Arabian Journal for Science and Engineering (2019) 44:9529–9543
https://doi.org/10.1007/s13369-019-03892-w
RESEARCH ARTICLE - COMPUTER ENGINEERING AND COMPUTER SCIENCE
Embedded Fuzzy Logic Control System for Refrigerated Display
Cabinets
Kemal Tutuncu1
· Recai Ozcan2
Received: 8 December 2018 / Accepted: 16 April 2019 / Published online: 11 May 2019
© King Fahd University of Petroleum & Minerals 2019
Abstract
Having done in this study, embedded fuzzy logic control system (EFLCS) was designed and implemented for closed refrigerated display cabinets (CRDC) to meet the required storage conditions for the pastry productions stored in CRDCs. The
system keeps the temperature and relative humidity (RH) of CRDC at approximately + 4 ◦ C and 80% RH, respectively. It
has two fuzzy logic controllers. One of them controls the speed levels of the fans, and the other controls the steam level of
ultrasonic atomizer. Temperature and RH values are read by sensor SHT11 and transferred to PIC18F4620 microcontroller
that is programmed with fuzzy Logic approach. On the other hand, the compressor was controlled with on–off control in the
range of 3–5 ◦ C. On the condition of starting from + 7 ◦ C temperature, the time to approach to the set values (4 ◦ C and 80%
RH) for traditional system and EFLCS is 191.8 and 109.6 s, respectively. Additionally, the ranges of temperature and RH
obtained by EFLCS are between 4.44 and 3.69 ◦ C and between 81.33% RH and 78.57% RH, respectively. The temperature and
RH values obtained by traditional system are between 5.56 and 3.2 ◦ C and between 61.81% RH and 57.45% RH, respectively.
Traditional system never reached to desired humidity value (80% RH). It has been seen that developed EFLCS becomes stable
in shorter time than traditional system and kept the desired values as almost constants.
Keywords Fuzzy logic control · Embedded system · Refrigerated display cabinet · PWM · SHT11
1 Introduction
Refrigerated display cabinets (RDCs) are great and vital as
they are part of the cold chain for food products [1]. It is easier
to reach the desired weather conditions in CRDCs compared
to open RDC (ORDC) [2]. Particularly the temperature and
humidity are the conditions that should be provided in the
pastry products.
After making the pastry products, it may be necessary
to display a certain period of time in the store for sale, if
this time is too long and the necessary storage conditions
for the product are not provided, the pastry products may
deteriorate or loss mass. The ideal conditions are adversely
affected due to the not achievable ideal relative humidity
range, the temperature fluctuations and the door of cabinet
B
Kemal Tutuncu
ktutuncu@selcuk.edu.tr
1
Department of Electric Electronics Engineering, Selcuk
University Technology Faculty, 42130 Konya, Turkey
2
Department of Electric and Energy, Selcuk University Bozkir
Vocational School, 42630 Konya, Turkey
which is often opened for product sales. Therefore, the shelf
life of products in CRDC is shortened.
For refrigerated foods, generally between − 1 and + 5 ◦ C
is the acceptable temperature range [3]. Therefore, the temperature and the humidity of the environment where the cake
will be hold must be kept at a certain value. Ideal temperature and humidity can be considered as + 4 ◦ C and 80%
RH, respectively, in order to prevent growing pathogenic
microorganisms. Figure 1 shows how pathogenic bacteria
grows according to the temperature change.
During the product display in RDCs, moisture loss or gain
will continue to occur until the environment and food components (cream and etc.) that surround the food reach the
thermodynamic balance [5]. Due to dehydration, the appearances of unwrapped foods are deteriorated and limit the shelf
life. Consumers are preferred newly loaded products compared to the product that have been displayed for some time
[6]. Furthermore, the evaporation of water from the product
is the mass loss of the salable product. In a survey conducted,
attention was focused to the importance of relative humidity.
Relative humidity decreased from 95 to 40% caused significant mass loss of food [7]. Not only does the humidification
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Fig. 1 Bacterial growth rate for human pathogens at different temperatures [4]
process have a positive effect on the microbial quality of the
products, but also extends the shelf life. Using humidification
equipment to increase the humidity of the cabinet in which
the product is stored is a way of reducing the problems mentioned [8].
