IJECA-ISSN: 2543-3717. June 2021 Page 13 International Journal of Energetica (IJECA) https://www.ijeca.info ISSN: 2543-3717 Volume 6. Issue 1. 2021 Page 13-17 Dynamic modelling of an earth-to-air heat exchanger for air cooling on the building in hot temperate climate of Beni Mellal Morocco Ismail Arroub 1 , Ahmed Bahlaoui 1 , Soufiane Belhouideg 1 , Abdelmadjid Kaddour 2 1 Team of Applied Physics and New Technologies (EPANT), Polydisciplinary Faculty, Beni Mellal, MOROCCO 2 Unité de Recherche Appliquée en Energies Renouvelables, URAER, Centre de Développement des Energies Renouvelables, CDER, 47133, Ghardaïa, ALGERIA ismail.arroub@gmail.com Abs tract – In this article, we examined the passive cooling techniques built into a building in hot temperate climate. Our work aims to reduce the energy de mand for cooling and progre ss the thermal comfort of building by decreasing overheating hours. The dynamic simulations of the energy performance in a building with an earth -air heat exchanger (EAHX) are performed in the summer period using TRNSYS software. The building is situated i n Beni Mellal city (Morocco) where the climate is a hot temperate one. The results of the si mulations show a significant potential for air cooling. Indeed, for the hottest day of July (retained for this study), when the outside temperature is 44.8 °C and the cooled temperature (inside) is 29 °C, the difference of 15.8 °C is obtained. Also, an evaluation of the relative humidity is provided. Finally, we recommend that the Moroccan thermal code encourage the use of passive cooling techniques; precisely in temperate climate. Keywords: Energy efficiency, building, earth-air heat exchanger, passive cooling, TRNSYS Received: 24/04/2021 – Accepted: 15/06/2021 I. Introduction Buildings energy consumption in Morocco arranged second, after transport, with 25% of total energy uptake in this country, including 7% for the services sector and 18% for residential [1]. The energy consumption of Moroccan buildings is predictable to an incre ment rapidly in the ne xt years fo r t wo reasons; the first is significant increase of household equipment rate in HVA C fac ilit ies, hot water and lighting due to the lower prices of these facilit ies and the amelioration of living standards. And the other is substantial development of the buildings sector. Over the last decade, there has been an uprising interest in imple ment ing cooling and heating systems for buildings focused on renewable energy sources. Because of its high thermal ine rtia, the ground attenuates the temperature variations that occur at the earth surface. Furthermore, it causes a difference between the temperature in the soil and that at the surface [2]. Methods for exploring geothermal energy are ground source heat pump, geotherma l e lectricity, earth -air heat e xchanger (EA HX) etc. A mong of them, an EAHX has the advantages of a simp le system, low operation cost and easy implementation [3]. To supply comfortable Circu mstances in the Bu ildings of suffic ient ground space, a passive technology of cooling or heating, known as an EAHX can be utilized efficiently and effect ively. It is a lso nominated earth tube heat exchanger, ground source heat pump, ground tube heat exchanger or Canadian well. The idea o f utilizing ground therma l inert ia for a ir conditioning is not a new method, but a modified concept that goes back to the last decades. The a ir used is oftentimes outside air for ventilation, but also rentable for totally or partially http://www.ijeca.info/ http://www.ijeca.info/ mailto:ismail.arroub@gmail.com Ismail Arroub et al IJECA-ISSN: 2543-3717. Page 14 managing the construction thermal loads. The climatic conditions affect strongly the system performances. Thus, at adequate depth, the ground temperature is lower / (higher) than that of the external air during the summer / (winter). The constant temperature in the ground can be used for cooling and heating applications [4]. In case of the outside air is sucked through the EAHX system, in wh ich the pipes inhumed in the soil; the air can be heated during the winter and cooled heated during the summer. Consequently, the EAHX can minimize the energy destined for cooling or heating or furthermore it enhances the therma l co mfort in the buildings [5-7]. Several researchers have studied