Upgrading HVAC and Control Systems for Energy-Efficient Greenhouses

This report reviews the upgradation of HVAC and control systems in commercial greenhouses, specifically focusing on applications in the Middle East's climatic conditions to enhance crop yield while maintaining an energy-efficient approach. The review covers conventional and sustainable green...Read More

A review on
upgradation of HVAC
and Control systems of
commercial green
houses in Middle East
Climatic Conditions to
increase the yield with
an energy efficient
approach.
Mattara ChalillSubin, Ramanujam
Karthikeyan, and Snehaunshu Chowdhury
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Keywords: Sensible heat; Greenhouse
HVAC; latent heat; cooling load
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Introduction
Open field agriculture has a lot of constraints
in maintaining consistent crop production, such
as unfavourable topographical conditions and
environmental conditions like fluctuating
temperature, humidity etc. They typically provide
secure environments for having the better growth
of plants in the present controlled environment
with optimum temperature, humidity, ventilation,
air-velocity, and soil moisture content
conditions. Greenhouse farming started the
revolution of mechanized farming automation
with automatic climate as well as fertigation
mechanisms (Baptista and et. al. 2000).
Still, popular control systems utilize heating,
making use of carbon dioxide enrichment along
with ventilation in order to provide suitable
conditions for plant growth. Gerasimov &
Lyzlova propose the implementation of a
controller system based on these parameters to
enable farmers to monitor their greenhouses
online. The primary objective associated with this
review is to summarize the various studies carried
out in the field of mechanized greenhouse
farming to develop a cost-effective sustainable
commercial greenhouse using evaporative
cooling technology in conjunction with automatic
climate control and different covering material
upgradations. These could broadly be divided
into two categories: (i) Major factors related to
HVAC systems and related controls in all types
of green house system which consists of both
commercial and Sustainable greenhouses and (ii)
Associated factors influencing the HVAC
systems and related controls. The sustainable
greenhouse has given much more priority than
the commercial form of agriculture through
leading up gradation in HAVC system and related
controls in green house as a sustainable form of
greenhouses activities are helpful in reducing the
need of precious natural resources like land and
water and at the same time and in a
simultaneously way sustainable greenhouse also
leads to higher yields per unit area and enhanced
productivity as compared to a field grown crops.
1. Materials and methods
1.1 Conventional Greenhouse Heating
ventilation and air-conditioning (HVAC)
Systems
Existing greenhouse systems, I.e.
Conventional Greenhouse systems are
considered as experiencing high heat loss rates
due to the high energy demands of the materials
used to construct the greenhouse envelopes. As
Ganguly & Ghosh explained, greenhouses that
have cooling and ventilation systems need
constant supply of electricity. The use of fan
driven cooling pad system is basically made to
taking away the heat generated by the supplying
components as the pad and fan systems which
consist of exhaustive fans at the basic one of the
end of the greenhouse along with a circulating
water pump at other end through and over a
porous pad which is mainly installed at the
another opposite end associated with the
greenhouse provides. Further to ensures and to
maintain a constant level of temperatures all the
vents and associated doors are being closed when
the fans operate. Thus, this driven cooling pad
systems is helpful in removing energy from the
air which leads to a lower the temperature of the
air being introduced into the greenhouse
(Baptista et. al. 2010). The cooling process was
highly inefficient as it seemed to not achieving
its maximum productivity and also leading to a
high amount of wastage of resources and also
seemed to failing in making the best use of
limited time and resources. This high level of
inefficiency is seen in the process of
recirculation as it has been observed that the
conditioned closed space in the conventional
green house is done without the use of air grills
on the top or sides which reduces its efficiency
and lead to a poor and inefficient process that
require much more time and resources. In many
mechanical systems, use of metal blades on the
axial fans, reducing their efficiency of operation.
Deployment of a large workforce to maintain and
regulate the indoor variables like, temperature,
relative humidity etc.is also forms a vital factor
gar is giving significant affect in the value of net
realization which is mainly caused by range
recurring of a cooling pad along with the
recirculation system maintenance. Figure 1 show
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the photographic view of the existing green
house.
