Energy and Exergy Economic Analysis of Cogeneration Cycle of Homemade CCHP With PVT Collector

Transcription

1 Canadian Journal of Basic and Applied Sciences PEARL publication, 2015 CJBAS Vol. 03(08), , August 2015 ISSN Energy and Exergy Economic Analysis of Cogeneration Cycle of Homemade CCHP With PVT Collector Navid Tonekaboni, Hessamoddin Salarian, Esmaeel Fatahian, Hossein Fatahian. Department of Mechanical Engineering- Energy Conversion, Islamic Azad University of nour branch,iran. Keywords: Cogeneration, renewable energy, Exergy economic Exergy, CCHP Abstract According to the increasing environmental pollution and fossil fuel prices, use of equipment with high efficiency and use of clean and free energy is the fundamental solution to solve the perennial problem. Meanwhile, the use of cogeneration systems for power and heat (CHP, Combined Heat and Power) and power, heat and cold (CCHP, Combined Cooling, Heating and Power) with high efficiency 87 percent is one of the best choices. To solve the problem of pollution and the high price of fossil fuels, using clean sources (renewable) because they are free is the best alternative as source of energy systems. Among all renewable sources, solar energy because of availability and permanent is being investigated in this project. In this paper, we attempt to locate potential to select the best location for the cogeneration of solar cycles. Also, exergy and economic exergy (financial analysis) cycles of power cogeneration, solar heat and cold (Solar CCHP) have dealt with combination collector PVT (Photovoltaic and Thermal). Thermo economic which is a way to calculate the thermodynamic and financial discussion is used in this paper. The efficiency and period of return on investment of a 2-unit building with an area of 200 meters in the southern region of Iran country (Zahedan) is calculated. 1. Introduction Cogeneration of electricity and heat (CHP) is an energy-saving method in which electricity and heat are produced at the same time. Heat from electricity production can be used in district heating or used in the manufacturing industries. Next Category is evolved systems that generate electricity and heat which use an auxiliary unit (absorption chiller) to produce the cooling load are known (CCHP) systems. Cogeneration systems of power, heat and cold (CCHP) are as well as power and heat (CHP) with this difference that the cooling energy is produced. Cooling energy is used for cooling residential space, keeping foods and drinks (refrigerating room). (CCHP) systems are generally small-scale power plants and their applications are the same as (CHP) systems. In these systems, electricity doesn t use for cooling applications in compressors and heat from reciprocating Corresponding Author : , navid.tonekaboni@yahoo.com Received : 11 July 2015 ; Accepted: 20 Agust 2015

2 engines radiators and as heat source for absorption chillers are used. Cogeneration cycles in terms of primary energy sources divide into two categories. In the first category the primary source are fossil fuels and in the second one they use renewable sources of energy. In renewable sources, using sun as the primary source is more than other resources and it is because of extensive energy source in the whole earth surface. Useful measures in the field of exergy analysis can be noted modeling (CCHP) systems with various operating conditions by Yu Yin Ginkgo and colleagues. This modeling was carried out for different (CCHP) systems and under various conditions of time and temperature [1]. In 2009, a thermodynamic analysis of cogeneration units with fuel cells was conducted by Yiping Dai and his colleagues worked on the basis of liquid water and ammonia [2]. In April 2010, an article entitled optimize the performance of systems (CCHP) by Yu Ying Jing was presented with a genetic algorithm [3]. Important parameters of this research can be named considering the economic and environmental performance of cogeneration system. In 2011, researches on exergy economic performance analysis (CCHP) systems based on the Bray ton cycle was carried out and under the same title was published in This analysis was conducted by Friso and all analysis has been done by software called Engineering Equation Solver (EES) [4]. In this study, an analysis of exergy and exergy economic cogeneration cycle of power, heat and cold (CCHP) has been done with PVT hybrid collectors for a 2-unit building with an area of 200 meters in the Zahedan city of our country with hot and dry regions. In this study, according to atmospheric conditions and meteorological data of our country, Zahedan city that is one of the most ideal city in our country for using solar technology is chosen and after that by gaining requirements loads of cooling, heating and electrical cogeneration cycle (CCHP) is chosen and exergy and energy analysis, obtaining time period of returning investment and effective factors in efficiency of these cycles are fully investigated and calculated. 2. Building description In order to analyze exergy and energy of a cogeneration cycle, first the building must be studied and rates of electricity and heating and cooling load it in 15-day intervals obtained. In this project, the a 2-unit building with an area of 200 meters has been examined. This building is in the Zahedan city which is hot and dry areas of the country. The need for cooling, heating and electrical has been carefully calculated during periods of 15 days for 12 months. In terms of the amounts of required heating, cooling and electrical energy is determined. The amounts listed in the following table are available. This building was built in compliance with the National Building Regulations and 225

