| by Kenneth Chase | 55 comments

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

hey guys Paul here from the engineering
mindset calm in this video we’re going to be looking at the differences between
chillers AHU’s and RTU’s 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 dan Foss for sponsoring this
video since we’re discussing air-conditioning
systems is worth mentioning that Dan Voss have solutions that can help you
increase efficiency and bring your system in line with refrigerant
regulations across all types dan Foss have a deep understanding of chillers
air handling units and rooftop units and they’ve a broad portfolio of parts to
help you enhance performance and reduce your energy costs find out more about
their air conditioning solutions at Air Conditioning.danfoss.com so first of
all let’s take a look at chillers Cheers 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 called just tells the engineer how
the chillers condenser is rejecting heat from the building but don’t worry we’re
going to cover how both 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 coils these units circulate the air
around the local space as well as the building the air is M forced across the
heat exchangers containing the chilled water which extract C 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
chillers condenser via a refrigerant loop the condenser absorbs this heat and
then dumped this into the condenser water loop and this runs between the
chillers condenser and the cooling tower up in the
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
now we’ve covered this system in great detail previously in our videos there’s
some links on the screen now or 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 carpark the
air-cooled chillers also generate chilled water which is pumped around the
building to air handling units as well as phone call units etc 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 coil units this unwanted heat is a gain 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
he said 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 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 a haeju’s and RT use air handling it’s
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 disrobe
air around the building and will contain fans to achieve this they will both take
in fresh ambient air and clean this for 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 AHU’s for short
AHU’s are typically located inside the building though you can find these
in the rooftop plant rooms and it’s becoming more common to find these more
robust weather-tight AHU’s 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 that have multiple smaller eh
use feeding different parts to provide a better indoor environment as well as
resulting in energy savings AHU’s 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 is connected to district cooling networks they choose
are connected to ductwork which provides a defined route for the air to travel
around the building in a simple form an H you 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 exchangers
which as discussed are typically fed from central plant units once the air
has passed over these coils it will be pushed out around the building another
set of ductwork 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 their video description below are to use
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
the purpose is to distribute conditioned air around defined areas within a
building are to use are also connected to ductwork which provides a defined
route for the conditioned air to travel along are to use typically have their
own inbuilt 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 RTu has 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 the unit and this is used to
control the temperature the fresh ambient air is sucked in via the fan and
passes across the dampers and 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 will be ejected or recirculated if that option is available
and the conditions are right ok guys that’s it for this video but before I
close this out I just want to say another special thanks to our sponsor
den Foss one last time don’t forget to check out their broad portfolio of air
conditioning parts and solutions by heading over to air conditioning Danfoss
comm don’t forget to hit the like subscribe and share button if you’ve
enjoyed this video and it has helped you you can also follow us on Facebook
Instagram Twitter and don’t forget to check out our website the engineering
mindset comm once again thanks for watching


The Engineering Mindset

Nov 11, 2017, 9:19 pm Reply

⚠️ Found this video super useful? Buy Paul a coffee to say thanks: ☕

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The Engineering Mindset

Nov 11, 2017, 9:19 pm Reply

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Shahbaz Ali

Nov 11, 2017, 6:04 am Reply

Thank you very much for providing valuable knowledge for free.

Ashok Kumar Sharma

Nov 11, 2017, 8:09 am Reply

fantastic video sir. please upload wirring diagram video of AHUS ,chiller, vrf sir…please

P Ganesh Iyer

Nov 11, 2017, 2:49 am Reply

Many thanks.

Mechanical Junkie

Dec 12, 2017, 6:43 pm Reply

I thought that RTUs typically recirculate the return air back into the building. They can have make up air intakes which is a manually adjusted damper to allow fresh air into the system or an economizer which is an automatic damper with return air and outdoor temp sensors. The economizer will allow less fresh air in if it is farther from the set temp than return air and more in if they are close in temperature or the fresh air is closer to set temp. Is that incorrect and they typically discharge the return air and pull in fresh air from outside for supply air? I'm just an apprentice only worked on a handful of small RTUs.


Dec 12, 2017, 6:39 am Reply

A video on calculations using psychometry chart requested


Dec 12, 2017, 3:26 pm Reply

Is rtu a package ac?

Its Me

Dec 12, 2017, 7:40 am Reply

Please make a video animation on boiler installation and piping all process please!

Squirtle Hvac

Jan 1, 2018, 6:58 am Reply

Can you do refrigeration rack systems?
Thanks 🙂

Mohd Zakri

Feb 2, 2018, 3:16 am Reply

can u explain about ccfcu please


Feb 2, 2018, 10:50 pm Reply

Thank you for this amazing video.. Regards..

Murugan k

Mar 3, 2018, 11:54 pm Reply

thank you for this video valuable in knowledge ….

Mohammed Sawas

Mar 3, 2018, 7:11 pm Reply

Can't we just install the chiller next to the water tower on the roof to save some water pipes ?

Masudur Rahman

Mar 3, 2018, 10:31 am Reply

great concept….Tnx.

florentino cervantes

Mar 3, 2018, 4:10 pm Reply

Its really helps for a beginner like me in HVAC. Thanks for sharing.

Todd Medium Wellington III

Apr 4, 2018, 3:16 pm Reply

How do they get these big units on the roofs?

Bladimir Becelinoff

Apr 4, 2018, 12:48 pm Reply

Thank you so much sir-

My Way

Apr 4, 2018, 2:44 pm Reply

Is there a difference between AHU and FAHU? Thanks.

