Application Considerations
Of these methods, VFD modulation
isthe quietest and most energy efficient; it can also
prolong the life of the fan motor by "soft
starting" it. IGV modulation provides reliable
operation at a lower first cost; IGV is not available
on Q-Fan.
Application consideration:
- Regardless of the fan control method (CV or VAV) used, it’s important to provide a means of monitoring outdoor airflow.
Over time, filter loading and other system effects can
change static pressures and eventually reduce airflow — including ventilation airflow — below the design volume flow rate.
Diffuser Module
Designed to provide even airflow, the diffuser module is typically used immediately
upstream of a final-filter or coil module.
Plenum Module 
(Figure A-24) Before leaving the air handler, supply air is sometimes discharged
into a plenum module; the air stream’s rapid
expansion as it passes into the plenum reduces turbulence and creates an end reflection
that dampens low-frequency sound. Four configurations
enable supply-duct connections from any side; unless otherwise noted, all are available
with 2-inch, insulated casing walls of solid or
perforated construction.
- Top-mounted plenum modules mount atop a horizontal or vertical fan module.
Openings can be factory- or field-cut.
- Front-mounted plenum modules mount on the front of a horizontal or vertical fan module.
- Down-discharge plenum modules mount on a horizontal fan module. A removable bottom panel covers the discharge
opening.
- Top-mounted plug-fan plenum modules mount atop a plug-type fan module. In addition to the casing options
cited above, an insulated, 4- inch perforated
double-wall casing is available.
Turning Module
(Figure A-25) This plenum-type module alters the direction of airflow and reduces turbulence. It can also serve as an
effective sound attenuator. When compared to a
field-mounted rectangular duct silencer, the turning
module is less expensive to install, has a lower pressure drop and provides more predictable performance. Lining the
turning module attenuates high- frequency sound, while
the "plenum effect" (expansion and end
reflection) of the module itself attenuates low-
frequency sounds.
Humidification Module
(Figure A-26) ASHRAE Standard 62- 1989 suggests maintaining a relative humidity
of no less than 30 percent to provide a comfortable,
healthy indoor environment. The Modular Climate Changer’s humidification module is a custom option that uses "low- pressure"
steam to add moisture to the air. Factory mounting
within the air handler lowers the humidifier’s
installed cost and keeps moisture out of the supply duct, while factory- provided controls provide accurate, reliable
performance.
Application considerations:
- Never position the humidification module immediately downstream of a housed fan
or blow-thru coil module.
- Extra dispersion distance may be needed if the humidification module is placed
upstream of a final filter or electric heat coil.
- Airflow through the humidifier must be horizontal and of relatively uniform velocity (i.e., 400 to 700 fpm).
- To prevent condensate formation, the relative humidity leaving the humidifier should not exceed 83 percent; the humidification
module must also be long enough to assure that the
passing air stream completely absorbs the steam. Consult the factory for application-specific
guidance.
- Vertical airflow turns immediately up- and downstream of the humidification module necessitate a large module.
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