Consumers prefer indoor CRDCs because of pastry products in Turkey usually displayed as unpacked. Traditional
CRDCs which are produced in Turkey have generally only
on–off temperature control. There is no humidity control, and
humidity is supplied by fans that are directed to the water at
the bottom of CRDC. The humidity value is at most 65% RH,
and the ideal humidity value (80% RH) is not reached. The
basic motivation of this study is to reach the ideal humidity
and temperature values in shorter time than traditional system and to preserve these values. In this way, it is ensured
that the shelf life of the cakes is longer than it was before.
Microbiological safety of chilled foods is the main key factor and requires product design and cold chain management.
Many technology areas are used to make safe products and
ensure shelf life [9]. In recent years, computer and communication technology has seen great progress based on real-time
status information on cold stores and RDC. RDCs can have
integrated temperature and humidity control to extend the
shelf life of non-pre-packaged foods. Thus, the measurement
and control of food environment conditions can be part of the
safety and quality system [10]. Embedded systems are computer systems designed for a specific purpose. These systems
include not only hardware, but also embedded software [11].
Thanks to this embedded software and hardware, CRDC can
be controlled depending on the critical values of temperature
and humidity.
In this study, an EFLCS that can easily be mounted
to compatible current CRDCs without too many changes
was designed and implemented. Developed EFLCS simultaneously receives information from different sensors and
simultaneously activates different actuators. Contribution to
the development of alternative solutions to meet the current
requirements for CRDCs such as desired RH and temperature
values was aimed.
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There are some studies in the literature related to control
system for ORDC in various countries that are out of scope of
this study [12–18]. Because, ORDCs do not have doors and
use different techniques such as air curtain and air guiding
strip, to replace the doors and to provide the air conditioning. The parameters to be controlled are different from the
parameters of CRDC. Additionally, there are not many studies conducted with control system for CRDC that are similar
to developed EFLCS in this study. Experimental and numerical control studies for CRDC in recent years are shown in
Tables 1 and 2, respectively [19–38]. When both tables are
examined, it has been seen that the methods used for controlling aims are FLC, mode control, PID control, fuzzy expert
system, On–off control and sliding mode control. Additionally, the controlled parameters are mainly temperature and
humidity [19–38]. Only several studies [24,29,35,37] have
one additional control parameter. At this point, it should be
declared that there is no benchmark to compare CRDC studies [19–38] to each other since different sizes of areas (from
an incubator to big cold storage) and zones (food storage,
health, livestock and etc.) were air-conditioned. It means that
CRDC studies are domain-specific ones and there is no way
of comparing the time for reaching target values, the stabilities, etc. with previously developed systems or studies.
Thus, the authors of these papers [19–38] only compared
their methods with traditional systems applied on their areas.
Due to these reasons, developed EFLCS was compared with
traditional system that exists on CRDC used in this study.
2 Material and Method
The embedded system can be defined as microcontroller
/microprocessor-based system designed to control a function or function range. The embedded system includes: a
processor capable of performing the required tasks within
the system, a memory that stores the software and the data
generated during the operation, peripheral units for communicating with the outside world, a software for efficiently
running the system, an algorithm which has the ability to
interpret the sensors data and generate the control signal
according to this data [39]. In general, an embedded system is implemented by: (1) circuit design and simulation,
(2) experimental demonstration of the designed circuit (on
a breadboard), (3) application of the circuit (soldering), (4)
packaging [40].
Microcontroller needs to be programmed to operate
according to certain parameters. FL, which can incorporate
human thinking ability and experience into the control system, promises both to fix the system in a shorter time and
to provide oscillation at lower intervals. FL is also a popular
tool that provides decision support for analyzing data classes
and makes it flexible by analyzing ambiguous data [41].