Figure 2 - 3D View of the Exterior of the Conventional
Greenhouse Ventilation
Figure 3- Sectional view of the Conventional
Greenhouse Ventilation
In recent years, large number of the
researchers have dwelt on the control of factors
affecting the indoor conditions of the
greenhouses. Researchers have investigated the
efficiency of using specifically designed HVAC
systems (Bot, 1983) as well as the use of wet
pads (Coelho, de Moura Oliveira, and
Boaventura Cunha, 2005) and spray cooling
(Bot, 1989) Natural ventilation is taken as the
most fundamental and vital technique that
facilities education in the usage of energy while
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making buildings. This phenomenon is based on
the fact that of rage cooling power and capacity
of an ambient air could be easily harnessed to
increase the overall level of indoor thermal
comforts which is vital and necessary required to
have mechanical space conditioning lessens.
Apart from this, the concept of Natural
Ventilation is based on natural forces which
comprises of use of wind from the natural
surrounding environment along with the
buoyancy forces which get developed by the
temperature gradients present within building. In
order to take advantage of either deriving force
or the combination of both building can be
designed in a proper way (Beven and Binley,
1992). Further, being an old technology still the
natural ventilation serves and leads to enhanced
experience of recent resurgence of better meeting
interest mainly in Europe where a large number
of major research initiatives is seemed to
conducted to evaluate this vital concept of
natural ventilation.
1.2 Sustainable greenhouse
Greenhouse structures enhance developing sit
uations of vegetable, fruit
and decorative vegetation.
Commercialgreenhouses protects flora from unfa
vourable atmospheric dealers and, collectively wi
th appropriate gadget, impacts and in the
end modifies the crop
microclimate, consequently lengthening
the market place accessibility of
products, enhancing their high-satisfactory and p
ermitting better yields. Thus,
the consistent global growth within side
the region protected via way of means
of greenhouses has led to enhanced generation of
the want for growing sustainable blanketed hortic
ulture. Sustainable-greenhouse horticulture may
be finished via way of means of method of
various
2. MAJOR FACTORS AFFECTING THE
UPGRADATION OF HEATING
VENTILATION AND AIRCONDITIONING
SYSTEMS AND ASSOCIATED CONTROL
SYSTEMS.
Sustainable greenhouse horticulture is
mainly associated with use of various means of
different cultivation techniques along with some
better management and use of adequate upgraded
equipment along with the innovative materials.
The basic and true aim of sustainable greenhouse
is at reducing the agro-chemicals other energy
use and water consumption along with leading
reduction in waste generation to moves towards a
more sustainable and vital greenhouse which
leads to enhancement in production with
optimum use of resources. It has been analysed
that the up gradation of heating ventilation and
use of air conditioning systems which are
associated control systems lead to a more
adequate and upgraded form of tools and
technique to build and structure a more efficient
and better sustainable green house (Boaventura
Cunha, 2003).
2.1. Greenhouse Ventilation
For the successful growth of crops in
agricultural greenhouses, there is a need to
control and to maintain temperature and
humidity at optimum levels. These optimum
conditions are a necessity for the successful
survival and yield of the crops. Settles et al. did
an analysis using a basic greenhouse model to
identify the controlled parameters like
temperature, relative humidity and air velocity
for plant growth in early days. The Control
parameters mainly consists of the factors that are
the one which can be controlled or managed as
per the need. With respect to current Green
house ventilation the various controllable factors
comprise of temperature, relative humidity and
air velocity for plant growth in early days which
are taken into full control and can be managed as
per the need and requirement.
In a common way it has been that the
structure of used as a ventilation vent that’s
forms a part of greenhouse would have a much
significant impact on the level of the ventilation
of the greenhouse. Greenhouse structures, design
and geometry comprises of structure ir model
which is prepared to conquer the adversity of
external which comprises of the wind, rain,
snow, etc. Along with the environmental factors,
and internal consists of live and dead loads in
order to have maximizing of the solar radiation
that is available for the crop. The structural
components of greenhouse and their geometry
are seemed to directly affected or associated with
the solar radiation transmission (Bot, 1989b).
