Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate

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Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate Abderrahim Bazgaou a,⇑, Hicham Fatnassi b, Rachid Bouharroud c, Kabira Ezzaeri a, Lahoucine Gourdo a, Ahmed Wifaya c, Hassan Demrati a, Hayat El Baamrani a, Aicha Idoum a, Ahmed Bekkaoui d, Ahmed Aharoune a, Lahcen Bouirden a a

Thermodynamics and Energetics Laboratory, Faculty of Science, Ibn Zohr University, BP8106, 80006 Agadir, Morocco Université Côte d’Azur, INRA, CNRS, ISA, France National Institute of Agronomic Research INRA Agadir, Morocco d Agronomic and Veterinary Institute Hassan II, Rabat, Morocco b c

a r t i c l e

i n f o

Article history: Received 11 October 2019 Accepted 18 October 2019 Available online xxxx Keywords: Solar heating cooling system Quartzitic sandstone Surplus air thermal energy storage Agricultural yield Greenhouse microclimate

a b s t r a c t The solar thermal storage is an important issue for greenhouse applications in winter period. For the reason that greenhouse operations, such as heating and cooling, consume a large amount of energy. The thermal storage is important to minimize the cost of greenhouse production. Surplus air thermal energy (SATE) is available in greenhouses during all the year, even in the cold period, hence its use in greenhouse applications is possible. In this present work, a solar heating cooling system (SHCS) with quartzitic sandstone as thermal storage material to store and use the SATE in greenhouse production was operated for cooling and heating processes and its performance was evaluated during winter period. This system consists of a quartzitic sandstone and including thermal storage blocks and pipes with fans to manage those processes in greenhouse. This system was located in the Souss-Massa region, Morocco. The heating and cooling of inside air by SHCS can improve the greenhouse microclimate and tomato yield. The results show that the air temperature in greenhouse equipped with SHCS exceeds than that of the control one about 3 °C at night and 6 °C lower during day, with fewer fluctuations. Moreover, the relative humidity was 10% lower at night. The SATE stored was varied between 15.68 and 140 MJ/day in plastic greenhouse with an area of 165 m2 during day, and 65% of this heat recovered at night. The SHCS was improved the tomato yield about 1.74 kg/m2 than that of normal production. An economic analysis revealed that this system is very profitable and could generate profits for farmers. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Plasma and Energy Materials ICPEM2019.

1. Introduction The agricultural greenhouse behaves like a complex physical and biological system, that carries out heat exchanges with the outside and used for the protection of the plant when it is impossible to grow outside due to climate and diseases. The greenhouse is a system that improves crop yields by creating comfortable growing conditions. The responsible parameters for the crop growth are light, temperature, relative humidity and nutrients. These factors must be controlled and maintained at optimal levels, ⇑ Corresponding author. E-mail address: [email protected] (A. Bazgaou).

which consumes a large amount of energy [1,2]. The conventional systems use the fossil fuels for heating greenhouses [3], which increase the cost of greenhouse production [4]. Consequently, the investment price increases also. For that, many studies have been realized to minimize energy consumption or replace conventional energy sources with renewable and new sources [5–11]. The new systems are based on solar energy as a heat source, this energy will be stored during the day for use it at night in heating applications. Moreover, the solar energy can be stored in thermal storage materials according to three modes: sensible, latent and chemical energy storage [12]. In studies of Singh et al. [13] showed the technological and economical aspects make sensible heat storage better than latent heat

https://doi.org/10.1016/j.matpr.2019.10.101 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Plasma and Energy Materials ICPEM2019.

Please cite this article as: A. Bazgaou, H. Fatnassi, R. Bouharroud et al., Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.101