Air-conditioned zone
Method
Evaluation factors
Target values
Control factors
Year
References
Oyster mushroom cultivation
Fuzzy logic control
Temperature
Between 15 and 30 ◦ C
Relay
2018
[19]
Humidity
Between 80 and 90%
Sprayer
Between 26 and 29 ◦ C
Exhaust fan
2018
[20]
Fan
2018
[21]
2017
[22]
Closed house chicken barn
Fuzzy logic control
Temperature
Humidity
Between 50 and 70%
Infant incubator
Mode control
Temperature
Between 27 and 37 ◦ C
Suction
Alarm
RTC
Agricultural green house +
MATLAB simulation
Comparison of fuzzy logic self-tunning and PID
Temperature
30 ◦ C
Piezoelectric-transducer
Humidity
60%
Heater
Air conditioning system + MATLAB
simulation
Comparison of real system and MATLAB
simulation
Temperature
(29–30–35–43–47) ◦ C
Compressor
2017
[23]
Humidity
(32–24)%
Temperature
4, 5 ◦ C
Fans
2017
[24]
Humidity
92,50%
Humidifier
Light intensity
12,50%
Dehumidifier
2017
[25]
2015
[26]
2016
[27]
2015
[28]
2014
[29]
Cold storage
Fuzzy logic control
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Table 1 Similar experimental studies in recent years
Luminance controller
Greenhouse
Fuzzy logic control
Temperature
User defined
Electric pump
Humidity
User defined
Humidifier
Heater
Lighting
Extractor
Fungus cultivation
Fuzzy logic control
Temperature
Between 20 and 28 ◦ C
Relay
Humidity
Between 80 and 90%
Electric pump
Temperature
Between 18 and 34 ◦ C
Lamp
Humidity
Between 40 and 70%
Fan
Lamp
Maintenance comfortable room
Mode control
Electric pump
Exhaust fan
Infant incubator
Poultry house
PID control
Comparison of fuzzy logic and on–off control
User defined
Heater
Humidity
User defined
Alarm
Temperature
23 ◦ C
Heater
Humidity
60% Fan
Cooler
CO2
3000 ppm
Humidifier
NH3
25 ppm
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Temperature
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Table 2 Similar numerical studies in recent years
Air-conditioned zone
Method
Evaluation factors
Control factors
Year
References
Variable speed direct expansion air
conditioning system
Fuzzy logic control
Temperature
Compressor
2018
[30]
Variable speed refrigeration system
Comparison of fuzzy logic control
and simulation
Temperature
Compressor
2018
[31]
Temperature control on LABVIEW
PID control
Temperature
Heater
2017
[32]
İndoor air temperature and
humidity
Weights based fuzzy logic control
İndoor temperature
Fan
2017
[33]
İndoor humidity
Compressor
Automotive refrigeration system
Comparison of on–off control and
sliding mode control
Temperature
Compressor
2017
[34]
2016
[35]
2016
[36]
2015
[37]
2014
[38]
Humidity
Test temperature
Air conditioning system on
MATLAB fuzzy toolbox
Fuzzy logic control
Evaporator fan-VFD frequency
Heating load
Condenser fan-VFD frequency
Temperature
Fan
Humidity
Compressor
Oxygen level
Fin direction
Operation (AC or dehumidifier)
İndoor temperature
Comparison of thermostats control
and fuzzy logic control
İndoor temperature
Heating system
Outdoor temperature
Air conditioning system
Outdoor humidity
HVAC system with LABVİEW
and MATLAB simulink
Centralized chilled water system
on MATLAB simulink
Fuzzy expert system
Fuzzy logic control
İndoor temperature
Heat valve
İndoor humidity
Cold valve
İndoor oxygen
Exhaust motor
Outdoor temperature
Water pump
Temperature
Damper position
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Ambient temperature
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Fig. 2 General scheme of design
Developed EFLC system is aimed for keeping temperature and humidity inside a CRDC manufactured in Turkey
at approximately + 4 ◦ C and 80% RH, respectively. Input
variables are temperature and humidity information, whereas
output variables are speed levels of fans (3) and the steam
level of UA. The temperature is provided by evaporative
cooling, and the humidity is supplied by UA as cold steam.
