Hey there guys, Paul here from
theengineeringmindset.com.
In this video we are going to be learning how refrigerants
work in HVAC systems.
Now to become an HVAC engineer it is absolutely essential
you understand how the refrigerant works,
how it changes phases and how it moves the thermal energy
around the system.
Guys, I'd just like to take a moment to thank Danfoss,
our sponsor for today's episode.
Danfoss is your go to source for information and resources
that can help you through the cooling industries transition
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They have a deep understanding of all the new regulations
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and they're ready to share their knowledge
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They've also made helpful tools like
their refrigerant retro-fit guide, the low GWP tool
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You can visit them now by visiting refrigerants.danfoss.com.
All right, so jumping into the video,
now it doesn't matter what type of system
you look at all the way from
the refrigerator in your home,
to simple split units and even large industrial chillers;
essentially they all work the same.
And that's because they pass the refrigerant between
the main components of the evaporator, the compressor,
the condenser and the expansion device.
When we say refrigerant what we mean is a fluid that can be
easily boiled from a liquid into a vapor,
and also be condensed from a vapor back into a liquid.
And this needs to be able to occur again and again and again
without failure.
So, what is used as a refrigerant?
Well, we could use water that will work
and it is used in absorption chillers.
Now if you haven't watched our video on absorption chillers
I highly recommend you do so.
We've also got a lot of other interesting videos such as
air cooled chillers and just general HVAC
building services videos.
So do check these out when you get a moment.
But the reason we don't typically use water in common
refrigeration units is because there are specially made
refrigerants designed specifically for the task of these
and so they are able to perform much better.
On the screen you'll see some of the more common
refrigerants that are used currently
and that is R22,
R134A
and R410A.
If you don't know what there R numbers mean,
then don't worry, we are going to be looking at the
different types of refrigerants in the next video;
along with the pros and cons of them,
especially their potential impact on the environment.
As you can see on the screen, these refrigerants have
extremely low boiling points compared to water.
So they need very little heat in order to boil
and evaporate into a vapor and this means they
can extract heat more rapidly.
You can see that at atmospheric pressure then the boiling
point of water is 100°C
or 212°F,
but
R134A has a boiling point of just
- 26.3°C
or -15.34°F.
So we can use room temperature to boil these
and take the heat away from the room
and disburse that out to the atmosphere.
But for now lets see how the refrigerants
actually move around the system.
So we'll start with the compressor because it's
the driving force of the refrigerant,
pushing it around the system.
And there's a lot of different types of compressors
but in this video we're gonna just look at basic
piston type, just make it very clear
and easy to understand how it works.
So the refrigerant is entering into the compressor
as a saturated vapor,
and it's at a low temperature and low pressure.
The compressor pulls the refrigerant in
and rapidly compresses it.
This forces the molecules together
so the same amount of molecules fit into a smaller space.
This increases the collision rate of the molecules
because they are all constantly bouncing around.
As they collide they convert their
kinetic energy into heat.
At the same time all the energy that is put in by
the compressor is converted into internal energy
within the refrigerant, this results in the refrigerant
increasing in internal energy, enthalpy,
temperature and pressure.
And you'll know this if you've ever used a bike pump
the pump gets very hot as the pressure increases.
The refrigerant now comes from the compressor
around into the condenser.
The condenser is where all the unwanted heat is rejected
out into the atmosphere.
This will include all of the heat from the building
as well as the heat from the compressor.
When the refrigerant enters the condenser
it needs to be at a higher temperature
than the air around it in order for the heat to transfer.
The greater the temperature difference,
the easier the heat transfer will be.
The refrigerant enters as a super heated vapor
at high pressure and high temperature.
And it passes along the tubes of the condenser.
Fans will blow air across the condenser to remove the heat,
just like you might blow on a hot spoon of soup
to cool it down.
As the air blows across the tubes it removes the
thermal energy from the refrigerant.
As the refrigerant gives up this heat,
it will condense into a liquid.
So by the time the refrigerant leaves the condenser
it will be a completely saturated liquid,
still at the higher pressure but also slightly cooler
although it's enthalpy and entropy will have decreased.
Now you'll see this if you pour boiling water into a glass,
you'll see all the steam start to rise out of it
and also the steam as it comes into contact with the glass,
which is at a cooler temperature,
it will condense and that steam will then form a vapor.
And that will then, as it condenses it will then roll down
and make it's way into the bottom of the glass again
back into a liquid.
Next the refrigerant makes it's way from the condenser
around and into the expansion devise.
In this case we've got a thermal expansion valve.
The expansion valve meters the flow
of refrigerant into the evaporator,
and in this example we're using a thermal expansion valve
which uses a capillary bolt to control the flow
through the valve, depending on
the temperature at the outlet of the evaporator.
The valve is a bit like a spray nozzle.
It has a high pressure on one side within the bottle,
and there's a low pressure side just past the nozzle.
When the trigger is squeezed it lets the fluid pass,
and this will be a mixture of liquid and vapor.
So as the refrigerant passes through the expansion valve,
it will do just this and it will expand
because the pipework after it going into the evaporator
is at a lower pressure so the refrigerant
will be able to expand to fill this.
As it expands it reduces in pressure and temperature,
just like if you hold a deodorant can
or a spray paint can and you press the nozzle
you'll feel it get colder and the walls of the container
will become less pressurized as you do so.
So the refrigerant will leave the expansion valve,
at a low pressure and temperature
and it'll head straight into the evaporator.
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