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

If you pick this article, You will be able understand; → Why AC rated in Tons, Not in kW?
→ Definition of Ton

→ How many kW and HP are there in 1 Ton?

→ How to convert Ton to Kw and vice versa?
→ How much Current in Ampere will a 2 Tons AC draw in Single Phase & Three Phase

System?
→ How many 2 Ton A.C (Air conditioner) can I run on a 25 kVA Generator?

→ What is the suitable rating of MCB for 2 Ton and 1 Ton AC (Air conditioner) and why?

and much more…

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 (R_T) is approximately equivalent to 12,000 BTU/h or 3,516.8528 W or 4.7142Hp.

A Ton of refrigeration (R_T) is a unit of power used to describe the heat-extraction capacity of air conditioning and refrigeration equipment. 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 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 R_T(Refrigeration Ton) = 3.5168528 kW…

1 R_T = 3.5168528 kW

1 kW = 0.284345 R_T(Refrigeration Ton)

1 kW = 0.28434517 R_T

So,

The power P in kW = Power P in R_T (Refrigeration Ton) times 3.5168528….

P_(kW) = P_(RT) × 3.5168528

Example

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

Solution:

P_(kW) = 3 R_T × 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 V_LxI_L 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 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.

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Why Power Plant Capacity Rated in MW and not in MVA?

For the following reasons, a Power plant capacity rating may be expressed in MW instead of MVA.

In a Generating station, the prime mover (Turbine) generates only and onlyActive Power. That’s why we rated a power plant capacity in MW instead of MVA. Its mean no matter how large your generator is, but it depends on the capacity of the  engine (Prime mover/Turbine) I.e. a 50MW turbine connected to a 90MVA alternator in a power plant will generate only 50MW at full load. In short, a power plant rating is specified in terms of prime mover /Turbine (Turbine rating may be seen by nameplate rating which is in MW or Horsepower (HP) not in MVA) and not by the alternator set coupled to it.

Another thing is that, electric power company charges their consumer for kVA while they generate kW (or MW) at the power station (Power plant).They penalize their consumer for low Power factor because they are not responsible for low power factor and kVA but you. Moreover, in power plant, power factor is 1 therefore MW is equal to MVA …… (MW = MVA x P.f).

Another interesting & funny answer by one of our Facebook page fan…“Power House means, house of the Power, and we know that the unit or power is Watt. That’s why we rated power plant capacity in MW and not in MVA”.   

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Why Battery rated in Ah (Ampere hour) and not in VA.

Battery stores charge in the form of chemical energy and then converts it into electrical energy to utilize for a specific time. The amount of available charge is the capacity of a cell or battery which may be expressed in Ah (Ampere-hour). Moreover, in a charged battery, the numbers of molecules are limited to create a flow of electron in electric circuits, so, there must be a limited number of electrons in a cell/battery which they motivate through a circuittofully discharge. Now we have the option to rate the battery capacity in Number of flowing electrons for a specific time, but, it would be a headache, because there are a vast number of electrons in it.  So we have another option (1C (Coulomb) = 6.25 x 10¹⁸electrons, or 6,250,000,000,000,000,000 electrons.

In addition, 1A (Ampere) = 1 coulomb of electrons per second and,

1h = 3600 Seconds

Therefore;

1Ah = (1A) x (3600s) = (C/s) x (3600s) = 3600 C.

∴ A (1 Ampere) = 1 Coulomb per second = C/s

But,

Why make up a new unit for battery capacity rating when an old one unit is doing just fine? L

Of course! To make your lives as technicians and students more difficult.    

As they do for electricity units… i.e. 1 Unit of Electricity = 1kWh = 1 board of Trade Unit…

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How Steam turbine Works?

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Thermal Power Generation Plant or Thermal Power Station

Thermal power generation plant or thermal power station is the most conventional source of electric power. Thermal power plant is also referred as coal thermal power plant and steam turbine power plant. Before going into detail of this topic, we will try to understand the line diagram of electric power generation plant.

Theory of Thermal Power Station

The theory of thermal power stationor working of thermal power stationis very simple. A power generation plant mainly consists of alternatorruns with help of steam turbine. The steam is obtained from high pressure boilers. Generally in India, bituminous coal, brown coal and peat are used as fuel of boiler. The bituminous coal is used as boiler fuel has volatile matter from 8 to 33 % and ash content 5 to 16 %. To increase the thermal efficiency, the coal is used in the boiler in powder form.

In coal thermal power plant, the steam is produced in high pressure in the steam boilerdue to burning of fuel (pulverized coal) in boiler furnaces. This steam is further supper heated in a super heater. This supper heated steam then enters into the turbine and rotates the turbine blades. The turbine is mechanically so coupled with alternator that its rotor will rotate with the rotation of turbine blades. After entering in turbine the steam pressure suddenly falls and corresponding volume of the steam increases. After imparting energy to the turbine rotor the steam passes out of the turbine blades into the condenser. In the condenser the cold water is circulated with the help of pump which condenses the low pressure wet steam. This condensed water is further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is again heated in high pressure.

For better understanding we furnish every step of function of a thermal power station as follows,

1) First the pulverized coal is burnt into the furnace of steam boiler.

2) High pressure steam is produced in the boiler.

3) This steam is then passed through the super heater, where it further heated up.

4) This supper heated steam is then entered into a turbine at high speed.

