Friday, April 11, 2008

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


Anonymous said... Reply To This Comment

Thanks for info sharing. But do you have any idea on the HOME SECURITY SYSTEM. Reason wise is burglar broken into my cousin in USJ yesterday.

Voyager8 said... Reply To This Comment

Yes. Home security should be a SYSTEM. Wikipedia's definition for "system" is a set of interacting or interdependent entities, real or abstract, forming an integrated whole.

Here are a few things to safeguard home security:
1. Live within a gated and guarded community. Even if the housing area was originally not designed to be G&G by developer, the residents community can act together to implement one for themselves. I have seen this kind of residents initiative in some housing areas in Puchong, including Taman Wawasan, Puchong Jaya, etc.

2. Install alarm system.

3. Install roof security mechanism.

4. Install reflective film onto glass windows so that you can see clearly from inside, but outside can hardly see into your house.

5. Maintain good relationship with neighbours to look after each other.

6. Buy comprehensive home insurance that covers lost from natural disasters, thefs and burglars.

I shall cover the above in more detail in the upcoming articles in the near future.

Unknown said... Reply To This Comment

A good air conditioning specialist will stand by its work by offering a free labor guarantee of at least two years. You should feel completely confident knowing that if someone was not done correctly, it will be repaired quickly and at no extra cost.

NY Ac duct cleaning

Hazree said... Reply To This Comment

in your post, window seems to general. kindly specify the window size for the said calculation.
thanks in advance.

Voyager8 said... Reply To This Comment

Hi Hazree,

It is assumed that you keep all the windows and doors closed most of the time when you use the air-cond.

You might need a higher HP air-cond if you have really big glass window facing West, shines by direct sunlight, and don't have any blinds/curtains. This kind of situation is common for shoplots with large display windows.

Aircondirect said... Reply To This Comment

Thanks for the tips on how to select a air conditioner units.

chong said... Reply To This Comment


how about those regualr aircond and those with inverter technology?


Voyager8 said... Reply To This Comment

Hi chong,

Those with inverter technology should be more cost effective.

I wrote about it before:

Hazree said... Reply To This Comment

Dear Voyager,
thanks for the reply. for the said calculation, what is the standard window sizing?

2' x 2'? if bigger than the standard size, surely needs bigger air cond maaa....

dream mummy said... Reply To This Comment

Thank you for sharing,
My question: does ceiling height matters? My house has ceiling high enough to add another floor to the house.

Voyager8 said... Reply To This Comment

@dream mummy

Height shouldn't have major impact, because cool air flows down and hot air flows up.

Kate Dunkin said... Reply To This Comment

You have been a great help for me, I have been online all morning looking at new air conditioner units because mine has broken down and is beyond repair. I just want to make sure I don't get ripped off though in the process or end up with the same problem I am in now in a couple of months. You have definitely educated me, thank you for sharing!

Unknown said... Reply To This Comment

thanks for the beautiful information

Unknown said... Reply To This Comment

I don't have a window but a former two-door space equivalent to 10 windows. It is open all the time and adjoins another room. It is actually a second aircon that I need. The formula is quite helpful, I can already decide how much HP I need. Thanks a lot.

Unknown said... Reply To This Comment
This comment has been removed by the author.
' n i C k ' said... Reply To This Comment

Thanks for ur helpful info.

What if u have half wall partitions (top to down) between kitchen and living rooms which have another partition again before u reach the main door, will the air flow be fast enough to flow to another area ?

Voyager8 said... Reply To This Comment

@' n i C k '

You can make use of ceiling fan to tremendously increase the airflow.

Unknown said... Reply To This Comment

its working..thank you so much..follow exactly as per your guide..

Unknown said... Reply To This Comment

What horse power 5000

Post a Comment

Hint: Click on the "Older Posts" link to continue reading, or click here for a listing of all my past 3 months articles.