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 to natural and climate
friendly refrigerants. They have a deep understanding
of all the new regulations and their effects, and they're ready to share their knowledge and solutions with you. They've also made helpful tools like their refrigerant retro-fit
guide, the low GWP tool and also the Coolselector®2 app which is available for
free on their website. 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. The evaporator receives the refrigerant and the fan blows the
warm air across the coils. The temperature of the air must be higher than the temperature
of the cool refrigerant and this allows it to absorb more energy and to boil the refrigerant
completely into a vapor. Much like heating a pan of water. The heat will cause the water
to evaporate into steam vapor, and the vapor will carry away the heat. If you place your hand
over the steam of the pan, then you will find it is really hot. So, please don't do that at home. Remember the refrigerants
have very low boiling points, so the room temperature air is enough to boil it into a vapor. The refrigerant leaves
as a saturated vapor at a low pressure and temperature. The temperature only changes slightly, which confuses many people, but the reason it does not increase is because it's undergoing a phase change from a liquid to a vapor. So the thermal energy is being used to break the bonds between the molecules, but their enthalpy and
entropy will increase and this is where the energy is going. The temperature will only
change once the fluid is no longer undergoing a phase change. All right, guys, that's it for this video. Thank you very much for watching. I hope you enjoyed that and it helped you. Just before we go, I'd like
to say one more quick thanks to Danfoss for sponsoring this episode. And remind you to check out their free refrigerant resources available at refrigerants.danfoss.com
