Mammoth 800 to 5500 CFM: Dedicated Outdoor Air System with Enthalpy Wheels (VHC) - Manual (Page 14)

MAMM-VHC-IOM-1A (JANUARY 2013) 14
For proper performance the unit must operate and be
balanced at the design supply and exhaust airflow rates.
Permanent or temporarily field supplied and installed flow
measuring stations (FMS) can be used to measure airflow
or by using other ASHRAE suggested methods. Where
space is limited in the outdoor air or exhaust air ducts
for measurements, pressure drop readings can be taken
across the enthalpy wheel rotor and airflow extrapolated
from the curves in Appendix L for the wheel effectiveness
category or thickness. Heat recovery performance is tested
in accordance to AHRI Standard 1060 and is accurate to
within +/− 5% if there is no dirt buildup in the heat recovery
wheel rotor.
When FMS are used it is important to locate it in the “warm
side” ductwork to minimize the effects of differences in air
density especially during cold outside conditions. Air den-
sity variations can affect the FMS by more than 15%. The
FMS should be located downstream from straight sections
of duct and not immediately after fans or obstructions that
will cause turbulent flow.
Imbalanced airflow may cause supply air temperatures
to be below freezing. Adequate freeze protection such as
glycol or low limit temperature protection for downstream
coils or reheat to protect building systems must be field
provided.
Setting Flow Rate
Units supplied with belt driven double width double inlet
fans have an adjustable motor sheave factory set at the
midpoint of travel at rpm for the flow rate and external static
specified. With optional VFD driven motors this factory set-
ting is at 60 Hz. For 100% outdoor and exhaust, flow rate
should be balanced with motors operating at high speed
and at 60 Hz by adjusting the motor sheave pitch diameter.
The VFD can be used for fine tuning depending on se-
quence.
With the optional direct driven plenum supply fan the VFD
is used for speed setting and balancing at the required
Hertz.
With the optional internal bypass the airflow rate may be
reduced. Consult the factory for setting the flow rate during
internal bypass.
WARNING
Disconnect the main power switch to the unit before per-
forming service and maintenance procedures.
!
IMPORTANT
On initial power up, the unit will perform a system check
and operate at high speed for five seconds.
Airflow Balancing