Why AC rated in Tons, Not in kW?
Before Willis Carrier invented the modern air
conditioner, people used to cool buildings in the summertime with ice harvested
from rivers and lakes in the wintertime.
When ice is below freezing and it absorbs heat, the temperature increases. When
ice is at its melting point, 32° F, and it absorbs heat, its temperature
doesn't change. Instead, it melts. If you've had a physics or chemistry class,
you may recall that the amount of heat needed to melt ice is called the
latent heat of fusion. In Imperial units, that number is 143 BTUs per pound.
That's actually a lot of heat to pump into a pound frozen water. Once the ice is melted into liquid water, it takes only 1 BTU per pound to raise the temperature 1 degree. So if you've got a pound of ice at 32° F, you put 143 BTUs into it to melt it completely. Then it takes only 180 more BTUs to raise the temperature of that pound of water from 32° F to 212° F, the boiling point.
Anyway,
getting back to our main discussion, if you have a ton of ice, it takes (143
BTU/lb) x (2000 lbs) = 286,000 BTUs to melt it completely. You could do that in
one hour or 10 hours or a year, depending on how quickly you pump heat into it.
Somewhere along the line, though, someone decided to use 1 day—24 hours—as the
standard time reference here. If the ice melts uniformly over the 24 hours, it
absorbs heat at the rate of 286,000 / 24 hrs = 11,917 BTU/hr.
Rounding that number up makes it a nice, round 12,000
BTU/hr. In air conditioning jargon, then, a ton of AC capacity is equal to
12,000 BTU/hr. There it is.
If
you're wondering how this term got institutionalized, it was probably the usual
way. People in the industry start using it, and then the professional
organizations make it official. An architecture website has a quote from 1912 that claims the American
Society of Mechanical Engineers standardized it. It sounds likely, but their
numbers don't work out, so I'm gonna go with Honest Abe on this one and remain
skeptical (until someone in the comments shows me what's wrong with my thinking
anyway).
Definition of Ton :
A Ton of refrigeration (RT) is approximately
equivalent to 12,000 BTU/h or 3,516.8528 W or 4.7142Hp.
A Ton of refrigeration (RT) is a unit of power
used to describe the heat-extraction capacity of air conditioning and
refrigeration equipments. It is defined as the heat of fusion absorbed by
melting 1 short ton of pure ice at 0 °C (32 °F) in 24 hours.
How many kW and HP are there in 1 Ton?
1 Ton = 3.5168525 kW = 4.714Hp
Explanation
1 Ton =
12,000 BTU/h
1 Watt = 3.412141633 BTU/h
1 Watt = 3.412141633 BTU/h
1 Ton =
12,000 / 3.412141633 = 3,516.8528 Watts = 3.5168528 kW.
1 Ton = 3,516.8528
Watts = 3.516 kW.
Also
1 Ton =
3,516.8528W / 746 = 4.7142798928 Hp →→→ (1 Hp = 746 Watts)
1 Ton = 4.714 Hp
How to convert Ton to Kw and vice versa?
One RT(Refrigeration
Ton) = 3.5168528 kW…
1 RT = 3.5168528 kW
1 kW =
0.284345 RT(Refrigeration
Ton)
1 kW =
0.28434517 RT
So,
The power P in
kW = Power P in RT (Refrigeration Ton) times 3.5168528….
P(kW) = P(RT) × 3.5168528
Example
Convert 3
Ton AC into kW i.e. Convert 3 RT to
kW.
Solution:
P(kW) = 3 RT × 3.5168528
P(kW) = 10.55 kW
3 Ton AC = 10.55 kW
How much Current in Ampere will a 2 Tons AC draw in
Single Phase & Three Phase System?
Suppose,
There are 230V and Power factor = Cosθ
= 0.95 in Single Phase AC system…
1 Ton =
3,516.8528 Watts = 3.516 kW.
2 Ton = 2
x 3.516 kW = 7.032kW = 7032W
Power in
a Single Phase AC System
P = VxI
Cosθ and current…
I = P /
(V x Cosθ)….. Where Cosθ = Power factor
I = 7032W / (230V x .95)
I = 32.18 A
Therefore,
a 2 Ton AC (Air-condition in Single Phase AC system will take 31.18 Ampere
Current
Andin Three Phase
System
Suppose,
There are 440V and Power factor = Cosθ
= 0.85 in Three Phase AC system…
Power in
a Three Phase AC System
P =√3 x VLxIL Cosθ and current….
I = P /(
√3xVxCosθ)
I = 7032W
/ (1.732 x 440V x .85) Where Cosθ
= Power factor and √3 = 1.732
I = 10.855 A
Therefore,
a 2 Ton AC (Air-condition in Three Phase AC system will take 10.855 Ampere
Current
Good to Know:This is
just calculation based on Electrical
formulas. In real, Air conditioner current
depends a lot on operating conditions such as ambient temperature, refrigerant
pressure, Energy Efficiency Ratio (EER) etc. for instance, if EER is 6, then
input power for 2 Tons Air conditioner is 24000BTU/ 6 = 4000 watts..
If this is a 230 volt system, then air conditioner load current would be = 4000/(230x.95) = 18.5 A
If this is a 230 volt system, then air conditioner load current would be = 4000/(230x.95) = 18.5 A
For More
detail…Check the Air conditioner Name plate rating.
Another similar rating is
Coefficient
of power (COP) which is the output power in watts divided by input power,
so with a COP = 1.8, for instance, input power for 2 Tons Air conditioner is 7032W / 1.8 = 3906 watts. Now
you can find current by using the above method which is equal to 18A approx.
How many 2 Ton A.C (Air conditioner) can I run on a 25
kVA Generator?
2 Ton = 2
x 3.516 kW = 7.032kW = 7032W
The
Efficiency of Utility Power Generator is 90% approximately.
Efficiency
of Generator = 25kVA x (90/100) = 22.5kVA
Now the
Number of 2 Ton AC (Air conditioners) which you can run on a 25 kVA Generator
smoothly..
22.5kVA / 7032W
= 3
So you
can run Three Air conditioners of 2 Tons each on a 25kVA Generator.
What is the suitable rating of MCB for 2 Ton and 1 Ton AC
(Air conditioner) and why?
As we
have calculated the load current for 2 Ton AC Air conditioner…
Calculated
Current for 2 Ton A.C = I = 32.18 A
Now 40A
Class “C” MCB (miniature circuit breaker) would be suitable for 2 Ton AC
(air-condition) because in starting time it takes more current of the full load
current
And 20 A
Class “C” MCB would be better for 1 Ton AC (air-condition)
Good to Know:
Class
“’C’ Type MCBs
Class “C”
Type MCBs are suitable for installations with high inrush of current at the
starting switching time. in other words, equipment and devices having inductive
loads such as air-conditioners, induction motors, fluorescent lamps,
transformers etc...
