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Development and performance evaluation of an intelligent air purifier/humidifier using fuzzy logic controller

26 Jun.,2023

Abstract

This study aimed to develop and implement a fuzzy logic controlled-intelligent air purifier/humidifier. The concepts of passive purification and evaporative humidification were used to build this device, and engineering ideas and theories were used to guide the development of electrical and mechanical systems. Additionally, a fuzzy logic controller was designed, built and integrated into the air purifier/humidifier device to help with its operation. It does this by analysing input signals from all the sensors (dust, volatile organic compound gas, humidity and water level) and activating the actuators (suction and blow fan). On the Arduino IDE, a C/C++ programming code was developed and uploaded onto the Arduino Uno R3 board, which houses the ATmega328P microcontroller processor. In estimating the clean air delivery rate (CADR), noise level and moisture delivery rate, the performance of the developed air purifier/humidifier was assessed. Additionally, the electrical systems’ power consumption and the fuzzy logic controller’s ease of use were each assessed. In light of the room capacity taken into consideration, the findings obtained demonstrated that the proposed air purifier/humidifier device satisfies the minimum standard requirement of a CADR of 140m3/hr. The outcome also revealed that the designed device’s noise level is lower than the typical threshold for an air purifier, which is less than 40 db. Additionally, after 68 minutes, the device raised the humidity level in a controlled area from 21% to 40%.

1 INTRODUCTION

Careful study of the atmosphere and weather conditions shows the understanding that the air we breathe in is usually unhealthy [1]. Good quality air should not be compromised in any given circumstance with its effect on individuals’ health, satisfaction and productivity. According to Aversa et al. [2], there are instances when interior air pollution levels can be up to five times greater than outdoor levels and, in some cases, much more. A dry, dusty, particle-contaminated air mass is usually experienced during the dry season, characterized by the Harmattan wind [3]. Studies have considered the level of volatile organic compounds (VOCs) and harmful air pollutants present in the atmosphere and observed that people who are exposed to these pollutants and VOCs often experience wheezing, asthma attacks, respiratory infections, eyes irritation, nausea and high hospital admission among others [4–6]. A dry airy environment denotes less humidity that can cause dehydration, irritation, fatigue, dry skin and other skin infections coupled with certain bacteria that thrive in a less humid environment [7, 8]. Cool, dry and dusty air is incomparable to fresh and moist air, which is why planting trees and flowers are encouraged within our surroundings. Living things produce oxygen and water vapour (moist air) as their by-products [9].

Hence, because the combined situation of dry, dusty air and VOCs gases poses a more significant health hazard, proper action must be taken to eliminate any possible risk to an acceptable degree. An air purifier/humidifier system is an indoor appliance device designed to purify the air of dust particles and hazardous gases emitted from materials. Dust particles and hazardous gases emission are a result of temperature and relative humidity changes or from outdoor activities of industries (paint, cement, etc.) within the area, thereby improving the indoor air quality [10, 11]. Also, it is designed to humidify the indoor space that happens to be less humid or dry due to climate conditions by applying moisture into the environment to maintain the indoor relative humidity percentage [12].

Furthermore, in an air-conditioned room, the air circulated is dry as the system was designed to dehumidify the air within the space, reducing the body’s perspiration activity rate [13]. The most typical air purifier device known is the standard air-conditioner unit that has the function of air purification and dehumidification. Hence, in a dry environment, it cannot humidify the atmosphere, which is a problem for people’s health [14]. This situation, as stated, can lead to various health issues such as breathing problems, asthma, influenza, damaged dry skin, dry eyes and irritation [15]. Also, the domestic air conditioner is associated with high energy consumption, which invariably increases the operation cost and does not alert the individuals within the room of the gas hazard available at any time [16]. Similarly, humidifiers that use ultrasonic and steam technology have high energy consumption [17, 18] and cause burns, especially in little children. Moreover, these air purifier/humidifier systems do not possess the feature to last long during operation, especially when there is a power outage [19].

