Experimental study of a stand-alone earth to air heat exchanger for heating and cooling in arid regi

Abstract

Keywords: Earth to air heat exchanger; Sub-soil temperature; Arid region; Heating; Cooling

Earth To AIR HEAT Exchanger

Used since 3000-years B.C. [6–10], the earth to air heat exchanger EAHE technique is old heating, cooling, and natural ventilation strategy that is integrated not only in the buildings and living space but also in the food storage places. Just like Ground Air Collector (GAC) and earth air tunnel, the conception of the earth to air heat exchanger EAHE is very simple. A number of pipes that are made of local materials (clay, Polyvinyl chloride or PVC, steel, etc.) are buried underground at a defined depth, where the subsoil undisturbed temperature stays constant around the year. The outside air enters from the inlet section of EAHE, it submits a thermal exchange (by convection) with the sub-soil by the medium of pipe material during its passage

Figure 1. Site study vertical underground temperature profile ‘September 2018’.

equal to 18.4°C, 18.7°C, and 18.4°C for thermal conductivities of 0.52, 2, and 4 W/m. K, respectively. Maerefat and Haghighi [58] and Mohammed et al. [59] studied the coupling of the EAHE with a solar chimney in the same building. Li et al. [60] conducted an experimental investigation between May and August 2017 on the EAHE technique in China.They found a direct relationship between thethermal characteristics of soil and earth to air heat exchanger performance in the cooling purpose. The temperature drop by 14.6°C at the outlet section and the total cooling capacity was 8792 W.

Figure 2. Experimental set-up of the stand-alone earth to air heat exchanger.

In this paper, the potentials of stand-alone earth air heat exchanger in the region of Béchar are investigated by experiments. The region of the study, which is located in the North-west of the city of Béchar, is classified as an agricultural zone activity. The vertical temperature profile of the site for September 2018 is presented in Figure 1. At a depth of 1.5 m, the annual undisturbed sub-soil temperature is 28°C.

Stand-Alone EAHE Experimental Set-Up

The site of the study is located in an agricultural zone having sandy loam soil without treatments (see Figures 2 and 3).The characteristics of the experimental device are described as follow: – PVC tube with a good thermal conductivity (λ = 0.2 W/ m.K). – The thickness of the PVC tube is 2 mm. – Elbow: PVC elbows (110 mm of diameter) serve as inlet and outlet sections. – The length of the underground horizontal tube is 60 m. – The length of the vertical tube is 3 m for each part, where ½ of it is underground. – Working fluid: atmospheric air. – The inlet section is oriented in the direction of prevailing winds, and the outlet section is oriented in the opposite direction.

– The vertical parts of the EAHE device are thermally insulated to eliminate the chimney effect. – An openloop system is used. – The depth of buried pipes is 1.5 m underground. – The site altitude is 806 m. To measure the EAHE effects, DL-53 wireless temperature and relative humidity sensors were placed at the inlet and outlet sections of EAHE (Figure 2).For the region of the study, 3.7 m/s was the annual mean wind speed. Figure 4 presentsthe mean wind speed across 30 years for the Béchar region (November 1977 to 2006). This important resource will be the driving force for the air circulation inside the device without any contribution of fans or other exterior devices. The inlet section has faced the North and the outlet section is directed to the South.

Results And Discussion

The study of a stand-alone EAHE in arid regions is a combination of temperature and humidity analysis. The inlet of the earth to the air heat exchanger is exposed directly to the sunlight, which explains the higher temperature (39°C). But, even with this high temperature, the EAHE had the capacity to reduce this value until 27.6°C at the outlet section, which corresponds to a decrease by 11.4°C (Figure 5). For the variation of the inlet temperature difference [Max-Min], the mean temperature was 32.14°C. The outlet section was characterised by 22.6°C for a temperature difference [Max-Min], which indicates the capacity of the system to stabilise this variation from 32.1°C at the inlet to 22.6°C at the outlet (approximately 9.54°C). The analysis of the inlet temperature variation indicates how the outside climatic conditions such as air temperature and humidity, sunlight, and wind velocity can cause such variation from 36 or 37°C at 10 o’clock in the morning to

