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Feasibility Analysis of CCHP System with Thermal Energy Storage Driven by Micro Turbine
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 105 (2017) 2396 – 2402
The 8th International Conference on Applied Energy – ICAE2016
Feasibility analysis of CCHP system with thermal energy storage driven by micro turbine Lang Wang, Jianfeng Lu, Weilong Wang*, Jing Ding School of Engineering, Sun Yat-Sen University, Guangzhou 510006, PR China
Abstract The combined cooling, heating and power (CCHP) system with thermal energy storage (TES) driven by micro turbine is studied in this paper, which are used in the restaurant and commercial building. The impact of the introduction of TES on the energy and economic performance of CCHP system has been analyzed. The result shows that the CCHP systems with TES had higher capital cost and less energy consumption and operation cost, compared with that without TES. And the annualized life cycle cost of CCHP system with TES was slightly lower than that without TES. Additionally, the economic benefit of CCHP system with TES is worse than the conventional separate production (SP) system, although the primary energy consumption of it is significantly lower than the SP system. ©©2017 Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 2016The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.
Keywords: CCHP; Thermal energy storage; Energy saving ratio; Life cycle assessment
1. Introduction Currently, the energy shortage and environmental pollution are hindering the sustainable development around the world. Hence, the combined cooling, heating and power (CCHP) system is becoming more popular worldwide, due to its good potential for reducing energy consumption and pollutants emission [12]. The overall energy efficiency of CCHP system is usually above 75%, which is higher than the separate production (SP) system [3]. Nevertheless, the widespread application of CCHP system is limited by the variability of energy demands, which led to so large installed capacities of devices that they operate under off-design condition for a long period [4]. One of the effective solutions to alleviate the adverse impact caused by variability of energy demands is adapting thermal energy storage (TES) to increase the recovered waste heat from power generation unit [4-7]. In this paper, the CCHP systems with TES in the restaurant and commercial building were studied. The primary energy consumption were calculated and
* Corresponding author. Tel.: +86-020-39332320. E-mail address: [email protected].
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.688
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Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
analyzed. And the economic benefit of them were evaluated through the life cycle approach, where the capital cost and operation cost were considered. The impact of TES on the energy and economic performance of CCHP system were investigated. 2. Methodology 2.1. The system model description The schematic diagram of CCHP system with TES is depicted in Fig. 1. The system operates following the electric load. All the electric load is provided by micro turbine, while the waste heat from it is utilized by absorption chiller to cover the cooling load and recovered by heat exchanger to produce the heating load. If the recovered waste heat is not enough to meet thermal load, electric chiller or gas-fired boiler would be turned on to supplement them, while the redundant waste heat would be stored in TES.
Fig. 1. The schematic diagram of CCHP system with TES
The part-load performance of Micro Turbine is described as: FPGU
0.128 0.8575EPGU˗mexhaust
0.3442 0.6708EPGU˗Texhaust
0.8126 0.1886 EPGU
(1)
whereCEPGU,CFPGU,Cmexhaust andCTexhaust are the ratios of the electric output, fuel consumption, exhaust gas flow and exhaust gas temperature to their rated values, respectively. The exhaust gas from micro turbine is utilized by absorption chiller, of which the COPABC is calculated as: COPABC
Kc u Tgen Tcond Tgen u Tevap Tcond Tevap
(2)
where Tgen, Tcond and Tevap are the generation temperature, condensing temperature and evaporating temperature of absorption chiller respectively, and ηc is thermodynamic perfection of absorption chiller. The rated electric efficiencies and rated exhaust gas temperature of micro turbine is 33% and 300ć. For absorption chiller, Tcond and Tevap are 303 K and 280 K, while Tgen is equal to Texhaust, and ηc is 0.138. , The COP of electric chiller is 3. The efficiency of electric grid and gas-fired boiler are 36% and 0.9. 2.2. Case study The energy demands of restaurant and commercial building were shown in Fig. 2, of which the daily
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Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
electric loads were both 1000 kWh. The typical summer days are assumed to be 213, and the typical winter days are set to be 90. 2.3. Evaluation criteria The Primary Energy Saving Ratio (PESR) and Relative Energy Saving Ratio (RESR) were used to evaluate the energy performance of CCHP system and impact of TES on it, which are calculated as: PESR 1 PECCCHP PECSP
(3)
RESR 1 PECCCHPTES PECCCHP
(4)
where PECCCHP and PECSP are the primary energy consumptions of CCHP system and SP system respectively, and PECCCHP-TES is the primary energy consumption of CCHP system with TES. The life cycle cost consists of operation cost and capital cost, which is expressed as: d u 1 d
n
ALCC
¦ C u Capacity u i
1 d
i
i 1
n
n
1
(5)
E u Cgrid V fuel u C fuel
Where C and Capacity are the capital cost and capacity of equipment, i denotes the type of equipment, E is the electricity bought from electric grid, Vfuel is the consumed fuel, Cgrid and Cfuel are the prices of electric from grid and natural gas respectively, d is the discount rate, and n is the life cycle of system. The parameters required for the economic assessment are summarized in Table 1 and Table 2.
