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

Subsystem Interoperation report

of Prototype Greenhouse

Installation

Adapt2change – LIFE09 ENV/GR/296 “Adapt

Agricultural Production to climate change and limited water supply”

Project

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 Closed Greenhouse ................................................................................................. 11

2.2 Expected energy conservation in greenhouse horticulture .................................... 12

3 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 Greenhouse Energy Conservation ........................................................................... 24

3.5 Insect Screens .......................................................................................................... 25

4 Prototype Greenhouse subsystems ................................................................................ 26

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

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

4.2 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

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

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

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


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

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

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

5.6 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


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

7 Appendices ...................................................................................................................... 71

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

8 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-year-

round 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


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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-to-

water 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 U-

shaped 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.

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.

Figure 2-1 Greenhouses in Larisa


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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


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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,


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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.


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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).


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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).

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


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


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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.


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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)

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


21

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



22

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 (15.6

oC) 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).


23

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).


24

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.


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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).


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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:


27

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).


28

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)


29

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)

o 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 U-

tube per borehole, the network length is estimated around 435 m (900 m

for the project’s 2 Greenhouses).

o 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.

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.

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

http://www.redaproject.org/


30

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.


31

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.


32

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.


33

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:


34

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.


35

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

Figure 4-4 Galileo Irrigation information system


36

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.


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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:


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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).


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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.

Figure 4-5 Galileo Main control system


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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


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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 non-

magnetic 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.


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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 re-

heat. 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).


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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.


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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).


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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


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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 closed-

loop 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.


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Figure 4-9 Sensors settings


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Figure 4-10 Thermal Cooling Panel


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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).


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In the Adapt2change system, the greenhouse is equipped with rooftop windows used to

reduce temperature, when the user decides to switch to semi-closed operation mode. In this

case, the system will be activated only when solar heat reaches threshold limits.

During the evening, greenhouse temperature is reduced in a short time span, benefiting

plants.

The system can also be used together with the lighting system, because when the screens

are closed, relative humidity increases and the cooling system can then be used to

dehumidify the air.

5.2.1 Daytime cooling

If the cost of cooling is relatively reasonable, cooling can also take place during the day. The

rooftop ventilation windows are then kept closed in order to increase CO2 concentration,

which improves crop yield.

5.3 Subsystems Inter-operation

In this section we will present the inter-operation between subsystems. Subsystem

Automation is very important in terms of an energy efficient Greenhouse. Subsystem units

are located inside the Greenhouse (two units) and in the engine room (one unit). The inter-

operation of the automated subsystems will be achieved with the use of an Ethernet

connection. The Ethernet network will be controlled by a main computer, in order to

monitor and adjust system's automations. Specifically, the geothermal subsystem will be

controlled by the engine unit, while the other subsystems will be controlled by the units

inside the greenhouse.

Based on the above description, as critical and important parameters for the function of the

input devices, we will consider indoor temperature and humidity. The operation of

greenhouses can be broadly divided into two parts: summer months operation and winter

months operation. Below the scenarios for different automated functions are analyzed

according to internal temperature and humidity. For better understanding of the automated

procedures, flowcharts are used. In each scenario, optimal temperature is 25 °C,while

optimum relative humidity is 65%.


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5.4 Semi-closed Greenhouse automated functions during

summer

During summer in the region of Larissa (latitude=22°25'0'', longitude=39°38'0'', elevation =

72,2m), the dry bulk temperature system parameter (DBCOOL) has value of 37 °C with 1%

design conditions in accordance with the Technical Directive 2425/86 of the TEE (Technical

Chamber of Greece).

This is the threshold temperature and it is exceeded by the external temperature by 1%

average for the summer season, i.e. (1/100) x 2,928 h = 30 h per year. The summer season in

the Regulation is defined as the period from June 1 to September 30.

5.4.1 Scenario 1

In the first scenario, one of the critical parameters that vary in the Greenhouse is

temperature. Temperature is greater than the threshold values, thus the subsystems will

function automatically in order to decrease Greenhouse indoor temperature.

In this scenario, the first indications from the indoor temperature sensors show a change of

5°C. In the beginning, the main system will monitor outside sensors values and determine

whether cooling is possible through natural ventilation. In this case, the first subsystem put

into function is the natural ventilation subsystem, which is a more energy efficient solution.

If additional cooling capacity is needed and indoor temperature is not changing, a time limit

is set in order to close the rooftop windows and to enable the cooling subsystem, the fans

and the geothermal subsystems. These subsystems are activated in order to balance cooling

and humidity levels. It is very important to ensure that the Greenhouse climate will reach

the required humidity levels in spite of any temperature changes. The system will continue

to check conditions through a loop process and activate or deactivate the subsystems.

