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Laboratory research on combined cooling, heating and power (CCHP) systems
Energy Conversion and Management 50 (2009) 977–982
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Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Laboratory research on combined cooling, heating and power (CCHP) systems L. Fu *, X.L. Zhao, S.G. Zhang, Y. Jiang, H. Li, W.W. Yang Department of Building Science, School of Architecture, Tsinghua University, Beijing, PR China
a r t i c l e
i n f o
Article history: Received 14 May 2008 Accepted 16 December 2008 Available online 10 February 2009 Keywords: Combined cooling, heating and power Distributed generation Absorption heat pump Liquid desiccant dehumidification Condensation heat recovery
a b s t r a c t Combined cooling, heating and power (CCHP) systems offer the potential for a significant increase in fuel use efficiency by generating electricity onsite and recycling the exhaust gas for heating, cooling, or dehumidifying. A challenge for CCHP system is the efficient integration of distributed generation (DG) equipment with thermally-activated (TA) technologies. The China Ministry of Science and Technology and Tsinghua University launched the 863 Hi-Tech Program in 2007 to focus on laboratory and demonstration research to study the critical issues of CCHP systems, advance the technology and accelerate its application. The research performed at the Building Energy Research Center (BERC) Laboratory focuses on assessing the operational performance and energy efficiency of the integration of current DG and TA technologies; developing and verifying mathematical models of the individual devices and all the systems. The test laboratory is a flexible test-bed for the configuration of DG (presently a 70-kW natural gasfired internal combustion engine (ICE) with various heat recovery units, such as an flue gas-to-water heat recovery unit (FWRU), a jacket water heat recovery unit (JRU), liquid desiccant dehumidification systems (LDS), an exhaust-gas-driven double-effect absorption heat pump (EDAHP), and a condensation heat recovery unit (CRU)). In the winter, the exhaust gas from the ICE is used in the FWRU or used to drive the EDAHP directly, and the exhaust gas from the EDAHP is used in the CRU. The water flows from the CRU can be directed to the evaporator side of the EDAHP as the low-grade heat source. The water flows from the condensation side of the EDAHP, in conjunction with the jacket water flows from the JRU, is used for heating. In the summer, the exhaust gas from the ICE is used to drive the EDAHP for cooling directly, the exhaust gas from the EDAHP is bypassed to the exit via automated damper controls. The waste heat of the jacket water is used to drive the liquid desiccant dehumidification systems, to realize the separate control of heat and humidity. The automated damper is used in order to test various configurations and operating modes. The testing results show that the operating parameters and efficiencies of the overall system depend on different configurations. Under certain combinations of CCHP, the efficiency of the overall system can be as high as 90% (based on lower heating value of the natural gas). Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Distributed generation (DG) technology is becoming more reliable and prevalent because of the losses reduction on transmission and distribution lines by placing the generator next to the load. Recent developments in DG technologies have opened new opportunities for relatively small-scale combined cooling, heating and power (CCHP) systems that can be used in buildings. The CCHP system is always the combination of DG with thermally-activated (TA) technologies which could recover the waste heat for cooling or heating. The CCHP, in conjunction with other energy efficient building technologies, will maximize the efficiency of energy use, reduce harmful emissions to the environment, improve power
* Corresponding author. Tel.: +86 1062773885; fax: +86 1062770544. E-mail address: [email protected] (L. Fu). 0196-8904/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2008.12.013
quality and reliability compared with large central power plants [1]. The University of Maryland’s Center for Environmental Energy Engineering has worked closely with DOE’s Oak Ridge National Laboratory, and carried out a great deal of research. Two different CHP systems are studied, and some test and research results based on these two systems have been reported [2–6]. In China, CHP technology is still a promising energy conversion technology under development for application [7]. Typical examples can be found at the Shanghai Huangpu Central Hospital, Pudong International Airport, the Beijing Gas Company building and Tsinghua University [8,9]. But until now, there have been no reports of any detailed research on their performance. The China Ministry of Science and Technology, cooperated with Tsinghua University, launched the 863 Hi-Tech Program in 2007 to focus on laboratory and demonstration research to study the critical issues of CCHP systems, advance the technology and accelerate its application.
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Nomenclature AHP CCHP CHE COP CRU CT DAS DES DG EDAHP FWRU ICE JRU LR LD LDS LHV NG CP
absorption heat pump combined cooling, heating and power condensation heat exchanger coefficient of performance condensation heat recovery unit cooling tower data acquisition system distributed energy system Distributed generation exhaust-gas-driven double-effect absorption heat pump flue gas-to-water heat recovery unit internal combustion engine jacket water heat recovery unit liquid regenerate unit liquid desiccant unit liquid desiccant dehumidification systems lower heating value of natural gas natural gas specific heat (kJ/kg °C)
A laboratory for testing CCHP was commissioned at Building Energy Research Center (BERC) Laboratory. The scope of the facility is to test DG in combination with TA technologies for optimum waste heat recovery and overall energy efficiency. The objectives of the laboratory include collection of performance data on current DG and TA technologies both individually and operated as an integral part of an CCHP systems, development of models of different devices and verification of an system model based on integrated operation. 2. System and equipment The CCHP system in the laboratory (Fig. 1) is the combination of a gas-powered internal combustion engine (ICE) with other heat recovery units, including a jacket water heat recovery unit (JRU), an flue gas-to-water heat recovery unit (FWRU), liquid desiccant dehumidification systems (LDS), an exhaust-gas-driven double-effect absorption heat pump (EDAHP), and a condensation heat recovery unit (CRU). The ICE, JRU, FWRU, EDAHP are all located
Q
q G t W M r
x h
heating/cooling capacity (kW) density of water (kg/m3) volumetric flow rate (m3/s) temperature (°C) electric power (kW) mass flow rate of the air (kg/s) latent heat of vaporization (kJ/kg) humidity ratio (kg/kg) enthalpy (kJ/kg)
Subscripts e electric fa fresh air o out door air s supply air in inlet out outlet
on the basement of the building, and the liquid regenerate machine and liquid desiccant unit are located on the roof and second floor of the building, respectively. The 70 kW natural gas-powered ICE, has six cylinders with four strokes, which is designed to operate at a rated speed of 1500 rpm, a rated voltage of 400 V. The high-frequency power produced from the ICE is converted to 50 Hz 3-phase electric power through power conditioning device. In the winter, the exhaust gas from the ICE can either be routed to the FWRU or used to drive the EDAHP directly, and the exhaust gas from the EDAHP is used in the CRU. The water flows from the CRU which recovered the condensation heat of the exhaust gas can be directed to the evaporator side of the EDAHP as the low-grade heat source. The water flows from the condenser side of the EDAHP, in conjunction with the hot water flows from the JRU, is used for heating. In the summer, the exhaust gas from the ICE is used to drive the EDAHP for cooling directly, the exhaust gas from the EDAHP is bypassed to the exit. The cooling tower (CT) is used. The waste heat recovered from JRU is used to regenerate the liquid, and the regeneration stream
Fig. 1. CHP Laboratory at Building Energy Research Center.
