- [Narrator] Air conditioners give you much-needed
thermal comfort during a scorching summer.
More specifically, air conditioners help
to maintain the room temperature at the optimum level.
They also help remove airborne particles
and humidity from the room.
Let's find out how these devices work.
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in the production of this video.
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by accessing the free e-lessons
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Let's start with a very simple approach
to understanding the functioning of an air conditioner.
An air conditioner has two connected coils
with continuously flowing refrigerant fluid inside them.
The coil inside the room is called the evaporator
and the coil outside the room is called the condenser.
The fundamental principle of an air-conditioner is simple.
Just keep the evaporator cold,
more specifically colder than the room temperature
and the condenser hot,
more specifically hotter than the surroundings.
With these conditions, the continuously flowing fluid
will obviously absorb the heat from the room
and eject it out to the surroundings.
This is the fundamental rule of an air conditioner.
Let's see how this rule is implemented in practice.
To achieve this objective, two more components
are needed inside your air conditioner,
a compressor and an expansion valve.
As you can probably guess,
the compressor increases the pressure of the refrigerant.
Here, you can see a working example
of a reciprocating type compressor.
The compressor handles the refrigerant
in its gaseous state so that as it compresses the gas,
the temperature rises along with the pressure.
The temperature at the compressor outlet
will be far higher than the atmospheric temperature.
Therefore, if you pass this hot gas
through the condenser heat exchanger,
you can easily eject the heat.
A fan in the condenser unit makes this task easier.
During this heat ejection phase,
the gas gets condensed to a liquid.
An expansion valve is fitted at the exit of the condenser.
The purpose of the expansion valve
is to restrict the refrigerant flow,
thus reducing the pressure of the fluid.
Here comes the main trick.
You might be aware that it is possible to boil
a liquid just by reducing the pressure around it.
This phenomenon happens inside the expansion valve as well.
As the pressure drops,
one part of the refrigerant liquid is evaporated.
However, for this evaporation to happen,
some energy should be supplied to it.
This energy comes from within the refrigerant
so its temperature drops.
This is how the cold refrigerant is produced
inside an air conditioner.
This low temperature refrigerant
should be at a temperature lower than the room temperature.
So by passing the room's air over the evaporator coil,
the room temperature will drop.
The refrigerant gets converted to vapor
during this heat absorption process.
You might have heard a term called ton
associated with the air conditioners.
The ton represents how much heat the evaporator
can absorb from the room.
In simple words, it represents
an air conditioner's heat removal capability.
In this way we have achieved
the fundamental rule of an air conditioner.
The temperature is lower than the room temperature
in the coil inside the room
and the temperature is more
than the atmospheric temperature
in the coil outside the room.
In an actual air conditioner,
the compressor sits near to the condenser
and the expansion valve sits near to the evaporator.
There are some practical issues with this design.
Near to the evaporator coils,
the air temperature will be quite low.
This will lead to water condensation
on the evaporator coils.
That's why we need a pipe
to remove this water condensate.
Modern air conditioners use scroll compressors
instead of the reciprocating type.
You can see how the compression process happens
from this animation.
They are silent and they have good speed control.
Do you know how your air conditioner
is able to maintain an almost steady room temperature
irrespective of the load?
Modern air conditioners use a variable
speed motor technology called inverter technology
for better temperature control.
Just by adjusting the motor speed,
the compressor speed, the refrigerant flow rate,
and the cooling capacity can be controlled accurately.
Here comes an interesting design challenge
for the air conditioner.
The compressor of an air conditioner is designed
to handle only vapor and a small fraction of liquid content
can affect its performance and damage the compressor.
For these reasons, it is desired that the evaporator
convert all of the liquid to vapor
and even increase the temperature of the vapor
by five to eight degrees celsius after the conversion.
How does it make sure that the fluid
which enters the compressor is purely vapor?
This condition is maintained
by a special kind of expansion valve
called a thermostatic expansion valve.
The abbreviation is TXV.
The TXV is similar to the expansion valve we saw earlier
but here the temperature of a bulb controls the needle.
The bulb is connected to the evaporator exit.
The refrigerant inside the bulb is separated
from the main refrigeration cycle by a diaphragm.
When the bulb is hot, the refrigerant inside it
will be evaporated and the needle will move down.
We know the sudden cooling of the refrigerant
is achieved across the expansion valve
with the help of the restriction.
The narrower the restriction,
the cooler the outlet refrigerant will be.
Let's consider a bad situation for the compressor.
Assume the evaporator temperature is not so low,
so the evaporator absorbs very low heat
and all the liquid in it will not be converted to vapor.
Thus, the refrigerant, which leaves for the compressor,
will not be superheated.
This low temperature at the evaporator exit
will immediately be sensed by the ball
and will cause the needle to move upwards
and make the restriction narrower.
The narrow restriction causes a good temperature drop,
thus the evaporator will receive much cooler fluid
and it can absorb a great amount of heat.
This will make sure that all the liquid
will be converted to vapor.
Thus, the complex task of having a vapor only condition
at the compressor inlet
is automatically maintained by the TXV.
Let us clear up a common misconception at this stage.
TXVs do not control the room temperature,
they just make sure that the compressor
receives the refrigerant in pure vapor form.
The refrigerant flow rate and the room temperature
are controlled by the speed of the compressor.
Due to their simplicity and efficiency,
TXVs are widely used in the industrial
and domestic applications.
To learn more about TXVs
and hundreds of other cooling topics,
please check out Danfoss Learning,
a free training and certification hub
brought to you by Danfoss.
Visit Learning.Danfoss.com
or click the link in the video description.
Thank you!