26 (7) (2006) 680–687. [15] J. Bassols, B. Kuckelkorn, J. Langreck, R. Schneider, H. Veelken, Trigeneration in the food industry, Applied Thermal Engineering 22 (6) (2002) 595–602. [16] Galip Temir, Durriye Bilge, Ozlem Emanet, An application of trigeneration and its economic analysis, Energy Sources 26 (2004) 857–867.
An experimental investigation of a household size trigeneration Lin Lin a, Yaodong Wang b,c,*, Tarik Al-Shemmeri d, Tom Ruxton d, Stuart Turner d, Shengchuo Zeng b, Jincheng Huang b, Yunxin He b, Xiaodong Huang b a Nanning College for Vocational Technology, Nanning, Guangxi 530003, China Mechanical Engineering College, Guangxi University, Nanning, Guangxi 530004, China Northern Ireland, Centre for Energy Research and Technology, School of Built Environment, University of Ulster, Newtownabbey BT37 0QB, United Kingdom d Faculty of Computing, Engineering and Technology, Staffordshire University, Stafford ST18 0AD, United Kingdom b
c
Received 12 February 2006; accepted 31 May 2006 Available online 17 July 2006
Abstract A household size trigeneration based on a small-scale diesel engine generator set is designed and realized in laboratory. Experimental tests are carried out to evaluate the performance and emissions of the original single generation (diesel engine generator); and the performances of the whole trigeneration including the diesel generator within the trigeneration system, the heat exchangers which are used to recover heat from engine exhaust, the absorption refrigerator which is driven by the exhaust heat; and the emissions from the whole trigeneration. Comparisons of the test results of two generations are also performed. The test results show that the total thermal efficiency of trigeneration reaches to 67.3% at the engine full load, comparing to that of the original single generation 22.1% only. Within the range of engine loads tested, the total thermal efficiencies of trigeneration are from 205% to 438% higher than that of the thermal efficiency of single generation. The CO2 emission per unit (kW h) of useful energy output from trigeneration is 0.401 kg CO2/kW h at the engine full load, compared to that of 1.22 kg CO2/kW h from single generation at the same engine load. Within the range of engine loads tested, the reductions of CO2 emission per unit (kW h) of trigeneration output are from 67.2% to 81.4% compared to those of single generation. The experimental results show that the idea of realizing a household size trigeneration is feasible; the design and the set-up of the trigeneration is successful. The experimental results show that the innovative small-scale trigeneration is able to generate electricity, produce heat and drive a refrigeration system, simultaneously from a single fuel (diesel) input. 2006 Elsevier Ltd. All rights reserved. Keywords: Trigeneration; Diesel engine generator; Performance; Emissions
1. Introduction Trigeneration is a simultaneous production of power, heat and cooling/refrigeration [1], as shown in Fig. 1. Although the basic theories and technologies for the power *
Corresponding author. Address: Northern Ireland, Centre for Energy Research and Technology, School of Built Environment, University of Ulster, Newtownabbey BT37 0QB, United Kingdom. Tel.: +44 28 90366807. E-mail address: [email protected] (Y. Wang). 1359-4311/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2006.05.031
generation, heat exchange, and absorption refrigeration are not new, combining them together is a quite new idea. The concept of trigeneration comes to use is only at the mid1990s. Some investigations have been conducted by a number of researchers [2–16], which showed an encouraging effect on raising the energy efficiency and reducing greenhouse gases emissions. The results from the investigations show that trigeneration have the advantages over single electricity generations and cogenerations (Combined heat and power): the total energy efficiency is higher; the emissions of CO2 and the other waste gases are lower; and it
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Nomenclature COP F P Q g
coefficient of performance coefficient of CO2 emission per kW h of power (useful energy) output (kg CO2/kW h) power (kW) heat flow rate, extracted or supplied (kW) thermal efficiency
G h HE EB tri
generator in the absorption system heating heat exchanger engine block trigeneration
Subscripts e electrical generation, electrical power E evaporator
Fig. 1. Trigeneration and the test rig: (a) design of trigeneration and (b) the completed trigeneration test rig.
