International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
Performance Evaluation of a Solar Still
Integrated with a Greenhouse
Shristhi Shrestha1, Sarad Shrestha2, Pradip Bawari3
1
Lecturer Electrical and Electronic, Centre for Computer and Communication Technology.
Chisopani, South Sikkim
2,3
Bachelor in Mechanical Engineering, Bengal Engineering and Science University
Abstract : The present work discusses the
performance evaluation of a solar still integrated
with a greenhouse for the climatic conditions of
Gangetic Bengal which witness a hot and humid
climate for greater part of a year. A thermal model
as available in literature [3] has been used for
analyzing the performance of the greenhouse
integrated solar still for the climatic conditions of
Gangetic Bengal. Plant and water temperature, as a
function of climatic and design parameters, were
obtained by solving coupled single-order differential
equations using the Runge-Kutta method. A
computer code has been developed using MATLAB
software to compute the greenhouse room air
temperature, temperature of the transparent cover,
basin liner temperature and the mass of the distillate
along with the plant and water temperature. The
study revealed that the maximum amount of distillate
production took place in the month of April and is
significantly high during the other summer months.
This distillate can be used as potable water for use
in rural areas where it is scarce. Thus, this
integrated system reinforces the viability of
generation of substantial amount of fresh water
along with sustainable crop production in the rural
parts of Gangetic Bengal in Indian subcontinent.
Keywords — Stand still, green house, solar
distillation, Runge Kutta
I. INTRODUCTION
In India the solar radiation is abundant and the
climate in the plains is rather hot and dry for greater
part of a year especially during the summer, while
the coastal parts witness a hot and humid climate.
The excessive heat is detrimental to the growth of
the plants. So for a greenhouse installation located
in the plains of Gangetic Bengal, the main objective
is cooling. Also in the plains of Indian subcontinent,
there is considerable scarcity of potable water. In the
present work a greenhouse has been considered to be
integrated with a solar still to facilitate a conducive
microclimate for the growth of plants and
simultaneous production of fresh water which can be
utilized for drinking and irrigation. Thus, solar
distillation unit integrated with greenhouse system
may be a viable solution not only to provide the
modest demand of good quality water to closed
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system cultivation, but also to maintain controlled
temperature by reducing the effect of sensible heat
load addition to the greenhouse. All the incoming
solar radiation may not be the cooling load for the
greenhouse. About 2% of the total transmitted solar
radiation is used in photosynthesis. Though the rate
of transpiration varies from crop to crop but 48% of
the transmitted solar radiation is used for this
process [2]. The rest of the 50% of solar radiation
needs to be removed by the cooling system. The
utilization of that 50% solar radiation in the
distillation system in conjunction with greenhouse
provides dual advantages of reducing cooling load
for the greenhouse and also supplying fresh water to
the inside plants [2]. If this technology is
successfully implemented, the desalination of water
can be produced in a cost effective manner and also
our dependence on fossil fuels for desalination can
be reduced.
II. BASIC BLOCK OF THERMAL MODEL
A. SOLAR ENERGY
Solar energy, radiant light and heat from the sun,
has been harnessed by human beings since ancient
times using a range of ever-evolving technologies.
Solar Energy is clean and environmental friendly
renewable energy source. Solar energy is very large
and inexhaustible. The power from the sun
intercepted by the earth is about 1.8 x 1011 MW [1],
which are many thousands of times larger than the
present consumption rate of all commercial energy
sources. Its major advantage is that it is an
environmentally clean source of energy and is free
and available in adequate quantities in almost all
parts of the world. Solar energy technologies include
solar heating, solar photo voltaic, solar thermal
electricity and solar architecture, which can make
considerable contributions to solving some of the
most urgent problems the world now faces.
B. SOLAR STILL:
Fresh water is the essence of life and is a basic
human requirement for domestic, industrial and
agricultural purposes. Increasing human activities
like urbanization, population explosion, pollution
caused by industrial, agricultural and domestic
wastes have resulted in large escalation in demand
for fresh water in the recent years. Solar still can be
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
a method of production of pure water.
The
technology for distillation of water using solar
energy was known to mankind since long. Earlier
designs attempted to generate salt from the sea water.
