Aprilaire 1750A Installation Instructions Manual page 16

VENTIlATION OR AIR CyClING
DETERMINE fRESH AIR DElIVERy RATE
1 . Measure the negative static pressure of the return system at the location where the outdoor air duct enters the return duct .
2 . See Table 4 for estimated inlet airflow in CFM, based on duct type, length, and available negative pressure . Use an airflow measuring device
for a more accurate airflow delivery rate .
3 . Record the Delivered CFM . __________
TAblE 4 – CfM Delivered
Duct length 0.05
flex
10 ft. 60
20 ft. 55
30 ft. 50
Note: For the table above, 6" flex duct is laid loose with two, wide 90° bends and a fully opened damper . Rigid pipe values are based on 6" duct,
two 90° elbows, and a fully open damper . In both cases, the air intake is through a metal vent hood with inlet screen . Airflow may need to be
adjusted up or down for variations in duct work .
DETERMINE CyClE TIME
1 . Use the Required CFM and Delivered CFM from the above steps to determine the Cycle Time from Table 5 .
2 . The values are listed for a 1 hour Cycle Period . For a 2 hour Cycle Period, set the Cycle Time to twice the values listed in Table 5 .
3 . The values highlighted in gray cannot be set due to the maximum 60 minute Cycle Time . A second ventilation device (i .e ., bigger duct or
second duct) will be required to meet ventilation needs .
TAblE 5 – Cycle Time Setting (minutes) for Airflow Delivered vs. Airflow Required for 1 hour Cycle
CfM Delivered
20
60 20
80 15
100
15
120 10
140 10
160 10
16
(CONTINUED)
Negative Static Pressure ("w.c.) as Measured for Return Duct or Plenum
0.1
Pipe flex Pipe
65 85 90
60 80 85
55 75 80
30 40
30 40
25 30
20 25
15 20
15 15
10 15
0.15 0.2
flex Pipe flex
105 110 120
100 105 115
95 100 110
CfM Required
50 60
50 60
40 45
30 35
25 30
20 25
20 25
0.25
Pipe flex Pipe
125 135 140
120 130 135
115 125 130
70 80 90
70 80 90
55 60 70
40 50 55
35 40 45
30 35 40
25 30 35
0.3
flex Pipe
150 160
140 150
130 140
100
100
75
60
50
45
40