Fig. 2. Hourly energy load of the restaurant and commercial building in the typical summer and winter day Table 1. The unit prices of equipment Equipment
Micro turbine
Absorption chiller
Electric chiller
Gas-fired boiler
Cooling energy storage system
Heating energy storage system
Unit price (̞/kW)
6663.83
2150
970
300
124
120
Table 2. The time-of-use electricity price Time period (h)
0:00-8:00
8:00-14:00, 17:00-19:00, 22:00-24:00
14:00-17:00, 19:00-22:00
Electric price (̞/kWh)
0.3199
0.61
0.9871
3. Results and discussion
Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
3.1. Simulation results of the CCHP systems with TES The hourly thermal load of CCHP system with TES in the restaurant and commercial building were depicted in Fig. 3 and Fig. 4. Fig. 3. (a) shows that the cooling energy produced by absorption chiller was higher than the cooling load of restaurant during 1 a.m. to 8 a.m.. The redundant cooling energy was stored in the TES, and the most was discharged to supplement cooling load at 1 p.m., when the electric chiller was not required. And then the electric chiller was used to supply the additional cooling load during 2 p.m. and 11 p.m.. In the typical winter day, the heating energy stored in the TES was higher than that discharged from TES, and gas-fired boiler was not required to supplement, as shown in Fig. 3. (b).
Fig. 3. Hourly cooling/heating load of the CCHP system with TES for the restaurant: (a) in the typical summer day; (b) in the typical winter day
Fig. 4. Hourly cooling/heating load of the CCHP system with TES for the commercial building: (a) in the typical summer day; (b) in the typical winter day
The simulation result of CCHP system with TES in commercial building is similar to that in restaurant. Fig. 4. (a) shows that electric chiller was not required to provide the additional cooling energy during 9 a.m. and 12 a.m., due to the cooling energy discharged from TES. At 1 p.m., the cooling energy stored in TES was not enough to cover the additional cooling load, and the electric chiller was used. As shown in Fig. 4. (b), the gas-fired boiler was not used, and the heating energy in TES was discharged only at 9 a.m.. 3.2. The evaluation of CCHP systems with TES
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Fig. 5 shows the PESRs and RESRs of CCHP systems with TES in the restaurant and commercial building. It could be concluded that the CCHP systems with TES in the restaurant and commercial building have great advantage of energy consumption over the SP system, according to the positive PESRs of them shown in Fig. 5. (a). The reason why CCHP system has less primary energy consumption is that utilizing the waste heat of micro turbine diminished the energy consumption for providing thermal load. In the typical summer day, the PESR of CCHP system with TES in commercial building is slightly higher than that in restaurant, due to the slight variation of energy demands of commercial building where the additional thermal energy is less. However, in the typical winter day, the PESR of CCHP system in commercial building is significantly lower than that in restaurant, which is mainly attributed to the fact that the heating load of commercial building is less than restaurant. Based on the annual energy analysis, the CCHP system with TES in restaurant is better than that in commercial building. As illustrated in Fig. 5. (b), it is clear that the introduction of TES reduced the primary energy consumption of CCHP systems in the restaurant and commercial building. The annual RESR of CCHP system with TES in restaurant is 1.58%, while the annual RESR of that in commercial building is 2.37%. It shows that the contribution of TES on the energy saving is related to the energy demands profile.
