Greenhouse Subsystem Interoperation Report

Subsystem Interoperation report
of Prototype Greenhouse
Installation
Adapt2change – LIFE09 ENV/GR/296 “Adapt
Agricultural Production to climate change and limited water supply”

Final Version 2012-07-23

Subsystem Interoperation report study – adapt2change greenhouse units – Larissa 2012

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Disclaimer
This document describes work undertaken as part of the 01/11/2011 tender between the
TEI of Larissa and the Emmanouilides and GreenGears Ltd consortium. All views and opinions
expressed therein remain the sole responsibility of the authors and do not necessarily
represent those of the Institute.

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Table of Contents
1

Introduction ....................................................................................................................... 7

2

General description of Greenhouse installation ............................................................... 9
2.1
2.2

3

Closed Greenhouse ................................................................................................. 11
Expected energy conservation in greenhouse horticulture .................................... 12

Effects of Environmental Conditions on Plant Growth ................................................... 14
3.1

Plant growth parameters ........................................................................................ 14

3.1.1

Light ................................................................................................................. 14

3.1.2

Temperature .................................................................................................... 15

3.1.3

Relative humidity ............................................................................................. 15

3.1.4

Carbon Dioxide ................................................................................................ 15

3.1.5

Air Speed.......................................................................................................... 17

3.1.6

Pollutants ......................................................................................................... 18

3.1.7

Root Environment ........................................................................................... 18

3.2

Environmental Control ............................................................................................ 19

3.2.1

Solar Radiation................................................................................................. 19

3.2.2

Energy Conservation........................................................................................ 21

3.2.3

Humidity Control ............................................................................................. 21

3.3

Estimating Heating and Cooling Loads .................................................................... 23

3.3.1

Heating ............................................................................................................ 23

3.3.2

Cooling ............................................................................................................. 23

3.4
3.5
4

Greenhouse Energy Conservation ........................................................................... 24
Insect Screens .......................................................................................................... 25

Prototype Greenhouse subsystems ................................................................................ 26
4.1

Geothermal subsystem ........................................................................................... 27

4.1.1
4.2

Closed loop heat exchangers ........................................................................... 27

Geothermal climate-conditioning system description ............................................ 28

4.2.1

Closed loop heat exchanger dimensioning...................................................... 28

4.2.2

Geothermal system Dimensioning .................................................................. 29

4.2.3

Horizontal Closed loop heat exchanger with closed and indirect pipe network
30

4.3

Control unit.............................................................................................................. 35

4.3.1

Open loop controller ....................................................................................... 35

4.3.2

Closed loop controller ..................................................................................... 36

4

4.4

Control Unit Design ................................................................................................. 37

4.4.1

Control Unit ..................................................................................................... 38

4.4.2

Controller Architecture.................................................................................... 38

4.4.3

Inter-operational connections ......................................................................... 39

4.5

Air recycling subsystem ........................................................................................... 40

4.5.1

Condensation and air recycling network ......................................................... 40

4.5.2

Ventilation system (metallic air duct) ............................................................. 40

4.5.3

Cooling system (cold condenser)..................................................................... 40

4.5.4

Air heating system (heat exchanger) ............................................................... 42

4.5.5

U-shaped heat exchanger................................................................................ 42

4.6

Analogical Blinds ...................................................................................................... 42

4.7

Cooling – natural ventilation subsystem ................................................................. 42

4.7.1

Natural ventilation........................................................................................... 43

4.7.2

Cooling ventilation........................................................................................... 44

4.7.3

Subsystem operation ....................................................................................... 44

4.8

Hydroponics............................................................................................................. 46

4.8.1
4.9
5

The Hydroponics subsystem ............................................................................ 46

Thermal-cooling panels ........................................................................................... 46

Operation Mode .............................................................................................................. 49
5.1

Closed Greenhouse ................................................................................................. 49

5.2

Semi-closed Greenhouse operation ........................................................................ 49

5.2.1

Daytime cooling ............................................................................................... 50

5.3

Subsystems Inter-operation .................................................................................... 50

5.4

Semi-closed Greenhouse automated functions during summer ............................ 51

5.4.1

Scenario 1 ........................................................................................................ 51

5.4.2

Scenario 2 ........................................................................................................ 53

5.4.3

Scenario 3 ........................................................................................................ 55

5.4.4

Scenario 4 ........................................................................................................ 57

5.5

Semi-closed Greenhouse automated functions during winter ............................... 60

5.5.1
5.6

Scenario 5 ........................................................................................................ 60

Closed Greenhouse automated functions both during summer and winter .......... 63

5.6.1

Scenario 1 (summer – closed G.H mode) ........................................................ 63

Scenario 2 (summer – closed G.H mode) ........................................................................ 65
5.6.2

Scenario 3 (summer – closed-semi closed G.H mode) .................................... 67

5

5.6.3
7

Appendices ...................................................................................................................... 71
7.1

8

Scenario 4 (winter – closed G.H mode) ........................................................... 69

Appendix I ................................................................................................................ 71

References ....................................................................................................................... 72

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1 Introduction
Achieving sustainability is one of the main challenges the agriculture industry faces today,
since the EU Water Framework Directive 2000/60/EC, the Groundwater Directive
2006/118/EC and the Common Agricultural Policy are pushing further towards minimizing
soil and water pollution in order to reach “good ecological status” for EU water bodies.
Furthermore, sustainable resource management and food security while dealing with the
effects of climate change is yet another challenge for the industry.
The introduction of innovative greenhouse installation methods could be an effective
solution for all of these issues. Sustainability also depends on production costs, which are
usually calculated per m2 or ha of the cultivated area or even per plant in the case of
greenhouses. Production costs represent about 70 - 80% of greenhouse total chain costs,
with water and energy consumption being the main factors affecting these costs. This
greenhouse project minimizes production costs by introducing water and air recycling
combined with shallow geothermal energy use. Given the fact that the amount of excess
energy required for water recycling in greenhouses is enormous, shallow geothermal energy
is a cheap renewable energy resource that can actually provide this amount of excess
energy.
In greenhouses, water supply is a key factor because it carries nutrients and reduces plant
temperature through transpiration. Nevertheless, plant transpiration might not be enough
to reduce plant and greenhouse air temperature. Thus, many techniques have been
developed in order to achieve ambient air cooling as well. All of these techniques involve
water spraying for heat absorption. Because of the higher temperatures within a
greenhouse, water evaporates and is rejected through ventilation system. Farmers then
need to re-compensate for this loss by pumping more water into the greenhouse, an
imitation of the natural transpiration process in essence. Water vapor concentration and
recycling can fully recover water losses within a greenhouse. The energy requirements for
this process are enormous but of low enthalpy. For this reason, shallow geothermal energy
use is the perfect energy resource for this project. The advantages of shallow geothermal
energy reclamation are quite obvious:




It can be found anywhere and it is a renewable energy resource.
The infrastructure required is based on relatively low tech equipment, which can be
applied easily anywhere.
Integrated geothermal energy systems have a considerable advantage over
independent utilization of other renewable energy resources because the
disadvantages of renewable energy like instability in energy production , do not
apply.

The stable, widely distributed and flexible nature of geothermal energy is highly appreciated
in recycling and thermal systems and it has a key role in project’s greenhouse system. The
project suggests that the use of soil heat capacity can provide in any greenhouse all-yearround low cost thermal energy. Shallow geothermal energy is the low-temperature heat
found a few meters underground, stemming mainly from soil solar heat retention during the

7

day. Shallow geothermal energy is widely stored, huge in amount, rapidly renewable, easy to
collect and valuable for sustainable development.
Apart from energy cost minimization, through shallow geothermal energy exploitation water
recycling can save up to 90% of greenhouse irrigation needs. Recycling water can reduce
pressures on water resources, while providing high quality greenhouse agricultural products.
Water recycling as a process is also linked to the control of environmental conditions within
a greenhouse by balancing temperature and humidity.
The project’s demonstration units are fully controlled by a state–of-the-art automation
system, which is based on Distributed Control Systems (DCS) and the use of decentralized
elements or subsystems to control distributed processes. A DCS typically uses custom
designed processors as controllers and a both proprietary interconnections and
communication protocol. Input and output modules form component parts of the DCS. The
processor receives information from input modules and sends information to output
modules. The input modules receive information from input sensors in the process and
transmit instructions to the output devices in the field. DCS presents certain advantages
over traditional monolithic control systems:
 Installation cost reduction due to fewer required input/output wiring.
 Scalability which affects total system size. Theoretically, a DCS can be scaled up to a
high extent as the added peripheral control systems communicate with the central
unit through a higher capacity communication protocol. Traditional control systems
present a bottleneck as they become large, resulting in system delays or missed
events.
 Greater flexibility in hardware due to its decentralized nature.
 Greater flexibility in software development due to the autonomous operation of
each control unit.
 Energy compliance due to its ability to meet prevailing energy conditions.
Remote Control Support (RCS). This Adapt2change project will generate a fully automated
greenhouse system. Although the proposed system is highly sophisticated, it can easily be
controlled even by inexperienced personnel. The system will support Remote Control
Support (RCS) for users. Through this module, farmers will be able to consult with partners
for production requirements and they in turn will be able to monitor and advise farmers in
real time.