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storage. Compared to the other storage modes, it is the most common technology [14] that is simple in design and operation, inexpensive and most economical in heat storage system [15–17]. Moreover, the sensible heat storage materials are inexpensive and have larger thermal conductivities when compared with most of phase change materials used [18]. Particularly, the solar heating system with rocks as thermal storage material has been successfully applied in CSP for solar energy storage [19–21]. In applications based on sensitive thermal energy storage, the rocks are good suitable materials [11]. In greenhouse applications, the most favorable storage mode for producers is the sensible heat storage. Many applications of heat storage systems with this storage mode are cited in literature [22–29]. This mode is used in this field due to its rentability, low cost of investment, long lifetime and short repayment period. In Mediterranean regions, the greenhouse encounters overheating problems during daytime due to intense solar radiation and extreme cold at night even if winter period. Therefore, the greenhouse temperature often exceeds the optimal growth value for crops in this period. Solar thermal energy is available more than necessary in the greenhouse during the day, this energy is named surplus air thermal energy (SATE). Storage of SATE in thermal storage materiel offers the cooling effect during the day and its recovery gives the heating effect at night in greenhouse. There are many applications of using SATE in passive mode by the choice of soil or water as a storage material, which transfers heat between air and storage system in greenhouse [30–36]. Accordingly, the heat storage capacity is limited also the heating and cooling operations efficiency are low. To resolve this problem, the SATE is stored through an active way using solar collectors or thermal system with heat storage materials (rocks, water, PCMs, . . .) [37–43]. Consequently, the heat storage capacity and the heat recovery efficiency will be improved. On the other hand, the true efficiency of a heating system is its profitability and its profits for farmers. Moreover, Russo et al. [44] showed that the active heating systems ensuring thermal conditions suitable for cultivation in greenhouses in the winter period within the Mediterranean area. A number of researches concerning the use of SATE in a greenhouse are available in the literature. Yang and Rhee [45] evaluated a heat pump system using the excess thermal energy available inside the greenhouse (SATE) during winter period, and found that the energy conservation and the SATE amount are maximal in March. A heating and cooling system is developed by Yang et al. [46,47] using the SATE in a greenhouse which performed the recovery and supply of the heat according to design purposes. They pointed out that the greenhouse energy conservation was achieved by using SATE. However, they noticed that the developed system cannot provide a sufficient amount of energy for heating operation during cold and cloudy days. Concerning the effect of heating and cooling on the agronomic parameters, such as crop growth and agricultural yield, the studies are scarce in literature. Our work is to study the operation of solar heating cooling system, with quartzitic sandstone as a thermal storage material and air as heat transfer fluid, during the winter period and its effect on the greenhouse microclimate and production. The SHCS performance and its recovery efficiency are also analyzed and discussed. 2. Surplus air thermal energy (SATE) in greenhouses In moderate climate regions, the solar radiation is intense even if during the winter period. Consequently, a large quantity of energy available in greenhouse can be evaluated for heating and cooling operations. During day, the equation of energy balance for the greenhouse system is represented in Eq. (1). The solar energy Qsolar is transmitted inside the greenhouse through the cover Qcover and absorbed by the plants Qplants, the soil Qsoil and

the air Qair. In case of the greenhouse ventilation is natural, the air inside the greenhouse is practically stable, so the amount of heat is accumulated into this air resulting in the increase of air temperature and exceeding the optimum temperature of the crops. This energy called SATE QSATE can be released by cooling. Moreover, in the absence of solar radiation at night, the heating must therefore be used to maintain an optimal value of the temperature. If we use a heating source, the equation of energy balance is expressed by Eq. (2). In this experiment study, the SATE stored during the day is used as heating source Qheating at night. This operation is totally possible for applying inside the greenhouse because it receives a large amount of solar thermal energy during the day.

