Feasibility Study of Hydroponic System in Tropical Climate

Swinburne University of Technology
Sarawak Campus
School of Engineering and Sciences

Feasibility of Hydroponic System in Tropical Climate
Bachelor of Engineering
(Mechanical)

Stansfield Chua Hua Ming
4217667

November 2013

Content
Declaration…………………………………………………………………………………....I
Acknowledgement…………………………………………………………………………...II
Abstract……………………………………………………………………………………..III
1. Introduction………………………………………………………………………………1
1.1 Project objective……………………………………………………………………...2
1.2 Job distribution………………………………………………………………………3
2. Literature Review………………………………………………………………………..5
2.1 Background…………………………………………………………………………..5
2.2 Hydroponic system…………………………………………………………………...6
2.2.1 Types of hydroponic system……………………………………………………….6
2.2.1.1 Static or Deep water Solution Culture (DFT & DRF)…………………………6
2.2.1.2 Continues-flow Solution Culture/Nutrient-Film Technique (NFT)…………...7
2.2.1.3 Aeroponic…………………………………………………………………………8
2.2.2 Comparison between DRF, DFT, NFT and Aeroponic………………………….9
2.3 NFT as the choice for tropical hydroponic system………………………………..10
2.4 Insulator and insulation system……………………………………………………11
2.4.1 Insulation analytical analysis…………………………………………………….11
2.4.2 ComsolMultiphysics simulation…………………………………………………14
2.5 Nozzle-delivery system……………………………………………………………...18
2.5.1 Spray nozzle background………………………………………………………...19
2.5.2 Spray nozzle pattern……………………………………………………………...19
2.5.3 Droplet size………………………………………………………………………...20
2.5.4 Cooling effect of spray nozzle…………………………………………………….21
3. Methodology…………………………………………………………………………….23
3.1 Model Description…………………………………………………………………..23
3.1.1 Solidworks2012 Control Test Rig Design………………………………………..24
3.1.2 Fabricated Model………………………………………………………………....25
3.2 Measurements……………………………………………………………………….28
3.2.1 Flow rate measurement…………………………………………………………...28
3.2.2 Water temperature of the system measurements……………………………….29
3.3 Assumption………………………………………………………………………….31
4. Result…………………………………………………………………………………….35
5. Analysis and Discussion………………………………………………………………...39
6. Recommendation………………………………………………………………………..40
7. Conclusion……………………………………………………………………………….40
Reference………………………………………………………………………………………A
Appendices………………………………………………………………………………………B

List of Figure
Figure 1: DFT / DRF. (Maria Swan, 2011)……………………………………………………6
Figure 2: NFT (NA, 2012)…………………………………………………………………….7
Figure 3: Aeroponics. (NA, 2010)…………………………………………………………….8
Figure 4: Difference between aeroroots and nutriroots. (Te-Chen Kao 1991)………………..9
Figure 5: Aeroponic roots. (Derek Jacoby 2010)…………………………………………….10
Figure 6: The two-dimensional model of the pipe with and without insulation……………..14
Figure 7: Temperature distribution throughout the pipe with applied condition…………….15
Figure 8: Heat flux loss to the outer layer indicated by colors and arrow…………………...16
Figure 9: The thermal resistance against increased in insulation thickness………………….17
Figure 10: Variation of nozzle head………………………………………………………….19
Figure 11: Hollow Cone Nozzle……………………………………………………………...20
Figure 12: Classification of droplet size……………………………………………………...21
Figure 13: Nozzle illustration………………………………………………………………...22
Figure 14: Isometric exploded view of the model. 1) Storage container2) Pump 3) Planting gutter channel…………………………………………………………………….24
Figure 15: Isometric view of the full sketch model…………………………………………..24
Figure 16: The completed fabricated model………………………………………………….25
Figure 17: Bridge…………………………………………………………………………….25
Figure 18: Ball valves………………………………………………………………………..26
Figure 19: Level gauge indicating the system tilt level………………………………………27
Figure 20: Flow rate measurement…………………………………………………………...28
Figure 21: Measurement location…………………………………………………………….29
Figure 22: The 3 thermometers used. Aquarium digital thermometer, alcohol thermometer, andUyigao UA-902C digital thermometer………………………………………30
Figure 23: Transient heat conduction in semi-infinite solids plotted using EES. (Cengel, 2011)……………………………………………………………………31
Figure 24: Complementary error function table. (Cengel, 2011)…………………………….32
Figure 25: Graph of soil and ambient temperature…………………………………………...34
Figure 26: Day 1……………………………………………………………………………...35
Figure 27: Day 2……………………………………………………………………………...36
Figure 28: Day 3……………………………………………………………………………...36
Figure 29: Day 4……………………………………………………………………………...37
Figure 30: Day 5……………………………………………………………………………...37
Figure 31: Day 6……………………………………………………………………………...38
Figure 32: Day 7……………………………………………………………………………...38
Figure 33: Reading record paper………………………………………………………………C
Figure 34: Site location mark with “x”…………………………………………………..D
Figure 35: Close up of the site………………………………………………………….D

