CFR •
A
PPLICATION AND
S
ELECTION
6
CFR Catalog • ©
December, 2005 Environmental Technologies, Inc.
PURPOSE OF SERIES FLOW
FAN TERMINALS
Series flow fan powered termi-
nals offer improved space comfort
and flexibility in a wide variety of
applications. Substantial operat-
ing savings can be realized through
the recovery of waste heat, reduced
central fan horsepower require-
ments and night setback operation.
Heat Recovery.
The CFR recovers
heat from lights and core areas to
offset heating loads in perimeter
zones. Additional heat is available
at the terminal unit using electric,
steam, or hot water heating coils.
Controls are available to energize
remote heating devices such as wall
fin, fan coils, radiant panels, and
roof load plenum unit heaters.
IAQ.
The CFR enhances the indoor
air quality of a building by providing
constant air motion, and higher air
volumes in the heating mode than
typically provided by straight VAV
single duct terminals or parallel flow
fan terminals. The higher air
capacity provides continuous air
motion in the space and lowers the
heating discharge air temperature.
This combination improves air cir-
culation, preventing accumulation
of CO
2
concentrations in stagnant
areas. Increased air motion
improves occupant comfort. The
higher air capacity also improves
the performance of diffusers and
minimizes diffuser “dumping”.
ACOUSTICAL CONCEPTS
The focus on indoor air quality is
also having an effect on proper
selection of air terminal equip-
ment with respect to acoustics.
Sound.
At the zone level, the
terminal unit generates acoustical
energy that can enter the zone along
two primary paths. First, sound from
the unit fan can propagate through
the downstream duct and diffusers
before entering the zone (referred
to as Discharge or Airborne Sound).
Acoustical energy is also radiated
from the terminal casing and trav-
els through the ceiling cavity and
ceiling system before entering the
zone (referred to as Radiated Sound).
To properly quantify the amount of
acoustical energy emanating from
a terminal unit at a specific oper-
ating condition (i.e. CFM and static
pressure), manufacturers must mea-
sure and publish sound
power
levels.
The units of measurement, decibels,
actually represent units of power
(watts). The terminal equipment
sound power ratings provide a
consistent measure of the generated
sound independent of the envi-
ronment in which the unit is
installed. This allows a straight for-
ward comparison of sound
performance between equipment
manufacturers and unit models.
Noise Criteria (NC).
The bottom
line acoustical criteria for most
projects is the NC (Noise Criteria)
level. This NC level is derived from
resulting sound
pressure
levels in
the zone. These sound
pressure
lev-
els are the effect of acoustical
energy (sound
power
levels)
entering the zone caused by the ter-
minal unit and other sound
generating sources (central fan sys-
tem, office equipment, outdoor
environment, etc.).
The units of measurement is once
again decibels; however, in this
case decibels represent units of
pressure (Pascals), since the human
ear and microphones react to pres-
sure variations.
There is no direct relationship
between sound power levels and
sound pressure levels. Therefore,
we must predict the resulting sound
pressure levels (NC levels) in the zone
based in part by the published
sound power levels of the terminal
equipment. The NC levels are total-
ly dependent on the project specific
design, architecturally and mechan-
ically. For a constant operating
condition (fixed sound power
levels), the resulting NC level in the
zone will vary from one project to
another.
ARI 885.
A useful tool to aid in pre-
dicting space sound pressure levels
is an application standard referred
to as ARI Standard 885. This stan-
dard provides information (tables,
formulas, etc.) required to calculate
the attenuation of the ductwork, ceil-
ing cavity, ceiling system, and
conditioned space below a termi-
nal unit. These attenuation values
are referred to as the “transfer
function” since they are used to
transfer from the manufacturer’s
sound power levels to the esti-
mated sound pressure levels resulting
in the space below, and/or served
by the terminal unit. The standard
does not provide all of the neces-
sary information to accommodate
every conceivable design; howev-
er, it does provide enough
information to approximate the
transfer function for most appli-
cations. Furthermore, an Appendix
is provided that contains typical
attenuation values. Some manu-
facturers utilize different assumptions
with respect to a "typical" project
design; therefore, cataloged NC
levels should not be used to com-
pare acoustical performance. Only
certified sound power levels should
be used for this purpose.
GENERAL DESIGN
RECOMMENDATIONS FOR A
QUIET SYSTEM
The AHU.
Sound levels in the
zone are frequently impacted by cen-
tral fan discharge noise that
either breaks out (radiates) from the
ductwork or travels through the dis-
tribution ductwork and enters the
zone as airborne (discharge) sound.