4°C in the early morning and night time, see Figure 6. For the outlet, the variation between the day’s highest temperature is 29.3°C in and the lowest (7 to 8°C) during the nighttime was 22.6°C, which is more stable in comparison with the inlet. EAHE acts as a thermal regulator reducing the outlet temperature difference between the maximum and minimum values throughout the day. To explain the EAHE capacities, the hourly mean temperature ΔT = Tinlet -Toutletis calculated (Figure 7). The analysis of the difference in hourly mean temperature from day 1 to day 8 present the following working regime: To describe the stand-alone earth to air heat exchanger working regime in an arid region, the daily mean temperature differences between the inlet and outlet sections are calculated. Twenty-four hours of the thermal behaviour of the experimental device from day 1 to day 8 show clearly the major behaviour of the stand-alone EAHE for the

Figure 4. Wind rose of Béchar city – November (1977– 2006) [49].

Figure 5. EAHE inlet (A) and outlet (B) [Max-Min] air temperature values (°C).

Figure 6. EAHE inlet and outlet temperature (left) and ΔT=Tinlet-Toulet (right).

winter season. Day 3 makes the exception due to the big dependence on the local climate. From 00h to 08h: in the early morning ΔT was negative (Toutlet> Tinlet), the outside air entering from the inlet is passing through the EAHE and becoming warmer (by 4 to 9°C). This regime presents the heating regime. From 09h to 17h: because of the sunlight, the upper part of the pipe and the outside air become warmer. Passing inside the EAHE, the air loses some degrees and ΔT becomes positive (Toutlet< Tinlet). That’s led to a cooling mode. From 18h to 23h: After the sunset, the outside air temperature reduces. The system was able to rise the outlet temperature by 2 to 5°C in a heating regime. For day 3, ΔT was positive during all the days (Toutlet < Tinlet) and the cooling regime was the only regime (a reduction in temperature by 0.5 to 6°C). This exception can be explained by the irregular blowing regime of winds during this day and sometimes Vwind ≈ 0 m/s. It is also remarked that, generally, the air relative humidity that leaves the device changes with the change in inlet air temperature.The relative humidity in humidification is characterised by a maximum of 19% in the best case, and it is reduced in dehumidification phenomena by 27% in the best case.

Conclusion

Geothermal presents an advantageous energy source that can be used for many purposes, such as the production of electrical or thermal energy, use as a heat source or sink for building heating and cooling and many other applications. Based on the previous experimental measurements in the same site of the study, the annual undisturbed subsoil temperature of the site was found to be about 28°C. In

our paper, an experimental study of a stand-alone earth to air heat exchanger EAHEthat works naturally without any exterior devices was performed. The purpose was to explore the performance of the EAHE under weather conditions(sun, air temperature and humidity, and wind speed). The obtained results showed the big potential of the stand-alone earth-to-air heat exchanger for the pre-heating or heating, pre-cooling or cooling, and natural ventilation of dwellings and buildings in arid regions. At the inlet and outlet sections of EAHE, values of the temperature were, respectively, as follows: T inlet min= 4.2°C (day 6) and T inlet max = 39°C (day 2), T outlet min= 7.4°C (day 6) and T outlet max = 31.5°C (day 8). These results show clearly the range in which the system works without any contribution of an exterior device. The daily thermal analysis of the stand-alone EAHE showed that the daily work regime of the system is as follow: From 00h to 08h: Heating regime The outside air temperature was low, it entered from the EAHE inlet and passed through the device. The air temperature raised during its passage due to the thermal exchange between the air and the sub-soil by the medium of PVC pipe. Reaching the outlet, the air temperature raised by 4 to 9°C. From 09h to 17h: Cooling regime The outside air warmed up and the upper part of the EAHE inlet was exposed directly to the sunlight. The inlet air temperature reached sometimes 39°C. EAHE was able to reduce the outlet air temperature by 0.5 to 11°C. From 18h to 23h: Heating regime After the sunset and the reduction of outside temperature, the EAHE reduced the outlet temperature of air by