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2 General description of Greenhouse installation
This Adapt2Change project proposes a new concept for water and energy management in
greenhouse agriculture. Greenhouses are used as solar heat collectors, where water can be
found in both vapor and liquid state. Thus, water circulation is the basic means of thermal
energy transfer within the greenhouse, powered by solar radiation. The proposed
sustainable greenhouse water-energy management system operation is described in the
following steps, as shown in Figure 2-1:
An air recycling cooling duct around the greenhouse is installed containing two air-towater heat exchangers, which cool and/or heat the air. The process begins with the
increase of air temperature inside the greenhouse, triggering plant transpiration and the
addition of cool air through the installed cooling system as shown in Figure 2-1, while
increasing humidity.
Summer operation
 The cooling system’s aim is to absorb excess greenhouse thermal load and trap heat
into humid air.
 On the surface of each heat exchanger, the cooling of humid air creates
condensation, releasing additional thermal energy and distilled water.
 The cool and dry air falls back into the greenhouse in two stages in order to protect
plants.
o

In the first stage cool and dry air enters the anteroom. In the anteroom, air
is mixed with hot and humid air.

o

In the second stage, mixed air enters the greenhouse, where it is heated and
humidified triggering the cycle again.

The proposed shallow geothermal system provides the necessary energy for the
proposed cooling and condensation system air. The heat pump also provides additional
cooling energy in order to successfully condense vapors and produce distilled water.
Winter operation
 During winter, the shallow geothermal subsystem provides the necessary energy for
heating in the greenhouse.
 The dehumidification process takes place even during winter time and it uses a Ushaped heat pipe.
 Heated dry air flows back into the greenhouse in two stages in order to protect
plants.
o

In the first stage hot dry air enters the anteroom. In the anteroom, it is
mixed with cold humid air.

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o

In the second stage, mixed air enters the greenhouse, where it is cooled and
humidified triggering the cycle once again.

This concept has significant advantages compared to standard greenhouse water – energy
management systems. On one hand, humid air allows excess thermal energy storage at a
given temperature, because of the use of latent heat in addition to sensible heat. This
higher energy density of humid air means that the same amount of energy can be
transported by much lower air volume flow, which can be sustained by forced buoyancy. On
the other hand, the evaporation and condensation processes increase the efficiency of the
heat transfer.
Separation of the greenhouse and the heat exchanger (placed outside the greenhouse and
into the duct) allows more room for both elements and further cost reduction. Additionally,
the evaporation and condensation processes open the possibility for water purification as
part of the water recycling system. Moreover, the energy collected in the heat exchanger is
transferred to the soil through the shallow geothermal system, thus achieving even greater
energy saving.

Figure 2-1 Block diagram of the main system

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2.1 Closed Greenhouse
The prototype is a closed greenhouse designed with water recycling as its main focus on. It
consists of a 200 m2 greenhouse, with a standard galvanized iron structure and polyethylene
plastic cover. Around the greenhouse a cooling duct is installed with two heat exchangers
inside it. The prototype includes sophisticated measurement systems (temperature, air
humidity and water flow) in order to give comprehensive information about its physical
behavior. Sensors and actuators connected to low level controllers activate a model-based
optimal control system.

Figure 2-1 Greenhouses in Larisa

In the closed greenhouse, the system is powered by solar energy, which establishes a water
recycling cycle. The heat exchangers in the duct can also function as a water distillation
system during further vapor condensation. Alternatively, the collected water can
immediately be reused in the hydroponic system. The use of shallow geothermal energy
provides low cost energy for climate control within the duct and the greenhouse.
Furthermore, the dehudimidification process during winter with the use of a U-shaped heat
pipe on the first heat exchanger, allows the reuse of hot air produced between the two heat
exchangers, saving about 75% of energy requirements.
Therefore, the system contributes to significant energy and water saving. Also, in terms of
greenhouse farming, the proposed system can lead to an improvement in products due to:
 The extension of the productive period by the state-of-the-art greenhouse climate
control system introduced
 The opportunity given for CO2 air enrichment
 The reduction in the use of pesticides.
 The opportunity given for cultivation in arid areas.

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2.2 Expected energy conservation in greenhouse horticulture
In energy efficient greenhouse concepts, durable energy resources such as solar, wind or
geothermal energy should be included. In the case of Adapt2Change greenhouse project,
solar and geothermal energy are used in order to satisfy energy requirements and
additionally power water recycling. In closed greenhouses, excess solar thermal energy
during the summer is controlled through evaporation and it can be collected and stored in
the soil. Theoretically this heat is expected to be reused during winter to heat the
greenhouse. This concept results in a primary energy use reduction of 33% to 75%,
compared to traditional greenhouses with ventilation windows (Opdam et al., 2005). Apart
from soil seasonal energy storage, this technical concept consists of a geothermal heat
pump, daytime storage, heat exchangers and air treatment units, which transfer cool air into
the greenhouse as described above.
In this concept, ventilation windows are closed and therefore CO2 levels, temperature and
humidity can be controlled according to the specific needs of the crop (De Gelder et al.,
2005). In order to reduce investment costs, farmers in practice can choose between a semi
closed and a closed greenhouse system. Cooling capacity in semi closed systems is lower
than that of a closed greenhouse. Therefore, when the active cooling capacity is insufficient
to keep the temperature below the maximum allowed, ventilation windows are used
(Heuvelink et al., 2007). CO2 emission in (semi)closed greenhouses is considerably lower
than in open greenhouses. In a recent experiment, in which tomatoes were grown with a
CO2 supply capacity of 230 kg ha-1 h-1 up to a maximum concentration of 1000 ppm, in the
open greenhouse 54.7 kg CO2 m-2 was supplied whereas in the closed greenhouse this was
14.4 kg CO2 m-2 (Qian et al., 2009).
Specific characteristics of climate in (semi)closed greenhouses with cooling ducts under the
gutters are: high CO2 concentrations, vertical temperature gradients, high humidity,
combined conditions of high light intensity and high CO2 concentration, and increased rates
of air flow (Qian et al., 2011). Elings et al. (2007) investigated whether increased air flow
rates cause photosynthetic adaptation in full grown tomato plants. Air circulation did not
change the photosynthesis light-response curves. Yield increase was therefore attributable
only to the instantaneous effects of elevated CO2 concentrations (Elings et al., 2007;
Heuvelink et al., 2007). Körner et al. (2009) showed that at high irradiance, the optimum
temperature for crop photosynthesis increased with CO2 concentration. This shift in
optimum temperature was with 1.9 °C much lower than that reported for leaves (Cannell
and Thornley, 1998), due to the fact that the leaves deeper in the canopy do not assimilate
at saturating light levels (Körner et al., 2009).
Higher humidity causes a reduction in transpiration rate, and thereby increased
temperatures of the top of the canopy. In systems where cooling ducts are below the
gutters, temperature differences of 5 ºC between roots and top of the plant can occur (Qian
et al., 2011). This affected the time necessary for fruits to mature. At lower temperatures,
fruits need more time to ripen (Verkerk, 1955). Tomato fruits were found to be more

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sensitive to temperature in their later stages of maturation (De Koning, 1994; Adams et al.,
2001) at which they are at lower temperatures in (semi)closed greenhouses.
The development of new greenhouse concepts is ongoing. Current examples are greenhouse
systems which convert natural energy resources such as solar energy into high-value energy
like electricity. Sonneveld et al. (2006, 2007) designed a system with a parabolic NIR
reflecting greenhouse cover. This cover reflects and focuses the NIR radiation on a specific
PV (photo voltaic) cell to generate electricity (Electricity producing greenhouse).

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3 Effects of Environmental Conditions on Plant
Growth
Environmental conditions such as solar radiation, temperature, water/humidity, nutrients,
air flow, etc can be limiting factors for plant growth and distribution depending on species
adaptation and sensitivity. . For example, water is a major limiting factor in deserts because
of its scarcity and only certain species are adapted to the desert’s extreme environmental
conditions..
More specifically, plant growth involves essential processes such as photosynthesis,
respiration, transpiration etc. These processes include important chemical reactions that are
affected by environmental conditions. Photosynthesis is the process by which light in the
390–700 nanometer wavelength intervals, is converted into chemical energy. During this
reaction, CO2 and water (H2O) in the presence of light and chlorophyll are converted into
carbohydrates and oxygen. Respiration is the reverse process of photosynthesis, during
which carbohydrates and fats are broken down with the release of CO2, H2O, and energy.
These chemical reactions are dependent on temperature, with limits between 10–30°C for
most economically important plants. Net photosynthesis depends on temperature, light
intensity, water and nutrient availability, while respiration is mostly temperature sensitive.
Therefore, environmental conditions can cause stress in plants affecting growth either
directly or indirectly. Given the fact that a greenhouse is constructed and operated in order
to provide an acceptable environment for plant growth and an expected profitable
enterprise, environmental conditions must be thoroughly understood and taken into
account during greenhouse system management planning.

3.1 Plant growth parameters
3.1.1 Light
Visible light (390–700 nanometers) is essential for photosynthesis, while its intensity,
duration and spectral distribution affect plant development and growth (Aldrich et. al.,
1994). The red and blue wavelengths are used most efficiently during photosynthesis, while
the change from vegetative to reproductive development in many plants is controlled by red
(660 nanometers) and far red (730 nanometers) light (Aldrich et. al., 1994). Ultraviolet light
(290–390 nanometers) is generally detrimental to plants (Aldrich et. al., 1994).
Light intensity is the most critical variable influencing photosynthesis and depending on its
value, flower crops can be classified as sun or shade plants. Sun plants can be grown in full
sunlight with no adverse effects, while shade plants are injured if exposed to light intensities
above a specific level (Aldrich et. al., 1994). Furthermore, photoperiodic plants respond to
the relative day and night duration Photoperiodism affects flowering and is generally
independent of light intensity (Aldrich et. al., 1994). Photoperiodic plants can be further
grouped as long day, short day, or day neutral, with the duration of darkness being more

14

important than that of light. The number of 24-hour light/dark cycles required for flower
initiation varies with species and variety (Aldrich et. al., 1994).

