How Chiller, AHU, RTU work – working principle Air handling unit, rooftop unit hvac system

Hey there guys, Paul here from In this video, we're
going to be looking at the differences between
chillers, AHUs, and RTUs. Coming up, how to recognize
each of the units, the basics of how each unit works, the differences between each
unit, and where to locate them. Before we jump into the
content of today's video, I just want to take a
moment to thank our partners over at Danfoss for sponsoring this video.

Since we're discussing
air conditioning systems, it's worth mentioning that
Danfoss have solutions that can help you increase efficiency and bring your system in-line with refrigerant regulations
across all types. Danfoss have a deep understanding of chillers, air handling
units, and rooftop units and have a broad portfolio of parts to help you enhance performance
and reduce your energy cost. Find out more about their
air conditioning solutions at So first of all, let's
take a look at chillers. Chillers are used to generate
chilled or cold water which is pumped around the building to provide air conditioning
by collecting unwanted heat. There are two main types of chillers which are air cooled or water cooled.

The term water or air cooled just tells the engineer how the chiller's condenser is rejecting heat from the building. But don't worry, we're going to cover how both of these work in just a moment. Water cooled chillers
are typically located in the basement or the
lowest floor of a building. This type of chiller needs a cooling tower to reject the heat from the building. The chiller produces chilled water and pushes this around the building to air handling units and fan cool units. These units circulate the air around the local space, as well as the building. The air is then forced across the heat exchangers
containing the chilled water, which extracts the unwanted heat before the air is distributed
throughout the building.

The unwanted heat that is
extracted from the air collects in the chilled water
loop, which is pumped back to the chiller where it will transfer over to the chiller's condenser
via a refrigerant loop. The condenser absorbs this heat and then dumps this into
the condenser water loop, and this runs between
the chiller's condenser and the cooling tower up on the roof. The cooling tower will force ambient air across the condenser water to extract the unwanted heat and reject this heat out of the building and
into the atmosphere.

So in this instance, the
condenser of the chiller has been cooled by water so it is
now a water cooled chiller. Water cooled chillers are typically used on large commercial properties
with high cooling loads. You can tell if a building
has a water cooled chiller because it will need a cooling tower, which is typically located on the roof. There will usually be
more than one chiller and cooling tower and it's not uncommon to have at least two or three, even more just for redundancy as well as
variations in cooling demand. And we've covered this system in great detail previously
in other videos. There's some links on the
screen now, where if you want to learn more you can see
the description below. Air cooled chillers, air
cooled chillers are typically located on the roof of the building or outside say in the car park. The air cooled chillers
also generate chilled water which is pumped around the building to air handling units as well
as fan cool units, et cetera, in order to cool the building
and pick up unwanted heat.

The air is forced to
circulate around the building and local space and will
pass across heat exchanges within the air handlers
and fan cool units. This unwanted heat is again transferred over to the condenser of the
chiller from the evaporator. It is transferred via a refrigerant, which loops between the
evaporator and the condenser and is forced by the compressor. The difference with this type of chiller is that the fan blows
air across the condenser which removes the unwanted heat. So in this instance, the
condenser of the chiller has been cooled by air, therefore
it is an air cooled chiller. Air cooled chillers are
typically located outside because they need access
to a lot of ambient air in order to reject the heat.

pexels photo 3964736

This type of chiller can usually be found on medium to large commercial property, and there's an example
on-screen now of how these units look in the real-world
on the roof of an office. Again, we've covered this in great detail in previous videos. There's a link on-screen now for that, or see the video description
below to learn more. AHUs and RTUs, air handling
units and rooftop units. Now these two systems both
serve a very similar purpose and they can even look fairly alike. Both of these are used
to distribute air around the building and will
contain fans to achieve this. They will both take in fresh ambient air and clean this through
a filter before heating or cooling the air to suit the
demands within the building. The main difference between
these two is how the air is heated or cooled and
we'll look at each of these to learn the basics of how
they work in just a moment.

Air handling units are also
referred to as AHUs for short. AHUs are typically located
inside the building, although you can find these
in the rooftop plant rooms and it's becoming more common to find these more robust weathertight
AHUs sitting out in the open on the roof to free up
space within the building. Their purpose is to distribute air around defined areas within the building. Sometimes one AHU will
supply the whole building. But it's common in newer buildings to have multiple smaller
AHUs feeding different parts to provide a better indoor environment, as well as resulting in energy savings. AHUs typically do not have their own cooling system built-in. Instead they will be connected to a central plant, water
or air cooled chiller. Occasionally, they will use
some sort of split AC unit and you can also find these connected to district cooling networks. AHUs are connected to
duct work, which provides a defined route for the air
to travel around the building. In a simple form, an AHU will use a fan to suck in fresh ambient outside air, which will then pass through some filters to remove any dust and dirt.

It will then pass through the cooling and heating coil heat
exchanges, which as discussed, are typically fed from
central plant units. Once their air has
passed over these coils, it will be pushed out around the building. Another set of duct
work will be collecting the warm used air from these rooms and will bring this back
to the AHU via another fan. This fan will then eject the air from the AHU and the
building, and there are many different setups for this, and again, we've covered this in
detail in previous videos. There's a link on-screen
now where you can watch that or see the video description below. RTUs, rooftop units, these
units are always located on the roof, as the name suggests. They are very common in shops and small commercial properties and are popular because
they are simple, compact, self-contained, all-in-one HVAC units. Their purpose is to
distribute conditioned air around defined areas within a building.

RTUs are also connected to
duct work, which provides a defined route for the
conditioned air to travel along. RTUs typically have their own
indoor refrigeration system to provide cooling only,
but they can also contain a heat source such as a gas fired heater or an all-electric heat pump. RTUs house all the components
within the rooftop unit. This contains a number of dampers
to control the flow of air and can allow air recirculation
if conditions are right. The unit will also contain
filters to clean the air, as well as heating and cooling coils and at least one central fan. The refrigeration system is also connected to the back or the side of unit, and this is used to
control the temperature. The fresh ambient air is sucked in via the fan and passes across the dampers. It then passes through
the filters to remove any dust and dirt before its temperature is adjusted in the heat exchanger. The fan then pushes this out into the building to condition the space.

Another duct will collect the
warm used air from the rooms and will distribute this
back to the rooftop unit where it will be ejected or recirculated if that option is available
and the conditions are right. Okay guys, that's it for this video. But before I close this
out, I just want to say another special thanks to our
sponsor Danfoss one last time. Don't forget to check
out their broad portfolio of air conditioning parts and solutions by heading over to Don't forget to hit the like,
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video, and it has helped you. You can also follow us on
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