Air Conditioner Efficiency

The wet season is ending and the weather is starting to warm up, now is a good time to think about your air conditioning. Are your air conditioners working well enough? Let us look at common problems with selecting and maintaining air conditioners.


How big an air conditioner do you need?

It is important to select the correct size of air conditioner for a room. Too small and the air conditioner will be working too hard, the room will not be cool enough and you may get condensation problems. Too large and your air conditioner may be constantly switching on and off.

You can find a simple calculator to help you decide what size of air conditioner you will need on our website at

This is based on the most commonly used air conditioners these days which are split units with a CoP of 4. CoP stands for Coefficient of Performance – how efficient the air conditioner is. Modern air conditioners can move 4 kilowatts of heat by using only 1 kilowatt of electricity.


Standard air conditioner sizes available for domestic use:

The range of sizes varies between companies. Having said that they do tend to fall into specific preferred sizes. Generally speaking standard air conditioner sizes available for domestic use are:


½ PK ¾ PK 1 PK 1.5 PK 2 PK 2.5 PK
4,800 BTU 7,200 BTU 9,600 BTU 14,400 BTU 19,200 BTU 24,000 BTU
373 watts 560 watts 746 watts 1,120 watts 1,492 watts 1,865 watts


Sizes measurement watts, BTUs horsepower and PK:

Different brands of air conditioners use different ways of indicating their size, for this reason 3 different size equivalents are given above:

  1. PK (pronounced peka is Dutch for Horse Power or HP) which is the common sizing of air conditioners in Indonesia.
  2. BTUs (British Thermal Units) the common sizing used in America.
  3. The electrical power rating in watts (this is watts of input power not output watts).


Input power versus output power

It is important to note that the PK, HP and watts figures indicate the amount of power input, the BTU figures indicate the amount of cooling output achieved. The actual cooling achieved in BTUs depends on the efficiency of the air conditioner. The above figures are given as an approximate guide of what you might expect with normal modern air conditioners.


How insulated is your room? It makes a difference

Insulation makes a huge difference. The better a room is insulated the less air conditioning you will need. As a rough guide:

1.     A well insulated room might have thick solid walls, an insulated ceiling, close fitting doors and few or double glazed windows and not many people in it.

2.     A medium insulated room might have solid concrete walls, close fitting doors, an insulated roof and few standard windows.

3.     A poorly insulated room might have large window area, poorly fitting doors, a roof or walls that give off heat internally or a lot of people in it.


It is very important to clean air conditioners regularly

Air conditioners make our lives comfortable especially in the tropical climates. Air conditioners are often required to work very hard running for many hours each day particularly in working environments.

The indoor ‘evaporator’ unit draws in large volumes of air from the room and blows it over the cooling fins of the air conditioner’s cooling coil to remove heat before returning it to the room.

Similarly the outdoor compressor unit draws in outside air and blows it over the heat dissipation fins of the compressor coil to carry away heat to the atmosphere.

An enormous volume of air passes through an air conditioner over a period of weeks and much of this air is laden with dust from internal rooms and from the outside atmosphere (particularly if there is a busy traffic area close by).

The dust gets lodged on the heat transfer surfaces and builds up over time acting as insulation on the fins of the coils and greatly reducing the air conditioner’s ability to transfer heat, as a result the air conditioner has to work for longer periods to remove the same amount of heat and of course it uses more power.


How often should you clean your air conditioners?

In most situations it is advisable to clean your air conditioner (both the indoor and outdoor units) every 3 months. If you are in a very dusty environment (schools are notorious for being dusty with regular traffic of many people) it is wise to clean them more often than this. Conversely if the air conditioner is not used very often then obviously you do not need to clean them as frequently.

Cleaning your air conditioners regularly keeps them running efficiently and saves you money. It is important that air conditioners are cleaned correctly using equipment designed for the job.

Also note that some air conditioner cleaners only clean the internal unit, it is important that the external unit also gets cleaned.


Air conditioner installation

Correct installation of an air conditioner is important to make sure that it is electrically safe, that the flow of air is good and that it is positioned correctly in the space it is to cool. Particular care needs to be taken too when working out where the pipes and particularly the water drain from the indoor unit will go.


Air conditioner servicing

There are a number of aspects of an air conditioner that may require servicing:

  1. Leakage of refrigerant which will result in the air conditioner not blowing cold air.
  2. A blocked drain which will result in water dripping from the indoor unit.
  3. Failure of the compressor which may be caused by electrical supply problems.
  4. A burnt out circuit board in the AC controller unit usually caused by problems with the electrical supply.
  5. Air conditioner not cold enough due to an excessive build up of dirt on the heat transfer fins.

Air conditioners are usually very reliable machines. Obviously they vary from one manufacturer to another and there are certain brands we prefer to install for our clients because we feel they are better value for money and also because the extensive experience of our tradesmen tells us which are most reliable.


Previous “Fixed Abode” articles can be found subject indexed on our website at Opinions expressed are those of Phil Wilson. He can be contacted through the website or the office on 0361 288 789 or 08123 847 852.


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