06-06
1. Actual take-offs from the system layout drawings, that is, without
any approximation for fittings, system components, etc.
2. Equal friction or static regain method.
E. FAN AND MOTOR SELECTION: The brake horse power (BHP) calculated on
the basis of total air quantity and fan static pressure shall be
increased by 10% to account for drive losses and field conditions.
The motor selection shall make an allowance for:
1. Altitude
2. Temperature
3. Inlet/Outlet Conditions
4. System Effect Factors Per AMCA 210
The fan(s) shall be selected to operate in the stable region at or
near the maximum static efficiency.
F. REFRIGERATION EQUIPMENT SIZING:
1. Select cooling capacity on the basis of a psychrometric chart for
each air handling unit where the fan motor heat gain for the supply
and return air fans is accounted for.
2. When extensive chilled water or refrigerant piping is involved,
system losses and its impact on the cooling coil selection shall also
be evaluated.
3. Additional safety margin is not required.
2.10 DUCT SIZING CRITERIA
A. LOW VELOCITY DUCTWORK: All supply air ductwork on the downstream side
of the air terminal units, all return air ductwork, and all exhaust
air ductwork shall be low velocity/low pressure type.
The maximum
air velocity and static pressure drop shall be limited to 7.6 m/s
(1,500 feet per minute) and 25 Pa (0.1 Inch Water Gage (WG) per 30 m
(100 equivalent feet) of duct length, respectively. The supply air
ductwork between the fan discharge and the inlet of the air terminal
units shall be low velocity design unless the conditions do not
permit so.
B. MEDIUM VELOCITY DUCTWORK: The supply air ductwork between the fan
discharge and inlet to the air terminal units can be medium velocity
type.
Medium velocity ductwork shall be used only if the available
space conditions can not accommodate low velocity duct sizes.
The
maximum velocity and the static pressure drop shall be limited to 13
m/s (2,500 fpm) and 63 Pa (0.25 inch water gage) per 30 m (100
equivalent feet) of duct length, respectively.
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