5) In turbine this steam force rotates the turbine blades that means here in the turbine the stored potential energy of the high pressured steam is converted into mechanical energy.

Line Diagram of Power Plant

6) After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades and enters into a condenser.

7) In the condenser the cold water is circulated with help of pump which condenses the low pressure wet steam.

8) This condensed water is then further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is then again heated in a high pressure heater where the high pressure of steam is used for heating.

9) The turbine in thermal power station acts as a prime mover of the alternator.

Overview of Thermal Power Plant

A typical Thermal Power Station Operates on a Cycle which is shown below.

The working fluid is water and steam. This is called feed water and steam cycle. The ideal Thermodynamic Cycle to which the operation of a Thermal Power Station closely resembles is the RANKINE CYCLE.

In steam boiler the water is heated up by burning the fuel in air in the furnace & the function of the boiler is to give dry super heated steam at required temperature.

The steam so produced is used in driving the steam Turbines. This turbine is coupled tosynchronous generator (usually three phase synchronous alternator), which generates electrical energy.

The exhaust steam from the turbine is allowed to condense into water in steam condenser of turbine, which creates suction at very low pressure and allows the expansion of the steam in the turbine to a very low pressure. The principle advantages of condensing operation are the increased amount of energy extracted per kg of steam and thereby increasing efficiency and the condensate which is fed into the boiler again reduces the amount of fresh feed water.

The condensate along with some fresh make up feed water is again fed into the boiler by pump (called the boiler feed pump).

In condenser the steam is condensed by cooling water. Cooling water recycles through cooling tower. This constitutes cooling water circuit.

The ambient air is allowed to enter in the boiler after dust filtration. Also the flue gas comes out of the boiler and exhausted into atmosphere through stacks. These constitute air and flue gas circuit. The flow of air and also the static pressure inside the steam boiler (called draught) is maintained by two fans called Forced Draught (FD) fan andInduced Draught(ID) fan.

The total scheme of a typical thermal power station along with different circuits is illustrated below.

Inside the boiler there are various heat exchangers, viz.’ Economiser’, ‘Evaporator’ (not shown in the fig above, it is basically the water tubes, i.e. downcomer riser circuit), ‘Super Heater’ (sometimes ‘Reheater’, ‘air preheater’ are also present).

In Economiser the feed water is heated to considerable amount by the remaining heat of flue gas.

The Boiler Drum actually maintains a head for natural circulation of two phase mixture (steam + water) through the water tubes.

There is also Super Heater which also takes heat from flue gas and raises the temperature of steam as per requirement.

Efficiency of Thermal Power Station or Plant

The overall efficiency of a thermal power station or plant varies from 20% to 26% and it depends upon plant capacity.

INSTALLED PLANT CAPACITY	AVERAGE OVERALL THERMAL EFFICIENCY
upto 1MW	4%
1MW to 10MW	12%
10MW to 50MW	16%
50MW to 100MW	24%
above 100MW	27%

Thermal Power Plant Location

A thermal power station or thermal power plant has ultimate target to make business profit. Hence for optimizing the profit, the location of the station is much important factor. Power generation plant location plays an optimizing part in the economy of the station.

The most economical , location of power plant can be determined by graphical method as described below,
The most economical and ideal power plant location is the center of gravity of the load because for such a power generation plant the length of the power transmission network will be minimum, thus the capital cost to the system is reduced.
Let’s explain the graphical method, say, X and Y be two reference axes.
Let’s Q1(x1, y1), Q2(x2, y2), Q3(x3, y3), Q4(x4, y4),……………………………………….and Qn(xn, yn) are n numbers of load centers. From the above graph we get, the coordinates of the center of gravity of the load, Q(x, y) where

Obviously the location of thermal power station is best at the center of gravity of the load, but many times it is not possible to establish a thermal power plant at the CG of the load. Since normally CG point of the load may be at the heart of the city. so other many points to be considered to decide the best optimized location of the power plant.
1) The electric power generation plant must be constructed at such a place where the cost of land is quite reasonable.

2) The land should be such that the acquisition of private property must be minimum.

3) A large quantity of cooling water is required for the condensers etc of thermal power generation plant, hence the plant should preferably situated beside big source of natural water source such as big river.

4) Availability of huge amount of fuel at reasonable cost is one of the major criterion for choosing plant location.

5) The plant should be established on plane land.

6)The soil should be such that it should provide good and firm foundation of plant and buildings.

7) The thermal power plant location should not be very nearer to dense locality as there are smoke, noise steam, water vapors etc.

8) There must be ample scope of development of future demand.

9) Place for ash handling plant for thermal power station should also be available very near by.

10) Very tall chimney of power station should not obstruct the traffics of air ships.

Advantages & Disadvantages of Thermal Power Station

Advantages:
1) Economical for low initial cost other than any generating plant.

2) Land required less than hydro power plant.

3) Since coal is main fuel & its cost is quite cheap than petrol/diesel so generation cost is economical.

4) There are easier maintenance.

5) Thermal power plant can be installed in any location where transportation & bulk of water are available.

Disadvantages:
1) The running cost for a thermal power station is comparatively high due to fuel,maintenance etc.

2) Large amount of smoke causes air pollution.The thermal power station is responsible for Global warming.

3) The heated water that comes from thermal power plant has an adverse effect on the lives in the water and disturbs the ecology.

4) Overall efficiency of thermal power plant is low like less 30%.

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