The fans that are placed near the evaporator are used to
reach the desired level of CRDC temperature easily. The
temperature and humidity information is transferred by the
SHT11 sensor to the PIC18F4620 that is programmed with
FL approach. Symmetric fuzzification, Mamdani inference
mechanism and weight average method for defuzzification
are used for programming PIC18F4620. Depending on these
transferred values, the fans and UA are operated to provide the necessary air conditioning for the cake. The gas
compressor is on–off controlled in the range of 3–5 ◦ C to
keep the inside temperature of CRDC at 4 ◦ C by relay
G5LE-1-ACD model of OMRON company. In addition, the
values of all input and output variables can be monitored
instantaneously through the interface screen. The scheme of
developed EFLCS is shown in Fig. 2.
bit analog-to-digital converter module. This module has 13
inputs and provides conversion of an analog input signal to
a corresponding 10-bit digital number. The PIC18F4620 is
operated in three modes. These modes are Normal, Idle and
Sleep.
The PIC18F4620 microcontroller is selected to develop
EFLCS because it has built-in USART support, many digital outputs, 64 kB program memory and different operating
modes.
The input/output ports on the control card enables PIC
microcontroller to communicate with peripheral devices and
the computer. The data cables from the sensors are connected
to the input ports of the control card, the fans and UA and
the relay pins are connected to the output ports. The control
card also has a COM port. The control card can be connected
to the computer via this port. Thus, the interface program on
the computer can display and record the input/output data.
This function has no effect on the operation of EFLCS. FLbased software on the PIC18F4620 evaluates the information
from the sensors and sends the control signals to the fans,
relay and UA via this card for the purpose of making the air
conditioning of CRDC. Therefore, the control card has the
most important function in developed EFLCS.
2.1 Control Card with Microcontroller
2.2 Sensors
Microchip’s PIC18F4620 40-pin microcontroller unit (MCU)
has 64K flash, 1K EEPROM, Capture/Compare /PWM
modules and built-in USART support. It also has a 10-
The SHT11 sensor measures temperature and humidity
values simultaneously in an environment. For developed
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EFLCS, eight expansion slots were integrated to control card
to make connection with SHT11 sensors. Since the measurements of temperature and humidity in five different regions
of CRDC (lower left, lower right, upper left, upper right and
near evaporator) were needed, only five of the expansion slots
were used to connect five pins of SHT11 sensors. Fifth sensor on the evaporator was used to increase the efficiency of
evaporator by minimizing the snow on the evaporator surface.
For efficient air conditioning system, the difference between
the average temperature of the cooled area and temperature of cooler liquid inside the evaporator must not exceed
5◦ C. In case of having the temperature difference more than
5◦ C, the water steam starts condensing. This causes snow
on the evaporator and decrease in relative humidity ratio of
the cooled area. To eliminate this situation and to keep this
temperature difference under 5◦ C, air circulation must be
provided between the evaporator and cooled area. Figure 3
shows SHT11 connection schema.
SHT11 measures and sends these data in digital form
to microcontroller since it has built-in analog-to-digital
converter (ADC). SHT11 uses a bidirectional (two-wire)
interface for data communication with microcontroller.
2.3 Driver and Fans
Fig. 3 SHT11 connection circuit [42]
Fig. 5 The fan
Fig. 4 a YASKAWA V1000
model inverter/driver and b
YASKAWA V1000 control
inputs [43]
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The frequency converter arranges the output voltage for the
fans used in this study according to the analog signals coming from the control card. In developed EFLCS, YASKAWA
V1000 model inverter/driver was used as frequency converter
to drive the fans. This driver features 1.5 kW, single phase,
220-V 50 Hz input and 200-V output. Figure 4a shows the
YASKAWA V1000 inverter/driver, and Fig. 4b shows the
control inputs.
YASKAWA V1000 inverter/driver’s pulse width modulation (PWM) is V/f (voltage/frequency) -controlled, and the
output frequency is between 0 and 400 Hz. The output voltage
waveform has a constant amplitude. Variable output voltage is obtained by switching the source voltage at regular
intervals. The output voltage is determined by adjusting the
amplitude of the signal in each cycle. The fans were driven
by this output voltage. Each fan used in developed EFLCS is
120 cm × 120 cm × 38 cm and operates with 0–220 V AC.