the impact of pipe dia meter and length and found that, these parameters affect the performance of EAHX system [8]. In the 50 40 30 20 10 0 May June July August September EAHX system, the difference in air te mperature between outlet and inlet sections of the pipe is imp roved by increasing the length of the pipe [9]. But weakened with the increase in the dia meter of the pipe [10-12]. In a recent works, the authors install two EA HX systems (U- shaped pipe) to evaluate the dry and wet EAHX system performance. They observed that the knee point position is greater in dry EAHX co mpared to the wet EAHX system [13,14]. The objective o f the current a rtic le is to study a dynamic therma l simulat ion in a building with integrated the EAHX for a hot-dry c limate c ity of Ben i Me lla l- Morocco- along the period between the months of May and September of 2020. II. Methodology II.1. Weather data and location The meteorologica l data used in this study were taken fro m a typica l year weather file fo r the city o f Beni Mellal, (32.36°N, -6.4°E). Several pertinent weather data are presented in Figure 1 and Figure 2 for the atmospheric temperature and relat ive humidity respectively, for five months from May to Septe mber o f 2020. The amb ient temperature o f theses five months varies between 8.1 °C and 44.8 °C which are the lowest and highest temperatures observed during this period at May and July respectively. The large a mplitude of the temperature perturbations is the characteristic of a hot temperate climate. Figure 1. Ambient temp erature (°C) for the p eriod from 1 st M ay to 30 th Sep tember 2020 More the air is warm, more it contains the vapor. Conversely, when the a ir cools the vapor condenses and forms liquid water droplets: the saturation threshold increases with temperature. Fro m the figure the relative humid ity varies between 30% and 65% for the five months. When the temperature increases, during the hot month, the re lative hu midity decreases and vice versa, at the cold month. An increase in the relative hu mid ity accompanies this decrease in temperature as is observed in Figures 1 and 2. In the month of July the temperature reaches up to 45 °C and the climate are hot in this city most often. Consequently, fresh air is necessary for the inhabitants of the region to live healthy life with their good mental and physical health. 70 60 50 40 30 20 May June July August September Figure 2. Relative humidity (%) for the p eriod from 1 st M ay to 30 th Sep tember 2020 T e m p e ra tu re ( °C ) R e la ti v e h u m id it y ( % ) Ismail Arroub et al IJECA-ISSN: 2543-3717. Page 15 II.2. Reference building The building is a concrete hypothetical one which represents a typical villa building in country of Morocco. The studied building is located in Beni Me llal and is North-fac ing built on a floor area of 109 m 2 , with a ceiling height of 2.8 m. It consists of a ground floor composed of seven pieces distributed over the whole area building as shown in Figure 3. Figure 3. Building 2D p lan II.3. Dynamic simulation models In this artic le, dynamic thermal simu lation was carried out through TRNSYS which designates Transient System Simu lation software to simulate the building. The systems are simulated using components called “types” that are interconnected through time-dependent inputs and outputs. The building was simulated using Type 56 (TRNBuild) and connected to the soil using an Earth -Air Heat Exchanger (EAHX) Type 556 [15]. A time step of 1h was used to reduce computation time. The building was Sp lit into 7 therma l zones as it is presented in figure 3. Each roo m was specified as a therma l zone in order to find detailed informat ion on each one of them. The study is made for roo m 1 and the simu lation starts on 1 st May and ends on 30 th September for the year of 2020. For the computational study, the effect of the inclination pipe and its vertica l parts is not considered into account since the horizontal part of the pipe is long enough. Thus, the EAHX is formed by only 1 p ipe of PVC (polyviny l ch loride) with 35 m length. The pipe is assumed horizontal, and inhumed at the mean depth of 2.5 m. The thermo-physical characteristics of the PVC p ipe, soil and air at average a mbient temperature (20 °C) are reported in Table 1. Table 1. Phy sical p