Figure 7. Daily mean temperature difference ΔT=Tinlet -Toutlet.

approximately 0.4 to 5.5°C. This phase serves as a preparation for the next phase (00h to 08h). Day 3 was characterised by a Cooling-Humidification regime for all the day, which confirmed the big dependence of the EAHE on weather conditions. If the wind changes its direction or the day was cloudy, the outlet parameters like temperature and humidity change also. In an arid region and during the winter season under normal and ordinary climatic conditions (sunny day, wind blow in prevailing wind direction, normal exterior temperature and humidity), the stand-alone EAHE works in 24 hours as follow: 62.5% (heating) and 37.5% (cooling) for the thermal regime. Stand-alone Earth to Air Heat Exchanger without any contribution of an exterior device like fans has given the following results and advantages: • Increase of the air temperature by 10°C in the heating regime • Reduction of theair temperature in the cooling regime by 11.9°C • The EAHEreduced the relative humidity by 62.5% (RHoutlet < RHinlet) generally between (00h to 09h and 18h to 23h) and increased it by 37.5% (RHoutlet > RHinlet) between (10h to 17h). • Creation ofthe dehumidification and humidification regimes in the same day, but this situation could lead to the development of micro-organisms inside the buried tube by condensation. • Reduction of the need for fan or blower and reduce energy consumption. • The system is 100% ecological, natural and renewable with zero green-house gases. The EAHE technique seems much promoted for the pre-heating, pre-cooling, and natural ventilation of dwellings and buildings in arid regions. For the next step of the study, earth to an air heat exchanger with solar protection of the upper part to eliminate the direct sunlight effect will be studied. For future works, a real scale room will be realised, where the earth to air heat exchanger will be connected to study its ability to enhancement of the inside thermal comfort in arid regions.

Acknowledgments

Authors wish to thanks Mr. Sakhri Ali, Mr. Nairi Abdelkarim and Mr. Bouandas Mokhtar for providing the site and tools for the experimental work.

Data Availability Statement

No new data were created in this study. The published publication includes all graphics collected or developed during the study.

Conflict Of Interest

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Ethics

There are no ethical issues with the publication of this manuscript.