Q solar ¼ Q cov er þ Q plants þ Q soil þ Q air þ Q SATE

ð1Þ

Q heating ¼ Q cov er þ Q plants þ Q soil þ Q air

ð2Þ

3. Materials and methods 3.1. Greenhouse and SHCS The experimental studies are realized in two canarian greenhouses with plastic cover of 200 lm thick and same dimensions in geometry. Each one has a floor area of 165 m2, 15 m in length and 11 m in width. The heights of the ridge and the side wall are 5 m and 4 m, respectively. First greenhouse named experimental greenhouse equipped with a heating cooling system with quartzitic sandstone as a thermal storage material, and the second is the control greenhouse for comparative studies. Thus, the two greenhouses are practically identical and exposed to the same weather conditions, also in the absence of the SHCS system the microclimate in the two greenhouses is identical. They are located in Souss-Massa region (Altitude: 80 m, Longitude: 9° 23, Latitude: 30° 13), Morocco, with East–West orientation. This orientation is more energy efficient for greenhouses during winter period [48]. During day, aeration of both greenhouses is provided by natural ventilation through the East and West walls, at night these walls are closed. The description and views of the two greenhouses and the solar heating cooling system are illustrate in Fig. 1. Solar heating cooling system consists of three rows of quartzitic sandstone and each row contains two blocks separated. Each block has one inlet and one outlet of air. The total volume of quartzitic sandstone is 9 m3 meaning 1.5 m3 for each block (Fig. 2). The inlet and outlet PVC tubes are installed at a height of 2.5 m and 0.5 m, respectively. All inlets and outlets are equipped by fans with a 2.15 m3/min of volume flow rate and a consumption of 18 Watt each. 3.2. Crop The crop planted in the two greenhouses was tomato (cv. Solanum lycopersicum L.), at January 9, 2017 in soil-less container on a carbonaceous substrate with a density of 2 plants/m2. The planting rows were oriented north-south, perpendicular to the direction of the prevailing wind. Experimental greenhouse and control one were fertigated using the same irrigation system; and received the same quantity of water and fertilizers. 3.3. Choice of quartzitic sandstone as thermal storage material Table 1 present thermo-physical properties of some conventional materials found in literature in comparison with quartzitic sandstone. From the table, the quartzitic sandstone have a greater thermal capacity compared to concrete, brick, graphite and lead;

Please cite this article as: A. Bazgaou, H. Fatnassi, R. Bouharroud et al., Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.101

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Fig. 1. Descriptive and views of the two greenhouse and the solar heating cooling system.

but lower than alumina, cofalit and copper. The latter is costly and has high thermal expansion [49]. Alumina and cofalit require energy and high cost for production [49]. Consequently, the quartzitic sandstone can be used as filler material for high temperature (CSP applications) and low temperature (agricultural applications) in thermal energy storage systems due to its large availability, compatibility with air as heat transfer fluid and many other advantages such as good thermal conductivity and high specific heat, as well as thermo-mechanical and chemical stability. 3.4. Functioning principle of heating system During daytime, the inlet and outlet fans are working in permanence for stored SATE and recovered it at night. These fans are managed the heating and cooling operations inside the greenhouse and consume less energy (5.2 kWh/day) compared to powerful fans. The choice of this fans type is to reduce the cost of greenhouse production.

In order to store a large amount of SATE, the rocks geometry is small and more at least spherical (5 at 10 cm in diameter). The type of rocks used call quartzitic sandstone with 852 J/kg.K in specific heat capacity at 25 °C according to the work of Tiskatine et al. [50]. The porosity of rock block is 35%. Bazgaou et al. [51] used the same solar system for improvement the greenhouse microclimate at night. The system works according two different settings of thermostat (30 °C during day and 12 °C at night). During day, only the input fans are functioned for solar thermal storage. In this case, the cooling effect is absent due to non-operation of the output fans and the short operating time of the inlet fans (if inside temperature exceeds 30 °C). At night, only output ones are operated for heating greenhouse (if inside temperature is below 12 °C). This experiment can realize the heating and cooling effects using the SHCS system. The fans have a low consumption and require time to heat or cool all the places in the greenhouse, while the time difference between the two phases of storage and destocking is low, which imposes the permanent operation of all the fans.

Please cite this article as: A. Bazgaou, H. Fatnassi, R. Bouharroud et al., Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.101

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A. Bazgaou et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 2 Accuracy of measuring sensors and its range use. Sensors

Measurement Range

Accuracy

Pyranometer CMP11 CNR4 Net Radiometer

0 to 4000 W/m2

Level accuracy 0.1°

–40 to 80 °C 0 to 100% RH 0 to 2000 W/m2 T: 40 °C to +60 °C RH: 0–100% ±5000 mV ±1000 mV ±200 mV ±50 mV ±20 mV

Expected accuracy for daily totals ± 10%

Vaisala HMP60

Data Logger CR3000

±0.6 °C ±3% RH (0 to 90%) ±5% RH (90 to 100%) ± (0.04% of reading + offset), 0 °C to 40 °C ± (0.07% of reading + offset), from 25 °C to 50 °C ± (0.09%) reading + offset), 40 °C to 85 °C

All agronomic factors measurements were recorded from the beginning until the end of the crop cycle. Fig. 2. Part view and dimensions of a single block of SHCS.