Documented use of solar stills began only in the
sixteenth century for production of fresh potable
water and to purify liquids [2]. An early large-scale
solar still was built in 1872 to supply drinking water
to a mining community in Chile. Mass production
occurred for the first time during the Second World
War when 200,000 inflatable plastic stills were made
to be kept in life-crafts for the US Navy [2]. The
solar still is a model of the water cycle on earth
comprising of evaporation, condensation and
precipitation. Solar still uses the greenhouse effect
to trap energy from the Sun. Distillation can be a
simple process–heat is first added to a liquid to
evaporate it and form vapour. Then heat is removed
from the vapour to condense it back to liquid. The
incident solar radiation is transmitted through the
glass cover and is absorbed as heat by a black
surface in contact with the water to be distilled. The
water is thus heated and gets converted into water
vapour. The vapour condenses on the glass cover,
which is at a lower temperature due to contact with
ambient air and this condensed water is pure which
runs down into a gutter from where it is ultimately
fed to a storage tank.
C. GREENHOUSE
Optimal growth of plants results when favourable
environmental conditions in terms of temperature,
humidity, intensity of light and carbon dioxide
prevail. Thus, every type of flora grows successfully
in a typical season. Greenhouse can be defined as an
artificially constructed sophisticated structure that
provides near to ideal conditions for plant growth
and production round the year. Inside environment
of a greenhouse is controlled by controlling the plant
growth factors like light, temperature, humidity, air
composition, air circulation rate etc. Cultivation of
crops in greenhouse is increasing from high altitude
and temperate regions to the warmer regions of
tropics and subtropics. During summer months,
cooling is considered to be the basic necessity for
greenhouse crop production in tropical and
subtropical regions to overcome the problems of
high temperatures.
III. LITERATURE REVIEW
A lot of research and development works have
been carried out in greenhouse cum solar still and
related technologies for decades together and quite a
good number of publications are available in the
literature. Srivastava and Tiwari [3] developed a
thermal model for performance evaluation of a
distillation-cum-greenhouse system as a function of
design and climatic parameters. Numerical
computations were carried out for a typical day in
January for Chennai, India. Plant and water
temperatures, as a function of climatic and design
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parameters, were obtained by solving two
simultaneous single-order differential equations
using the Runge-Kutta method. Greenhouse air,
transparent cover, basin liner temperature and
distillate output were also worked out by using
the value of plant and water temperature.
Analysis showed that there was a significant
effect in the plant, water temperatures and distillate
output due to a change in the fraction of the
solar radiation incident on the north wall, depth of
water, and the inclination of the roof whereas the
heat capacity of the plant had a marginal effect on
the temperatures and distillate output. The study
revealed that vegetables can be grown in a warm and
humid climate in a coastal region by the construction
of a distillation-cum-greenhouse unit. Eugenio et al.
[4] studied the performance of a solar still integrated
in a greenhouse for Mediterranean climatic
conditions in south-eastern Spain. The desalination
module was equipped with 28 water basins located
at the top of an experimental greenhouse. The inner
surface of the roof was used as a condensation
surface and the fresh water produced was collected
in a storage tank. Fresh water production and hourly
variation of the distillate were evaluated. Contrary to
what happens in traditional solar stills, distillation
took place after solar noon and during the night due
to the low absorption of solar irradiation when the
solar still is integrated into a greenhouse. They
concluded that installation of solar still reduced the
radiation inside the greenhouses the temperature in
crop area stayed below the proper limits. The solar
still integrated in a greenhouse roof did not produce
a considerable amount of fresh water compared to
conventional solar stills, nor did it follow the same
distillation pattern. This is because it was necessary
to use transparent basins to transmit the maximum
solar radiation to the crop area. Radhwan et al.[5]
presented an experimental investigation of the
thermal performance of an agricultural greenhouse
with a built-in solar distillation system. A set of
solar basins with saline water were placed on the
greenhouse roof to reduce the greenhouse cooling
load and to produce the required fresh irrigating
water by solar distillation. The ventilation air
entered the greenhouse through an evaporative
cooler for cooling in summer, and was partially recirculated for heating in winter. The combined
greenhouse-solar distillation system utilized
abundant solar energy in hot climates to partially
reduce greenhouse cooling load in summer, and
to partially produce required irrigation water by
solar distillation. The results indicated that the
greenhouse inside temperature was 8 to10 degrees
less than the ambient temperature. Chaibi et al. [6]
carried out a study to analyze differences in seasonal
crop yields between greenhouses with solar-still
desalination and conventional roofs in arid climates
because in greenhouses with roof-integrated water
desalination, solar transmission is reduced by an
absorbing glass sheet covered by a layer of flowing
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
water and a top glass sheet. A simulation model of
the thermal and optical performance of this system
was detailed. The yield reduction was about 25% for
a desalination case with the capacity to cover the
water demand corresponding to a lettuce crop.