Therefore, this study and its novelty aim to design and construct a controllable air purifier/humidifier device that uses a less energy consumption process in its operation by employing fuzzy logic and passive air purification and evaporative technology for the humidification function. This will involve designing and constructing an air purifier/humidifier for indoor air quality, constructing a backup power system and evaluating its performance. This device is to be used within a confined space volume of 35 m3 and with a standard 50 Hz, 220 AC power supply that will be converted and stepped down to a DC input of 9 V and a battery power source. The device will perform functions such as purifying (i.e. eliminating dust, pollen and other VOC gases), humidifying and using an alert signal (alarm) to notify the user in critical atmospheric conditions. Furthermore, the fuzzy logic controller was linked with the electronic components, such as the sensors and actuators needed to aid the functionality of an air purifier/humidifier device. The system adopts a two-way communication, whereby it supplies power to the sensor components interacting with the environment and sends data readings as input to the controller. According to its programmed fuzzy logic algorithm, the controller processes this input data and sends a response signal to the needed actuators for necessary actions.

2 METHODS

2.1 Design model of the air purifier/humidifier

Figure 1 shows how the microcontroller (Arduino) communicates with the device’s major passive/active components by sending and receiving a signal every time it is in operation mode. The battery source powers the microcontroller, which requires between 7 and 12 V to operate. The optical dust, MQ-135 (gas sensor), DHT11 (temperature and humidity sensor) and water level sensor has a two-way communication system that involves being powered by the microcontroller by receiving signal and, in return, sends information back to the microcontroller in the form of signal. The microcontroller uses this signal to drive the actuators (DC motor, LCD, buzzer and push–pull motor) and the buzzer according to the programmable algorithm, which in this case was achieved using an Arduino IDE (C/C++ programmable language).

Figure 1

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Design model of the air purifier/humidifier.

2.2 Working principle of the air purifier/humidifier

When the dust sensor or gas detector sensor senses contaminants in the air, the microcontroller activates the back fan to create a suction pressure (counter-clockwise direction) that takes dirty air into the device. These dirty air particles go through the first purification phase when it passes the pre-filter phase. First, the pre-filter removes large particles such as hair, pebbles, pollen particles, pet dander and dust particles greater than particulate matter 10 (PM10), thereby prolonging the lifespan of the high-efficiency particulate air (HEPA) filter by preventing it from getting clogged. Then, as shown in Figure 2, the pre-filtered air proceeds to the next purification phase, which is done by the HEPA filter. The HEPA filter traps at least 99.97% of dust particles of 0.3 μm (PM2.5) and above, and since these particles are the hardest to filter, they are regarded as the most invasive particle size. It also removes bacteria and viruses due to its antibacterial technology.

Figure 2

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Purification process working principle.

After the air has been purified of dust particles, there is a need to remove VOCs gases, which leads to the third phase of the purification process, carried out by the activated carbon filter. The activated carbon filter uses the principle of adsorption based on its large surface area/pore structure due to its carbon particles, letting contaminants come into contact with the filter’s active sites as much as possible. Chlorine, sediment and VOCs can all be removed most efficiently with active charcoal carbon filters, as well as formaldehyde and odour from the air [20]. The purified air is afterwards carried out into the environment by a front fan (axial direction of airflow) at a specific speed rate that is in sync with the back fan. All three filters are housed in one filter holder of three slots, which is detachable from the device whenever there is a need to change any of the filters (pre-filter, HEPA filter and carbon filter). This arrangement is for ease of maintenance of the device and no energy consumption during purification.

There are many different ways and techniques to raise the humidity in your home, but this technology is centred on mechanical mechanisms. When the sensor senses the drop in relative humidity of the environment, the back fan creates suction pressure and the process takes in the dry air, which is blown over a wick immersed into a container from where it draws up water according to the principle of capillarity. As seen in Figure 3, this technology is referred to as the wick system, whereby a foam, cloth or sponge wick draws water out of a reservoir [21]. The reservoir in this technology is a water container that holds water. It is detachable from the device for ease of refill when the water level becomes very low and washing to eliminate black fungus/mould. The front fan blows over the wick tip letting the air absorb moisture circulating the room. As the room’s relative humidity increases, the moisture content deposited through the wick decreases, making the technology self-regulating.

Figure 3

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Air humidification process working principle.

2.3 Design consideration

Based on the goal of the study, several parameters were put into consideration. These parameters informed the decision on the design approaches and components/materials selected in this study. Some of these parameters are the following.