3.7. Calculation of solar thermal energy stored and recovered

3.5. Measurement of climatic parameters in greenhouse Several climatic factors are measured inside greenhouse and on the meteorological station. The equipment Kipp and Zonen pyranometer CMP11 was used to measure the global solar radiation. The amount of solar energy available inside the greenhouse, named net solar radiation, was measured by CNR4 Net Radiometer, this parameter corresponds to the subtraction of the part of the solar radiation reflected by the components of the greenhouse to that transmitted through the greenhouse cover. Temperature and relative humidity of inside air were measured in the center by Vaisala (HMP60) at a height of 1.5 m. A data logger CR3000 was used to record all measurements of climatic factors, all the measured values are collected for each 5 s with the average saved after 10 min. The sensors precision is exposed in Table 2.

The solar radiation is intense, in moderate climate regions even in winter period. Consequently, the inside air temperature exceeds the optimal growth temperature. At daytime, the greenhouse air becomes very hot, therefore a thermal energy (SATE) is available more than necessary. The SHCS with quartzitic sandstone stores this thermal energy, which causes the decrease of inside temperature (cooling operation). Meanwhile, the amount of SATE stored is calculated using the Eq. (3). At night, in the absence of solar radiation, the inside air becomes cold. Therefore, the SHCS begins to release an amount of the stored thermal energy (heating operation) causing an increase of inside air temperature. The amount of SATE recovered is calculated using the Eq. (4).

Q stored ¼

t f ;c X

Q recov ered ¼

3.6. Monitoring of the agronomic factors

ma cp;a :ðT in;Gcontrol ðtÞ  T in;Gexperimental ðtÞÞ

ð3Þ

t¼t i;c tf ;h X

ma cp;a :ðT in;Gexperimental ðt Þ  T in;Gcontrol ðtÞÞ

ð4Þ

t¼t i;h

The performance of the SHCS is studied by monitoring and measuring the following agronomic parameters: the average height of the tomato plant using a wood ruler, the number of tomato fruits harvested per plant and their weight by an electronic balance which has a resolution of 0.5 g. Twenty plants were selected randomly in each greenhouse to measure the tomato evolution at 0, 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, 99, 107, 114, 120, 128, 135, 143, 150 days after plantation for plant height and during 8 harvesting periods for the number of tomato fruits per plant and their weight. These 8 harvests are between April 11 and June 8, 2017.

where ma and cp;a are the air mass inside the greenhouse, 742.5 kg, and air specific heat at 25 °C, 1005 J/kg.K. T in;Gcontrol ðtÞ and T in;Gexperimental ðtÞ are the temperatures (°C) of inside air of control greenhouse and experimental greenhouse, respectively. t i;c and tf ;c are initial and final times of the cooling operation, respectively. Moreover, ti;h and t f ;h are initial and final times of the heating operation, respectively. The fluctuation of the amount of SATE stored is associated to the weather conditions such as ambient temperature and global solar radiation. Accordingly, the climate data of sunny, cloudy and rainy days, during the month of February 2017, were collected and

Table 1 Comparison between quartzitic sandstone and some conventional materials. Material

Specific heat (J/kg K)

Thermal capacity (kJ/m3 K)

Thermal conductivity (W/m K)

Source

Quartzitic sandstone Concrete Brik Alumina Cofalit Graphite Copper Lead

852 800 840 800 917 505 401 131

2300 1792 1512 3168 2861 1126 3448 1485

4.02 1.7 0.5 18 2.05 138 378 35.25

[47] [13,48] [49,50] [51,52] [53,54] [49] [13,49] [55]

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compared between the total SATE stored and the thermal energy recovered. The SHCS in agricultural greenhouse was dynamically functioned according to the amounts SATE stored and thermal energy recovered. The system efficiency (g), calculated by the ratio of the quantity energy recovered (Qr) and the total thermal energy stored (Qs), is expressed by the following equation (Eq. (5)):

g¼

Qr Qs

ð5Þ

The thermal load leveling (TLL) is an indicator that represents the fluctuation of the air temperature in greenhouse. The performance study of SHCS as an active system installed inside the greenhouse was therefore evaluated in terms of TLL. In greenhouse, a better environment for plants is ensured when the inside temperature has minimum fluctuations. In this case, the TLL should have a minimum value [52]. This parameter is calculated by the Eq. (6).

