Fuzzy logic controller based on geothermal recirculating aquaculture system

Egyptian Journal of Aquatic Research (2014) 40, 103–109

H O S T E D BY

National Institute of Oceanography and Fisheries

Egyptian Journal of Aquatic Research
/>www.sciencedirect.com

FULL LENGTH ARTICLE

Fuzzy Logic Controller based on geothermal
recirculating aquaculture system
Hanaa M. Farghally, Doaa M. Atia *, Hanaa T. El-madany, Faten H. Fahmy
Electronics Research Institute, Cairo, Egypt
Received 24 December 2013; revised 18 June 2014; accepted 19 July 2014
Available online 13 August 2014

KEYWORDS
Geothermal energy;
Aquaculture;
Fuzzy Logic Control

Abstract One of the most common uses of geothermal heat is in recirculation aquaculture systems
(RAS) where the water temperature is accurately controlled for optimum growing conditions for
sustainable and intensive rearing of marine and freshwater fish. This paper presents a design for
RAS rearing tank and brazed heat exchanger to be used with geothermal energy as a source of
heating water. The heat losses from the RAS tank are calculated using Geo Heat Center Software.
Then a plate type heat exchanger is designed using the epsilon – NTU analysis method. For optimal
growth and abundance of production, a Fuzzy Logic control (FLC) system is applied to control the
water temperature (29 °C). A FLC system has several advantages over conventional techniques;

relatively simple, fast, adaptive, and its response is better and faster at all atmospheric conditions.
Finally, the total system is built in MATLAB/SIMULINK to study the overall performance of
control unit.
ª 2014 Hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries.

Introduction
Geothermal energy is the energy derived from the natural heat
of the earth. The earth’s temperature varies widely, and geothermal energy is usable for a wide range of temperatures from
room temperature to over 300 °C. Geothermal energy can be
used for both electricity generation and direct uses depending
on the temperature and chemistry of the resources (Boyd and
Lund, 2003; Gelegenis et al., 2006). Currently, direct uses are
on commercial level and are replacing fossil fuels in uses of
low heat applications (Kiruja, 2011; Mburu, 2009). Direct
* Corresponding author.
E-mail address: (D.M. Atia).
Peer review under responsibility of National Institute of Oceanography
and Fisheries.

utilization of geothermal energy consists of various forms for
heating and cooling instead of converting the energy for electric power generation. The major areas of direct utilization
are swimming, bathing and balneology, space heating and
cooling including district heating, agriculture applications,
aquaculture applications, industrial processes, and heat pumps
(Lund et al., 2005, 2011; Lund, 1997).
Catching fish from the wild may not yield enough products
to meet consumer demand and simultaneously keep the natural ecosystem in balance. The Food and Agriculture Organization of the United Nations estimates that by 2030, about 40
million tons of seafood will be necessary to keep up with
demand. Catfish is one type of fish that is quite popular in
Egypt and readily available, either in the village or town (De

Graaf and Janssen, 1996; Krause et al., 2006). The health
benefits of catfish are rich in omega-3 fatty acid content, but

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104
increasing consumption of all types of fish and seafood is recommended to derive the best health benefits, catfish are excellent sources of protein that are low in fat, catfish is high in
vitamin D, farm-raised catfish contains low levels of omega-3
fatty acids and a much higher proportion of omega-6 fatty
acids. The protein in fish is of high quality, containing an
abundance of essential amino acids, and is very digestible for
people of all ages. Catfish is also generally lower in fat and
calories than beef, poultry or pork. It is also loaded with
minerals such as iron, zinc and calcium.
The use of artificial intelligence has become more common
in industrial and manufacturing process control systems in
recent years. The advantages of AI systems include: (1) the
rapid transfer of expert knowledge throughout an industry,
especially those young industries that do not have enough
available experts; (2) a reduction in labor costs due to automation of all primary functions; (3) improved process stability
and efficiency; and (4) improved understanding of the process
through the development and testing of the rules. Their usefulness in aquaculture has been advocated due to all of these
reasons (Lee, 2000). RAS represent a new and unique way to
farm fish. Instead of the traditional method of growing fish
outdoors in open ponds and raceways, this system rears fish
at high densities, in indoor tanks with a controlled environment. Attempts to advance these systems to commercial scale
food fish production have increased dramatically in the last
decade (Blancheton, 2000; Timmons et al., 2002; Timmons
and Ebeling, 2007; Bijo, 2007; Molleda, 2007).

