Unit Options
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IM 926-3 • ROOFPAK APPLIED SYSTEMS
Field Output Signals
The following outputs may be available for field connections to
a suitable device.
Entering Fan Temperature Sensor
The entering fan temperature (EFT) sensor and an associated
“Lo Airflow Problem” alarm are provided on VAV units with
MicroTech III control and gas or electric heat. The EFT sensor
is located in the supply fan section of the unit at the supply air
funnel.
Heat is disabled whenever the airflow is detected to be too low
for safe heating operation. This condition is indicated when the
supply air temperature exceeds the mixed air temperature by
more than 60°F (16°C).
NOTE:
This value is not always 60°F. It depends on whether
the unit is gas or electric heat and on the burner/
baffling arrangement on gas heat units.
In this case, a “Lo Airflow Problem” alarm is generated and
heat is not enabled until the alarm is manually cleared. Refer
to the operation manual supplied with the unit for information
).
Duct High Pressure Limit
The duct high pressure limit control (DHL) is provided on all
VAV units. The DHL protects the duct work, the terminal boxes,
and the unit from over pressurization, which could be caused
by, for example, tripped fire dampers or control failure.
The DHL control is factory set to open when the discharge
plenum pressure rises to 3.5" wc (872 Pa). This setting should
be correct for most applications; however, it is adjustable.
Removing the front cover of the device reveals a scale showing
the current setting. Turning the adjustment screw (located on
the bottom of the device) adjusts the setting up or down.
If the DHL switch opens, digital input MCB BI 14 on the Main
Control Board de-energizes. The MicroTech III controller then
shuts down the unit and enters the Off-Alarm state. The alarm
must be manually cleared before the unit can start again.
Refer to the operation manual supplied with your unit for more
information on clearing alarms (
Figure 100: Field Output Schematic
VAV Box Signal/Fan Operation Signal
Digital Output #10 (MCB-DO10) may be selected as either the
Fan Operation output or the VAV output via the keypad. The
VAV/Fan Op selection can be selected by accessing the Unit
Setup menu in the Extended Menu section.
Fan Operation
The Fan Operation Output (MCB-DO10) supplies 24 V (AC) to
terminal 116 on the field terminal block (TB2) when the output
is on. To use this signal, wire the coil of a field supplied and
installed 24 V (AC) pilot relay across terminals 116 and 117 on
TB2. When this output is on, 24 V (AC) is supplied from the
T3 control transformer through the output relay to energize the
field relay. Refer to the as-built wiring diagrams.
The Fan Operation output is on when the unit is not OFF and
when both the unit is OFF and airflow is detected. It is OFF
when the unit is off and airflow is not detected.
VAV Box Output
The VAV Box Output (MCB-DO10) supplies 24 V (ac) to
terminal 116 on the field terminal block (TB2) when the output
is on. To use this signal, wire the coil of a field supplied and
installed 24 V (AC) pilot relay across terminals 116 and 117 on
TB2. When this output is on, 24 V (AC) is supplied from the
T3 control transformer through the output relay to energize the
field relay. Refer to the as-built wiring diagrams.
In the Heating state, the VAV Output is turned off to indicate
that hot air instead of the normal cool air is being supplied to
the VAV boxes. The VAV boxes are driven to their Heating
Position when hot air is provided based on either the normally
open or normally closed contacts of the VAV output. The VFD
will continue to be controlled to maintain the desired duct static
pressure. This output is also off when the unit is in the Startup
or Recirculation states. If this output is in the Heat (OFF)
position when the unit enters the Fan Only state or Minimum
DAT Control state, the output remains off for an adjustable
Post Heat Time (while the unit VFDs are driven to minimum
speed) or until the VFD gets to its minimum speed if the Post
Heat Time is set greater than 0. The Post Heat Timer can be
adjusted via the keypad/display Timer Setting menu in the
Extended Menus.
During unoccupied operation, the VAV Box Output is in the
Cool (ON) position unless airflow is detected. When airflow is
detected, it switches to the Heat (OFF) position.
Summary of Contents for RoofPak RPS Series
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