Fig. 5. The primary energy saving ratios and relative energy saving ratios of CCHP systems with TES for restaurant and commercial building
The economic evaluation results of CCHP systems with TES in the restaurant and commercial building are depicted in Fig. 6 and Fig. 7 respectively. In this paper, the discount rate is set to be 10%, and the life cycle is 20 years. Compared with the SP system, the CCHP systems with TES in the restaurant and commercial building had higher capital cost and lower operation cost. Totally, the economic performance of CCHP systems with TES in the restaurant and commercial building are different from each other, while the Annualized Life Cost Saving (ALCS) of the one in restaurant is -11.59% and it of that in commercial building is -21.73%. As shown in Fig. 6 (b) and Fig. 7 (b), the capital costs of CCHP systems with TES in the restaurant and commercial building are higher than those without TES respectively, while the operation costs were reduced by the introduction of TES due to the less energy consumption. Consequently, the ALCS of CCHP systems with TES in the restaurant and commercial building are 0.86% and 1.13% respectively, which means that the economic benefits of CCHP system could be improved by the introduction of TES.
Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
Fig. 6. The economic analysis result of CCHP system with TES in the restaurant
Fig. 7. The economic analysis result of CCHP system with TES in the commercial building
4. Conclusion The CCHP systems with TES driven by micro turbine in the restaurant and commercial building have been investigated in terms of energy and economic performance. The simulation result shows that the TES could store the redundant thermal energy and discharge to supplement thermal load, which led the gas-fired boiler to be not required in the typical winter day. The PESRs of CCHP systems with TES in the restaurant and commercial building are positive, while the ALCC of them are higher than SP system on account of so high capital cost. It is clear that the introduction of TES could reduce the primary energy consumption and annualized life cycle cost of CCHP system. With the introduction of TES, the capital cost of CCHP system increased, and the operation cost decreased due to the energy saving caused by TES. By comparing, it was found that the potential of TES for reducing the primary energy consumption and improving the economic benefit of CCHP system is dependent on the energy demands profile.
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Acknowledgements This work was supported by the funding of Nature Science Foundation of China (U1507113), Nature Science Foundation of China (51436009), Science and Technology Planning Project of Guang Dong Province (2015A010106006), and Science and Technology Program of Guang Zhou (201510010248). References [1] Li M, Jiang XZ, Zheng D, Guangbiao Zeng, Shi L. Thermodynamic boundaries of energy saving in conventional CCHP (Combine Cooling, Heating and Power) systems. Energy 2016;94:243-9. [2] Li L, Mu H, Gao W, Li M. Optimization and analysis of CCHP system based on energy loads coupling of residential and office buildings. Applied Energy 2014;136:206-16. [3] Xu D, Qu M. Energy, environmental, and economic evaluation of a CCHP system for a data center based on operational data. Energy and Buildings 2013;67:176-86. [4] Jiang XZ, Zeng G, Li M, Shi L. Evaluation of combined cooling, heating and power (CCHP) systems with energy storage units at different locations. Applied Thermal Engineering 2016;95:204-10. [5] Martínez-Lera S, Ballester J, Martínez-Lera J. Analysis and sizing of thermal energy storage in combined heating, cooling and power plants for buildings. Applied Energy 2013;106:127-42. [6] Saeed Mostafavi Tehrani S, Saffar-Avval M, Kalhori S B, Mansoori Z, Sharif M. Hourly energy analysis and feasibility study of employing a thermocline TES system for an integrated CHP and DH network. Energy Conversion and Management 2013;68:281-92. [7] Facci AL, Andreassi L, Ubertini S, Sciubba E. Analysis of the influence of thermal energy storage on the optimal management of a trigeneration plant. Energy Procedia 2014;45:1295-304.
