with the collaboration of Iranian Society of Mechanical Engineers (ISME)

Document Type : Research Article

Authors

1 Department of Biosystems Engineering, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran

2 Department of Chemistry Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract

Introduction
Greenhouse cultivation has been increased in response to population growth, reduction in available supplies and arable lands and raising the standards of living. The quality and quantity of the products are profoundly affected by the greenhouse temperature. Therefore, providing an appropriate heating system is an elementary requirement for greenhouse cultivation. A number of factors such as glazing material, greenhouse configuration, product type, and climate conditions should be considered to design a greenhouse heating system.
Due to the environmental concerns associated with the fossil fuels, renewable energy-powered heating systems such as geothermal, solar and biomass- are increasingly considered as the alternative or supplementary to the traditional fossil fuel heating equipment in greenhouses. In this way, a number of researchers have developed different greenhouse heating systems to reduce fossil fuel consumption. In Iran, because of appropriate available solar irradiance, the solar heating systems can be efficiently employed for greenhouse cultivation.
A compound solar greenhouse heating system was experimentally and analytically investigated in the present study. To verify the obtained heat transfer equations, a set of experiments were carried out at Biosystems Engineering Campus of the Shahid Bahonar University of Kerman.
 Materials and Methods
The designed system was comprised of a Parabolic Trough solar Collector (PTC), a dual-purpose modified Flat Plate solar Collector (FPC) and a heat storage tank. The modified FPC was located inside the greenhouse to act as a heat exchanger to transfer the stored heat to the greenhouse atmosphere during the night. The FPC also collects the solar radiations during the sunshine hours to enhance the thermal energy generation. Heat transfer equations of the PTC and the FPC were written and the useful energy gain of the heating system was determined at the quasi-static condition during the day. Experimental verification of the analytical models was conducted using regression coefficient (r) and root mean square percent deviation (e) criteria as follows:
where Xi and Yi are respectively the ith analytical and experimental data and n shows the number of observations.
 Exergy analysis of the PTC and the FPC were carried out and the effect of the different fluid flow rates through the PTC on the exergy efficiency of the different components was investigated using the experimental data.
Results and Discussion
Increasing the fluid flow rate increased outlet temperature of the PTC due to the increase in heat removal factor and inlet temperature; whereas, caused a reduction in outlet temperature of the FPC. Since the thermal efficiency of the PTC improved with the fluid flow rate, the PTC fraction enhanced when the flow rate increased from 0.5 to 1.5 kg min-1. However, the PTC fraction values were less than 50% and sometimes have dropped below zero.
The exergy efficiency of the PTC improved with increasing the flow rate. The reason was that the difference between the inlet and outlet temperatures of the PTC increased with the flow rate at the similar conditions of solar irradiance and ambient temperature. The highest exergy efficiency of the FPC was observed at the flow rate of 0.5 kg min-1.
Conclusion
The results of the study revealed that:
There was a suitable agreement between the obtained analytical expressions and the experimental data based on root mean square percent deviation and regression coefficient criteria.
The highest stored energy in the tank was around 40.02 MJ at the flow rate of 0.5 kg min-1.
Increasing the flow rate improved the PTC exergy efficiency.

