نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری مهندسی مکانیزاسیون کشاورزی دانشگاه شهید چمران اهواز

2 دانشیار گروه مهندسی بیوسیستم، دانشگاه شهید چمران اهواز

3 استادیار گروه مهندسی بیوسیستم، دانشگاه شهید چمران اهواز

10.22055/agen.2024.45418.1703

چکیده

به منظور بررسی تاثیر طول لوله و همچنین سرعت هوای در ‏حال‏ چرخش بر روی ضریب عملکرد، راندمان سرمایش و دمای هوای خروجی در یک گلخانه مجهز به سامانه زمین‌گرمایی در اراک، آزمایشی به صورت فاکتوریل در قالب طرح بلوک‏های کامل‏تصادفی با دو عامل طول لوله در سه سطح (17، 34 و 52 متر) و سرعت هوا در دو سطح (5 و 10 متر ‏بر ثانیه)، در سه تکرار انجام شد. انتقال هوا از طریق لوله پی‏وی‏سی به قطر 20 سانتی‌متر که در عمق سه متری نصب شده بود، انجام می‏شد و نوع چرخش هوا از نوع حلقه‏باز بود. شاخص‏های آزمایش در محدوده ساعات گرم روز و به مدت یک هفته در اواخر تیر اندازه‏گیری شدند. نتایج آزمایش نشان داد بهترین عملکرد سامانه از نظر مقدار کاهش دمای خروجی و شاخص‌های راندمان و ضریب عملکرد، در طول لوله 34 متر و سرعت هوای 10 متر بر ثانیه به دست آمد. دمای خروجی دمنده، راندمان و ضریب عملکرد در این حالت به ترتیب °C 7/25، 69/0 و 2/3 به‏دست آمد. شاخص‏های عملکردی در دو طول لوله 52 متر و 34 متر مشابه بودند. در دو سرعت آزمون شده، اختلاف معنی‏داری بین شاخص‏های اندازه‏گیری شده مشاهده نشد. با این حال با طول لوله17 متر، بیشترین شاخص‏های عملکردی سامانه در سرعت هوای پنج متر‏بر‏ثانیه مشاهده شد. شاخص‏های عملکردی سامانه در این طول در سرعت پنج متر‏بر‏ثانیه به ترتیب°C27، 54/0 و 7/1 و در سرعت 10 متر بر ثانیه به ترتیب °C30، 34/0 و1/2 بود. در صورتی که طول لوله زیاد باشد (بالای 34 متر) پیشنهاد می‏شود جهت افزایش توان سرمایشی تولید‏شده (ضریب عملکرد سامانه) سرعت هوای دمنده بر روی 10 متر‏بر‏ثانیه تنظیم شود. تغییرات روند 24 ساعته نشان داد بیشترین شاخص‏های عملکردی سامانه، در ساعات گرم روز اتفاق می‏افتد و استفاده از این سامانه در ساعات خنک توصیه نمی‏شود.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Investigating the effect of pipe length and air speed on the performance indicators of a geothermal system in cooling a sample greenhouse

نویسندگان [English]

  • Abolfazl Hedayatipour 1
  • Mohsen Soleymani 2
  • Mostafa Kiani Deh Kiani 3

1 Ph.D. Student of Agricultural Mechanization Engineering, Department of Biosystems engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.

2 Associate professor, Department of Biosystems engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran

3 Assistant professor, Department of Biosystems engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran

چکیده [English]

Introduction In recent years, due to its availability and low environmental pollution, the use of Earth-Air Heat Exchanger (EAHE) has been developed as an efficient energy system in heating and cooling residential buildings and agricultural greenhouses. In this system, air is circulated by a fan through a pipe buried deep in the ground. Depending on the geographical location and soil type, the soil temperature at a depth of 2-3 meters remains unchanged throughout the season. Of course, this depth varies throughout the year and according to climatic changes. The heat exchange between the soil and the air inside the pipe depends on the type of soil and its moisture content, the length and diameter of the air transmission pipe, the depth of burial and the velocity of the air flow (air velocity). Air circulation can be done in an open-loop or closed-loop circuit.
Materials and Methods: A factorial experiment was conducted in the form of a completely randomized block design with two factors (pipe length at three levels (34, 17 and 52 meters) and air velocity at two levels (5 and 10 m/s)) in three replications, to investigate the effect of these factors on the coefficient of performance (COP), system efficiency and outlet air temperature. The experiment was conducted in a greenhouse in Arak city, Iran, in Joune 2022. This 150 square meter greenhouse was equipped with geothermal equipment. Air was circulated through a 200 mm diameter PVC pipe buried three meters deep in the ground. Air was circulating through an open loop circuit. Dependent variables were measured during the hot hours of the day (from 12:00 to 18:00) for one week at the end of July. The air temperature at the fan inlet and at 17, 34 and 52 meters along the pipe was measured by a single-channel data logger. Hourly changes in outlet air temperature, COP and efficiency were measured in a 24-hour period and plotted using Excel software.
Results and Discussion
The outlet air temperature for the pipe length of 34 and 52 m did not change when the air velocity decreased from 10 m/s to 5 m/s. But for the pipe length of 17 m, the maximum temperature, COP and efficiency were observed at an air velocity of 5 m/s. Regardless the air velocity, the average temperature of the outlet air for the three levels of the pipe length was 28.5, 25.5 and 25.3°C, respectively. The outlet air temperature was almost the same for the 34 and 52 m pipe lengths. In other words, the optimal length of the pipe is about 34 meters. The mean efficiencies for these two pipe length levels were 0.69 and 0.66, but the COP depended on the air velocity. The average COP for air velocity of 5 and 10 m/s was obtained 1.4 and 2.5, respectively. Based on these results, the best performance of the system in terms of output temperature reduction, cooling efficiency and COP is obtained in situation that the length of the pipe is 34 m and the air velocity is 10 m/s. when the length of the pipe is 17 meters, the temperature of the air outlet at two velocities of 10 and 5 m/s was 29.9 and 27 °C, respectively. The cooling efficiency and COP at two velocity of 10 and 5 m/s, were 0.34, 0.54; and 2.1, 1.7 respectively. If the desired temperature is 28-30 °C, pipe length of 17 m and the air velocity of 5 m/s is recommended. The results of hourly performance analysis showed that the highest difference between inlet and outlet air temperatures, is obtained at middle hours of the day. The higher the ambient temperature, the higher the efficiency of the EAHE system.

Conclusion
This system successfully met the cooling needs of a model greenhouse in the weather conditions of Markazi Province in June. Based on the results, the optimal pipe length and air velocity were obtained as 34 m and 10 m/s, respectively. The average air outlet temperature and cooling efficiency were 25.5, 0.66 and 2.5 respectively. The higher the ambient temperature, the higher the EAHE efficiency. This is mainly due to the higher temperature difference between the outgoing and incoming air during the hottest hours of the day. As a result, system efficiency and COP increase at the hottest hours of the day.

کلیدواژه‌ها [English]

  • Renewable energy
  • Sustainable Engineering
  • COP
  • Efficiency
  • Geothermal Pump
  • System Performance