ScienceDirect Energy Procedia 105 (2017) 2396 – 2402
The 8th International Conference on Applied Energy – ICAE2016
Feasibility analysis of CCHP system with thermal energy storage driven by micro turbine Lang Wang, Jianfeng Lu, Weilong Wang*, Jing Ding School of Engineering, Sun Yat-Sen University, Guangzhou 510006, PR China
Abstract The combined cooling, heating and power (CCHP) system with thermal energy storage (TES) driven by micro turbine is studied in this paper, which are used in the restaurant and commercial building. The impact of the introduction of TES on the energy and economic performance of CCHP system has been analyzed. The result shows that the CCHP systems with TES had higher capital cost and less energy consumption and operation cost, compared with that without TES. And the annualized life cycle cost of CCHP system with TES was slightly lower than that without TES. Additionally, the economic benefit of CCHP system with TES is worse than the conventional separate production (SP) system, although the primary energy consumption of it is significantly lower than the SP system. ©©2017 Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 2016The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.
Keywords: CCHP; Thermal energy storage; Energy saving ratio; Life cycle assessment
1. Introduction Currently, the energy shortage and environmental pollution are hindering the sustainable development around the world. Hence, the combined cooling, heating and power (CCHP) system is becoming more popular worldwide, due to its good potential for reducing energy consumption and pollutants emission [12]. The overall energy efficiency of CCHP system is usually above 75%, which is higher than the separate production (SP) system [3]. Nevertheless, the widespread application of CCHP system is limited by the variability of energy demands, which led to so large installed capacities of devices that they operate under off-design condition for a long period [4]. One of the effective solutions to alleviate the adverse impact caused by variability of energy demands is adapting thermal energy storage (TES) to increase the recovered waste heat from power generation unit [4-7]. In this paper, the CCHP systems with TES in the restaurant and commercial building were studied. The primary energy consumption were calculated and
* Corresponding author. Tel.: +86-020-39332320. E-mail address: [email protected].
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy. doi:10.1016/j.egypro.2017.03.688
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Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
analyzed. And the economic benefit of them were evaluated through the life cycle approach, where the capital cost and operation cost were considered. The impact of TES on the energy and economic performance of CCHP system were investigated. 2. Methodology 2.1. The system model description The schematic diagram of CCHP system with TES is depicted in Fig. 1. The system operates following the electric load. All the electric load is provided by micro turbine, while the waste heat from it is utilized by absorption chiller to cover the cooling load and recovered by heat exchanger to produce the heating load. If the recovered waste heat is not enough to meet thermal load, electric chiller or gas-fired boiler would be turned on to supplement them, while the redundant waste heat would be stored in TES.
Fig. 1. The schematic diagram of CCHP system with TES
The part-load performance of Micro Turbine is described as: FPGU
0.128 0.8575EPGU˗mexhaust
0.3442 0.6708EPGU˗Texhaust
0.8126 0.1886 EPGU
(1)
whereCEPGU,CFPGU,Cmexhaust andCTexhaust are the ratios of the electric output, fuel consumption, exhaust gas flow and exhaust gas temperature to their rated values, respectively. The exhaust gas from micro turbine is utilized by absorption chiller, of which the COPABC is calculated as: COPABC
Kc u Tgen Tcond Tgen u Tevap Tcond Tevap
(2)
where Tgen, Tcond and Tevap are the generation temperature, condensing temperature and evaporating temperature of absorption chiller respectively, and ηc is thermodynamic perfection of absorption chiller. The rated electric efficiencies and rated exhaust gas temperature of micro turbine is 33% and 300ć. For absorption chiller, Tcond and Tevap are 303 K and 280 K, while Tgen is equal to Texhaust, and ηc is 0.138. , The COP of electric chiller is 3. The efficiency of electric grid and gas-fired boiler are 36% and 0.9. 2.2. Case study The energy demands of restaurant and commercial building were shown in Fig. 2, of which the daily
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Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
electric loads were both 1000 kWh. The typical summer days are assumed to be 213, and the typical winter days are set to be 90. 2.3. Evaluation criteria The Primary Energy Saving Ratio (PESR) and Relative Energy Saving Ratio (RESR) were used to evaluate the energy performance of CCHP system and impact of TES on it, which are calculated as: PESR 1 PECCCHP PECSP
(3)
RESR 1 PECCCHPTES PECCCHP
(4)
where PECCCHP and PECSP are the primary energy consumptions of CCHP system and SP system respectively, and PECCCHP-TES is the primary energy consumption of CCHP system with TES. The life cycle cost consists of operation cost and capital cost, which is expressed as: d u 1 d
n
ALCC
¦ C u Capacity u i
1 d
i
i 1
n
n
1
(5)
E u Cgrid V fuel u C fuel
Where C and Capacity are the capital cost and capacity of equipment, i denotes the type of equipment, E is the electricity bought from electric grid, Vfuel is the consumed fuel, Cgrid and Cfuel are the prices of electric from grid and natural gas respectively, d is the discount rate, and n is the life cycle of system. The parameters required for the economic assessment are summarized in Table 1 and Table 2.
