CFR •
A
PPLICATION AND
S
ELECTION
8
CFR Catalog • ©
December, 2005 Environmental Technologies, Inc.
SELECTION GUIDELINES
The CFR fan terminal has been
designed to provide maximum
flexibility in matching primary air
valve capacities (cooling loads)
with unit fan capacities. The over-
all unit size is dictated by the fan
size. With each unit fan size, mul-
tiple primary air valve sizes are
available to handle a wide range
of cooling capacities.
The fan should be sized first to
determine the unit size. The selec-
tion is made by cross plotting the
specified fan capacity and external
static pressure on the appropriate
fan performance curves (see page
16). Terminals utilizing hot water
heating coils require the summa-
tion of the coil air pressure drop
and the design E.S.P. to determine
the total E.S.P. It is common to have
more than one fan size which can
meet the design requirements.
Typically, the selection begins with
the smallest fan that can meet the
capacity. Occasionally this selec-
tion may not meet the acoustical
requirements and thus the next larg-
er fan size should be selected.
“Upsizing” may also occur when it
is necessary to meet the design
capacity on the medium or low
motor tap.
Fan selections can be made any-
where in the non-shaded areas.
Each fan performance curve depicts
the actual performance of the rel-
ative motor tap without additional
fan balance adjustment. Actual
specified capacities which fall below
a particular fan curve (low, medi-
um or high) is obtained by adjust-
ment of the electronic (SCR) fan
speed controller. After the proper
fan is selected, the unit size is
fixed and then the appropriate
primary air valve is selected. Most
of the unit fan sizes have three air
valve sizes to select from. The mid-
dle size will typically be utilized. It
is the size that is matched with the
unit fan to deliver 100% cooling
capacity for the majority of fan selec-
tions.
The larger primary air valve will be
used in applications where the
system fan is undersized, requiring
a larger air valve to take advantage
of lower pressure losses. While help-
ing in this fashion, a penalty is paid
by having a higher controllable min-
imum airflow setpoint than could
be achieved with a smaller inlet size.
The smaller primary air valve will
most often be utilized with ther-
mal storage systems where lower
than normal primary air tempera-
tures are utilized. In these cases,
the maximum design primary air-
flow is less than the fan capacity
(typically 60 to 80%), and therefore
a smaller air valve may be appro-
priate.
SYSTEM PRESSURE
CONSIDERATIONS
Since the terminal unit fan is select-
ed to move 100% of the design
airflow to the zone, all down-
stream pressure losses are neglected
when determining minimum pri-
mary air inlet pressure to the unit.
The central fan is only required to
overcome the minimal loss through
the unit air valve, reducing the
central fan total pressure and
horsepower requirements. Due to
extremely low pressure drop of the
air valve, central fan operating
inlet static pressures may be as low
as 0.5" w.g.
COMMON MISAPPLICATION
It should be noted that a conven-
tional Series Flow Fan Terminal
cannot be applied as a booster fan.
In problem areas where there is
insufficient primary airflow capac-
ity, this terminal will not aid in
pulling more air from the primary
duct. Instead the unit fan will draw
air from the plenum inlet which has
less resistance.
The induction opening should
never be sealed, as this will cause
problems should the primary air-
flow increase beyond the unit fan
capacity. In this condition, the fan
casing becomes pressurized which
will eventually stall the fan motor
and cause premature failure.
An ENVIRO-TEC
®
Windows
®
based Computer Selection
Program is also available for com-
plete CFR automated selection.
Содержание CFR
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