Goosen et al. [7] developed a thermodynamic model
with an aim to develop humidification–
dehumidification desalination technology for farms
in arid coastal regions who suffer from salt infected
soils and shortages of potable groundwater. The
specific aim of their research was to determine the
influence of greenhouse-related parameters on a
process, called Seawater Greenhouse, which
combines fresh water production with growth of
crops in a greenhouse system. A thermodynamic
model was developed based on heat and mass
balances. The dimension of the greenhouse had the
greatest overall effect on the water production and
energy consumption. Sablani et al.[8] performed a
thermodynamic simulation study on the influence
of
greenhouse-related
parameters
on
a
desalination process that combines fresh water
production using humidification-dehumidification
with the growth of crops in a greenhouse. In this
system, the surface seawater trickles down a
porous front wall evaporator through which air is
drawn into the greenhouse. The saturated air
passes through a condenser, which is cooled
using cold deep seawater or cool seawater coming
out of the evaporators. Analyses showed that the
dimensions of greenhouse (i.e., width to length
ratio) had the greatest overall effect on water
production and energy consumption. The overall
water production rate increased from 65 to 100
m3.d-1 when the width to length ratio increased
from 0.25 to 4.00. Similarly the overall energy
consumption rate decreased from 4.0 to 1.4
kWh.m-3 when the width to length ratio
increased from 0.25 to 4.00. Ghosal et al. [9]
developed a mathematical model for the analysis of
solar desalination system combined with a
greenhouse for both composite and warm humid
climate
of
India. They derived analytical
expressions for water temperature, greenhouse
room air temperature, glass cover temperature,
flowing water mass flow rate over the glass cover,
hourly yield of fresh water and thermal
efficiency in terms of design and climatic
parameters for a typical day of summer and
winter period. Temperature rise of flowing water
mass with respect to distance and time in solar
still
unit were also incorporated
in
the
mathematical modeling. The yield of fresh water
was found to be higher in warm humid climate
than composite climate. It was found that the yield
and the fall in greenhouse maximum room air
temperature decreased with increase of flow rate.
The yield in Chennai (warm humid climate) was
higher than that in Delhi (composite climate). A
detailed simulation model was developed for
analysis of the thermal and optical characteristics of
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the desalination system concept by Chiai [10]. The
work described laboratory experiments with a small
roof
module and
presented measurements
compared to simulations obtained in order to
validate the thermal model of the system. The
laboratory work was carried out with artificial light
from a solar simulator operated in a nicely controlled
thermal environment. The main conclusion was that
a good agreement was obtained between simulated
and measured variations of fresh water production
values for various design and operational parameters
of the system. The most important indication was
that geothermal water at elevated temperatures
combined with this roof technology was the
alternative with the highest water production
capacity. M.T. Chiai [11] presented a simulation
model for fresh water production and derived
performance parameters for a water desalination
system integrated in a greenhouse roof. Several
typical daily weather patterns taken from a 10-year
period for three arid regions in Tunisia were
analyzed .The most important conclusion was that
the roof-integrated still concept had a fresh water
production capacity on a sufficient level for
irrigation of plants in a greenhouse environment.