The design considered an office space volume of 35 m3, which is within the scope of the work.
The use of low energy consumption technologies (passive purification technology and evaporative humidification technology) and electronic components within a maximum operating voltage of 5 V.
The VOC gas and dust particle consideration levels are between PM2.5 and PM10 [22].
The VOC gases being considered for purification from the air are NH3, alcohol, benzene, CO and CO2 [23].
The acceptable humidity level is between 40% and 60%; below this level is a dry condition and above this level is a too-humid condition [24].
A dual power source was considered (i.e. main supply and backup battery system) and a backup battery lasting capacity of 12 hours.
A corrosion-resistant casing material with high impact strength and little deformation was considered during design.
The design considered a low-noise motor fan and soundproof casing material to achieve a less than 40-db device according to the recommended standard by WHO and EPA [25].

2.4 Design assumption

In this study, it was assumed that the device is ingress protected (IP54), i.e. protected from limited dust ingress and water spray from any direction. Materials selected and manufacturing processes were geared towards achieving this factor. All components are compactable with the Arduino Uno board and will not result in overheating of the system. The voltage and current for each component are the rated and required value according to manufacturer specifications and will not harm the Arduino Uno board.

2.5 Electronic components details

Table 1 contains the central electronic parts used in developing the air purifier/humidifier, along with the datasheets details for each one, as provided by the manufacturer.

Table 1

S/N

Components

Specification

1 Optical dust sensor module Supply voltage ranges from 3.3 V DC to 5 V DC with a maximum current of 20 mA during operation. Resistance is 150

|$\varOmega$|⁠

. 2 DHT11 sensor module Voltage supply ranges from 3.5 V DC to 5 V DC and a maximum current of 2.5 mA. 3 MQ-135 sensor module Voltage supply of 5 V DC and current of 40 mA. 4 Water level sensor Voltage supply of 5 V DC and current of 20 mA. 5 LCD display module (1602A model) Voltage supply of 5 V DC, current consumption of 2 mA without backlight and backlight current consumption of 150 mA. 6 Passive buzzer Voltage supply of 5 V DC and current range from 10 mA to 30 mA. 7 DC motor Voltage supply of 5 V DC and current of 100 mA. 8 TIP122 transistor Vbe is 2.5 V DC, Ic is 3A, and Vce is 3 V DC at on characteristic. 9 Atmega 328P microcontroller Board voltage range of 5 V DC to 9 V DC and output of 3.3 V DC, 5 V DC and current of 400 mA during operation. S/N

Components

Specification

1 Optical dust sensor module Supply voltage ranges from 3.3 V DC to 5 V DC with a maximum current of 20 mA during operation. Resistance is 150

|$\varOmega$|⁠

Table 1

S/N

Components

Specification

1 Optical dust sensor module Supply voltage ranges from 3.3 V DC to 5 V DC with a maximum current of 20 mA during operation. Resistance is 150

|$\varOmega$|⁠

Components

Specification

1 Optical dust sensor module Supply voltage ranges from 3.3 V DC to 5 V DC with a maximum current of 20 mA during operation. Resistance is 150

|$\varOmega$|⁠

2.6 Design circuitry between controller and electronic components

A comprehensive circuitry design (arrangement) of the different electronic components utilized in the development of the air purifier/humidifier device controller is shown in Figure 4. The Arduino board supplies a maximum of 5 V DC from each pin to other connected components and a maximum of 400 mA during operation. Hence, transistors, diodes and resistors were used to regulate the current output of each attached component according to their datasheet recommended value.

Figure 4

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Electronic circuit diagram of the air purifier/humidifier.

The controller’s electronic circuitry, as seen in Figure 4, was created and simulated on Proteus 8 Professional Software to determine the current consumed by each electronic component to decide on the choice of Arduino board size to use based on the total consumed current. As the case may be, DC ammeters were connected before or after the electronic components. The consumed current by the components was displayed on a DC ammeter and recorded, as seen in Table 2. Furthermore, the power required for each component was obtained using Ohm’s law equation and the datasheet given in Table 1.

Table 2

Initial data

Result

Simulated result (current)

Optical dust sensor

|$P=0.0726W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx1}}$|

DHT 11

|$P=0.0125W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx2}}$|

MQ-135

|$P=0.2W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx3}}$|

LCD screen

|$P=0.0075W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx4}}$|

Water level sensor

|$P=0.0875W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx5}}$|

Passive buzzer

|$P=0.1W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx6}}$|

DC motor

|$P=0.56W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx7}}$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx8}}$|

Total 1.0426 W 191.18 mA Initial data

Result

Simulated result (current)