References

1. [1] Hussein AK. Applications of nanotechnology in renewable energies-A comprehensive overview and understanding. Renewable and Sustainable Energy Reviews 2015;42:460-76.
2. [2] Hussein AK, Walunj A, Kolsi L. Applications of nanotechnology to enhance the performance of the direct absorption solar collectors. Journal of Thermal Engineering 2016;2(1):529-40.
3. [3] Li D, Li Z, Zheng Y, Liu C, Hussein AK, Liu X. Thermal performance of a PCM-filled double-glazing unit with different thermophysical parameters of PCM. Solar Energy 2016;133:207-20.
4. [4] Hussein AK. Applications of nanotechnology to improve the performance of solar collectors – Recent advances and overview. Renewable and Sustainable Energy Reviews 2016;62:767-92.
5. [5] Hussein AK, Li D, Kolsi L, Kata S, Sahoo B. A review of nano fluid role to improve the performance of the heat pipe solar collectors. Energy Procedia 2017;109:417- 24.
6. [6] Tiwari GN, Akhtar MA, Shukla A, Khan ME. Annual thermal performance of greenhouse with an earth-air heat exchanger: An experimental validation. Renewable Energy 2006;31:2432-46.
7. [7] Trombe A, Pettit M, Bourret B. Air cooling by earth tube heat exchanger: experimental approach. Renewable Energy 1991;1:699-707.
8. [8] Ozgener L. A review on the experimental and analytical analysis of earth to air heat exchanger (EAHE) systems in Turkey. Renewable and Sustainable Energy Reviews 2011;15:4483-90.
9. [9] Ozgener O, Ozgener L. Determining the optimal design of a closed loop earth to air heat exchanger for greenhouse heating by using exergoeconomics. Energy and Buildings 2011;43:960-5.
10. [10] Nayak S, Tiwari GN. Energy metrics of photovoltaic/thermal and earth air heat exchanger integrated greenhouse for different climatic conditions of India. Applied Energy 2010;87:2984-93.
11. [11] Yildiz A, Ozgener O, Ozgener L. Exergetic performance assessment of solar photovoltaic cell (PV) assisted earth to air heat exchanger (EAHE) system for solar greenhouse cooling. Energy and Buildings 2011;43:3154-60.
12. [12] Sobti J, Singh SK. Earth-air heat exchanger as a green retrofit for Chandīgarh - a critical review. Geotherm Energy 2015;3(1):1-9.
13. [13] Nayak S, Tiwari GN. Theoretical performance assessment of an integrated photovoltaic and earth air heat exchanger greenhouse using energy and exergy analysis methods. Energy and Buildings 2009;41:888-96.
14. [14] Ghalambaz M, Mehryan SAM, Hajjard A, Veismoradi A. Unsteady natural convection flow of a suspension comprising Nano-Encapsulated Phase Change Materials (NEPCMs) in a porous medium. Advanced Powder Technology 2019.
15. [15] Mehryan SAM, Heidarshenas MH, Hajjar A, Ghalambaz M. Numerical study of melting-process of a non-Newtonian fluid inside metal foam. Alexandria Engineering Journal 2020;59(1):191-207.
16. [16] Mehryan SAM, Vaezi M, Sheremet M, Ghalambaz M. Melting heat transfer of power-law non-Newtonian phase change nano-enhanced n-octadecane-mesoporous silica (MPSiO2). International Journal of Heat and Mass Transfer 2020;151:119385.
17. [17] Zhu CX, Wang CC, Tang YC. Performance and flow distribution of the plate heat exchanger with supercritical fluid of carbon dioxide. Journal of Thermal Engineering 2015;1(3):143-51.
18. [18] Vaza J, Sattler MA, dos Santos ED, Isoldi LA. Experimental and numerical analysis of an earth-air heat exchanger. Energy and Buildings 2011;43:2476-82.
19. [19] Kumara R, Kaushik SC, Garg SN. Heating and cooling potential of an earth-to-air heat exchanger using artificial neural network. Renewable Energy 2006;31:1139-55.
20. [20] Ghosal MK, Tiwari GN, Das DK, Pandey KP. Modelling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse. Energy and Buildings 2005;37:613-21.
21. [21] Ghosal MK, Tiwari GN. Modelling and parametric studies for thermal performance of an earth to air heat exchanger integrated with a greenhouse. Energy Conversion and Management 2006;47:1779-98.