Thermal modeling, based on heat and mass transfer
relations, of a greenhouse integrated with a solar still
were discussed in details by Lawrence et al. [12].The
effect of the system (viz. heat capacity of plants/pot
mixture, water mass, and orientation, etc.) as well as
climatic parameters (solar insolation, ambient air
temperature and ventilation due to wind, etc.) were
incorporated in the energy balance for various
components of the system in order to validate the
theoretical results. An experiment was carried out
for a typical greenhouse in Port Moresby. It was
observed that the amount of distilled water obtained
was sufficient to grow the plants inside the
greenhouse. K.Voropoulos et al. [13]experimentally
investigated the validity of a basic model widely
used for the simulation of dynamic behaviour of
solar stills in the case of a real-scale greenhouse-type
still. The different modes of heat and mass transfer
were analyzed on the basis of continuous
measurements of the main working parameters of
the still. Davies et al. [14] developed a prototype
seawater greenhouse which combined a solar
desalination system within environment for
cultivating crops in which transpiration is minimized.
Results from the prototype greenhouse were used to
calibrate a computational fluid dynamic model. The
model was used to evaluate three proposed options
for improving the performance. Sampath Kumar et
al. [15] reviewed different studies on active solar
distillation system. Thermal modelling was done for
various types of active single slope solar distillation
system. From this review of literature, it is inferred
that considerable work in terms of experimental and
model development have been done with respect to
greenhouse integrated solar still in the last few
decades.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
IV. THERMAL MODEL DEVELOPMENT
A schematic diagram of a solar still integrated
greenhouse, indicating the solar energy absorbed by
the roof and wall is shown in Fig. 1. The absorbed
solar radiation by the basin liner is partially
transferred to water mass and the rest is transferred
to the greenhouse through conduction, convection
and radiation. The stored energy in the water causes
evaporation of the same, which later condenses to
form fresh water. The remaining solar energy that is
transmitted is absorbed by the plants and the floor.
The absorbed energy is finally transferred to the air
inside the greenhouse through convection and
radiation from the plants and thus the greenhouse air
gets heated. A part of the energy absorbed by the
floor is also conducted to the ground.
Fig1. Schematic diagram of a solar still integrated
with greenhouse
A. Basic Assumption:
Following assumptions have been made while
developing the thermal model of the greenhouse
integrated solar still:
i) The analysis is based upon quasi-steady-state
condition.
ii) Heat capacity of air inside the greenhouse is
neglected in comparison to the heat capacity of
plants.
iii) Properties of the plant mass have been
considered to be equivalent to water mass for all
thermal analyses proposed due to a high content
of water in the plant.
iv) Moist air in the solar still and greenhouse
cover, solar still bottom, plant and soil surfaces
are saturated.
v) No stratification in temperature of the basin
liner, water, transparent cover, plant and
greenhouse enclosure has been considered due to
the low unit operating temperature range.
vi) Ground heat loss from the floor to the ground
is considered in the steady-state mode.
B. Thermal Model Development :
In this section a thermal model as available in
literature [3] has been used for analysing the
performance of the greenhouse integrated solar
still for the climatic conditions of Gangetic
Bengal. The details of the thermal model have
been discussed in the subsequent paragraphs.
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Table I: Input Parameters to the Thermal Model
SL. Area Value(m2) SL. Area Value(m2)
No.
No.
1
Ad
3
6
Ar
104
2
Ae
15
7
As
45
3
Ag
90
8
Asr
52
4
An
45
9
Aw
18
5
Anr
52
10
Ap
200
The energy balance for the different components
of the solar still-cum-greenhouse is as follows:
Basin liner: The amount of energy incident in
the form of radiation is partly absorbed by the
water mass and the rest is transferred to the room.
Thus, mathematically
(1)
The L.H.S of Eq. (1) denotes the rate of
energy absorbed by the basin liner, while the first
term in R.H.S of Eq. (1) represents the rate of
energy transferred to the water and the second
term represents the rate of energy transferred to
the room. In Eq. (1), denotes the absorptive of
the solar still basin, denotes the transmissivity of
the basin liner and represents the transmissivity
of the water mass ,represents the fraction of solar
radiation which is incident on the roof of the
greenhouse, while
is the Convective heat
transfer coefficient from basin liner to water. In
the present work the value has been considered
to be 0.2 [3], and has been considered to be 0.9
[3] and has been taken as 100 W/m2 0C [3].
