5.1.3 Air side system
An FCU system allows individual small areas to operate independently to suit the cooling demand and operation
schedule. Independent FCU control is recommended to enable better environmental control of zones without over-
cooling. Meanwhile, FCUs should be switched off or set to operate at a higher temperature during unoccupied periods.
For large spaces such as arcades and public areas in shopping malls, central all-air system by using AHU is
recommended. To minimise power consumption by the fans, the air distribution ductwork should be sufficiently sized to
avoid high air resistance. Meanwhile, various energy saving features, such as free cooling, heat wheels,
and multi-speed motors, should be considered wherever viable. A comparison of various
energy saving schemes for an AHU are listed for reference.
Items
Energy saving schemes
Multi-speed motor
Free cooling
Heat wheel
Desiccant
dehumidifier
Brief description Operation of fan and
AHU at reduced
capacity
Cooling by 100% fresh
air in cold weather
conditions
Recovery of waste
cooling energy from
building exhaust
R.H. control method
other than re-heat
Saving objectives Fan power
Year-round cooling
energy
Cooling energy for
fresh air
Avoid simultaneous
cooling and heating
Application
High fluctuation of
occupant level
AHU room space and
louver is available
High building exhaust
rate and exhaust
system centrally
allocated
R.H. control is essential
and plant space is
available.
Season of operation Any period when
occupant level is low
Mild and cold season Hot season
Wet season
Cost
Minimal
Relatively low
Relatively high
Relatively high
Plant area
No extra plant space Extra space for
accommodation of
bulky ductwork and
exhaust air fan
Extra space for
accommodation of heat
wheel, central fresh air
and exhaust fans.
Extra space for
accommodation of
dehumidification
equipment
Other architectural
implication
Nil
Extra louver area
Nil
Nil
Figure 105 Comparison of different energy saving schemes for air handling unit (AHU)
5
Energy efficient building systems for shopping malls and shop spaces
5.1
Heating, ventilation and air-conditioning (HVAC)
128 Hong Kong Green Shop Guide
