Air Distribution Systems

The air distribution system is the most neglected component in a normal air conditioning system.  Poor design and workmanship are the rule.  Significant gains in energy efficiency and comfort can be realized with little or no additional cost.

All ducts leak, even new ones.  Air will follow the path of least resistance.  Air leaking from a supply duct in an attic will be replaced by outside air sucked in through a crack or hole somewhere in the building.

Ductless is the ideal solution.  Ductless systems have a fan coil unit directly discharging into each room. 

Install ducts in conditioned spaces where leaks do not draw-in unconditioned raw air.  Ducts can be designed and installed in furr-downs or chases, sealed and insulated, from outside air.  Ducts can be installed in basements that are conditioned and sealed.  Ducts can also be installed in conditioned, insulated attics.

Many supply ducts are undersized or improperly installed.  This creates conditions where the fan must work harder to push air where it needs to go.  The pressure in ducts is called static pressure.  Ducts should be designed for under ½” of static pressure.

The most abused portion of the air distribution system is the return air.  Most return air systems are undersized.  A supply fan that is starved for air cannot cool the space.  Return air grills are usually undersized.  When a homeowner installs a high efficiency filter, additional restrictions reduce the air flow.  Poor maintenance with dirty filters will further restrict air flow.  Many compressors are lost as a result of restricted return air.  Water damage from frozen coils can also result.

Significant energy can be saved by designing the air distribution system for variable flow air delivery vs on off delivery.  Only the amount of air needed to cool the space is delivered. Reducing the speed of a blower motor 10% reduces the energy required 30%.  Variable speed indoor blower motors on a properly designed air distribution system is a good idea.  Air conditioning systems operate at full capacity only a fraction of the time.