3.1.2 Temperature
Plant temperature is affected by solar radiation energy transfer, convective heat transfer,
and transpiration from the plant surface (Aldrich et. al., 1994). The relationship between
plant growth and temperature is more complex than light because it affects the reaction
rate of various metabolic processes (Aldrich et. al., 1994). Greenhouse crops are grown at
specific night temperatures with a daytime minimum increase of -2°C (Aldrich et. al., 1994).
Recommended night temperatures for several greenhouse crops are given in Appendix I
(Aldrich et. al., 1994).

3.1.3 Relative humidity
Relative humidity is the ratio of the actual pressure of water vapor in the air to the vapor
pressure if the air was saturated with moisture at the same temperature.
Water vapor moves from one location to another because of vapor pressure differences,
thus relative humidity influences plant transpiration by affecting the vapor pressure
difference between the leaf’s surface and surrounding air (Aldrich et. al., 1994). Normal
plant growth generally occurs at a relative humidity of 25–80%. A secondary effect of
relative humidity is the response of plant pathogenic organisms. For example, most
pathogenic spores will not germinate at relative humidity below 95% (Aldrich et. al., 1994).

3.1.4 Carbon Dioxide
Carbon dioxide is the raw material which along with water, is required for photosynthesis
and is usually a limiting factor in the greenhouse environment (Aldrich et. al., 1994). In a
tight greenhouse, carbon dioxide concentration may be 400 ppm before daylight and drop
to 150 ppm shortly after light is available (Aldrich et. al., 1994). The ambient level of CO2 in
the atmosphere is 340 ppm (Manitoba Agriculture, Food and Rural Initiatives, 2012). At 150
ppm respiration begins and photosynthesis stops. At this low level the plant will no longer be
able to obtain CO2 from the atmosphere and photosynthesis is restricted. Eventually the
plant will use all of the CO2 present, photosynthesis will stop and the plant will die
(Manitoba Agriculture, Food and Rural Initiatives, 2012). The rate of photosynthesis at 350
ppm will be consistent with growing conditions outside of a controlled greenhouse
environment, given that ambient levels in the atmosphere are 340 ppm (Manitoba
Agriculture, Food and Rural Initiatives, 2012).
With no other limiting factors such as heat, light and nutrients, the plants will
photosynthesize at a rate consistent with ambient conditions (i.e. outside of the
greenhouse). There may be a slight increase in photosynthetic efficiency due to the higher
than ambient level in the greenhouse, however this increase will probably be insignificant
(Manitoba Agriculture, Food and Rural Initiatives, 2012). The level of 1000 ppm is very close
to the optimum level required, given no other limiting factor and 1200 ppm will allow a plant
to photosynthesis at the maximum rate (Manitoba Agriculture, Food and Rural Initiatives,

15

2012). At this level most plants will respond favorably by increasing photosynthesis,
however this is dependent on all the other limiting factors being optimum for the plant.
Therefore at 1000 ppm the photosynthetic rate should be almost at maximum for most
plants (Manitoba Agriculture, Food and Rural Initiatives, 2012). At 10,000 ppm the
photosynthetic rate will be very low due to the closing of the plant stomata and the
exclusion of air into the leaf interior (Manitoba Agriculture, Food and Rural Initiatives, 2012).
This level is sufficient to cause toxic effect to plants and damage, eventually leading to
death. In any case, such high levels of CO2 are very hazardous to workers in the greenhouse,
as they too would experience carbon dioxide poisoning (Manitoba Agriculture, Food and
Rural Initiatives, 2012).
Greenhouse CO2 supplementation may be worth investigating for growing cut flowers,
however in the case of vegetables, CO2 supplementation usually does not increase
production enough to offset the added cost of supplementation (Manitoba Agriculture, Food
and Rural Initiatives, 2012). Below, the methods of greenhouse CO2 supplementation and
their advantages and disadvantages are described (Manitoba Agriculture, Food and Rural
Initiatives, 2012):
Methods of Supplementation: There are several methods of CO2 supplementation in a
greenhouse environment and the crop being grown would be the deciding factor for
whether or not to use supplementation as a growing tool. Once the decision has been made
that CO2 supplementation will enhance the productivity of the greenhouse, the farmer must
understand the advantages and disadvantages of each system. There are a number of low
tech approaches the greenhouse farmer can use.
A cheap method is the venting of flue gases from a fossil fuel heating system directly into the
greenhouse. This method is extremely dangerous to plant and human health as the flue
gases can contain toxic compounds such as sulfur dioxide, ethylene, nitrogen oxides and
ozone. These gases are products of incomplete combustion and are created from damaged
or non-oxygenated enough heating systems, but they can also be present as contaminants in
the fuel source.
Another low-tech method supplementation is composting plant material in the greenhouse.
Composting produces carbon dioxide but it can produce harmful gases, as well as create a
reservoir for disease pathogens and insects. The CO2 generated by composting could also be
hard to control and unreliable.
Carbon dioxide generators using hydrocarbon fuels are common in greenhouses. These
generators are specifically designed to produce CO2 from the combustion of hydrocarbon
fuels. However, if the generator is not properly supplied with adequate amounts of oxygen,
the burners are out of adjustment or the fuel source contains high levels of sulfur, harmful
contaminants may be produced possibly damaging greenhouse crops. These generators also
produce heat during the process and can be used to supplement the heating system during
cold weather. Generators can also cause temperature to rise in the greenhouse,
necessitating venting.

16

The safest method for CO2 supplementation is the use of compressed carbon dioxide from
cylinders. This compound is pure and free of contaminants and is easily regulated. The
possibility of contaminant gas production is eliminated and no supplementary heat is
produced but it is also more expensive than the previous methods described. Since the cost
of supplementation must not exceed its benefits, this method must be considered carefully.
Pressurized carbon dioxide may not be easily available at a reasonable price. However, with
a high value crop such as cut flowers the elimination of the risks would far outweigh the
extra cost of this method.
Advantages and Disadvantages: The beneficial effects of CO2 supplementation do not
always translate into increased profits due to a limited response from plants. This may be
due to other limiting factors such as adequate levels of nutrients, water and/or light.
Supplementation will not increase production and profits if all systems in the greenhouse
are not already at optimum. The farmer must understand that if there is another limiting
factor for production besides CO2, then increasing one factor alone will not always increase
overall production. Only if the farmer is supplying all the other factors and the only limiting
factor in the production regime is CO2, will supplementation increase production.
Carbon dioxide can produce larger plants, larger flowers, higher quality plants, flowers, can
decrease the time from planting to resale and flowering in some plant species. This decrease
in maturity time can save considerable heating costs by allowing the farmer to start the
plants later and shorten the time the greenhouse is heated. It is also important to
understand that supplementation must be done at a proper time in the growing season
depending on the growth habits of plants, since older plants will not respond as dramatically
as younger ones, unless the older plants are replacing old growth with new growth. The
greenhouse must also be prepared for supplementation. If the greenhouse is not properly
sealed, excess infiltration of outside air will diminish the effect of added CO2. Also a
greenhouse that is too well sealed may inhibit the natural air exchanges needed to remove
excess CO2 from the internal greenhouse atmosphere and create toxic levels of CO2.
The ambient high level of CO2 at sunrise in a greenhouse is caused by plant respiration
during the night. The respiration process continues in daylight but at a reduced rate since
the plant must be able to produce enough carbohydrates through photosynthesis to
overcome the loss of carbohydrates by respiration throughout the day and night. Therefore
CO2 supplementation is most effective during the period of active growth in the day light.
Supplementation should begin in the morning for a short period until desired levels are
reached, then the generator should be shut down and the carbon dioxide levels allowed to
return to ambient before nightfall.

3.1.5 Air Speed
Air speed influences many factors that affect plant growth, such as transpiration,
evaporation, leaf temperature and carbon dioxide availability. In general, air speeds of 20–
50 ft/min (fpm) across leaf surfaces facilitate carbon dioxide uptake (Aldrich et. al., 1994). At
an air speed of 100 fpm, carbon dioxide uptake is reduced, and at 200 fpm, growth is
inhibited (Aldrich et. al., 1994).

17


3.1.6 Pollutants
The most common pollutants are photochemicals, oxidants, ethylene, sulfur dioxide,
fluorides, ammonia, and pesticides (Aldrich et. al., 1994). Ethylene is produced during
ignition of gaseous or liquid fuels and at concentrations of 1 ppm or less, causes injury to
some plants (Aldrich et. al., 1994). Sulfur dioxide is produced by burning sulfur-producing
fuels; exposure to concentrations of 1 ppm for 1–7h causes injury to most plants (Aldrich et.
al., 1994). Mercury vapor is damaging at very low concentrations. Phenols are damaging and
as volatiles from wood preservatives, will burn petals and foliage (Table 3–1) (Aldrich et. al.,
1994).

Table 3-1 Levels at which air pollution can occur (Aldrich et. al., 1994)

3.1.7 Root Environment
Rooting media (soil) provide plant support, serve as a source of water and plant nutrients
and permit diffusion of oxygen (Aldrich et. al., 1994). During respiration, oxygen moves into
the roots and carbon dioxide is released (Aldrich et. al., 1994). The media should have
sufficient pore size and distribution to provide adequate aeration and moisture retention
necessary for acceptable crop production (Aldrich et. al., 1994). Media ranges from mineral
soil and amended soil mixes to soilless media such as gravel, sand, peat, or liquid films

18


3.2

Environmental Control

Environmental control in greenhouses includes control and modification of day and night
temperatures, relative humidity, and carbon dioxide levels for optimum plant growth
(Roberts, 2005). Temperature and humidity extremes are usually encountered during winter
and summer (Roberts, 2005). A well-designed production facility will normally provide an
environment with temperature set points between 13°C and 29°C, humidity levels high
enough to reduce water stress and low enough to discourage disease and fungus outbreaks
in the crop (Roberts, 2005). When CO2 enrichment is required, 1000 µmol/mol (ppm) is
often considered the desired target level (Roberts, 2005).

