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Product Overview
The model is a vertically-configured make-up air unit
designed for outdoor installations. It contains a highly
efficient direct-fired gas burner to provide a heat source
for the building or to simply temper the air. The unit is
designed to provide sufficient air to replace air that is
exhausted from the building and will also produce heat
as needed. The make-up air volume produced by the
unit can be regulated in a number of different ways,
depending on the characteristics of the building.
The unit draws in fresh, outdoor air through a filter bank
in the bottom of the unit and it then moves upward
through a combustion chamber or through an optional
burner bypass damper. A blower mounted in the top of
the unit then forces the air into the building ductwork.
Airflow Arrangement
The unit can be ordered in a number of different
configurations to provide 100% outdoor air or 80%
recirculated air and 20% outdoor air. These units
can also be ordered with a variable air volume (VAV)
capability for flexibility in response to building air
handling needs.
100% Outdoor Air
If the unit is configured only for 100% outdoor air, it
draws outdoor air as needed through the filter bank
at the bottom. The air moves upward through the
combustion chamber and then it is blown into the
building through user-supplied ductwork. The supply air
volume is typically constant and can only be altered by
changing the blower or motor pulleys.
80/20 Recirculated Air
When the unit is used as a primary heat source for
the building, the unit will draw 80% of the needed air
from the building and mix it with a minimum of 20%
fresh outdoor air. Outdoor air is drawn through the
combustion chamber and then mixed with the indoor
air after the direct-fired gas heater has heated the air.
The supply air volume is typically constant but the
percentage of recirculated air can be modulated.
Variable Air Volume (VAV)
The VAV function can be selected when the outdoor air
volume required by the building varies. This requires
the installation of one bypass damper and selection of
an appropriate motor/blower control system. This may
involve installation of a Variable Frequency Drive (VFD)
controller. Both bypass damper and VFD are factory
installed.
4
Model VSU Make-Up Air
Subassemblies
Filter Section / Vertical Mounting Stand
The filter section of the unit is factory installed in the
mounting stand and shipped ready for installation on
the concrete mounting pad. Each filter unit has a large
access panel on the control end of the unit except for
the housing size 50, which has an access door on both
ends. Filters are either 2 in. thick pleated paper or 2 in.
thick permanent metal type. Filters are changed by
removing the access door(s) and sliding the filters in or
out on their tracks.
The unit's vertical mounting stand is fabricated of
heavy-gauge, painted angle iron and flat stock steel.
The nominal 24 in. high stand will support the entire unit
so that the bottom of the filter unit is held 24 in. above
ground level. For housing size 50, a nominal 48 in. high
stand is minimum. In locations where heavy snowfall
is common, greater minimum clearance should be
specified in order to minimize the possibility of clogging
filters with snow or debris. The stand with filter bank is
shipped to the jobsite as a separate assembly. The unit
filter bank is permanently installed in the mounting stand
prior to shipment.
Optional Service Platform
A service platform
is available
for permanent
attachment to the
mounting stand.
The platform
is shipped
unassembled
and requires
field assembly.
It is attached to the
vertical mounting stand
by installing bolts with spacers
between the two assemblies.
The service platform should be
attached to the unit only after the
burner and blower assemblies are
permanently set in place. Ladders
are not provided by factory.
®
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