Assessment of the Inside Greenhouse Temperature Heated by a

Storage System

Lalmi Djemoui, Bensaha Hocine and Benseddik Abdelouahab

Renewable Energy Applied Research Unit 47133, Renewable Energy Development Center

CDER,Ghradaia ,Algeria

Keywords: Greenhouse, inside and outside temperature, numerical simulation, Rayleigh and Nusselt number.

Abstract: The ansys fluent R 14.5 computational fluid dynamics Code was used in this study to estimate the inside

greenhouse temperature Heat transfer, radiation and temperature, all this parameters are treated in this study

with differents Rayleigh number values .The external boundary conditions are introduced via User Defined

Functions .Turbulence was modelled by the k- ɛ model and the solar radiation using the Discrete Ordinates

model .The plants are not considered in this study .As a result this study make possible to improve design

of greenhouses and its thermal needs as well as the positioning of heating and cooling systems w and

geometrical configuration.

1 INTRODUCTION

As a complex biological forms and energetic system

in which most heat exchange and mass modes are

involved (Naijun Zhou et al 2017):Radiative,

exchanges by conduction through the soil and walls,

convective exchanges on the surface of the cover,

plants and soil and air exchange due to the

permeability of the greenhouse or ventilation.

The different modes of exchanges defined above do

not have the same importance and some can be

simplified or neglected according to the desired

precision and the simulation objective Nessim

Arfaoui et al, 2017).

The main greenhouse environmental factors, which

are different from the outside, are temperature, light

and humidity. Each of these factors is conditioned in

the greenhouse by its level outside the enclosure, by

the properties of the roofing material and by the

characteristics specific to this greenhouse (F.

Berroug et al, 2011).

Tunnel-type plastic greenhouses are widely used

around the world, especially in the Saharan countries

because of their low investment cost (M. Lazaar,

2004).

These are efficient in winter and spring, where solar

energy is useful and sufficient for greenhouse

production. On the other hand, these greenhouses

lose their effectiveness in summer where, the

climate is very hot, which causes excessive

overheating and strong hygrometries inside (T.

Boulard et al , 2000).

These extreme weather conditions affect the quality

and quantity of the product and promote the

development of certain diseases. On the physical

plane, the greenhouse is a complex energy system in

which all the different modes of thermal and mass

exchange mentioned above (Reski Khelifi et al, 2018).

If they are relatively simple and well known, their

coupling causes difficulties in the modelling of the

system.

In this system, natural convection is a particularly

important mechanism for heat exchange between

indoor air and all other solid surfaces (floor, walls,

roof, culture, air conditioning and heating systems)

(Erdem Cuce et al , 2016).The aim objective of this

study consists to predict the storage system effect at

the thermal behavior of an agricultural greenhouse in

semi-arid climate . The study based on how to

ameliorate the efficient of the production in this

region using its date climate. The outline of this

paper is: We started by an introduction, the Climatic

condition like the solar radiation, outside

temperature, relative humidity and the win speed are

treated in the second parts. The third parts reserved

to the description of the experimental greenhouse

test facility and storage system. In fourth parts, a

numerical simulation of the heated greenhouse was

254

Djemoui, L., Hocine, B. and Abdelouahab, B.

Assessment of the Inside Greenhouse Temperature Heated by a Storage System.

DOI: 10.5220/0009773102540259

In Proceedings of the 1st International Conference of Computer Science and Renewable Energies (ICCSRE 2018), pages 254-259

ISBN: 978-989-758-431-2

presented with interpretation of the obtained results

and we finished by a conclusion and some

perspectives

2 POTENTIAL SOLAR ENERGY OF

AREA STUDY

In this study, experiments were carried out in two

greenhouses at the Applied Research Unit on

Renewable Energy at Ghardaïa from Algeria.

