10
Single-Duct and Retrofit Terminal Units IOM
Adjusting Minimums and Maximums
• When adjusting the minimum and maximum airflow
settings, the output responds slowly to changes in the
set point. Wait for the flow rate to stabilize after making
an adjustment (usually 20 to 30 seconds) before making
further adjustments. Also, if the damper position is all
the way closed or open when starting this step, turn the
adjustment one full turn, and then wait 20 to 30 seconds
for a change in the flow reading of the Magnehelic gauge.
If no change occurs after this time, repeat until the flow
rate changes.
LO STAT ΔP Setting
is the desired airflow limit when the thermostat pressure is
less than, or equal to, the reset start point.
•
For DA Cooling or RA Heating: Adjust LO STAT ΔP to the
desired minimum airflow with 0 psig (or a pressure less
than the reset start point) at port “T”. The LO STAT ΔP
must be set first. The LO STAT ΔP will affect the HI STAT
ΔP setting. (Turn Clockwise)
•
For RA Cooling or DA Heating: Adjust LO STAT ΔP to the
desired maximum airflow with 0 psig (or a pressure less
than the reset start point) at port “T”. The LO STAT ΔP
must be set first. The LO STAT ΔP will affect the HI STAT
ΔP setting. (Turn Counter Clockwise)
HI STAT ΔP Setting
is the desired airflow limit when the thermostat pressure
is greater than, or equal to, the reset stop-point. The reset
stop-point is the reset span pressure added to the reset
start point pressure.
• For DA Cooling or RA Heating (See Figure 7): Adjust HI
STAT ΔP to the desired maximum airflow with 20 psig (or
a pressure greater than the reset stop point) at port “T”.
The HI STAT ΔP must be set last. The HI STAT ΔP setting
will be affected by the LO STAT ΔP setting. (Turn Counter
Clockwise)
• For RA Cooling or DA Heating (See Figure 7): Adjust HI
STAT ΔP to the desired minimum airflow with 20 psig (or
a pressure greater than the reset stop point) at port “T”.
The HI STAT ΔP must be set last. The HI STAT ΔP setting will
be affected by the LO STAT ΔP setting. (Turn Clockwise)
NOTES:
•
If the LO STAT ΔP Limit must be set at 0 (zero minimum),
do not turn the LO STAT ΔP knob fully clockwise. The knob
will adjust one and one-half turns after a zero minimum is
reached. Turning the LO STAT ΔP knob fully clockwise will
result in a negative reset condition. This means that when
the controller begins to reset at the reset start point, it
must first overcome the negative adjustment and will
not begin to reset from 0 until a higher thermostat reset
pressure is reached. This negative reset will also reduce
the effective range of the controller by reducing the low
end reset, narrowing the reset span. If a zero minimum is
required, adjust the LO STAT ΔP knob until the controller
just begins to crack the damper open, and then back-off
one-quarter turn and verify zero airflow. (This is typically
2-1/2 knob rotations counter clockwise from the fully
clockwise position.)
•
After the LO STAT ΔP and HI STAT ΔP initial adjustments
are made, cycle the thermostat pressure a few times to
settle the internal reset mechanisms and verify settings.
Fine-tune the settings if necessary. The thermostat
pressure may be left at a high pressure and the “G” port
cap may be removed and replaced to cycle the reset
mechanism.
RESET START Setting
is factory set at 8.0 psig. This is the lowest thermostat
pressure that the LO STAT ΔP airflow will begin to reset
towards the HI STAT ΔP airflow. To change the RESET START
setting; regulate thermostat pressure to the “T” port to
the desired reset start point pressure, adjust RESET START
adjustment until pressure at the “G” port is slightly higher
than 0 psig, i.e., 0.1 psig.
NOTE:
• For Dual Duct Units the Reset Start Must To Be Adjusted
To 3.0 Psig. ON THE HEATING SIDE ONLY.
• The “G” port taps into the controller’s internal reset
chamber, which always starts at 0 psig. The RESET START
adjustment is a positive bias adjustment that sets the
desired thermostat start point to the controller’s internal
reset start point of 0 psig.
RESET SPAN Setting
is factory set at 5.0 psig. This is the required change in
thermostat pressure that the controller will reset between
the LO STAT ΔP setting and the HI STAT ΔP setting. To change
the RESET SPAN setting; adjust RESET SPAN adjustment
until pressure at the “G” port equals the desired reset span
pressure.
(Do Not Adjust)
NOTE:
• The “G” port taps into the controller’s internal reset
chamber, which will always be at a pressure between 0
psig and the RESET SPAN pressure.
Figure 9 – Reset Cycle for CSC 3011 Control
MAX
LO STAT
Δ
P
HI STAT
Δ
P
DA HEATING
ROOM TEMPRATURE
Reset
Span
Reset
Span
Reset
Span
Reset
Span
Δ
Reset Sart*
0
3
8
13 psig
MIN
F
L
O
W
MAX
LO STAT
Δ
P
HI STAT
Δ
P
DA COOLING
RA HEATING
RA COOLING
ROOM TEMPRATURE
Δ
Reset Sart*
0
3
8
13 psig
MIN
F
L
O
W
MAX
LO STAT
Δ
P
HI STAT
Δ
P
ROOM TEMPRATURE
*May require changing the RESET START from 8.0 to 3.0 psig if
sequencing is involved.
Δ
Reset Sart*
0 psig
3
8
13
0 psig
3
8
13
MIN
F
L
O
W
MAX
LO STAT
Δ
P
HI STAT
Δ
P
ROOM TEMPRATURE
Δ
Reset Sart*
MIN
F
L
O
W