Optical dust sensor

|$P=0.0726W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx1}}$|

DHT 11

|$P=0.0125W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx2}}$|

MQ-135

|$P=0.2W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx3}}$|

LCD screen

|$P=0.0075W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx4}}$|

Water level sensor

|$P=0.0875W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx5}}$|

Passive buzzer

|$P=0.1W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx6}}$|

DC motor

|$P=0.56W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx7}}$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx8}}$|

Total 1.0426 W 191.18 mA Open in new tab

Table 2

Initial data

Result

Simulated result (current)

Optical dust sensor

|$P=0.0726W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx1}}$|

DHT 11

|$P=0.0125W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx2}}$|

MQ-135

|$P=0.2W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx3}}$|

LCD screen

|$P=0.0075W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx4}}$|

Water level sensor

|$P=0.0875W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx5}}$|

Passive buzzer

|$P=0.1W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx6}}$|

DC motor

|$P=0.56W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx7}}$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx8}}$|

Total 1.0426 W 191.18 mA Initial data

Result

Simulated result (current)

Optical dust sensor

|$P=0.0726W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx1}}$|

DHT 11

|$P=0.0125W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx2}}$|

MQ-135

|$P=0.2W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx3}}$|

LCD screen

|$P=0.0075W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx4}}$|

Water level sensor

|$P=0.0875W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx5}}$|

Passive buzzer

|$P=0.1W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx6}}$|

DC motor

|$P=0.56W$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx7}}$|

|$\raisebox{-44pt}{\includegraphics{\bwartpath ctad004fx8}}$|

Total 1.0426 W 191.18 mA Open in new tab

From Table 2, the total simulated current to be consumed by the electronic components based on design is summed to 191.18 mA, and the power required is 1.0426 W. Due to its rating, an Arduino Uno R3 (ATmega328P) board was selected to supply the required voltage and current to power all the electronic components. According to the Arduino Uno R3 board datasheet, the maximum output current that can be consumed from the board is 400 mA, which is below the total simulated current of simulated current.

2.7 Design of power source/back-up power system

Power is a crucial element for the efficiency and functionality of a device in terms of reliability. The device gets its power source from an AC 220 V, which is converted and stepped down to 5 V DC at 2A with a DC power adapter. This 5 V DC voltage was supplied as input to the battery charger connected to the rechargeable lithium-ion battery TP4056 module connected to the battery bank. The rechargeable battery bank (whose circuit diagram is given in Figure 5), which contains lithium batteries of 3.7 V, is connected to the DC-DC converter (TPS630020), which serves as a voltage booster unit to achieve the required output voltage (5 V) for the microcontroller. Lithium-ion batteries were chosen for the air purifier/humidifier because they have a high energy density and less self-discharge compared with other rechargeable batteries [26]. With the total current of the air purifier/humidifier as 191.18 mA and the power required output as 1.0426 W, as given in Table 2, the expected lasting time of the power source/backup power system is 12 hours.

Figure 5

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Power source circuit diagram.

2.8 Design of device body case

The device body framework consists of two sections. The main section houses the filters, fans, water reservoir and power source system, while the top houses the electronic components and control board. The top section contains the different electrical circuits, including the sensors, LCD, circuit board and their connection to the microcontroller. The device’s front was designed at an angle of 90o to enable the unit effectively circulate the purified air around the room. This is because of the rectangular form of the office space. The design also contains fins that help purify air circulation around the office space and other parts labelled as shown in Figure 6.

Figure 6

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Schematic of the device body case.

Initially measuring the numerous section parts, the device’s fabrication was successfully carried out using the aluminium composite flat board based on Figure 6. Then, the various section parts were assembled on the body frame using V-threaded screws 10 mm in length. The front and back channel was first assembled to the body frame, followed by the case of the electronic component at the top, before finally assembling the power source cover at the back of the device. The reason for using a V-threaded screw is its ease of maintenance [27]. Figure 7 shows the developed air purifier/humidifier.

2.9 Design of fuzzy logic controller

The foundation of the fuzzy control system is the developed fuzzy logic controller. The model architecture for the fuzzy logic controller can be seen in Figure 8. It is made up of the diagnostic rules that link the specified parameters to produce an output result.

Database. It stores the fuzzy input and output space divisions and normalizes the crisp input values (i.e. covers crisp input to fuzzy input). Each parameter’s range and membership function are specified.
Fuzzy rule base. The kind of fuzzy rules and their origin and line of descent are all contained in the fuzzy rule base. An IF...THEN sentence is used to express it.
A fuzzy inference system. The fundamental task is to determine how much each rule in the fuzzy rule base contributed to the total output of the control output variable.
Defuzzification. It de-normalizes the output into its physical domain and turns the collection of updated control output values (fuzzy input) into single point-wise (crisp) values.