In circumstances where (Figure 5-1):

30°C> Tempin > 25°C

Humin = 65% RH

The top window will open incrementally at a rate proportional to the forthcoming change of

temperature. This will continue (within a certain time limit) until the desired change is

achieved. If the conditions described above continue even after the time limit, then:

Rooftop windows will be closed. The cooling system and fans will change to operation mode. The blinds will open. The geothermal system will start its operation with the first coil on heat mode

and the other on cooling mode.


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Figure 5-1 Scenario 1


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5.4.2 Scenario 2

The second scenario is more complex and in a way simulates reality. The critical parameters

changing in the Greenhouse are temperature and humidity. At first temperature is greater

than threshold values, thus the subsystems will function automatically in order to decrease

indoor Greenhouse temperature. However this function will increase humidity.

Indoor temperature sensors have shown a change of 6°C. At first the main system

deactivates the rooftop windows stopping natural ventilation in order to force automatic

cooling thus activating the cooling - fans and the geothermal (in dual coil cooling mode)

subsystems. To balance humidity levels, the blinds are activated. The result of this procedure

may balance the temperature to 30°C but humidity increased over the desired 65%. So the

main system will check conditions through constant sensor readings and automatically set

the subsystems to balance humidity levels as well by closing the rooftop windows and blinds

and turning off the cooling subsystem and fans through the main system. Simultaneously the

geothermal subsystem will change in one coil heat mode and the air recycling subsystem will

be activated. This procedure will continue until the sensors receive the threshold

temperature and humidity readings.


36°C> Tempin> 30°C

Humin=65%RH.

The procedures that will take place are:

Closing rooftop windows.

Activation of cooling system and fans.

Opening blinds.

Geothermal system activation with two coils in cooling mode.

For the collection of vapor water in conditions of optimum indoor temperature and humidity

100% RH> Humes> 65% RH, the following steps are executed:

Close Blinds.

Close Windows.

Turn off Fans.

Turn off cooling system.

Activation of the air recycling subsystem.

Operation of the geothermal system with the first coil to heat mode.


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5.4.3 Scenario 3

The third scenario involves humidity changes. Temperature is changing within threshold

values, but humidity is greater than threshold values. The goal in this scenario is to simulate

subsystem functions in order to balance Greenhouse’s humidity conditions. In this situation

another challenge is to ensure temperature stability for crop growth.

Scenario 3 begins with high humidity value 65%. At first the main system puts the first

geothermal coil to heating mode and in order to stabilize humidity levels within threshold

values, it deactivates (if active) the blinds, the rooftop windows, the cooling subsystem and

the air recycling subsystem. The interoperation of the subsystems offers the ability to

control all system function at any time and with a time dependent operation mode.

Therefore, the cooling subsystem fans are programmed to operate in time periods. This

optimizes system control and humidity level regulation. The system then checks sensor

readings in order to activate or deactivate the subsystems according to Greenhouse

condition requirements.


65% RH > Humεσ > 40% RH

Tempin=25°C

The main system responds with the following actions:

Close Blinds. Close rooftop windows. Deactivate cooling subsystem. Fan activation based on set time operating periods. Deactivate air recycling subsystem. Operation of the geothermal system with the first coil on cooling mode.


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Figure 5-4 Fan and cooling subsystem Programming for time limits e.t.c

5.4.4 Scenario 4

In this scenario the main system responds to outdoor conditions in order to reduce energy

needs by using natural energy resources for Greenhouse cooling. The outside temperature is

<25% so the case here is how the main system will try to exploit lower outdoor

temperatures. Note that inside conditions favor temperature increase, thus the goal here is

to simulate subsystem functions for natural cooling. This scenario presents how subsystems

interoperate if natural cooling is not efficient.

Temperature is 30 °C in the Greenhouse and humidity is within normal levels. Firstly, the

main system activates the first geothermal coil to heating mode and in order to maintain

desirable humidity levels, it deactivates (if active) the cooling subsystem and fans while

activating the rooftop windows and the air recycling subsystem for air to enter the

Greenhouse. To balance climate conditions, the geothermal system operates with the first

coil on heat and the second coil on cooling mode. The main system will continue to monitor

sensor readings in order to activate or deactivate subsystem functions.

If temperature sensor values are over the limit, an alternative cooling procedure will initiate.

The main system will force Greenhouse cooling by activating the fans, the cooling subsystem

and the blinds while closing the rooftop windows.


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30°C >Tempin > 25°C

Humin > 65% RH.

When outside temperature is < 25°C, the steps to be followed will be:

Open rooftop windows. Operation of air recirculation subsystem. Operation of the geothermal subsystem with the first coil on heat mode and the

other on cooling mode. Turn off fans. Turn off cooling subsystem.

