Free hvac lessons

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• 

  Eng.Nescafee

  Lesson#1 Introduction to HVAC systems
  
  In this lesson we will talk about:
  
  · The goal of HVAC system.
  
  · Comfort requirements.
  
  · Dissecting HVAC system to loops.
  
  1.The goal of HVAC system:
  
  The goal of the heating, ventilating, and air conditioning (HVAC) system is to create and maintain a comfortable environment within a building.
  
  
  2- Comfort Requirements:
  
  A comfortable environment, however, is broader than just temperature and humidity. Comfort requirements that are typically impacted by the HVAC system include:
  
  · Dry bulb temperature
  · Humidity
  · Air movement
  · Fresh air
  · Cleanliness of the air
  · Noise levels
  
  
  3- Dissecting HVAC system:
  
  Dissecting HVAC system is a method for understanding the components of different types of HVAC system.
  
  The premise of this method is that any HVAC system can be dissected into basic subsystems will be referred to "loops".
  
  There are five primary loops that can describe any type of HVAC systems:
  · Air side loop.
  · Chilled water loop.
  · Refrigeration loop.
  · Heat rejection loop.
  · Control loop.
  
  #-Link-Snipped-#
  #-Link-Snipped-#
  Please note that not every system will use all five loops.
  
  
  Now this lesson is finished write your questions about this lesson in the comments below we will talk in the next lesson about every loop in details see you soon
  To View Lesson#1 Source you can Enterhvac-worldhvac-world
• 

  Kaustubh Katdare

  Guys, I guess the lessons are being copied from some source. We'd appreciate if you could write your own tutorials.
• 

  Eng.Nescafee

  various sources
  
  really i have many sources on my lessons but i write the lesson in my own way after i read it and understand it and i have many sources i choose the source that i see it will be useful to you (Understand me)
• 

  Tkelly

  Very nicely, compilled & usefull data for HVAC tech. people.
  
  Tom
  
  
• 

  gohm

  I work a lot with designing HVAC systems as well for any help/questions
• 

  Eng.Nescafee

  gohm

  I work a lot with designing HVAC systems as well for any help/questions

  thank you for your replay sure i will need you
• 

  Eng.Nescafee

  Lesson#2 Air side loop - 1
  
  - In the previous lesson we talked about:

  
  ·The goal of HVAC system.
  · Comfort requirements.
  · Dissecting HVAC system to loops.
  
  - In this lesson we will dissecting air side loop to 3 components as the following:
  
  · Conditioned space.
  · Supply fan and filter.
  · Cooling Coil.
  
  - After dissecting the air side loop to these components we will talk about each component in details
  
  
  
  1.Conditioned space:
  
  1.1 Dry bulb temperature& humidity:
  
  In order to maintain the dry bulb temperature in the conditioned space Sensible heat must be added or removed at the same rate as it leaves or entered the space.
  
  To maintain humidity level in the conditioned space latent heat must be added or removed at the same rate as it leaves or enter the space.
  
  Most HVAC systems deliver conditioned (heated, cooled, humidified or dehumidified) air to the conditioned space to add or remove sensible, latent Heat to or from the conditioned space.
  
  In this lesson we will talk about cooling mode only, we will talk about heating mode later
  
  The conditioned air is called supply air, the air that carries the sensible and latent heat out of the space is called return air.
  
  
  Air+side.bmp (image)
  
  
  In the cooling mode the supply air absorbs sensible and latent heat from the conditioned space.
  
  The amount of sensible and latent heat absorbed depend on temperature and humidity as will as the quantity of the supply air
  Assuming a fixed quantity of supply air , if the supply air is cooler it can remove more sensible heat from the conditioned space ,if the supply air is drier it can remove more latent heat from the space.
  
  1.2 Overview of cooling load components:
  
  In order to determine how much supply air is needed for a given space, how cold and dry it must be it must to determine the rate at which sensible And latent heat enters the conditioned space.
  
