58
RT-SVX063E-EN
Direct-Drive Supply Fan Speed
Adjustment
Units equipped with a DDP Supply Fan do not use belt/
sheave arrangements to adjust fan speed.
This adjustment (if required) is made through the Fan
VFD by setting the supply fan Min/Max frequency at
each supply fan VFD using Table 23, p. 58.
Table 23. RPM and Hz ranges for DDP supply fan
speed adjustments
Fan Speed (RPM) VFD Frequency Range (Hz)
Max Min Max Min
2400 888 83 31
2300 851 79 29
2200 814 76 28
2100 777 72 27
2000 740 69 26
1900 703 66 24
1800 666 62 23
1700 629 59 22
1600 592 83 31
1500 555 79 29
1400 518 74 27
1300 481 68 25
1200 444 63 23
Table 23. RPM and Hz ranges for DDP supply fan
speed adjustments (continued)
Fan Speed (RPM) VFD Frequency Range (Hz)
Max Min Max Min
1100 407 58 21
1000 370 53 20
NNoottee:: Maximum operating speed cannot exceed fan
wheel mechanical limit.
System Airflow Measurements
VAV and CV Systems with DDP Supply
Fan and Motorized Impeller Relief Fan
(optional)
Supply and Relief Airflow Measurement
Piezometer pressure taps are available to measure
supply and relief airflow. Piezometer pressure taps can
interface with customer-supplied airflow monitoring
systems using the F or K-factors and equation shown in
the tables below. Attach one end of the pressure
differential gauge to a connection in the fan cone
throat, and the second to the fan inlet plate to read
pressure immediately upstream of the fan.
Table 24. Piezo airflow calculation
Unit
Fan
dia, in
F C1 A
20,25,30
16.5 1518.6 753.06 0.55
40,50,55
18.2 1821.9 692.03 0.72
20,25,30,-
40,50,55
20 2185.8 692.03 0.87
20,25,30,-
60,70,75
22.2 2713.9 692.03 1.07
40,50,55
24.5 3285 692.03 1.3
60,70,75
27 3397.6 692.03 1.58
Notes:
1. Measure pressure from inlet side of fan to piezo
tap at the cone throat.
2. Fan inlet will be the high pressure side.
3. dP can be up to 25 in h
2
0.
4. Coefficients are for one fan. For two fans double
result or F and C1 values.
5. For standard density of 0.075 lb/ft^3, Supply Fan
CFM = CFM = F * √ dP
6. For non-standard density, Supply Fan CFM = CFM
= C1 * A * √ (dP / ρ), where dP is the piezo
pressure differential and rho is the actual air
density.
SSttaarrttuupp tthhee UUnniitt
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