The geometry of the greenhouse designs is
basically reflected in terms of ratio of expected
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length and width which is mainly seemed to have
a length of each was assumed to be 30 m, were
as the widths is taken were around 10, 10 and 8,
respectively to maintain the proper geometry and
design of green house. Various studies have been
carried out to understand the effect of the vent
structure and orientation in commercial
greenhouses (Albright and et. al 2001).
Generally, the ventilation system has been
classified as three which on the basis of green
house design and construction comprise of side,
roof and the combination of the two in
greenhouses.
Commercial greenhouses that utilize
conventional air conditioning systems are not as
effective in terms of cooling, and with a
humidity controls they ought to be, with the
possibility that they are operating at half of their
microclimate control potential. The concept of
the microclimate is mainly defined as a
fundamental factor which is based on the
temperature, humidity and speed of moving air.
Thus, the microclimate control potential system
is mainly designed for having a climate control
of a sustainable greenhouse for increasing or
lowering the temperature and relative humidity.
The use of only natural ventilation is made and
the forced ventilation is not taken into account as
the many additional equipments and tools are
required by the forced ventilation which leads to
and resulted in form of increase in the cost of
green house. Thus, to maintain the cost
efficiency and ensures a greenhouse with
normally advisable use of techniques implication
of natural ventilation is made and use of Forced
ventilation is not made (Coelho, de Moura
Oliveira, and Boaventura Cunha, 2005).
2.1.1. Natural Ventilation
Natural ventilation is the best suitable
mode of ventilation for commercial greenhouses,
if the external weather conditions are moderate
in nature. Thus, CFD (computations fluid
dynamic) are predict according to the mode and
are verified from experimental data but Not all
are verified with experimental data as it could be
complex and time consuming process. Apart
from this the use of both CFD model and
analytical model is made. The CFD model
which stands for Computational fluid dynamics
modelling is basically based on the set of
principles which comprises of fluid mechanics
and utilizing numerical methods and algorithms
in order to solve and analysis a given problem in
more effective and better way through making
use and involvement of fluid flows.
Apart from this, the Computational fluid
dynamics Model can also be utilised to integrate
chemical reactions along with a combustion
processes within which the fluid flows are used
to provide a three-dimensional understanding of
boiler performance. Therefore, implication and
utilisation of Computational fluid dynamics
models attempts and have a main aim to have
more effective analysis of problems and facts
through simulating the interaction among various
forms of liquids and gases where the surfaces are
defined by boundary conditions (De Zwart,
1997). Beside this, the Computational fluid
dynamics model are also useful and effective in
tracking the flow of solids through a system by
employing the principles of the Navier-Stokes
equations. Simulations are then conducted by
solving the equations iteratively as either a
steady-state or transient condition to have better
analysis and understanding of the collected data.
Thus, as the CFD modelling is having a
dominance in the field and it also lead a
significant and more specific applications to fuel
blending and the behaviour of fuel blends thus, it
is applied and adopted in Greenhouse to have
better analysis of data to form a more effective
and vita decisions regarding the flow of air and
temperature tend to keep inside the green house
to maintain a proper microclimate.
On the other hand, the analytical model,
basically represents a set of mathematical models
and other statistical tools and techniques to have
a close form of solution to support enhanced
decision making and conclusion. The analytical
model makes and apply use of equation to
describe the changes which are taken in a system
and can be expressed as a mathematical form of
analytic function (Dincer, and Cengel, 2001).
Therefore, the main aim of analytical model
comprises of effective use of mathematical
analytical functions and models to have a closer
and effective results and solutions for a problem.
Enveloped a greenhouse model which can log
the controlled variables in a greenhouse located
in Lisbon. Hornero et al. studied the green house
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ventilation variance using two dimensional
lattice. The two parameters which are studied
comprises of temperature and the relative
humidity the variance of which are used and
taken to have analysis about the green house
ventilation variance. This particular model was
successfully checked for single span and
multispan greenhouses. Improvised the naturally
ventilated greenhouse model to predict the
micro-climate inside the greenhouse. The term
micro climate mainly comprises of information
about the inside environment (microclimate) and
conditions present in a greenhouse which is
mainly influenced by factors such as. light,
temperature, humidity and carbon. dioxide
concentration (Du, Bansal and Huang, 2012).