  The figure below shows the typical sources of sensible and latent heat which are commonly called room cooling loads:
  
  ·Conduction heat gain from outdoors through glass windows and skylights.
  ·Solar radiation heat gain through glass windows and skylights.
  ·Combined conduction and solar radiation heat gain to external walls and roofs.
  ·Conduction heat gain through the ceiling, internal Partitions and floors.
  ·Internal heat gain generated by people, lights, appliances and equipments in the space.
  ·Heat gain from infiltrating into the space from outdoors.​

  Cooling+load+components.JPG (image)

  
  In addition to those sources displayed on the figure there is other common sources of sensible and latent heat sources:
  
  ·Heat gain from outdoor air deliberately brought into the building for ventilation purposes.
  ·Heat generated by fans and motors in the system.
  ·Conduction heat gain through ducts
  For further information on the various components of building cooling loads refers to later lessons.
  
  2.Supply fan and filter:
  
  The next component of the airside loop is a supply fan that delivers the supply Air (SA) to the space. In the example in the Figure below, air is supplied to theConditioned space to maintain a desired temperature of 75ºF (23.9ºC) and relative humidity 50% in the space (we neglected the cooling coil in this figure; we will explain it in the next component of the air side loop).​

  Supply+fan+and+filter.JPG (image)
  This same supply fan is often used to also draw the return air out of the space.
  

  
  Alternatively, some systems use a second fan, called a return fan, to draw air from the space and move it back to the equipment that contains the supply fan.
  
  
  Another one of the comfort requirements is to provide an adequate amount of Fresh, outdoor air to the space. In this example, the required amount of outdoor air (OA) for ventilation is brought into the building and mixed with the recirculated portion of the return air (RA).
  
  
  The remaining return air, that which has been replaced by outdoor air, is exhausted as exhaust air (EA) from the building, often by an exhaust (or relief) fan.
  
  
  In this example, outdoor air at 95ºF (35ºC) dry bulb mixes with recirculated return air at 75ºF (23.9ºC) dry bulb. This mixture contains 25 percent outdoor air and 75 percent recirculated air, so the resulting temperature of the mixed air (MA) is 80ºF (26.7ºC) dry bulb.
  
  
  Another comfort requirement is to ensure that the air in the conditioned space is clean, the mixed air passes through a filter to remove many of the airborne contaminants.
  
  
  
  3.Cooling coil:
  
  the supply air must be cold enough to absorb excess sensible heat from the space and dry enough to absorb excess moisture (latent heat).
  
  
  A heat exchanger, commonly known as a cooling coil, is often used to cool and dehumidify the supply air before it is delivered to the space.
  
  
  In this example in the figure below, the cooling coil cools and dehumidifies the entering mixed air from 80ºF (26.7ºC) dry bulb to a supply-air temperature of 55ºF (12.8ºC) dry bulb.​

  Cooling+coil.JPG (image)

  
  
  
  
  A typical cooling coil includes rows of tubes passing through sheets of formed fins. A cold fluid, either water or liquid refrigerant, enters one header at the end of the coil and then flows through the tubes, cooling both the tubes and the fins.
  
  
  Another Figure shows an example of a cooling coil that has chilled water flowing Through it. As the warm, humid mixed air passes through the coil, it comes into contact with the cold tubes and fins. Sensible heat is transferred from the air to the fluid inside the tubes, causing the air to be cooled.​

  cooling+coil+2.JPG (image)

  
  
  
  
  Additionally, if the outside surface temperature of the tubes and fins is below the dew-point temperature of the entering air, moisture contained in the air will condense on the tubes and fins.​

  
  This condensed liquid then flows down the fin surfaces into a drain pan located under the coil, and is piped away. The air (supply air) leaving the coil is colder and drier than when it entered.​

  
  
  ** Now this lesson is finished write your questions about this lesson in the comments below in the next lesson we will complete the air side loop subject see you soon
  
  
  To View the source Lesson2 you can enter hvac-world
  ​
• 

  Eng.Nescafee

  Lesson#3 Air Side Loop-2
  
  - In the previous lesson we talked about:

  
  ·The goal of HVAC system.
  · Comfort requirements.
  · Dissecting HVAC system to loops.
  