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is used to drive the liquid desiccant unit, to produce the low humidity air, which realize the separate control of heat and humidity [10,11]. The automated damper is used in order to test various configurations and operating modes. The operating mode I: ICE + JRU + FWRU The operating mode II: ICE + JRU + EDAHP + CRU The operating mode III: ICE + JRU + LDS(including liquid regenerate unit and liquid desiccant unit) + EDAHP + CT
of data the DAS can provide are as follows: temperature, humidity, gas/air/exhaust/liquid flow rate, electricity, and current, pressure, equipment status, and weather station data. Most of the sensors output are 4–20 mA current, which has the advantage of avoiding signal attenuation over long wires. The current signal is converted into 0.88–4.4 VDC voltage, with which the required data value is calculated through the DAS program and then stored in the computer. 4. Results and discussion
The operating models I and II are winter mode and the operating mode III is summer mode. On the operating mode I, the ICE’s exhaust gas which has a temperature of about 510 °C is directed to the heat recovery units. The ICE’s exhaust passes through the FWRU and leaves it at a temperature of about 90 °C. On the operating mode II, the ICE’s exhaust gas is directed to EDAHP and leaves it at a temperature of about 170 °C, and then is directed to CRU and leaves it at a temperature lower than 30 °C. On the operating mode III, the ICE’s exhaust gas is directed to EDAHP and leaves it at a temperature of about 170 °C, and the recovered heat from the JRU at a temperature of 60 °C is used to regenerate the desiccant liquid in the liquid regenerate unit. The regenerated liquid is used to drive the liquid desiccant unit, to produce the low humidity air. Although, the current configuration at the CCHP Laboratory only includes ICE-based CCHP systems; it could be extended to encompass many other DG systems such as microturbines and fuel cells. Our near term plans include getting a fuel cell to test with the heat recovery equipment at the Laboratory. 3. Experiment conditions and procedure The previous tests studied the steady and dynamic performance of operating mode II [12], the current tests studied the overall efficiency of different configurations. The water temperature depends on several parameters which includes the ICE loading, and the water flow rate, so these tests were performed at a constant ICE power output of 60 kW. ICE power output, hot water, cooling water and chilled water flow rates were held constant under the steady operating mode. A data acquisition system (DAS) was installed to measure all relevant temperatures, relative humidity, pressures, flow rates, and power consumption to calculate the performance of the CCHP systems under all operating conditions. The test instrumentation and their measurement accuracies are given in Table 1. The DAS is completely separate from the control system, and the readings that the DAS provides can be completely customized. The types
4.1. System performance on mode I (ICE + JRU + FWRU) On the mode I, the natural gas flow rate is 23.74 m3/h, the ICE’s excess air coefficient is 1.11, the hot water flow rate from the JRU and hot water flow rate from the FWRU are 7.1 m3/h and 1.15 m3/h, respectively. The temperature of exhaust gas entering and leaving the FWRU is shown in Fig. 2. The Inlet temperature of the flue gas is 510.12– 510.49 °C, and the outlet temperature of flue gas is 92.97–93.42 °C. It is well known that the flue gas dew point of natural gas would be 40–55 °C depending on the different excess air coefficients, so the condensation heat of the flue gas cannot be used on the mode I. The energy loss is serious in the waste heat recovery system, and the energy utilization of the system could be improved. The heating or power capacity of different equipments is shown in Fig. 3. The JRU heating capacity is defined as
Q JRU ¼ C PJRU qJRU GJRU ðt JRUin t JRUout Þ
ð1Þ
where CP JRU is the water heat capacity at the average temperature; qJRU is the density of water at the average temperature; GJRU is the volumetric flow rate of jacket water; and tJRU in and tJRU out are the jacket water temperatures entering and leaving the JRU, respectively. The FWRU heating capacity is defined as
Q FWRU ¼ C PFWRU qFWRU GFWRU ðtFWRUin tFWRUout Þ
ð2Þ
where CP FWRU is the water heat capacity at the average temperature; qFWRU is the density of water at the average temperature; GFWRU is the volumetric flow rate of FWRU water; and tFWRU in and tFWRU out are the water temperatures entering and leaving the FWRU, respectively. As illustrated in Fig. 3, the output of the ICE is stabilized in a range from 59.86 kW to 60.72 kW at this time. The heating capacity of the JRU is about 84.01–85.41 kW, and the heating capacity of
600
Standard flow nozzles plus inclined differential manometer Platinum RTD
±1%
Air temperature
±0.5%
0
Time Fig. 2. Flue gas temperature of FWRU.
13:24:17
±0.5%
100 13:24:03
Platinum RTD
200
13:23:50
±1% ±0.5% ±0.5 °C/ ±0.1 °C ±0.5%
13:23:36
Electrical power meter Ultrasonic flow meter T thermocouple/resistance temperature device (RTD) Analysis instrument of exhaust
Inlet of FWRU Outlet of FWRU
300
13:23:22
±1%
13:23:08
Natural gas flow meter
13:22:55
Natural gas flow rate Electrical power Water flow rate Water temperature Exhaust components Exhaust temperature Air flow rate
400
13:22:41
Measurement precision
13:22:27
Instruments
500
13:22:13
Parameters
Temperature(
)
Table 1 Parameters of the measurement instruments.
L. Fu et al. / Energy Conversion and Management 50 (2009) 977–982
jacket water is about 35.97–36.76%, and the thermal recovery efficiency of the flue gas is about 17.81–18.11% (average 17.96). The thermal recovery of the flue gas is much smaller than the thermal recovery of the jacket water. The flue gas temperature exiting the ICE is as high as 510.12–510.49 °C, how much heat the flue gas contains? So the flue gas enthalpy at the temperature of 510 °C is computed, which accounts for about 34% of the natural gas input energy (based on LHV). Therefore, the energy loss accounts for 47% of the input energy of FWRU, which is computed as (34– 17.96%)/34%. 4.2. System performance on mode II (ICE + JRU + EDAHP + CRU)
13:24:17
13:24:03
13:23:50
13:23:36
13:23:22
13:23:08
13:22:55
13:22:41
ICE FWRU JRU 13:22:27
90 80 70 60 50 40 30 20 10 0
13:22:13
Heating/power capacity(kW)
980
On the mode II, the hot water flow rate from the EDAHP is 16.07 m3/h, and the water flow from the CRU is 10.56 m3/h, and the hot water flow rate from the JRU is 4.41 m3/h. There are three temperature test points along the flue gas pipeline, mounted on the outlet of the ICE, the outlet of the EDAHP, and the outlet of the CRU. The test results for the three temperature points are illustrated in Fig. 5. According to this figure, the temperature of the flue gas exiting the ICE is about 519.27 °C, and the temperature of the flue gas entering and leaving the CRU is 166.96 °C and 18.99 °C, respectively, so the flue gas passes through the CRU and the condensation heat of it is recovered. The energy loss leaving the system is just equal to the flue gas enthalpy at a temperature of 18.99 °C, which accounts for about 3.3% of the natural gas input energy (based on LHV).The energy utilization on operating mode II is improved greatly than mode I. The heating and powering capacity of different equipments is shown in Fig. 6. It should be noted that the EDAHP heating capacity comes from two parts, one part comes from the generator side (flue gas waste heat from 519.27 °C to 166.96 °C), the other part comes from the evaporator side (flue gas waste heat from 166.96 °C to 18.99 °C which was recovered in CRU), so the heating capacity of EDAHP should include the heat recovery of CRU. The input of EDAHP is the generator side and evaporator side, and the output of the EDAHP is the condenser side. The EDAHP heating capacity is defined as
Time
13:24:17
13:24:03
13:23:50
13:23:36
13:23:22
13:23:08
13:22:55
13:22:41
ICE+JRU+FWRU ICE+JRU ICE
13:22:27
90 80 70 60 50 40 30 20 10 0
13:22:13
Efficiency(%)
Fig. 3. Heating or power capacity of different equipments (mode I).