Figure 5 shows one of the fans driven by the driver used in
the design.
The frequency converter receives the control signal from
the control card of developed EFLCS in the range of 0–10
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Vdc. The values of voltage, current and frequency that correspond to control signal value are produced as outputs and
also can be monitored via this device. In this way, precautions
can be taken against undesirable situations that may occur in
the system.
2.3.1 Obtaining PWM Control Signal
Fig. 6 PWM signals with different duty cycles and sample switching
circuit [44]
Fig. 7 Control signal for PWM level 50
PWM is a way of obtaining energy by consecutive pulses
instead of a continuously changing (analog) signal. This
pulse width is increased or decreased to regulate the energy
flow. Figure 6 shows PWM signals with different duty cycles
and sample switching circuit.
The control signal 0–10 Vdc required to control the driver
was controlled by adjusting the pulse width of the voltage
from 10 Vdc source. This adjustment or setting is implemented by triggering the IRF52N MOSFET through 0–5 Vdc
output of microcontroller.
The PWM range of microcontroller is set to be between 0
and 255. In developed EFLCS, the input read by the sensors
is evaluated by the program that makes use of FL approach
and is loaded to microcontroller. Thus, the sharp values are
obtained. These sharp values are assigned to the task period
of the PWM signal to be generated by the PIC18F4620. This
task period with a start value of zero is reassigned as soon as
the sensors are read. Two examples are given below:
For PWM level 50 The oscilloscope output of the control
signal for PWM level 50 is shown in Fig. 7.
The oscilloscope image of the driver’s output signal corresponding to this signal (PWM level 50) is shown in Fig. 8a,
and the oscilloscope image of the average of the driver’s output signal is shown in Fig. 8b.
Fig. 8 a The driver’s output signal for PWM level 50 and b average of the driver’s output signal for PWM level 50
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Fig. 9 Control signal for PWM level 200
For PWM level 200 The oscilloscope output of the control
signal for PWM level 200 is shown in Fig. 9.
The oscilloscope image of the driver’s output signal corresponding to this signal (PWM level 200) is shown in Fig. 10a,
and the oscilloscope image of the average of the driver’s output signal is shown in Fig. 10b.
occur. After the main voltage is reduced by a transformer, it
is converted to a 1.65 MHz frequency signal by an electronic
circuit. This signal is transferred to a transducer mounted in
a water reservoir. The transducer converts this signal to high
frequency vibration. With the effect of the 1.65 MHz frequency signal, it changes its thickness by 1.65 million times
a second. As a consequence of the high frequency vibration
of the transducer surface and the momentum of the water
due to the inertia of the water, this vibration of the water cannot keep up with it, which causes the water column to form
in the transducer. During the transducer is shrinking in the
negative direction, the water cannot follow this rapid movement and instantaneous vacuum occurs in the region above
the transducer. Due to the vacuum, cavitation starts on the
surface of the water and causes water particles to form under
low temperature and pressure. During the positive expansion
of the transducer, the water particles move rapidly toward
the surface of the water column and collide with each other
at high velocities. At the wave center of the sound waves
on the water surface, the smallest water particles are broken
down into 1-micron-sized mist particles. The produced mist
is easily absorbed by the air and transported by the air current [45,46]. Figure 11 shows the operation of the ultrasonic
atomizer.
Blyss brand UA humidifier which has 220–240 V, 50 Hz,
32 W input values was used in developed EFLCS.
2.4 Humidifier
2.5 View of the Developed System
The device that performs the cold humidification process
is called UA. UA produces cold mist at approximately frequency range 1–2 MHz. The main material of UA is the
asymmetric quartz crystals which, when the required frequency value is reached, cause mechanical vibrations to
Figure 12 shows the developed EFLC system (unmounted)
for CRDC. CRDC (dimensions 45 cm × 1.5 m × 1 m) used in
this study and also the location of the equipment of the developed EFLC on this CRDC (mounted) are shown in Fig. 13.