has more choices for useful energy outputs, i.e., electricity, heat and cooling/refrigeration. The results show that trigeneration has both of the economic and environmental merits. Most of these researches are theoretical/computational simulation [5–14]. Only a few of them are the experimental/ practical studies on trigeneration systems [4,15,16]. The systems they studied are all on quite big scales. The household size trigeneration system, which are suitable for the independent households in remote or isolated areas where no central power supplies are available, has not been studied. The objective of this study is to investigate the feasibility to realize a household trigeneration system and to carry out experimental tests to investigate the performance and the exhaust emission characters of the system, comparing to those of the original single power generation system. The trigeneration, a small-scale combination of power generation with a heat recovery unit and a small-scale absorption refrigerator is designed and has been realized in laboratory. This trigeneration is based on a diesel engine generator set, coupling with a heat recovery system which makes use of the waste heat from the exhaust gas and the cooling system of the engine to supply heating, and an absorption refrigerator which utilizes the exhaust heat from the engine to generate refrigeration effect. This com-
bination may provide three kinds of energy supply for the demands of a family uses. The following sections will present the character of the realized trigeneration; the experimental results from the investigation, including the energy efficiency and the CO2 emission of the trigeneration system, and a comparison with the original single power generation system. 2. Experimental set-up and test plan Fig. 1(a) shows the simplified schematic diagram of the experimental study of the trigeneration system and the test rig set-up. It consists of a test-bed, a diesel engine and a generator, a heat exchanger, an absorption refrigerator, a fuel tank, an air box, a data acquisition system, a computer, an operation panel, four exhaust emission analyzers, and various sensors to measure the oil pressure, the exhaust temperature at the manifold, etc. Fig. 1(b) shows the photo of the realized trigeneration system in the laboratory. 2.1. The engine and generator A Lister–Petter T series diesel engine, which is shown in Fig. 2(a), is selected for the study and is mounted on a test
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Fig. 2. Experimental equipments: (a) diesel engine and generator, (b) heat exchangers, (c) absorption refrigerator and (d) emission analyzers.
bed. The engine is type TS2, two cylinders, swept volume 1270 ml, normal aspiration, 9.5 kW capacity, 238 g/kW h brake specific fuel consumption, fixed speed (1500 rpm). It is a generator engine equipped for Lister–Petter series diesel generator. It is an air-cooled, direct injection diesel engine. The Leroy Somer LSA410 type generator, which is also shown in Fig. 2(a), 415 V, synchronous, 10 A full load current, prime power output for three phases is 8.4 kW (10 kV A) at 1500 rpm, single bearing, was connected to the engine by a prop shaft. 2.2. Heat exchangers Two heat exchangers, which are shown in Fig. 2(b), are selected for the experimental tests to recover heat from the engine exhaust gas according to the maximum heat output from the exhaust gas and the availability in the laboratory. The heat exchangers are cross flow, multi-flattened tubeand-finned, compact, and made of aluminium. The sizes of the two heat exchangers are respectively: Heat exchanger 1: height 550 mm, width 610 mm, thickness 50 mm. Heat exchanger 2: height 750 mm, width 710 mm, thickness 65 mm.
2.3. Absorption refrigerator An Electrolux absorption refrigerator is used in the experiment, which is shown in Fig. 2(c). It is a commercially
available refrigerator. It can be powered by electricity, or liquefied petroleum gas (LPG). When it is run by alternating current power (230 V), the power input is 105 W; when it is run by direct current supply (12 V), the input is 100 W; when it runs by LPG gas, the input is 186 W. The capacity of the refrigerator is 60 l; the capacity of the freezer is 6 l. 2.4. Emission analyzers Four exhaust gas analyzers, which are shown in Fig. 2(d), made by the Analytical Development Company Ltd (Hoddesdon, Hertfordshire, EN11 0DB, England), are used to analyze the exhaust emissions from the engine, i.e., carbon monoxide, carbon dioxide, hydrocarbon and oxides of nitrogen. Prior to testing, the analyzers were calibrated separately by using the special sample gases supplied by BOC Ltd. 2.5. Experimental plan A plan is designed for the experimental investigation of the performance of the trigeneration system. 2.5.1. The plan for the performance of engine generator running on a single generation scheme A series of tests are designed to evaluate the engine generator performance when it runs on a single generation scheme. In the tests, the engine load varies between idle to full loads; relevant data is to be recorded such as the engine generator power output; fuel consumption, engine exhaust temperature and emissions. The tests are to be
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conducted and repeated three times, in order to increase the reliability of the test results.
during the whole experiment process. The test results are shown in the following figures and tables.