Time Fig. 4. Efficiency of different configurations (mode I).
the FWRU is about 41.49–41.91 kW. The efficiency of different configurations is shown in Fig. 4. The efficiency and performance calculation are calculated by using the following equations:ICE efficiency based on lower heating value (LHV) of natural gas is defined as
EICE ¼
We 100ð%Þ Q inLHV
ð3Þ
Q EDAHPðþCRUÞ ¼ C P
where CP C-EDAHP is the heat capacity of the hot water flows from the condenser side of the EDAHP at the average temperature; qC-EDAHP is the density of the hot water flows from the condenser side of the EDAHP at the average temperature; GC-EDAHP is the volumetric flow rate of the water flows from the condenser side of the EDAHP;
)
where QJRU is the heat recovered by the JRU and WJRU is the electric power consumed by the JRU pump.Efficiency of the system consisting of the ICE, JRU and FWRU is defined as
Temperature (
500
ð4Þ
EICEþJRUþFWRU ¼
W e þ Q JRU þ Q FWRU 100ð%Þ Q inLHV þ W JRU þ W FWRU
ð5Þ
where QFWRU is the heat recovered by the FWRU and WFWRU is the electric power consumed by the FWRU pump. As illustrated in Fig. 4, the electrical efficiency of ICE is about 25.67–26.27%, and overall efficiency of ICE + JRU is 61.97–63.09%, and overall efficiency of ICE + JRU + FWRU is about 79.85–81.19%. We also can compute that the thermal recovery efficiency of the
400 300
Out of ICE Out of EDAHP Out of CRU
200 100 0 19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
EICEþJRU
qC-EDAHP GC-EDAHP ðt C-EDAHP in tCEDAHP out Þ ð6Þ
where We is the net electric power generated by the ICE and Qin LHV is the natural gas input (based on LHV).Efficiency of the system consisting of the ICE and JRU is defined as
W e þ Q JRU ¼ 100ð%Þ Q inLHV þ W JRU
C-EDAHP
Time Fig. 5. Temperature distributions on the flue gas pipeline.
981
ICE EDAHP(+CRU) JRU
120 100
ICE EDAHP(+CT) LDS(+JRU)
80 60 40 20 0
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
Cooling/powering capacity (kW)
100 90 80 70 60 50 40 30 20 10 0
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
Heating/powering capacity (kW)
L. Fu et al. / Energy Conversion and Management 50 (2009) 977–982
Time
Time
Fig. 8. Heating or powering capacity of different equipments (mode III).
Fig. 6. Heating or powering capacity of different equipments (mode II).
and tC-EDAHP in and tC-EDAHP out are the water temperatures entering and leaving the condenser side of the EDAHP, respectively. As illustrated in Fig. 6, the output of the ICE is stabilized in a range from 60.00 kW to 60.91 kW at this time. The heating capacity of the JRU is about 86.34–87.63 kW, and the heating capacity of the EDAHP is about 72.24–76.63 kW. Compared with the mode I (illustrated in Fig. 3), it is shown that the heating capacity of EDAHP is improved greatly than the heating capacity of FWRU. The efficiency of different configurations is shown in Fig. 7. Efficiency of the system consisting of the ICE, JRU, EDAHP and CRU is defined as
EICEþJRUþEDAHPðþCRUÞ ¼
W e þ Q JRU þ Q EDAHPðþCRUÞ 100ð%Þ Q inLHV þ W JRU þ W EDAHPðþCRUÞ
ð7Þ
100 90 80 70 60 50 40 30 20 10 0
ICE+JRU+EDAHP(+CRU) ICE+JRU ICE
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
Efficiency (%)
where QEDAHP(+CRU) is the recovered heat by the combination of EDAHP and CRU, and WEDAHP(+CRU) is the electric power consumed by the pumps of EDAHP and CRU system. As illustrated in Fig. 7, the electrical efficiency of ICE is about 25.20–25.30%, and overall efficiency of ICE + JRU is 61.22–61.93%, and overall efficiency of ICE + JRU + EDAHP + CRU is about 91.03– 93.24%. We also can compute that the thermal recovery efficiency of the jacket water is about 35.92–36.71%, and the thermal recovery efficiency of the flue gas (EDAHP + CRU) is about 29.73–31.95% (average 30.84%). The thermal recovery efficiency of the flue gas on mode II is 11.92–13.84% higher than the thermal recovery efficiency on mode I. Also the flue gas enthalpy at the temperature of 519.27 °C is computed, which accounts for about 35.80% of the natural gas input energy (based on LHV). Therefore, the energy loss just accounts for 13.85% of the input energy of EDAHP and CRU, which is computed as (35.80–30.84%)/35.80%.
Time Fig. 7. Efficiency of different configurations (mode II).
4.3. System performance on mode III (ICE + JRU + LDS + EDAHP + CT) On the mode III, the chilled water flow rate from EDAHP is 9.57 m3/h, and the cooling water flow rate from EDAHP is 15.3 m3/h, and the hot water flow rate from the JRU is 6.27 m3/h. On this operating mode, the temperature of exhaust gas entering and leaving the EDAHP is also approximately 519 °C and 167 °C. The cooling or power capacity of different equipments is shown in Fig. 8. The EDAHP should be used together with CT, the EDAHP cooling capacity is defined as
Q EDAHPðþCTÞ ¼ C PEEDAHP qEEDAHP GEEDAHP ðt EEDAHPin t EEDAHPout Þ ð8Þ where CP E-EDAHP is the heat capacity of the chilled water flows from the evaporator side of the EDAHP at the average temperature; qE-EDAHP is the density of the chilled water flows from the evaporator side of the EDAHP at the average temperature; GE-EDAHP is the volumetric flow rate of the chilled water flows from the evaporator side of the EDAHP; and tE-EDAHP in and tE-EDAHP out are the chilled water temperatures entering and leaving the evaporator side of the EDAHP, respectively. The LDS cooling energy comes from the waste heat recovered of JRU, so the LDS should be used together with JRU, and the LDS cooling capacity is defined as
Q LDSðþJRUÞ ¼ COP LR COP LD Q JRU
ð9Þ
where COPLR and COPLD are the coefficient of performance of the liquid regenerate unit and liquid desiccant unit, which are defined as
COP LR ¼
Mfa ðxo xs Þ r o Q JRU
ð10Þ
COP LD ¼
Mfa ðho hs Þ Mfa ðxo xs Þ r o
ð11Þ
where Mfa is the mass flow rate of the inlet fresh air of the liquid desiccant unit; ro is the latent heat of vaporization; xo and xs are the humidity ratio of the outdoor air and supply air; ho and hs are the enthalpy of the outdoor air and supply air, respectively. As illustrated in Fig. 8, the cooling capacity of the EDAHP is about 39.01–39.62 kW, and the cooling capacity of the LDS is about 112.24–113.92 kW. The cooling capacity of LDS is much higher than that of EDAHP, so the liquid desiccant system could improve the system’s performance greatly. The efficiency of different configurations on operating mode III is illustrated in Fig. 9. Efficiency of the system consisting of the ICE, EDAHP and CT is defined as
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L. Fu et al. / Energy Conversion and Management 50 (2009) 977–982
ing using ICE + LDS(+JRU) + EDAHP(+CT). Therefore, the only way to increase the efficiency of the whole CCHP is to maximize the use of the heat recovered by the ICE and to utilize the remaining heat of exhaust gas in other waste-heat driven equipments capable of using low quality waste heat like the CRU and LDS.