The renewed interest in recirculating systems is due to their
perceived advantages: the possibility to be placed near the fish
markets, high product quality, shorter production cycles due to
high food conversion factors and a constant monitoring of the
farm environment in order to improve rearing conditions
(Timmons et al., 2002) The functional parts of a RAS include
a growing tank, sump of particulate removal device, biofilter,
aeration subsystem, water circulation pump, and water heating
system depending on the water temperature and fish species
selected. Ozone and ultraviolet sterilization may be advantageous to reduce organic and bacterial loads (Timmons and
Ebeling, 2007). This paper is concerned with the Recirculation
Aquaculture Systems (RAS). The design of the culture tank and
the heat exchanger are presented. The Fuzzy Logic Controller
is proposed to control the RAS temperature using the
MATLAB/SIMULINK simulation program.
Materials and methods
System design methodology
This section discusses the system components’ design of geothermal system, load design, Heat Exchanger, and Fuzzy Logic
Control as given below. The required RAS components are
indicated in Fig. 1.
Geothermal system design
The Umm Huweitat well in eastern desert is taken as a case
study. Geothermal water flows from the well at 70 °C
(Swanberg et al., 1983) and average flow rates of 0.12 L/s.
The geothermal water passes through one side of the heat
exchanger, and flows into the reinjection well. On the secondary

H.M. Farghally et al.
Fine & Dissolved
Solids Removal

Carbon Dioxide
Removal
Fish Culture
Tank

Aeration

Disinfection

Waste solids
Removal

Figure 1

Biological
Filtration

Recirculating aquaculture system components.

side of the heat exchangers, fresh water is circulated through
the heat exchanger and to the rearing tank system so that there
is no actual contact or mixing between the geothermal water
and rearing tank. The secondary hot water at 50 °C enters the
RAS tank.
Geo-Heat Center Software inputs
The Geo-Heat Center Software was developed for using in
conjunction with geothermal direct use systems. The software
includes several tools among them is the ‘‘HEATOOLS’’
which allows the calculation of the steady state heat loss from

an indoor pond (or pool) in the evaporative, convective and
radiant modes (Geothermal Direct – Use Software, 2012). In
this case, the calculations assume that the pond (or pool) is
located in an enclosed building such that evaporative and convective losses are driven only by natural convection of the air.
The inputs to this software are the geothermal fluid temperature, the pond water temperature, the air temperature inside
the building, the pond surface area, and the air relative humidity inside the structure housing the pond.
Heat exchanger design
Heat exchangers are devices that are used to transfer heat
between two or more fluid streams at different temperatures.
They can be classified as either direct contact or indirect contact type where the media are separated by a solid wall so that
they never mix. Due to the absence of a wall, direct contact
heat exchangers could achieve closer approach temperatures,
and the heat transfer is often accomplished with mass transfer.
The indirect contact heat exchangers are focused where a plate
wall separates the hot and cold fluid streams, and the heat flow
between them takes place across this interface. Plate heat
exchangers and shell-and-tube heat exchangers are examples
of indirect contact type heat exchangers (Thulukkanam, 2013).
A plate heat exchanger is a compact one which provides
many advantages and unique application features. These
include flexible thermal sizing, easy cleaning for sustaining
hygienic conditions, achievement of close approach temperatures due to their pure counter-flow operation, and enhanced
heat transfer performance (Smith, 1995).
Most geothermal fluids, because of their elevated temperature, contain a variety of dissolved chemicals. These chemicals
are frequently corrosive toward standard materials of construction. As a result, it is advisable in most cases to isolate
the geothermal fluid from the process to which heat is being
transferred.