DECLARATION

I hereby declare that this report entitled “Feasibility of Hydroponic System in Tropical Climate” is the result of my own project work except for citations and references which have been duly acknowledged and it has not been previously or concurrently submitted for any other degree at Swinburne University of Technology Sarawak Campus.

Name :Stansfield Chua ID : 4217667
Date : 19th May 2013

ACKNOWLEDGEMENT

This project and report could not have been possible and done without the guidance of my academic supervisor, Dr. Soon Kok Heng. It is with his assistance and guidance that I am able to manage to overcome all the obstacle and doubt I encounter in this project. I would like to also acknowledge Chua Hua Beng and Slyvester Mutang, my project group mate for your patience and contribution you guys have put into this project together with me.

ABSTRACT

This report is based on a study of the feasibility of hydroponic system in tropical climate. A fabricated NFT system is built and tested in an open field in Swinburne University of Technology Sarawak Campus. The temperature data of the points in the system is collected, tabulated and compared with the assumption made in this report. The study was an overall success.

1.
2. Introduction

With the increase of development in Malaysia to achieve its vision of a developed country by the year 2020, sectors such as infrastructure sector and information technology have significantly improve throughout the decade while the agriculture sector is still operated using predecessor technology and techniques.
Malaysian Investment Development Authority (MIDA) 2013 reported that in 2011, Malaysia imported RM34.5 billion worth of food where RM4.2 billion is for fruit and vegetable and exported only RM20.6 billion worth of food to countries including Singapore, USA, Indonesia and Republic of China. This shows a change in food habits and demand in the country towards imported food produce which is not a healthy trend and increases Malaysia’s food insecurity.
In a report release by the Ministry of Agriculture and Agro-Based Industry Malaysia (MOA) in 2012, it can be seen there is 7.74% decrease in food farming land in Malaysia in the past decade and it is predict to decrease another 8.1% by the year 2020. The factors for this decrease is the conversion of food farming land to housing areas to accommodate the increasing occupant, conversion to manufacturing industry to meet output demands, the relatively higher planting of cash crop than food produce and etc.
Other than that, according to a study done by MARDI, an increase of 10 in temperature could decrease crop output by 9% to 10% and with the rising pollution index and temperature that Malaysia is experiencing, food farming and industry related to it in Malaysia will suffer setbacks in the future.
In order to overcome the food insecurity contributed by multiple factors, better management and technology needs to be implore to the agriculture food farming sector to reduce our dependency toward importing food for the occupant consumption.
This report will look into the feasibility of introducing hydroponic system to cultivate food crop in Malaysia. Australia is a famous country that has uses hydroponic system to increase their food crop because large portion of the land in Australia are infertile. However, Australia experience temperate climate while Malaysia experience tropical climate and climate factor plays an important factor when deciding which type, what configuration and modification needs to be adjust when producing crop in hydroponic system in tropical country.