  - In this lesson we will dissecting air side loop to 3 components as the following:
  
  · Conditioned space.
  · Supply fan and filter.
  · Cooling Coil.
  
  - After dissecting the air side loop to these components we will talk about each component in details
  
  
  
  1.Conditioned space:
  
  1.1 Dry bulb temperature& humidity:
  
  In order to maintain the dry bulb temperature in the conditioned space Sensible heat must be added or removed at the same rate as it leaves or entered the space.
  
  To maintain humidity level in the conditioned space latent heat must be added or removed at the same rate as it leaves or enter the space.
  
  Most HVAC systems deliver conditioned (heated, cooled, humidified or dehumidified) air to the conditioned space to add or remove sensible, latent Heat to or from the conditioned space.
  
  In this lesson we will talk about cooling mode only, we will talk about heating mode later
  
  The conditioned air is called supply air, the air that carries the sensible and latent heat out of the space is called return air.
  
  
  Air+side.bmp (image)
  
  
  In the cooling mode the supply air absorbs sensible and latent heat from the conditioned space.
  
  The amount of sensible and latent heat absorbed depend on temperature and humidity as will as the quantity of the supply air
  Assuming a fixed quantity of supply air , if the supply air is cooler it can remove more sensible heat from the conditioned space ,if the supply air is drier it can remove more latent heat from the space.
  
  1.2 Overview of cooling load components:
  
  In order to determine how much supply air is needed for a given space, how cold and dry it must be it must to determine the rate at which sensible And latent heat enters the conditioned space.
  
  The figure below shows the typical sources of sensible and latent heat which are commonly called room cooling loads:
  
  ·Conduction heat gain from outdoors through glass windows and skylights.
  ·Solar radiation heat gain through glass windows and skylights.
  ·Combined conduction and solar radiation heat gain to external walls and roofs.
  ·Conduction heat gain through the ceiling, internal Partitions and floors.
  ·Internal heat gain generated by people, lights, appliances and equipments in the space.
  ·Heat gain from infiltrating into the space from outdoors.​

  Cooling+load+components.JPG (image)

  
  In addition to those sources displayed on the figure there is other common sources of sensible and latent heat sources:
  
  ·Heat gain from outdoor air deliberately brought into the building for ventilation purposes.
  ·Heat generated by fans and motors in the system.
  ·Conduction heat gain through ducts
  For further information on the various components of building cooling loads refers to later lessons.
  
  2.Supply fan and filter:
  
  The next component of the airside loop is a supply fan that delivers the supply Air (SA) to the space. In the example in the Figure below, air is supplied to theConditioned space to maintain a desired temperature of 75ºF (23.9ºC) and relative humidity 50% in the space (we neglected the cooling coil in this figure; we will explain it in the next component of the air side loop).
  Supply+fan+and+filter.JPG (image)This same supply fan is often used to also draw the return air out of the space.
  
  
  Alternatively, some systems use a second fan, called a return fan, to draw air from the space and move it back to the equipment that contains the supply fan.
  
  
  Another one of the comfort requirements is to provide an adequate amount of Fresh, outdoor air to the space. In this example, the required amount of outdoor air (OA) for ventilation is brought into the building and mixed with the recirculated portion of the return air (RA).
  
  
  The remaining return air, that which has been replaced by outdoor air, is exhausted as exhaust air (EA) from the building, often by an exhaust (or relief) fan.
  
  
  In this example, outdoor air at 95ºF (35ºC) dry bulb mixes with recirculated return air at 75ºF (23.9ºC) dry bulb. This mixture contains 25 percent outdoor air and 75 percent recirculated air, so the resulting temperature of the mixed air (MA) is 80ºF (26.7ºC) dry bulb.
  
  
  Another comfort requirement is to ensure that the air in the conditioned space is clean, the mixed air passes through a filter to remove many of the airborne contaminants.
  
  
  3.Cooling coil:
  
  the supply air must be cold enough to absorb excess sensible heat from the space and dry enough to absorb excess moisture (latent heat).
  
  
  A heat exchanger, commonly known as a cooling coil, is often used to cool and dehumidify the supply air before it is delivered to the space.
  