Fuzzy Logic Controller based on geothermal RAS

105

The task of heat transfer from the geothermal fluid to a
closed process loop is most often handled by a plate heat
exchanger. The two most common types used in geothermal
applications are: bolted and brazed (Rafferty, 2012).
To design or predict the performance of a heat exchanger, it
is essential to determine the heat lost to the surrounding atmosphere for the analyzed configuration. The heat power emitted
from hot fluid (Qh), and the heat power absorbed by cold fluid
(Qc) can be calculated as follows (neglecting potential and
kinetic energy changes) (Shah and Sekulic, 2003);
:

:

:

:

Qh ¼ mh ðhhi À hho Þ ¼ mh Ch ðThi À Tho Þ

ð1Þ

Qc ¼ mc ðhci À hco Þ ¼ mc Cc ðTci À Tco Þ
:

ð2Þ

:

where mh , mc are mass flow rate of hot and cold fluid, respectively, hhi, hho are inlet and outlet enthalpies of hot fluid,
respectively, hci, hco are the inlet and outlet enthalpies of cold
fluid, respectively, Thi, Tho are the inlet and outlet temperatures
of hot fluid, respectively, Tci, Tco are the inlet and outlet temperatures of cold fluid, respectively, and Ch, Cc are the specific
heats of hot and cold fluid, respectively.
From energy conservation, Qc = Qh = Q, and the heat
transfer rate Q is related to the overall heat transfer coefficient
(U) and to the log mean temperature difference (LMTD) by
means of (Shah and Sekulic, 2003):
Qc ¼ U A LMTD Cf

e¼

Cmax ðThi À Tho Þ
Cmin ðThi À Tci Þ

Dt1 À Dt2
 
1
ln Dt
Dt2

e¼

Cmax ðTco À Tci Þ
Cmin ðThi À Tci Þ

Dt1 ¼ Tho À Tci

ð5Þ

Dt2 ¼ Thi À Tco

ð6Þ

Desired
Temperature

ð8Þ

The heat transfer rate is given by (Thulukkanam, 2013):
Q ¼ e Cmin ðThi À Tci Þ

UA
Cmin

ð10Þ

Cr ¼ Cmin =Cmax

ð11Þ

The epsilonÀNTU relationship is given for a simple double
pipe heat exchanger for counter flow (Thulukkanam, 2013):
e¼

1 À exp½ÀNTUð1 À Cr ފ
;
1 À Cr exp½ÀNTUð1 À Cr ފ

Control
Unit

Figure 2

Thermostatic
Valve

Rearing
Tank

Proposed water temperature control subsystem.

Gain 1

Scope 1

Scope

-K Saturation 1

60

d

Gain 3
2
ce

Tank
Temperature
(Th)

Scope 2

e

e

ð12Þ

Cr < 1

m.

+
-

1

ð9Þ

The value of NTU is defined as (Thulukkanam, 2013):
NTU ¼

ð4Þ

ð7Þ

Otherwise, if the hot fluid is the minimum fluid, then the
effectiveness is defined as (Thulukkanam, 2013):

ð3Þ

The LMTD is derived as (Shah and Sekulic, 2003):
LMTD ¼

where A is the total surface area for heat exchange, and Cf is a
correction factor.
The epsilon–NTU method is one of the heat exchanger
analysis methods. The effectiveness/number of transfer units
(NTU) method was developed to simplify a number of heat
exchanger design problems. The heat exchanger effectiveness
(e) is defined as the ratio of the actual heat transfer rate to
the maximum possible heat transfer rate if there were infinite
surface area. It depends upon whether the hot fluid or cold
fluid is a minimum fluid. That is the fluid which has the
:
smaller capacity coefficient C ¼ m Cp . If the cold fluid is
the minimum fluid then the effectiveness is defined as
(Thulukkanam, 2013):

-K Gain 2

Saturation 2

Fuzzy Logic
Controller

Scope 3

Figure 3

FLC design using MATLAB/SIMULINK.

1
du


106

H.M. Farghally et al.

Degree of membership

1

NB

NM

ZE

NS

PS

PM

PB

0.8

0.6

0.4

0.2

0
-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Error

Figure 4

Membership function for input and output.