Fig. 10 a The driver’s output signal for PWM level 200 and b average of the driver’s output signal for PWM level 200
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As the sensor 5 is located near the evaporator, it cannot be
seen in Fig. 13.
2.6 Software of the System
The developed control system (EFLCS) together with PIC
codes that is written to get information from sensor and
to activate the actuators was transferred to microcontroller
using PIC-C language with Hi-Tech PIC compiler. The interface software that displays the input–output values instantly
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on the computer screen was developed using Microsoft
Visual Studio Program C# language.
2.6.1 Software of the Interface
The interface was designed to view and record the levels of
both the steam of UA and the speeds of the fans that are controlled by developed EFCL. The interface is provided via the
Universal Synchronous/Asynchronous Receiver/Transmitter
(USART) RC6 port for communication with microcontroller.
A screenshot of the designed interface program is shown in
Fig. 14.
Fig. 13 CRDC with developed EFLC system (mounted)
Fig. 11 The operation of the ultrasonic atomizer [47]
Fig. 12 Developed EFLC
system (unmounted)
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Fig. 14 Screenshot of the
interface program
2.6.2 Software of Microcontroller
The inputs and outputs of the entire system are controlled by
this software which is developed by using PIC-C language
and transferred to microcontroller.
2.7 The Algorithm
The values (humidity and temperature) from the SHT11 sensors were used as inputs, and speed level of 3 simultaneously
operated fans and steam level of UA were used as outputs.
As previously stated, UA is operated in levels (0–10 steps)
depending on the average of the temperature and humidity
values from the four sensors placed in the upper and lower
parts of CRDC. Therefore, two inputs (average temperature
and average humidity) and one output (steam level) EFLCS
were designed for UA.
On the other hand, the speed levels of the fans depend on
the temperature difference and average temperature values.
The average temperature value is the average of the temperature values read from the four sensors placed in the upper and
lower parts of CRDC. As mentioned previously for efficient
air conditioning system, the difference between the average
temperature of the cooled area and temperature of cooler
liquid inside the evaporator must not exceed 5 ◦ C. Due to
this reason, the temperature difference between evaporator
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temperature and the average of the temperature values read
from the four sensors placed in the upper and lower parts of
CRDC is used to determine the current speed level values
of the fans. Therefore, two inputs (average temperature and
the temperature difference) and one output (fan speed level)
EFLCS were designed for fans.
Both the code necessary for microcontroller to receive the
information from the sensors and EFLCS code to operate
the steam level of UA and speed levels of fan in accordance
with this information were written and loaded to microcontroller. As a final addition, microcontroller was also loaded
with the codes necessary for on–off control of the compressor between 3 and 5 ◦ C to keep the temperature inside CRDC
constant at 4 ◦ C through a relay. When the design of EFLCS
was completed, experiments were made on CRDC for different values of humidity and temperatures.
Normally, a fuzzy system is performed in three steps:
fuzzification: mapping the actual values of the variables in
the fuzzy set, inference: determining the rules that should be
used according to the rule base, defuzzification: determining a numerical output according to the result obtained in
the Inference step [48]. In this study, Mamdani implication
method was used as inference mechanism, and the weight
average method, which is most commonly used for the fuzzy
applications and is limited to symmetric output membership
functions [49], is used for the defuzzification process.
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Fig. 15 Membership functions of average temperature input
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Fig. 17 Membership functions of steam level of UA
Table 3 Rule table for steam level of UA
Inputs
LT
MT
TT
HT
ET
TLH
TLUAL
TLUAL
TLUAL
LUAL
LUAL
LH
MUAL
MUAL
MUAL
LUAL
LUAL
TH
HUAL
MUAL
MUAL
LUAL
LUAL
MH
EUAL
EUAL
HUAL
HUAL
HUAL
HH
EUAL
EUAL
EUAL
EUAL
EUAL
Fig. 16 Membership functions of average humidity input
2.8.2 Fuzzification of Output
In the following sections, only the fuzzy membership
functions of the inputs and outputs and also the rule tables are
mentioned. The inference and defuzzification processes were
carried out according to the previously mentioned methods
and loaded to microcontroller.
