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Direct Drive Fan Alignment
Direct drive fans are aligned in the factory. However, Carrier rec-
ommends checking alignment before starting the unit.
1.
Ensure the radial distance between fan wheel and inlet cone
appears visually equal in all directions.
2.
For direct drive plenum fans with NEMA motors, ensure that
the fan wheel to inlet cone overlap is within the correct range.
See the section Direct Drive Plenum Fans on page 206.
3.
Motor and fan are balanced as an assembly. If either changes,
rebalancing is required.
Fan Airflow Measurement Piezometer Ring
The Piezometer system is based on the principle of a flow nozzle.
The inlet funnel is used as the flow nozzle, and the flow can be
calculated by measuring the static pressure drop through the inlet
funnel. The pressure drop is measured from the tap located on the
face of the inlet funnel to the piezometer in the throat. The front
pressure tap, located on the face or outer portion of the inlet ring,
is connected to the high-pressure side of the transducer and the
piezometer ring is connected to the low-pressure side.
CALCULATION WHEN USING THE PIEZOMETER
For standard air ( = 0.075 lb/ft
CFM
=
•
K (K Factor) value: Obtain from Table 6 on page 29.
•
P (Delta Pressure): The differential in static pressure
from the piezometer and the front pressure tap (in. wg).
If the K factor is not shown in Table 6, perform a pitot tube tra-
verse either before or after the fan where the airflow is most uni-
form (preferably in the straightest portion of the duct) and at the
same time note the Delta Pressure read by the control system. Use
the following formula to calculate the K Factor:
K
CFM
=
CAUTION
Do not exceed maximum fan speed rpm with variable
frequency drive. Equipment damage may result.
):
3
K
P
P
Outdoor Hoods and Louvers
Three options are available: fixed rear intake hoods, intake lou-
vers, and collapsible exhaust box hoods. All hoods and louvers
have an intake screen to prevent unwanted entry of birds and
debris. There is an additional screen available to prevent snow
from entering the intake louver. It is attached to the outside of
the louver. It can be factory or field installed. The intake hoods
have easily serviceable demisters via small hinged doors. In-
take louvers are a wind-driven rain design that will allow no
more than 0.01 oz per sq ft of free area water penetration at
1250 fpm. This is the maximum velocity required by AMCA
(Air Movement and Control Association) 511. Higher veloci-
ties are possible without significant water intrusion.
Most fixed rear hoods (Fig. 57) and intake louvers (Fig. 58)
ship installed and should require no further assembly. If a rear
hood is shipped attached to the skid, do not install the rear
hood in the air-handling until the rest of the unit and splits have
been completely assembled. Otherwise, the combination of just
the hood and mixing box may become a tipping hazard.
Fig. 57 — Rear Intake Hood (Size 30 Shown)
Collapsible exhaust box hoods ship covering the exhaust outlet of
the unit and/or inside the unit and require some basic assembly.
Fasteners, washers and gasket material for installation of the hood
come taped inside the exhaust section. Figure 59 shows an explod-
ed view of the assembly in its shipping position, and how the vari-
ous parts assemble to form the hood.
120
UNIT
GASKET
SCREW TYPICAL
ENTIRE PERIPHERY
INTAKE HOOD
A39-
2347ef
OPEN DOOR TO
REMOVE DEMISTERS
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