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Rooftop Units explained - RTU working principle hvac

WEBVTT
Kind: captions
Language: en

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Hey there, guys.
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Paul here from TheEngineeringMindset.com.
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In this video, we're going to
be discussing rooftop units.
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Coming up, what is an
RTU, where are they used,
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how do they work, the different types,
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as well as the components
inside, such as heat exchangers,
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filters, fans, ductwork,
grilles, air hoods, et cetera.
00:00:21.600 --> 00:00:23.510
If you like the information
you see on this channel,
00:00:23.510 --> 00:00:25.214
and I really hope you do,
then it's easy to keep
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heading up to Danfoss Learning
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who have kindly sponsored this video.
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Danfoss want to encourage
people all around the world
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So they built a free
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packed full of courses on
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engineering topic,
including additional lessons
00:00:41.830 --> 00:00:43.530
about rooftop units.
00:00:43.530 --> 00:00:45.540
All you have to do to get
started is click the link
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in the video description
below, create your free
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Danfoss Learning profile, and
then pick your first class.
00:00:51.380 --> 00:00:52.580
Pop engineers quiz,
00:00:52.580 --> 00:00:55.110
what does a package air
conditioning unit mean?
00:00:55.110 --> 00:00:57.020
Tell me your answers in
the comments section below,
00:00:57.020 --> 00:01:00.520
and I will reveal the answer
at the very end of the video.
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Okay, rooftop units, as the
name suggests, rooftop units,
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or RTU for short, are
located on the roof of shops
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and small commercial buildings
to provide air conditioning
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to defined areas.
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These are packaged air conditioning units,
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and they are so popular because
they are simple, compact,
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self-contained, all-in-one HVAC units.
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Their purpose is to
distribute conditioned air
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within defined areas of a building.
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Rooftop units are connected to ductwork
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which provides a defined
route for the conditioned air
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to travel along.
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Now in our last video,
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we looked at air handling units, or AHUs.
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I would encourage you to watch
that if you haven't already.
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Links are in the video description below.
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If you have watched that,
you'll probably notice
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that these units are very similar.
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Rooftop units are a type of air handler.
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The main difference is that
they are usually more compact,
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and they're always installed on the roof.
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So they need to be more
robust and weatherproof
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to deal with things like sun,
rain, snow, wind, et cetera.
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Additionally, AHUs will often
be connected to central plants
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such as chillers and boilers
to provide the heating
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and cooling, but RTUs are self-contained
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and have everything they
need all in one unit.
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That's why they're called
package air conditioners,
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and we'll look inside
some models just shortly
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to understand why.
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There are many types of rooftop units,
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and we'll look at four
different typical versions
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starting with the most basic.
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This first unit is fresh
air only so that means
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that there's no recirculation
of air occurring.
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It takes 100% fresh air and conditions it.
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The return air is usually removed
by an external exhaust fan
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to balance the air pressure
within the building,
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but we won't cover that
part in this video.
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First, we have the housing.
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This needs to protect all the
mechanical and the electrical
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equipment inside the unit
from the sun, wind, rain,
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snow, frost, et cetera.
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There will be some access
panels built into this
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to allow engineers to
access the components inside
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and perform maintenance.
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At one end, there would
typically be an air hood.
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This is where the outside ambient air
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will be drawn into the machine.
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The hood is shaped this way to
stop water, snow, and debris
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from entering into the unit.
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There will usually be
a mesh across the inlet
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of the air hood which will
prevent wildlife and objects
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from entering, as this
will cause blockages
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and damage the fan.
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The next thing we might
find are some dampers.
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Not every unit has these, but
newer models typically do.
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These are basically sheets of
metal which rotate together.
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They open fully to allow
air to enter the unit
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or they close to seal
the unit and prevent air
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from entering or leaving.
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Some dampers can vary their open position
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to somewhere between fully
opened and fully closed,
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especially if recirculation is used,
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and we'll look at that later in this video
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after this basic model.
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After the dampers, we'll find the filters.
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These will usually just slide
out from the service door.
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Their purpose is to clean
the air by capturing the dirt
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and the dust which is
contained within the incoming
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fresh outside air.
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If we don't have filters
installed, then the fan,
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heat exchangers, mechanical
components, and the ductwork
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are all going to slowly
be covered by the dust,
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and it's going to reduce the effectiveness
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and the efficiency of the machine.
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If too much dust builds
up on these components,
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then it's eventually going to lead
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to the failure of the machine.
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After the filters, we'll have some coils.