2.5.2. The plan for the performance of trigeneration A series of tests are also designed to evaluate the performances of trigeneration. In these tests, the engine load varies between idle to full load, the same as that of single generation; and the required parameters are to be recorded in order to evaluate the total output of power, heat and refrigeration effect, which including
3.1. Test results of engine generator performance and the comparison
• engine generator power output; • heat recovered from heat exchangers and the engine cooling system; • heat input to the generator in the absorption refrigerator; • refrigeration effect generated in the absorption refrigerator; • evaluation of coefficient of performance (COP) of the absorption refrigerator; • emissions from the trigeneration system. The tests are also to be conducted and repeated three times, in order to increase the reliability of the test results. 3. Test results and discussion
800
6
700
5
600 BSFC (kW)
7
4 3 2
500 400 300 200
1
100 0
0 0
25
50
75
SG
TG
0
100
25
50
Engine Load (%)
SG
35.0 30.0 25.0 η e ( %)
Pe (kW)
The diesel engine generator system runs well on the single generation scheme and the trigeneration scheme mentioned above. There are no engine faults happening
The test results of the performances of engine generator on the conventional single generation scheme (SG) from the three tests on average are shown in Fig. 3. The test results of the performances of engine generator on the trigeneration scheme (TG) from the three tests on average are also shown in the figure. Table 1 presents the comparison of the performances of engine generator on SG and on TG. The results show that the electrical power outputs are nearly the same; the differences are very small; the maximum difference is 2.0%. The test results of brake specific fuel consumption (BSFC) of engine generator on SG and TG are also shown in Fig. 3. A comparison of SG with TG is also shown in Table 1. The results show that the BSFCs of SG and TG are nearly equal each other, the differences are small; the largest is only 3.5%. The test results of thermal efficiencies of engine generator on SG and TG are also showed in Fig. 3. A comparison of SG with TG is also showed in Table 1. The test results show that the thermal efficiencies of engine generator on SG and TG are nearly the same. The maximum difference is 3.1% in absolute value, as shown in Table 1. From the test results and the comparisons above, it can be seen that when the engine generator runs on
20.0 15.0 10.0 5.0 0.0 0
25
50 SG
75 TG
100
Engine Load (%)
Fig. 3. Variation of Pe, BSFC and ge with engine load and comparison of SG with TG.
75 TG
100
Engine Load (%)
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Table 1 Comparison of electrical power output, brake specific fuel consumption and thermal efficiency of the diesel engine generator run on SG and TG Engine load (%)
SG
TG
SG
TG
SG
TG
Pe (kW) differences between SG and TG
Relative Pe differences (%)
Differences of BSFC (g/kW h)
Relative of BSFC differences (%)
Differences of ge
Relative difference of ge (%)
0 25 50 75 100
0.00 0.01 0.00 0.09 0.01
0.0 0.7 0.0 2.0 0.2
–
–
4 14 5 13
0.6 3.1 1.4 3.5
0.0 0.1 0.5 0.3 0.7
0.0 0.8 2.6 1.4 3.1
trigeneration scheme, the engine and generator performances are still the same as those of single generation. The results show that the design and the implement of the addition of the heat recovery system and the absorption refrigerator to the engine generator does not influence the performance of the engine generator. This gives a good base for the following comparison of the performances of TG system with that of SG system. 3.2. Engine emissions The emissions from the diesel engine on SG and TG are shown in Fig. 4 and a comparison of the emissions from the two systems are showed in Table 2. The results show that the differences of emissions for the two generations are for CO2 emission, the differences are between 0.4% and 2.9%; for CO emission, the differences are from 0.0% to 8.3%; for HC emission, the error are between 4.2%
and 42.9%; for NOx emission, the differences are from 0.0% to 3.7%. The results show that the differences are mostly very small and are negligible. 3.3. Test results of heat recovered from engine exhaust and engine cooling system Experiments of trigeneration are performed and the data of the heat collected from engine exhaust and engine cooling system (engine block) are recorded to evaluate the amount of heat energy obtained from the TG system. The test results are presented in Fig. 5. The results show that the heat recovered from engine exhaust with two heat exchangers is from 1.70 kW at the engine no load to 4.91 kW at the engine full load; the heat obtained from the engine cooling system (engine block) is from 3.84 kW at the engine 0% load to 6.43 kW at the engine full load; the total amount of heat obtained from TG is from
9
0.06
7
0.05
6
0.04
CO (%)
CO2 (%)
8
5 4
0.03 0.02
3 2
0.01
1
0 0
0 0
25
50 SG
TG
50 SG
75 100 Engine Load (%)
75 TG
100
Engine Load (%)
1 200
40 35
1 000 NOx (ppm)
30 HC (ppm)
25
25 20 15
800 600 400
10 200
5
0
0 0
25
50 SG
75 TG
100
Engine Load (%)
0
25
50 SG
75 TG
100
Engine Load (%)
Fig. 4. Variation of CO2, CO, HC and NOx content in exhaust with engine load and comparison of SG with TG.