2.8 Steam Level Control Design of UA
In FL control of UA, the average value of the temperature
in CRDC for any moment is the first input value and the
average value of the humidity in CRDC for any moment is
the second input value. EFLCS decides at what steam level
of UA will be driven according to these inputs at related
moment. Depending on this decision or calculated output
value, microcontroller generates a PWM signal to drive UA
to reach the calculated steam level of UA at related moment.
2.8.1 Fuzzification of Inputs
The symmetric triangular membership function was used for
moderate temperature (MT), tolerable temperature (TT) and
high temperature (HT), whereas the trapezoidal membership
function was used for low temperature (LT) and excessive
temperature (ET). The average temperature input was defined
by five membership functions as shown in Fig. 15.
The symmetric triangular membership function was used
for low humidity (LH), tolerable humidity (TH) and moderate
humidity (MH), whereas the trapezoidal membership function was used for too low humidity (TLH) and high humidity
(HH). The average humidity input was defined by five membership functions as shown in Fig. 16.
The symmetric triangular membership function was used
for low UA level (LUAL), moderate UA level (MUAL) and
high UA level (HUAL), whereas the trapezoidal membership
function was used for too low UA level (TLUAL) and excessive UA level (EUAL). UA steam level was defined by five
membership functions as shown in Fig. 17.
2.8.3 Rule Table
The rule table for steam level of UA is shown in Table 3.
2.9 Speed Level Control Design of the Fan
In FL control of the fans, the difference between the evaporator temperature and the average temperature inside CRDC for
any moment is first input and the average temperature inside
CRDC for any moment is second input. EFLCS decides at
what speed levels of fans will be driven according to these
inputs at related moment. Depending on this decision or
calculated output value, microcontroller generates a PWM
signal for the YASKAWA V1000 driver to produce an output
voltage value from 0 to 10 V to drive the fans to reach the
calculated speed levels of fans at related moment. So, all the
fans run at the same required speed level to provide required
air conditioning in CRDC.
2.9.1 Fuzzification of Inputs
The symmetric triangular membership function was used for
low difference between average temperature and the evaporator temperature (LATET), moderate difference between aver-
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Table 4 Rule table for speed level of fan
Inputs
TLATET
LATET
MLATET
LT
MT
TT
HLATET
ELATET
TLFS
TLFS
LFS
LFS
LFS
TLFS
LFS
LFS
LFS
LFS
LFS
MFS
MFS
MFS
LFS
HT
HFS
EFS
MFS
MFS
MFS
ET
EFS
EFS
HFS
MFS
MFS
Fig. 18 Membership functions of difference between average temperature and evaporator temperature
Fig. 19 Membership functions of level of fan speed
age temperature and the evaporator temperature (MATET)
and high difference between average temperature and the
evaporator (HATET), whereas the trapezoidal membership
function was used for too low difference between average
temperature and the evaporator temperature (TLATET) and
excessive difference between average temperature and the
evaporator (EATET). The range for the difference between
the average temperature and the evaporator temperature was
defined by five membership functions as shown in Fig. 18.
The second input used for fan speed control design is the
average humidity. Since the fuzzification of average humidity
was explained in “design of steam level control design of
UA” section (Sect. 2.8), the tables and figures will not be
mentioned here again.
2.9.2 Fuzzification of Output
The symmetric triangular membership function was used for
low fan speed (LFS), moderate fan speed (MFS) and high
fan speed (HFS), whereas the trapezoidal membership function was used for too low fan speed (TLFS) and excessive
fan speed (EFS). The speed level of fan was defined by five
membership functions as shown in Fig. 19. Since all fans will
run with the same speed level, the value of this output will
be used to drive all fans.
2.9.3 Rule Table
The rule table for speed level of fan is shown in Table 4.
123
Fig. 20 Comparative graph of EFLCS and traditional system regarding
the instantaneous temperature control
3 Results and Discussions
For comparison aim, the records (temperature and humidity)
taken from sensors at certain intervals (13.7 s) were transferred to the computer. By using these records, graphics were
obtained by Originlab program. First, the records of classical
system were kept and then the records of developed EFLCS
were kept using the same CRDC. Experiments were carried out at 23 ◦ C outdoor temperature and 55% RH outdoor
humidity. The comparative graph of EFLCS and traditional
system regarding the instantaneous temperature control is
shown in Fig. 20. First of all, equal and long-term operation was carried out to stabilize both systems. Then, both
systems were provided to continue running for 850 s more.