ICE+EDAHP(+CT)+LDS(+JRU) ICE+EDAHP(+CT) ICE
Efficiency (%)
100 90 80 70 60 50 40 30 20 10 0
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
5. Conclusions
Time Fig. 9. Efficiency of different configurations (mode III).
EICEþEDAHPðþCTÞ ¼
W e þ Q EDAHPðþCTÞ 100ð%Þ Q inLHV þ W EDAHPðþCTÞ
ð12Þ
where QEDAHP(+CT) is the cooling energy recovered by the combination of EDAHP and CT, and WEDAHP(+CT) is the electric power consumed by the pumps of EDAHP and CT system. Efficiency of the system consisting of the ICE, EDAHP, CT, JRU and LDS is defined as
EICEþEDAHPðþCTÞþLDSðþJRUÞ ¼
W e þ Q EDAHPðþCTÞ þ Q LDSðþJRUÞ Q inLHV þ W EDAHPðþCTÞ þ W LDSðþJRUÞ 100ð%Þ
ð13Þ
ICE+EDAHP(+CT)+LDS(+JRU)
ICE+EDAHP(+CT)
ICE+JRU+EDAHP(+CRU)
ICE
ICE+JRU
Efficiency (%)
100 90 80 70 60 50 40 30 20 10 0
ICE+JRU+FWRU
where QLDS(+JRU) is the cooling energy recovered by the combination of LDS and JRU, and WLDS(+JRU) is the electric power consumed by LDS and JRU system. As illustrated in Fig. 9, the overall efficiency of ICE + EDAHP + CT is 41.51–41.67%, and the overall efficiency of ICE + EDAHP + CT + LDS + JRU is about 85.45–86.21%. We also can compute that the efficiency of the LDS + JRU is about 43.94–44.54%, so the LDS system could make a great progress in the system’s performance. Compared with the mode I and mode II, it is shown that the overall efficiency of mode III is higher than mode I, and lower than mode II. Fig. 10 shows a comparison of the different configurations efficiencies. The various configurations include: ICE (producing electric power only), ICE + JRU, ICE + JRU + FWRU, ICE + JRU + EDAHP(+CRU), ICE + LDS (+JRU), and ICE + LDS(+JRU) + EDAHP(+CT). It is evident in Fig. 10 that the minimum efficiency (25–26%) is attributed to the electric power generation only, and the maximum efficiency (91–93%) in the winter is due to the combined production of electric power and heating using ICE + JRU + EDAHP(+CRU), and the maximum efficiency (85–86%) in the summer is due to the combined production of electric power and cool-
Fig. 10. Efficiencies of the different configurations.
Performance tests of several ICE-based CCHP systems were performed at the BERC Laboratory to assess the different configurations performance. These tests were performed at a constant ICE power output of 60 kW. ICE power output, hot water, cooling water and chilled water flow rates were held constant under the steady operating mode. In the winter, the electrical efficiency of ICE is about 25–26%, and the thermal recovery efficiency of JRU is about 36–37%. The addition of the FWRU to the system contributed 18% to the overall efficiency, and the addition of EDAHP(+CRU) to the system contributed 30%–32% to the overall efficiency. In the summer, addition of the EDAHP(+CT) to the system contributed 44– 45% to the overall efficiency. The maximum efficiency (91–93%) in the winter is due to the combined production of electric power and heating using mode II (ICE + JRU + EDAHP(+CRU)), and the maximum efficiency (85– 86%) in the summer is due to the combined production of electric power and cooling using mode III (ICE + LDS(+JRU) + EDAHP(+CT)). Therefore, it is showed that the only way to increase the efficiency of the whole CCHP is to maximize the use of the heat recovered by the ICE and to utilize the remaining heat of exhaust gas in other waste-heat driven equipments capable of using low quality waste heat like the CRU and LDS. Acknowledgements This study was conducted under the auspices of the 863 HiTech Program, and was financed by the Foundation for Advanced Energy Technology Research, Ministry of Science and Technology, China. References [1] Zaltash A, Petrov AY, Rizy DT, Labinov SD, Vineyard EA, Linkous RL. Laboratory R&D on integrated energy systems (IES). Appl Therm Eng 2006;26:28–35. [2] Marantan A. Optimization of integrated micro turbine and absorption chiller systems in chp for buildings applications. Ph.D. Dissertation, Mechanical Engineering, University of Maryland, College Park; 2003. [3] Labinov S, Zaltash A, Rizy DT, Fairchild PD, Devault RC, Vineyard EA. Predictive algorithms for microturbine performance for BCHP systems. ASHRAE Trans 2002;108:670–81. [4] Popovic P, Marantan A, Radermacher R, Garland P. Integration of microturbine with single-effect exhaust-driven absorption chiller and solid wheel desiccant system. ASHRAE Trans 2002;108:1–9. [5] Rizy DT, Zaltash A, Labinov SD, Petrov AY, Vineyard EA, Linkous RL. CHP Integration (or IES): maximizing the efficiency of distributed generation with waste heat recovery. In: Proceedings of power system conference; 2003, pp. 1– 6. [6] Liao X. The development of an air-cooled absorption chiller concept and its integration in CHP systems. Ph.D. Dissertation, Mechanical Engineering, University of Maryland, College Park; 2004. [7] Fu L, Jiang Y. Operation optimization of a CHP plant for space heating. Int J Energy 2000;25(3):283–98. [8] Zhu CZ. CHP applications in the US and Europe used for reference in China. Popular Utilization of Electricity 2003; 2 (only in Chinese). [9] China Energy Conservation Investment Corporation. Market assessment of cogeneration in China 2001 [only in Chinese]. [10] Liu XH, Li Z, Jiang Y, Lin BR. Annual performance of liquid desiccant based independent humidity control HVAC system. Appl Therm Eng 2006;26: 1198–207. [11] Liu XH, Zhang Y, Qu KY, Jiang Y. Experimental study on mass transfer performances of cross flow dehumidifier using liquid desiccant. Energy Convers Manage 2006;47(15–16):2682–92. [12] Fu L, Zhao XL, Zhang SG, Jiang Y, Li H, Yang WW, Sun ZL. The steady and dynamic performance of an innovative natural gas CHP system. ASME Trans 2008. ASME2008-54160.