22. [22] Ghosal MK, Tiwari GN. Parametric studies for heating performance of an earth to air heat exchanger coupled with a greenhouse. Int. J. Energy Res. 2005;29:991-1005.
23. [23] Ghosal MK, Tiwari GN, Srivastava NSL. Thermal modeling of a greenhouse with an integrated earth to air heat exchanger: an experimental validation. Energy and Buildings 2004;36:219-27.
24. [24] Pongsoi P, Wongwises S. Determination of fin pitches for maximum performance index of l-footed spiral fin-and-tube heat exchangers. Journal of Thermal Engineering 2015;1:251-62.
25. [25] Tittelein P, Achard G, Wurtz E. Modelling earth-to-air heat exchanger behaviour with the convolutive response factors method. Applied Energy 2009;86(9):1683-91.
26. [26] Ramírez-Dávila L, Xamán J, Arce J, Álvarez G, Hernández-Pérez I. Numerical study of earth-to-air heat exchanger for three different climates. Energy and Buildings 2014;76:238-48.
27. [27] Doğan B, Erbay LB. Experimental analysis of the effect of cold fluid inlet temperature on the thermal performance of a heat exchanger. Journal of Thermal Engineering 2016;2(1):583-92.
28. [28] Shukla A, Tiwari GN, Sodha MS. Parametric and experimental study on thermal performance of an earth-air heat exchanger. Int. J. Energy Res. 2006;30:365-79.
29. [29] Sharma B, Bhushan G, Sachdeva G. Effect of flow structure on heat transfer in compact heat exchanger by using finite thickness winglet at acute angle. Journal of Thermal Engineering 2017;3(2):1149-62.
30. [30] Chel A, Tiwari GN. Performance evaluation and life cycle cost analysis of earth to air heat exchanger integrated with adobe building for New Delhi composite climate. Energy and Buildings 2009;41:56-66.
31. [31] Diaz-Mendez SE, Patiño-Carachure C, Herrera-Castillo JA. Reducing the energy consumption of an earth-air heat exchanger with a PID control system. Energy Conversion and Management 2014;77:1-6.
32. [32] Ravisankar R, Venkatachalapathy VSK, Alagumurthi N. Application of nanotechnology to improve the performance of tractor radiator using cu-water nanofluid. Journal of Thermal Engineering 2018;4(4):2188-200.
33. [33] Thiers S, Peuportier B. Thermal and environmental assessment of a passive building equipped with an earth-to-air heat exchanger in France. Solar Energy 2008;82:820-31.
34. [34] Shukla A, Tiwari GN, Sodha MS. Thermal modelling for greenhouse heating by using thermal curtain and an earth-air heat exchanger. Building and Environment 2006;41:843-50.
35. [35] Kumar KP, Siddhardha R, Raju R, Kumar KS. Response surface based optimization of ribbed isosceles triangular twisted tape heat exchanger using entropy augmentation generation number with al2o3 nano working fluid. Journal of Thermal Engineering 2019;5(3):210-21.
36. [36] Misra R, Bansal V, Agarwal GD, Mathura J, Aseri T. Thermal performance investigation of hybrid earth air tunnel heat exchanger. Energy and Buildings 2012;49:531-5.
37. [37] Misra R, Bansal V, Agrawal GD, Mathur J, Aseri TK. CFD analysis based parametric study of derating factor for earth air tunnel heat exchanger. Applied Energy 2013;103:266-77.
38. [38] Darius D, Misaran MS, Rahman MdM, Ismail MA, Amaludin A. Working parameters affecting earth-air heat exchanger (EAHE) system performance for passive cooling: a review. IOP Conf. Series: Materials Science and Engineering 2017;217:12-21.
39. [39] Pourfayaz F, Kasaeian A, Fard MM. A proper selection of hot and cold utilities in a plant containing multiple heat exchanger networks. Journal of Thermal Engineering 2019;5(4):341-54.
40. [40] Oudjehani N, Abahri K, Tahakourt A, Belarbi R. Evaluation of earth-air heat exchangers efficiency in hot and dry climates. Advanced Materials Research 2013;739:318-24.
41. [41] Menni Y, Azzi A, Chamkha AJ. Modeling and analysis of solar air channels with attachments of different shapes. International Journal of Numerical Methods for Heat & Fluid Flow 2019;29(5):1815-45.