Figure 8

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Fuzzy logic controller design model.

Figure 9 shows the algorithm of how the device operates in terms of its executable command and functions.

Figure 9

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Flow chart operation algorithm.

2.10 Implementation using MATLAB

In the course of designing the controller, the possible range of input and output variables was determined. This design adopted the Mamdani-type system because of its widespread acceptance, intuition and suitability to human input with a triangular membership function. It also has the characteristics of simplicity, ease of calculation and fewer complexes when splitting values (low, medium, high, very high) and works with a straightforward algorithm of linguistic expression [28, 29]. The system works with four input variables (temperature, relative humidity, dust particle and VOCs particle) and two output variables (fan speed and humidifier servo motor), as shown in Figure 10.

2.10.1 Humidity, dust particle and VOCs particle—input variables

The advisable room relative humidity should be between 40% and 60% [24]; however, for a humidifier, relative humidity should be <40% [30]. Dust particles, as well as VOC gas particles, were measured in parts per billion. According to Stratigou et al. [22], the accepted dust density for safe health is less than an average of 0.035 mg/m3 per day and an average of 0.012 mg/m3 per annum for PM2.5 and less than an average of 0.150 mg/m3 per day and an average of 0.028 mg/m3 per year for PM10. The acceptable threshold limits for VOCs gases in homes and offices, as given by Al-Hemoud et al. [31], are ethanol (1000 ppb), formaldehyde (0.3 ppb), acetone (1000 ppb), benzene (0.1 ppm) and dichlorobenzene (50 ppb). Furthermore, the acceptable VOC gas level by EPA should not exceed 25 ppb [32]. Hence, in this study, as given in Figure 11 and Table 3, a safe level of 0 to 25 ppb VOC gases will be considered.

Figure 11

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The plot of membership function for (a) humidity, (b) dust particles and (c) VOCs particles.

Table 3

Humidity

Dust particle

VOCs particle

Membership function

Range (%)

Membership function

Range (%)

Membership function

Range (%)

Dry (D) 0–40 Normal (N) 0–0.1 Normal (N) 0–25 Humid (H) 30–100 High (H) 0.05–0.2 Unsafe Level (UL) 20 and above Very High (VH) 0.15 and above Humidity

Dust particle

VOCs particle

Membership function

Range (%)

Membership function

Range (%)

Membership function

Range (%)

Dry (D) 0–40 Normal (N) 0–0.1 Normal (N) 0–25 Humid (H) 30–100 High (H) 0.05–0.2 Unsafe Level (UL) 20 and above Very High (VH) 0.15 and above Open in new tab

Table 3

Humidity

Dust particle

VOCs particle

Membership function

Range (%)

Membership function

Range (%)

Membership function

Range (%)

Dry (D) 0–40 Normal (N) 0–0.1 Normal (N) 0–25 Humid (H) 30–100 High (H) 0.05–0.2 Unsafe Level (UL) 20 and above Very High (VH) 0.15 and above Humidity

Dust particle

VOCs particle

Membership function

Range (%)

Membership function

Range (%)

Membership function

Range (%)

Dry (D) 0–40 Normal (N) 0–0.1 Normal (N) 0–25 Humid (H) 30–100 High (H) 0.05–0.2 Unsafe Level (UL) 20 and above Very High (VH) 0.15 and above Open in new tab

2.10.2 Fan speed and humidifier stroke—output variables

In this study, the fan speed had a minimum motor speed of 1000 rpm and a maximum speed of 2000 rpm. The humidifier system comprises a wick immersed in a water reservoir and connected to a solenoid push–pull that reciprocates. Table 4 and Figure 12 show the output variables’ membership function and MATLAB plots.