T in;max  T in;min T in;max þ T in;min

solar noon, Rt/Rg and Rnet/Rg respectively. The greenhouse with the SHCS, as a medium of heat storage, allows to store the thermal energy during day and decrease overheating (cooling operation), then recovered it at night to improve the air temperature in greenhouse (heating operation). Fig. 4 shows the evolution of air temperature inside experimental and control greenhouses (25 at 27 January 2017). The fluctuation of inside air temperature in the two greenhouses is closely attributed to weather factors such as ambient temperature and solar radiation. The difference in temperature between the two greenhouses is 4–6 °C during the day (T in;Gcontrol > T in;Gexperimental ) and 2–3 °C at night (T in;Gexperimental > T in;Gcontrol ). Meanwhile, the inside air

3.8. The thermal load leveling

TLL ¼

5

ð6Þ

4. Results and discussion In the Mediterranean regions, the inside air temperature exceeds the optimum value during the winter period. An experimental study for performances evolution of solar heating cooling system has been carried out during the cold season. The measurement companion of climatic parameters is realized during the month of February 2017, contrary to the agronomic measurements is realized during all the study period. Those performances are analyzed and discussed. The performances of SHCS are summarized in the quantity of SATE stored during daytime and the heat recovered at night, also its reduction of the air temperature fluctuations in greenhouse and its recovery efficiency.

temperature of experimental greenhouse was lower of 35 °C during the day and above of 10 °C at night. This effect is shown by Gourdo et al. [53], the use of solar heating system in the greenhouse allows to cool it during day and to heat it at night. Fig. 5 presents the SHCS effect on relative humidity inside the greenhouse. At night, the experimental greenhouse reduces the value of the relative humidity about 8–10% lower than the control one. The solar system creates a passive dehumidification process due to the increase of the air temperature inside the experimental greenhouse. During daytime, the relative humidity is also varied inversely with inside air temperature. In Wacquant et al. [54] studies show that the optimal value of relative humidity for crop growth is 75%, for beyond that the crops commence to stress. Another studies of Ameer et al. [55] are modelized and simulated a dehumidification system for examine the maneuverability and operational performance of the greenhouse. This model is capable to eliminate the humidity generated by crops and maintain it in the required range. This profitable system is constructed based on the abundant and cheaper materials according to the Tiskatine et al. [56] studies. The operation of SHCS consumes less energy and improves the climatic conditions inside the greenhouse.

4.1. Comparative study of greenhouses climate Fig. 3 displayed the evolution of global solar radiation (Rg) during the three typical days during 25 at 27 January 2017. The figure shows also the amount of solar radiation transmitted (Rt) inside the greenhouse and net solar radiation (Rnet). The global solar radiation reaches 640 W/m2, 75% of this energy is transmitted in greenhouse by the plastic cover and 63% is available to heat the inside air greenhouse, these percentages are calculated during

Fig. 4. Evolution of temperature as a function of time during 25 at 27 January 2017.

Fig. 3. Evolution of global, transmitted and net solar radiation as a function of time during 25 at 27 January 2017.

Fig. 5. Evolution of relative humidity as a function of time during 25 at 27 January 2017.

Please cite this article as: A. Bazgaou, H. Fatnassi, R. Bouharroud et al., Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.101

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4.2. The operation of the system The recorded results of the system operation are exposed in Fig. 6 during 3 days of January 2017. The heat was supplied for heating greenhouse beginning from 18:00 to 9:00 the next day. The storing of excess thermal energy is started after 10:00 am. The heating operation was restarted at 20:00. The total amount of SATE stored during those three days (Eq. (3)) is about 146.88 MJ, 109.58 MJ and 199.46 MJ, respectively, although the total daily quantity of heat recovered (Eq. (4)) for heating operation is about 91.07 MJ, 68.88 MJ and 106.02 MJ, respectively. Meanwhile, the inside air temperature of experimental greenhouse was controlled at 2 to 3 °C higher than the control greenhouse at night and 4 to 6 °C lower during the daytime. Concerning the system efficiency, the SHCS can be recovered at night 62% of SATE stored during the day. 4.3. Energy stored and energy recovered An experimental study of a heating system is realized in February 2017 of the winter period. In this study, we compared the amount of SATE stored and the corresponding recovered thermal energy between sunny, cloudy, and rainy days. The amounts of stored SATE and thermal energy recovered are presented in Fig. 7 during the February month. Although the amount of SATE stored was varied between 40.21 and 140 MJ/day for sunny days, 15.68 and 20 MJ/day for cloudy days, thus 5.01 MJ/day for rainy days. The corresponding recovered thermal energy is between 25.50 and 75.79 MJ/day, 5.95 and 7.69 MJ/day and 0.93 MJ/day, respectively. The fluctuations of the stored thermal energy (SATE) and the recovered heat are attributed to weather conditions such as global solar radiation and ambient temperature. The solar radiation is the heat source of SATE, and ambient temperature is associated to heat