If the above steps do not reduce indoor temperature after a certain period of time and while

the outside temperature remains the same, then:

The rooftop windows will close.

The air recirculation subsystem will remain active.

The geothermal subsystem will continue to work with the aforementioned logic.

The fans will be activated.

The cooling subsystem will be activated.

The blinds will be activated.


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5.5 Semi-closed Greenhouse automated functions during winter

In terms of temperatures during winter in the region of Larissa (latitude=22°25'0'',

longitude=39°38'0'', elevation = 72,2 m), the average minimum outdoor temperature has a

value of -7 °C according to the Technical Directive 2425/86 of the TEE (Technical Chamber of

Greece).

5.5.1 Scenario 5

In this scenario the system responds to temperature increase and humidity changes. Note

that Greenhouse temperature and humidity must have specific values regardless of the

season. Therefore, with a low outdoor temperature during winter, the subsystems will be

activated in order to heat the Greenhouse and balance humidity. The heating process may

dry the air and damage the crops, thus the goal in this scenario is to simulate subsystem

functions for heating.

Greenhouse temperature is 20°C and humidity has reached 100%. The main system activates

the first geothermal coil to heating mode and then the system will deactivate the cooling

subsystem, the rooftop windows, the fans and the blinds while activating the air recycling

subsystem. If the temperature values remain low even after the aforementioned actions, the

second coil will change its operation from cooling to heat mode. The main system will

continue to monitor sensor readings in order to activate or deactivate functions.


25°C >Tempin > 20°C

100%RH >Humin >50% RH.

The actions to be followed will be:

Turn off cooling system. Close rooftop windows. Turn off fans. Operation of the geothermal subsystem with the first coil on heat mode and the

other on cooling mode. Turn off blinds. Activate the air recirculation subsystem.

If low temperature values persist, the second coil will change to heat mode.


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5.6 Closed Greenhouse automated functions both during

summer and winter

As mentioned previously, the Greenhouses will have the capacity of working as closed

systems without any air input from the outside. Inside air will be recycled in order to achieve

economy in resources and optimum climate conditioning for the crops. In this chapter,

scenarios are built for a closed Greenhouse operation.

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

In this scenario the system responds to temperature increase and humidity changes.

During summer, outdoor temperature is very high and the system must achieve

maximum efficiency without outside air input. The goal in this scenario is to simulate

subsystem functions for very high summer temperatures.

The outside temperature is 34 °C and thus the indoor temperature starts to increase,

while humidity is 40%. The main system activates both geothermal pumps to cooling

mode and the air recycling subsystem. If greenhouse temperature is still high, the second

coil will operate on cool mode. The main system will continue to monitor sensor readings

in order to activate or deactivate functions.


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Scenario 2 (summer – closed G.H mode)

In this scenario (Figure 5-8), the main system responds to temperature increase. During

summer nights, outside temperature is high but within desired levels and the main system

must maximize its efficiency without outside air input. The goal in this scenario is to simulate

subsystem functions for summer nights when a balanced cooling operation is required.

Outdoor temperature is 28°C and in the Greenhouse, temperature starts to increase with

a humidity of 40%. The main system activates both geothermal pumps to cooling mode as

well as the air recycling subsystem. If temperature is still high, the second coil will operate

on cool mode. The main system will continue to monitor sensor readings in order to

activate or deactivate functions.


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

In this scenario the main system responds to temperature increase. This is an example of a

closed –semi closed operation (Figure 5-9). In this case, the main system will be operating

under very high outdoor temperatures. The goal is to simulate subsystem functions for

maximum cooling efficiency.

Outdoor temperature is 34°C and indoor temperature starts to increase, while humidity is

50%. At first the main system activates both geothermal coils to cooling mode and the

recycling subsystems. If indoor temperature sensor readings show higher than desired

values, the main system automatically changes its operation to “semi-closed”. The cooling

subsystem will then be activated as well as the rooftop windows, the fans and the blinds.

The main system will continue to monitor sensor readings in order to activate or deactivate

functions or change its operation modes.


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

In this scenario, the main system responds to temperature decrease (Figure 5-10). During

winter, outdoor temperature is low and the system must achieve maximum efficiency

without outside air input. The goal in this scenario is to simulate subsystem functions for

winter when a balanced heating operation is needed.

Outside temperature is low and indoor temperature starts to decrease while humidity is

40%. The main system activates both geothermal pumps to heating mode as well as the air

recycling subsystem. If temperature increases, the second coil will start to operate in cool

mode. The main system will continue to monitor sensor readings in order to activate or

deactivate functions.


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7 Appendices

7.1 A

ppend

ix I

Figure 7-1 Storage temperatures of various Plants. American society of heating, refrigeration and air conditioning engineers, Atlanta, GA,1992


72

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