In this report, our aim is to study, analyze and assess the performance of NFT system, one of the branches of hydroponic system when expose to the tropical climate and report our findings.

1.1 Project objective

Our project main objective isto obtain the range of temperature in the selected hydroponic system solution when exposed to outdoor tropical climate weather over a period of selected time and compare it to the root temperature limit.

In Objective 1, we study the effect of tropical climate on the hydroponic system solution temperature relative to the ambient temperature using a fabricated control test rig.
In Objective 2, we modify our test rig by installing suitable insulator and we study its effect in reducing heat flux in the hydroponic system.
In Objective 3, we change the solution delivery system of our test rig and we study the effect of it reducing heat flux in the hydroponic system.
In Objective 4, we design and fabricated a prototype model to be use in tropical climate and test it performance.

For HES5102 Research Project, we will only cover up Objective 1.

1.2 Job distribution

My job in this project is to:
Build Control Test Rig
Produce the Solidworks Design
Obtain the roots temperature data
Research on hydroponic background

My individual Gantt chart can be seen in the next page.

3. Literature Review
2.1 Background

The Ministry of Agriculture & Agro-Based Industry Malaysia (MOA) give a statement that the production of the agro-food sector is mostly done on smaller scale and lack the use of technology. This leads to low productivity, low competitiveness of the overall agro-food industry.
In maintaining adequate food supply, YB Datuk Seri Noh pointed out that the main challenge is the shortage of land for agriculture. He also pointed out that land for the production of food is estimated to drop further from 922000 hectares in 2010 to 841000 hectares by the year 2020 due to conversion of food farming areas into oil palm estate and industrial area (Jurutera, January 2013).
Automation and mechanization plays an important role to encourage more small-scale farmer to own and use small machinery and equipment to increase agricultural produce especially in the food farming industry. This leads to the proposal of the usage of hydroponics system as automated farming equipment which has been done in Genting Highlands to grow temperamental plants. The contributing factor and advantage of hydroponic system is that is has high yield on small area and vertical space can be utilized (Venter.D, pg 55). Furthermore it can be grown anywhere ranging from low quality soil, desert, tropical or hard surface.

2.2 Hydroponic system

Hydroponic system is defined as the science of growing plants without the use of soil but with the use of inert medium (M.Resh, pg. 2). Present day, the development of plastics, suitable pump, plastics plumbing and solenoid valves has made modern hydroponic system automated, reducing dependency on human manpower. In large cities, there is a potential for hydroponic greenhouse roof-top garden as describe in a Scientific American (November 2009) article written by D. Despommier.
The requirements when choosing a hydroponic site location are an area that is near level as possible or one that can be easily leveled, good internal drainage with minimum percolation rate of 1in. /h, a region that has a maximum amount of sunlight, areas not having excessive strong winds.These requirements would help to ensure improve success rate in the system. (M.Resh, pg. 5-6)

2.2.1 Types of hydroponic system
2.2.1.1 Static or Deep Water Solution Culture (DFT & DRF)

Figure 1: DFT / DRF

The Static Solution or Deep Water Culture is a fairly simple system where the roots of the plants are either partially or completely submerged in the nutrient rich solution. In order to keep the solution oxygenated, an air pump is connected to an air stone which is submerged in the solution and thus providing the roots of the plants with enough air. There are 2 semi branch of static culture which is deep flowing technique (DFT) and dynamic root floating (DRF)

2.2.1.2 Continues-flow Solution Culture/Nutrient-Film Technique (NFT)

Figure 2: NFT

Continues Flow Culture is the more commonly used method where only the roots of the plants are exposed to a shallow flowing stream or film of nutrient rich solution that is pumped up from a reservoir below the growing tray. After the nutrient solution has passed through all the roots, it then flows back to the reservoir where it is again pumped back into the growing tray. The cycle is then repeated until the plants or cultures are mature enough for harvesting. This method may be the most commonly used.