Contents lists available at ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Laboratory research on combined cooling, heating and power (CCHP) systems L. Fu *, X.L. Zhao, S.G. Zhang, Y. Jiang, H. Li, W.W. Yang Department of Building Science, School of Architecture, Tsinghua University, Beijing, PR China
a r t i c l e
i n f o
Article history: Received 14 May 2008 Accepted 16 December 2008 Available online 10 February 2009 Keywords: Combined cooling, heating and power Distributed generation Absorption heat pump Liquid desiccant dehumidification Condensation heat recovery
a b s t r a c t Combined cooling, heating and power (CCHP) systems offer the potential for a significant increase in fuel use efficiency by generating electricity onsite and recycling the exhaust gas for heating, cooling, or dehumidifying. A challenge for CCHP system is the efficient integration of distributed generation (DG) equipment with thermally-activated (TA) technologies. The China Ministry of Science and Technology and Tsinghua University launched the 863 Hi-Tech Program in 2007 to focus on laboratory and demonstration research to study the critical issues of CCHP systems, advance the technology and accelerate its application. The research performed at the Building Energy Research Center (BERC) Laboratory focuses on assessing the operational performance and energy efficiency of the integration of current DG and TA technologies; developing and verifying mathematical models of the individual devices and all the systems. The test laboratory is a flexible test-bed for the configuration of DG (presently a 70-kW natural gasfired internal combustion engine (ICE) with various heat recovery units, such as an flue gas-to-water heat recovery unit (FWRU), a jacket water heat recovery unit (JRU), liquid desiccant dehumidification systems (LDS), an exhaust-gas-driven double-effect absorption heat pump (EDAHP), and a condensation heat recovery unit (CRU)). In the winter, the exhaust gas from the ICE is used in the FWRU or used to drive the EDAHP directly, and the exhaust gas from the EDAHP is used in the CRU. The water flows from the CRU can be directed to the evaporator side of the EDAHP as the low-grade heat source. The water flows from the condensation side of the EDAHP, in conjunction with the jacket water flows from the JRU, is used for heating. In the summer, the exhaust gas from the ICE is used to drive the EDAHP for cooling directly, the exhaust gas from the EDAHP is bypassed to the exit via automated damper controls. The waste heat of the jacket water is used to drive the liquid desiccant dehumidification systems, to realize the separate control of heat and humidity. The automated damper is used in order to test various configurations and operating modes. The testing results show that the operating parameters and efficiencies of the overall system depend on different configurations. Under certain combinations of CCHP, the efficiency of the overall system can be as high as 90% (based on lower heating value of the natural gas). Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Distributed generation (DG) technology is becoming more reliable and prevalent because of the losses reduction on transmission and distribution lines by placing the generator next to the load. Recent developments in DG technologies have opened new opportunities for relatively small-scale combined cooling, heating and power (CCHP) systems that can be used in buildings. The CCHP system is always the combination of DG with thermally-activated (TA) technologies which could recover the waste heat for cooling or heating. The CCHP, in conjunction with other energy efficient building technologies, will maximize the efficiency of energy use, reduce harmful emissions to the environment, improve power
* Corresponding author. Tel.: +86 1062773885; fax: +86 1062770544. E-mail address: [email protected] (L. Fu). 0196-8904/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2008.12.013
quality and reliability compared with large central power plants [1]. The University of Maryland’s Center for Environmental Energy Engineering has worked closely with DOE’s Oak Ridge National Laboratory, and carried out a great deal of research. Two different CHP systems are studied, and some test and research results based on these two systems have been reported [2–6]. In China, CHP technology is still a promising energy conversion technology under development for application [7]. Typical examples can be found at the Shanghai Huangpu Central Hospital, Pudong International Airport, the Beijing Gas Company building and Tsinghua University [8,9]. But until now, there have been no reports of any detailed research on their performance. The China Ministry of Science and Technology, cooperated with Tsinghua University, launched the 863 Hi-Tech Program in 2007 to focus on laboratory and demonstration research to study the critical issues of CCHP systems, advance the technology and accelerate its application.
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Nomenclature AHP CCHP CHE COP CRU CT DAS DES DG EDAHP FWRU ICE JRU LR LD LDS LHV NG CP
absorption heat pump combined cooling, heating and power condensation heat exchanger coefficient of performance condensation heat recovery unit cooling tower data acquisition system distributed energy system Distributed generation exhaust-gas-driven double-effect absorption heat pump flue gas-to-water heat recovery unit internal combustion engine jacket water heat recovery unit liquid regenerate unit liquid desiccant unit liquid desiccant dehumidification systems lower heating value of natural gas natural gas specific heat (kJ/kg °C)
A laboratory for testing CCHP was commissioned at Building Energy Research Center (BERC) Laboratory. The scope of the facility is to test DG in combination with TA technologies for optimum waste heat recovery and overall energy efficiency. The objectives of the laboratory include collection of performance data on current DG and TA technologies both individually and operated as an integral part of an CCHP systems, development of models of different devices and verification of an system model based on integrated operation. 2. System and equipment The CCHP system in the laboratory (Fig. 1) is the combination of a gas-powered internal combustion engine (ICE) with other heat recovery units, including a jacket water heat recovery unit (JRU), an flue gas-to-water heat recovery unit (FWRU), liquid desiccant dehumidification systems (LDS), an exhaust-gas-driven double-effect absorption heat pump (EDAHP), and a condensation heat recovery unit (CRU). The ICE, JRU, FWRU, EDAHP are all located
Q
q G t W M r
x h
heating/cooling capacity (kW) density of water (kg/m3) volumetric flow rate (m3/s) temperature (°C) electric power (kW) mass flow rate of the air (kg/s) latent heat of vaporization (kJ/kg) humidity ratio (kg/kg) enthalpy (kJ/kg)
Subscripts e electric fa fresh air o out door air s supply air in inlet out outlet
on the basement of the building, and the liquid regenerate machine and liquid desiccant unit are located on the roof and second floor of the building, respectively. The 70 kW natural gas-powered ICE, has six cylinders with four strokes, which is designed to operate at a rated speed of 1500 rpm, a rated voltage of 400 V. The high-frequency power produced from the ICE is converted to 50 Hz 3-phase electric power through power conditioning device. In the winter, the exhaust gas from the ICE can either be routed to the FWRU or used to drive the EDAHP directly, and the exhaust gas from the EDAHP is used in the CRU. The water flows from the CRU which recovered the condensation heat of the exhaust gas can be directed to the evaporator side of the EDAHP as the low-grade heat source. The water flows from the condenser side of the EDAHP, in conjunction with the hot water flows from the JRU, is used for heating. In the summer, the exhaust gas from the ICE is used to drive the EDAHP for cooling directly, the exhaust gas from the EDAHP is bypassed to the exit. The cooling tower (CT) is used. The waste heat recovered from JRU is used to regenerate the liquid, and the regeneration stream
Fig. 1. CHP Laboratory at Building Energy Research Center.