loss. During this growing period of February, ambient temperature and global solar radiation were registered from the weather station located above the greenhouse (Fig. 8). The amount of global solar radiation received by the greenhouse is varied between 350 W/ m2 and 800 W/m2, with an ambient temperature varied between 3 °C as minimum value at night and 30 °C as a maximum value during day. 4.4. System efficiency The solar system with high heat capacity of quartzitic sandstone is able to recover the most of the thermal energy stored. Fig. 9 shows the ratio of thermal energy recovered and stored SATE calculated by Eq. (5) as a function of time in February 2017. The results show, the thermal energy recovered for sunny days is varied between 54 at 65% of energy stored, 38 at 43% for cloudy days and 18% for rainy days. The system efficiency is depending of the weather conditions. This heating requirements coverage was very optimistic compared to other studies. Bouadila et al. [57] found the energy efficiency of solar heating system with latent storage energy varied between 32% and 45%. 4.5. Thermal load leveling (TLL) The performance of SHCS has been evaluated, as an active system for the greenhouse, in terms of TLL (Eq. (6)). The use of this term is to quantify the fluctuations of inside air temperature. The TLL should have lower value, during the winter period, by integrating heating method leading to the increase in the term (Tin,max + Tin,min) and the decrease in the term (Tin,max-Tin,min) as compared to TLL without heating equipment for favorable environment and crops growth [52,58]. The results for daily variation of TLL with and without solar system are illustrate in Fig. 10. These results show that the high values of TLL are recorded inside the control greenhouse and the minimum values in the experimental greenhouse, with a reduction in temperature fluctuations of about 30%. The lower values of TLL mean that the fluctuations of air temperature decrease and thereby, improve the desired environment for crop inside the greenhouse equipped by SHCS. 4.6. Agronomic performance

Fig. 6. Recovered and stored thermal energy during 25 at 27 January 2017.

The 20 plants are randomly selected in each greenhouse. These plants are spread over 4 rows (5 plants/row). We measured the height and the yield of each, also the tomato production for each harvest in the two greenhouses. In this section, we analyze and discuss the effect of solar system on crop growth and agricultural production of tomatoes.

Fig. 7. The stored and recovered thermal energy by SHCS system in February 2017.

Fig. 8. Variation of mean ambient temperature and global solar radiation on days of February 2017.

Please cite this article as: A. Bazgaou, H. Fatnassi, R. Bouharroud et al., Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.101

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nocturnal temperature is improved. Moreover, the increase of nocturnal temperature improves the plant height in heated greenhouse compared to unheated one. Gourdo et al. [60] and Bazgaou et al. [51] confirm also this positive effect of solar heating systems on the growth of tomato crops.

Fig. 9. Efficiency of solar heating cooling system in February 2017.

Fig. 10. Thermal load leveling of experimental greenhouse and control greenhouse as a function of days (February 2017).

4.6.2. Tomato production Fig. 12 shows the comparison of tomato production for each harvest in the greenhouse equipped by SHCS and the control one during the 8 harvesting periods. We observed the tomato production in experimental greenhouse is higher compared to than that of control one from the 1st until the 7th harvest with a difference of 24 kg as a maximum value. The integration of the SHCS in greenhouse application is able to improve the agricultural production by 29% of normal production [51]. These results are in agreement with Canakci and Akinci [61] that show the heating is a process to improve the yield of tomato crop. Concerning the agronomic efficiency, an increase of 1.74 kg/m2 in agricultural yield was observed. This suitable agronomic effect of the solar heating systems on agricultural yield was also reported by Bargach et al. [38], who found an gain of 20 g/plant (i.e. 10 g/m2 with a density of 0.5 plant/m2) on the melon production using a solar flat plate collectors. Similarly, Goudro et al. [53] show that the integration of a solar system with rocks as a thermal storage material increases the tomato yield by about 22% i.e. 1.2 kg/m2. The heating process increases the yield of the tomato, but its combination with another cooling process is more profitable. The performance of SHCS in greenhouse production was due to the improvement of the climatic conditions under the greenhouse given the better conditions for the development of tomato crop as shown in the Section 4.5.