3 insulation has been implemented correctly. Cogeneration system design should be based on maximum use to be enough at peak times of system capacity for loads of cooling, heating and electricity. Inappropriate design of air conditioning systems causes inappropriate conditions for residents and dissatisfaction of people. In case of inability of selected photovoltaic panels to supply electrical power we should purchase the additional requirements of network systems that causes initial investment returns later. Zahedan is located in the southern region of our country and the weather is the best option for use of solar systems. This city with average 3475 hours of sunshine has the highest radiation among all provincial capitals. Other important factors include the lack of days with negative temperatures and average wind speed of 10 kilometers per hour make Zahedan the best center in all provincial capitals to use solar systems. Table 1. he consumption of cooling, heating and electrical loads of a 2-units building with total area of 200 square meters in hot and dry region. Month Electrical load(kw) Heating load (Kw) Cooling load (Kw) 15 March-1 April April-15 April April-1May May-15May May-1 June June-15 June June-1July July-15July July- 1 August August-15 August August-1 September September-15 September September- 1 October October- 15 October October- 1 November November- 15 November November- 1 December December-15 December December-1 January January- 15 January January- 1 February February-15 February February-1 March March-15 March According to the above table and applying 10% safety factor, we conclude that cogeneration system should be capable of producing 35 kilowatts of electricity for listed buildings, 80 KW heating load and 50 KW cooling load. 3. Cogeneration system of solar power, heat and cool (Solar CCHP) 226

4 Solar cogeneration system consists of hybrid collector, auxiliary heaters, sanitary hot water and heating environment heat exchanger suppliers, absorption chiller, cooling tower, reservoir, storage batteries and pumps [6]. According to the loads obtained for the building tried to calculate the collector surface and determines the required capacity exchangers and cooling systems and chiller. Cogeneration of solar system are shown in the following figure entirely. Figure 1. A view of a cogeneration system of power, heat and cold Solar (Solar CCHP) with parabolic collector[5] 4. Hybrid collectors In this optimization, it is tried to replace used collectors in cogeneration solar cycles with PVT collectors and auxiliary gas heater with electric heater have been replaced. In this method, the duty of supplying hot water is on thermal section of collector (Thermal) and supplying the need of electricity is on the photovoltaic cells. a view of a PVT collector is shown. The view of a PVT collector is shown below. Figure 2. The view of a PVT collector [7] In this method by radiating solar on collector surface, required electricity provides by photovoltaic cell. 227

5 By increasing temperature, using surface reduces in photovoltaic cells so that this rate reaches 50% of their standard at 130. This issue is fully resolved in PVT hybrid collectors. By absorbing collector heat with the water efficiency will remain always in the top 80%. In fact, we always achieve the maximum energy obtainable from the sun with hybrid PVT collectors. PVT hybrid collectors are cogeneration units of electricity and heat which can be installed and used auxiliary in main system. Because of not permanent sunlight in day and night and inappropriate climate this system cannot be used alone and it is necessary to provide the need of hot water storage tank, electric storage battery and auxiliary heater for hot water in order to provide heating needs during night hours. These collectors have 4 times efficiency more than regular collectors [8]. Different types of solar collectors can be used in conventional solar systems and typically, evacuated tube collectors are used. In this type of collector output temperature is in the range of 50 to 200 C. In most cases, the temperature rarely exceeds in the range of 75 degrees and it is necessary to have auxiliary heaters to supply steam for entering to turbine. In this optimization, single-fluid PVT hybrid collectors have been used and the fluid is water. Because of providing electricity by photovoltaic cells, there is no longer need to an auxiliary heater to supply water with high temperature over 100 degrees and auxiliary heaters are only for using during night hours. According to deleting turbine and water steam from system, cycle average temperature came down and there is no need for high-pressure pipes for transferring water steam from the heater output to the turbine input. Other changes done in this system are more needing batteries to store electricity generated by photovoltaic cells to provide electrical needs and the need of auxiliary heater to electric power. These batteries should have the ability to store electricity for common needs and have auxiliary heaters electricity during the night hours. According to the above table, using flat plate collectors in cogeneration cycles causes permanent use of auxiliary heaters and there is no need of auxiliary heaters in other types of collectors too, and system always works at temperature over 100 C. We know that upper working temperature causes high costs and depreciation of system. By using hybrid collectors PVT, system working temperature reduces and always works at temperature range of 80 C. Noting this point is necessary that metallic pipes can be used at temperature range of 80 C but using high pressure metallic pipes is necessary at temperature 100 C and upper. 5. Calculation In order to calculate by considering temperature and humidity of different points of cycle, we calculate amounts of energy and exergy. We put output temperature of solar collector 75 C and 228

6 calculate collectors based on this temperature. In this step, we obtain amount of collectors for mentioned building 186 meters. After calculating amount of collectors, we design system by considering need of maximum heating and cooling load and analyze energy and exergy of different points Energy analysis Based on thermodynamic first law, energy analysis is based on following levels. First, solar radiation energy on collector[8]. (1) Then, collector efficiency calculation which is hybrid in this project[8]. ( ) (2) Actual energy is calculated by crossing efficiency in collector energy. (3) In the next step, we calculate heating, cooling loads and required load for providing sanitary hot water [6]. Cooling load calculation formula = (4) COP calculation formula for cooling load Cop= (5) Formula for calculating heating loads ( ) (6) Formula for calculating required sanitary hot water ( ) (7) According to above equations, we calculate efficiency by following formula 229