Patil and Tantu used various regression models
to study the temperature variance in a naturally
ventilated greenhouse. Furthermore, subsequent
researches were carried out to predict the indoor
climatic conditions of naturally ventilated
greenhouses using tracer gas, sonic anemometers
etc. The exact conditions which are used is based
on the indoor climatic conditions inside the
greenhouse to provided an area where plants are
grown in a controlled atmosphere. The various
variables on which the indoor climatic conditions
depend comprises of Humidity, temperature and
sterility are all environmental conditions kept at
a constant by a greenhouse. Further the expected
temperature kept under the indoor climatic
conditions and air velocity ranges from 80 to 85
degrees Fahrenheit (Effat, Shafey and Nassib,
2015). American society of Agricultural
Engineers recommend a ventilation rate as 0.04
m3s-1. The results which are discussed are
obtained from analysis of proper temperature
(ranges from 80 to 85 degrees Fahrenheit) and
relatively humidity for better growth and
enhanced productivity of crops. In other studies
conducted by Bazea et al., ventilation rates
between 0.36 kg s-1 to 1.65 kg s-1 for a
greenhouse produced maximum yield. Many of
the studies about l ventilation variance was
validated using computational fluid dynamic
techniques in order to compare the results with
natural ventilation (El Ghoumari, Tantau and
Serrano, 2005). Rate of Ventilation variance
were taken to be developed to select the most
relevant parameters which are leading significant
influencing on the performance and also these
confirmed that they are associated with the
surface area of the vent-opening along with the
wind speed together with the explaining the
largest part of the taken variance of air exchange
rate measurements.
2.1.2. Fan induced Ventilation
Ventilation supplemented using the axial and
roof mounted fans, blowers, motors etc. can be
categorised under forced ventilation or fan
induced ventilation. Fan induced ventilation can
control the indoor temperature of the greenhouse
to the ambient level or even lesser. The
evaporative cooler in simple words can be
defined as a fan equipped green houses
ventilation combinations used under the
conventional greenhouse combinations. Further,
An evaporative cooler which is also commonly
known as swamp cooler, swamp box, desert
cooler and wet air cooler is basically a device
that is used and lead to cools air through the
evaporation of water. Further studies were
carried out for developing a simple model of fan
ventilated greenhouse with fan pad evaporative
cooling system. This gained wide acceptability in
the past due to reduced quantum of investment
and improved yield (Kittals et al.) Developed a
successful mathematical model to determine the
cooling potential of a fan pad evaporative
cooling system. Temperature and humidity
gradient models were determined for a
commercial greenhouse and the variance was
found inside the green house and on the
temperature that is set out to be 5 oC to 10o C.
This work was provided by the Kittal who had
also improved the model by including shading
factors (Haefner, 2005).
A Fan induction ventilation system that is
making use of mounted fans, blowers, motors etc
for one or more zones is vital to have better
control over management and inside conditions.
Greenhouse ventilation forms a most important
and crucial part of any sustainable or other form
of greenhouse which involves removing air from
inside the greenhouse and replacing it with
outside air. Having proper ventilation is
important and vital for green house as when the
water get evaporated, heat energy is lost from the
air which reduces its temperature thus, proper
mounted fans, blowers, motors etc are needed to
maintain proper flow of air and ensures an
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effective ventilation system (Hameed and
Sorensen, 2010). Further, it has been also
observed that the and pad system has been the
taken as most standard and vital standard system
for evaporative cooling. Beside this, for having
proper vitalisation in each zone, a Fan induction
ventilation system includes a heat exchanger
which is taken as a means for leading a better
driving of a heating or cooling the liquid through
the way of using an effective heat exchanger, on
the basis of some adjustable flow rate that leads
to primary air injector and also comprises of a
secondary air induction inlet along with a more
effective and better zone temperature control.
Table 1 presents an analysis of the literature
sources that inform the review process.
