To know what tonnage of AC to buy, one needs to do a heat load calculation of the room to be air conditioned. Very often, a thumb of rule of 100 sq ft = 1.0 ton is applied to calculate the room AC tonnage. However, this method may not be accurate.

The size of the windows, location of the walls (west or east facing), floor, number of people expected to occupy the room, other gadgets in the room and lighting, amongst others, all play a role in calculating the right tonnage for the room. It is recommended to request for a technician to visit the room and allow him to do a heat load calculation. For a quick calculation, please visit the tonnage calculator section in the Blue Star site.
The right AC tonnage is a critical step since buying an undersized air conditioner may provide inadequate cooling with perhaps the compressor never cutting off, and buying an oversized one may result in high power bills.

One should note the star labelling on the AC. The star rating varies from 1 Star to 5 Star. More the stars, the more energy efficient the AC, and better will be the corresponding savings.

The star rating is defined by the Bureau of Energy Efficiency guidelines and air conditioners of all brands are tested and certified by a third party agency for the star-rating.

High energy efficiency design involves increased components in the heat exchange area due to which the input costs increase. Hence, a higher star AC such as a 5 Star AC costs more than a 2 Star one.

To take an informed choice related to energy and monetary benefits in an AC, one needs to calculate the energy and corresponding monetary savings.Payback period in years = Incremental higher price/energy saving in a year over a lower star AC.

Buying a 5 Star AC is a good decision in the long term especially given the fact that consumers nowadays use their air conditioners for much longer periods and the power tariff is likely to increase over the years.

Window and standard split air conditioners have a compressor that runs at a fixed speed. The compressor is therefore either on or off depending on the set temperature.

The Inverter AC thinks and adjusts according to your needs. Its compressor has variable speed and changes its frequency according to the ambient load. As the frequency changes, the speed of the compressor also changes. This eliminates any temperature fluctuations and helps maintain a comfortable temperature. For example, a 1.5 ton Inverter AC can decrease its capacity to 1 ton or increase its capacity to 1.75 tons, as per the requirement. As there is no cut in and cut off, the Inverter AC saves up to 30% more power.

One should look out for various types of filters available in an AC, such as a bio filter and a catechin filter which trap dust particles, mites as well as eliminate bacteria and viruses. Thus the air inhaled is pure and healthy.

Most air conditioning units also have a dehumidifier, which reduces humidity in the air, making it cooler and more comfortable. Also one should check the noise level of the model, which usually ranges from 30-60 decibel.

The sleep mode of an AC is an intelligent feature as it automatically adjusts the temperature during the night so that it’s comfortable throughout. An auto restart facility to help restore the original setting after a power break.

Having a timer in the AC enables the users to turn it on or off on schedule.
A feature called ‘i-feel’ helps maintain the set temperature around the person rather than the air conditioner. A sensor in the remote signals the thermostat in the unit which adjusts the cooling accordingly making it more comfortable.

While perfumes do create a good atmosphere, they should be used cautiously as some people can be allergic to them.

The best way to keep the foul smell out is to open windows and use fans to bring in a lot of fresh air before the AC is started. Keeping the AC room clean is also equally important.

The Window AC should be installed at a height of 5 feet behind the user. The air draft from the air conditioner should not hit the user directly.

A normal Window AC or Split AC will throw air upto 15 feet. However, special split units are available to throw air upto 30 feet.

Window ACs and Split ACs of lower tonnage work on single phase. However, it is better to have a 3-phase supply, and distribute the other loads like geysers, washing machines, pumps and lights in the other 2 phases.

The compressor which is the most critical component in the AC works between 190- 240V. With voltages in most parts of India going well below 190V, a voltage stabiliser is recommended for an AC.

Once installed, the AC needs fresh air to work efficiently, so one needs to ensure that the outdoor unit is not blocked. Also, the moisture from the room, collected as water, needs to be drained out properly.

The outdoor unit should be made of corrosion-resistant galvanised steel. Providing curtains/blinds/sunfilm on windows reduces heat input into the room. Protecting the AC from direct sunlight can boost its efficiency by almost 5%. Also a false ceiling or insulating the ceiling reduces heat input in the room. The filter should be easily accessible so that it can be removed and cleaned regularly as an unclean filter obstructs optimal cooling as well as increases energy consumption by 10%.

Ideally, electrical appliances such as the television, lamps should not be placed close to the AC. These appliances generate heat which is sensed by the thermostat, causing an overload on the running of the compressor.

For every degree less than 24oC, the AC will consume 3-5% more energy. So, the thermostat should be set at a comfortable high temperature, preferably 25oC.

Filter cleaning depends on the frequency of usage and the atmospheric conditions. For normal applications, it is recommended to clean the filter once in 15 days.

Also, the AC should be serviced once in 3-4 months for optimal performance and longer life of the machine.