  
  In this example in the figure below, the cooling coil cools and dehumidifies the entering mixed air from 80ºF (26.7ºC) dry bulb to a supply-air temperature of 55ºF (12.8ºC) dry bulb.​

  Cooling+coil.JPG (image)

  
  
  
  
  A typical cooling coil includes rows of tubes passing through sheets of formed fins. A cold fluid, either water or liquid refrigerant, enters one header at the end of the coil and then flows through the tubes, cooling both the tubes and the fins.
  
  
  Another Figure shows an example of a cooling coil that has chilled water flowing Through it. As the warm, humid mixed air passes through the coil, it comes into contact with the cold tubes and fins. Sensible heat is transferred from the air to the fluid inside the tubes, causing the air to be cooled.​

  cooling+coil+2.JPG (image)

  
  
  
  
  Additionally, if the outside surface temperature of the tubes and fins is below the dew-point temperature of the entering air, moisture contained in the air will condense on the tubes and fins.​

  
  
  This condensed liquid then flows down the fin surfaces into a drain pan located under the coil, and is piped away. The air (supply air) leaving the coil is colder and drier than when it entered.​

  
  
  
  
  ** Now this lesson is finished write your questions about this lesson in the comments below in the next lesson we will complete the air side loop subject see you soon
  
  
  Source:hvac-world ​
• 

  raj87verma88

  Good initiative buddy and an equally good tutorial. Keep up with the good work.
• 

  Eng.Nescafee

  Lesson#4 Air Side Loop-3
  
  In the previous lesson we had talked about the part load operation in the air side loop as the following:
  
  
  

  • A constant quantity of the supply air and a variable supply temperature [Constant-volume system] .

  
  

  • A variable quantity of the supply air and a constant supply temperature [variable-air volume(VAV system)].

  
  In this lesson we will talk about an examples of the air side loop as the following:
  
  
  

  • The fan coil unit.

  
  

  • The air handling unit

  
  1-Fan coil unit:
  
  

  The figure bellow illustrate an example of a vertical fan coil unit that would be installed in the conditioned space .
  [Note: The fan coil unit which illustrated in this figure is the wall type which installed on the wall not the horizontal concealed type which installed above the false ceiling]
  ​

  
  fan+coil+unit.JPG (image)The return air from the space is drawn in the unit at the base and can be mixed with outdoor air that enters through a separate damper in the back of the unit.
  [Note:The outdoor air is not at this figure]
  
  The mixed air passes through a filter, supply fan and cooling coil before being discharged from the top of the unit, directly into the conditioned space.
  
  2-Air handling unit:
  
  The figure below illustrate anther example of the air side loop is a central air handling unit
  
  air+handling+unit.JPG (image)
  A central air handler is typically installed outside the conditioned space possibly on the roof or in a dedicated mechanical room
  
  The return air from the space is drawn into the return air dampers and mixes with outdoor air that enters through another set of dampers
  
  The mixed air passes through the filters,the supply fan and the cooling coil before discharged from the air handler
  
  the central air handlers needs a method for delivering the supply air to the conditioned space.A supply air distribution system,typically constructed of a sheet metal ducts,fittings and diffusers is used to direct the supply air from the central air handler to one or more conditioned space.
  [Note:sometimes fan coil units need an air distribution system when it used in a large conditioned space to provide good air distribution in the space]
  
  The figure below illustrate a central handler and duct work which deliver the supply air to multiple VAV terminal units.
  air+distribuation.JPG (image)
  From each VAV terminal unit the supply air travels through a section of flexible duct to remotely located diffuser.Diffuser are used to distribute the supply air effectively to the conditioned space.
  
  Proper air diffusion as an important comfort consideration,especially in VAV systems,to avoid dumping cold supply air on the occupants of the space.
  
  In the figure below,air returns from the conditioned space to the central air handler through an open ceiling plenum.The plenum is the space between the ceiling and the roof or the above floor
  
  air.JPG (image)In some special applications a separate return air duct system may be required to direct the return air back to the air handler
  
  [FONT="]** Now this lesson is finished write your questions about this lesson in the comments below in the next lesson we will begin talking about the chilled water loop see you soon.
  
