All about Air Conditioning

OK, maybe not ALL about it since I’m only talking about the cooling part. In this post, I’m just going to talk about how to choose an air-conditioner and how to maximize its usage while minimizing energy consumption.

There are a few things that affect how cold aircon feel so take note of these points when buying your next air-con.

1. Blower speed – The higher the better to circulate the air & draw out the heat & humidity. Setting your blower speed to AUTO is the best. When you first switch on the aircon, the blower will be high but as the temperature approach the set temperature, the blower will slow down. If you use a fan to circulate the air, it’ll work even better! But after the walls & furniture cool down, the fan should be switched off because fan/blower noise is irritating & distracting especially when watching a movie.

* Remember, the aircon will cool the walls/floor/ceiling first due to larger surface area.

2. Temperature (inside the room, outside the compressor) – Inside the room, depends on what you’re cooling. If you always have party with many people + you have a big amplifier, set lower (see heat capacity). The thermostat will try to increase cooling power (for inverter) and turn the blower on ‘high’ longer. I set mine to 27’C when watching a movie on my home theatre & it’s cool enough if the blower is directed at the sofa.

Outside the compressor, if the weather is really hot, the compressor need to turn on the fan higher to exchange heat more efficiently and this increases power consumption. My compressor is facing the evening sun so I got 2 compressors that can handle 100% of the BTU load.

3. Humidity – this is the reason we feel stuffy, high humidity reduces our skin ability to cool down from evaporation and makes our lungs work harder to extract oxygen from the air. A good aircon can extract an insane amount of water from the air. My aircon can probably fill a bucket in an hour.

4. Direction of flow – self-explanatory. Want to feel COLD NOW? Stand in front of the aircon blower. Ladies should stand aside to avoid the cold air and dry skin.

5. Blower heat capacity (also compressor wattage for multi-split) – calculate the amount of heat (in BTU) that you expect the blower to extract. This depends on room volume. Budget in extra 10% in Singapore for hi-res HDB/Condo, or 20% if there’re many windows. Budget in 30% if you always have parties. People generate a huge amount of heat.

For compressor, it depends on how many blowers you have. With 3 blowers or more, always go for inverter. I used to have a non-invertor System3 for my old 3-room HDB, it seriously uses tons of energy but it was cheap. Now I have 1 System3 + 1 System2 to cool 5 rooms. Both are invertor systems and even though my room size has doubled, my current air-con actually uses LESS power on average! Based on this calculation, I should breakeven in 5 years.

Correct calculation of heat capacity will ensure you feel cool & save power since the compressor don’t have to struggle to exchange heat. For compressor, ensure you have at least 80% of the wattage required for extracting the Total BTU the blowers can sustain. This is because for invertor system, most of the time, it wouldn’t be operating at max capacity (if you do your math right).

For non-invertor multi-split, when any blower is on & temperature is above thermostat setting, the compressor is also ON FULL. On a hot day, the compressor is always on, maxing out on exchanging heat even though my 1 blower isn’t able to extract that much BTU. So to save some energy, buy up to 80%. Your room wouldn’t cool as fast when ALL blowers are on but it wouldn’t cost so much money to operate.

6. Room size/shape – depending on room size & shape, placement of the blower should be as near to where the people will be as possible. If you have odd shape room like an L-shape or has different segments, consider a blower in each segment. My living room is conjoin to my dining room so I have a 12000BTU blower for the living room & a 9000BTU for the dining room.

To calculate your BTU budget, use this calculator.

7. Room insulation & how many windows – make sure your doors have as little gap as possible to reduce air movement. Large windows are nice but also allow more sun in and trap the IR inside the room. If you don’t have IR film on your windows, increase your BTU budget, especially if you have evening sun. Curtains & blinds will help by reflecting some of the IR back outside the house and create an air buffer.

8. Coolant & Drainage piping – This is usually neglected but making sure the refrigerant flows smoothly to/from the compressor to the blowers without leaking and without choking at the bends is very important.

Just as important is making sure the drainage pipes for the water extracted from the air is piped out without leaking & causing a mess especially if everything is buried in walls & ceilings.

Make sure you have a reputable contractor to install these pipes! Some brands insist on using their contractor, like Fujitsu Singapore. Go for it! Make sure your interior designer or renovation contractor can work well with the aircon contractor. This will ensure a good installation, an efficient aircon & no trouble in the future.

I hope this has helped you in choosing the correct aircon. If you have any comments or suggestions on what to add in this article, please comment below.


7 thoughts on “All about Air Conditioning

  1. Hello from Paris France
    Thank you for your blog. I wonder if you can help me in an emergency situation.
    Paris is being hit by 40 centigrade heatwave with ozone alerts for people like mYelford fighting long cancer. These temperatures are bizarre and happened once 22 years ago.
    I have explored air purifiers first and discovered very high prices that were not for the latest USA technology. Your idea of converting an air conditionerous filter sounds right. I just need to pick the right machine quickly.
    I am not sure I follow all the technical requirements.
    We have aurconditioners that say they are reversible which seems to mean that an air heater van be used to heat a room in the winter while using he function differently for cold. I am more interested in breathing cleaned cool not COLD air this season between two small linked rooms with the tube sealed to a window. The total size of the space is 30 square meters. Ceilings are high 5 metres, I think.
    Could you please reduce the techs to a commercial version that i could look for immediately on line. Protecting against ozone is more important that COLD whichthyosis could be dangerous for me.
    Thank you.


    1. Hi Rachel, sorry for the late reply. I not sure what you were asking until now. Many modern air conditioners have both cooling AND heating functions. Just go to your local air-con dealers to get indoor units that uses outdoor compressor.


    1. Having the door open/close regularly and having full-height window definitely affects your AC’s cooling power. Be sure to increase the BTU budget especially if your windows is facing the east/west direction. If you’re talking about the outdoor compressor unit, it shouldn’t affect too much as these are built to work in the elements.


  2. Air conditioning unit is an indoor cooling and dehumidification unit which was designed specifically to provide thermal comfort. Now-a-days these units come with additional features like disinfection, heating and cooling of the air.

    The working of this unit is basically similar to a refrigerator. In simple terms the unit just takes the heat from the indoor room resulting in drop of the indoor temperature making you feel comfortable. The unit contains a special chemical called the refrigerant which has a unique property. This chemical can change from gas to liquid within a short amount of time


  3. Hey, I’m a HVAC technician and I noticed that you link to a BTU calculator on X page, I have made a similar calculator based on more standardized and up to date calculations, meaning it’s essentially more accurate.

    Would you consider trying it out and possibly adding it as a reference? Here it is:

    I can also share the post to my following – via newsletter and Facebook, perhaps we can even collaborate in some other way, I often do guest posts and would love to work with you!

    Thanks in advance,

    Dave Miller


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