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is used to drive the liquid desiccant unit, to produce the low humidity air, which realize the separate control of heat and humidity [10,11]. The automated damper is used in order to test various configurations and operating modes. The operating mode I: ICE + JRU + FWRU The operating mode II: ICE + JRU + EDAHP + CRU The operating mode III: ICE + JRU + LDS(including liquid regenerate unit and liquid desiccant unit) + EDAHP + CT
of data the DAS can provide are as follows: temperature, humidity, gas/air/exhaust/liquid flow rate, electricity, and current, pressure, equipment status, and weather station data. Most of the sensors output are 4–20 mA current, which has the advantage of avoiding signal attenuation over long wires. The current signal is converted into 0.88–4.4 VDC voltage, with which the required data value is calculated through the DAS program and then stored in the computer. 4. Results and discussion
The operating models I and II are winter mode and the operating mode III is summer mode. On the operating mode I, the ICE’s exhaust gas which has a temperature of about 510 °C is directed to the heat recovery units. The ICE’s exhaust passes through the FWRU and leaves it at a temperature of about 90 °C. On the operating mode II, the ICE’s exhaust gas is directed to EDAHP and leaves it at a temperature of about 170 °C, and then is directed to CRU and leaves it at a temperature lower than 30 °C. On the operating mode III, the ICE’s exhaust gas is directed to EDAHP and leaves it at a temperature of about 170 °C, and the recovered heat from the JRU at a temperature of 60 °C is used to regenerate the desiccant liquid in the liquid regenerate unit. The regenerated liquid is used to drive the liquid desiccant unit, to produce the low humidity air. Although, the current configuration at the CCHP Laboratory only includes ICE-based CCHP systems; it could be extended to encompass many other DG systems such as microturbines and fuel cells. Our near term plans include getting a fuel cell to test with the heat recovery equipment at the Laboratory. 3. Experiment conditions and procedure The previous tests studied the steady and dynamic performance of operating mode II [12], the current tests studied the overall efficiency of different configurations. The water temperature depends on several parameters which includes the ICE loading, and the water flow rate, so these tests were performed at a constant ICE power output of 60 kW. ICE power output, hot water, cooling water and chilled water flow rates were held constant under the steady operating mode. A data acquisition system (DAS) was installed to measure all relevant temperatures, relative humidity, pressures, flow rates, and power consumption to calculate the performance of the CCHP systems under all operating conditions. The test instrumentation and their measurement accuracies are given in Table 1. The DAS is completely separate from the control system, and the readings that the DAS provides can be completely customized. The types
4.1. System performance on mode I (ICE + JRU + FWRU) On the mode I, the natural gas flow rate is 23.74 m3/h, the ICE’s excess air coefficient is 1.11, the hot water flow rate from the JRU and hot water flow rate from the FWRU are 7.1 m3/h and 1.15 m3/h, respectively. The temperature of exhaust gas entering and leaving the FWRU is shown in Fig. 2. The Inlet temperature of the flue gas is 510.12– 510.49 °C, and the outlet temperature of flue gas is 92.97–93.42 °C. It is well known that the flue gas dew point of natural gas would be 40–55 °C depending on the different excess air coefficients, so the condensation heat of the flue gas cannot be used on the mode I. The energy loss is serious in the waste heat recovery system, and the energy utilization of the system could be improved. The heating or power capacity of different equipments is shown in Fig. 3. The JRU heating capacity is defined as
Q JRU ¼ C PJRU qJRU GJRU ðt JRUin t JRUout Þ
ð1Þ
where CP JRU is the water heat capacity at the average temperature; qJRU is the density of water at the average temperature; GJRU is the volumetric flow rate of jacket water; and tJRU in and tJRU out are the jacket water temperatures entering and leaving the JRU, respectively. The FWRU heating capacity is defined as
Q FWRU ¼ C PFWRU qFWRU GFWRU ðtFWRUin tFWRUout Þ
ð2Þ
where CP FWRU is the water heat capacity at the average temperature; qFWRU is the density of water at the average temperature; GFWRU is the volumetric flow rate of FWRU water; and tFWRU in and tFWRU out are the water temperatures entering and leaving the FWRU, respectively. As illustrated in Fig. 3, the output of the ICE is stabilized in a range from 59.86 kW to 60.72 kW at this time. The heating capacity of the JRU is about 84.01–85.41 kW, and the heating capacity of
600
Standard flow nozzles plus inclined differential manometer Platinum RTD
±1%
Air temperature
±0.5%
0
Time Fig. 2. Flue gas temperature of FWRU.
13:24:17
±0.5%
100 13:24:03
Platinum RTD
200
13:23:50
±1% ±0.5% ±0.5 °C/ ±0.1 °C ±0.5%
13:23:36
Electrical power meter Ultrasonic flow meter T thermocouple/resistance temperature device (RTD) Analysis instrument of exhaust
Inlet of FWRU Outlet of FWRU
300
13:23:22
±1%
13:23:08
Natural gas flow meter
13:22:55
Natural gas flow rate Electrical power Water flow rate Water temperature Exhaust components Exhaust temperature Air flow rate
400
13:22:41
Measurement precision
13:22:27
Instruments
500
13:22:13
Parameters
Temperature(
)
Table 1 Parameters of the measurement instruments.
L. Fu et al. / Energy Conversion and Management 50 (2009) 977–982
jacket water is about 35.97–36.76%, and the thermal recovery efficiency of the flue gas is about 17.81–18.11% (average 17.96). The thermal recovery of the flue gas is much smaller than the thermal recovery of the jacket water. The flue gas temperature exiting the ICE is as high as 510.12–510.49 °C, how much heat the flue gas contains? So the flue gas enthalpy at the temperature of 510 °C is computed, which accounts for about 34% of the natural gas input energy (based on LHV). Therefore, the energy loss accounts for 47% of the input energy of FWRU, which is computed as (34– 17.96%)/34%. 4.2. System performance on mode II (ICE + JRU + EDAHP + CRU)
13:24:17
13:24:03
13:23:50
13:23:36
13:23:22
13:23:08
13:22:55
13:22:41
ICE FWRU JRU 13:22:27
90 80 70 60 50 40 30 20 10 0
13:22:13
Heating/power capacity(kW)
980
On the mode II, the hot water flow rate from the EDAHP is 16.07 m3/h, and the water flow from the CRU is 10.56 m3/h, and the hot water flow rate from the JRU is 4.41 m3/h. There are three temperature test points along the flue gas pipeline, mounted on the outlet of the ICE, the outlet of the EDAHP, and the outlet of the CRU. The test results for the three temperature points are illustrated in Fig. 5. According to this figure, the temperature of the flue gas exiting the ICE is about 519.27 °C, and the temperature of the flue gas entering and leaving the CRU is 166.96 °C and 18.99 °C, respectively, so the flue gas passes through the CRU and the condensation heat of it is recovered. The energy loss leaving the system is just equal to the flue gas enthalpy at a temperature of 18.99 °C, which accounts for about 3.3% of the natural gas input energy (based on LHV).The energy utilization on operating mode II is improved greatly than mode I. The heating and powering capacity of different equipments is shown in Fig. 6. It should be noted that the EDAHP heating capacity comes from two parts, one part comes from the generator side (flue gas waste heat from 519.27 °C to 166.96 °C), the other part comes from the evaporator side (flue gas waste heat from 166.96 °C to 18.99 °C which was recovered in CRU), so the heating capacity of EDAHP should include the heat recovery of CRU. The input of EDAHP is the generator side and evaporator side, and the output of the EDAHP is the condenser side. The EDAHP heating capacity is defined as
Time
13:24:17
13:24:03
13:23:50
13:23:36
13:23:22
13:23:08
13:22:55
13:22:41
ICE+JRU+FWRU ICE+JRU ICE
13:22:27
90 80 70 60 50 40 30 20 10 0
13:22:13
Efficiency(%)
Fig. 3. Heating or power capacity of different equipments (mode I).