3.2.1 Solar Radiation
A greenhouse is built and operated to produce crops and return a profit to the owner
(Aldrich. et. al. 1994). In many areas, sunlight is the limiting factor in production, especially
during the winter; therefore, a greenhouse should provide optimum use of available sunlight
(Aldrich. et. al. 1994). The amount of sunlight available inside the greenhouse is affected by
its structural frame, covering material, surrounding topography, cultural features and
orientation, while outside sunlight availability depends on latitude, time of year, time of
day, and sky cover (Aldrich. et. al. 1994).
A greenhouse cover with high solar energy transmissivity can produce temperatures that are
higher than optimum for the crop zone (Aldrich. et. al. 1994). Most surfaces within a
greenhouse have high absorption rates and thus convert incoming radiation to thermal
energy (Aldrich. et. al. 1994). Figure 3–1 graphically shows greenhouse energy exchange
during daylight. Table 3–2 lists solar radiation and infrared radiation transmissivities of
several glazing materials from surfaces at about 26°C, while Table 3–3 lists solar radiation
absorption and emissivity levels of various surfaces at about 26°C (Aldrich. et. al. 1994).
Transmissivity is the percent (in decimal form) of solar energy transmitted solar rays strike
the surface at a right angle to the surface. Emissivity is the ratio of the total radiation
emitted by a body to the total radiation emitted by a black body of the same area for the
same time period.

19


Figure 3-1 Greenhouse energy exchange during daylight (Aldrich. et. al. 1994)

Table 3-2 Transmissivity of glazing materials (Aldrich. et. al. 1994)

Table 3-3 Solar absorptivity and emissivity for several surfaces (Aldrich. et. al. 1994)

20


3.2.2 Energy Conservation
Any greenhouse system that minimizes heat loss, will reduce energy consumption, though a
compromise may be necessary to satisfy light requirements while reducing heat loss (Aldrich
et. al., 1994). For example, a second layer of light-transmitting material will reduce
conduction loss by about one-half and light transmission by about one-tenth of a single layer
(Aldrich et. al., 1994). Mobile insulation can be installed, which is stored during the day and
encloses the crop volume during the night. Material stored in the greenhouse causes some
light loss and may interfere with normal greenhouse traffic (Aldrich et. al., 1994). A properly
installed double glazing layer or thermal blanket will also reduce air exchange between the
greenhouse and the outside environment. Estimates of overall heat transmission values can
be made for thermal blanket installations. Some values are given in Table 3–4.
Table 3-4 Air exchanges for greenhouses (Aldrich. et. al. 1994)

3.2.3 Humidity Control
A tight greenhouse reduces air exchange and increases relative humidity (Aldrich et. al.,
1994). Thermal blankets or double glazing layers will also result in increased relative
humidity because reduced air exchange will in turn reduce the amount of water vapor
removed from the greenhouse (Aldrich et. al., 1994). Additional insulation will result in
higher inside surface temperatures, reducing the condensation potential. The condensation
rate depends on the rate of air flow across the surface, the rate of heat condensation
removal from the surface and the rate of evaporation from other surfaces in the greenhouse

21

In general, relative humidity of inside air will be controlled by the temperature of the coldest
surface inside. For example, if the inside surface temperature is 3°C and the inside ambient
temperature is 16°C, the inside relative humidity will be about 40% (Aldrich et. al., 1994).
Table 3–5 illustrates the effects of different energy conservation construction practices on
inside surface temperatures.
Table 3-5 Inside surface temperatures of greenhouse enclosures and maximum relative humidities with 60°F
o
(15.6 C) inside air (Aldrich et. al., 1994)

The simplest method for relative humidity control during cool or cold weather is to bring in
cool air inside, heat it and allow it to absorb moisture before exhausting it to the outside
(Aldrich et. al., 1994). The evapotranspiration rate for greenhouse crops will vary depending
on the crop and available solar radiation. A greenhouse filled with mature pot plants may
lose up to about 0.07 kg of water vapor per square foot of greenhouse floor area per hour
during the day; loss at night will be less (Aldrich et. al., 1994). If evaporated moisture is not
removed, relative humidity will increase until the air is saturated or until condensation
begins on a cold surface (Aldrich et. al., 1994).
Horizontal air flow in the greenhouse will help alleviate the problem by moving air across
plant surfaces to keep them dry. Air flow also increases mixing and prevents temperature
stratification in the greenhouse (Aldrich et. al., 1994). If outside air is at -6°C and 80%
relative humidity is brought into the greenhouse and heated to 16°C, it will absorb 0.0005 lb
of water vapor per cubic meter of air if the final relative humidity is 70% (Aldrich et. al.,
1994). It would take 90 m3 of air/h to remove the 0.15 lb of water vapor produced per
square foot of greenhouse floor area and it would require about 300 Btu/h to warm the air
to 16°C (Aldrich et. al., 1994). A change in any of these conditions would result in changes in
air flow and heat required (Aldrich et. al., 1994).

22


3.3

Estimating Heating and Cooling Loads

3.3.1 Heating
The estimated heat loss for temperature control is based on the construction system, a
minimum inside temperature, and an outside temperature generally taken as -12°C below
average minimum temperature (Aldrich et. al., 1994). For most locations above 40° North
latitude, a temperature difference of 15°C will result in an adequate installed heating
capacity (Aldrich et. al., 1994). Thus, if the outside temperature is -17°C, the greenhouse air
temperature can be held at 15°C.
The proposed greenhouses cover a total area of 432 m2 with 12 m x 18 m each and arcs with
6 m width. The maximum height of construction shall be 5,25 m at the top, while the gutter
3,50 m. The distance between the uprights of each Greenhouse will be 2 m. The distance
between the two chambers A + B will be 7 m.

3.3.2 Cooling
Estimates of cooling requirements for greenhouses are based on acceptable temperature
differences between inside and outside air, only if outside air is used to remove solar heat
(Aldrich et. al., 1994). A reasonable compromise is to design for a minimum temperature
difference of -4°C. Thus, if the outside temperature is 20°C, the inside air temperature will
be about 25°C (Aldrich et. al., 1994). An air exchange ratio of 8 cfm/m2 of floor area will
generally satisfy this requirement (Aldrich et. al., 1994). If additional cooling is needed,
evaporation can be used if the relative humidity outside is low enough (Aldrich et. al., 1994).
Apart from being too costly, mechanical refrigeration is a rather non environmentally
friendly method for greenhouse cooling.
The proposed greenhouses can be used again, this time to illustrate sizing a cooling system.
Fans should be placed in one sidewall and the air pulled across the 30 m width of the
greenhouse. Air should not be moved more than 46 m from inlet to exhaust. The
temperature at which fans start can be set to satisfy the farmer. The vent opening on the
opposite side of the greenhouse should be adjustable to keep the air speed through the
opening at about 250 fpm. Ventilation is often required during cool, clear weather to reduce
humidity levels. This is accomplished by installing powered inlet louvers in gable ends with
attached perforated polyethylene tubes for air distribution (Aldrich et. al., 1994).

23


3.4 Greenhouse Energy Conservation
There are a number of practices that can be used in this project in order to achieve optimum
energy conservation conditions. These include:
 The use of energy curtains at night to reduce the amount of heat loss through the
roof and sidewalls. This is probably the most effective energy conservation step the
greenhouse operator can make as it can save up to 65% of the total heat loss
through the greenhouse glazing on the roof and 35% of the heat loss through the
side walls. This can constitute an annual saving of 20-40% off the energy bill.
 Insulation of the end walls and gable ends. This will lower the amount of heat loss
through these structures without significantly affecting the greenhouse light
absorption capacity.
 The foundation and perimeter should be insulated to prevent heat loss through the
ground. This can account for a significant amount of heat loss in some cases.
 All cracks, holes, slits in the plastic and air spaces between the glazing and other
materials need to be sealed to lower the air infiltration rate.
 Vent inlets and fan outlets need to be sealed from leakage and, if possible, all
exposed metal should be insulated since metals are good heat conductors. This can
be accomplished by using weather stripping around the fan and vent shrouds and
then spraying insulation over the vent covers to protect the metal.
 Closing the greenhouse during the coldest part of the year will save a considerable
amount of energy and will also contribute to the reduction of the insect population
and in some cases plant diseases.
 Decreasing greenhouse temperature will also save energy, however lowering the
temperature too much will harm the plants and could reduce productivity.
Therefore, it is advisable to lower the heat at night and increase it during the day.
Selecting cool climate plants in the coldest part of the season could also reduce
energy consumption.
 Proper maintenance of all greenhouse equipment will ensure system operation at
peak capacity and efficiency, while saving energy. This includes all heating
mechanisms and electrical equipment, such as motors.