rop erties Thermal conductivity (W/m.K) Specific heat (KJ/Kg.K) Density (kg/m 3 ) Soil 1.4 1.3 1400 Air 0.025 1.01 1.16 PVC 0.17 1.3 1400 III. Discussion of the results In this part, the essential results obtained by means of the dynamic therma l simu lations carried out in this study are plotted and discussed in detail. The results concern the variations of the relative humid ity and temperature with and without the EAHX in continuous operation over the period of the year 2020 (1 st May - 30 th September of 2020), as mentioned above. It should be noted that the results are presented for the room 1. Figures 4 and 5 illustrate the Te mperature evolution and Relat ive humidity in the roo m 1 respectively, with and without integration of the EA HX. The air temperature in the build ing passed 35 °C in the hottest day localized on July, but with the integration of the EAHX, this temperature is varied between 20°C and 29 °C; which corresponds to the range of the therma l comfo rt te mperature. On the other hand, the corresponding relative hu mid ity is a round 40% , Although the outside temperature reaches more than 44 °C. The re lative humidity shows a decrease profile when the system (EAHX) has a preheating effect (see Figure 5). We note that the EA HX could be used also for the air preheating; for e xa mp le, the beginning of the month May (see Figure 4), but this aspect is not treated since we are only interested in the building cooling. 40 35 30 25 20 15 10 May June July August September Figure 4. Ambient temp erature (°C) in the room 1 for the p eriod from 1 st M ay to 30 th Sep tember 2020 Wit hout EAHX Wit h EAHX T e m p e ra tu re ( °C ) Ismail Arroub et al IJECA-ISSN: 2543-3717. Wit hout EAHX Wit h EAHX Page 16 70 50%. This range of variation in relative humidity does not present any risk of condensation. 60 40 50 35 40 30 20 May June July August 30 25 September Figure 5. Relative humidity (%) in the room 1 for the p eriod from 1 st M ay to 30 th Sep tember 20220 As a comple ment, Figure 6 and Figure 7 present the time evolution o f the evaluated te mperature and relat ive humid ity respectively, in the studied roo m, during a typical days of summe r (the three hottest days of the year) corresponding to July 19 th , 20 th and 21 th of 2020. It is noted that the ma ximu m / min imu m te mperature, in the studied room, is obtained for the 19 th July and equal to 35.8 °C / 25.2 °C. Th is affects the therma l comfo rt zone caused by the lack of refresh. The air temperatures obtained at the outlet of EAHX is varying in the range of 23 °C - 29 °C; which gives a fa irly significant difference o f 6.8 °C between the te mperature inside the studied room and that of the cooled a ir (see Figure 4). Note that the amb ient air te mperature in the outside which occurs at 19 th July is 44.8 °C, while the temperature of the air cooled by the EAHX is 29 °C; which gives a fa irly significant difference of 15.8 °C (see Figure 1 and Figure 6). The percentage of this reduction is about 35%. Consequently, the above results show that the earth - air heat exchanger is a system mo re adapted to air re freshing in the buildings inside Beni Me lla l city, since it provides a quasi-constant air temperature of appro ximately 26 °C, with re lative humid ity that is almost 40% when the te mperature in outside exceeds 40 °C. The re lative hu midity of the a ir varies with the room temperature. When the temperature increases, during the day, the relative hu midity decreases and vice versa, at the night. The gro wth of the air re lative hu midity accompanies this decrease in te mperature as is observed in Figures 6 and 7. Thus, the relative humid ity of the amb ient air varies between 25% and 55% while the humidity of the air refreshed oscillates between 27% and 20 19th July 20th July 21th July Figure 6. Temp erature (°C) inside the room 1 for three hottest day s of the y ear 70 60 50 40 30 20 19th July 20th July 21th July Figure 7. Relative humidity (%) in the room 1 for three hottest day s of the y ear IV . Conclusion In this study, we focused on reduction the demand for cooling energy in a typical building by blocked overheating through the installation of the EAHX. The reference building was divided into 7 therma l zones and simulated in TRNSYS 18. The dynamic simulation of the EAHX shows