4.6.1. The average height of tomato plants Fig. 11 shows the average height of tomato plants in experimental and control greenhouses as a function of days after planting. The figure also illustrates the difference in average height of plants in the two greenhouses. The effect of solar heating cooling system is clear in the 7th day after planting inside the first greenhouse compared to the second one. The difference in average height increases with time, such as varied between 1.5 cm in the first week after system operation and 35 cm in the end of cycle. This gain in average height improves the number of bouquets, consequently the tomato production. These results are in agreement with those of Adams et al. [59] which showed, in their studies, that the positive effect on the growth and development of tomato plants is observed when the

The heating costs in greenhouse production represent, generally, a large part of production costs. In some cases, energy consumption in greenhouses accounts for 50% of the cost of greenhouse production. In Mediterranean regions, during winter period, the greenhouse encounters overheating problems during the day due to intense solar radiation and extreme cold at night. Hence, the use heating and cooling systems to produce crops throughout the year is necessary. The solar heating cooling system proposed in this study has shown a significant gain in yield and profit, particularly, in cold period.

Fig. 11. The evolution of the average height in the two greenhouses and the difference between them as a function of days after planting.

Fig. 12. Tomato production during harvest period in both greenhouses.

4.7. Economic analysis

Please cite this article as: A. Bazgaou, H. Fatnassi, R. Bouharroud et al., Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.101

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Table 3 Economic analysis of solar heating cooling system. SHCS costs (EUR/m2)

Total costs (EUR/m2) Exportable yield (Kg/m2)

Quartzitic sandstone Labor Energy cost Control Greenhouse Experimental greenhouse

Difference of yields Kg/m2 Average gain of Yield % Average profit of the heating system (EUR/m2) Average profit of the combined heating system (EUR/ha)

0.75 0.44 0.12 1.31 5.97 7.72 1.75 29% 0.46 4635

To evaluate the economic profitability of this SHCS system, we have computed the profit of the tomato crop for 8 harvesting periods with a density of 2 plants/m2. The cost related to the installation of this system in the greenhouse, with an area of 165 m2, is around of 0.75 EUR/m2 including transport (1 EUR = 10.70 MAD). The energy cost of conventional systems per month can reach 1.03 EUR/m2 [62,63]. In this work, the SHCS energy cost is around 0.12 EUR/m2. These results show the efficiency of the solar system used in this study in comparison to other systems. In the standard production of tomatoes under canarian greenhouses, with a density of 2 plants/m2, is about 5.97 kg/m2. The solar heating cooling system improved this value to 7.72 kg/m2, giving a difference in yield of 1.75 kg/m2 and an average gain of 29%. The average profit of this system is 0.46 EUR/m2 i.e. 4635 EUR/ha as shown in table 3.

5. Conclusion The solar heating cooling system, with quartzitic sandstone as a thermal storage material, to improve inside greenhouse microclimate was evaluated. This storage material is the best candidate used in a thermal storage system due to large amount stored SATE. The use of SHCS has significantly improved the inside air temperature and reduced the relative humidity at night, and the reverse during the day with less fluctuations. A beneficial effect of heating and cooling greenhouse with this SHCS system positively influences the tomato development and increase its production. From the economic point of view, the cost/benefit and financial profitability analyses demonstrated that the heating and cooling greenhouse with this SHCS system is very profitable and could generate profits for farmers. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This work was financially supported by CNRST (Centre National pour la Recherche Scientifique et Technique, Morocco) in the framework of the PPR2015/56 project. Special acknowledgments are dedicated to L. Hamouch director and A. Taoufik technician of INRA experimental farm for their technical assistance on the field. References [1] B. Von Elsner et al., Review of structural and functional characteristics of greenhouses in European Union countries, part II: typical designs, J. Agric. Eng. Res. (2000).

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Please cite this article as: A. Bazgaou, H. Fatnassi, R. Bouharroud et al., Efficiency assessment of a solar heating cooling system applied to the greenhouse microclimate, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.101