System design with Fuzzy Logic Controller

Results and discussions

Fuzzy Logic Control (FLC) has excelled in dealing with systems that are complex, ill-defined, non-linear or time-varying
(Reznik, 1997; Dadios, 2012) FLC is relatively easy to implement, as it usually needs no mathematical model (Reznik,
1997) of the control system. Fuzzy Logic has rapidly become
one of the most successful of today’s technologies for developing sophisticated control systems because of its simplicity. The
proposed control unit is adopted in Fig. 2. The proposed control unit is presented in Fig. 3. The block diagram of system
design with FLC using MATLAB/SIMULINK is shown in
Fig. 3. The desired temperature is compared with the water
tank temperature to produce the error signal which is used
as input signal to FLC. Membership function values are
assigned to the linguistic variables, using seven fuzzy subsets:
NB (negative big), NM (negative medium), NS (negative
small), ZE (zero), PS (positive small), PM (positive medium),
and PB (positive big). The values of input error (e) and change
of error (ce) are normalized by an input scaling factor. The triangular shape of the membership function of this arrangement
presumes that, for any particular input there is only one dominant fuzzy subset. The composition operation is the method
by which the controlled output is generated. The Max–Min
method is used for decision making. The output membership

function of each rule is given by the minimum method. The
membership functions of inputs and output are shown in
Fig. 4. Table 1 shows the rule base of the FLC. As the system
usually requires a non fuzzy value of control, a defuzzification
stage is needed. The center of gravity method is used for the
defuzzification algorithm because this method is simple and
fast.

RAS tank, heat exchanger, heat load, and RAS simulation
results are mentioned as follows.

Table 1

RAS tank
Recirculating aquaculture systems are designed to raise large
quantities of fish in relatively small volumes of water by treating the water to remove toxic waste products and then reusing
it. Circular tank is selected to be considered for the following
reasons:
 Improves the uniformity of the culture environment.
 Allows a wide range of rotational velocities to optimize fish
health and condition.
 Rapid concentration and removal of settleable solids.
Table 2

Brazed plate heat exchanger design parameters.

Parameter

Symbol

Value

Inlet temperature of cold fluid
Outlet temperature of cold fluid
Inlet temperature of hot fluid
Outlet temperature of hot fluid
Heat capacity rate of hot fluid
Heat capacity rate of cold fluid
Minimum heat capacity rate
Maximum heat capacity rate
Heat capacity ratio
Number of transfer units
Effectiveness
Log mean temperature difference
Overall heat transfer coefficient
Area of heat exchanger

TCi
Tco
Thi
Tho
Ch
Cc
Cmin
Cmax
Cr
NTU
e
LMTD
U

A

22 °C
50 °C
70 °C
45 °C
501.6 J/kg °C
321.86 J/kg °C
321.86 J/kg °C
501.6 J/kg °C
0.6416
821.28
0.5833
21.4 °C
4684.59 W/m2 °C
57 m2

Rule base of Fuzzy Logic Controller.
Change of error (ce)

Error (e)

NL
NM
NS
ZE
PS
PM
PL

NL

NM

NS

ZE

PS

PM

PL

NL
NL
NL
NL
NM
NS
ZE

NL
NL
NL
NM
NS
ZE
PS

NL
NL
NM
NS
ZE
PS
PM

NL
NM
NS
ZE
PS
PM
PL

NM
NS
ZE
PS
PM
PL
PL

NS
ZE
PS
PM
PL
PL

PL

ZE
PS
PM
PL
PL
PL
PL

Table 3 The input data of RAS using Geo Heat Centre
Software.
1.
2.
3.
4.
5.

Resource temperature
Surface area
Water temperature
Air temperature
Relative humidity

52 °C
50 m2
29 °C
28 °C
72.53%

Fuzzy Logic Controller based on geothermal RAS
Table 4
1.
2.
3.
4.
5.
6.

107
workers handling fish within the tank and safety issues. The
RAS tank design parameters is estimated such as (depth, diameter, area) diameter to depth ratio is chosen to be 5:1, depth is
equal to 1.6 m, diameter is equal to 8 m, and tank area is equal
to 50.24 m2.

The output data of Geo Heat Centre Software.