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Table 2 Comparison of engine emissions of CO2 (%), CO (%), HC (ppm) and NOx (ppm) in exhaust Engine load (%)
SG
TG
SG
TG
SG
TG
SG
TG
Differences of CO2
Relative differences of CO2 (%)
Differences of CO
Relative differences of CO (%)
Difference of HC (ppm)
Relative difference of HC (%)
Difference of NOx (ppm)
Relative difference of NOx (%)
0 25 50 75 100
0.05 0.08 0.12 0.12 0.03
2.6 2.7 2.9 2.1 0.4
0.002 0.000 0.001 0.001 0.002
8.3 0.0 5.6 5.3 3.6
6 3 2 1 4
42.9 16.7 10.0 4.2 13.3
3 0 7 6 39
1.3 0.0 1.3 0.8 3.7
12.00 10.00 Q (kW)
8.00 6.00 4.00 2.00 0.00 0
25
50
75
100
Engine Load (%) Heat from enigne exhaust
Heat from Engine Block
Total heat
Fig. 5. Variation of heat from exhaust and engine block with engine load in trigeneration.
5.54 kW at the engine 0% load to 11.34 kW at the engine full load. 3.4. Test results of refrigerator performance driven by the heat from engine exhaust in trigeneration The parameters of the performance of refrigerator were recorded and evaluated when the trigeneration were running on five engine loads (0%, 25%, 50%, 75% and 100%), according to the test plan. The test results presented and discussed below are mainly concerned about the most important parameters for the refrigerator as following: • heat input into the generator in the absorption refrigerator QG; • refrigeration effect generated QE; • coefficient of performance (COP) of the absorption refrigerator; • Generator (boiler) temperature in the refrigerator tG; • Evaporator temperatures in the refrigerator tE1 (in freezer) and tE2 (in food compartment). The generator temperature is the indicator of the heat energy input to the refrigeration system; the evaporator temperature is the indicator of the refrigeration effect generated in the refrigerator. The following table present the test results of QG, QE, and COP; and the following figures present the following temperatures: refrigerator boiler tem-
perature tG; refrigerator evaporator temperature 1 (at the point in freezer) tE1; refrigerator evaporator temperature 2 (at the point in refrigerator food compartment) tE2. The test results for temperatures in the refrigerator are showed in Fig. 6 and Table 3. Table 3 also includes the test results for the original power supplies as reference cases (AC power, DC power and liquid petroleum gas). From Fig. 6 and Table 3, it can be seen that: At the engine load of 0%, the generator temperature is between 126 C and 132 C (see Fig. 6(a)). The final evaporator temperatures at freezer point and at food compartment point do not change; these indicate that there is no refrigeration effect generated in the refrigerator. At the engine load of 25%, as showed in Fig. 6(b), the generator temperature is between 169 C and 178 C. The final evaporator temperatures at freezer point and at food compartment point keep the same value as that the value at the starting points; these also indicate that there is no refrigeration effect generated in the refrigerator. At the engine load of 50%, it can be seen that the generator temperature is between 202 C and 205 C (see Fig. 6(c) and Table 3). The final evaporator temperature at freezer point is 17.5 C; the temperature at food compartment point is 0.8 C, when the environment air temperature is 25.0 C; these indicate that there is refrigeration effect generated in the refrigerator. In this case, the heat input to the refrigerator QG is 184 W on average for the three tests; the refrigeration effect QE is 6.1 W; and the coefficient of performance of the refrigeration system is 0.033. At the engine load of 75%, as shown in Fig. 6(d) and Table 3, the generator temperature is between 209 C and 218 C. The final evaporator temperature at freezer point is 24.9 C; at food compartment point is 8.2 C, when the environment air temperature is 24.0 C. The heat input to the refrigerator QG is 210 W on average for the three tests; the refrigeration effect QE is 7.2 W; and the coefficient of performance of the refrigeration system is 0.035. At the engine load of 100%, as showed in Fig. 6(e) and Table 3, the generator temperature is between 227 C and 245 C. The final evaporator temperature at freezer point is 20.1 C; at food compartment point is 1.9 C, when the environment air temperature is 24.5 C.