Around of 77% of Algerian area presented arid and

semi-arid regions. The characteristics of this region

(Ghardaïa) are:

•Location 595Km south of the Mediterranean sea

• Latitude and 32°36 N

•Longitude3°80E

•Altitude of 469 m above the sea level

•Rate of sunny days per year: 77%

• Annual daily average of global solar irradiance

about 7 kWh/m

at horizontal surfaces.

Figs.1 shows the global solar radiation variation of

January 2016.It can be seen that the global solar flux

radiation has the same trend variation as the ambient

temperature Fig.2.

It is observed also that the peak of average radiation

is registered in the period of 10 h to 16h (800 W/m

)

with a highest ambient temperature surrounding

30°C. The least average radiation is 200W/m

with

an ambient temperature around 5° C. It can be

conclude that the heating period in this month is a

largest than the storage period. The relative humidity

is a counter variation like the temperature, it can be

seen that high values observed in the morning and

night periodic at the low temperature Fig.3. It can be

conclude in this figure that the relative humidity can

be passed the85 %. Fig.4 shows the average win

speed in the same month. It can be seen that highest

values does not break the 10m/s, it is the calm month

(Lalmi Djemoui et al, 2016).

Figure 1: Global solar radiation variation, January 2016

Figure 2: Temperature variation, January 2016

Figure 3: relative humidity variation ; January 2016

Figure 4: Average speed variation ; January 2016

Assessment of the Inside Greenhouse Temperature Heated by a Storage System

255

0 5500 11000 16500 22000 27500 33000 38500 44000 49500

Inside temperature Outside temperature

2.1 Experimental Investigation

The two tunnel greenhouse test bench complete

occupied and without storage system are shown in

the Fig 5. It has a height of 3m, 25m of length and

8m of width, which leads to a volumetric of

528m3.The greenhouse has a north-south direction,

with optimal deviation angle of 32° to the West. It

has doors (opening) at the side walls create for

ventilation (Efrén Fitz-Rodríguez et al, 2010).

The polyethylene covers the experimental

greenhouse with a low density. The thermal

proprieties of the cover material are presented in the

Tab. 1(Serm J et al, 2011)

Figure 5: The two experimental greenhouses test facility in

URAER

2.2 Experimentation and results

In the two greenhouses with and without storage

system, courgettes plants are transplanted on the 27

th of December 2017 and the harvesting started on

the 14 th of March 2018.

The major environmental factors that affect the

growth and the precocity of the production of

greenhouse plants are temperature, light and

humidity.

The courgettes plants have two optimum

temperatures, one during the day; which varied

between 24 and 32 °C, and the other nocturnal

temperature that is the most crucial temperature

varied between 16 and 19 °C. A courgettes crop

(local variety) was planted in both greenhouses and

planted at 20 plants in the row and arranged in (8)

eight rows with 30 cm between the rows and 20 cm

between the plants.

Fig.6 shows the yearly inside and outside

temperature evolution in 2016. It can be seen that

the inside temperature is larger than the outside

temperature. It is clear to see that in the hot months

the inside temperature can reach 65°C hover in the

cold months is taken the small values like 5°C. It is

important to say that heating is necessary in the cold

month and especially during the night. In the author

hand the ventilation is necessary in the hot months

like the august.

Figure 6: Yearly instantaneous temperature

Inside and outside the greenhouse

3. NUMERICAL STUDY

The flow inside the greenhouse is assumed to be

two-dimensional (2d), incompressible and turbulent.

Geometrical configuration with all boundaries

condition considered in this study showed in the

Fig.9

The airflow and the heat transfer are describe by the

Navier stokes equations. The time average Navier

stokes equation, for the mass, momentum and

energy transport are solved using ansys Fluent

14.5.Physical properties of the air confined in the

greenhouses are given in the Tab.1. Turbulence was

treated via the re k- ɛ model, and the radiation

modelling was simulated using the DISCRETE

Ordinate model.

