Quantcast Types of Duct Systems - 14279_281

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Q39. Q40. Q41. Q42. Q43. Q44. Q45. What  is  the  most  important  thing  you  should know before you perform a diagnosis on a system problem? A  refrigerant  leak  appears  in  what  way  at  the point of the leak? What  is  the  most  common  cause  of  leaks  on automotive air-conditioning systems? For a refrigerant to be a suitable flushing agent, it  must  remain  in  what  state  during  flushing operations? Which  part  of  an  automotive  air-conditioning system  is  replaced  because  it  is  impossible  to clean? A type IV certification is also known as what type of certification? Who   approves   organizations   to   certify technicians? DUCTWORK Learning  Objective:  Understand  the  basic  types of  ductwork  systems  and  the  components  of  those systems for distribution of conditioned air. Distributed  air  must  be  clean,  provide  the  proper amount of ventilation, and absorb enough heat to cool the  conditioned  spaces.  To  deliver  air  to  the conditioned space, air carriers are required, which are called  ducts.  Ducts  work  on  the  principle  of  air pressure difference. If a pressure difference exists, air will flow from an area of high pressure to an area of low pressure.  The  larger  this  difference,  the  faster  the  air will flow to the low-pressure area. CLASSIFICATION  OF  DUCTS There  are  three  common  classifications  of ducts—conditioned  air  ducts,  recirculating-air  ducts, and   fresh-air   ducts.   Conditioned   air   ducts   carry conditioned air from the air conditioner and distribute it to the conditioned area. Recirculating air ducts take air  from  the  conditioned  space  and  distribute  it  back into  the  air  conditioner  system.  Fresh  air  ducts  bring fresh air into the air-conditioning system from outside the  conditioned  space. Ducts  commonly  used  for  carrying  air  are  of  a round, square, or rectangular shape. The most efficient duct is a round duct, based on the volume of air handled per perimeter distance. In other words, less material is needed for the same capacity as a square or rectangular duct. Square  or  rectangular  duct  fits  better  to  building construction. It fits above ceilings and into walls and is much easier to install between joists and studs. TYPES OF DUCT SYSTEMS There are several types of supply duct systems (fig. 7-42) that deliver air to room(s) and then return the air from  the  room(s)  to  the  cooling  (evaporator)  system. These supply systems can be grouped into four types: 1. Individual round pipe system 2. Extended plenum system 3. Reducing trunk system 4. Combination (of two or more systems) Return  air  systems  are  normally  of  three types—single  return,  multiple  return  (fig.  7-42),  or combination of the two systems. CONSTRUCTION Ducts may be made of metal, wood, ceramic, and plastic. Most commonly used is sheet steel coated with zinc  (galvanized  steel).  Sheet  metal  brakes  and forming   machines   are   used   in   fabricating   ducts. Elbows  and  other  connections,  such  as  branches,  are designed  using  geometric  principles.  Some  types  of duct connections used in constructing duct systems are shown in figure 7-43. Sheet metal ducts expand and contract as they heat and  cool.  Fabric  joints  are  often  used  to  absorb  this movement. Fabric joints should also be used where the duct  connects  to  the  air  conditioner.  Many  ducts  are insulated to lower noise and reduce heat transfer. The insulation  can  be  on  the  inside  or  the  outside  of  the duct. Adhesives or metal clips are commonly used to fasten the insulation to the duct. As we are only briefly discussing  construction  here,  you  can  find  construc- tion  and  fabrication  methods  in  the  Steelworker, volume  2.  It  details  design  and  fabrication  of  steel ductwork. 7-43



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