Table 4

Humidity

Dust particle

Membership function

Range (%)

Membership function

Range (%)

Off (O) 0–500 Off (O) 0–2 Low (L) 400–1000 High (H) 1–10 High 900 and above Humidity

Dust particle

Membership function

Range (%)

Membership function

Range (%)

Off (O) 0–500 Off (O) 0–2 Low (L) 400–1000 High (H) 1–10 High 900 and above Open in new tab

Table 4

Humidity

Dust particle

Membership function

Range (%)

Membership function

Range (%)

Off (O) 0–500 Off (O) 0–2 Low (L) 400–1000 High (H) 1–10 High 900 and above Humidity

Dust particle

Membership function

Range (%)

Membership function

Range (%)

Off (O) 0–500 Off (O) 0–2 Low (L) 400–1000 High (H) 1–10 High 900 and above Open in new tab

Figure 12

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Plot of membership function for (a) fan speed and (b) humidifier stroke.

2.10.3 Rule base and defuzzification

The input variables were processed and calculated using AND method, MAX aggregate method and defuzzification using the CENTROID method to produce the crisp value output as given in Figure 13. From the input variable ranges (7) and output variable ranges (5), 12 rule bases were developed as given below.

If (Humidity is Dry) and (Dust-Particulate-Matter is Normal) and (VOC-Particulate-Matter is Normal Level), then (Fan is High) (Humidifier is High) (1)
If (Humidity is Dry) and (Dust-Particulate-Matter is High) and (VOC-Particulate-Matter is Normal Level), then (Fan is High) (Humidifier is High) (1)
If (Humidity is Dry) and (Dust-Particulate-Matter is Very High) and (VOC-Particulate-Matter is Normal Level), then (Fan is High) (Humidifier is High) (1)
If (Humidity is Dry) and (Dust-Particulate-Matter is Normal) and (VOC-Particulate-Matter is Unsafe Level), then (Fan is High) (Humidifier is High) (1)
If (Humidity is Dry) and (Dust-Particulate-Matter is High) and (VOC-Particulate-Matter is Unsafe Level), then (Fan is High) (Humidifier is High) (1)
If (Humidity is Dry) and (Dust-Particulate-Matter is Very High) and (VOC-Particulate-Matter is Unsafe Level), then (Fan is High) (Humidifier is High) (1)
If (Humidity is Humid) and (Dust-Particulate-Matter is Normal) and (VOC-Particulate-Matter is Normal Level), then (Fan is Off) (Humidifier is Off) (1)
If (Humidity is Humid) and (Dust-Particulate-Matter is High) and (VOC-Particulate-Matter is Normal Level), then (Fan is Low) (Humidifier is Off) (1)
If (Humidity is Humid) and (Dust-Particulate-Matter is Very High) and (VOC-Particulate-Matter is Normal Level), then (Fan is High) (Humidifier is Off) (1)
If (Humidity is Humid) and (Dust-Particulate-Matter is Normal) and (VOC-Particulate-Matter is Unsafe Level), then (Fan is High) (Humidifier is Off) (1)
If (Humidity is Humid) and (Dust-Particulate-Matter is High) and (VOC-Particulate-Matter is Unsafe Level), then (Fan is High) (Humidifier is Off) (1)
If (Humidity is Humid) and (Dust-Particulate-Matter is Very High) and (VOC-Particulate-Matter is Unsafe Level), then (Fan is High) (Humidifier is Off) (1)

Figure 13

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MATLAB rule viewer showing defuzzification of aggregate variables.

3 RESULTS AND DISCUSSION

3.1 Performance evaluation of the developed air purifier/humidifier

The performance of the developed air purifier/humidifier was evaluated based on the standard functionality of the clean air delivery rate (CADR), noise level and moisture delivery rate of the humidifier.

3.1.1 Clean air delivery rate

In determining the CADR of the developed air purifier/humidifier, dust was introduced into a confined room space of 35 m3 (based on design consideration), particulate matters (dust, CO2 and alcohol) were measured and the room was left to purify itself naturally for an hour. The exact process was carried out. However, in this case, the developed air purifier/humidifier was placed in the room and the particulate matter was measured after an hour. With the air change per hour (ACH) of dust, CO2 and alcohol as 4.2, 5 and 4, respectively, the theoretical CADR (the ACH’s product and the room’s volume) is 140 m3/hr. Table 5 gives the CADR of the room with and without the air purifier/humidifier device.