Water mass: The amount of energy available in
water is partly stored in water as thermal energy
and the rest is transferred from water to the
transparent cover. Thus mathematically,
The L.H.S of Eq. (2) denotes rate of energy
absorbed by the water mass while the first term
in R.H.S of Eq. (2) represents rate of energy
transferred to water mass by conduction and the
second term represents the rate of energy
transferred to the condensing cover. In Eq. (2) h1
denotes the overall heat transfer coefficient from
water to the condensing cover whose value in has
been assumed to be 12.5 W/m2 0C [3].
Condensing cover: The amount of energy
available to the transparent cover from the water
is lost to the surrounding by radiation. Thus
mathematically,
(3)
The L.H.S of Eq. (3) denotes rate of thermal
energy available on condensing cover from water
mass while R.H.S of Eq. (3) denotes the rate of
thermal energy lost from transparent cover to
ambient. It denotes the convective and radiative
heat transfer coefficient from cover to ambient.
In the present work, its value has been assumed
to be 9.5 W/m2 0C [3].
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
Greenhouse plants: The amount of solar flux
absorbed by the plants is partly stored as thermal
energy within the plants and the remaining part of
it is radiated, convected and evaporated to the
greenhouse. Thus mathematically,
(4)
L.H.S of Eq. (4) represents the rate of solar flux
absorbed by plants in the greenhouse, while the
first term in R.H.S of Eq. (4) denotes the amount
of solar energy stored by plant and the second
term denotes the rate of thermal energy
transferred to the greenhouse by radiation,
convection and evaporation. In Eq.(4) αp denotes
the absorptivity of the plant, Fn denotes the
transmitted fraction of solar energy available to
north wall, τ denotes the relative humidity, Sw the
intensity of solar radiation available on the wall
and hp represents the heat transfer coefficient
between the plant and enclosure air of the
greenhouse. In present work the value of αp, and
have been considered to be 0.4, 0.2, 0.05 and 0.7
[3] respectively. The value of has been considered
to be 5.7 W/m2 0C [3].
Greenhouse floor: The amount of solar flux
available to the floor is conducted and convected
to the enclosed air of the greenhouse.
Thus mathematically,
The L.H.S of Eq. (5) denotes rate of solar energy
absorbed by the greenhouse floor and the first term
in R.H.S denotes rate of energy transferred to the
greenhouse by conduction and the second term
denotes the rate of energy transferred to the
greenhouse by convection. In Eq. (5)
denotes the
absorptivity of the floor
is the heat transfer
coefficient between the floor and the air of the
greenhouse. In the present work the value of
has
been considered to be 0.3 [1] and the value of
has
been considered to be 5.7 W/m2 0C [1].
Greenhouse enclosed air: The amount energy
available to the enclosed air of the greenhouse from
the sun, plants, floor and basin liner is partly
transferred to the room by convection and radiation,
partly stored in the room and rest lost to the ambient
from canopy cover, door and ventilators.
Thus mathematically,
enclosed air of the greenhouse and the third term
denotes rate of energy transferred to enclosed air by
radiation and convection. The first term in R.H.S of
Eq. (6) denotes rate of thermal energy stored by
greenhouse air and the final term denotes
rate of
energy lost by the greenhouse air to ambient through
canopy cover, door and ventilators. In Eq. (6)
is the overall heat transfer coefficient from
inside of the greenhouse to ambient through walls
and roofs,
is the heat transfer coefficient between
room air and ambient through the door of the
greenhouse, is the number of air changes taking
place in the greenhouse to maintain the required
condition, is the volume of greenhouse and
denotes the evaporative heat transfer coefficient
from the plant to the enclosed room. In our present
work as per our assumptions
~ 0.0 and the
value of N has been taken as 1 [1]. Also
,
and
are considered to be 5.4, 3.99, 48.45 W/m2
0
C [1].
Our objective is to find the plant temperature,
and
water temperature,
from the six equations which
have been deduced from the energy analysis of the
model [1]. We substitute the other temperature terms
(viz.