2.2.1.3 Aeroponics

Figure 3: Aeroponics

Aeroponics system is usually used for cultures or plants which have sensitive roots and would get water logged easily when in constant contact to liquids. This system closely resembles the Continues Flow Culture however with a slight difference. Instead of using a continuously flowing stream or film of nutrient rich solution, the Aeroponics system uses multiple mistifiers that are connected to a pump installed in the reservoir to convert the liquid solution to a fog or mist form. The mist then comes into contact with the roots of the plants which are suspended above the mistifiers. Any excessive solution which does not come into contact with the roots of the plants then drip down and collect in the reservoir. The solution is then repeats this cycle to provide ample nutrient and air to the roots of the plants.
2.2.2 Comparison between DRF, DFT, NFT and Aeroponic

The 2 root that plants grow in a hydroponic system are aeroroot to absorb oxygen and nutriroot to absorb the nutrient solution. A comparative test between DRF, DFT and NFT show that while DFT does not induce aero root growth even though it can maintain a more stable temperature in the nutrient solution. However, NFT is the inverse of that with better induction of aero root growth but fluctuating temperature in the nutrient solution which can cause root rot and rot death at higher temperature (Venter. D, 2010, pg. 192-193).
Figure 4.Difference between aeroroots and nutriroots.

However, according to an article in Hydroneeds, NFT system is better because the plant roots are exposed to adequate supplies of water, oxygen and nutrients compare to the rest. This is because there is a conflict between the supply of these requirements in DRF and DFT which can results in an imbalance of one or both of the requirements. The disadvantage of NFT is that it has very little buffering against interruptions in the flow during power cut but overall it is one of the more productive techniques.
Aeroponic in the other hand has an increased aeration of nutrient solution which delivers more oxygen to plant roots, stimulating growth and helping to prevent pathogen formation leading to better root formation and overall growth as seen in figure 5. However, the cost to set up out weight it advantages.

Figure 5.Aeroponic roots

2.3 NFT as the choice for tropical hydroponic

We can conclude from the comparison above that NFT is more suitable for planting in tropical climate. The major factor in this decision is that the cost and availability of material is cheaper and more abundant in tropical countries and its ability to induce aeroroots compared to other techniques.
Ambient temperature in the tropics range from, even higher at times, making it important to maintain constant temperature in NFT nutrient but it is more important that any hydroponic system used in the tropics must have the ability to induce aeroroots (Venter.D, 2010, pg 193). Therefore, the NFT temperature fluctuation has to be dealt with in the situation of it being used in tropical climate.

2.4 Insulator and insulation system

In order to maintain a stable temperature in the hydroponics system, we can look into insulator to be applied on the external exposed areaminimize the temperature fluctuations faced in the NFT system.
The basic function of a thermal insulation system is to reduce the flow heat as effectively as possible over a long service life to provide a satisfactory return on insulation investment and to maintain thermal stability in the targeted area. Thermal insulation systems play an important role in efficient operation of industrial plants because the appreciable value of energy employed in heating and refrigeration. (Way & Hilado, 2010)

2.4.1 Insulation analytical analysis
Researchers demonstrated that in order to calculate heat flow passing through a pipe with or without insulation, it is necessary to calculate the thermal resistance for each material layer. For cylinders this thermal resistance varies not only with the insulation thickness and thermal conductivity, but also with the pipe outer diameter and the average material temperature.
The thermal resistance of each insulation layer is calculated using the following equation:

Where: = the outer radius of that layer [m]
= the inner radius of that layer [m]
= the thermal conductivity of that layer [W/m.K]

The total thermal resistance of a pipe, with or without insulation layer(s) and surface heat transfer resistances to inner fluid and extern ‘air’, can be calculated with following equation:

Where:
= inner surface heat transfer resistance between fluid and material (1/hi) [m2.K/W] = outer surface heat transfer resistance between fluid and material (1/hi) [m2.K/W]