Evaporative loss
Convective loss
Radiant loss
Conductive loss
Total loss
Water flow requirement

7713
152
346
1202
9413

0.12

W
W
W
W
W
lps

153.5338953
3.0284064
6.8770062
23.9117922
187.382646

W/m2
W/m2
W/m2
W/m2
W/m2

Heat exchanger
A plate heat exchanger is a type of heat exchanger that uses
metal plates to transfer heat between two fluids. This has a
major advantage over a conventional heat exchanger in that
the fluids are exposed to a much larger surface area because
the fluids spread out over the plates. This facilitates the transfer of heat, and greatly increases the speed of the temperature
change. Brazed plate heat exchanger is selected for geothermal heating which provides different advantages that include
their corrosion resistant materials availability such as the titanium and stainless steel at affordable price. The units are efficient and compact with rates of heat transfer three to ten
times than those of tube and shell exchangers. Due to the

simple construction of brazed plate heat exchanger, such
units can be developed in small sizes, economically. The
brazed plate heat exchanger is made by stainless steel. The
brazed plate heat exchanger design parameters are shown in
Table 2.

3

Load (W*10^4)

2.5
2
Winter

1.5

Summer
1
0.5
0
0

5

10

15

20

25

Time (hr)

Figure 5

Load variation of RAS over the year.

Selection of a tank diameter: depth ratio is also influenced
by factors such as the cost of floor space, water head, fish
stocking density, fish species, and fish feeding levels and
methods. Choices of depth should also consider ease of

Heat load calculation
Using the Geo Heat Centre software, the input data of
RAS (resource temperature, surface area, water temperature,

m

0.8176
Display 2

Scope 3

t
Scope 5

e

load sum

0.07668
84 .2

m

Scope

Display 1
I/p

Ref

o/p

load wint

tg
tp

Control Subsystem
Scope 1
RAS Subsystem
th

Qmax

70

Thi

Scope 2

thi
Tho

Scope 4
22

Tci
Tco

tci

Heat exchanger Subsystem

Figure 6

84 .12
Display

MATLAB/SIMULINK of RAS system.


108

H.M. Farghally et al.

50

Conclusion
Summer
Winter

Tank temperature (C)

40

30

20

10

0

0

5

10

15

20

Time (hr)

Figure 7

Water temperature variation over the day using FLC.

Geothermal energy is a clean and renewable energy resource
which can be found in many places in the world and especially
in the tectonically active areas. This paper presented the design
of RAS used for catfish using geothermal energy. A well at
Umm Huweitat which is located on the Red Sea and approximately 20 km north of the city of Safaga is used as a source of
geothermal energy. A brazed heat exchanger was designed
using the epsilon–NTU analysis method. The Fuzzy Logic
Controller (FLC) was proposed to control the water temperature at the desired value of 29 °C for maximizing the RAS production. The FLC was built in the MATLAB/SIMULINK
model. The FLC presented in this paper possessed excellent
tracking of the desired water temperature.
References

20
Summer

15

Winter

10

Error

5
0
-5
-10
-15

-20

0

5

10

15

20

Time (hr)

Figure 8

Error signal variation using FLC.

air temperature, and relative humidity) are indicated in Table 3.
The total loss is composed from the evaporative loss, convective loss, radiant loss, and conductive loss (output data) are
obtained and illustrated in Table 4. Heat load distribution over
the year of RAS is shown in Fig. 5.
RAS simulation
The MATLAB/SIMULINK of the overall system is indicated
in Fig. 6. The RAS consists of the RAS unit, the control unit
and heat exchanger unit. The simulation is carried out over
one day in two different seasons of the year.
The fuzzy control methodology is used to fix the water
temperature for optimum growth of the Catfish. At optimum temperature (29 °C), Catfish grow quickly, convert
feed efficiently, and are relatively resistant to many

diseases.
Fig. 7 indicates the response of the water temperature
variation over the day using fuzzy controller. It is
observed that, the water temperature tracks the reference
very well and the temperature profile is very close to the
reference temperature within almost the whole daily variation. On the other hand, the error result is zero as shown
in Fig. 8.

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