Keywords

1. Akpinar, E. K., and F. Koçyiğit. 2010. Energy and exergy analysis of a new flat-plate solar air heater having different obstacles on absorber plates. Applied Energy 87: 3438-3450.
2. Alpuche, M. G., C. Heard, R. Best, and J. Rojas. 2005. Exergy analysis of air cooling systems in buildings in hot humid climates. Applied Thermal Engineering 25: 507-517.
3. Anifantis, A. S., A. Colantoni, and S. Pascuzzi. 2017. Thermal energy assessment of a small scale photovoltaic, hydrogen and geothermal stand-alone system for greenhouse heating. Renewable Energy 103: 115-127.
4. Attar, I. and, A. Farhat. 2015. Efficiency evaluation of a solar water heating system applied to the greenhouse climate. Solar Energy 119: 212-224.
5. Bahrehmand, D., M. Ameri, and M. Gholampour. 2015. Energy and exergy analysis of different solar air collector systems with forced convection. Renewable Energy 83: 1119-1130.
6. Benli, H., and A. Durmuş. 2009. Performance analysis of a latent heat storage system with phase change material for new designed solar collectors in greenhouse heating. Solar Energy 83: 2109-2119.
7. Bergman, T. L. 2012. Adrienne S. lavine, Frank P. Incropera, David, Introduction to Heat Transfer: John Wiley & Sons. Inc.
8. Bot, G., N. van de Braak, H. Challa, S. Hemming, T. Rieswijk, G. Van Straten, and I. Verlodt. 2005. The solar greenhouse: state of the art in energy saving and sustainable energy supply. Acta Horticulturae 691: 501-508.
9. Bouadila, S., M. Lazaar, S. Skouri, S. Kooli, and A. Farhat. 2014. Assessment of the greenhouse climate with a new packed-bed solar air heater at night, in Tunisia. Renewable and Sustainable Energy Reviews 35: 31-41.
10. Dincer, I., and Y. A. Cengel. 2001. Energy, entropy and exergy concepts and their roles in thermal engineering. Entropy 3: 116-149.
11. Dincer, I., and M. A. Rosen. 2012. Exergy: energy, environment and sustainable development. Newnes.
12. Duffie, J. A., and W. A. Beckman. 1974. Solar energy thermal processes. University of Wisconsin-Madison, Solar Energy Laboratory, Madison, WI. Report no.
13. Dutta Gupta, K., and S. K. Saha. 1990. Energy analysis of solar thermal collectors. Renewable Energy and Environment, Himanshu Publications, New Delhi, India: 283-287.
14. Esen, M., and T. Yuksel. 2013. Experimental evaluation of using various renewable energy sources for heating a greenhouse. Energy and Buildings 65: 340-351.
15. Farahat, S., F. Sarhaddi, and H. Ajam. 2009. Exergetic optimization of flat plate solar collectors. Renewable Energy 34: 1169-1174.
16. Ge, Z., H. Wang, H. Wang, S. Zhang, and X. Guan. 2014. Exergy analysis of flat plate solar collectors. Entropy 16: 2549-2567.
17. Ghosal, M., and G. Tiwari. 2004. Mathematical modeling for greenhouse heating by using thermal curtain and geothermal energy. Solar energy 76: 603-613.
18. Hepbasli, A. 2012. Low exergy (LowEx) heating and cooling systems for sustainable buildings and societies. Renewable and Sustainable Energy Reviews 16: 73-104.
19. Jafari, M., H. Mortezapour, K. Jafari Naeimi, and M. H. Maharlooei. 2017. Performance Investigation of a Solar Greenhouse Heating System Equipped with a Parabolic Trough Solar Concentrator and a Double-Purpose Heat Exchanger. Journal of Agricultural Machinery 7 (2): 364-378. (In Farsi).
20. Jafarkazemi, F., and E. Ahmadifard. 2013. Energetic and exergetic evaluation of flat plate solar collectors. Renewable Energy 56: 55-63.
21. Jaramillo, O., M. Borunda, K. Velazquez-Lucho, and M. Robles. 2016. Parabolic trough solar collector for low enthalpy processes: An analysis of the efficiency enhancement by using twisted tape inserts. Renewable Energy 93: 125-141.
22. Joudi, K. A., and A. A. Farhan. 2014. Greenhouse heating by solar air heaters on the roof. Renewable Energy 72: 406-414.
23. Kahrobaian, A., and H. R. Malekmohammadi. 2013. Exergy Optimization Applied to Linear Parabolic. Journal of Algorithms and Computation 42: 131-144.
24. Kalogirou, S. A. 2013. Solar energy engineering: processes and systems. Academic Press. Elsevier.
25. Kalogirou, S. A., S. Karellas, V. Badescu, and K. Braimakis. 2016. Exergy analysis on solar thermal systems: a better understanding of their sustainability. Renewable Energy 85: 1328-1333.
26. Karsli, S. 2007. Performance analysis of new-design solar air collectors for drying applications. Renewable Energy 32: 1645-1660.
27. Mehrpooya, M., H. Hemmatabady, and M. H. Ahmadi. 2015. Optimization of performance of combined solar collector-geothermal heat pump systems to supply thermal load needed for heating greenhouses. Energy Conversion and Management 97: 382-392.
28. Mortezapour, H., B. Ghobadian, M. Khoshtaghaza, and S. Minaee. 2012. Performance analysis of a two-way hybrid photovoltaic/thermal solar collector. Journal of Agricultural Science and Technology 14: 767-780.
29. Nayak, S., and G. Tiwari. 2008. Energy and exergy analysis of photovoltaic/thermal integrated with a solar greenhouse. Energy and Buildings 40: 2015-2021.
30. Padilla, R. V., A. Fontalvo, G. Demirkaya, A. Martinez, and A. G. Quiroga. 2014. Exergy analysis of parabolic trough solar receiver. Applied Thermal Engineering 67: 579-586.
31. SABA. 2013. Iran Energy Balance Sheet.
32. Santamouris, M., A. Argiriou, and M. Vallindras. 1994. Design and operation of a low energy consumption passive solar agricultural greenhouse. Solar Energy 52: 371-378.
33. Shrivastava, R., V. Kumar, and S. Untawale. 2017. Modeling and simulation of solar water heater: A TRNSYS perspective. Renewable and Sustainable Energy Reviews 67: 126-143.
34. Taki, M., Y. Ajabshirchi, S. F. Ranjbar, A. Rohani, and M. Matloobi. 2017. Evaluation of heat transfer mathematical models and multiple linear regression to predict the inside variables in semi-solar greenhouse. Journal of Agricultural Machinery 7 (1): 204-220. (In Farsi).
35. Tiwari, G. 2003. Greenhouse technology for controlled environment. Alpha Science Int'l Ltd.
36. Utlu, Z., and A. Hepbasli. 2007. A review on analyzing and evaluating the energy utilization efficiency of countries. Renewable and Sustainable Energy Reviews 11: 1-29.
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