Installation manual

McQuay IM 487-4 85
Unit Options
Smoke and Fire Protection
McQuay optionally offers factory installed outdoor air, return
air, and exhaust air dampers as well as smoke detectors in the
supply and return air openings, complete with wiring and
control. These components often are used in the building’s
smoke, fume, and fire protection systems. However, due to the
wide variation in building design and ambient operating
conditions into which our units are applied, we do not
represent or warrant that our products will be fit and sufficient
for smoke, fume, and fire control purposes. The owner and a
fully qualified building designer are responsible for meeting
all local and NFPA building code requirements with respect to
smoke, fume, and fire control.
Smoke Detectors
Optional smoke detectors can be located at the supply and
return openings. The wiring for these smoke detectors is
shown on any of the “Typical Main Control Circuit” wiring
schematics within the “Wiring Diagrams” section on pages
64–86.
The sequence of operation for these detectors is as follows:
When smoke is detected by either sensor, the normally closed
sensor contacts open. This removes power from binary input
BI8 on the Main Control Board.
The MicroTech II controller responds by shutting down the
unit. The controller is placed in the Alarm Off state and cannot
be restarted until the alarm is manually cleared. Refer to the
operation manual supplied with the unit for information on
clearing alarms (OM138 or OM137).
The smoke detectors themselves must be reset manually once
they have tripped. Power must be cycled to the smoke detector
to reset.
Freeze Protection
An optional freezestat is available on units with MicroTech II
control that have hot water, chilled water, or steam heating
coils. The sensing element is located on the downstream side
of the heating coil in the heating section of the unit. If the
freezestat detects a freezing condition and closes, the
MicroTech II controller takes different actions, depending on
whether the fans are on or off. The freezestat is an auto reset
type of control; however, the controller alarm that it causes is
manually reset if the fan is on and auto reset if the fan is off.
Fan On Operation
If the freezestat detects a freezing condition while the fan is
on, the MicroTech II controller shuts down the fans, closes the
outdoor air dampers, opens the heating valve, and sets a 10-
minute timer. The MicroTech II controller’s active alarm is
“Freeze Fault.”
When the 10-minute timer expires, the controller begins checking the freezestat
again. If the freezestat is open, the heating valve closes. If the freezestat closes
again, the heating valve opens, and the 10-minute timer resets.
The unit remains shut down until the “Freeze Fail” alarm is
manually cleared. Refer to the operation manual supplied with
the unit for information on clearing alarms (OM138 or
OM137).
Fan Off Operation
If the freezestat detects a freezing condition while the fan is
off, the MicroTech II controller opens the heating valve and
sets a 10-minute timer. The MicroTech II controller’s active
alarm is “Freeze Problem.”
When the 10-minute timer expires, the controller begins
checking the freezestat again. If the freezestat is open, the
heating valve closes. If the freezestat closes again, the heating
valve opens, and the 10-minute timer resets.
When the freezestat opens again, the “Freeze Prob” alarm
automatically clears. This feature protects the coil and allows
the system to start normally after a cold night.
Entering Fan Temperature Sensor
The entering fan temperature (EFT) sensor and an associated
“Lo Airflow Problem” alarm are provided on VAV units with
MicroTech II 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
clearing alarms (OM138 or OM137).
WARNING
Improper smoke, fire, or fume air handling can result in
severe personal injury or death.