, ,
,
) by expressing them as a
function of plant temperature and water temperature.
Doing so we get two differential equations in terms
of and
which can be represented as follows:
+
And
+
=
(t)
(7)
+
+
=
(t)
(8)
In Eq. (7)
=-(
= (
)/(
+
)
-
(9)
) /(
(10)
(11)
In Eq. (8)
(12)
(13)
(14)
Here denotes absorptivity,
is product of
absorptivity and
denotes the fraction of solar
energy absorbed by the plants.
In Eq. (9)
(15)
(16)
(17)
The first term in L.H.S of Eq. (6) denotes rate of
solar energy absorbed by enclosed air of the
greenhouse, second term denotes rate of energy
radiated, convected and evaporated from plants to
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In Eq. (10)
(18)
(19)
In eq. (11)
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
(20)
(21)
(22)
In Eq. (12)
(23)
In Eq. (20),
The fraction of solar energy absorbed by greenhouse
air is given by,
(24)
The fraction of solar energy absorbed by greenhouse
floor is given by,
system. As evident from the figure, the solar
radiation intensity increases from 6:00 AM to 12
Noon and then it again decreases. The maximum
solar intensity of radiation is about 776 W/m2. The
graph also shows the hourly variation of
corresponding ambient temperature which also
shows a similar trend, first increasing with time of
the day, reaching a peak and then again decreasing.
(25)
And the fraction of solar energy absorbed by basin
liner is given by,
(26)
In Eq. (21)
(27)
The value of and
can be worked out from Eq.
(7) and Eq. (8) by application of classical fourth
order Runge - Kutta method by using the input
parameter of table 1 [1] and the climatic condition as
provided [1]. After knowing the value of the plant
and water temperature, the other parameters like the
value of the enclosed room air temperature ,
condensing cover's , basin liner temperature ,
, and the mass of the distillate output can be
determined with the help of following expressions:
(28)
Fig. 2: Hourly variation of solar intensity It, Id and
ambient temperature Ta for a typically warm and humid
day of April.
Fig3 shows the variation of plant and water
temperature for the month of April considering the
data plotted in Fig.2. It is observed that there is a
significant variation in water temperature and the
maximum temperature reaches nearly to 500C
around 3 PM which leads to better evaporation of
water from the still resulting in higher amount of
distillate. It is also found that the plant temperature
varies very less compared to the variation in ambient
temperature and water temperature. It is seen from
the curve that the development of a greenhouse
integrated solar still.
(29)
(30)
(31)
In Eq. (31)
denotes the rate of evaporative heat
transfer from water surface to the condensing cover.
Now,
(32)
is the mass of distillate output.
RESULT AND CONCLUSION
Computer codes were generated using MATLAB
software to analyse the performance of the system
using the thermal model discussed above. The model
considers ambient temperature and intensity of solar
radiation as input and predicts the greenhouse room
air temperature, condensing cover temperature, basin
liner temperature and the mass of the distillate for a
given set of constant parameters. In present work the
analysis has been done for three different months
representing three different seasons of a year, while
cumulative distillate output has been computed and
presented graphically for all the months of a year.
Fig 2 shows the hourly variation of intensity of
global and diffused solar radiation for a
representative day in April in Kolkata. The same has
been used to calculate the sensible heat load to the
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Fig.3: hourly variation of plant temperature (Tp) and water
temperature (Tw) of a day in April.
Fig 4 shows the hourly variation of intensity of
global and diffused solar radiation for representative
day in June (representing hot and humid climate) in
Kolkata. The same has been used to calculate the
sensible heat load to the system. As evident from the
figure, the solar radiation intensity increases from
6:00 AM to 12 Noon and then it again decreases.
The maximum solar radiation intensity is around 659
W/m2 at 12 noon and the maximum ambient
temperature is 35 0C at 1:30 PM.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
and the maximum temperature reaches nearly to 31
0
C around 3 PM which leads to better evaporation of
water from the still resulting in higher amount of
distillate. It is also found that the plant temperature
varies very less compared to the variation in ambient
temperature and water temperature similar to what is
observed for the month of April and June. It is seen
from the curve that the plant temperature varies
between 18 to 26 0C which is very conducive for
cultivation of target plants.