Fig. 2. Hourly energy load of the restaurant and commercial building in the typical summer and winter day Table 1. The unit prices of equipment Equipment
Micro turbine
Absorption chiller
Electric chiller
Gas-fired boiler
Cooling energy storage system
Heating energy storage system
Unit price (̞/kW)
6663.83
2150
970
300
124
120
Table 2. The time-of-use electricity price Time period (h)
0:00-8:00
8:00-14:00, 17:00-19:00, 22:00-24:00
14:00-17:00, 19:00-22:00
Electric price (̞/kWh)
0.3199
0.61
0.9871
3. Results and discussion
Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
3.1. Simulation results of the CCHP systems with TES The hourly thermal load of CCHP system with TES in the restaurant and commercial building were depicted in Fig. 3 and Fig. 4. Fig. 3. (a) shows that the cooling energy produced by absorption chiller was higher than the cooling load of restaurant during 1 a.m. to 8 a.m.. The redundant cooling energy was stored in the TES, and the most was discharged to supplement cooling load at 1 p.m., when the electric chiller was not required. And then the electric chiller was used to supply the additional cooling load during 2 p.m. and 11 p.m.. In the typical winter day, the heating energy stored in the TES was higher than that discharged from TES, and gas-fired boiler was not required to supplement, as shown in Fig. 3. (b).
Fig. 3. Hourly cooling/heating load of the CCHP system with TES for the restaurant: (a) in the typical summer day; (b) in the typical winter day
Fig. 4. Hourly cooling/heating load of the CCHP system with TES for the commercial building: (a) in the typical summer day; (b) in the typical winter day
The simulation result of CCHP system with TES in commercial building is similar to that in restaurant. Fig. 4. (a) shows that electric chiller was not required to provide the additional cooling energy during 9 a.m. and 12 a.m., due to the cooling energy discharged from TES. At 1 p.m., the cooling energy stored in TES was not enough to cover the additional cooling load, and the electric chiller was used. As shown in Fig. 4. (b), the gas-fired boiler was not used, and the heating energy in TES was discharged only at 9 a.m.. 3.2. The evaluation of CCHP systems with TES
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Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
Fig. 5 shows the PESRs and RESRs of CCHP systems with TES in the restaurant and commercial building. It could be concluded that the CCHP systems with TES in the restaurant and commercial building have great advantage of energy consumption over the SP system, according to the positive PESRs of them shown in Fig. 5. (a). The reason why CCHP system has less primary energy consumption is that utilizing the waste heat of micro turbine diminished the energy consumption for providing thermal load. In the typical summer day, the PESR of CCHP system with TES in commercial building is slightly higher than that in restaurant, due to the slight variation of energy demands of commercial building where the additional thermal energy is less. However, in the typical winter day, the PESR of CCHP system in commercial building is significantly lower than that in restaurant, which is mainly attributed to the fact that the heating load of commercial building is less than restaurant. Based on the annual energy analysis, the CCHP system with TES in restaurant is better than that in commercial building. As illustrated in Fig. 5. (b), it is clear that the introduction of TES reduced the primary energy consumption of CCHP systems in the restaurant and commercial building. The annual RESR of CCHP system with TES in restaurant is 1.58%, while the annual RESR of that in commercial building is 2.37%. It shows that the contribution of TES on the energy saving is related to the energy demands profile.
