Daikin H-Series, Technical Manual

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Selection Process
Selection Process
Drive Package
The following are the design requirements for 2FGN250HY1 unit:
Model: 2FGN250HY1
Supply Air Quantity = 9000 CFM
External Static Pressure = 350 Pa
Step 1: From the fan curve (at 9000 CFM),
Standard operating system;
Internal Static Pressure =
250
Pa
Step 2: Therefore at 9000 CFM and 350 Pa external static pressure,
Total Static Pressure = 250 + 350 Pa
= 600 Pa
Step 3: From the blower curve, the design requirement calls for RPM about 880 RPM.
From the table:
Motor pulley = 90 mm
Blower pulley = 180 mm
Motor RPM = 1440
In order to obtain 880 RPM, we calculate the new blower pulley as:
(while maintaining the motor pulley)
Db = 90 x (1440/880)
= 147.27 mm
Let us take close approximation of 147 mm diameter pulley size
Recheck, with Db =
147 mm
Blower pulley = 1440 x (90/147)
= 882 RPM
We thus need to change the blower pulley from 180 mm to 147 mm in order to obtain the higher operating
static pressure.
Step 4: When the pulley is changed, the V-belt length must be rechecked. We have for horizontal air throw
configuration:
V-belt length, L = 2C + 1.57 (Db + Dm)
= (2x165) + 1.57(120+100) (2x640) + 1.57(147+90)
= 1652.09
We thus can use a belt with a length of 1650 mm
where, C = distance between the centres of the two pulleys
Db = diameter of blower pulley
Dm = diameter of motor pulley
Step 5: From the blower curve, we can also notice that the motor power input has maintained within the current
operating range of the standard unit’s motor.
Summary:
i) Fan motor kW = 5.5 kW
ii) Blower pulley diameter = 147 mm
iii) V-belt size = 1650 mm
Note: Factory supplied rooftop is only with standard drive package.
All other changes are only given as example and need to be field supply.