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Exhaust Fans
The exhaust axial fans are used to minimize the
overpressure in the building caused by the introduction
of fresh air.
This option is typically used when the fresh air intake
needed is between 40 to 50% of the nominal air flow or
when the return air duct pressure drop is higher than
25Pa (<70Pa or 150Pa according to option selected).
This option includes hoods, gravity dampers and axial
fans.
Optional service Terminal allow to adjust exhaust fans
start and stop value according to fresh air damper
position.
When the supply air fan is ON, the exhaust fans turn on
whenever the position of the fresh air dampers meet or
exceed the exhaust fan set point. (If the potentiometer is
set at 40%, the exhaust fans will start when the fresh air
dampers will meet or exceed 40% opening).
Operation
• When the exhaust fans are OFF :
- The barometric dampers open when the air pressure
inside the building increases.
As the building pressure increases, the pressure in
the unit return section also increases, opening the
dampers and relieving the air.
- If return air pressure drop>building overpressure
(∆P>Pb – Patm) → barometric damper is closed.
- If return air pressure drop<building overpressure
(∆P< Pb – Patm) → barometric damper opens and
a maximum of 25% of the nominal airflow can be
exhausted.
• When the exhaust fans turn ON :
- Around 50% of airflow can be exhausted, depending
on the pressure drop in the return air duct.
- The two fans work always together, on stage ON-OFF.
- Each fan has two speeds, which makes 2 configurable
speeds by changing the wiring on site.
- The exhaust fan is started when fresh air dampers
meet or exceed a preset percentage of fresh air.
Configured for Return roofcurb (ESP=250 PA)
Figure 17 - Exhaust fan
30
Configured for Return roofcurb
(ESP=250 PA)
2 types of return roofcurbs modules have been
developped (downflow and horizontal flow) in order
to minimize overpressure in the buildng caused by
the introduction of fresh air when there is a significant
pressure drop in the return duct (250 Pa maximum) and
when supply fan is not enough to overcome both supply
and return external static pressure.
The module is fully controlled and powered by the
rooftop control. The assembly detail is given in the
submittal shipped with the document package sent
with the unit.
Figure 18 - Return roofcurb downflow
Figure 19 - Return roofcurb horizontal flow
Exhaust Fan EC
The exhaust fans EC are used to minimize overpressure
in the building caused by the introduction of fresh air.
This option is typically used when large fresh air intake
needed (40 to 50% of the nominal airflow) or when the
return air duct pressure drop is higher than 70Pa. This
option includes hoods, gravity dampers and EC Exhaust
fans. Exhaust fans speed has to be adjusted during the
commissioning using the optional service Terminal to
balance building pressure.
Options
RT-SVX056D-GB
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