that this system serve air te mperature decrease up to 15.8 °C for the hottest day established in July. The obtained results reveal that the EAHX is a therma l system mo re adapted to air re freshing in the build ing, as it provides a quasi- constant air temperature of approximately 26 °C, with Wit hout EAHX Wit h EAHX Wit hout EAHX Wit h EAHX R e la ti v e h u m id it y ( % ) T e m p e ra tu re ( °C ) R e la ti v e h u m id it y ( % ) Ismail Arroub et al IJECA-ISSN: 2543-3717. Page 17 relative humidity that is about 40% when the outside temperature e xceeds 40 °C. Globa lly, these results indicated that the EAHX is an efficacious system for a ir refreshment inside the building in hot t e mperate c limate as in Beni Mella l region, because it provoke an adequate air te mperature for hu man comfort in the hot season (May-September). Furthermore, in such climate the EAHX can also be used for air heating. References [1] AM EE, M oroccan Agency for En er gy Efficiency "Thermal regulation of construction in M orocco", 2013. [2] S. F. Ahmed, G. Liu, M . M ofijur, A. K. Azad, M . A. Hazrat and Y. M . Chu, "Phy sical and hy brid modellin g techniques for earth-air heat exchan gers in reducin g buildin g ener gy consump tion: Performance, ap p lications, p rogress, and challen ges" So lar Ener gy , Vol 216, 2021, p p . 274-294. [3] J. W. Lund, D. H. Freeston and T. L. Boy d, "Direct app lication of geothermal en er gy ", Geothermics, Vol 34, 2005, p p . 691-727. [4] D. Yang, H. Wei, R. Sh i, and J. Wan g, "A demand- oriented ap p roach for integratin g earth-to-air heat exchan gers into buildin gs for achievin g y ear-round indoor thermal co mfort" Ener gy Conversion and M anagement, Vol 182, 2019, p p . 95-107. [5] J. Kaur, P. Sin gh and H. Kaur, "A review on the analy tical analy sis and modellin g of earth air tunnel heat exchan ger system", Elk Asia Pacific Journals-Sp ecial Issue, ISBN: 978-81-930411-4-7. [6] A. Chel, "Perfor mance evalu ation and lif e cy cle cost analy sis of earth to air heat exchan ger integrated with adobe buildin g for New Delhi comp osite climate", Energy and Buildings, Vol 41, 2009, p p . 56-66. [7] D. Belatrache, S. B entouba and M . Bourouis, "Numerical analy sis of earth air heat exchan gers at op eratin g conditions in arid climates", International Journal of Hy drogen Energy , Vol 42, No 13, 2017, p p . 8898-8904. [8] A. Amadeh, M . Habibi and A. Hakkaki-Fard, "Numerical simulation of a ground- coup led heat p ump system with vertical p late heat exchan gers: A comp rehensive p arametric study ", Geothermics, Vol 88, 2020, p . 101913. [9] Y. Zhao, R. Li, C. Ji, C. Huan, B. Zhang and L. Liu. "Parametric study and design of an earth-air h eat exchan ger usin g model exp eriment for memor ial heating and coolin g", App lied Thermal En gineerin g, Vol 148, 2019, p p . 838-845. [10] K. K. Agrawal, M . Bhardwaj, R. M isra, G. D. Agrawal and V. Bansal, "Op timization of op erating p arameters of earth air tunnel heat exchan ger for sp ace cooling: Taguchi method ap p roach", Geothermal En er gy , Vol 6, No 10, 2018, p p . 1-17. [11] B. Sin gh, R. Kumar and A. K. Asati, "Influence of p arameters on p erformance of Earth air heat exch an ger in hot-dry climate", Journal of M echanical Science and Technology , Vol 32, No 11, 2018, p p . 5457-5463. [12] K. K. Agrawal, R. M isra, G. Das A grawal, M . Bhardwaj and D. K. Jamuwa, "Effect of diff erent design asp ects of p ip e for earth air tunnel heat exchan ger sy stem: a state of art", International Journal of Green Energy , Vol 16, No 8, 2019, p p . 598-614. [13] K. K. Agrawal, R. M isra, T. Yadav, G. D. Agrawal and D. K. Jamuwa, "Exp erimental study to investigate the effect of water imp regnation on thermal p erforman ce of Earth air tunnel heat exchan ger for summer coo lin g in hot and arid climate", Renewable Energy , Vol 120, 2018, p p . 255-265. [14] K. K. Agrawal, T. Yadav, R. M isra and G. Das Agrawal, "Effect of soil moisture contents on thermal p erforman ce of earth-air-p ip e heat exchan ger for winter heatin g in ar id climate: In situ measurement", Geothermics, Vol 77, 2019, p p . 12-23. [15] TESS libr ary mathematical refer ence. In: TESSLibs 17: comp onent Libraries for the TRNSYS simu lation environment, Vo l. 4. M adison, Wisconsin: Thermal Energy Sy stem Sp ecialists, LLC; 2013.