Air Distribution Arrangements

Air Distribution Arrangements

Types

Single Duct

Single zone
Terminal Reheat
Induction Reheat
Multi Zone
Bypass multi zone

Dual Duct

 

*Note: The above distribution system arrangements can be constant volume or variable volume type air flow

Single Duct – Single Zone Distribution
-Simplest form of system

-Most inexpensive

-Responds only to 1 zone or space condition

-Can be single or dual fan

-Can incorporate re-heat coils for de-humidification

-Economizers can be used

-Constant or variable volume

-Energy efficiency = good





Single Duct – Terminal Reheat Distribution
-Modification of single zone

-Air and water system

-Responds to multiple zones or space conditions

-Can be single or dual fan

-Incorporates a re-heat coil at each zone for individual temp control

-Terminal box can be: Reheat unit (medium velocity) or induction unit (high velocity)

-Economizers can be used

-Energy efficiency is poor

-*Note: Induction units were designed for use in exterior rooms of multi story buildings where a high sensible loss occurs yet at the same time cooling is required in the interior of the building

-Terminology:
-Primary Air: Supply from main plenum
-Secondary Air: Room induced from primary



Single Duct – Multi Zone Distribution
- Modification of a single duct system

-All air system

-Two separate plenums: 1 heating/ 1 cooling

-Responds to multi zone or space conditions

-Hot deck temp is determined by outdoor stat

-Cold deck is maintained at 55°F

-Zone air is mixed by zone mixing dampers located with in the main plenum

-One supply duct to each zone

-Economizers can be used

-Fan arrangement – Blow thru

-Induction unit not normally used

-Constant Volume



Single Duct – Bypass Multi Zone Distribution
- Modification of a single duct system

-Air + water system

-Two separate plenums: 1 for cooling / 1 for heating

-Cold deck maintained at 55°F

-Responds to multi zone or space temp

-Normally used in milder climates because it uses return air heated by space or zones as primary heat. If further heat is required the system is equipped with terminal reheat coils located at terminal box of each zone

-Terminal type could be induction type

-Fan arrangement = Draw thru

-Constant volume
Dual Duct System
-Most expensive type of system

-All air system

-Responds to unlimited number of zones or condition spaces

-Fan arrangements: Hot deck / Cold deck

-Mixing boxes located at each zone

-Economizers are not recommended

-Single or dual fan








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