Table 5

S/N

Particulate matter

With device (m3/hr)

Without device (m3/hr)

Standard minimum capacity (m3/hr)

1 Dust 150 44.68 140 2 CO2 175 55.26 140 3 Alcohol 140 33.87 140 S/N

Particulate matter

With device (m3/hr)

Without device (m3/hr)

Standard minimum capacity (m3/hr)

1 Dust 150 44.68 140 2 CO2 175 55.26 140 3 Alcohol 140 33.87 140 Open in new tab

Table 5

S/N

Particulate matter

With device (m3/hr)

Without device (m3/hr)

Standard minimum capacity (m3/hr)

1 Dust 150 44.68 140 2 CO2 175 55.26 140 3 Alcohol 140 33.87 140 S/N

Particulate matter

With device (m3/hr)

Without device (m3/hr)

Standard minimum capacity (m3/hr)

1 Dust 150 44.68 140 2 CO2 175 55.26 140 3 Alcohol 140 33.87 140 Open in new tab

From the result obtained in Table 5, it was observed that the developed air purifier/humidifier device meets the minimum standard requirement of 140 m3/hr based on the room capacity considered. According to Mølgaard et al. [33], higher ACH and CADR values imply a more effective system. The higher the values, the more effective and efficient the device purification process is within the set confined office space of 35 m3 based on the tested conditions. The obtained result is higher than the air purifier developed by Jaradat—Moh’d and Al-Nimr [34], which obtained a CADR of 15 m3/hr for a room space of 36 m3. A better CADR result obtained in this study can be attributed to the presence of two fans (suction and blow) designed to give a higher air flow rate.

3.1.2 Noise level

The device’s noise level was recorded at 1-hour intervals for 5 hours to determine the average decibel level through a sound metre. The device was kept in operation and isolated from external noise by placing it in a soundproof room where the taken device’s decibel values were recorded. Table 6 shows the obtained result on the noise level performance evaluation of the developed air purifier/humidifier.

Table 6

Time interval (hr)

Noise level (dB)

1 34 2 34 3 36 4 35 5 34 Average decibel 34.6 Time interval (hr)

Noise level (dB)

1 34 2 34 3 36 4 35 5 34 Average decibel 34.6 Open in new tab

Table 6

Time interval (hr)

Noise level (dB)

1 34 2 34 3 36 4 35 5 34 Average decibel 34.6 Time interval (hr)

Noise level (dB)

1 34 2 34 3 36 4 35 5 34 Average decibel 34.6 Open in new tab

From the result obtained, the average noise level of the developed air purifier/humidifier is 34.6 db. This is a result of the two dc motors; each rated at 20 db and ~5.4 db, cancelled out due to soundproof material used in developing the device’s body. Furthermore, the noise level of the developed device is lower than the standard required noise level value for an air purifier that stands at <40 db [25, 35].

3.1.3 Moisture delivery rate

The function of the humidifier, which was incorporated into the air purifier/humidifier design, was tested to determine its ability to humidify the room at different time duration and raise the humidity level back to 40%. Table 7 shows the duration it took to raise the room’s humidity under the various test conditions back to 40% relative humidity.

Table 7

S/N

Relative humidity level range (<40% to 40%)

Time duration (mins)

1 32–40 43 2 25–40 58 3 21–40 68 S/N

Relative humidity level range (<40% to 40%)

Time duration (mins)

1 32–40 43 2 25–40 58 3 21–40 68 Open in new tab

Table 7

S/N

Relative humidity level range (<40% to 40%)

Time duration (mins)

1 32–40 43 2 25–40 58 3 21–40 68 S/N

Relative humidity level range (<40% to 40%)

Time duration (mins)

1 32–40 43 2 25–40 58 3 21–40 68 Open in new tab

Figure 14

Open in new tabDownload slide

Developed fuzzy controller interfaced with sensors and actuators.

From Table 7, it was observed that the time taken to raise the humidity level increased as the humidity range increased, implying that the time duration is dependent on the difference between the dryness percent of the environment compared with the 40% relative humidity set point. This result is close to the findings of Eggie [36], whose air humidifier increased the humidity level of a controlled room from 20% to 40% in ~60 minutes.

3.2 Fuzzy logic controller

After designing the fuzzy logic controller model, a prototype was developed and tested for functionality to fulfil the aim of this study. Figure 14 shows the controller prototype and design model. The developed fuzzy logic controller was tested based on the standard functionality test of ease of operation and power consumption compared with the theoretically calculated values.

3.2.1 Ease of operation

A functionality test was used to evaluate the device’s functionality without human manipulation and, as a result, test the smartness of the device. Its sensors and actuators are expected to power on when there is a need for the purifier or humidifier to purify/humidify the air and power off when the air purity condition and humidity are normal and humid, respectively. Figure 15 shows that the controller can be said to have played its role in coordinating the device’s activities. For example, it was seen that the fan output speed reduces or increases depending on the condition of the room and is powered down when every condition is seen as normal.

