In this article we will discuss about:- 1. Meaning and Objective of Air-Conditioning 2. Parts of Air Conditioner 3. Working 4. Electric Circuits.
Meaning and Objective of Air-Conditioning
Air conditioning may be defined as the production of an artificial atmosphere specially adopted to particular requirement or air-conditioning means control of temperature, humidity, purity and movement of air.
The working conditions and comfort of human beings is improved by air-conditioning. The humidity is maintained at 60% being most suitable for human beings. By air conditioning we heat the rooms in winter and cool them in summer. The air is also made dust free.
Its objective is to produce comfortable and healthy conditions for the occupants by treating air so as to control simultaneously the prevailing conditions of temperature, humidity distribution and cleanliness in the conditioned space.
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It includes the air conditioning of spaces and surroundings which are occupied by human being e.g. residences, theatres, departmental stores, cinema halls, restaurants, dancing hall, hospitals, night clubs, seminar halls and control rooms in power houses etc.
The inner temperature of our body is 37°C and outer temperature is about 26.5°C. Under normal conditions our body emits 2500 K cals per 24 hours and amount of heat dissipated is governed by surrounding temperature, air temperature and humidity of air.
In order that we may feel convenient and comfortable, our body should dissipate 2500 K cals per 24 hours. For this achievement the surrounding atmosphere should be maintained at a temperature of 22°C to 25°C during summer and 17°C to 20°C during winter and humidity between 40 to 60 percent.
The amount of heat required for personal comfort in a room or office depends upon the following factors:
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1. The temperature of the outside air.
2. Area of window
3. Material of which walls, floors and ceiling are composed.
4. Weather the building is to be heated continuously or intermittently.
Parts of Air Conditioner:
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The various parts of a room air conditioner are:
1. Compressor unit
2. Condenser
3. Receiver
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4. Evaporator
5. Capillary tube
6. Impeller fan
7. Centrifugal fan
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8. Partition
9. Air filter
Working of Air Conditioner:
In the case of a window type air-conditioner, the evaporator faces towards the inside of the room whereas the condenser faces towards the outside of the room as shown in Fig. 6.10.
The centrifugal fan sucks air from the room and passes it over the evaporator coils. As the room air passes over the evaporator coils (the surface temperature of the coils is very low) it is cooled and this cooled air is supplied to the room. An impeller fan sucks outside air through the sides and throws it over condenser and cools down the refrigerant passing through the condenser tubes.
The evaporator side and the condenser side are completely separated from each other by means of a partition.
Electrical Circuit of Air Conditioner:
The following electrical components are fitted with the air conditioner:
1. Motor compressor with overload protection.
2. Starting Relay
3. Starting and running capacitor
4. Fan motor with capacitor
5. Thermostat
6. On/Off switch with speed control
Fig. 6.11. shows the electrical circuit of the air conditioner. Starting relay is connected in series with the running winding of motor.
Working:
When the supply is ‘ON’, the high current flows in the motor starting winding, it starts and also the relay contacts close and connect the starting capacitor to the starting winding. As the motor gradually reaches the normal speed, the current in the running winding decreases, making the relay open, thus disconnecting the supply to the starting winding of the motors.
The overload protector protects the motor against excessive overload. This protection is provided inside the compressor and its function is to open the compressor motor circuit. Basically it is a bimetallic disc with contacts. When excessive current flows in the motor, the temperature increases, thus opening the circuit automatically to stop the motor.
The electrical circuit comprises the following components:
1. Fan Motor:
1 – ϕ split phase motor is used for fan motor. The fan motor is provided with an overload protection placed in winding so that in the event of overheating it is protected.
2. Starting Capacitor:
The starting capacitor (CS) is of large capacity. The rating of any capacitor is given in terms of voltage and KVAR, whereas its capacitance is in microfarad. It remains in the circuit for a short time, till the motor starts.
3. Running Capacitor:
The running capacitor (CR) is of smaller capacitance but heavy duty and are oil filled. It remains in the circuit continuously and improves the starting torque and power factor.
4. Thermostat:
The function of thermostat is to monitor the room temperature and start or stop the motor. When the room temperature increases, the contacts of thermostat close and start the compressor and when the temperature decreases the contacts open up and the compressor of the air conditioner stops.
Advantages of Room Air Conditioners:
1. Saving in installation.
2. Only those rooms which need cooling will have their units running.
3. Low initial cost.
4. Flexibility of operation.
5. Duct work is eliminated.