Table1: Reviewed Papers, Approaches, and
Parameters Studied
Author Innovations with the parameters studied
Settles Airflow systems Air flow visualization in a greenhouse
Ishii et al. Natural ventilation Proposed the use of mild pump heating to enhance
cooling in greenhouses in mild climates.
He et al. Greenhouse vents Proposed the use of vent openings to regulate
greenhouse microclimates.
Bartzanas et al. Greenhouse ventilation Proposed a model vent arrangement to enhance
windward ventilation
Wei et al. Experimental evaluation Proposed the use of removable back walls in greenhouse
ventilations.
Zhou et al. Dehumidification Proposed the use of outdoor heated air through a heat-
release system.
Joudi and Hasan Solar-assisted desiccant
system
Utilized a solar-assisted desiccant system to implement
cooling and heating in greenhouses.
On the basis of above stated table
regarding the various innovation with respect to
better ventilation and air flow in a green house it
has been find out that Settles provides a better
innovation related with the airflow systems
which emphasis and focuses on the Air flow
visualization in a greenhouse. Apart from this, it
is also observed that Ishii provides better
information about the natural ventilation which
basically makes use of a mild pump for heating
purpose in order to enhance the level of cooling
in greenhouse especially in mid climates.
Further, a finding about the Green house vents is
also made that basically comprises of a use of a
vent opening which is utilised to regulate and
control microclimate inside a green house.
Beside this, BartZanas also facilitates an
understanding about the Greenhouse ventilation
which leads to enhance windward ventilation
through making use of a better model based on
vent arrangement. At last, it has been find out
that a novel approach for ventilation is provided
by the Katsoulas who proposed a vent opening
innovation in order to improve the ventilation
inside green house by making use of fog
evaporative cooling system. It has been also
observed that the use and application of vent
openings also ensures and lead to improvement
the microclimate inside the green house through
leading a proper effect on the relative humidity
to maintain a proper temperature and ventilation
inside the greenhouse.
2.2. Greenhouse Cooling- Cooling using
Evaporative Systems
Various researchers have explored the
utilization of evaporative systems in temperature
management of greenhouses. An evaporative
system mainly comprises of an intake chamber
along with various filter(s), supply fan, direct-
contact or indirect-contact which act as a heat
exchanger in order to maintain the proper cooling
and temperature inside a greenhouse. Use of
exhaust fan, water sprays, re-circulating water
pump, and water sump etc are made to have a
proper and efficient evaporative-cooling systems
which are mainly characterised by low energy use
compared with a refrigeration cooling system.
Further, use and implication of fan and Pad
Evaporative Cooling Systems are also made
which uses the heat in the air to evaporate water
from plants and other wetted surfaces inside the
greenhouse that can be used to cool the
greenhouse as much as 10 to 20ºF below as
compare with the outside temperature. Joudi and
Hasan studied the effectiveness of using
absorption type evaporative coolers in the
Baghdad. The sun blocks are used as a shading or
upgraded covering material which act as an
energy curtains and plays a vital role in
controlling the light and heat levels in the
greenhouse. Thus, it has been observed by the
researcher that Sun block are used as for
regulating light levels and trapping in (or out) the
heat to maintain a proper inside microclimate and
temperature through all the change of season and
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make it more easier to keep better condition
inside the green house for better growth of crop
through having on the right track through just
about any season. Apart from this that Sun block
are also useful in acting a covering material for
crop that ensures proper amount of heat and light
and at the same time also blocks and eliminates
the harmful UV rays to reach and harm the crop.
Beside this, it has been also observed that the use
of Evaporative cooler is also vital to ensure
effective cooling along with air condition as it has
been analysed that utilisation of Evaporative
cooler are utilised to perform both functions.
Thus, making use and efficient utilisation of
Evaporative coolers is better and suitable while
covering HVAC (Heating, ventilation, and air
conditioning) as it performs both the important
and crucial function if cooling and conditioning
the air (Linker, Kacira and Arbel, 2011).
Figure 4 Box type evaporative cooling system
Figure 5: Air and Water Flow Direction in an
Evaporative Cooler
Effective results from the evaporative coolers
require the cooling pads to be saturated at all
times. The discharge between the fans and
cooling pads also have to be negotiated
effectively employing proper motor controls.
