November 16, 2015

Why AC rated in Tons, Not in kW or KVA? A Guide about Air-conditioning system and Refrigeration.

Why AC rated in Tons, Not in kW or kVA? A Guide about Airconditioner and Refrigeration

Why AC rated in Tons, Not in KW?

AC (Air-conditions and Refrigeration are always rated in Tons.
Air conditioners are always rated in Tons capacity instead of kW because Air conditioners are designed on the basis of quantity of heat removal from room, hall or specific area. Quantity of heat is termed in Tons means if an air conditioner is able to remove 1000 kilocalories of heat or 4120 kilojoules or 12000 BTU of heat in an hour that AC rated as 1 Ton of AC because 1000 Kilocalories or 4120 kilojoules or 12000 BTU equal to one Ton of heat. Also, this is the same case for freezer and refrigerator i.e. refrigeration system.

Good to know:
BTU = British thermal unit. A measurement of heat, specifically, the amount of heat needed to raise the temperature of a pound of water by 1°F.

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

1 Ton = 12,000 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.
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
The power P in kW = Power P in RT (Refrigeration Ton) times 3.5168528….
P(kW) = P(RT) × 3.5168528

Convert 3 Ton AC into kW i.e. Convert 3 RT to kW.
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

For More detailCheck 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.

A general AC (Airconditioner ) Name plate rating Data:

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