UNIT 13
AIR CONDITIONING
(PART II)
OBJECTIVES
GENERAL OBJECTIVE
To know the concept of air conditioning
SPECIFIC OBJECTIVES
At the end of this unit, you would be able to:
- label the final circuit for air conditioning unit
- state the protection rate for air conditioning unit
- state the wiring cables size for air conditioning unit
INPUT
- FINAL CIRCUIT FOR AIR CONDITIONING UNIT
Figure 13.1: Window air conditioner
Circuits for air conditioning units vary slightly between the manufacturers. The best source for schematics of the electrical system is the manufacturer’s services manual and bulletins. In this unit we will be concerned primarily with the circuits of domestic air conditioning equipment.
The basic or simple air conditioning unit consists of a
plug, a thermostat, overload protector, compressor,
condenser, evaporator, capacitors for the motors, and
some kind of switching for control of the fan. The shaft
of the fan motor usually extends from both ends of the
motor. A fan blade is attached to one end to cool the
Figure 13.2 : Final circuit for a two speed, push button controlled window unit
(Source: Refrigeration & Conditioning Technology; William C. Whitman & William M. Johnson)
condenser, and another fan blade is attached to the other end of the motor to cause air to flow over the evaporator and cool the room. This way only one motor is used. This is the type of arrangement most often encountered in the window air conditioner.
The air conditioning unit that fits into the window (see Figure 13.1), usually has at least two speeds. The fan is used in some cases without the compressor running. Thus,
there are three modes of cooling; (i) fan only, (ii) fan at high speed and cooling furnished by the compressor, and (iii) fan at low speed and cooling furnished by the compressor. This basics window unit consists of the compressor, the fan motor, the thermostat, and push buttons for the selection of the type of cooling desired (see Figure 13.2).
The figure below show us the line cords and plugs for various voltages used on air conditioner units.
(Source: Refrigeration & Conditioning Technology; William C. Whitman & William M. Johnson)
- The Main Part of Window Unit
MAIN PART | FIGURE |
1. Push button switches
| Figure 13.3: Push button switches used in a window unit for fan and compressor control |
2. Thermostat - is variable by twisting a knob. - this moves the bimetallic strips closer together to provide the proper operation of the thermostat in relation to the room temperature. - have a number of design configurations, depending on the manufacturer. - the temperature sensor located on the inlet side of the evaporator senses the air returned to the air conditioner from the room being conditioned. | Figure 13.4: Bimetallic strips used in thermostat
|
3. Fan - the fan is two speed. It has an auxiliary winding with a capacitor in series with it. - the run windings are arranged so that when one of them is in the circuit it runs at high speed. - when the two run windings are placed in series, it slows down and the fan speed is LO. This permanent split-capacitor motor is commonly used in two or three speed configurations for fans. | Figure 13.5: Circuit for fan |
Test your UNDERSTANDING before you continue to the next input
ACTIVITY 13 A
- What is meant by modes of cooling?
- Where is the location of the temperature sensor located in an air conditioner?
- How do you make a high speed fan run slower?
FEEDBACK TO ACTIVITY 13 A
- There are three modes of cooling ; (1) fan only, (2) fan at high speed and cooling furnished by the compressor and (3) fan at low speed and cooling furnished by the compressor.
- The temperature sensor located on the inlet side of the evaporator senses the air returned to the air conditioner from the room being conditioned.
13.3 The fan is two speeds. It has an auxiliary winding with a capacitor in series with it. the run windings are arranged so that when one of them is in the circuit it runs at high speed. When the two run windings are placed in series, it slows down and the fan speed is LOW.
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ELECTRICAL MACHINERY & CONTROL
- PROTECTION RATE FOR AIR CONDITIONING UNIT
YOU can work with air conditioning equipment safely if a few common sense rules are followed
From time to time, air conditioning units encounter problems with the electrical and the mechanical aspects of their operation. There are cases when they are moved and damaged and in other cases they are repaired with incorrect components or wired into the incorrect circuits.
Safety first has its direct and implied meaning. The main rule for electrical safety is to see to it that the main circuit breaker is in the off position and locked before starting to remove or check air conditioning. The electric installation will require the installation of the compressor motor pump and fan motors together with automatic temperature and humidity controls which must be located in selected position in the building.