An example calculation done by other researcher is shown below:

A metal pipe with thermal conductivity of 52 W/mK and an insulated layer of 5 cm thick with thermal conductivity of 0.03 W/mK. The inner radius of the pipe is 1.60 cm and outer radius is 2.13 cm. The inner surface heat transfer resistance coefficient to inner flowing liquid is 1/2000 m.K/W and outer resistance coefficient to the air is 1/8 m².K/W.
The thermal resistance over the pipe without insulation is:

The total resistance of the 5 cm insulation is:

The heat flowing through the pipe surface is calculated using the following equation:

The temperature of the liquid is 60⁰C and the air temperature is 20⁰C, the heat flow through the pipe surface without insulation is:

When the pipe is insulated the heat flow passing through the pipe is:

If the temperatures of inner and outer surfaces are known, the temperature at any point in the material layer(s) can be calculated with the following equation:

2.4.2 ComsolMultiphysicsnumerical simulation
Fig. 6 illustrate the two-dimensional model of the pipe with insulation layer (left) and without insulation layer (right) is given, the colors in the figure indicate the thermal conductivity of the materials.

Fig 6. The two-dimensional model of the pipe with and without insulation

In this simulation model, the same temperatures, conductivities and surface heat transfer coefficients used in the calculations are applied in the parameter values. The temperature distribution through the pipe and insulation under these conditions are shown in Fig. 7.

Fig 7. Temperature distribution throughout the pipe with applied condition

The heat flux through out the material is shown in Fig 8.

Fig 8.Heat flux loss to the outer layer indicated by colors and arrows.

By multiplying the maximum heat flux, which accorded to the inner surface with the circumference of the inner surface, the total loss of heat flux can be calculated.
For the pipe without insulation:

For the pipe with insulation:

In conclusion, the results from the ComsolMultiphysics numerical simulation are the same than the results obtained in the analytical calculations.

Fig 9. The thermal resistance against increased in insulation thickness

In Fig 9, it can be seen that the thickness of the insulation layer is not proportional tothe total thermal resistance but move in a curve line. The relationship shown in the graph is based on the insulation material used in the previous calculation and simulation.

2.5 Nozzle-delivery System

Nozzle delivery system is another aspect that can we study to reduce the temperature fluctuation in the nutrient solution of the NFT and provide aconducive root-zone atmosphere in the system.
The system will be supplied with a combination of air and small particles of liquid nutrient solution (Vickers et al 2009, p. 1). This will satisfy the condition of aeroroots induction in tropical hydroponic system.
Nozzle delivery system works by delivering nutrient solution from a high pressured pump which passes through atomizing spray nozzle. The solution passing through the nozzle head would then be atomized and come out as a mist or fog. The spray cooling effect can be observedand its effect in reducing the temperature of the root-zone area.

2.5.1 Spray nozzle background

Figure 10. Variation of nozzle head

Nozzle can be used to control the direction of a fluid flow and it has the ability to change the characteristic of a fluid flow such as rate of flow, speed, direction, mass, shape, pressure, spray etc. The different combination of these characteristic has led to the variation of nozzle head design show in figure 10.
Spray nozzle is a precision nozzle that disperses liquids into spray by producing a very fine spray of atomized liquids with droplets size microns in measurements. Some of the practical example of spray nozzleusage includes spray paintings, carburetors,perfumes, antiperspirants and aerosol spray.

2.5.2 Spray nozzle pattern

Spray patterns in spray nozzles can be identify as solid stream spray, hollow cone spray, full cone spray, flat spray and multiple plume spray.
Hollow cone fits the direction of our studies as this type of spray nozzle is best for applications requiring good low pressuresatomization and quick heat transfer.
Hollow cone nozzle featuresa large and unobstructed flow passage, giving it the property of high resistance to clogging. Hollow cone also nozzles provide the smallest drop size distributions. The relative range of drop sizes tends to be narrower than other hydraulic styles (Lefebvre 1989).