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These coils will be used
to cool or heat the air
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by adding or removing thermal energy.
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Depending on where in the
world the RTU is located
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and the ambient conditions it faces,
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some units will be cooling only,
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though occasionally they
will be heating only,
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and some will be heating and cooling.
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If the unit is cooling only,
then it would typically have
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a single coil which is connected
to a refrigeration unit.
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If the unit is heating
only, then it will either
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be connected to a heat pump, a gas burner,
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or an electrical heating element.
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If unit is heating and
cooling, then it'll either have
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two heat exchangers, where
one will be a cooling coil
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which is connected to
a refrigeration unit,
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and that will provide the cooling,
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and the other will likely
be a true heat exchanger
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which is connected to a gas burner,
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or it might be an electrical
heater to provide the heating.
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Alternatively, a unit might
provide both heating and cooling
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using a single coil which
is connected to a heat pump.
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We've covered heat pumps
in a previous video.
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Links for that are in the
video description below.
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Most units will use a refrigeration system
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to provide the cooling.
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The compressor, condenser,
fan, and controls
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are usually located at the rear
of the unit or at the side,
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and these will be used to
reject the heat and keep it away
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from the intake and the conditioned air
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which is inside of the unit.
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After the coils, we'll find the fan.
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This is usually a belt-driven
centrifugal type fan,
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but it can also be an EC type fan
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which are more energy efficient.
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The fan pulls the air in from outside
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then through the dampers, filters, coils,
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and they will push this
through the ductwork
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to be distributed around the building.
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That's our most basic
type of rooftop unit.
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So what else might we find?
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Some units might
recirculate the internal air
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for a return ductwork system.
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This is used to save
energy, especially in winter
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when the outside air is very cold
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and a return air is very warm.
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We can use this to reduce
the heating load by mixing
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some of the warm return air in with
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the cold fresh air intake.
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In this design, we find a
return air damper in the unit.
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This will work in sync
with the intake air damper
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and the two will vary their
position to change the mixture
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of how much fresh air
and how much return air
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is passing through the unit.
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There will always be a
certain amount of fresh air
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entering into this type
because otherwise the building
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would simply fill up with CO2
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and create a very unhealthy atmosphere.
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As the damper opens, the
suction of the fan will pull air
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in through the ductwork.
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When the damper closes,
no air will be drawn in.
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Another version we'll come across,
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and this type is very common,
in this design, we again
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have the return air damper, but this time
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some of the air or all of the air
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can be rejected to atmosphere.
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The temperature of the
outside air and the return air
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and sometimes the CO2
levels of the return air
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will dictate how much air will be rejected
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and how much will be
mixed and recirculated.
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In this type of unit, when
the outside air temperature
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is below or close to the
desired indoor air temperature,
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100% fresh air can be
blown into the building,
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and none of it will be recirculated.
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All of it will be rejected
as the cooling demand is met.
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This is referred to as free cooling cycle
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or an air side economizer cycle.
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The final version we'll
look at has a heat wheel
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built into the unit.
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This is growing in popularity
with the increasing need
00:07:04.470 --> 00:07:07.560
for energy efficiency in
buildings to reduce CO2 emissions
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but also energy and utility costs.
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This unit first pulls
air in through the hood.
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The amount of air entering
is controlled by the damper.
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The air then passes through
a filter to catch the dirt
00:07:18.600 --> 00:07:22.037
and the dust and protect the
surface of the heat wheel.
00:07:22.037 --> 00:07:24.551
It will then pass through the heat wheel.
00:07:24.551 --> 00:07:27.620
The heat wheel is a rotating
heat exchanger which picks up
00:07:27.620 --> 00:07:30.267
the waste heat or CoHP from
the return discharge air,
00:07:30.267 --> 00:07:33.400
and then transfer this over
to the incoming fresh air
00:07:33.400 --> 00:07:35.560
without the two air streams mixing.
00:07:35.560 --> 00:07:37.750
These heat wheels are
not completely airtight.
00:07:37.750 --> 00:07:39.800
So a little bit of air mixing will occur.
00:07:40.900 --> 00:07:42.900
The heat wheel is used
to offset the heating
00:07:42.900 --> 00:07:45.540
and sometimes cooling demand
when conditions are right.
00:07:45.540 --> 00:07:48.590
This will save energy,
as well as utility costs.
00:07:48.590 --> 00:07:49.440
After the heat wheel,
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the air flows through to another filter.
00:07:51.870 --> 00:07:53.890
Just before the filter, we have a damper
00:07:53.890 --> 00:07:55.830
on the return air stream.