42. [42] Menni Y, Azzi A, Chamkha AJ, Harmand S. Effect of wall-mounted V-baffle position in a turbulent flow through a channel: analysis of best configuration for optimal heat transfer. International Journal of Numerical Methods for Heat & Fluid Flow 2019;29(10):3908-37.
43. [43] Menni Y, Azzi A, Chamkha A. Computational thermal analysis of turbulent forced convection flow in an air channel with a flat rectangular fin and downstream V-baffle. Heat Transfer Research 2019;50(18):1781-818.
44. [44] Maurya RS, Singh S. Numerical investigation of isothermal flow around impingement plates in a shell and tube exchanger. Journal of Thermal Engineering 2017;3(5):1442-52.
45. [45] Sakhri N, Menni Y, Chamkha AJ, Lorenzini E, Kaid N, Ameur H, Bensafi M, Sahel D. Study of heat and mass transfer through an earth to air heat exchanger equipped with fan in south west of Algeria. International Journal of Heat and Technology 2019;37(3):689-95.
46. [46] Sakhri N, Draoui B, Menni Y. Experimental study of earth to air heat exchanger performance in arid region. First step: in - situ measurement of ground vertical temperature profile for different depths. Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 2019;56(2):183-94.
47. [47] Sakhri N, Menni Y, Chamkha AJ, Salmi M, Ameur H. Earth to Air Heat Exchanger and Its Applications in Arid Regions - An Updated Review. Italian Journal of Engineering Sciences 2020;64(1):83-90.
48. [48] Sakhri N, Menni Y, Chamkha AJ. Heating capacity of an Earth to Air Heat Exchanger in Arid regions – Experimental investigation. Journal of Applied and Computational Mechanics 2020. Doi: 10.22055/JACM.2020.31237.1843.
49. [49] Sakhri N. La ventilation naturelle dans les régions arides, Enjeux, Potentiels et perspectives. Editions Universitaires Européennes- ISBN: 978-613-8-46249-1. 2019 international Book Market Service Ltd., member of Omni Sriptum Publishing Group.
50. [50] Moussaoui A, Sakhri N, Draoui B, Rahmani L, Bensafi M. Design and modeling of a solar tower chimney effect intended for electrical energy production in Beni-Abbes site. IOSR journal of Mechanical and Civil Engineering 2016;13(5):134-41.
51. [51] Anand Y, Gupta A, Tyagi SK, Anand S. Variable capacity absorption cooling system performance for building application. Journal of Thermal Engineering 2018;4(5):2303-17.
52. [52] Ameur H, Menni Y. Laminar cooling of shear thinning fluids in horizontal and baffled tubes: Effect of perforation in baffles. Thermal Science and Engineering Progress 2019;14:100430.
53. [53] Bansal V, Misra R, Agrawal GD, Mathur J. Performance analysis of earth-pipe-air heat exchanger for summer cooling. Energy and Buildings 2010;42:645-8.
54. [54] Bansal V, Misra R, Agrawal GD, Mathur J. Performance analysis of earth-pipe-air heat exchanger for winter heating. Energy and Buildings 2009;41:1151-4.
55. [55] Bansal V, Mathur J. Performance enhancement of earth air tunnel heat exchanger using evaporative cooling. International Journal of Low-Carbon Technologies 2009;4:150-8.
56. [56] Mohapatra T, Rout SK. Experimental investigation and performance optimization of a cross flow heat exchanger by entropy generation minimization approach. Journal of Thermal Engineering 2019;5(2):1-12.
57. [57] Moussaoui A, Sakhri N, Draoui B, Rahmani L, Bensafi M. Changing the geometry of the Wind Tower and its Influence on Aerodynamic Behavior and Natural Ventilation. IOSR Journal of Mechanical and Civil Engineering 2016;1(4):13-9.
58. [58] Maerefat M, Haghighi AP. Passive cooling of buildings by using integrated earth to air heat exchanger and solar chimney. Renewable energy 2010;35:2316-24.
59. [59] Mohammed AH , Al-zuwaini H, Sergeev V, Socolova E, Skulkin S. Passive cooling by integrate solar chimney with earth to air heat exchanger. International Journal of Mechanical Engineering and Technology 2019;10(2):1375-90.
60. [60] Li H, Ni L, Yao Y, Sun C. Experimental investigation on the cooling performance of an Earth to Air Heat Exchanger (EAHE) equipped with an irrigation system to adjust soil moisture. Energy & Buildings 2019;196:280-92.

Share and Cite