Time Fig. 4. Efficiency of different configurations (mode I).
the FWRU is about 41.49–41.91 kW. The efficiency of different configurations is shown in Fig. 4. The efficiency and performance calculation are calculated by using the following equations:ICE efficiency based on lower heating value (LHV) of natural gas is defined as
EICE ¼
We 100ð%Þ Q inLHV
ð3Þ
Q EDAHPðþCRUÞ ¼ C P
where CP C-EDAHP is the heat capacity of the hot water flows from the condenser side of the EDAHP at the average temperature; qC-EDAHP is the density of the hot water flows from the condenser side of the EDAHP at the average temperature; GC-EDAHP is the volumetric flow rate of the water flows from the condenser side of the EDAHP;
)
where QJRU is the heat recovered by the JRU and WJRU is the electric power consumed by the JRU pump.Efficiency of the system consisting of the ICE, JRU and FWRU is defined as
Temperature (
500
ð4Þ
EICEþJRUþFWRU ¼
W e þ Q JRU þ Q FWRU 100ð%Þ Q inLHV þ W JRU þ W FWRU
ð5Þ
where QFWRU is the heat recovered by the FWRU and WFWRU is the electric power consumed by the FWRU pump. As illustrated in Fig. 4, the electrical efficiency of ICE is about 25.67–26.27%, and overall efficiency of ICE + JRU is 61.97–63.09%, and overall efficiency of ICE + JRU + FWRU is about 79.85–81.19%. We also can compute that the thermal recovery efficiency of the
400 300
Out of ICE Out of EDAHP Out of CRU
200 100 0 19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
EICEþJRU
qC-EDAHP GC-EDAHP ðt C-EDAHP in tCEDAHP out Þ ð6Þ
where We is the net electric power generated by the ICE and Qin LHV is the natural gas input (based on LHV).Efficiency of the system consisting of the ICE and JRU is defined as
W e þ Q JRU ¼ 100ð%Þ Q inLHV þ W JRU
C-EDAHP
Time Fig. 5. Temperature distributions on the flue gas pipeline.
981
ICE EDAHP(+CRU) JRU
120 100
ICE EDAHP(+CT) LDS(+JRU)
80 60 40 20 0
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
Cooling/powering capacity (kW)
100 90 80 70 60 50 40 30 20 10 0
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
Heating/powering capacity (kW)
L. Fu et al. / Energy Conversion and Management 50 (2009) 977–982
Time
Time
Fig. 8. Heating or powering capacity of different equipments (mode III).
Fig. 6. Heating or powering capacity of different equipments (mode II).
and tC-EDAHP in and tC-EDAHP out are the water temperatures entering and leaving the condenser side of the EDAHP, respectively. As illustrated in Fig. 6, the output of the ICE is stabilized in a range from 60.00 kW to 60.91 kW at this time. The heating capacity of the JRU is about 86.34–87.63 kW, and the heating capacity of the EDAHP is about 72.24–76.63 kW. Compared with the mode I (illustrated in Fig. 3), it is shown that the heating capacity of EDAHP is improved greatly than the heating capacity of FWRU. The efficiency of different configurations is shown in Fig. 7. Efficiency of the system consisting of the ICE, JRU, EDAHP and CRU is defined as
EICEþJRUþEDAHPðþCRUÞ ¼
W e þ Q JRU þ Q EDAHPðþCRUÞ 100ð%Þ Q inLHV þ W JRU þ W EDAHPðþCRUÞ
ð7Þ
100 90 80 70 60 50 40 30 20 10 0
ICE+JRU+EDAHP(+CRU) ICE+JRU ICE
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
Efficiency (%)
where QEDAHP(+CRU) is the recovered heat by the combination of EDAHP and CRU, and WEDAHP(+CRU) is the electric power consumed by the pumps of EDAHP and CRU system. As illustrated in Fig. 7, the electrical efficiency of ICE is about 25.20–25.30%, and overall efficiency of ICE + JRU is 61.22–61.93%, and overall efficiency of ICE + JRU + EDAHP + CRU is about 91.03– 93.24%. We also can compute that the thermal recovery efficiency of the jacket water is about 35.92–36.71%, and the thermal recovery efficiency of the flue gas (EDAHP + CRU) is about 29.73–31.95% (average 30.84%). The thermal recovery efficiency of the flue gas on mode II is 11.92–13.84% higher than the thermal recovery efficiency on mode I. Also the flue gas enthalpy at the temperature of 519.27 °C is computed, which accounts for about 35.80% of the natural gas input energy (based on LHV). Therefore, the energy loss just accounts for 13.85% of the input energy of EDAHP and CRU, which is computed as (35.80–30.84%)/35.80%.
Time Fig. 7. Efficiency of different configurations (mode II).
4.3. System performance on mode III (ICE + JRU + LDS + EDAHP + CT) On the mode III, the chilled water flow rate from EDAHP is 9.57 m3/h, and the cooling water flow rate from EDAHP is 15.3 m3/h, and the hot water flow rate from the JRU is 6.27 m3/h. On this operating mode, the temperature of exhaust gas entering and leaving the EDAHP is also approximately 519 °C and 167 °C. The cooling or power capacity of different equipments is shown in Fig. 8. The EDAHP should be used together with CT, the EDAHP cooling capacity is defined as
Q EDAHPðþCTÞ ¼ C PEEDAHP qEEDAHP GEEDAHP ðt EEDAHPin t EEDAHPout Þ ð8Þ where CP E-EDAHP is the heat capacity of the chilled water flows from the evaporator side of the EDAHP at the average temperature; qE-EDAHP is the density of the chilled water flows from the evaporator side of the EDAHP at the average temperature; GE-EDAHP is the volumetric flow rate of the chilled water flows from the evaporator side of the EDAHP; and tE-EDAHP in and tE-EDAHP out are the chilled water temperatures entering and leaving the evaporator side of the EDAHP, respectively. The LDS cooling energy comes from the waste heat recovered of JRU, so the LDS should be used together with JRU, and the LDS cooling capacity is defined as
Q LDSðþJRUÞ ¼ COP LR COP LD Q JRU
ð9Þ
where COPLR and COPLD are the coefficient of performance of the liquid regenerate unit and liquid desiccant unit, which are defined as
COP LR ¼
Mfa ðxo xs Þ r o Q JRU
ð10Þ
COP LD ¼
Mfa ðho hs Þ Mfa ðxo xs Þ r o
ð11Þ
where Mfa is the mass flow rate of the inlet fresh air of the liquid desiccant unit; ro is the latent heat of vaporization; xo and xs are the humidity ratio of the outdoor air and supply air; ho and hs are the enthalpy of the outdoor air and supply air, respectively. As illustrated in Fig. 8, the cooling capacity of the EDAHP is about 39.01–39.62 kW, and the cooling capacity of the LDS is about 112.24–113.92 kW. The cooling capacity of LDS is much higher than that of EDAHP, so the liquid desiccant system could improve the system’s performance greatly. The efficiency of different configurations on operating mode III is illustrated in Fig. 9. Efficiency of the system consisting of the ICE, EDAHP and CT is defined as
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L. Fu et al. / Energy Conversion and Management 50 (2009) 977–982
ing using ICE + LDS(+JRU) + EDAHP(+CT). Therefore, the only way to increase the efficiency of the whole CCHP is to maximize the use of the heat recovered by the ICE and to utilize the remaining heat of exhaust gas in other waste-heat driven equipments capable of using low quality waste heat like the CRU and LDS.
