Automatic Temperature Controlled Household Electric Ceiling Fan

Oduah U.I., and Osuntola F.O, Physics Department, University of Lagos, Nigeria

Abstract:

An automatic temperature controlled household electric ceiling fan is designed and developed in this research.

The device uses a temperature sensor; a comparator unit and relay switch to automatically regulate the speed of

the electric ceiling fan, creating breeze to enhance convective heat transfer. The developed household electric

fan automatically changes speed in five different ascending levels with respect to the calibrated temperature

range of the environment. The operation of this innovative device makes it suitable for users who may not be

able to access the manual electric fan regulator. A sudden change in weather conditions affecting the ambient

temperature might harm a person sleeping under a manually regulated fan. Depending on the temperature of the

environment, the fan automatically regulates its speed, making the device safe for sleeping, very convenient for

patients in the hospital, infants and all users. The aerofoil of the cross section of the applied blades, the smooth

and even three blades, the length and width of the blades all improved the air velocity distribution of the device.

The developed temperature controlled household ceiling fan achieved improved ventilation of the room up to

20% using enhanced blades designed with due consideration to fan aerodynamics. The ceiling fan blades spin

with reduced noise and created uniform flow pattern across the room.

Keywords: Air distribution, Ceiling fan, Comparator, Fan speed control, Temperature sensor, Ventilation.

1. Introduction

Electric fan is one of the most popular electrical appliances widely used in tropical locations

for convective heat transfer to achieve cooling due to its cost-effectiveness, low power

consumption, and efficiency in attaining excellent ventilation (Cory, 2010). Presently, the

regular electric fans used in the house consist of a speed regulator calibrated into five

ascending order which is manually controlled to the desired speed (FarexRefieved, 2012).

This sometimes poses a challenge for a user that is not fully conscious while the fan is in

operation for example; when a person is sleeping; when a baby is in the room alone; or for

the patients in the hospital unaided.

Corresponding Author: Oduah, U.I.

Email: email

Ilorin Journal of Science

Volume 3, Number 1, 2017, pp. 50 –60 (Printed in Nigeria)

JOURNAL OF SCEINCE

ILORIN

Oduah U.I. and Osuntola F.O. ILORIN JOURNAL OF SCIENCE

Consider a scenario when a person is in deep sleep and with the fan set to the highest speed

because of a hot weather. If the weather suddenly changes and is very cold, the person will

be extremely cold and might catch cold or even result to pneumonia. Similarly, a baby that is

under the fan alone might develop cold or when in extremely hot weather, develop heat

rashes if the fan speed is not properly controlled. The inconvenience and the risk of not

regulating the speed of a fan timely to suit the ambient temperature has been a major

challenge which is the focus of this research (Dougherty, 1993).

The objective of this research project is to design and construct an efficient automatic

household electric ceiling fan that can auto-switch the fan regulator to control the fan speed

to suit the ambient temperature. This is different from a remote sensing device which will

require the manual operation of the fan regulator using a remote control (Jaeger, 2004).

However, this device uses a temperature sensor which automatically controls the fan

regulator switch to achieve the desired downward breeze. The temperature sensor is

connected to variable resistors and comparator that will logically let out signals to the Ne555

timer monostable vibrator that in turn switches the relay. The speed of the fan blades

respond to the signal from the temperature sensor by switching high when the ambient

temperature rises and low when the temperature falls (Terahja, 2003). The feedback from the

temperature sensor is set automatically to trigger the comparator which presents a logical

output to variable resistors set in the conventional five speed fan regulator distribution. The

fan therefore automatically adjusts to five different speed levels as determine by the ambient

temperature.

2. Materials and Methods

The components used in the construction of the prototype automatic temperature controlled

fan for household are: Transformer, Temperature sensor, Resistors, Comparator (LM339),

Capacitor, Monostable multivibrator(555 timer), Transistor, Power diode, and Relay switch.

