Selecting right capacity AC

“What capacity AC shall I use for my room?” is a common question from the interested buyers. The required capacity of AC will depend on the amount of heat to be removed from the room. More the heat coming into the room, higher is the capacity of AC required to cool the room. The heat load varies depending on

• Location (city): A 150 sq.ft room in coastal cities like Chennai, Mumbai and Kolkota will need lesser cooling capacity AC than at cities like Hyderabad, Nagpur, New Delhi etc.
• Solar radiation heat through exposed roof, glass windows etc.
• The temperature we want to maintain in the room, during peak summer (24°C + 1°C is recommended)
• The no. of people, no. of lightings, electrical gadgets (computers etc.) in the room
• Orientation of building (one generally may not have much of a choice here, unless he/she is building their house)

The salesmen at the showrooms have been equipped with a ‘Heat Load Calculation template’ by the AC manufacturers to suitably guide the customers. Over a period of time, from the experience of repeatedly doing these calculations, some thumb-rules also have emerged like 1TR (3.5KW) capacity AC can handle approximately 100 – 150 sq.ft room etc.  

If the AC is optimally chosen, without over-sizing, it will help consumers in spending less on the initial purchase price and also the running cost and maintenance charges for the 8 – 10 years of the life of AC. Some useful tips are furnished below, to help the consumers to reduce the capacity of AC required:

Minimise solar radiation heat into the room

• If the roof is exposed to direct sun rays, insulate the roof with minimum 2” underdeck thermocole insulation. This is a ‘must do’ and a good investment to reduce the running cost.
• If any windows are exposed to direct sun rays, use a drape or venetian blind to keep away the radiation heat from entering the room.

Do not specify lower room temperature

Air conditioning is not chilling! The AC is supposed to provide comfort room conditions like temperature (24°C + 1°C), relative humidity (<65%RH), clean filtered air, free of dust (done by the air filter in the AC) and air movement in the room.

If you specify lower room temperature, say 20°C in summer, the salesman can still satisfy you by offering a next higher capacity AC! But your initial investment, running cost expenses month-after-month and annual maintenance contract amount will increase!

Partition / isolate the AC room

The room fitted with AC should be fully covered on all sides, with a firmly closing type door. If you are air conditioning your living room, which is open to the kitchen on one side, then you need to provide a partition