This is a more energy saving along with cost
effective and providing a simple, and much more
environment friendly technique to have better air
conditioning. Evaporative cooling systems are
suitable for high temperature, low relative
humidity ambient conditions. Various types and
forms of evaporative coolers are there which
comprises of indirect, direct and the modified
types of coolers have which been investigated by
past researchers. Use of these units can be for a
more direct contact which are taken as
evaporative cooling unit and also comprise of
units of indirect contact evaporative technique.
The annual total coal requirement for manaintin
and running a HVAC system basically ranged
from the amount of 160.34–466.78 t/ha, along
with the total cost of the while system is taken
between 37,412and 108,916 $/ha. Apart from
this the Total annual fixed on the basis of the cost
per hector was taken to be ranged between
10,325 and 14,328 $/year where as the total
variable cost is also fluctuating and varying from
the 20.1–30.9 $/h. Further, the toatal cost which
was calculated was estimated to the total annual
and hourly costs per ha as up to 65,891.5–
151,220.6 $/year and 23.8–34.2$/h, respectively
(López-Cruz and et. al., 2012a). The upgradation,
therefore, aims at minimizing this cost by the use
of the efficient evaporative coolers, where the
cooling load itself is reduced by using a covering
material appropriate for Middle East’s climatic
condition, Figure 5 shows the structure of such an
upgraded greenhouse.
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Figure 6: Single span Greenhouse with
individual box type evaporative coolers and
ventilation fans (V -flow fans) (EVPC –
Evaporative Coolers)
An in-depth analysis of these factors are
discussed as a part of qualitative analysis along
with leading more concentration and focus on
further evaluation of these factors for making use
as commercial greenhouse (López-Cruz and
Goddard, 2012b).
Page 10 of 25

There are existing technologies which implement
the evaporative cooling technique to manage
temperatures. One such technology system which
reduces air temperature without altering the air
moisture content is the indirect evaporative cooling
system. In such systems, the process air stream not
makes a direct connect with the cooling fluid stream
although there is sensible heat transfer between
them leading to the cooling of one stream. It has
been evaluated that the large water surface has been
provided by the pads or wet porous material in
which the moisture of air contact is more easily
achieved, therefore, the pad or porous material is
continuously wetted through dripping water on it
mainly at from the upper edge of the vertically
mounted pads. The indirect evaporative cooling has
an efficiency of 60–70%. This is providing a
representation and information about the level of
Energy efficiency through evaporative cooling than
direct evaporative coolers as it has been observed
that the evaporating water into the air provides a
much more natural and energy efficient modes of
cooling especially in a low humidity area. Thus, an
analysis can be made that The indirect evaporative
cooling has an efficiency of 60–70% as compared
with the direct evaporative coolers as it cost nearly
about the one-half as much to some other cooling
system and also make use about of only one-quarter
as much energy thus it is more efficient than other
systems (López-Cruz and et. al. 2014).
At the time of high summer temperatures, it
has been observed that the natural and forced
ventilation systems are commonly used as a
greenhouse in order to prevent the rise of inside air
temperature from getting too high i.e from above
the level of desired temperatureIt has been
observed that in the conventional greenhouse
system use of fan is made at one side where as the
other side is covered with a cooling pad which are
termed and taken as packing material for
conventional greenhouse. Thus, here the discussion
about the thickness and width of cooling pad
structure is made which is taken a packing material
and should have a proper thickness to proper rate of
water flow (Luo and et. al., 2005. The authors also
report a pessimistic correlation between
temperature and wind velocity variation as the
forced ventilation reduces the influence and impact
of the wind velocity on the temperature gradient. In
a simple evaporative cooling systems, the
temperature of ambient air resent in the wet bulb
cannot be warmer than the produced air as it cannot
be cooler than wet bulb temperature.
