How Do I Choose an Air-conditioner?

Ever wonder who invented the first modern air-conditioner? Well here is the answer. In 1902 a young electrical engineer named Willis Haviland Carrier designed the air-conditioner to solve a humidity problem at the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, N.Y. The paper stock at the plant would sometimes absorb moisture from the warm summer air, making it difficult to apply the layered inking techniques of the time. Carrier treated the air inside the building by blowing it across chilled pipes. The air cooled as it passed across the cold pipes, and since cool air can't carry as much moisture as warm air, the process reduced the humidity in the plant and stabilised the moisture content of the paper. Reducing the humidity also had the side benefit of lowering the air temperature and a new technology was born. 
Air-conditioning Basics
Contrary to popular belief, air-conditioning is not about adding cool air to the room, but more about drawing heat away from it. The end result is a space with significantly less heat, which makes it feel cooler to occupants. Air conditioning takes advantage of the effects of evaporation. For example, a swab of alcohol makes a person's skin feel cooler as the liquid evaporates. The alcohol doesn't lower the person's skin temperature, but rather draws away heat from the air as it turns to a gas. Air-conditioning contain a chemical called refrigerant (freon), which has the unique ability to change from a gas to a liquid in a short amount of time. The refrigerant is pumped into the unit at the factory, along with a small amount of lubricating oil for the compressor. Typical air-conditioners units consisting of a compressor, a condenser, an expansion valve and a thermostat. Motorised fans help to circulate the conditioned air, while thin metal fins allow heat to dissipate quickly. 
Types of Air-conditioners 
There are 4 types of air cooling system available in Singapore.
  1. Non-inverter: This unit only has a single speed compressor motor that is either on or off. It works similar to a fan heater that switches off when the desired temperature is reached and on again when the temperature drops to a set level.
  2. Inverter: This unit uses a variable speed compressor motor similar to a car. It simply slows down and speeds up as needed to hold a selected comfort setting. Inverter technology provides a more precise room temperature without the temperature fluctuations of fixed speed systems.
  3. Portable: This unit is a self-contained portable appliance that cools the air in a single room or moderately sized space. Unlike traditional window ACs, portable air-conditioners do not sit in the window. They typically sit on the floor within the space you are trying to cool. All portable ACs exhaust hot air as part of the cooling process. This hot air is usually directed out of the cooled space using a hot air discharge hose, also known as an exhaust hose. This air hose is often vented out of a window, into a drop ceiling, or through a wall to an adjacent space.
  4. Window: This system is technically called a "unitary" air-conditioning system and consists of a self contained air-conditioning unit that is placed in a window. The unitary system has all the refrigeration components in one compact box. It ejects heat out one end and blows cooled air out the other end.
The first question you need to ask yourself is whether you want a window AC or a split model. Window units are cheaper and easier to install. Split ACs are quieter, more aesthetically pleasing and have better air distribution. The  split unit consists of two systems, a compressor unit which is outside the house and one to four units inside. This means that installing them may require renovation work, which can be expensive. Usually, single split inverter unit will cost about $3000 and a system 4 inverter $5200. The non-inverter single split unit  will cost around $1000 and a system 3 non-inverter $3000. 
There are a few thing you need to check, the first been the star rating. Air-conditioners are awarded a one to five stars rating, with one being the least efficient. A unit with a higher star rating is more expensive than the one with fewer stars. Most air-conditioning units also have a dehumidifier, which reduces humidity in the air, making it cooler and more comfortable. Also remember to check the noise level of the model, which usually ranges from 30-60 decibel. The next thing to do is to measure the room in which you want to install an air-conditioner. A thumb rule used internationally is that for every square foot, you need 20 Btu/hr (British Thermal Units per hour). 
For more information on how to properly size a room 
Keep in mind that there are other factors can also affect the size of AC you need for a particular space:
  • For a heavily shaded room, reduce the BTU capacity by 10%; if it is sunny, increase it by 10%
  • If more than two people occupy the room regularly, add an additional 600 BTU per each extra person
  • Kitchens produce a lot of heat, so add 4,000 BTU to your total
Finally you will most likely consult an HVAC contractor that handles installations. Professionals typically use the scientifically accurate "Manual J" method to determine the right size but it is still a good idea to be familiar with the factors involved. In this way you will be able to have control over the decisions been made.


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