How to select air-conditioner wisely

It is obvious that the world's temperature has been rising over the years, and nowadays most family has installed air-cond in their house. I learnt about the following when I planned for the air-conds in my house before I moved in.

Disregard the brand and additional features, when selecting an air-cond which main function is to cool down the room, there are 3 major ratings to look for, beside the Horse Power (HP).


BTU/hour - measurement on cooling capacity:

This is the actual cooling capacity unit of the air-cond and must match with the room size to be cooled. The room won’t cool efficiently and cost effectively if the BTU/hr rating is too low or too high for the size of the room.

BTU/hr is proportional to the Horse Power of the air-cond, but there is no fixed conversion formula between them, and varies from different models and brands of air-cond. Among air-conds with the same HP capacity, the higher the BTU/hr the better.

In general:

• 1 HP air-cond has BTU capacity ranging between 9000-10,000.
• 1.5 HP air-cond has BTU capacity ranging between 11,000-13,000.
• 2 HP air-cond has BTU capacity ranging between 15,000-25,000.
• 2.5 HP air-cond has BTU capacity above 20,000.

An effective rule of thumb to determine the BTU capacity required to cool a room effectively is to multiply the square feet of the room by 25; add 1,000 for every window and 400 for each occupant in the room. If the window is facing west directly shined by the sunlight, add 10% to the calculated result for cooling during daytime.

For example, if your bedroom is 12' x 12' with 2 windows, 2 people will be sleeping there at night, the suitable BTU capacity for the air-cond in the bedroom will be:

(12x12) x 25 + 2 x 1000 + 2 x 400 = 3600 + 2000 + 800 = 6400

Therefore, a 1 HP air-cond should be enough for this bedroom.


EER - measurement on efficiency in electricity consumption:

The Energy Efficiency Ratio (EER) is calculated by dividing the BTU capacity by the number of watts. The higher the EER number the more efficient the air-cond unit should be. The EER rating generally ranges from 8-11.5, and should not be lower than 5.


Airflow - measurement on cooling speed:

The cooling speed of air-cond is determined by the ability of airflow travelling in cubic feet per minute (CFM). In normal words, CFM is the volume of air moved by the air-cond blower per minute.

For 1 HP air-conds, airflow generally varies between 210CFM-300CFM. Higher airflow provides faster cooling as well as better air circulation.


Related article: Increasing the efficiency of your air-cond