12
TABLE 2 – AIRFLOW DELIVERY VS NEGATIVE STATIC PRESSURE AS MEASURED FOR RETURN DUCT OR PLENUM (IN WC)
DUCT
LENGTH
0.05 0.10 0.15 0.20 0.25 0.30
FLEX PIPE FLEX PIPE FLEX PIPE FLEX PIPE FLEX PIPE FLEX PIPE
10 FT 60 65 85 90 105 110 120 125 135 140 150 160
20 FT 55 60 80 85 100 105 115 120 130 135 140 150
30 FT 50 55 75 80 95 100 110 115 125 130 130 140
TABLE 3
Airflow Required >>
20 30 40 50 60 70 80 90 100
Airflow Delivered KNOB SETTINGS (in minutes) FOR AIRFLOW DELIVERED vs AIRFLOW REQUIRED (1 HR CYCLE)
60
20 30 40 50 60
70 80 90 100
80
15 25 30 40 45 55 60
70 75
100
15 20 25 30 35 40 50 55 60
120
10 15 20 25 30 35 40 45 50
140
10 15 15 20 25 30 35 40 45
160
10 10 15 20 25 25 30 35 40
90-968A
STEP 2: DETERMINE THE FRESH AIR DELIVERY RATE
A. Measure the negative static pressure of the return system and consult Table 2 below for approximate inlet airflow.
An airflow measuring device (Nailor-Hart, etc.) will give the airflow exactly.
B. For the table below, the flex duct is laid loose with 2 wide 90° bends, and the damper is fully open. For the rigid pipe, the
values are based on two 90° elbows, and the damper is fully open. For both cases the air intake is through a metal vent hood
with a bird screen. Adjust airflow accordingly for variations.
STEP 3: DETERMINE CYCLE TIME
A. The Cycle Period determines how often the dehumidifier should look to ventilate. This is
variable from 30 minutes to 3 hours (see Figure 13). Once the ventilation requirement is met,
ventilation will not occur until the start of the next Cycle Period.
B. The CYCLE TIME dial determines how long during every Cycle Period the damper will open
and ventilation will occur. The dial can be adjusted from OFF to between 1 to 60 minutes (see
Figure 14). This will give outdoor air ventilation and HVAC fan operation from 1 to 60 minutes
every Cycle Period.
C. Refer to Table 3 to determine the Cycle Time setting based on airflow delivered and airflow
required. The values listed in the table are for a 1 hour Cycle Period. For a 2 hour Cycle Period,
the Cycle Time would be set to twice the value (if in the white area of the table). The values
in the black portion of the table cannot be set due to the 60 minute Cycle Time limit.
FLOAT SWITCH
If the dehumidifier is installed in an attic or another location requiring
leak protection, the unit should be placed in a drain pan with a
normally closed condensate overflow safety switch (also known as a
float switch). The float switch should be wired to the float switch
terminals on the dehumidifier control board. See Figure 18. Remove
the jumper at the float switch terminals. The compressor is disabled
when the float switch is open. The dehumidifier will continue to
ventilate when the float switch is open.
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