Fig. 4 Hourly variation of solar intensity It, Id and ambient
temperature Ta for a typically warm and humid day of
June.
Fig.5 shows the variation of plant and water
temperature for the month of June considering the
data plotted in Fig.4 as input. It is observed that
there is a significant variation in water temperature
and the maximum temperature reaches nearly to 47
0
C around 3 PM which leads to better evaporation of
water from the still resulting in higher amount of
distillate. It is also found that the plant temperature
varies very less compared to the variation in ambient
temperature and water temperature. It is seen from
the curve that the plant temperature varies between
28 to 32 0Cwhich is very conducive for cultivation.
Fig.5 : Hourly variation of plant temperature (Tp) and
water temperature (Tw) in a day of June.
Fig 6 shows hourly variation of intensity of global
and diffused solar radiation for a representative day
in November (representing hot and humid climate)
in Kolkata. The same has been used to calculate the
sensible heat load to the system. As evident from the
figure, the solar radiation intensity increases from
6:00 AM to 12 Noon and then it again decreases.
The maximum solar radiation intensity is only about
560 W/m2 at 12 noon and the maximum ambient
temperature is 30 0C at 1:30 PM.
Fig.7: Hourly variation of plant and water temperature in a
day of November.
Considering the three cases discussed above it can
be seen that there is a little difference between the
plant and greenhouse inside air temperature
especially during the off peak hours of a day. With
the increase in ambient temperature, the room air
temperature increases and thus the plant temperature
also increases. The maximum plant temperature is
recorded in between 1:00 pm and 2:00 pm. After this
interval the plant temperature begins to decrease.
The water temperature increases with the increase in
solar intensity of radiation. Also, as the ambient
temperature increases with the time of the day, the
heat transfer rate increases and thus the water
temperature also increases.
Fig 8 shows the monthly variation of mass of
distillate output in Kolkata. The mass of distillate
increases during the first three months and attains a
maximum value in April with a collection of approx.
2700 kg of distillate. There is a marginal decrease in
distillate production in May followed by a sharp
increase in the month of June. Again in September,
the mass of the distillate production increases and
after that it goes on decreasing for subsequent
months. It is maximum for the month of April as in
the month of April the intensity of solar radiation is
high coupled with high ambient temperature and low
relative humidity which favours quick evaporation
of water from the solar still which later condenses to
give fresh water.
Fig. 6 Hourly variation of solar intensity It, Id and ambient
temperature Ta for day in November.
Fig7 shows the variation of plant and water
temperature for the month of June considering the
data plotted in Fig.6 as input. It is observed that
there is a significant variation in water temperature
ISSN: 2231-5381
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Page 157
International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 3- March 2016
Fig.8: Monthly variation of mass of distillate output.
V. SUMMARY OF WORK AND CONCLUSION
In this project work, a thermal model of a
greenhouse integrated solar still as available in
literature [3] has been presented and analyzed for the
climatic conditions of Gangetic Bengal that witness
abundant solar radiation for greater part of a year.
From the study it is observed that for various
seasons of a climatic cycle, the variation in
greenhouse inside air and plant temperature is much
less compared to the temperature of the water in the
solar still. This will help to maintain a favourable
climate in the greenhouse for cultivation of target
flora and at the same time maximize the yield of
fresh water through distillation. The results of the
thermal model also indicate that the distillate output
is maximum during the month of April and is
significantly higher during the summer months
which can be used for generation of potable water
for use in rural areas where it is scarce. Thus, this
integrated system reinforces the viability of
generation of substantial amount of fresh water
using solar energy which would otherwise increase
the cooling load on the structure along with
cultivation of target plantation in greenhouses in the
rural parts of Gangetic Bengal in Indian
subcontinent.
[12] Yusuf Bilgiç, Cengiz Yıldız"The Effect of Extended Surfaces
on the Heat and Mass Transfer in the Solar Distillation Systems",
International Journal of Engineering Trends and Technology
(IJETT), V22(3),129-137 April 2015. ISSN:2231-5381.
www.ijettjournal.org. published by seventh sense research group
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