AC Tonnage - basic question.

kidrow

kidrow

Adept
Googling has just given me tech jargon like btu n heat required to melt ice at blah blah temps, etc. But my question basically is,
1. What happens if you fit an ac smaller than the tonnage recommended for the room? Will the room not cool enough to reach x temp? Or it will get there but it will take longer? Or the electricity consumed will be comparitively higher?
2. And what about the reverse situation? Ie if a 1.5 ton ac is fitted in a room which requires only 1 ton.
3. Do stars really matter? How much of a difference would there be between 1 star and 2 stars? How much would the usage have to be to make a difference?
4. Are the older acs bigger in size than their current counterparts, ton for ton? Ie is an earlier gen 1 ton ac the same size as todays 1-1.5 ton?
5. TIA. :)
 
1. All three - depending on how severely undersized it is, or how high the heatload.

2. You will essentially have more airflow and cooling power than the room can handle. Essentially, a waste of power.

3. Yes they do (though not directly) - if you use the AC frequently enough. Calculate your running hours and use the cooling power draw to figure how much KWH you consume. For example, an AC drawing 1000 watts is using 1 unit/hour. The cost of electricity varies from place to place, and there may be slabs for consumption levels. You will need this information to make a decision and hence there is no simple rule. Generally, if you use the AC overnight you need to look at energy efficiency and how much it costs to run a less efficient AC.

4. Could not understand - are you talking about the physical size? Largely it remains similar, there may be a few optimisations here and there but the throats are optimised for airflow so as long as a minimum CFM is maintained one can make the evaporator a little smaller (evaporator is the unit that fits inside your room, or the bit just behind the air exit in a window AC). The heat exchangers have remained similar size, as they are limited b the laws of thermodynamics. Compressors - no change really, maybe a slight reduction. I don't see ACs getting any smaller, if that's the question.
 

well since the discussion is going on

Cranky, wrt to you 2nd point, what about efficienty of the AC? would it not be better to run a 1.5 TON AC at 70% rather than a 1 TON AC at 100% power?

or the ACs are very efficient and the difference is negligible?
 
There is no way to reduce the cooling power of an AC, only the fan speed and preset temperature. When the AC is 'on', it is always at full tilt. The faster the fan moves (I presume this is what you mean by 100-70%), the less delta temperature the evaporator has.

Once the temperature of air coming into the inlets reaches the preset temperature (or close enough, depending on the control mechanism) the compressor simply shuts down and the fan continues. The fan speed can be varied in most units, so for the time period that the temperature is maintained (dependent on wall insulation and leakage, along with other heat sources) only the fan consumes any power.

It is arguable that a large AC will cool a room quicker. However larger ACs are usually more inefficient than smaller ones - heat/cold is best exchanged over small areas and the evaporators and heat exchangers of smaller ACs are, well, smaller, which makes them slightly better. Which is why it is good practice to size the airconditioner according to the room. This is not just about tonnage, but also about airflow, heat load, leakage, window size and a lot of other stuff which I do not pretend to even know about...

As you can probably tell, I'm in the stages of planning to buy an AC, and am agonising over much of this stuff myself ;)
 
Wow! Thanks for your replies guys.

@cranky, no, it doesn't seem like you're on the lookout for a new AC. It seems like you work in the industry. :D

@manu, thanks for the link. :hap2:

I guess I'll just try out a few calculators then, since it's best to be as precise as possible. But is it better to err on the side of having more tonnage than less?

I think the star rating matters most when comparing 5 star ACs to the rest. But between the 1 & 2 star rated machines, I guess the difference exists only for very heavy usage.

The question on physical size was related to guaging whether my old AC is a 1 or 1.5 ton. My dad says its a 1 ton AC, but the size is equivalent to the current 1.5 ton ACs available in the market. We've misplaced the bill & hence are only speculating about it.

Anyways, thanks for your replies guys. Much appreciated.
 
kidrow said:
Wow! Thanks for your replies guys.

@cranky, no, it doesn't seem like you're on the lookout for a new AC. It seems like you work in the industry. :D

@manu, thanks for the link. :hap2:

I guess I'll just try out a few calculators then, since it's best to be as precise as possible. But is it better to err on the side of having more tonnage than less?

I think the star rating matters most when comparing 5 star ACs to the rest. But between the 1 & 2 star rated machines, I guess the difference exists only for very heavy usage.

The question on physical size was related to guaging whether my old AC is a 1 or 1.5 ton. My dad says its a 1 ton AC, but the size is equivalent to the current 1.5 ton ACs available in the market. We've misplaced the bill & hence are only speculating about it.

Anyways, thanks for your replies guys. Much appreciated.
Click to expand...

I don't know about the rest of the stuff, but thanks for the info guys. However I am very sure that if we study comparitively, the physical size of aircons has reduced ton to ton. All the new 1.5 ton window ACs are have smaller dimensions than the 7yr old model in my room. L & B marginally, however Depth has been considerably reduced. How this has been possible I don't know. Compressor is the main component of the aircons, I am inclined to think that they have reduced in volume.

Do let me know if you find out otherwise.
 
you know i read all this ,,, and just went a bought a 3 star 1.5 ton samsung , cant spend one more night of this summer ...ITS HOT
 
One question... maybe counted as OT but what material can be used to seal doors & windows so that cool air does not escape easily. Some kind of rubber sealers or anything else..

In my room the biggest problem is door or must I say the flooring as well.. The Marble slab below the door is highly tilted to one side, so much so that when I open the door completely there is hardly 3-4 mm gap at the bottom but when I close the door then at one side there is 1.25 inch gap.... :(

The builder screwed it up completely.. I cannot remove the marble & the door frame...
 
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