Revue des Energies Renouvelables CER’07 Oujda (2007) 265 - 268
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Heating an agricultural greenhouse by using geothermal energy
Y. Babi 1*, A. Dobbi 1, M. Saighi 2 and B. Bouchekima 1
1Laboratoire de Développement des Energies Nouvelles et Renouvelables, Université de Ouargla, Ouargla, Algeria
2Laboratoire de Mécanique des fluides et Systèmes Energétiques, Université des Sciences et de la Technologie Houari Boumediene, Algiers, Algeria
Résumé - La géothermie est une énergie gratuite et renouvelable, qui peut participer considérablement dans l’économie, notamment dans le domaine de l’agriculture. L’insuffisance du maintien d’un climat adéquat au développement des plantes, dans la serre a interrompu une production en continu des produits cultivés, par conséquent une élévation de son prix de vente serait justifiée. A cet effet, et afin de remédier à cet inconvénient, nous avons mené une étude expérimentale et une modélisation du climat qui s’intéresse en premier lieu au chauffage des serres agricoles au moyen de l’eau géothermale, et voir sa répercussion sur le climat de la serre et par conséquent sur sa production agricole.
Keywords: Agricultural greenhouse - Geothermal water - Crop production - Solar greenhouse.
I. INTRODUCTION
Geothermal reservoirs of low to moderate temperature are used for heating homes, offices and greenhouses, aquaculture and food-processing plants and other applications. These applications provide a savings in energy costs to the consumer and produce only a very small percentage of the air pollutants emitted by burning fossil fuels.
Geothermal energy is not depending on climatic conditions. It allows to create an energy supplying structure from local resources. Since there are no expenses for fuels, geothermal energy is not directly depending upon the conditions of the international energy markets. Because of its special character, geothermal energy is an appropriate source for power generation, heat supply, cooling, energy storage, agricultural uses, fish farming, desalination of water, development of tourist and balneological applications and for health purposes.
Geothermal energy involves the lowest specific investment cost for gas reduction in comparison to other renewable energy sources. Geothermal energy is available for the consumer anytime, whenever there is need for it: 24 hours a day irrespective of the time of the day or night, independent of weather and climate. Geothermal energy is base-load energy. It offers the basis for a general energy supply from renewable sources. Anybody who is heading towards an overall application of renewable cannot pass geothermal energy. Those are the reasons why geothermal energy is one of the sustainable energy sources most widely used on earth.
The aim of our research in South Algeria is to use geothermal energy sources for greenhouse heating: to develop plants for crop production at lower temperatures and to improve the efficiency of this heating system.
2. GREENHOUSE HEATING
It is very important to determine the flow rate needed for irrigation in an oases during the heating period in order to calculate the appropriate area of the greenhouse project and to avoid water disequilibrium between heating and irrigation purposes. Theoretically, the greenhouses can
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exploit the maximum flow rate from the well, but for better use and optimization of geothermal resources without any losses of using a model for calculation of peak loading.
- It is necessary to calculate the total heat loss from the greenhouse in order to determine its heat demand from the geothermal water. The inside air temperature (Fig. 2, 3), is the internal temperature of the greenhouse. It can be called the reference temperature that is required by the crop during the night to ensure favorable conditions for its growth. The temperature value used is the minimum temperature desired to be maintained inside greenhouse during the heating period.
This value is chosen as the most favorable temperature for a crop during the night.
3. DESCRIPTION OF THE EXPERIMENTED GREENHOUSE
The greenhouse (Fig. 1), is located in Ouargla, in the south of Algeria. Climatic conditions in the region are characterized by low and high ambient temperatures during winter and summer, respectively. The absolute minimum during winter is close to -5 °C, while the mean minimum is close to 4 °C. During the summer period the absolute maximum is close to 43 °C.
Fig. 1: Arrangement of pipes
4. THERMAL BALANCE IN AGRICULTURAL GREENHOUSE At the covert
r chpi cond i l
i , ae l
i , ai c
i , al c
i , ai r g IR i i
p Q Q Q Q Q Q Q Q
t d
T C d
Vi = a + i + + + + + + (1)
Sensitive heat
ch c
i , v ren c
s , ai c
i , ai ai ai
ai Q Q Q Q Q
t d
T C d
V = + + + + (2)
Latent heat
ETP l
ren 1
p , ai l
s , ai ai ai ai
at Q Q Q Q
t d W V d
L = + + +
ρ (3)
Balance at ground
cond s c
s , ai l
s , ai r s s gs s s s
s Q Q Q Q Q
t d
T V d
C ρ = + + + + (4)
CER’2007: Heating an agricultural greenhouse by using geothermal energy 267 5. EXPERIMENTAL RESULTS
Fig. 2: Comparison between temperatures of outside air and inside in heated greenhouse
Fig. 3: Relative humidity: heating greenhouse (WC) and controlled greenhouse (WT)
Fig. 4: Measured and calculate temperature at type day of January
Fig. 5: Calculate and measured of relative humidity at a type day of February
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6. CONCLUSION
This research work concern the development of greenhouses heated by geothermal water in the southern of Algeria for producing commercial out-of- season vegetables and fruits (tomatoes, melons,...).
The experimental results (Fig. 4, 5) obtained are satisfying to develop this technique in the near future for supply population in these regions where the geothermal water, clean and free energy, exists on abundance.
NOMENCLATURE
Qsga Solar power, W Qlai Evaporation of water in
ground
QrIR Power by IR radiation, W Qla,pi Evaporation/condensation at inside wall
Qcai Convection between inside air and wall, W
Qlren Enthalpie transfer between inside and outside
Qcrh Power by radiation, W Lai Latent heat of vaporization i
,
Qlai Power by phase change, W QETP Evaporation-transpiration of crop
i ,
Qcond Power by conduction V Volume of ground in
greenhouse, m3 QSgs Solar radiation at ground of
greenhouse, W
C ai Specific heat of inside air (cal/kg°C)
QrS Power by radiation at ground, W
t d / T d V
Cai ai i Stocked energy in inside s
,
Qlai Power by latent heat (evaporation), W
Qcai Power by convection s
,
Qcai Power by convection at ground, W
ai
Qc Power by convection
between inside air and ground
s ,
Qlcond Power by conduction across ground, W
Qrend Power by renewal inside dry air
x Thick of ground, cm Qch Power by geothermal water
ai ,
Qcv Power by convection at crop
REFERENCES
[1] K. Popovsky, ‘Application Directe de l’Energie Géothermique en Agriculture, en Aquaculture et dans l’Industrie Alimentaire’, Yougoslavie CNRE, Article N° 4, FAO/CNRE, pp. 353 – 367, 1992.
[2] T. Boulard, E. Rarafnjohany and S. Baille, ‘Heat and Water Vapor Transfer in a Greenhouse with an Underground Heat Storage System - Part 1: Experimental Results, Agricultural and Forest Meteorology’, Vol. 175, pp. 175 – 184, 1989.
[3] C. Souter, ‘Use of Geothermal Energy for Agricultural Purposes’, Proceeding of the National Conf. on Geothermal Energy, pp. 148 – 158, 1989.
[4] A. Clot, 1977, ‘La Géothermie Basse Energie’, La Recherche, Vol. 8, N°76, p. 219, 1977.