Figure7: Problem Position and boundary condition for

tunnel greenhouse

3.1. Dynamical and thermical field

The Streamlines and isotherms of temperature

are shown in Fig.8 for different Rayleigh numbers

(Ra). The fluid flow intensifies and natural

convection increases and predominates on

conduction. The heated air particles at ground level

rise along the wall then, the cooled particles in

ICCSRE 2018 - International Conference of Computer Science and Renewable Energies

256

contact with the roof flow approximately the others

wall.

The influence of the Rayleigh number on the

streamline plots (right) and the isotherms (left) was

illustrated. For the different Rayleigh numbers the

flow characterized by two air circulation loops of the

stream lines.

For low Rayleigh numbers (Ra = 10

), the

isotherms of temperature are parallel. This

representation presented the domination of the

conduction for heat transfer.

As Rayleigh number increases, isotherms

become more and more wavy and heat transfer

becomes more pronounced. As a result, fluid flow

intensifies and natural convection increases and

dominates. The heated air particles at ground level

rise along the wall. Then, the cooled particles in

contact with the roof flow approximately a median

plane.

Figure8: left :isothermes right: isolines for Ra

=10

, Ra=10

Ra =10

Fig.9. shows the axial (right) and radial (left)

velocities evolution. It can be seen that the large

values of the radial velocity situate in the medium

axis in the heated particles rise to the roof .However

the large values of the axial velocity situate

approximately at the wall.

Figure9:Radial and axial velocity evolution

Figure10: saturation presuure and Relative

humidity evolution

The saturation pressure and relative humidity are

shown in Fig.10. We can see that there are same

evolution of the pressure and temperature and there

are counter evolution between the relative humidity

and the temperature.

The effect of the solar radiation at the air

behavior inside the greenhouse was presented in

Fig.11. The temperature evolution in three hours of

day at morning, midi and at night was presented in.

It can be seen that in the day the temperature can be

reach the 38°C but in the night decrease to 14°C.

Figure11:Temperature of radiation evolution at

morning, midi and night

Assessment of the Inside Greenhouse Temperature Heated by a Storage System

257

3. 2 Heat Transfer Exchange Evolution

The heat transfer evolutions inside the

greenhouse for different Rayleigh numbers are

represented by the local Nusselt number have been

given in Fig.12 and Fig.13.

Therefore, the logic is respected as long as there

is a concentration of isotherms at the corners

(ground), which explains a large number of Nusselt.

It is found that for a small Rayleigh number

varying between 10

to 10

the Nusselt number is

small, the conduction that dominates. With Rayleigh

number increase, the exchange rate increases and the

local Nusselt number becomes important. The rate

transfer can be given according to the mean Nusselt

number Fig.13.From these results; we can observe

the good according between the literature and the

present work for different Rayleigh numbers.

Figure12: Local Nusselt Number evolution

Ra =10

, Ra =10

Ra =10

Figure13: Mean Nusselt number evolution

Ra =10

, Ra =10

Ra =10

4. CONCLUSIONS

The study has an objective to estimate the

temperature inside a greenhouse doted with a storage

system .The study was focused on the use of the

environmental data climate to ameliorate the thermal

performances of the greenhouse during the in the

winter season. The obtained results have been

validate with the last work and the literature .We

have also shown that for the our imposed conditions

for low differences temperature between floor and

roof, the air circulation is characterized by two

recirculation cells rotating in the opposite direction.

Therefore, this study should make it possible to

improve the thermal design of greenhouse as well as

the positioning of heating systems with thermal

storage and geometrical configuration.

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Material

Density

[kg/m3

]

Specific

heat

capacity

Cp[J/kg.K]

Therma

conduct

ivity

[W/m.k

]

Emissivity

,ɛ[-]

Air

1.225

0.042

1006.43

0.90

Cover

(polyethyl

ene )

923.00

0.380

2300.00

0.70

Soil

1300.0

1.000

800.00

0.92

Table 1: Thermal proprities of materials

Assessment of the Inside Greenhouse Temperature Heated by a Storage System

259