7 { (8) All amounts are shown as average in below table. Table 2. Average results of energy analysis Parts Received energy(kw) Delivered energy(kw) First law efficiency)%( Dissipation(kw) Collector Chiller Total system Exergy analysis Based on thermodynamic second law, exergy analysis is on following steps. First, received exergy of collector from solar is calculated[8]. [ ( )] (9) In above formula, f is dilution constant. Received exergy from collector[8] : ( ) ( )( ) (10) In next step, we calculate exergy in cooling and heating from following formulas. Cooling exergy in summer[6]: = ( ) (11) Heating exergy in winter[6]: = ( ) (12) Now we calculate cycle second law efficiency from following formula and calculated amounts. { (13) Calculated average exergy amounts are shown completely in below table. 230

8 Parts Average received exergy(kw) Table 3. Result average of exergy analysis Average delivered exergy (kw) Average second law efficiency)%( Wasting average exergy (kw) Collector Chiller Hot water Total system Costs analysis First we calculate periodic cost of yearly cycle from following formula[8]: ( ) ( ) ( ) (14) According to energy price and cost of produced heating and cooling loads, we calculate financial return period of solar cogeneration cycle[8] [( ) ] ( ) (15) The costs and financial return period are shown in following table. Table 4. The costs and design financial return period. Equipment Price (Dollar) Total cost Yearly income of energy production 6410 Yearly income of cooling load production Yearly income of heating load Yearly income of sanitary hot water 3983 Cost of yearly gas consumption 278 Yearly electricity price 219 Yearly cost 9367 financial return period Equipment Collector cost Auxiliary heater Absorption chiller system Pump Cooling tower Battery and electrical converter Sundry costs Total costs Table 5. The costs of design. Price (Dollar)

9 Amount of collector received exergy from sun changes during year between range of 80 GJ to 150 GJ which is considered as average 112 GJ. Amount of received exergy is in range of 20 GJ to 50 GJ which is considered as average 34 GJ. Average of wasted exergy is calculated 79 GJ and second law efficiency is percent. Then, we calculate exergy for auxiliary heater which has the duty for compensation energy and similarly we calculate its exergy and wasting for other points of cycle and calculate thermodynamic second law efficiency. Second law efficiency for chiller is and for hot water is Average received exergy for total system is GJ and delivered exergy is GJ. Consequently, second law efficiency is percent. 6. Conclusion Considering the fact that one of the cleanest methods to provide energy is using solar cogeneration systems (Solar CCHP) with hybrid collectors PVT to provide needs of building heating, cooling and electrical, these results are obtained from first and second laws in these cycles. Yearly average of thermodynamic first law efficiency for this cycle is percent and yearly average of second law efficiency is calculated by exergy analysis percent. After calculating initial costs and saving, above cycle financial return period is with this method, this long time is because of PVT hybrid solar collectors high price. Because of high price of collectors, using more of this collector (in this study 186 square meter) increases cycle price and causes high initial financial return period. Effective factors on collectors efficiency can be noted lots of sunshine, low days with negative temperatures and low wind speed. As a result, it can be noted that the southern regions of our country with lots of sunny days, low days with sub-zero temperatures and low wind speed have more potential than other parts of the country to use the cogeneration cycles of power, heat and cold (CCHP). References [1] YU, YING GINGO.D.W. Wu, R.Z. Wang: Combined Cooling, Heating and Power,A Review. Progress in Energy and Combustion Science, 32, (2006). [2] Y. Daie, H. Cho, R. Luui, S.D. Eksioglu, L.M. Charma: Cost-optimized real-time operation of CCHP systems. Journal of Energy and Buildings, 41, (2009). [3] Jiang-Jiang Wang, You-Yin Jing, Chun-Fa Zhang.: Optimization of capacity and operation for CCHP system by genetic algorithm. Applied Energy, 87, (April 2010). [4] M.A. Smith: Small scale and micro combined heat and power, Ph.D. Thesis, De Montfort University, May2011. [5] Riffat SB, Zhao X. : A novel hybrid heat pipes solar collector/cchp system Part I: system design and construction. Renew Energy, 29, (2011). 232

10 [6] Bhargava AK, Garg HP, Agarwal RK.: Study of a hybrid solar system solar air heater combined with solar cells. Energy Conversion and Management, 31,471 9(1991). [7] Zondag HA, de Vries DW, van Helden WGJ, van Zolingen RJC, van Steenhoven AA.: The yield of different combined PV-thermal collector designs. Solar Energy,74, (2003). [8] Dubey S, Tiwari GN.: Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water heater. Sol Energy, 82, (2008). 233