Figure 11. Hollow Cone Nozzle

2.5.3 Droplet size

Researcher found that droplet micron size should be between 30 and 80 micron and not below 5 micronfor effective use in hydroponics system (Vickers et al 2009, p.1). The impact from this droplet size will not compromise the root growth.
Figure 12 below is taken from Ikeuchi USA, a nozzle manufacturing company. It shows the classification of spray droplet size. The fine atomization range is suitable in hydroponic system because it covers the range of suitable droplet size mention by Vickers above.

Figure 12.Classification of droplet size

2.5.4 Cooling effect of spray nozzle

When liquid is forced through a small orifice, shattering into a dispersion of fine droplets which then impact a heated surface, the droplets can spread on the surface and evaporate, removing large amount of energy at low temperatures due to the latent heat of evaporation in addition to substantial convection effect (Horacek, Kiger, Kim 2005, p. 1425–1438).
This cooling effect is produce from the adiabatic expansion of liquid through the nozzle. The mathematical equation is shown below:

Where: = initial temperature = adiabatic index; >1 = final temperature = initial volume = final volume

Figure 13. Nozzle illustration

Based on the equation and the figure above, is smaller than, therefore will be significantly lowerthan.

4. Methodology
3.1 Model Description
The team is required to build a NFT system as a control test rig to simulate the temperature fluctuation in the nutrient solution when expose to the morning to evening climate and weather condition.
Some of the fix variables that we set in our control test rig are

I. The gutter channel is 2 meters in length. Even though it is recorded by other researchers that the maximum length of the gutter can exceed up to 10-12 meter without causing depressed growth rate, our decision is because we have limited space, resources and budget to fabricate such lengthy channel in 3 months and we unanimously agreed that 2 meters will provide us with sufficient data to see temperature fluctuation in the system.
II. The flow rate inside the channel should flow 1 liter/min to 2 liter/min as this was the optimum range NFT flow rate discovered by researcher.

Some factors we take into consideration were
I. In order for the system to experience uniform heat exposure, we orientate the model to let it expose to the moving direction of the sun from east to west. Refer to Figure 34 and 35 in the appendices for the orientation view.
II. Rain would also impact the temperature fluctuation pattern so the data reading from it would be taken into account as we want the result reflect the climate condition as closely as possible. However, we will shield the system from rainwater increasing the volume of water and create discrepancy when cooler rainwater mixes with the system water. This is achieved by covering the system with thin plastic canvas.
III. The plastics pipes used in the control test rig should be food grade because ultimately, the purpose of a hydroponic system is to grow vegetable plants for us to harvest as food and safe food consumption should always be a priority.

3.1.1 Solidworks2012 Control Test RigInitial Design
Figure 14. Isometric exploded view of the model. 1) Storage container2) Pump
3) Planting gutter channel

Figure 15. Isometric view of the full sketch model

Figure 14 and 15 is the Solidwork2012 rendition of an NFT model we come up with. It is a rough design of what our expected fabricated model would look like once completed. The necessary component such as the planting gutter channel, pump, storage container, and support frame can be seen in the figures.

3.1.2 Fabricated Model

Figure 16.The completed fabricated model.

Figure 16 shows the completed fabricated model we build ourselves. The planting gutter channel and pipes are made from food grade PVC plastics, while the storage container is made from HDPE plastic. The pump used is an aquarium submersible pump.
In order for our system to have a water film layer inside the planting gutter channel, a 1 inch high bridge made from PVC sheet was place inside the exit pipe fitting as shown in figure 17.

Figure 17. Bridge

Initial testing saw the channel experiencing ponding but after cutting stilts onto the bridge, the channel produce an even water film layer.