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a
b
250
250 225
200
200
175
175
Temperature (ºC)
Temperature (ºC)
225
150 125 100
150 125 100
75
75
50
50
25
25 0
0 -25
0
50
100
150 200 Time (min)
-25
0
50
100
150 200 Time (min)
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
250
d 250
225
225
200
200
175
175 Temperature (ºC)
Temperature (ºC)
c
150 125 100 75
150 125 100 75
50
50
25
25 0
0 -25
0
50
100
150
200
-25
0
50
150
200
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE
e
100
Time (min)
Time (min)
250 225 200 Temperature (ºC)
175 150 125 100 75 50 25 0 -25
0
50
100
150
200
Time (min) 1 Fridge Boiler temperature tG 2 Evaporator temperature 1 tE1 3 Evaporator temperature 2 tE2
Fig. 6. Absorption fridge performances run by exhaust gas: (a) 0% engine load, (b) 25% engine load, (c) 50% engine load, (d) 75% engine load and (e) 100% engine load.
L. Lin et al. / Applied Thermal Engineering 27 (2007) 576–585 Table 3 Refrigerator performance comparison tE1 (C)
tE2 (C)
QG Q 0 G QE COP (W) (W) (W)
Tests
tG (C)
Run by AC power Run by DC power Run by LPG gas
200–205 18.2 3.4 105
470
8.1
0.0173
201–204 16.3
448
7.4
0.0165
201–204 26.0 1.5 186
7.3
0.0390
126–132 169–178 202–205 209–218 227–245
– – 6.1 7.2 7.4
– – 0.033 0.035 0.031
Run by engine exhaust gas (load, %)
0 25 50 75 100
– – 17.5 24.9 20.1
5.3 100
– – 0.8 8.2 1.9
– – 184 210 237
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ature of the refrigerator above 200 C; the results show that the COPs of the refrigerator driven by exhaust gas are higher than that of electrical power driven from the primary energy consumption point of view. But at the engine load of 0%, 25%, the temperature of exhaust gas is not high enough to drive the refrigerator. 3.5. Test results of the whole system performance of trigeneration compared to that of single generation The test results of the whole trigeneration system are presented as following:
The heat input to the refrigerator QG is 237 W on average for the three tests; the refrigeration effect QE is 7.4 W; and the coefficient of performance of the refrigeration system is 0.031. The test results show that at the engine load above 50%, the temperature of the exhaust gas is high enough to make the refrigerator work. The test results also show that the exhaust heat can be used as an energy resource for the absorption refrigerator if the exhaust gas is hot enough to make the boiler temper-
• power output and emissions from engine generator (as shown in 3.1 and 3.2); • heat recovered from heat exchangers and the engine cooling system (as shown in 3.3); • refrigeration effect generated in the absorption refrigerator; the coefficient of performance (COP) of the refrigerator (as shown in 3.4); • the performances of the total trigeneration. The detail test results of the whole trigeneration system from the engine load of 0–100% are shown in Fig. 7 and Table 4. From the figure and the table, it can be seen that
20 100
18 80
TG
14
60
12 ηt (%)
Useful Output (kW)
16
10 8 6
40 20
SG
4
0
2
0
0 0
25
50
75 100 Engine Load (%)
25
50
Single Generation
75 100 Engine Load (%) Trigeneration
5
1100
4
900 800
kg CO2/ kWh
SFC (g/kWh)
1000
700 600 500 SG
400
3
2 SG
300 200
1
TG
TG
100 0 0
25
50
75
100
Engine Load (%)
0 0
25
50
75
100 Engine Load (%)
Fig. 7. Variation of useful output energy, ge, SFC and CO2 emissions with engine load for TG and SG and their comparison.
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As for CO2 emission, a comparison of CO2 emission for these two kinds of generations is also shown in Table 5 and Fig. 7. From the figure and the table, it can be seen that
Table 4 Performance of trigeneration Load (%)
Qtri = Pe + Qh + QEB + QE (kW)
gtri (%)
BSFC (g/kW h)
Ftri (kg CO2/kW h)
0 25 50 75 100
5.54 8.06 11.14 14.18 17.83
64.6 64.0 68.3 67.1 67.3
131 131 126 120 128
0.418 0.422 0.395 0.402 0.401
• the CO2 emission per unit (kW h) of Electrical power output are from 1.22 to 2.27 kg CO2/kW h; • the CO2 emission per unit (kW h) of trigeneration output (electrical power + heating + refrigeration effect) are from 0.395 to 0.422 kg CO2/kW h. The CO2 emission per unit (kW h) of useful energy output of trigeneration are reduced by 67.2–81.4% compared to those of single generation. The emission quantities of CO2 emission from trigeneration are much lower than those from single generation.