24


3.5

Insect Screens

Greenhouse structures provide easy access for insect pests through ventilation openings,
vents, louvers, and poorly fitting doors and windows (Aldrich et. al., 1994). Screening vents,
doorways, and other openings can prevent many unwanted insects from entering, but they
will also limit the airflow unless openings are modified to make up for the reduction in clear
area for cooling air to enter (Aldrich et. al., 1994). There is a relationship between screen
opening and insect size for the screen to be effective. Many screen materials are made of
uniform threads called mesh (Aldrich et. al., 1994). The mesh refers to the number of
threads per m in each direction. A 64 mesh screen has 64 threads running in each direction
at right angles to each other (Aldrich et. al., 1994). The diameter of the threads must be
known in order to determine the net open area through which air can flow, in diameter, and
a 64 mesh screen, the total area covered with thread is 0.512" (64 x 0.008"). The amount of
open area is 0.488" (1 – 0.522"). With 63 openings across the meter, each opening is
0.007746" wide (0.488 / 63), giving an area of 0.00006 sq inches. Since there are 63 x 63 per
sq m, the total open area will be 0.008 sq m/sq m of screen (63 x 63 x 0.00006"). In other
words, the screen has an open area that is 23.8% of the total gross area of the vent or other
opening it is covering (Aldrich et. al., 1994).
A reduction in free area because of the screen, will mean that the same airflow in cfm for
which the original opening was designed will have to pass through the reduced area at a
much higher speed, resulting in higher energy loss or a higher pressure for the fan to work
against (Aldrich et. al., 1994). Therefore, when insect screens are installed, their gross area
must be large enough so their free area is equal to or greater than the opening they are
covering (Aldrich et. al., 1994).
Because of the small openings, insect screens tend to trap dust, dirt, and pollen rapidly. They
must be cleaned regularly to maintain the open area and desired airflow rate. This can be
done by washing or vacuuming (Aldrich et. al., 1994).
Christianson and Riskowski recommend designing screened openings for a 0.008 m water
pressure drop in addition to the pressure drops through the fan, housing, and louvers
(Aldrich et. al., 1994). Thus, where a fan may be selected based on a pressure drop of 0.125"
of water with no screens, it should be selected for a drop of 0.160 to 0.175" of water, if
insect screening is installed (Aldrich et. al., 1994).
There are several screen materials available, but some do not indicate the free opening area
or thread size nor do they indicate the relationship between airflow and pressure drop
through the screen. Without this information it is difficult to correctly select fan size for a
particular greenhouse installation (Aldrich et. al., 1994).

25


4 Prototype Greenhouse subsystems
The project’s innovative Greenhouse installations are designed in order to achieve an
automatic control of environmental parameters such as climate conditioning, energy
sources, energy management, growing substrate, water and nutrient supply, etc. All of these
parameters mutually influence each other and are affected by local environmental
conditions such as climate and resources availability. Rapid growth in technology and energy
resources require a dynamic and flexible approach in which one can select a wide range of
components (e.g. greenhouse dimensions, heating systems, covering materials, lighting,
conversion and storage systems) and settings for an effective operational control.
In this logic, the prototype systems used in the project include a geothermal subsystem, an
air recycling subsystem, a hydroponics subsystem, a cooling-dynamic subsystem and
thermal-cooling panels as shown in Figure 4-1.

Figure 4-1 Prototype Greenhouse subsystems

The advantages of prototype subsystem use can be summarized as follows:

26





It offers the opportunity for a multi-disciplinary approach to systems control.
It prevents trials and errors.
With the use of sensors the main system, produces a good overview of the
Greenhouses condition (temperature and humidity) at any time and reduces the
chance of energy loss or crop damage.

4.1 Geothermal subsystem
Controlling the efficiency of crop growth and quality is vital to an innovative Greenhouse
installation. In this case, for climate control purposes, a shallow geothermal system is
applied and installed. The operation of the shallow geothermal subsystem will provide the
necessary cooling energy for the condensation of water vapors gathered inside the
greenhouse. Water produced from the condensation process will be collected through the
water recycling subsystem. This is the first example of subsystem inter-operation.
The main geothermal system will include the installation of an external network of a closed
loop heat exchanger and all its essential mechanic equipment, such as the main geothermal
heating pump, various pipes, tanks, valves, pumps etc.

4.1.1 Closed loop heat exchangers
A closed loop heat exchanger can be constructed out of different materials; currently the
most common one is a PE100 SDR11 pipe with 25 mm, 32 mm or 40 mm diameters (EGEC,
2011). The common feature of the 2 heat exchangers is that they are part of a closed
hydraulic circuit; they contain a pumped circulation medium and exchange energy with the
surrounding ground through temperature difference. Usually, and with the best efficiency
and stability, the heat exchanger is installed in vertical drilled boreholes, but it can also be
installed horizontally, at an angle or integrated in a foundation structure of a building with
lower installation costs but with less energy efficiency (EGEC, 2011).
The most common form of heat exchanger is the single loop, but doublets or triplets are also
in use. A heat exchanger variant is the pipe in pipe concentric heat exchanger type (EGEC,
2011). Although pipes of different materials (copper, stainless, steel, PVC etc.) can be used,
the most common material is PE100 (EGEC, 2011). This material is extruded into the pipe
and the pipe coils are joined with a stub welded U-bend in the factory. PE100 like PE80 is a
mass produced standard product and is used in the gas and water industry throughout the
world (EGEC, 2011). Fittings to produce pipe connections are available from many sources.
The PE100 material has a thermal conductivity of 0,42 W/mK, is chemically inert and has an
anticipated life span of 100 years in low temperature applications. The PE is flexible and can
handle strain and some deformation. Joining techniques such as welding are available and
the material is not excessively costly (EGEC, 2011).
Normal operating temperature range for PE100 material is from –10 to 40 oC. For higher
temperatures PEX, Polybutene (up to 95 oC) is recommended (EGEC, 2011).

27


4.2 Geothermal climate-conditioning system description
There are two types of closed loop heat exchangers. The first involves a horizontal pipe
network and the second a vertical one. In more detail we can distinguish the following
configurations:





an underground horizontal pipe network,
a horizontal network in the form of threaded pipes in trenches,
a vertical network of pipes in boreholes
an open vertical network of pipes in water-boreholes

Figure 4-2 Galileo Heating programming

4.2.1 Closed loop heat exchanger dimensioning
The geothermal climate-conditioning system is designed according to the required cooling
loads for maximum demands in the range of 25 kW - 30 kW per greenhouse unit.
 The estimation of the closed loop heat exchanger's capacity is based on empirical
rules published in relative scientific bibliography.
o In case of a horizontal closed pipe network in general excavation, according
to the empirical rules and if we assume that for adverse soil conditions with
dry soil and loose material the SPF = 3.5 (seasonal performance factor), the
estimated space required is about 2.5 acres. Considering that the terrain
conditions are characterized by cohesive soils with normal humidity, the
necessary excavation area is limited to approximately 1 acre (2 acres for the
project’s 2 Greenhouses located in Larissa)

28

o

o

o

In case of a horizontal closed pipe network in trench, according to the
empirical rules, the installation will require a total of 290 m to 360 m of
trenches (580 m to 720 m for the project’s 2 Greenhouses located in Larissa)
In case of a vertical closed pipe network in boreholes, the installation will
require a pipeline network of 870 m in the borehole. This is assumed
according to the empirical rule that the SPF = 3.5 (seasonal performance
factor) and considering that soil and sediments are dry. In case of a single Utube per borehole, the network length is estimated around 435 m (900 m
for the project’s 2 Greenhouses).
In case of an open vertical network in water-boreholes the required pipe
network should be approximately 500 m in length for the project’s 2
Greenhouses located in Larissa. This is calculated considering the empirical
rules that the SPF = 3.5 (seasonal performance factor) and the potential
exploitation of groundwater is dynamic.

Figure 4-3 A simple description of a Geothermal Subsystem (http://www.redaproject.org
O.R.E.C)

4.2.2 Geothermal system Dimensioning
The application used for the proposed geothermal system calculations is the GS200v3
“Caneta Research” model. The application requires several input data, such as geometric
features of the closed loop heat exchanger, piping material properties, study area's climate
data, soil characteristics, heat pump characteristics, properties of the closed loop heat
exchanger's antifreeze mixture and heat/cooling required loads. For these calculations,
standard values from related scientific bibliography and values calculated for this study will
be used.
The properties of piping materials: type PE17, polyethylene, Series 160/SDR11, 1-1/2'' are
presented below.

29

 Soil Temperature: The soil temperature near the surface varies around the values of
mean temperature. At greater depths the ground temperature stays stable with
values similar to the mean annual air temperature in the region. The model requires
as input, a) the annual mean ground temperature (Tm), b) the surface amplitude
(As), c) the number of days in the year when minimum soil temperature occurs (to).
Typical values that were used are: Tm = 16.7 °C, As = 7 °C, to = 10 (days)
 Soil properties: For reasons of simplicity and lack of data, we considered typical
layering of geological materials with a total thickness of 150 m:
o 0 m-50 m depth: Silty-loam dry, with k = 0.6 W / m °C and a = 0.38 mm2 / s
for the summer and impregnated with k = 1.3 W / m °C and a = 0.56 mm2 / s
for the winter.
o 50 m-150 m depth: Sandy soil (sandy soil) dry, with k = 1.3 W / m °C and a =
0.48mm2 / s for the summer and impregnated with k = 2.5 W / m °C and a =
0.84mm2 / s for the winter.
 Heat pump properties (per heat pump): for the calculations we used:
COP = 4, EER = 10 and antifreeze material flow rate 1.2 l/s.
 Required cooling/heating loads: the monthly requirements in kWh for
heating and cooling were given.
 Antifreeze mixture properties: methanol mixture was chosen, 20%wt,
975Kg/m3, 4.1KJ / (KgK), 2.6g/ms.
The results of applying GS200v3 are presented in Appendix 2 and they include the following
scenarios:
 For a horizontal closed network excavation: depth 2.0m, 4 tubes with 1.0 m distance
between them, total area per greenhouse: 190 m x 3 m ~ 580m2.
 For a horizontal closed network in a trench, total trench length per greenhouse is
295 m.
 For a vertical closed borehole network (with a U-tube per borehole) the total length
of each borehole is: 420 m

4.2.3 Horizontal Closed loop heat exchanger with closed and indirect pipe
network
The network's configuration is based on the exploitation of the geothermal capacity of the
geological formations located in the study area. The basic elements of this system are the:
 The horizontal closed loop heat exchanger that is installed underground or in a
trench.
 The collection vault of the subsurface network.
4.2.3.1 Horizontal Closed loop heat exchanger design parameters
 General excavations



The pipes of the horizontal closed loop heat exchanger are installed deeper
than 1.2 m underground with pipe density 1.5-2.0 m per m2 of excavation.
The length of every network should not exceed 200 m.