Improved technology using Maisotsenko
cycle can provide a better result in energy friendly
evaporative cooling operation. This cycle is mainly
taken as an indirect evaporative cooling–based
cycle, that makes utilization of a much smarter
geometrical configuration for leading and ensuring
better air distribution. High level of efficiency is
required to achieve this level of geometry of the
cycle which produces cold air temperature which is
mainly lower than the temperature of the wet bulb
ambient. The energy sources of this type of cooler
is water in place of electricity thus, the usage of M-
cycle based leads coolers leads and ensures a more
significant way for energy saving as leads to more
than 80 % saving in terms of average consumption
and use of electricity (Mashonjowa and et. al.,
2013a).
11

The Maisotsenko cycle (M-cycle) in
greenhouse is used as an air-conditioning
technologies which offers better opportunities for
energy conservation and reduction of greenhouse
gas emissions thus leads to better growth of crop.
Further, The Maisotsenko cycle (M-cycle) also
improves the quality of the cooled air and maintain
a proper microclimate and temperature inside
greenhouse without use of any additional inputs for
the return air system. Its utilization also promises
great efficiency gains to the existing system,
making it a feasible, potential cycle for indirect
evaporative cooling systems. Therefore, through the
use of this cycle, it is possible to eliminate the
restrictions due to the use of simple evaporative
coolers and to achieve lower temperatures. Several
authors have reported their experimental findings
or system models regarding this process of
evaporative cooling. Mizushina et al. proved the
effectiveness of evaporative cooling by providing
empirical correlations for ensuring better transfer of
heat and mass coefficients which are taken as
corresponding to three different tube diameters
based on the constant water temperature as a vital
assumption., Kreid et al. and Leidenfrost and
Korenic had investigated the finned evaporative
coolers along with range of other condensers
(Mashonjowa and et. al., 2013b). They used to have
a demonstration about the fins to have significant
improvement in the heat transfer but only at the one
condition of having the wetting of the whole
surface is properly ensured. On the downside,
finned tubes tends to involve a much higher
corrosion and fouling as compared with a straight
one. To sum up, custom-designed evaporative
coolers can provide better performance in terms of
yield management for the commercial greenhouses.
Above discussions has been summarized in the
below tabular format in Table 5.
Table 2: Reviewed Papers, Approaches, and Parameters
Studied
Author Approach
Wang et al. Solar greenhouses
Li et al Regulation of greenhouse microclimates
Aljaburyaand Ridha Evaporative cooling
Haeussermann et al. Fogging systems
Erens & Dreyer Evaporative Cooling
Alahmer. Direct Evaporative cooling system
Mizushina et al Evaporative cooling system
Kreid et al Evaporative cooling system Investigated
2.3. Greenhouse Heating
Different greenhouse heating systems has been
adopted in the past, such as direct air heaters,
central pipe surface heating systems, geothermal
heating etc
Ghosal and Towar developed a greenhouse
model with geothermal energy suitable for freezing
temperature conditions. This study saw the authors
realize a remarkable temperature rise of
while it was freezing outside temperature of the
greenhouse. Carlini et al., through their
experimental study conducted in Viterbo, Italy,
proved the feasibility of geothermal plant through a
TRNSYS simulation and verified the results and
thereby confirming the efficacy of using geothermal
solutions. Table 5 summarizes the list of reviewed
papers with their major findings and conclusions
(Navas, and et. al., 1998).
Table 3: Reviewed Papers, Approaches, and
Parameters Studied
Author Approach A
Burdick Load calculations
Is
an
of
Aljaburya and Ridha Evaporative cooling
Pr
to
gr
Carlini et al Geothermal energy utilization D
ex
2.4 Effects of Utilizing Upgraded Climate
Control Systems (CMS)
The green houses must render controlled
environment for the production of plant with
sufficient humidity, temperature and sunlight. Green
houses requires to exposure to maximum light,
specifically in morning hours. The greenhouse
quality has everything to do with control technology
use in greenhouse. The facilities designed and
outfitted properly efficient systems of HVAC which
will develop better environment to assist in
continuously producing connoisseur grade product.
In order to upgrade the HVAC in greenhouse and
climate control, one of the ways include evaporative
cooling. The system involves cooling pad that is
made of porous material which has water that
flowing through it, keep it saturated on end wall of
greenhouse and at opposite end wall is a large
extraction fan which develops negative pressure in
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