• the useful energy outputs (Qtri) vary from 5.54 kW at the engine no load to 17.83 kW at the engine full load; • the thermal efficiencies of trigeneration vary from 64.6% at the engine no load to 67.3% at the engine full load; • the specific fuel consumptions are from 131 g/kW h at the engine load 0% and 25%, 126 g/kW h at the engine load 50%, 120 g/kW h at the engine load 75%, to 128 g/kW h at the engine full load; • the CO2 emissions are from 0.418 (kg CO2/kW h) at the engine no load, 0.422 (kg CO2/kW h) at the engine load 25%, 0.395 (kg CO2/kW h) at the engine load 50%, 0.402 (kg CO2/kW h) at the engine load 75%, to 0.401 (kg CO2/kW h) at the engine full load.
4. Conclusions From the results above, the following conclusions can be drawn: • When the engine generator runs as a single generation or in a trigeneration, the electric power outputs and the electrical thermal efficiencies are the same; the fuel consumptions are the same. • It is feasible to utilize the waste heat from exhaust gas of a diesel engine to drive the absorption refrigerator, when the engine load is over 50% with the exhaust gas hot enough to heat the generator above 200 C.
Table 5 shows the comparisons of the useful energy output, which includes electricity, heat and refrigeration effect, between trigeneration and single generation. From the results, it can be seen that the useful energy outputs from trigeneration are much higher than that of single generation: The increase rates are from 434% at the engine 25% load to 196% at the engine full load. Table 5 also shows the comparisons of the total thermal efficiency of trigeneration with the thermal efficiency of single generation. The total thermal efficiencies of trigeneration are from 205% to 438% higher than that of single generation. Table 5 shows the comparison of the brake specific fuel consumption of trigeneration with that of single generation. The fuel consumed by trigeneration is much less than that of single generation. The saving rates of fuel consumption for trigeneration over single generation are from 81.3% at the engine 25% load, to 66.1% at the engine full load.
The lowest evaporator temperature at the point in freezer of the refrigerator is 24.9 C; the temperature at the point in food compartment is 8.2C while the refrigerator is powered by the heat from engine exhaust gas at the engine load of 75%. • The total thermal efficiencies of trigeneration are from 205% to 438% higher than that of single generation under different engine loads. • The CO2 emission per unit (kW h) of useful energy output from trigeneration are reduced by 67.2–81.4% compared to those from single generation under different engine loads.
Table 5 Comparison of useful energy output, thermal efficiency, BSFC and CO2 emission of single generation to trigeneration Engine load (%)
Increase of output (kW) (Qtri Pe)
Increase rate (%) (Qtri Pe)/Pe (%)
Increase of efficiency (gtri ge)
Increase rate (%) (gtri ge)/ge (%)
Savings of BSFC (g/kW h) (BSFCSG BSFCTG)
Savings rate (%) (BSFCSG BSFCTG)/ BSFCSG
Savings of CO2 emission Fe Ftri (kg CO2/kW h)
Savings rate (%) (Fe Ftri)/ Fe
0 25 50 75 100
5.54 6.55 8.10 9.77 11.80
– 434 266 222 196
64.6 52.1 49.6 45.9 45.2
– 438 265 217 205
– 568 335 267 250
– 81.3 72.7 69.0 66.1
– 1.85 1.05 0.87 0.82
– 81.4 72.6 68.4 67.2
L. Lin et al. / Applied Thermal Engineering 27 (2007) 576–585
• The experimental results show that the idea of realizing a household size trigeneration is feasible and the design of the trigeneration is successful. The experimental results show that the innovative small-scale trigeneration is able to generate electricity, to produce heat and to drive a refrigeration system simultaneously from a single fuel (diesel) input. Acknowledgements The support of the Faculty of Computing, Engineering and Technology of Staffordshire University of UK and the support of the Mechanical Engineering College of Guangxi University of China are all greatly appreciated. References [1] Cogen Europe, The European Association for the Promotion of Cogeneration, The Future of CHP in the European Market – The European Cogeneration Study, May 2001. Available from:
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