Fig. 5. The primary energy saving ratios and relative energy saving ratios of CCHP systems with TES for restaurant and commercial building
The economic evaluation results of CCHP systems with TES in the restaurant and commercial building are depicted in Fig. 6 and Fig. 7 respectively. In this paper, the discount rate is set to be 10%, and the life cycle is 20 years. Compared with the SP system, the CCHP systems with TES in the restaurant and commercial building had higher capital cost and lower operation cost. Totally, the economic performance of CCHP systems with TES in the restaurant and commercial building are different from each other, while the Annualized Life Cost Saving (ALCS) of the one in restaurant is -11.59% and it of that in commercial building is -21.73%. As shown in Fig. 6 (b) and Fig. 7 (b), the capital costs of CCHP systems with TES in the restaurant and commercial building are higher than those without TES respectively, while the operation costs were reduced by the introduction of TES due to the less energy consumption. Consequently, the ALCS of CCHP systems with TES in the restaurant and commercial building are 0.86% and 1.13% respectively, which means that the economic benefits of CCHP system could be improved by the introduction of TES.
Lang Wang et al. / Energy Procedia 105 (2017) 2396 – 2402
Fig. 6. The economic analysis result of CCHP system with TES in the restaurant
Fig. 7. The economic analysis result of CCHP system with TES in the commercial building
4. Conclusion The CCHP systems with TES driven by micro turbine in the restaurant and commercial building have been investigated in terms of energy and economic performance. The simulation result shows that the TES could store the redundant thermal energy and discharge to supplement thermal load, which led the gas-fired boiler to be not required in the typical winter day. The PESRs of CCHP systems with TES in the restaurant and commercial building are positive, while the ALCC of them are higher than SP system on account of so high capital cost. It is clear that the introduction of TES could reduce the primary energy consumption and annualized life cycle cost of CCHP system. With the introduction of TES, the capital cost of CCHP system increased, and the operation cost decreased due to the energy saving caused by TES. By comparing, it was found that the potential of TES for reducing the primary energy consumption and improving the economic benefit of CCHP system is dependent on the energy demands profile.
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Acknowledgements This work was supported by the funding of Nature Science Foundation of China (U1507113), Nature Science Foundation of China (51436009), Science and Technology Planning Project of Guang Dong Province (2015A010106006), and Science and Technology Program of Guang Zhou (201510010248). References [1] Li M, Jiang XZ, Zheng D, Guangbiao Zeng, Shi L. Thermodynamic boundaries of energy saving in conventional CCHP (Combine Cooling, Heating and Power) systems. Energy 2016;94:243-9. [2] Li L, Mu H, Gao W, Li M. Optimization and analysis of CCHP system based on energy loads coupling of residential and office buildings. Applied Energy 2014;136:206-16. [3] Xu D, Qu M. Energy, environmental, and economic evaluation of a CCHP system for a data center based on operational data. Energy and Buildings 2013;67:176-86. [4] Jiang XZ, Zeng G, Li M, Shi L. Evaluation of combined cooling, heating and power (CCHP) systems with energy storage units at different locations. Applied Thermal Engineering 2016;95:204-10. [5] Martínez-Lera S, Ballester J, Martínez-Lera J. Analysis and sizing of thermal energy storage in combined heating, cooling and power plants for buildings. Applied Energy 2013;106:127-42. [6] Saeed Mostafavi Tehrani S, Saffar-Avval M, Kalhori S B, Mansoori Z, Sharif M. Hourly energy analysis and feasibility study of employing a thermocline TES system for an integrated CHP and DH network. Energy Conversion and Management 2013;68:281-92. [7] Facci AL, Andreassi L, Ubertini S, Sciubba E. Analysis of the influence of thermal energy storage on the optimal management of a trigeneration plant. Energy Procedia 2014;45:1295-304.