30



The pipes should be installed in a flat or slightly inclined surface with a
constant slope. In case of an inclined surface the pipes should be installed
perpendicular to the sloping ground.
 Trench: The trench depth ranges from 1.2 m to 2.0 m, the width should be at least
0.8 m and the length should range from 20 m to 30 m. Pipe length ranges from 125
m to 200 m per pit. The trench pipe type is HDPE-Pipe Hard PN 10.
 Soil: The typical yield is between 20-35 W / m² depending on the subsoil's geological
status and the requirement of maximum loads. The laboratory analysis of soil
samples will determine thermal conductivity and heat capacity.
 Piping circuits: The flow and diameter of pipes should be selected in order to ensure
system's turbulent flow of cooling fluid. Typical flow rates range from 3-3.5 L min-1
per kW of heat transfer.
 Standard option is high density polyethylene pipes (HDPE) with heat
welding.
 The closed pipe network of polyethylene pipes is preferred due to its low
price, high durability and resistance to corrosion. High density polyethylene
pipes (HDPE) have a typical outer diameter of 26-40 mm. The internal
diameter typically is 19 to 32 mm.
 The closed network in operation, undergo pressures in the range of 2 to 3
bar. Therefore, pipe materials must be minimum rating PN6 (6 bar), even if
the most common pipes used are SDR11 or PN10.
 It is important that the pipes are not be pressed or obstructed in any way.
 The collector pipes are covered with a protective layer of sand before the
trench is closed. In case of an open excavation, the excavation materials are
used.
 It is particularly important the parts of the pipes to have the same length in
order to achieve an equivalent pressure difference in the network.
4.2.3.2 Collector Network (Collection vault)
 The pipes should preferably be collected in the vault, inside or outside the network.
 The collector has a diameter of around 1.5 m and consists of prefabricated ring.
 The pipes connecting the greenhouse to the collector must be straight with a slight
tilt to the side of the collector in order to collect and remove various concentrates.
 The pipes should be insulated properly.
 The pipes should be installed at least 1.5 m away from water pipes and electrical
cables.
 Collector networks that allow isolation of different circuits are preferable.
4.2.3.3 Freezing Fluid




The heat transfer fluid to and from the surface is based on water and is
usually an antifreeze solution that withstands temperatures below 0 °C, if
necessary. Its freezing point is usually between -10 °C and -20 °C.
The fluid should be biodegradable and environmentally acceptable.

31

4.2.3.4 Vertical Closed loop heat exchanger with closed and indirect pipe network
The network's configuration is based on the geothermal capacity exploitation of the
geological formations located in the study area. The basic elements of this system are:
 The vertical closed loop heat exchanger installed underground or in a trench.
 The collection vault of the subsurface network.
4.2.3.5 Design parameters
 Boreholes:
-

Drilling depth is usually between 60-120 m and 6'' -8'' diameter.
To avoid thermal "manufacture", the distance between the vertical heat
exchangers should be greater than 10 m.
Borehole filling after the installation, should consist of a thermal conductive
mixture (eg cement, bentonite or water sand) or with excavation material
from drilling.

 Soil:
-

The typical yield is between 35-65 w/m² depending on the subsoil's
geological status and maximum load requirement. The laboratory analysis of
soil samples will determine thermal conductivity and heat capacity.
 Pipe network:
- The flow and diameter of pipes should be selected in order to ensure
system's turbulent flow of the freezing fluid. Typical flow rates ranging from
3-3.5 L min-1 per kW of heat transfer.
- Standard option for piping is high density polyethylene pipes (HDPE) with
heat welding. Polyethylene pipes are preferred due to their low price, high
durability and resistance to corrosion. High density polyethylene pipes
(HDPE) have a typical outer diameter of 26-40 mm. The internal diameter
typically is 19 to 32 mm.
- The closed network in operation, undergoes pressures of 2 to 3 bar,
therefore materials must have a minimum rating of PN6 (6 bar), even if most
common pipes used are SDR11 or PN10.
- It is important that pipes should not be pressed or obstructed in any way.
- Collector pipes have to be covered with a protective layer of sand before the
trench is closed. In case of an open excavation, the excavation materials can
be used.
 It is particularly important the parts of the pipes to have the same
length in order to achieve an equivalent pressure difference in the
network.
4.2.3.6 Collector’s Network (Collection vault)
 The pipes of the external network should be collected in the vault, inside or
outside the network.
 The collector has a diameter around 1.5 m and consists of prefabricated ring.

32

 The pipes from the greenhouse to the collector must be straight with a slight
tilt to the side of the collector in order to collect and remove various
concentrates. The pipes should be insulated properly.
 The pipes should be installed at least 1.5 m away from water pipes and
electrical cables.
 The collector network should allow the isolation of different circuits.
4.2.3.7 Horizontal Closed loop heat exchanger with open and indirect pipe network
The network's configuration is based on groundwater pumping to and from the
underground aquifer and thermal energy reclamation. The basic mechanical elements of this
system are:
 Water boreholes for pumping groundwater from and to the underground
aquifer.
 Submersible pumps.
4.2.3.7.1 Design parameters
 Water-Boreholes:





 Drilling must have a diameter greater than 220 mm.
 Groundwater depth should not exceed 15 m in order to minimize flow
problems due to friction.
 Groundwater temperature should not be less than 8°C.
 Groundwater properties (temperature, conductivity, contents) must be
determined through sampling and laboratory analysis.
 The use of submersible pumps is proposed in order to prevent air intake to
the system.
 For the preparation of the Implementation study we recommend the
development of a demo borehole or pump tests (of at least 48h long, at full
load). In addition we recommend a standard chemical analysis of subsurface
soil and groundwater.
 The results of the pumping tests will be used for the submersible pump
dimensioning. Additionally, drilling materials and residues will be disposed
of properly and cleared from the area.
 The submersible pump should have a nominal speed of 3600 rpm.
 Major issues to be considered during the heat exchanger design are
pressure falls, temperature inputs, and the quality of construction materials.
 Piping to and from the boreholes should have a slight inclination and should
be properly insulated against frost. Flow rate should not exceed 0.8m/s.
Underground heat source:
 Borehole typical energy output is approximately 70w/m depending on the
geological status and the requirement of maximum loads.
Pipe network:

33

 Pipe flow and diameter should be selected in order to ensure system's
turbulent flow of the freezing fluid. Typical flow rates ranging from 3-3.5 L
min-1 per kW of heat transfer.
 Standard option for piping is high density polyethylene pipes (HDPE) with
heat welding. Polyethylene pipes are preferred due to their low price, high
durability and resistance to corrosion. High density polyethylene pipes
(HDPE) have a typical outer diameter of 26-40 mm. The internal diameter
typically is 19 to 32 mm.
 The closed network in operation, undergoes pressures of 2 to 3 bar,
therefore pipe materials must have a minimum rating of PN6 (6 bar), even if
most common pipes are SDR11 or PN10.
 It is important that the pipes are not be pressed or obstructed in any way.
 The collector pipes are covered with a protective layer of sand before the
trench is closed. In case of an open excavation, excavation materials can be
used.
 It is particularly important the parts of the pipes to have the same length in
order to achieve equivalent pressure difference in the network.
4.2.3.8 Technical characteristics
By comparing calculations that were provided by the National and Kapodistrian University of
Athens and the data measured during the drilling test procedure, we calculated the amount
of energy required for the project’s Greenhouses and it is approximately 70 KW.
Geothermal load in the study area has an estimated capacity of 70W/m, therefore in order
to meet the energy needs of the greenhouses, 10 boreholes of 100 m depth are needed. The
distance between the boreholes should be at least 5 m, in order to avoid the possibility of
thermal ‘manufacture’.
The geothermal system that should be installed is closed and therefore the piping material
must be plastic polyethylene (PE100) with 40 mm diameter. Borehole filling will consist of
quartz sand in order to optimize the induction of heat from and to the plastic pipes.
Boreholes will be constructed with a geothermal drill that can perform bi-directional cutting
and drill in any type of soil. It is essential that the drillings will not in any way alter the
morphology and the landscape of the study area. Drilling machinery is equipped with a
closed drilling materials removal extension.
4.2.3.9 Thermal Heat Pump
The geothermal system uses an EPH Geo thermal pump with a scroll type compressor. This
pump is designed for indoor use with an automatic refrigerant cycle return. It provides 66
KW with 35/30oC water temperature, geoecxchanger temperature (0-3oC), cooling power of
71,3oC with water temperature at (12-7oC) and geoecxhanger temperature at 30-35oC. The
compression pump is equipped with R407 approved refrigerant. Lastly, the thermal pump
system will be equipped with 2 fully functional compressors with a noise level no higher than
68 dB(A). The Greenhouses is equipped with 2 heat pumps each.

34


Figure 4-4 Galileo Irrigation information system

4.3 Control unit
The proposed G.H. control unit consists of mainly the hydroponics subsystem as well as the
climate control subsystems. Irrigation is an essential component of crop production in many
areas of the world (Galande and Agrawal, 2012). In cotton for example, recent studies have
shown that proper timing of irrigation is an important production factor and delaying it can
result in losses of about USD 62/ha up to USD 300/ha (Vories et. al., 2003 in Usman and
Umair, 2012). Automation of an irrigation system can provide maximum efficiency by
monitoring soil moistures at optimum level (Cardenas-Lailhacar et. al. in Usman and Umair,
2012). The control unit is the pivotal block of the entire irrigation system, controlling water
flow enabling optimized results (Cardenas-Lailhacar et. al. in Usman and Umair, 2012).
Irrigation process can be controlled by two types of controllers: open loop controllers and
closed loop controllers (Usman and Umair, 2012), as described in the following paragraphs.

