air conditioning and hvac basics
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Air Conditioning and HVAC BasicsTRANSCRIPT
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Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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Air Conditioning and HVAC Basics
This explanation of air conditioning and HVAC basics will
expand a little bit on the air conditioning cooling
process.
The first topic to discuss about air conditioning and
HVAC basics will be the laws of thermodynamics that
describe how heat moves.
The laws of thermodynamics state that:
1. Heat is a form of energy, and
2. Heat energy will move from a place of high intensity
towards a place of lower intensity.
Kind of like water flowing down-hill, heat energy will
naturally and automatically move from a hot place to a
cooler place.
You don't have to do anything to make it happen.
Just like you don't have to do anything to a natural
magnet to make it work according to the laws of magnetism; you don't
have to do anything to heat to make it move from hot to cold.
The second topic of discussion about air conditioning and HVAC basics will
be about the types of heat: sensible heat and latent heat.
Sensible heat describes how hot something feels; and you measure it with
a thermometer.
Sensible heat is measured in degrees C, F, or K.
Latent heat measures the quantity of heat energy in a substance.
With regards to air conditioning and refrigeration, we need to understand
that latent heat is the heat that a substance absorbs or releases as it
warms, cools, and changes state (evaporates and condenses).
Latent heat is measured in British Thermal Units, or btu.
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Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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When latent heat energy is added to a substance, or when a substance
absorbs latent heat, the substance will feel "warmer".
When latent heat energy is removed from a substance, or when a
substance releases latent heat, the substance will feel "cooler".
1 lb. of water is a standard reference point for latent heat.
It takes 1 btu of latent heat to raise or lower the temperature of 1 lb of
water 1 degree F.
So if 1 lb of water is at 45 degrees F, and warms to 50 degrees F, it will
have absorbed 5 btu of latent heat.
And if that 1 lb of water is warmed to 212 degrees F, it will have absorbed
162 more btu of latent heat.
And now we're at 212 degrees F, the boiling point of water, and something
significant will happen that is an extremely important aspect of air
conditioning and HVAC basics.
By the time the 1 lb of water has totally evaporated, it will have absorbed
970 btu, which is almost 1,000 times more heat energy than it absorbed
warming from 211 to 212 degrees.
970 btu is the latent heat of evaporation of water, or, the amount of heat
energy required to evaporate 1 lb of water.
And when the water vapor, or steam, is cooled back down, it will release
that 970 btu of latent heat as it condenses from steam to water.
Latent heat moves the same way in an air conditioning and refrigeration
system, which is why we have evaporators and condensers in the systems,
So you can see that it is an essential topic when discussing air conditioning
and HVAC basics.
The evaporator is the place in the system where the refrigerant will absorb
immense quantities of latent heat as it evaporates.
It's the "cooling" coil, and absorbs latent heat from the air or water that
flows over it or through it.
The condenser is the place in the system where the refrigerant will release
that latent heat as it cools and condenses.
It will release the latent heat to the air or water that flows over it or
through it.
The third topic of air conditioning and HVAC basics will be the relationship
of pressure to temperature in a sealed system; a sealed container, or
refrigerant piping circuit.
In a sealed system, pressure and temperature follow each other.
If pressure rises, temperature rises. If pressure falls, temperature falls.
If temperature rises, pressure rises, and if temperature falls, pressure falls.
Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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Think of pressure as a lady named Priscilla Pressure, and temperature as a
man named Tommy Temperature.
They're madly in love, and wherever one goes, the other follows.
If Priscilla climbs a hill, Tommy follows.
And if Tommy skis in Aspen, Priscilla is skiing down the slope side by side
with him.
In a sealed system, Tommy Temperature and Priscilla Pressure walk side by
side, hand in hand; and wherever one goes, the other follows.
I emphasize the pressure temperature relationship because it is another
crucial point to comprehend when discussing air conditioning and HVAC
basics.
Because of this relationship, a technician can tell what's happening inside
the refrigerant piping by attatching a set of gauges to the system.
One gauge reads the low side, or suction pressure; and the other gauge
reads the high side, or discharge pressure.
The pressures and temperatures that the gauges indicate are another
important topic when discussing air conditioning and HVAC basics.
The low side gauge is actually reading the pressure of the entire low side of
the system, which is from the outlet of the metering device back to the
suction valve of the compressor.
The way I think of this is; I imagine the evaporator being a glass container,
with the metering device feeding refrigerant liquid in at the bottom, and the
suction line returning refrigerant vapor from the top of the container back
to the compressor.
When the unit is running, and conditions are normal, refrigerant will be
feeding into this container, and will fill it to about 1/2 full, so I imagine it as
about 1/2 full and boiling away, with the boiled off vapor returning to the
compressor.
And I imagine that the low side gauge is reading the pressure in the glass
container exactly at the top surface of the boiling refrigerant.
So the temperature that the gauge or a pressure/temperature chart will
indicate is the temperature right there at the boiling top surface of the
refrigerant.
This is the saturated suction pressure/temperature, and in an R 22 air
conditioning system it is normally around 40 degrees, which is equivalent to
68.5 psi.