Oduah U.I. and Osuntola F.O. ILORIN JOURNAL OF SCIENCE

Figure 1. Block Diagram for the Fan Blade Spinning Speed Control

The Figure 1 above shows the block diagram describing the basic operations of this unit. The

Power supply comprises of the step-down transformer (240v/19v), rectifier unit, filtering unit

and a 12volt voltage regulator. The 12volts voltage regulator supplies the 12volt dc voltage to

the circuit of the comparator function and variable resistors. The temperature sensor senses

the temperature that will trigger the variable resistor which then activates the comparator to

function (Terahja, 2006). The transmitted signal from the temperature sensor triggers the 555

timer monostable multivibrator which in turn controls the relay to switch between each level

of the fan speed automatically. So, the fan blades will adjust in speed according to the

temperature levels set for each speed level, 1, 2, 3, 4, and 5, ranging from lowest to highest

blade speed respectively.

The theoretical background of the application of the temperature sensor (LM35), comparator

(LM339), monostable multivibrator (555 timer), and the relay in the implementation of this

research project to achieve the desired fan performance results are outlined as subsections

below.

2.1 Principle of operation of temperature sensor (LM35)

Figure 2 shows a typical simple LM35 circuit. It works as follows:

Pin 1, is the input connected to the source, +vcc ranging from 4v and 30v. Here 12v is typical

value used in the construction of this device. Pin 2 is connected to a resistor. Vout voltage is the

voltage divider of pin 2 and the resistor. It has an output voltage that is proportional to the

Celsius temperature (the scale factor is 0.01v/ oC).

Oduah U.I. and Osuntola F.O. ILORIN JOURNAL OF SCIENCE

Temperature (oC) = Vout × 100oC/v ------Equation 1

Pin 3 is grounded. The LM35 does not require any external calibration or trimming and it

maintains an accuracy of ± 0.4 oC at room temperature and ± 0.8 oC over a range of 0oC to

100oC. Another important characteristic of the LM35 is that it draws only 60micro amps from

its supply source and possesses a low self-heat capability (Tooley, 2012). The sensor self-

heating causes less than 0.1oC temperature rise in still air.

Figure 2. LM35 circuit

2.2 Principle of operation of comparator (LM339)

A digital comparator evaluates two binary strings bit by bit and outputs a „1‟ if they are exactly

equal (Kal, 2004). It is a device used to compare the magnitude or size of two binary bit strings

or words. An exclusive NOR gate is the easiest way to compare the equality of bits. So, if both

bits are equal (0-0 or 1-1), the ex-NOR puts out a 1. As shown in Figure 3, the comparator

circuit works by simply taking two analog inputs, comparing them to produce the logical

output high “1” or low “0”. By applying the analog signal to the comparator „+‟ input called

“non-inverting” and „–„ input called “inverting”, the comparator circuit will compare the two

analog signals. If the analog input on +input is greater than the analog input on –input

(inverting) then the output will swing to logical “1” and this will make the open collector

transistor Q8 on the circuit below to turn ON. When the analog input on the +input (non-

inverting) is less than the analog input on –input(inverting) then the comparator will swing to

the logical “0” (the Q8 transistor turn OFF mode).

Oduah U.I. and Osuntola F.O. ILORIN JOURNAL OF SCIENCE

Figure 3. Comparator (LM339) circuit

2.3 Principle of operation of monostable 555 timer

Monostable 555 timer multivibrator circuit described in figure 4 below is a triggerable mono

shot pulse generator. The duration of the stable state or the pulse width is determined by the

charging time constant of the RC (Resistor Capacitor) network. This means once triggered, it

will ignore further inputs during a timing cycle. The timer starts when the input goes low, or

switched to ground level, and the output goes high (Robert, 2002).

The resistor Rt (100k) and Capacitor Ct (47µF) were selected for 5.2 seconds (T) timing

duration using the formula:

T = 1.1Rt* Ct ------Equation 2

Pin7 (discharge pin) is a transistor signal going to capacitor Ct which discharges when pin 7 is

on. Pin 2 (trigger pin) is triggered when a signal below 1/3Vcc is received and is responsible

for the transition of the flip-flop from the set to reset mode. Pin3 is for the output signal. Pin4