4.3.1 Open loop controller
It is also referred to as a non-feedback controller (Usman and Umair, 2012). This type of
controller is designed with the following principles (Usman and Umair, 2012):
 Receiving input and computing output for the system accordingly.
 No feed-back provision to determine whether the desired output or goal is achieved.
This is the simplest type in which basic parameters and instructions are pre-defined as
follows (Usman and Umair, 2012):
 When to start watering/a task

35

 When to end watering /a task
 Time delay intervals
During execution no measures are taken to check if the appropriate amount of water is
supplied (Usman and Umair, 2012). These controllers are low cost, but they are not very
good and cannot provide an optimal (or a good) solution for irrigation problems (Usman and
Umair, 2012).

4.3.2 Closed loop controller
This type of controller is based on a pre-defined control concept, utilizing feedback from the
controlled object/system in order to check the water supply needed for irrigation (Usman
and Umair, 2012). Several parameters must be taken into consideration in order to make an
optimal decision and these parameters remain fixed throughout the process. System
predefined fixed parameters include (Usman and Umair, 2012):






Type of soil
Plant species
Leaf coverage
Type and status of growth (height, root depth etc)
Water budget (economy or normal irrigation)

Other input parameters vary with time and should be monitored during irrigation (Usman
and Umair, 2012). These involve physical properties, such as (Usman and Umair, 2012):







Soil humidity
Air humidity
Wind speed
Radiation
Temperature
Soil salinity

The whole irrigation process is mainly based upon these specified physical variables, since
they can change the amount of water needed (Usman and Umair, 2012).
This project’s irrigation system exploits closed loop control. The control unit continuously
receives feedback from different sensors placed in the greenhouse, enabling data update on
important system parameters (Usman and Umair, 2012). The control unit decides how much
water will be released according to the input data collected from the sensors and the
system’s fixed parameters as described above (Usman and Umair, 2012). The system’s
output parameters include (Usman and Umair, 2012):
 Water and/or fertilizer valve opening/closing, while adjusting their amounts in
combination;
 Turning energy systems on/off (lights, heating, ventilation);
 Opening/closing greenhouse walls and roofs.

36


4.4 Control Unit Design
The control system consists of four interconnected stages (Usman and Umair, 2012):
 Sensor input data: In this stage different variables, like temperature, air humidity,
soil moisture, wind speed and radiation, are measured and passed to the next stage
as input data.
 Evapotranspiration Model: This block converts four input parameters into actual soil
moisture.
 Required Soil Moisture: This block provides information about the amount of water
required for proper plant growth.
 Controller: This stage compares the required soil moisture with actual soil moisture
and a decision is made dynamically.
System Parameter Modelling
Four variables that influence evapotranspiration are used and these are modeled according
to international scientific practice and literature (Javadi Kia et. al. in Usman and Umair,
2012) as follows.
Temperature:
This variable should be modeled as a continuous signal (normally as a sine wave that
simulates day and night temperature changes), but may show sharp changes in special
environmental conditions, therefore:




A sine wave with amplitude of 5oC;
A frequency of 0.2618 rad/h. This frequency is measured according to a time period of
24 h: 0.2168 rad/h = 2pi/T=2pi/24.
A constant bias (offset) of 30oC.

This stimulus generates a wave, which at its maximum can reach 35°C (midday) and at its
minimum +25°C (midnight). In this way, the temperature on any given day can be simulated
by changing the bias attached to the variable. This variation is obtained by uniform number
generation.
Air humidity:
• A sine wave with amplitude of 10%;
• Bias of 60% (constant);
• A frequency of 0.2618 rad/h
Wind speed:
• A sine wave with amplitude of 1 Km/h;
• Bias of 3.5 Km/h (constant);
• A frequency of 0.2618 rad/h
Radiation:

37

It is modeled as the maximum possible radiation at the earth’s surface (Rmax).
• A sine wave with amplitude of 2MJ/m2;
• Bias of 112MJ/m;
• A frequency of 0.2618 rad/h.
Required Soil Moisture:
It is solely dependent on plant species, type of growth and type of soil. The required soil
moisture is calculated according to the afore mentioned variables.

4.4.1 Control Unit
The control unit consists of an Artificial Neural Network (ANN) based controller, which
compares the required soil moisture and measured soil moisture (Usman and Umair, 2012).
The main function of this stage is to keep the actual soil moisture close to the required soil
moisture (Usman and Umair, 2012). As a result, the output of this process is the input for the
valve control system, which supervises the amount of water supplied in order to optimize
irrigation (Usman and Umair, 2012).
In the proposed method, Dynamic Artificial Neural Network (DANN) could be used. Dynamic
Networks are more powerful than static networks because they have a memory and they
can be trained to learn sequential and time varying patterns (Usman and Umair, 2012).
The controller has two inputs i.e. required soil moisture and calculated soil moisture from
the evapotranspiration model, and there is only one output valve positioning (Usman and
Umair, 2012). This makes the system configuration very simple and straight forward (Usman
and Umair, 2012).

4.4.2 Controller Architecture
The ANN controller is implemented using the following (Usman and Umair, 2012):






Topology: Distributed Time Delay Neural Network is used.
Training Function: Bayesian Regulation function is used for training.
Performance: Sum squared error is taken as performance measure.
Goal: The set goal is 0.0001.
Learning Rate: The learning rate is set to 0.05.

With this configuration the valve is only opened when required soil moisture exceeds the
measured soil moisture, otherwise it remains closed (Usman and Umair, 2012).

38


Figure 4-5 Galileo Main control system

Control unit Characteristics
The control unit should have:









The ability to control the compressor based on the return temperature of the water.
The ability to control and manage the outdoor pump.
The ability for remote control
An alarm system with historical alarm recording capacity (50 records max)
the ability to compensate external ambient temperature (dynamic set point)
the ability to measure the operating hours of compressor and condenser
Serial output in mod bus protocol RS485
The ability to start the compressor with a soft starter

4.4.3 Inter-operational connections
In the final stage of construction the thermal network will be connected with the
condensation equipment and specifically with the cold condenser and the heat exchanger.
Due to seasonal changes the system in the summer will reverse the freezing circle the
system will have all the necessary valves and their automatic control units.

39


4.5 Air recycling subsystem
This prototype subsystem controls the ambient conditions in the greenhouse according to
the data input from the temperature and humidity sensors. The system controls
components such as: heating and cooling systems and fans, in order to create the desired
temperature and humidity. In addition, the system controls of the greenhouse’s ventilation.
The subsystem operates according to a table containing desired values for different periods
of the day. If the system is correctly calibrated, it automatically maintains the desired
temperature and humidity.

4.5.1 Condensation and air recycling network
The ventilation and air recycling subsystem uses mechanical and natural means, in order to
control air flow from and to the Greenhouse or to increase the cooling procedure efficiency
inside the Greenhouse.
Subsystem description:
 The internal condensation network is connected to the geothermal pump and uses
geothermal energy to condense water vapors.
 Inside the Greenhouse vapor condensation is achieved through a rooftop pipe
network, in which freezing fluid is circulated appropriately and condensed vapors
are collected.
 The main mechanical elements consist of humidifiers, fan coil units and a ductwork:
 The dehumidifier is the main condensation unit. This unit regulates humidity
inside the Greenhouse.
 In connection with the dehumidifier, fan coil units are attached in front of the
Greenhouse in order to enhance the condensation process and achieve
maximum area coverage. Fan coil units are air conditioning devices, that
consist of a fan and a condensation circuit.
 The ductwork is used for water vapor collection.

4.5.2 Ventilation system (metallic air duct)
Outside the Greenhouse, a rectangular galvanized sheet steel air duct will be attached
(dimensions 1 m x 1 m). This ventilation system will receive air output from one of the four
fans of the cooling subsystem. Inter-operation between these subsystems will be achieved
through a T-shaped junction and a mechanical valve. The subsystems depending on the
temperature/humidity requirements will automatically control and regulate air recycling by
opening or closing the air valve.
The vent will be constructed in parts and each part will have hinges that will allow it to be
mounted quickly and easily. In addition, each part will contain insulating gaskets, in order to
ensure complete insulation and the elimination of pressure losses.

4.5.3 Cooling system (cold condenser)
The air recycling/condensation system contains a cold condenser inside the air duct in order
to dry outgoing air. After the T-shaped junction, the cold condenser will have the ability to

40

cool Greenhouse air emissions. In addition, the dehumidifier will contain a small tank with a
submersible pump, in order to collect water vapors. The water produced by the cooling
procedure will be used automatically by the hydroponics subsystem for irrigation. However,
this function requires a proper irrigation network. The condenser will be made of nonmagnetic stainless steel and its casing of galvanized sheet metal. The system will have a
cooling capacity of 60KW supplying approximately 20 L/h (during winter).
After delineation of the sites where the Greenhouses will be built, excavations will take
place in order to dig trenches for polyethylene water tanks. The first water tank (dim. 2 m x
2 m x 2 m) will be attached to the cooling subsystem's panel. The second water tank (dim. 2
m x 2 m x 2 m) will be placed under the water duct (to support the condensation system). All
tanks will be equipped with a submersible pump.

Figure 4-6 Metallic air duct

The great advantage of this inter-operational subsystem installation is that the Greenhouses
will actually regulate their cooling, heating and irrigation automatically, depending on their
needs at any time. Thus, the automatic control systems will calculate if irrigation is required
and which tanks will be used.