The high side gauge is reading the pressure of the entire high side of the
system, which is from the discharge valve of the compressor all the way to
the metering device.
The way I think of this is; I imagine the condenser being a glass container,
with the discharge gas flowing into the top of the container, and the
condensed liquid refrigerant flowing out the liquid line at the bottom of the
container.
Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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When the unit is running, and conditions are normal, refrigerant vapor will
be flowing into this container, cooling and condensing into liquid, and will
fill it to about 1/2 full, so I imagine it as about 1/2 full, with the condensed
liquid flowing out the liquid line at the bottom.
And I imagine that the high side gauge is reading the pressure in the glass
container exactly at the top surface of the condensed refrigerant.
So the temperature that the gauge or a pressure/temperature chart will
indicate is the temperature right there at the top surface of the condensed
refrigerant.
This is the saturated discharge pressure/temperature, and in an R 22 air
conditioning system it should normally be equivalent to ambient outdoor
temperature plus 20 to 30 degrees.
In this section of our discussion of air conditioning and HVAC basics, let's
describe how heat moves in an air conditioning system.
Lets say that the air to be cooled is at 80 degrees when it starts to flow
accross the evaporator.
Since the refrigerant is evaporating at 40 degrees, the heat in the 80
degree air will flow into the 40 degree refrigerant, cool air at about 60 to 65
degrees will flow out of the evaporator, and the refrigerant will totally
evaporate.
Lets also say that the outdoor air flowing accross the condenser is 85
degrees.
The refrigerant vapor will be condensing at about 110 to 120 degrees, so
the heat in the refrigerant will move into the 80 degree air, the air will
leave the condenser at about 105 to 115 degrees, and the refrigerant will
have totally condensed into liquid by the time it leaves the condenser.
The fifth topic of air conditioning and HVAC basics will be compressors.
The compressor is the pump that causes the refrigerant to circulate through
the system.
The compressor is rated to pump a set volume of vapor, so it will have a
set capacity or btu rating, dependng on the refrigerant being used, and the
operating temperature in the evaporator.
The compressor may be a reciprocating type, rotary type, screw type, or
centrifugal type; depending on the capacity of the unit, and whatever
design advantages the engineers might have been trying to optimize for the
unit.
The sixth topic of air conditioning and HVAC basics will be the evaporator.
In the evaporator, the refrigerant is evaporating at a relatively low
pressure, and as it does, it is absorbing latent heat from the air flowing
over the evaporator piping.
The evaporator is the coil that cools the air in an air conditioning system,
and it will have a blower to make the air flow.
Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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The seventh topic of air conditioning and HVAC basics will be the
condenser.
In the condenser, the refrigerant is condensing at a relatively high
pressure, and as it does, the latent heat absorbed in the evaporator is
released to the relatively cool air or water that is flowing over the
condenser piping.
The condenser is the unit usually placed outside the building, and when
running in the cooling mode, relatively hot air will be blowing out of it.
The eighth topic of air conditioning and HVAC basics will be the thermostat.
The thermostat is the switch that turns the unit on to cool or heat the
space.
If you are a home or business owner, and your air conditioning isn't
running, make sure the thermostat is actually turned on before you call for
service.
I have been on service calls, including expensive 1 am emergency overtime
calls, where the only problem was that the thermostat was not turned on to
"cool".
I have to admit, I have also been on service calls where I opened the unit
and started tracing out wiring only to find out that yes, you guessed it, the
thermostat was "off", and I hadn't checked it before starting work.
I hope this introduction to air conditioning and HVAC basics will help you
understand how the system works.
This is exactly the same information that I discuss in deep detail when
teaching air conditioning and HVAC basics in class and on the job.
These are a few of the topics that any air conditioning service technician
must understand very clearly to be able to trouble shoot a system
efficiently.
You might be interested in our Introduction to Refrigeration and Air
Conditioning e book.
It's 2 chapters reproduced from a U S Military training manual; and
discusses refrigeration, and air conditioning and HVAC basics.
It's about 100 pages, so it might take several minutes to download,
depending on your internet access.
If you're looking for troubleshooting information, you'll find some tips on
troubleshooting air conditioning, refrigeration, and chiller systems in our
System Evaluation Guide.
It's a PDF file, so you'll need Acrobat Reader to open it.
Otherwise, a good hardcopy HVAC Book will go into all the details about
these air conditioning and HVAC basics.
I hope this page has helped, and please, feel free to contact us with any
specific HVAC questions you might have, including questions about air
conditioning on Guam, and refrigeration on Guam.
Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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Are you learning the HVAC Trade "on the job"?
If you would be interested in developing your potential to become the
finest HVAC Technician you possibly can by studying a complete,
accredited HVAC Technician course at home; we highly recommend that
you contact Penn Foster Career School and request their free,
no-obligation information brochure.
Requesting the information is easy and only takes 2 minutes; and it
might be the first step towards changing your whole future.
You'll find a brief review of the course on our HVAC Training page.
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Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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Air Conditioning and HVAC Basics: A Simple Explanation. http://www.air-conditioning-and-refrigeration-guide.com/air-condition...
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