Figure 15

Open in new tabDownload slide

Simulation display of the fuzzy logic controller.

3.2.2 Power consumption

Based on the initial design calculation for load output capacity required to choose the microcontroller rating that will effectively control the various electronic components without overload, I total is 191.18 mA. Next, a multi-metre was used to measure the current, voltage and power consumed by the device at an interval of 1 hour for 12 hours, and the average value was recorded. This was done when the fuzzy logic controller was used and without the fuzzy logic controller, with Figure 16 showing the experimental setup. The main power supply was designed to charge the lithium-ion battery and power the device when the main power supply was out. The result of the power consumption test is shown in Table 8.

Figure 16

Open in new tabDownload slide

Voltage and current reading when (a) fuzzy controller is not used and (b) fuzzy controller is in use.

Table 8

Time (hr)

Current (mA)

Voltage (V)

1 110 4.5 2 200 4.5 3 190 4.5 4 150 4.5 5 100 4.5 Average value 150 4.5 Time (hr)

Current (mA)

Voltage (V)

1 110 4.5 2 200 4.5 3 190 4.5 4 150 4.5 5 100 4.5 Average value 150 4.5 Open in new tab

Table 8

Time (hr)

Current (mA)

Voltage (V)

1 110 4.5 2 200 4.5 3 190 4.5 4 150 4.5 5 100 4.5 Average value 150 4.5 Time (hr)

Current (mA)

Voltage (V)

1 110 4.5 2 200 4.5 3 190 4.5 4 150 4.5 5 100 4.5 Average value 150 4.5 Open in new tab

From the result obtained in Table 8, the average current consumed by the device during a 5-hour operation period was 150 mA, which corresponded to an average voltage of 4.5 V. The variance in the current readings within the operation period resulted from the controller regulating the motor’s state based on the purifier’s need to purify the environment. Also, due to the voltage drop in the use of the device, there was a difference in the voltage readings from the expected 5 V. By comparison, the consumed current for the device was less than the design and calculated current value of 191.18 mA resulting in 36.4% power saved by the developed air purifier/humidifier.

4 CONCLUSIONS

In this study, an air purifier/humidifier device that uses a fuzzy logic controller was designed, constructed and tested against certain experimental conditions to determine the device’s functionality. This device was built based on passive purification and evaporative humidification principles. Design considerations, design assumptions and electrical systems design were based on engineering principles and theories. Furthermore, a fuzzy logic controller was designed, constructed and embedded into the air purifier/humidifier device. This aids its functionality by receiving input signals from all the sensors (dust, VOC gas, humidity, water level), processing them and using them to activate the actuators (suction and blow fan). A C/C++ programming code was developed on an Arduino IDE and uploaded into the Arduino Uno R3 board that contains the ATmega328P microcontroller chip.

The performance of the developed air purifier/humidifier was evaluated to determine the CADR, noise level and rate of humidification. Furthermore, the ease of operation and the power consumption of the fuzzy logic controller and electrical systems were evaluated, respectively. The results showed that the developed air purifier/humidifier device meets the minimum standard requirement of 140 m3/hr regarding the room capacity considered. Also, the result showed that the noise level of the developed device is lower than the standard required noise level value for an air purifier that stands at <40 db. Furthermore, the device increased the humidity level of a controlled room from 21% to 40% in ~69 minutes. In addition, the developed air purifier/humidifier saved 36.4% power from the electrical analysis.

At the end of this study, the study recommends developing a backup power system that will last 24 hours to be applicable in homes when a grid power outage is more than 12 hours within a day. Furthermore, the integration of neural networks as an aspect of artificial intelligence is recommended in future studies.

Acknowledgements

The authors thank the staff and students of the Department of Mechanical Engineering, Ahmadu Bello University, Zaria, Nigeria.

Data Availability

Data and materials are available upon reasonable request.

Authors’ Contributions

E.O.P.: conceptualization, data curation, formal analysis, investigation, methodology, writing (original draft); UAU conceptualization, data curation, formal analysis, investigation, methodology, supervision, editing original draft. U.S.: conceptualization, data curation, formal analysis, investigation, methodology, supervision. O.A.N.: review and editing, data curation. All authors have read and approved the manuscript.

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