41


4.5.4 Air heating system (heat exchanger)
This subsystem is equipped with a heat exchanger in case heating is required. The subsystem
works together with the cooling condenser. After the air is dried by the cooling condenser, it
flows through the heat exchanger and depending on Greenhouse heating needs, the air can
be heated again before entering the Greenhouse. The system is actually an automatic
addition for heating support, controlled by the main control panel. The air heating system
will have a heating capacity of 60KW and will be made of non-magnetic stainless steel. Like
the cooling condenser, its casing will be made of galvanized sheet metal. In case of repairs or
maintenance, the device should be removed easily because of its strict design.

4.5.5 U-shaped heat exchanger
The U-shaped heat pipe installed on the first heat exchanger in the air duct, works in 3 steps:
i. Step 1. Incoming return from greenhouse air is pre-cooled to by the pre-cool heat pipe
coil.
ii. Step 2.The pre-cooled air flows through the first heat exchanger. By adding a pre-cool
heat pipe coil, the system now functions more efficiently and can perform higher levels
of latent cooling and increased dehumidification. Often times a smaller capacity AC
system can be chosen due to the increased cooling performance from the pre-cool coil.
iii. Step 3. The air leaving first heat exchanger is in an over cooled state and requires reheat. The re-heat heat pipe coil heats air by transferring energy from pre-cool heat
pipe.

4.6 Analogical Blinds
Depending on the arrangements and settings made in the central management system,
unprocessed air could be released back into the atmosphere (when not needed by the
system), or it could flow into the air duct. This can be achieved by using two analogical blinds
(Servo) placed inside the air duct.
Servo's feedback mechanism in the blinds can provide air recycling control or an exhaust
percentage, since it will allow blind aperture adjustment. A system management algorithm
will automatically adjust the opening of the blinds in order to optimize water production
from the dehumidifier, without compromising the greenhouse’s work efficiency by a sharp
humidity or temperature drop.

4.7 Cooling – natural ventilation subsystem
The natural ventilation subsystem controls natural air cooling, heating or maintaining
humidity inside the Greenhouse. The main sensors interoperate with this subsystem in order
to save energy. If climate conditions are not maintained within the Greenhouse, cooling and
heating are supported by other subsystems. The system controls components like the
rooftop windows according to input data. Thus, the windows can open or close according to
temperature, humidity, wind speed and direction, rain or even snow. Up to 10 different
windows (side and roof) can be installed (Galcon, 2005).

42


4.7.1 Natural ventilation
The Greenhouses will have adequate natural ventilation through the installation of rooftop
windows on top of each bay. The greenhouse windows must have the following
characteristics:
 Rooftop windows must be 1.7 m wide with an opening lid 2.3 m wide. The lid's angle
will follow the construction's geometry. The lid movement when opened will be
linear with a right angle to the ground. Maximum lid opening should be 60 cm. In
addition, rooftop windows should be placed in the center of each Greenhouse
chamber and should be resistant to high winds of up to 80 km/h.
 The window mechanism will be equipped with a C-shaped steel (ST57) rail andnylon
plastic wheels. driven by a heavy duty, double toothed rack 2.5 mm thick. The racks
will be made of galvanized metal sheets, using Sendzimir's construction method and
the main axis with 33 mm diameter and 4 mm thick, will drive the racks. The main
axis will slide on a Teflon (tetrafluoroethylene) constructed ring.
 The wheels’ horizontal movement will be converted to vertical through an
articulated arm with modular connections leading the window lid in a vertical
direction. In addition, the system must be equipped with a third safety driver for
oscillation prevention at very high winds.
 Windows will operate mechanically with an electric reducer, which operates with a
double speed reduction and a rotational velocity speed of 3.5 revs/min.
Furthermore, the main axis will be equipped with built in limit switches, in serial
connection to block movement in case of any malfunction. Finally, all friction
mechanisms should be permanently greased for minimizing maintainance needs.
 Note that window openings will be protected with a repellent net made from a ten
year guaranteed material in order to prevent the entrance of insects (aphids) inside
the Greenhouse.

43


Figure 4-7 Rooftop Windows general settings

4.7.2 Cooling ventilation
Greenhouse climate, compared to external barometric conditions should always have
negative pressure. In order to achieve this, we will use four axial fans with stainless steel
impellers and 0.75 hp engines each, providing 19.000m3/h of air in the greenhouse
environment.
In combination with the axial fans, a battery (dim. 11m x 2m) will be placed in a special
compartment. The gutter and the tank of the battery will be made from prepainted
galvanized steel sheets with a 10-year guarantee for corrosion. The cooling system paper will
be 10 cm thick and impregnated with cellulose.
The compartment where the thermal panel will be installed, should be covered with a
transparent polycarbonate mini trapezoid 0,8 mm thick and will have two 1 m x 2.2 m doors
to allow for cleaning and maintenance and they will also be covered with a transparent
polycarbonate mini trapezoid 0,8 mm thick.
Finally, inside the compartment there automatic air louvers (dim. 1m x 1m) will be installed
to import air and it will open whenever requested by the main Greenhouse control system.
These louvers will be made of galvanized steel and they will have an on / off motor.

4.7.3 Subsystem operation
 All electrical components will be encased in a polyester plastic insulated waterproof
table (IP65).

44

 The panel’s electrical circuit will consist of two different circuits: Primary and
auxiliary. The auxiliary circuit will contain all the necessary automations for the
rooftop windows natural ventilation and the ventilation system resources operation
– cooling. The operation of natural ventilation should be controlled by rain, wind
speed and temperature sensors. This will be done incrementally, depending on
temperature deviations from temperature values set by the user. The control panel
will have the option of manual or automatic operation through a touch screen
connected to the central management computer (PLC). In the same screen menu,
the user can review and easily monitor internal and external environmental
conditions (temperature, wind speed, rain, rooftop window location e.t.c).
 Through the central control panel, the user should be able to choose whether the
rooftop windows will operate with or without dynamic ventilation. The selections
will be made through the “WINTER – SUMMER” menus shown on the touch screen.
If the automatic dynamic ventilation is on, the system will work in relation to the
external temperature and humidity. Additionally, constant connection with the
server determines air fan speed and thermal panel watering.

Figure 4-8 Fan operation sensors

45


4.8 Hydroponics
4.8.1 The Hydroponics subsystem
Greenhouse hydroponic methods involve root submergence in nutrient enriched water,
allowing plant ammonia removal, which can become toxic to animals. Ammonia removal is
achieved because water is filtered through the hydroponic system and oxygen enriched. This
cleaner water is then sent back into the hydroponic system creating a continuous cycle.
Hydroponic systems consist of:
 Recirculation aquaponics: a loose growing medium like pebbles or clay pellet
constantly immersed in water. This kind of setup is likewise referred to as closedloop aquaponics system.
 Reciprocating aquaponics: a solid growing medium that is repeatedly saturated with
water and drained. This type can also be referred to as ebb and flow or flood and
drain aquaponics.

4.9 Thermal-cooling panels
The thermal-cooling panels will be controlled automatically by the central management
system. This operation will be achieved through a special algorithm that imports data from
the following sensors:
 Temperature
 Internal humidity
 Light
Sensor use can achieve optimal thermal panel operation at night and whenever needed,
without effecting natural air flow produced by the natural ventilation subsystem. Through
the central system's touch screen, the user can choose the operation schedule for the
thermal panel and adjust the parameters of the algorithm making the mechanism to
open/close. The menu should be in Greek and a graphical display of the panel’s position
should be available in order to allow practical, fast and reliable connection of a remote user.
An electric reducer should be included in the automation system that operates the panel’s
opening and closing movement. The engine can power 1 hp (0,75 KW) with a rotation speed
of 900 rpm. The final output of the gear is 3.5 rpm.

46


Figure 4-9 Sensors settings

47


Figure 4-10 Thermal Cooling Panel

48


5 Operation Mode
The prototype Greenhouse units can operate as closed and as semi-closed greenhouses.

5.1 Closed Greenhouse
Application of the adapt2change system makes it possible to operate a so-called closed
greenhouse. It is an innovative, environmentally friendly and extremely efficient means of
providing optimal climate conditions for plant grown in modern greenhouses.
When there is no need to open greenhouse vents, great benefits can be achieved through
higher carbon dioxide content, and a more efficient use of additional lighting. In addition,
the adapt2change system's ability to adjust temperature, improves crop timing significantly.
The adapt2change system closed greenhouse system, also efficiently prevents the ingress of
pests and pathogens, while reducing pesticide use, and boosting biological control inside the
greenhouse.
The benefits of the adapt2change closed greenhouse are:
 Higher carbon-dioxide contents can be maintained maximizing CO2 fertilization
benefits.
 Pathogenic organisms and pests will not be able to access the greenhouse.
 It enables more efficient biological control.
 Offers the possibility to use additional lighting more efficiently
 Increases greenhouse energy efficiency to a totally new level.
 Makes it possible to increase yield significantly!
 Low investment cost and short repayment period.
 Easy to install and operate.
 Low operating costs.
 Possibility to adjust and monitor temperature and humidity, enabling optimum
conditions maintenance.

5.2 Semi-closed Greenhouse operation
The semi closed greenhouse is a closed greenhouse where partly controlled ventilation is
used (e.g. through rooftop windows) in order to control indoor climate conditions. Although
fully controlled ventilation can cover a larger portion of the cooling and dehumidification
load, it leads to a considerable loss of excess heat, which could otherwise be stored.
Therefore, fully controlled ventilation has to be optimized based on an appropriate energy
management scenario.
The purpose of semi-closed greenhouse system is for the reduction of ventilation
requirements. In terms of energy, this makes sense for non-illuminated fruit vegetables,
tropical plants, and crops that require both warm and cold climate conditions (P.L.J. Bom
Greenhouses B.V., 2011).

49

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