Sun Shine

Apr 4, 2018, 7:20 am Reply

This is a beautiful general explanation of different cooling systems. After years of experience, I am amazed that I still learn something new from you. Thank you!

firoz khan

Apr 4, 2018, 4:39 am Reply

Thank you very much…that's a great explanation with good details, very useful

Awesome trips

Apr 4, 2018, 9:45 am Reply

Thank you very much…


May 5, 2018, 1:54 am Reply

So an ahu blows air into the buildings supply duct work and sucks out hot air in the building through the returns to the outside?

Tiffanius Smily

May 5, 2018, 1:48 am Reply

suscribing to this channel , good animation and good topics


Jun 6, 2018, 4:50 pm Reply

Outstanding video, simple and to the point!

H Pickmann

Jun 6, 2018, 9:12 pm Reply

i think the one in my property is a AHU connected to Central plant water.
But they raised the water price big time here, i need to know if they consume water instead of just recirculating the same? it has a water valve that i must open before functioning

Bahtera Studio

Jun 6, 2018, 3:21 pm Reply

thank you for posting this, i love it. its better than my lecture slides 🙂 thanks a bunch again.


Jul 7, 2018, 7:29 pm Reply

very nice

Tuyishimire Elie

Jul 7, 2018, 10:58 am Reply

this is very helpful for beginner!!!!!!

Adeola Oruku

Jul 7, 2018, 12:45 am Reply

Nice presentation.

Entertainment & knowledge With Ahmed

Jul 7, 2018, 9:03 pm Reply

thanks for the awesome demonstration and i want to ask you a side question ;are you England as your accent seems British ?


Jul 7, 2018, 11:30 pm Reply

love all your video. keep on doing it. from Malaysia

Kristen Dahmann

Jul 7, 2018, 12:21 am Reply

Where does the fresh air come from? Do you not need a DOAS paired with this? Thanks.

بو فارس بو فارس

Aug 8, 2018, 1:02 am Reply

What is the difference between RTU and DX unit ?
RTU looks like a package unit , isn't it ?

Naseeruddin Shaik

Aug 8, 2018, 8:07 am Reply

hello sir,
what is difference b/w FAHU & AHU ?
How they work together?
Are both same units?
can you please make a video on it?

America 1776

Aug 8, 2018, 7:32 pm Reply

This video taught me more than some worthless journeyman I’ve come across. ?

Dharmendra Kumar

Sep 9, 2018, 5:18 am Reply

Thank you sir

Achina Rambabu

Oct 10, 2018, 8:21 am Reply

Sir, please make a vedio on big shopping malls air conditioning system

rauf iram

Nov 11, 2018, 6:17 am Reply

very nice explained

Marlee Quirequire

Nov 11, 2018, 9:44 am Reply

are RTU's considered as PACUs?

Elang Zulfikar

Dec 12, 2018, 9:18 am Reply

Sir how does an economizer fit in an hvac system? Is it classified as an air handling unit like AHU and RTU? Thanks, any answer would be appriciated!

MCAN – Piano

Jan 1, 2019, 5:30 pm Reply

Do you mind if I ask something? Do you have any video about the difference between all-water HVAC system and all-air HVAC system and which units does they use AHU for all air HVAC and also AHU for all-water HVAC but what is the purpose of all-water because it still has ducts for AHU, I didnt exactly understand their difference and benefit over each other. It would be great if you had a video about it.

Your channel is great. I hope you will be so successful and I will be glad to support you :)) Thanks for everything.

Piyush Jain

Jan 1, 2019, 6:35 pm Reply

Good video


Jan 1, 2019, 2:48 am Reply

"wow usefull stuff!" – trump

Olga Cech

Feb 2, 2019, 2:24 pm Reply

thanks guys for making an effort to create educational videos, very helpful to understand the principles

khairi khairuddin

Feb 2, 2019, 1:37 am Reply

I have problem on my chiller.
Coil motor temperature are very high increase until 160’ degree celcius while on coupling/on load test on 60% run. Does anybody know what is the problem?

Mahbub Hassan

Feb 2, 2019, 8:32 am Reply

How do I maintain chilled water properties?

Javier Rosales

Mar 3, 2019, 9:01 pm Reply

Just discovered this channel. And like it a lot. I am a Plant Operation Director in the boston mass area. I would love to shoot a video over at my building. And use it to help others and myself how boilers/chillers/re circ pumps etc etc work with eachother. A real life video. Are you interested? I would love to due this at my commercial building. I would learn so much as well.

The Engineering Mindset

Apr 4, 2019, 2:17 pm Reply

Learn how BOILERS, AHU, FCU & PUMPs work together here: https://youtu.be/lDeuIQ4VeWk

Doc Brown

May 5, 2019, 10:22 pm Reply

I have seen geothermal systems augmenting var HVAC systems, not too often but here and there, aux system used to just help maintain a temp range. I've also seen rain collecting and filtering systems to augment coolers, someone just using available options to invest and s ave $$$ long term. Even saw a set of small wind generators on one rooftop to support the HVAC specifically. Seen a lotta unusual stuff too, but hey construction and environmental systems are a funky field. Enjoying the vids, most of it I know already but you never know where you may learn something new, and although no longer working it's fun to watch and the occasional flashbacks can be amusing, especially residential customers.

Stanford Leeham

May 5, 2019, 2:59 pm Reply

Diffusion too lavenders and rose

edu newton

Jun 6, 2019, 1:15 pm Reply

Many thanks for the video, it is really helpful


Aug 8, 2019, 2:23 pm Reply

Sir amazing, 12 month ago I subscribed ur channel, only 60 thousand . But now 340000 . awesome

Mohasina Mohammad

Aug 8, 2019, 3:59 am Reply

Sir I need carrier chiller reciprocating compressor semi hermetic compressor trableshout problem solve codes videos need to you send please

Toto Alboayz

Aug 8, 2019, 10:43 pm Reply

Thanks for sharing

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