00:07:55.830 --> 00:07:58.320
This allows us to recirculate
some of the return air
00:07:58.320 --> 00:08:00.500
into the fresh air,
and the quantities vary
00:08:00.500 --> 00:08:02.230
by using the dampers.
00:08:02.230 --> 00:08:04.880
Not all heat wheel RTUs
will have this feature.
00:08:04.880 --> 00:08:08.710
Some will use only 100%
fresh air intake and extract.
00:08:08.710 --> 00:08:11.210
If the unit doesn't have
the option to recirculate,
00:08:11.210 --> 00:08:14.163
the unit probably will not
have a second filter back here.
00:08:15.135 --> 00:08:17.870
After this, the air will flow
through the heat exchangers
00:08:17.870 --> 00:08:21.380
which will heat or cool the
air to the desired temperature.
00:08:21.380 --> 00:08:23.780
The fan will then distribute
the air through the building
00:08:23.780 --> 00:08:26.223
via the ductwork to the
designated locations.
00:08:27.097 --> 00:08:30.080
The return air is then
pulled back into the RTU
00:08:30.080 --> 00:08:31.413
for the return ductwork.
00:08:32.280 --> 00:08:34.500
Once it re-enters the
RTU, it has the option
00:08:34.500 --> 00:08:36.440
to either recirculate some of the air back
00:08:36.440 --> 00:08:38.920
into the fresh air
intake, otherwise it will
00:08:38.920 --> 00:08:41.590
all pass through a filter and
then through the heat wheel
00:08:41.590 --> 00:08:43.423
to recapture the waste heat.
00:08:44.720 --> 00:08:46.959
After the heat wheel, we
might find an extract fan.
00:08:46.959 --> 00:08:49.850
Otherwise, the pressure
caused by the main supply fan
00:08:49.850 --> 00:08:51.973
will force the air out in some designs.
00:08:53.110 --> 00:08:55.160
The air then passes
through the extract damper
00:08:55.160 --> 00:08:57.750
which is used to vary the
volume of return air mixing
00:08:57.750 --> 00:09:00.440
as well as the pressure
inside the building.
00:09:00.440 --> 00:09:02.800
After that, it passes through
a grille which just stops
00:09:02.800 --> 00:09:05.370
objects and wildlife from
entering into the unit.
00:09:05.370 --> 00:09:08.370
It will then be ejected from
the system into the atmosphere.
00:09:09.420 --> 00:09:11.940
Alright, before we wrap things
up, I just want to remind you
00:09:11.940 --> 00:09:14.690
to sign up for your free
Danfoss Learning profile.
00:09:14.690 --> 00:09:17.660
Doing so, gets you access
to over 1,500 e-lessons
00:09:17.660 --> 00:09:20.210
including several about rooftop units.
00:09:20.210 --> 00:09:21.250
Go give it a try now.
00:09:21.250 --> 00:09:23.810
00:09:23.810 --> 00:09:25.430
Engineers quiz answers.
00:09:25.430 --> 00:09:27.150
At the beginning of the video, I asked you
00:09:27.150 --> 00:09:30.240
what does the term package
air conditioning unit mean.
00:09:30.240 --> 00:09:32.830
The answer is that package
air conditioners contain
00:09:32.830 --> 00:09:35.140
all the main components within one casing.
00:09:35.140 --> 00:09:37.240
So that's the fans, the
filters, the cooling
00:09:37.240 --> 00:09:40.460
and heating coils, the compressors,
the controls, et cetera.
00:09:40.460 --> 00:09:44.640
The entire system is
prefabricated into one package.
00:09:44.640 --> 00:09:46.120
It comes from the manufacturer,
00:09:46.120 --> 00:09:48.780
and can be quickly installed as one unit.
00:09:48.780 --> 00:09:50.390
Okay, guys, that's it for this video.
00:09:50.390 --> 00:09:51.600
Thank you very much for watching.
00:09:51.600 --> 00:09:53.190
I hope you enjoyed this
and it has helped you.
00:09:53.190 --> 00:09:54.440
If so, then please don't forget
00:09:54.440 --> 00:09:55.760
to like, subscribe, and share,
00:09:55.760 --> 00:09:58.230
and leave your questions in
the comments section below.
00:09:58.230 --> 00:10:00.700
You can also follow us on
Facebook, Instagram, Twitter,
00:10:00.700 --> 00:10:02.560
and TheEngineeringMindset.com.
00:10:02.560 --> 00:10:05.227
Once again, thanks for watching.

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