My friend and I have a similar-sized room, both of us have a 1-ton AC from the same brand, just a few specs are different here and there. I run my AC for about 20-30 minutes at 24° C. My room gets so cold that I have to turn the AC off for a while. On the other hand, my friend runs their AC almost all the time they’re there in the room because as soon as you turn off the AC, within minutes the room gets uncomfortable.
Why is that you ask? Because I live on the first floor of an apartment building while my friend lives on the top floor.
The Problem Isn’t Always the AC
A lot of people think that you measure the room, check the tonnage chart, buy the recommended AC, and you’re done. In reality, cooling professionals consider a lot more than just room dimensions while calculating cooling requirements.
Things like sunlight exposure, window placement, ceiling height, insulation, occupancy, and most importantly, which floor the room is on can significantly impact how your AC performs.
That’s why two identical rooms can have completely different cooling experiences.
Your AC Is Fighting a Giant Hot Plate
If you live on the top floor and have no proper structure on top of your room, just a spare terrace, then that’s a slight disadvantage in the summer months.
What happens is that throughout the day, no matter the extremities of the sun or weather, that concrete slab is exposed to direct sunlight. While most people think the heat disappears once the sun sets, that’s not really what happens. Concrete absorbs heat continuously during the day and then slowly releases it over several hours. This is called thermal lag.
That’s the reason why if you live on the top floor, you would’ve noticed how your room remains warm. The outdoor temperature may have started dropping, but the roof is still radiating the heat it collected throughout the day, and for your AC, that means it has to work extra hours.
Why the Same AC Performs Differently
By now, you would have understood why the same AC performs differently in different rooms. A lot of people make the mistake of copying an AC recommendation from a friend or neighbour.
Your friend may be perfectly happy with a 1-ton AC, but if they live on the second floor and you live directly below the terrace, the two rooms are dealing with very different amounts of heat.
Cooling experts refer to this as the cooling load. In simple terms, it is the total amount of heat that an AC needs to remove from a room.
If you do the math, the larger the cooling load, the harder the AC has to work.
From what we have understood so far a top-floor apartment has a higher cooling load because heat is entering not only through windows and walls, but also through the roof itself. That’s why you see people do those hacks with thermocol and white cement to keep the roof cooler, and in turn the room cooler.
Lowering the Temperature Doesn’t Fix the Issue
When you don’t feel the cooling at 24°C, the response is to change the temperature to 22°C and eventually to 18°C, but despite that, in most top-floor cases, the room doesn’t feel cold.
The problem is that the AC isn’t struggling because it doesn’t know what temperature you want. It is struggling because fresh heat keeps entering the room.
You can’t change your apartment altogether, so there are a couple of things that you can do to help your AC cool a little better. Use blackout curtains, reflective window films, roof insulation, or terrace cooling treatments. This can help somewhat bring down the heat in your room and will help your AC cool better.
What This Means When Buying an AC
If you are buying an AC for your top-floor room, then the first thing you should do is not follow standard tonnage recommendations or copy somebody else’s setup.
You have to check your room’s square footage, which is important, but that’s only half of the work done. You also need to account for the amount of heat that’s entering your room.
Most tonnage recommendations are based on average conditions. So, they don’t completely account for a room that’s sitting directly below a sun-exposed terrace, receiving hours of direct sunlight every day, or dealing with poor insulation.
If you are living on the top floor, especially in a place like Delhi where the temperatures reach close to 50°C in the summer months, then it is recommended that you go for a slightly higher tonnage for your AC to account for the additional heat load that the room experiences every single day.