  Source:hvac-world
  [/FONT]
• 

  ShrinkDWorld

  😁😁😁😁😁😁
  THANKSS
  
  realy great work
• 

  gohm

  How about vav versus piu/fit(fan induction terminal)?
  
  cv(constant volume) versus vfd(variable frequency drive) units?
• 

  Eng.Nescafee

  i can,t understand your question can u explain more???
• 

  gohm

  Sure! Can you explain the differences between VAVs and PIU/FIT units? Give the pros and cons for both.
  
  Also, please share with us the differences between constant volume units and variable frequecy drive units.
  
  These both could be some good info to continue with your great thread.
• 

  Eng.Nescafee

  sure i will display the diffrences in uniquie lesson to can explain it in details
  
  Best regards;
  Eng.Mohamed Fawzy
• 

  Eng.Nescafee

  In the previous lesson hvac-world we had finished the air side loop which had been explained trough hvac-world,hvac-world andhvac-world
  
  In this lesson we will start the explanation of the second loop of the H.V.A.C. systems which called "Chilled Water Loop" as we mentioned in hvac-world
  
  We will dissecting the chilled water loop to 3 components as the following :
  
  
  

  • Cooling Coil.

  
  

  • Evaporator.

  
  

  • Pump and control valve.

  1-Cooling Coil :
  
  In hvac-world, a cooling coil is used to cool and dehumidify the supply air.as mentioned,the cold fluid flowing through the tubes of the coil may be either water or liquid refrigerant.
  
  Heat energy flows from a higher-temperature substance to lower-temperature substance .Therefore,in order for heat to be transferred from the air,the fluid flowing through the tubes of the cooling coil must be colder than the air passing over the tubes and fins.
  untitled.JPG (image)In the figure above chilled water at (42 F) flows through the coil,absorbing heat from the air.the water leaves the coil at a warmer temperature (57 F) .
  
  It has also mentioned that the water flowing through the cooling coil must be colder than the air passing through it.
  
  2-Evaporator:
  
  The evaporator is used to cool the water that returns from the coil at (57 F) back to the desired supply water temperature at (42 F) .the cool process is shown in the figure below.
  
  
  untitled.JPG (image)3-Pump and control valve:
  
  The third component of the chilled-water loop is a pump that moves water around the loop.This
  pump needs to have enough power to move the water through the piping,the evaporator,the tubes of the coil and any other accessories installed in the chilled water loop.the figure below shows the pump in the chilled water loop.
  
  untitled.JPG (image)
  Similar to hvac-world,the chilled water loop responds to changing cooling loads by varying either the temperature or the quantity of water delivered to the cooling coil.
  
  the most common method,however,is to vary the quantity of water flowing through the cooling coil by using a control valve.
  
  As the cooling load decreases,the modulating control valve reduces the rate of chilled water flowing through the coil,decreasing its coil capacity.
  
  At part-load conditions,a two way control valve reduces the rate of chilled-water flow through the coil.
  
  A three way control valve also reduces the rate of flow through the coil,but it bypasses the excess water to mix downstream with the water that flows through the coil.
  
  untitled.JPG (image)With a three-way valve,the quantity of water flowing through the system(water flowing through the coil plus water bypassing the coil) is constant at all loads.
  
  With the two way valve,the water flowing through the system varies,which allows the pump to reduce its capacity and save energy at part load.
  
  Important Note:
  The control valve is located at the downstream of the cooling coil to ensure that the tubes inside the coil are always full of water.if the valve located upstream of the cooling coil may modulate the water to the point which the water just trickles"very low flow"through the tubes and not filling the entire tube diameter,The result is bad heat transfer between the supply air and the cooling coil.
  
  [FONT= ]** Now this lesson is finished write your questions about this lesson in the comments below in the next lesson we will complete the chilled water loop topic see you soon[/FONT]
• 

  habeebknm

  Dear all, i want know what are the two things which controld by Double Regulating Valve ( DRV)/what is the meaning of double regulation???