Air conditioning equipment will be furnished and installed by heating contractor in four of the rental areas indicated as follows:
Table 13.1: Electrical requirements for air conditioning
Places Rating | Drugstore | Beauty Salon | Doctor’s Office |
Voltage | 208V,three-phase, 3 wire,60Hz | 208V,three-phase, 3 wire, 60Hz | 208V,three-phase,2 wire, 60Hz |
Hermetic refrigerant compressor-motor | Rated load current 20.2 A,208V three-phase | Rated load amperes 14.1A, 208V three-phase | Rated load amperes 16.8 at 208V single-phase |
Evaporator motor | Full load current 3.2A, 208V single-phase | Full load amperes 3.3 at 208V single-phase | Full load amperes 3.7 at 208V single-phase |
Condensor motor | Full load current 3.2A, 208V single- phase | Full load amperes 3.3 at 208V single-phase | Full load amperes 3.7 at 208V single-phase |
Minimum circuit ampacity | 31.65 A | 20.92 A | 24.7 A |
Overcurrent protection | 50A, time-delay fuse | 35A, time-delay fuse | 40A, time-delay fuse |
Test your UNDERSTANDING before you continue to the next input
ACTIVITY 13 B
13.4 State the differences of voltage, eveporator motor and condensor motor between doctor’s office and beauty salon.
13.5 A single package unit will be installed on the roof and will have the following electrical characteristics :- It has 208V, three-phase, 3 wire 60Hz, condensor-evaporator motor have full load amperes 14.1,208V single-phase and minimum circuit ampacity 20.92 amperes. Name this single package unit.
FEEDBACK TO ACTIVITY 13 B
13.4
Beauty Salon | Doctor’s Office |
- Voltage 208V,three-phase,2 wire, 60Hz. - Evaporator motor has full load amperes 3.3 at 208V single-phase - Condensor motor has full load amperes 3.3 at 208V single-phase | - Voltage 208V,single-phase,2 wire 60Hz - Evaporator motor has full load amperes 3.7 at 208V single-phase - Condensor motor has full load amperes 3.7 at 208V single-phase. |
13.5 Beauty Salon
- WIRING CABLE SIZE FOR AIR CONDITIONING UNIT
The choice of wiring system is affected by many factors such as the type of building, temperature, safety, cost and etc. The electrician needs to be able to decide upon the most suitable type of cable or wiring for a given situation.
A cable is a length of single conductor having one or several wires stranded together, or two or more such as conductors, each provided with its own insulation and laid up together. These insulated conductors may or may not be further covered with an overall sheath to prevent mechanical damage. The insulated conductors are referred to as the cores of the table.
For a one horse power (hp) to 2.5 horse power (hp) conditioning cable size 2.5mm is used. For conditioning unit with 2.5hp and above cable size 4mm is used. The selection for cable depends on the conditions of the place. For surface wiring the cables that we need is double PVC. For the best result in chosen the cable size is to calculate the rated. The unit for cable size is mV/A/m. We will use Table 13.2 and Table 13.3 to define the size and type of the cable. Example 13.1 will explain on how to choose the size and type of cable.
Example 13.1
One unit of air conditioning rated 240V/3hp/0.85 pf is installed from source terminal to the location at 100m. Define the size and type of cable.
Solution
Step 1: Find the current
1 horse power = 746Watt
#
Step 2: Find voltage drop
Based on the TNB/Suruhanjaya Tenaga law, voltage drop at customer load from the
source is more than 4% from the voltage source.
Step 3: Find size cable
Size cable = #
Refer to Table 13.2 to find the surface of cable.
Make sure the value must not more than 8.72mV/A/m.
From the Table 13.2, 7.3mV/A/m is aquarate to 8.72mV/A/m. Size for the surface
cable is 6mm2. BS 6004 is a type for a cable that can used installation air
conditioning.
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ELECTRICAL MACHINERY & CONTROL
Table 13.2: Voltage drop for specific cable
(Source: Peraturan bagi pemasangan elektrik)
(Refer to Appendix A)
Table 13.3: Kabel-kabel berteraskan tunggal yang bertebatkan PVC, tidak berperisai, bersalut atau tidak bersalut.
(Source: Peraturan bagi pemasangan elektrik)
(Refer to Appendix B)
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ELECTRICAL MACHINERY & CONTROL
SELF-ASSESMENT
If you face any problem, discuss it with your lecturer
You are approaching success. TRY all the questions in this self-assessment section and check your answers with those given in the feedback on Self-Assessment given on the next page.
Question 13-1
A. Match the statement below
The unit has a two speed fan and a compressor
that operates in conjunction with the high and Thermostat
low speed fan positions.
It is variable by twisting a knob.
this moves the bimetallic strips closer together Push button
to provide the proper operation of the thermostat
in relation to the room temperature.
It has an auxiliary winding with a capacitor in Fan
series with it.
Question 13-2
A. With the guidance from your lecturer :
i) Identify the protection rate for the air conditioning unit at your polytechnic
FEEDBACK TO SELF-ASSESMENT
Question 13-1
A.
The unit has a two speed fan and a compressor
that operates in conjunction with the high and Thermostat
low speed fan positions.
It is variable by twisting a knob.
this moves the bimetallic strips closer together Push button
to provide the proper operation of the thermostat
in relation to the room temperature.
It has an auxiliary winding with a capacitor in Fan
Question 13-2
A. Refer to your lecturer
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