ICE+EDAHP(+CT)+LDS(+JRU) ICE+EDAHP(+CT) ICE
Efficiency (%)
100 90 80 70 60 50 40 30 20 10 0
19:05:30 19:06:00 19:06:30 19:07:00 19:07:30 19:08:00 19:08:30 19:09:00 19:09:30 19:10:00 19:10:30 19:11:00 19:11:30 19:12:00
5. Conclusions
Time Fig. 9. Efficiency of different configurations (mode III).
EICEþEDAHPðþCTÞ ¼
W e þ Q EDAHPðþCTÞ 100ð%Þ Q inLHV þ W EDAHPðþCTÞ
ð12Þ
where QEDAHP(+CT) is the cooling energy recovered by the combination of EDAHP and CT, and WEDAHP(+CT) is the electric power consumed by the pumps of EDAHP and CT system. Efficiency of the system consisting of the ICE, EDAHP, CT, JRU and LDS is defined as
EICEþEDAHPðþCTÞþLDSðþJRUÞ ¼
W e þ Q EDAHPðþCTÞ þ Q LDSðþJRUÞ Q inLHV þ W EDAHPðþCTÞ þ W LDSðþJRUÞ 100ð%Þ
ð13Þ
ICE+EDAHP(+CT)+LDS(+JRU)
ICE+EDAHP(+CT)
ICE+JRU+EDAHP(+CRU)
ICE
ICE+JRU
Efficiency (%)
100 90 80 70 60 50 40 30 20 10 0
ICE+JRU+FWRU
where QLDS(+JRU) is the cooling energy recovered by the combination of LDS and JRU, and WLDS(+JRU) is the electric power consumed by LDS and JRU system. As illustrated in Fig. 9, the overall efficiency of ICE + EDAHP + CT is 41.51–41.67%, and the overall efficiency of ICE + EDAHP + CT + LDS + JRU is about 85.45–86.21%. We also can compute that the efficiency of the LDS + JRU is about 43.94–44.54%, so the LDS system could make a great progress in the system’s performance. Compared with the mode I and mode II, it is shown that the overall efficiency of mode III is higher than mode I, and lower than mode II. Fig. 10 shows a comparison of the different configurations efficiencies. The various configurations include: ICE (producing electric power only), ICE + JRU, ICE + JRU + FWRU, ICE + JRU + EDAHP(+CRU), ICE + LDS (+JRU), and ICE + LDS(+JRU) + EDAHP(+CT). It is evident in Fig. 10 that the minimum efficiency (25–26%) is attributed to the electric power generation only, and the maximum efficiency (91–93%) in the winter is due to the combined production of electric power and heating using ICE + JRU + EDAHP(+CRU), and the maximum efficiency (85–86%) in the summer is due to the combined production of electric power and cool-
Fig. 10. Efficiencies of the different configurations.
Performance tests of several ICE-based CCHP systems were performed at the BERC Laboratory to assess the different configurations performance. These tests were performed at a constant ICE power output of 60 kW. ICE power output, hot water, cooling water and chilled water flow rates were held constant under the steady operating mode. In the winter, the electrical efficiency of ICE is about 25–26%, and the thermal recovery efficiency of JRU is about 36–37%. The addition of the FWRU to the system contributed 18% to the overall efficiency, and the addition of EDAHP(+CRU) to the system contributed 30%–32% to the overall efficiency. In the summer, addition of the EDAHP(+CT) to the system contributed 44– 45% to the overall efficiency. The maximum efficiency (91–93%) in the winter is due to the combined production of electric power and heating using mode II (ICE + JRU + EDAHP(+CRU)), and the maximum efficiency (85– 86%) in the summer is due to the combined production of electric power and cooling using mode III (ICE + LDS(+JRU) + EDAHP(+CT)). Therefore, it is showed that the only way to increase the efficiency of the whole CCHP is to maximize the use of the heat recovered by the ICE and to utilize the remaining heat of exhaust gas in other waste-heat driven equipments capable of using low quality waste heat like the CRU and LDS. Acknowledgements This study was conducted under the auspices of the 863 HiTech Program, and was financed by the Foundation for Advanced Energy Technology Research, Ministry of Science and Technology, China. References [1] Zaltash A, Petrov AY, Rizy DT, Labinov SD, Vineyard EA, Linkous RL. Laboratory R&D on integrated energy systems (IES). Appl Therm Eng 2006;26:28–35. [2] Marantan A. Optimization of integrated micro turbine and absorption chiller systems in chp for buildings applications. Ph.D. Dissertation, Mechanical Engineering, University of Maryland, College Park; 2003. [3] Labinov S, Zaltash A, Rizy DT, Fairchild PD, Devault RC, Vineyard EA. Predictive algorithms for microturbine performance for BCHP systems. ASHRAE Trans 2002;108:670–81. [4] Popovic P, Marantan A, Radermacher R, Garland P. Integration of microturbine with single-effect exhaust-driven absorption chiller and solid wheel desiccant system. ASHRAE Trans 2002;108:1–9. [5] Rizy DT, Zaltash A, Labinov SD, Petrov AY, Vineyard EA, Linkous RL. CHP Integration (or IES): maximizing the efficiency of distributed generation with waste heat recovery. In: Proceedings of power system conference; 2003, pp. 1– 6. [6] Liao X. The development of an air-cooled absorption chiller concept and its integration in CHP systems. Ph.D. Dissertation, Mechanical Engineering, University of Maryland, College Park; 2004. [7] Fu L, Jiang Y. Operation optimization of a CHP plant for space heating. Int J Energy 2000;25(3):283–98. [8] Zhu CZ. CHP applications in the US and Europe used for reference in China. Popular Utilization of Electricity 2003; 2 (only in Chinese). [9] China Energy Conservation Investment Corporation. Market assessment of cogeneration in China 2001 [only in Chinese]. [10] Liu XH, Li Z, Jiang Y, Lin BR. Annual performance of liquid desiccant based independent humidity control HVAC system. Appl Therm Eng 2006;26: 1198–207. [11] Liu XH, Zhang Y, Qu KY, Jiang Y. Experimental study on mass transfer performances of cross flow dehumidifier using liquid desiccant. Energy Convers Manage 2006;47(15–16):2682–92. [12] Fu L, Zhao XL, Zhang SG, Jiang Y, Li H, Yang WW, Sun ZL. The steady and dynamic performance of an innovative natural gas CHP system. ASME Trans 2008. ASME2008-54160.