Civil Engineering Reference
In-Depth Information
pumps or electric preheat strip (if it is used for freeze protection instead of hot water
coil) in air handling unit, and hot water pumps or electric reheat strip (if it is used
for dehumidifi cation or heating instead of hot water coil). Duct air leakage, heat
transfer from ducts, and effi ciency loss in water coils are other sources that can
indirectly increase the energy consumption of the system. The small energy con-
sumed by the low-voltage power provided for control valves and dampers is the
other source of energy consumption.
8.12.3
Variable Air Volume System with Variable Volume
Terminal Units with Reheat
This system (Fig.
8.6
) is made of a central variable volume supply fan that supplies
conditioned air to all the room's variable air volume terminal units through a
medium pressure duct network. Quantity and temperature of the mixture of the air
which is delivered to each room is designed based on the room sensible load, the
quantity and temperature of the outdoor air in the mixture, and space thermostat
setting. The exiting air from all the spaces goes back to the air handling unit as
return air stream usually with the help of a return/exhaust fan. A variable frequency
drive modulates the supply fan to provide air fl ow equal to the sum of all the
terminal units' airfl ow in every instant. (Terminal units are also equipped with
Fig. 8.6
Variable air volume system with variable volume terminal units with reheat
