06-06
2.9 EQUIPMENT SIZING CRITERIA
A. LOAD CALCULATIONS: The cooling/heating loads shall be calculated in
accordance with the method outlined in ASHRAE Handbook of
Fundamentals.
B. SAFETY MARGIN: A safety margin of 10% shall be added to the
calculated internal heat gain and loss to allow for any future
increase in internal heat gain or other load demand. The calculated
air quantities for the occupied spaces shall be based on the addition
of the safety margin.
C. AIR LEAKAGE: An allowance of 4% shall be made for the leakage of air
through the ductwork before it reaches the occupied spaces. The
leakage allowance shall be applied to the sum of all individual peak
air quantities without any diversity.
D. STATIC PRESSURE: A safety margin of 10% shall be added to the fan
total static pressure of the system. The static pressure calculations
shall be based on:
1. Actual takeoffs 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 kW (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
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