According to the test results, the maximum temperature of the
traditional system is 5.56 ◦ C and the minimum temperature
is 3.2 ◦ C. For EFLCS, the maximum temperature is 4.44 ◦ C
and the minimum temperature is 3.69 ◦ C. Considering that
both systems are set at + 4 ◦ C, it seems that EFLCS has less
temperature fluctuation than traditional system.
The comparative graph of EFLCS and traditional system
regarding the instantaneous humidity control is shown in
Fig. 21. The humidity control results were obtained on the
same conditions as the temperature test. According to the
test results, the maximum humidity and minimum humidity
Arabian Journal for Science and Engineering (2019) 44:9529–9543
Fig. 21 The comparative graph of EFLCS and traditional system
regarding the instantaneous humidity control
9541
Fig. 23 The comparative graph of EFLCS and traditional system
regarding reaching the humidity set point
system could not reach the set value (could only reach 60%
RH in 342.5 s), whereas EFLCS reached set value in 191.8
s.
4 Conclusions
Fig. 22 The comparative graph of EFLCS and traditional system
regarding the reaching temperature set point
of traditional system are 61.81% RH and 57.45% RH, respectively. Regarding EFLCS, the maximum humidity is 81.33%
RH and the minimum humidity is 78.57% RH. Considering
that both systems are set at 80% RH, it seems that EFLCS
has obtained less humidity fluctuation around the set value
whereas traditional system even could not reach the set value.
The comparative graph of EFLCS and traditional system regarding the reaching temperature set point (+ 4 ◦ C)
is shown in Fig. 22. The time of reaching the set point was
measured instantly for both systems starting at + 7 ◦ C. Traditional system reached set value at 191.8 s and EFLCS at
109.6 s. EFLCS reached set value 82.2 s earlier than traditional system.
The comparative graph of EFLCS and traditional system
regarding the reaching humidity set point (80% RH) is shown
in Fig. 23. The time of reaching the set point was measured
instantly for both systems starting at 55% RH. Traditional
In traditional CRDC produced in Turkey, generally only temperature on–off control is carried out. In the pastry sector,
especially, the moisture level required for daily produced
products cannot be ensured, which leads to a short shelf
life. In this study, EFLCS for CRDC was developed to make
the shelf life of the cakes longer than it was before. Developed EFLCS kept CRDC temperature and humidity values
required for cakes at approximately + 4 ◦ C and 80% RH,
respectively. In addition, this study contributed to the literature by adding FL to the system developed by the authors
[50]. This study is a rare study in which PWM- and FLbased control system is used in the field of climate control.
Additionally, UA is used for the first time to supply required
humidity in CRDC manufactured in Turkey. Thus, a different
approach to this area is presented in this study.
As mentioned previously for efficient air conditioning system, the difference between the average temperature of the
cooled area and temperature of cooler liquid inside the evaporator must not exceed 5 ◦ C. With developed EFLCS, this
difference is kept under 5 ◦ C and the snow on the evaporator
surface was tried to be minimized to increase efficiency of
evaporator.
Within the scope of the study, UA could be developed and
the compressor could be driven at different speeds. Since each
one is the topic of different fields, available UA and on–off
control system were used during the compressor’s operating
periods. The authors of this work on the one side continue
123
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Arabian Journal for Science and Engineering (2019) 44:9529–9543
to work to drive the compressor at different speeds, on the
other side experimenting to demonstrate the superiority of
EFLCS’s energy consumption over as per traditional system.
In this context, three test forms (MIL/SIL/PIL) that are
successful and cost-effective solutions for automotive and
aerospace embedded systems [51] can be used in FLC algorithms to be developed.
Acknowledgements The works presented in this article were carried
out within the scope of the project numbered Selcuk University BAP
12101022. The authors thank Selcuk University BAP for their support.
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