Some of the important key differences between the fabricated model and the solidworks2012 are the fabricated model has 2 ball valves to manipulate the flow rate into the planting gutter channel as shown in figure 17. This is because we are using a high flow rate output pump and we are uncertain of its output into the channel. By adjust the ball valves, we can control the flow rate into the channel while excess flow rate flow back into the storage.

Figure 18 Ball Valves

In order for the system to operate smoothly, the control test rig has to have slight tilt of 1:40 to prevent ponding in the system while maintain a good flow. After shifting onto the testing field to be tested, we use a level gauge to check the level and small bricks to adjust the level. The end placement as shown in figure 19 shows the slight tilt is achieved.

Figure 19. Level gauge indicating the system tilt level

3.2 Measurements
3.2.1 Flow rate measurement

In the daily tests conducted, the flow rate is measured 1 hour prior the first temperature measurement taking. This is to ensure the flow rate in our system always maintain at 2 liter/min. We achieve this by manually measuring the exit volume of the system in 1 minute using a 2000ml beaker and a stopwatch as illustrated in figure 20.

Figure 20. Flow rate measurement

3.2.2 Water temperature of the system measurements

We measure the temperature of the system by measuring the water temperature inside the water storage container and the 7 holes along the planting gutter channel as shown in figure 21.

Figure 21. Measurement location

We do this by dipping a digital thermometer in each of the point recorded the reading down in the reading sheet in Figure 33 in the appendices.
The thermometers used in our test and their roles are listed below and shown in figure 22:
I. Uyigao UA-902C Digital Thermometer
II. Aquarium Digital Thermometer
III. Alcohol Thermometer

Figure 22. (From left to right) The 3 thermometers used. Aquarium digital thermometer, alcohol thermometer, and Uyigao UA-902C digital thermometer.

The 7 point measurement and water storage is taken using the Uyigao UA-902C digital thermometer, the ambient temperature is taken using the alcohol thermometer and the 2 unit of Aquarium digital thermometers are place at point 1 and 7 as backup units to show the temperature difference between these 2 points.
The water temperature is taken hourly from 10am to 5pm. The reading is taken in these times because the heating fluctuation is more prominent during these hours. Furthermore, it is a general knowledge that the temperature in tropical region tend to soar higher during midday and times it is in between.
The reading was also taken hourly because 10 – 30 minutes interval gave us only slight change in data while 2 hours interval omit important changes in the data. We have checked these time interval variable prior to actual data recording and we discover hourly interval is accurate enough to be recorded.

3.3 Assumptions
In order for a hydroponic system to work, the temperature of the nutrient solution has to be in the acceptable range that can be handled by the plant’s root. If the temperature rises over this range, it can cause root death in the plant, leading to the imminent death of the plant.
In our attempt to gather this Root Temperature Data (RTD), we have visit the vegetable research department of the Department of Agriculture Sarawak to find this information. However, they do not have nor ever research the acceptable range of temperature for the roots of vegetable. Furthermore, online database only shows the root temperature of temperate plants like lettuce, basil and alfalfa in temperate hydroponic system.
This leads us to create an assumption based on the application of heat transfer from the air to the certain depth of the soil where the root is using transient heat conduction in semi-infinite solids.

Figure 23. Transient heat conduction in semi-infinite solids plotted using EES

The variables in this assumption are:
From the 7 days of data that was collected, the highest ambient temperature difference was recorded at 19 of difference on 8th May 2013. The ambient temperature data of this day will be the use in our assumption.
The average soil properties is k=0.4 and
Average root burial depth is 7.5cm. (
Time interval is 1 hours.
The soil is to be considered as a semi-infinite medium.
The initial is 27

The calculation is as follows:
i.

Figure 24. Complementary error function table

ii. Based on the complementary error function, (Interpolation)

iii. Therefore
Time, hours
1
2
3
4
5
6
7
8
Ambient,
32
32
43
45
30
30
26
26

Using the ambient temperature data in the table above,

27.11

iv. Subsequent hours following the 1st hour can be calculated by changing the to the next hour reading, to the previous while maintain the at 0.022805.

The table below shows the temperature of the ground in the 8 hours of exposure which is then plotted into a graph.
Time, hours
1
2
3
4
5
6
7
8
Ambient,
32
32
43
45
30
30
26
26

27.11
27.22
27.58
28
28.04
28.08
28.03
27.98

Figure 25.Graph of soil and ambient temperature

The graph above show that based on our assumptions in using transient heat conduction in semi-infinite solids to determine the root temperature in ground, the incremental value of the soil temperature at depth of 7.5cm only see a difference of 0.97.

Therefore, we can assume that the maximum temperature that the roots can survive in the tropical climate particularly in our situation is 28. However, this method does not represent the real situation accurately as factors such as humidity and soil ratingwas not taken into account in our calculation.
Nevertheless,this has provided enough data and evidence to set a targeted solution temperature to achieve for further studies in this field.
5. Results

The control test was conducted from 7th May 2013 to 13th May 2013 at the empty field in outside the campus engineering workshop. Refer to appendix c.
The result is to shown the temperature fluctuation of an NFT system exposed to the various condition of equatorial climate weather that can be experience such as cloudy, windy, light rain, heavy rain and hot sun.

Below are the compilation of graphed result of the 7 days test conducted.

Figure 26. Day 1

Figure 27. Day 2 Graph

Figure 28. Day 3

Figure 29. Day 4

Figure 30. Day 5

Figure 31. Day 6

Figure 32. Day 7

6. Analysis and Discussion

Reviewing the result, we can observe and deduce that the pattern move in a similar manner daily in the 8 hour period. Some of the similarities that can be observed areat hour 1 (10am), the ambient temperature is higher than the reading points temperature and at hour 8 (5pm), the ambient temperature will drop lower than the reading points temperature which is expected.
The specific heat capacity, of water and air at 25 is 4.180 and 1.005. This shows that water need to absorb 4 times more energy than air to be at the same temperature. This explains why the ambient temperature heat up and cool down faster in the test compare to the system’s solution.
It can also be observed that highest temperature reading in the system’s water is at 42 , surpassing the limit set in our assumption that the temperature no more than 28. Our control test confirms the findings of Taiwanese researcher that the temperature of the solution in the NFT system will fluctuates and creates a non-conducive environment for the roots of vegetable to grow in tropical climate.
The 7 days result also shows an array of movement for each day. This is because when the tests are conducted during that 7 days, our test rig manage to experience windy condition, hot still air condition, heavy rain, early ambient peak and late ambient peak condition. These conditions are vital in our studies as we want to record temperature fluctuation affected by climate conditions experienced by the system so that we can understand NFT system better.
Overall, we can conclude that when the NFT system is exposed to the day’s sunlight cycle without thermal protection, the solution temperature will begin colder than the ambient temperature before the peak ambient temperature of the day, the temperature then willslowly rises as it receive heat from the surrounding and direct sunlight, and it will be hotter than the ambient drop temperature by the end of the sunlight cycle as both ambient and solution temperature continue to cool down into the night cycle.

7. Recommendation

Roots temperature is an important factor in any successful hydroponic system. We recommend that future work continuing this research use a better method to calculate the correct root temperature of plants in tropical climate or conduct experiments to discover it.
Other than that, we would recommend future researcher to use longer planting gutter channel up 10 meter in length to further study whether longer planting gutter channel can be use in NFT system in tropical climate without causing root death of depress growth.

8. Conclusion

In conclusion, the study was an overall success as we did not met much setback and we manage to produce quality data of the temperature fluctuation in NFT system when expose to tropical climate which is our project’s 1st objective in Research Project, HES5102.
We will look at using thermal insulator and better nutrient solution delivery system in our future work in Advance Research Project, HES5103 I our effort to engineer a NFT system suitable to be use in tropical climate.

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Appendices

Figure 33. Reading record paper

Figure 34. Site location mark with “x”

Figure 35. Close up of the site